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  • 1. Anderson, John B.
    et al.
    Conway, Howard
    Bart, Philip J.
    Witus, Alexandra E.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    McKay, Robert M.
    Hall, Brenda L.
    Ackert, Robert P.
    Licht, Kathy
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stone, John O.
    Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 31-54Article in journal (Refereed)
    Abstract [en]

    Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by similar to 13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by similar to 11 ka BP, just north of Ross Island by similar to 7.8 ka BP, and near Hatherton Glacier by similar to 6.8 ka BP. Farther south, Be-10 exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after similar to 13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis.

  • 2. Bentley, Michael J.
    et al.
    Cofaigh, Colm O.
    Anderson, John B.
    Conway, Howard
    Davies, Bethan
    Graham, Alastair G. C.
    Hillenbrand, Claus-Dieter
    Hodgson, Dominic A.
    Jamieson, Stewart S. R.
    Larter, Robert D.
    Mackintosh, Andrew
    Smith, James A.
    Verleyen, Elie
    Ackert, Robert P.
    Bart, Philip J.
    Berg, Sonja
    Brunstein, Daniel
    Canals, Miguel
    Colhoun, Eric A.
    Crosta, Xavier
    Dickens, William A.
    Domack, Eugene
    Dowdeswell, Julian A.
    Dunbar, Robert
    Ehrmann, Werner
    Evans, Jeffrey
    Favier, Vincent
    Fink, David
    Fogwill, Christopher J.
    Glasser, Neil F.
    Gohl, Karsten
    Golledge, Nicholas R.
    Goodwin, Ian
    Gore, Damian B.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hall, Brenda L.
    Hall, Kevin
    Hedding, David W.
    Hein, Andrew S.
    Hocking, Emma P.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johnson, Joanne S.
    Jomelli, Vincent
    Jones, R. Selwyn
    Klages, Johann P.
    Kristoffersen, Yngve
    Kuhn, Gerhard
    Leventer, Amy
    Licht, Kathy
    Lilly, Katherine
    Lindow, Julia
    Livingstone, Stephen J.
    Masse, Guillaume
    McGlone, Matt S.
    McKay, Robert M.
    Melles, Martin
    Miura, Hideki
    Mulvaney, Robert
    Nel, Werner
    Nitsche, Frank O.
    O'Brien, Philip E.
    Post, Alexandra L.
    Roberts, Stephen J.
    Saunders, Krystyna M.
    Selkirk, Patricia M.
    Simms, Alexander R.
    Spiegel, Cornelia
    Stolldorf, Travis D.
    Sugden, David E.
    van der Putten, Nathalie
    van Ommen, Tas
    Verfaillie, Deborah
    Vyverman, Wim
    Wagner, Bernd
    White, Duanne A.
    Witus, Alexandra E.
    Zwartz, Dan
    A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 1-9Article in journal (Refereed)
    Abstract [en]

    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.

  • 3. Bigg, G. R.
    et al.
    Clark, C. D.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Haflidason, H.
    Hughes, A. L. C.
    Levine, R. C.
    Nygard, A.
    Sejrup, H. P.
    Sensitivity of the North Atlantic circulation to break-up of the marine sectors of the NW European ice sheets during the last Glacial: A synthesis of modelling and palaeoceanography2012In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 98-99, p. 153-165Article in journal (Refereed)
    Abstract [en]

    The marine-based Atlantic periphery of the last NW European Ice Sheet experienced significant advances and retreats of its marine sector during its existence. It therefore had considerable potential to intermittently inject freshwater or ice pulses to the North Atlantic. These European inputs had poorly known consequences for ocean circulation and climate. Here we examine the history of the western margin of the European Ice Sheet, from 34 to 15 cal ka BP, and use a combination of modelling and proxy evidence to explore the impact on the North Atlantic of the fresh water and iceberg injections that accompanied phases of retreat of the marine sector of the NW European Ice Sheet. We find that the lack of geographical synchronicity in the responses of the different components of the 3000 km long sector meant that the scale of the climate consequences of ice discharge most likely remained regional, except during the final deglaciation phase, around 17-15 cal ka BP. At this time, as the later component of the recently introduced concept of an extended Heinrich event H1, both proxy and modelling evidence suggest rapid sector collapse led to partial shut-down of the Atlantic overturning and a basin-wide cooling.

  • 4. Bigg, Grant R.
    et al.
    Levine, Richard C.
    Clark, Chris D.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Haflidason, Haflidi
    Hughes, Anna L. C.
    Nygard, Atle
    Sejrup, Hans Petter
    Last glacial ice-rafted debris off southwestern Europe: the role of the British-Irish Ice Sheet2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 5, p. 689-699Article in journal (Refereed)
    Abstract [en]

    Ice-rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short-lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short-lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka.

  • 5. Clark, Chris D.
    et al.
    Ely, Jeremy C.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hughes, Anna L. C.
    Meehan, Robert
    Barr, Iestyn D.
    Bateman, Mark D.
    Bradwell, Tom
    Doole, Jenny
    Evans, David J. A.
    Jordan, Colm J.
    Monteys, Xavier
    Pellicer, Xavier M.
    Sheehy, Michael
    BRITICE Glacial Map, version 2: a map and GIS database of glacial landforms of the last British-Irish Ice Sheet2018In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 47, no 1, p. 11-27Article in journal (Refereed)
    Abstract [en]

    During the last glaciation, most of the British Isles and the surrounding continental shelf were covered by the British-Irish Ice Sheet (BIIS). An earlier compilation from the existing literature (BRITICE version 1) assembled the relevant glacial geomorphological evidence into a freely available GIS geodatabase and map (Clark etal. 2004: Boreas 33, 359). New high-resolution digital elevation models, of the land and seabed, have become available casting the glacial landform record of the British Isles in a new light and highlighting the shortcomings of the V.1 BRITICE compilation. Here we present a wholesale revision of the evidence, onshore and offshore, to produce BRITICE version 2, which now also includes Ireland. All published geomorphological evidence pertinent to the behaviour of the ice sheet is included, up to the census date of December 2015. The revised GIS database contains over 170000 geospatially referenced and attributed elements - an eightfold increase in information from the previous version. The compiled data include: drumlins, ribbed moraine, crag-and-tails, mega-scale glacial lineations, glacially streamlined bedrock (grooves, roches moutonnees, whalebacks), glacial erratics, eskers, meltwater channels (subglacial, lateral, proglacial and tunnel valleys), moraines, trimlines, cirques, trough-mouth fans and evidence defining ice-dammed lakes. The increased volume of features necessitates different map/database products with varying levels of data generalization, namely: (i) an unfiltered GIS database containing all mapping; (ii) a filtered GIS database, resolving data conflicts and with edits to improve geo-locational accuracy (available as GIS data and PDF maps); and (iii) a cartographically generalized map to provide an overview of the distribution and types of features at the ice-sheet scale that can be printed at A0 paper size at a 1:1250000 scale. All GIS data, the maps (as PDFs) and abibliography of all published sources are availablefor download from: https://www.sheffield.ac.uk/geography/staff/clark_chris/britice

  • 6. Clark, Chris D.
    et al.
    Hughes, Anna L. C.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jordan, Colm
    Sejrup, Hans Petter
    Pattern and timing of retreat of the last British Irish ice sheet2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 44, p. 112-146Article in journal (Refereed)
    Abstract [en]

    During the last glacial the ice sheet that subsumed most of Britain, Ireland and the North Sea attained its maximum extent by 27 ka BP and with an ice volume sufficient to raise global sea level by ca 2.5 m when it melted. We reconstruct the demise of this British-Irish Ice Sheet (BIIS) and present palaeo-glaciological maps of retreat stages between 27 and 15 ka BR The whole land area was investigated using remote sensing data and we present maps of moraines, meltwater channels, eskers, and drumlins and a methodology of how to interpret and bring them together. For the continental shelf, numerous large moraines were discovered recording an extensive pattern of retreat stretching from SW Ireland to the Shetland Isles. From an integration of this new mapping of glacial geomorphology (>26,000 landforms) with previously published evidence, compiled in the BRITICE database, we derive a pattern of retreat for the whole BIIS. We review and compile relevant dates (881 examples) that constrain the timing of retreat. All data are held within a Geographic Information System (GIS), and are deciphered to produce a best-estimate of the combined pattern and timing of retreat. Pattern information reveals an ice sheet mainly comprised of a shelf-parallel configuration from SW Ireland to NE Scotland but it spread far enough to the south to incorporate outlying ice domes over Wales, the Lake District and Kerry. Final disintegration was into a number of separate ice caps, rather than reduction as a single mass, and paradoxically, retreat was not always back to high ground. By 23 ka BP ice withdrew along its northern boundaries at the same time as the southern margins were expanding, including transient ice streaming down the Irish Sea and advances of lobes in the Cheshire Basin, Vale of York and east coast of England. Ice divides migrated south. By 19 ka the ice sheet was in crisis with widespread marine-based ice losses, particularly in the northern North Sea and the Irish Sea. Considerable dynamic-thinning occurred during this phase. Final collapse of all marine sectors occurred by 17 ka BP and with most margins beginning to back-step onshore. Disintegration of the North Sea 'ice bridge' between Britain and Norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted. The North Channel and Irish Sea ice streams had finally cleaved the ice sheet into separate Irish and Scottish ice sheets by 16 ka BP. Rates of ice loss were found to vary widely over space and time (e.g., 65-260 km(3) per year). The role of ice streams and calving losses of marine-based sectors are examined. Retreat rates of up to ca 150 ma(-1) were found for some ice stream margins. That large parts (2/3) of the BIIS were marine-based, drained by ice streams, and possibly with fringing ice shelves in places, makes it a useful analogue for the West Antarctic Ice Sheet (WAIS). This is especially so because the BIIS deglaciated in response to rising temperatures and a rising sea level (driven by melting of other ice masses) which are the current forcings that might cause collapse of the WAIS. Our reconstruction, when viewed from the opposite perspective, documents when fresh land became exposed for exploitation by plants, animals and Man, and records for how long such land has been available for soil and geochemical development and ecological succession.

  • 7.
    Clason, Caroline C.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Plymouth University, UK.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Selmes, Nick
    Lea, James M.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Liverpool, UK.
    Jamieson, Stewart S. R.
    Nick, Faezeh M.
    Holmlund, Per
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Controls on the early Holocene collapse of the Bothnian Sea Ice Stream2016In: Journal of Geophysical Research - Earth Surface, ISSN 2169-9003, E-ISSN 2169-9011, Vol. 121, no 12, p. 2494-2513Article in journal (Refereed)
    Abstract [en]

    New high-resolution multibeam data in the Gulf of Bothnia reveal for the first time the subglacial environment of a Bothnian Sea Ice Stream. The geomorphological record suggests that increased meltwater production may have been important in driving rapid retreat of Bothnian Sea Ice during deglaciation. Here we apply a well-established, one-dimensional flow line model to simulate ice flow through the Gulf of Bothnia and investigate controls on retreat of the ice stream during the post-Younger Dryas deglaciation of the Fennoscandian Ice Sheet. The relative influence of atmospheric and marine forcings are investigated, with the modeled ice stream exhibiting much greater sensitivity to surface melting, implemented through surface mass balance and hydrofracture-induced calving, than to submarine melting or relative sea level change. Such sensitivity is supported by the presence of extensive meltwater features in the geomorphological record. The modeled ice stream does not demonstrate significant sensitivity to changes in prescribed ice stream width or overall bed slope, but local variations in basal topography and ice stream width result in nonlinear retreat of the grounding line, notably demonstrating points of short-lived retreat slowdown on reverse bed slopes. Retreat of the ice stream was most likely governed by increased ice surface meltwater production, with the modeled retreat rate less sensitive to marine forcings despite the marine setting.

  • 8. Ely, Jeremy C.
    et al.
    Clark, Chris D.
    Spagnolo, Matteo
    Stokes, Chris R.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hughes, Anna L. C.
    Dunlop, Paul
    Hess, Dale
    Do subglacial bedforms comprise a size and shape continuum?2016In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 257, p. 108-119Article in journal (Refereed)
    Abstract [en]

    Understanding the evolution of the ice-bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created. However, the formation of the suite of landforms generated at this boundary - subglacial bedforms - is a contentious issue that is yet to be fully resolved. Bedforms formed in aeolian, fluvial, and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes. For subglacial bedforms, a size and shape continuum has been hypothesised, yet it has not been fully tested. Here we analyse the largest data set of subglacial bedform size and shape measurements ever collated (96,900 bedforms). Our results show that flutes form a distinct population of narrow bedforms. However, no clear distinction was found between drumlins and megascale glacial lineations (MSGLs), which form a continuum of subglacial lineations. A continuum of subglacial ribs also exists, with no clear size or shape distinctions indicating separate populations. Furthermore, an underreported class of bedform with no clear orientation to ice flow (quasi-circular bedforms) overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two, potentially merging these three bedform types into a larger continuum.

  • 9.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry
    Egilsson, Arnar
    Thorsteinsson, Tomas
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain, Melville Bay, northwestern Greenland2015In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 250, p. 29-40Article in journal (Refereed)
    Abstract [en]

    Geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate. Melville Bay, in northwestern Greenland, contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere, where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings. We present here the results of high-resolution, geomorphological mapping of the offshore and onshore landscapes in Melville Bay using multibeam sonar and satellite data, at 5- and 10-m resolutions respectively. The results show a similar areally-scoured bedrock-dominated landscape with a glacially modified cnoc-and-lochan morphology on the inner shelf (150-500 m depth) and on the nearby exposed coast. This is manifested by the presence of U-shaped troughs, moutonee-type elongated landforms, stoss-and-lee forms, and streamlined features. The submarine landscape shows features that are characteristic of bedrock in folded, faulted, and weathered metamorphic terrain, and, to a lesser extent, glacially molded bedforms; while coastal landforms exhibit higher relief, irregular-shaped basins, and more subdued fracture valleys. Although generally similar, the onshore and offshore landscapes contain examples of distinctly different landform patterns, which are interpreted to reflect a longer exposure to long-term deep weathering as well as to more recent periglacial weathering processes on land. The spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock. The lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the West Greenland Current flowing northward over the area in combination with limited sediment supply from long sea ice-cover seasons. The distribution and orientation of the landforms in the offshore part indicate ice movement toward the NW, and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day Melville Bay Trough.

  • 10. Graham, Alastair G. C.
    et al.
    Dutrieux, Pierre
    Vaughan, David G.
    Nitsche, Frank O.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Larter, Robert D.
    Jenkins, Adrian
    Seabed corrugations beneath an Antarctic ice shelf revealed by autonomous underwater vehicle survey: Origin and implications for the history of Pine Island Glacier2013In: Journal of Geophysical Research: Earth Surface, ISSN 2169-9011, Vol. 118, no 3, p. 1356-1366Article in journal (Refereed)
    Abstract [en]

    [1] Ice shelves are critical features in the debate about West Antarctic ice sheet change and sea level rise, both because they limit ice discharge and because they are sensitive to change in the surrounding ocean. The Pine Island Glacier ice shelf has been thinning rapidly since at least the early 1990s, which has caused its trunk to accelerate and retreat. Although the ice shelf front has remained stable for the past six decades, past periods of ice shelf collapse have been inferred from relict seabed “corrugations” (corrugated ridges), preserved 340 km from the glacier in Pine Island Trough. Here we present high-resolution bathymetry gathered by an autonomous underwater vehicle operating beneath an Antarctic ice shelf, which provides evidence of long-term change in Pine Island Glacier. Corrugations and ploughmarks on a sub-ice shelf ridge that was a former grounding line closely resemble those observed offshore, interpreted previously as the result of iceberg grounding. The same interpretation here would indicate a significantly reduced ice shelf extent within the last 11 kyr, implying Holocene glacier retreat beyond present limits, or a past tidewater glacier regime different from today. The alternative, that corrugations were not formed in open water, would question ice shelf collapse events interpreted from the geological record, revealing detail of another bed-shaping process occurring at glacier margins. We assess hypotheses for corrugation formation and suggest periodic grounding of ice shelf keels during glacier unpinning as a viable origin. This interpretation requires neither loss of the ice shelf nor glacier retreat and is consistent with a “stable” grounding-line configuration throughout the Holocene.

  • 11.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Clark, Chris D.
    University of Sheffield, Department of Geography.
    Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record2009In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, p. 3085-3100Article in journal (Refereed)
    Abstract [en]

    The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one ‘flowsets’ comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset crosscutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative ‘age-stack’ of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset – its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, ‘smudged’ landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories. The flowsets and their palaeo-glaciological significance that we derive for Ireland provide a regional framework and context for interpreting results from local scale fieldwork, provide major flow events for testing numerical ice sheet models, and underpin a data-driven reconstruction of the Irish Ice Sheet that we present in an accompanying paper – Part 2.

  • 12.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Clark, Chris D.
    University of Sheffield, Department of Geography.
    The sensitivity of subglacial bedform size and distribution to substrate lithological control.2010In: Sedimentary Geology, ISSN 0037-0738, E-ISSN 1879-0968, Vol. 232, p. 130-144Article in journal (Refereed)
    Abstract [en]

    The varied nature of a glacial substrate has often been invoked to account for the varied distribution, arrangement and morphological expression of subglacial bedforms. The ease and rate of sediment production from the bedrock substrate, and the rheological, mechanical and hydraulic properties of the resultant subglacial sediment layer have been argued, in certain samples or settings, to account for the local-to-regional distribution of bedforms and bedform types, and varying morphological expression such as size, shape, elongation, or spatial arrangement. From locally coherent observations and relationships it is tempting to extrapolate such patterns to express a more fundamental lithological control on subglacial bedform properties and formation. Here we use a large, systematically compiled dataset (> 30,000 subglacial bedforms inscribed by the Irish Ice Sheet) to explore potential lithological controls upon subglacial bedform distribution and morphological expression. We expect any lithological control upon form, size or distribution to be expressed through a spatial correlation between bedform properties and those of the bed lithology; we extract bedform morphometric and distribution statistics and underlying lithology data from datasets held in a geographic information system for comparative analyses. At ice sheet scale, i.e. considering our whole bedform population, we find no apparent relationship between the lithology of either bedrock or till substrate and bedform occurrence, density of arrangement, or size. Regional to local examples do, in contrast, exhibit some coincident changes in substrate and bedform expression. These are typically manifest as an abrupt shortening or lengthening of drumlins at a lithological boundary, superimposed upon more gradual, regional trends. However, not all local variability observed in the bedform population can be attributed to a lithological driver and, where it can be inferred, lithological control is often in tandem with, or subordinate to, other drivers such as topographic setting or ice dynamics. We propose a hierarchy of controls upon bedform form and distribution, strongly coupled to spatial scale: lithological differences can modulate local scale form and expression but bedform incidence and properties are primarily governed by ice sheet scale glaciological patterns and drivers. Only under certain (unknown) conditions at a local scale is the bedforming process sensitive to the lithological properties of the bed.

  • 13.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Clason, Caroline C.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Helanow, Christian
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography. Durham University, UK.
    Theoretical, contemporary observational and palaeo-perspectives on ice sheet hydrology: Processes and products2016In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 155, p. 1-27Article in journal (Refereed)
    Abstract [en]

    Meltwater drainage through ice sheets has recently been a key focus of glaciological research due to its influence on the dynamics of ice sheets in a warming climate. However, the processes, topologies and products of ice sheet hydrology are some of the least understood components of both past and modem ice sheets. This is to some extent a result of a disconnect between the fields of theoretical, contemporary observational and palaeo-glaciology that each approach ice sheet hydrology from a different perspective and with different research objectives. With an increasing realisation of the potential of using the past to inform on the future of contemporary ice sheets, bridging the gaps in the understanding of ice sheet hydrology has become paramount. Here, we review the current state of knowledge about ice sheet hydrology from the perspectives of theoretical, observational and palaeo-glaciology. We then explore and discuss some of the key questions in understanding and interpretation between these research fields, including: 1) disagreement between the palaeo-record, glaciological theory and contemporary observations in the operational extent of channelised subglacial drainage and the topology of drainage systems; 2) uncertainty over the magnitude and frequency of drainage events associated with geomorphic activity; and 3) contrasts in scale between the three fields of research, both in a spatial and temporal context The main concluding points are that modem observations, modelling experiments and inferences from the palaeo-record indicate that drainage topologies may comprise a multiplicity of forms in an amalgam of drainage modes occurring in different contexts and at different scales. Drainage under high pressure appears to dominate at ice sheet scale and might in some cases be considered efficient; the sustainability of a particular drainage mode is governed primarily by the stability of discharge. To gain better understanding of meltwater drainage under thick ice, determining what drainage topologies are reached under high pressure conditions is of primary importance. Our review attests that the interconnectivity between research sub-disciplines in progressing the field is essential, both in interpreting the palaeo-record and in developing physical understanding of glacial hydrological processes and systems.

  • 14.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Clason, Caroline C.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Mikko, Henrik
    Nyberg, Johan
    Peterson, Gustaf
    Smith, Colby A.
    Integrated use of LiDAR and multibeam bathymetry reveals onset of ice streaming in the northern Bothnian Sea2015In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 137, no 4, p. 284-292Article in journal (Refereed)
    Abstract [en]

    Geomorphological mapping from the new LiDAR (Light Detection and Ranging)-derived digital elevation model for Sweden and a high-resolution multibeam bathymetry data-set for the Gulf of Bothnia reveals a continuous system of glacial landforms crossing the transition between the modern terrestrial and marine environments. A palaeo-ice stream in the northern Bothnian Sea is reconstructed, with an onset tributary over the present-day angstrom ngermanland-Vasterbotten coastline. Systematic contrasts in landform morphology and lineation length indicate that this ice stream comprised a relatively narrow (approximate to 40km) corridor of fast flow, flowing first SW then S, and likely fed by converging flow around the upper Bothnian Sea. The geometry and landform associations of this system imply that ice, at the time period represented here, did not flow across the Gulf of Bothnia: SSE-ward ice flow indicators on the northern Swedish coast do not correspond directly with landform assemblages of the large SE-oriented Finnish deglacial lobes. Instead, we suggest they may contribute to a late-stage fast-flow event to the S and SW. Multibeam bathymetry data offer entirely new access into the rich, landform-scale geomorphological record on the seafloor of the Gulf of Bothnia. The combination of offshore multibeam with the new terrestrial LiDAR data provides unprecedented insight into and renewed understanding of the glacial dynamics of the Bothnian Sea sector of the Fennoscandian Ice Sheet, hitherto interpreted over large areas of unmapped ice sheet bed.

  • 15.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Clason, Caroline C.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Plymouth, UK.
    Nyberg, Johan
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmlund, Per
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The Bothnian Sea ice stream: early Holocene retreat dynamics of the south-central Fennoscandian Ice Sheet2017In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 46, no 2, p. 346-362Article in journal (Refereed)
    Abstract [en]

    The Gulf of Bothnia hosted a variety of palaeo-glaciodynamic environments throughout the growth and decay of the last Fennoscandian Ice Sheet, from the main ice-sheet divide to a major corridor of marine-and lacus-trine-based deglaciation. Ice streaming through the Bothnian and Baltic basins has been widely assumed, and the damming and drainage of the huge proglacial Baltic Ice Lake has been implicated in major regional and hemispheric climate changes. However, the dynamics of palaeo-ice flow and retreat in this large marine sector have until now been inferred only indirectly, from terrestrial, peripheral evidence. Recent acquisition of high-resolution multibeam bathymetry opens these basins up, for the first time, to direct investigation of their glacial footprint and palaeo-ice sheet behaviour. Here we report on a rich glacial landform record: in particular, a palaeo-ice stream pathway, abundant traces of high subglacial meltwater volumes, and widespread basal crevasse squeeze ridges. The Bothnian Sea ice stream is a narrow flow corridor that was directed southward through the basin to a terminal zone in the south-central Bothnian Sea. It was activated after initial margin retreat across the Aland sill and into the Bothnian basin, and the exclusive association of the ice-stream pathway with crevasse squeeze ridges leads us to interpret a short-lived stream event, under high extension, followed by rapid crevasse-triggered break-up. We link this event with a c. 150-year ice-rafted debris signal in peripheral varved records, at c. 10.67 cal. ka BP. Furthermore, the extensive glacifluvial system throughout the Bothnian Sea calls for considerable input of surface meltwater. We interpret strongly atmospherically driven retreat of this marine-based ice-sheet sector.

  • 16.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, John B.
    Ice-flow switching and East/West Antarctic Ice Sheet roles in glaciation of the western Ross Sea2012In: Geological Society of America Bulletin, ISSN 0016-7606, E-ISSN 1943-2674, Vol. 124, no 11-12, p. 1736-1749Article in journal (Refereed)
    Abstract [en]

    The long-term behavior of the East and West Antarctic Ice Sheets, and their respective responses to forcing provide essential context for assessment of modern dynamic changes in ice-flow regimes and ice-sheet and shelf margins. The western Ross Sea discharges ice from both the East and West Antarctic Ice Sheets, and the paleoglacial record from this region is therefore valuable in unraveling their long-term behavior. New, high-resolution multibeam bathymetric data reveal snapshots of well-preserved glacial landforms on the seafloor around Ross Island and McMurdo Sound. Glacial lineations, grounding zone wedges, draped recessional moraines, and meltwater channels record a series of different ice-flow events in the region, contradictions between which require major phases of ice-flow reorganization. From the glacial geomorphology, we reconstruct a four-stage model of ice-flow evolution for the last glacial cycle, consisting of: (1) northeastward flow into the Ross Sea from McMurdo Sound; (2) westward flow from the Ross Sea, around Ross Island, and onto the Victoria Land coast and coastal seafloor trough; (3) a deglacial phase of ice-sheet thinning, minor shifts in flow, and grounding line retreat into McMurdo Sound; and (4) grounding line pinning on Ross Island during regional retreat, uncoupling of a remnant Ross Island ice cap, and local oscillation of Victoria Land outlet glaciers. We find that East Antarctic Ice Sheet ice discharge had a strong influence on ice-flow geometry in this part of the Ross Sea during the last glacial stage, but that it was not necessarily in phase with the behavior of the West Antarctic Ice Sheet. It is similarly evident that the ice streams that drained the Ross Sea over the continental shelf at the Last Glacial Maximum did not all operate synchronously, and exerted different drawdown power at different times. Finally, we conclude that Ross Island acts as an important pinning point in the Ross Sea ice-sheet-shelf system, stabilizing grounding line retreat and encouraging lasting ice-shelf development.

  • 17.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Glacial landforms of extreme size in the Keewatin sector of the Laurentide Ice Sheet2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 15-16, p. 1894-1910Article in journal (Refereed)
    Abstract [en]

    Assemblages of glacial landforms of a 'mega-scale' are here identified in the Keewatin sector of the Laurentide Ice Sheet. Large till 'belts' or 'ridges', apparent only on satellite imagery and lying beneath the drumlins, flutes and ribbed moraine which comprise the known regional glacial landform record, form extensive and coherent patterns throughout the Keewatin region. Planform and crestline mapping from remotely sensed imagery yields a mapped population of >2500 individual landforms, whose dimensions are on average similar to 10 km long and similar to 1.5 km wide. Based on analysis of their morphology and morphometry, their spatial arrangement and pattern, and comparison with analogues and reference populations of glacial landform types, we interpret three morphological groups of different genetic origin. Two of these are examples of currently known landform types: i) a set of heavily overprinted, i.e. non-pristine, mega-scale glacial lineations, feeding from the heart of the Keewatin region north into Queen Maud Gulf; and ii) a 350 km long moraine zone, overrun by later ice flow paths, and likely associated with the terminal position of an ice sheet prior to the final deglacial episode. A third group, comprising a significant number of the Keewatin population, does not fit any existing category of glacial landforms. Here we report a major new finding: subglacial bedforms, of a mega-scale, transverse to the palaeo-ice flow direction. Mega-scale transverse bedforms have not been previously reported from any palaeo-(or contemporary) ice sheet. Close spatial integration with the ribbed moraine population in Keewatin suggests a similar mode of genesis. The Keewatin landforms indicate there is a fundamental transverse organisation of till at a scale beyond that of conventional transverse bedforms (ribbed moraine), and with as yet unknown implications for our understanding of subglacial processes and ice-bed coupling.

  • 18.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ananyev, Roman
    Chernykh, Denis
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Multiple re-advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat, south-central Sweden2015In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 44, no 4, p. 619-637Article in journal (Refereed)
    Abstract [en]

    Lake Vättern represents a critical region geographically and dynamically in the deglaciation of the Fennoscandian Ice Sheet. The outlet glacier that occupied the basin and its behaviour during ice-sheet retreat were key to the development and drainage of the Baltic Ice Lake, dammed just west of the basin, yet its geometry, extent, thickness, margin dynamics, timing and sensitivity to regional retreat forcing are rather poorly known. The submerged sediment archives of Lake Vättern represent a missing component of the regional Swedish deglaciation history. Newly collected geophysical data, including high-resolution multibeam bathymetry of the lake floor and seismic reflection profiles of southern Lake Vättern, are used here together with a unique 74-m sediment record recently acquired by drill coring, and with onshore LiDAR-based geomorphological analysis, to investigate the deglacial environments and dynamics in the basin and its terrestrial environs. Five stratigraphical units comprise a thick subglacial package attributed to the last glacial period (and probably earlier), and an overlying > 120-m deglacial sequence. Three distinct retreat-re-advance episodes occurred in southern Lake Vättern between the initial deglaciation and the Younger Dryas. In the most recent of these, ice overrode proglacial lake sediments and re-advanced from north of Visingsö to the southern reaches of the lake, where ice up to 400 m thick encroached on land in a lobate fashion, moulding crag-and-tail lineations and depositing till above earlier glacifluvial sediments. This event precedes the Younger Dryas, which our data reveal was probably restricted to north-central sectors of the basin. These dynamics, and their position within the regional retreat chronology, indicate a highly active ice margin during deglaciation, with retreat rates on average 175 m a(-1). The pronounced topography of the Vättern basin and its deep proglacial-dammed lake are likely to have encouraged the dynamic behaviour of this major Fennoscandian outlet glacier.

  • 19.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Simkins, Lauren M.
    Halberstadt, Anna Ruth W.
    Prothro, Lindsay O.
    Anderson, John B.
    Holocene reconfiguration and readvance of the East Antarctic Ice Sheet2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 3176Article in journal (Refereed)
    Abstract [en]

    How ice sheets respond to changes in their grounding line is important in understanding ice sheet vulnerability to climate and ocean changes. The interplay between regional grounding line change and potentially diverse ice flow behaviour of contributing catchments is relevant to an ice sheet's stability and resilience to change. At the last glacial maximum, marine-based ice streams in the western Ross Sea were fed by numerous catchments draining the East Antarctic Ice Sheet. Here we present geomorphological and acoustic stratigraphic evidence of ice sheet reorganisation in the South Victoria Land (SVL) sector of the western Ross Sea. The opening of a grounding line embayment unzipped ice sheet sub-sectors, enabled an ice flow direction change and triggered enhanced flow from SVL outlet glaciers. These relatively small catchments behaved independently of regional grounding line retreat, instead driving an ice sheet readvance that delivered a significant volume of ice to the ocean and was sustained for centuries.

  • 20.
    Gyllencreutz, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Freire, Francis
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glacial landforms in a hard bedrock terrain, Melville Bay off nortwestern GreenlandManuscript (preprint) (Other academic)
  • 21. Halberstadt, Anna Ruth W.
    et al.
    Simkins, Lauren M.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, John B.
    Past ice-sheet behaviour: retreat scenarios and changing controls in the Ross Sea, Antarctica2016In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 10, no 3, p. 1003-1020Article in journal (Refereed)
    Abstract [en]

    Studying the history of ice-sheet behaviour in the Ross Sea, Antarctica's largest drainage basin can improve our understanding of patterns and controls on marine-based ice-sheet dynamics and provide constraints for numerical ice-sheet models. Newly collected high-resolution multibeam bathymetry data, combined with two decades of legacy multibeam and seismic data, are used to map glacial landforms and reconstruct palaeo ice-sheet drainage. During the Last Glacial Maximum, grounded ice reached the continental shelf edge in the eastern but not western Ross Sea. Recessional geomorphic features in the western Ross Sea indicate virtually continuous back-stepping of the ice-sheet grounding line. In the eastern Ross Sea, well-preserved linear features and a lack of small-scale recessional landforms signify rapid lift-off of grounded ice from the bed. Physiography exerted a first-order control on regional ice behaviour, while sea floor geology played an important subsidiary role. Previously published deglacial scenarios for Ross Sea are based on low-spatial-resolution marine data or terrestrial observations; however, this study uses high-resolution basin-wide geomorphology to constrain grounding-line retreat on the continental shelf. Our analysis of retreat patterns suggests that (1) retreat from the western Ross Sea was complex due to strong physiographic controls on ice-sheet drainage; (2) retreat was asynchronous across the Ross Sea and between troughs; (3) the eastern Ross Sea largely deglaciated prior to the western Ross Sea following the formation of a large grounding-line embayment over Whales Deep; and (4) our glacial geomorphic reconstruction converges with recent numerical models that call for significant and complex East Antarctic ice sheet and West Antarctic ice sheet contributions to the ice flow in the Ross Sea.

  • 22. Hillier, J. K.
    et al.
    Smith, M. J.
    Armugam, R.
    Barr, I.
    Boston, C. M.
    Clark, C. D.
    Ely, J.
    Fankl, A.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gosselin, L.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hogan, K.
    Hughes, A. L. C.
    Livingstone, S. J.
    Lovell, H.
    McHenry, M.
    Munoz, Y.
    Pellicer, X. M.
    Pellitero, R.
    Robb, C.
    Roberson, S.
    Ruther, D.
    Spagnolo, M.
    Standell, M.
    Stokes, C. R.
    Storrar, R.
    Tate, N. J.
    Wooldridge, K.
    Manual mapping of drumlins in synthetic landscapes to assess operator effectiveness2015In: Journal of Maps, ISSN 1744-5647, E-ISSN 1744-5647, Vol. 11, no 5, p. 719-729Article in journal (Refereed)
    Abstract [en]

    Mapped topographic features are important for understanding processes that sculpt the Earth's surface. This paper presents maps that are the primary product of an exercise that brought together 27 researchers with an interest in landform mapping wherein the efficacy and causes of variation in mapping were tested using novel synthetic DEMs containing drumlins. The variation between interpreters (e.g. mapping philosophy, experience) and across the study region (e.g. woodland prevalence) opens these factors up to assessment. A priori known answers in the synthetics increase the number and strength of conclusions that may be drawn with respect to a traditional comparative study. Initial results suggest that overall detection rates are relatively low (34-40%), but reliability of mapping is higher (72-86%). The maps form a reference dataset.

  • 23.
    Hughes, Anna L.C.
    et al.
    Swansea University.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Clark, Chris D.
    University of Sheffield.
    Dating constraints on the last British-Irish Ice Sheet: a map and database: a map and database2011In: Journal of Maps, p. 156-184Article in journal (Refereed)
    Abstract [en]

    We present a collation of 975 published dates relevant to the timing of build-up and retreat of ice over the British Isles during the most recent glacial stage. The spatial distribution of dates is essential to interpreting the evolution of the ice sheet over time and space. For this reason the dates are presented as a map showing the spatial distribution across the UK and Ireland. Full documentation for each date, attributed to its source publication and detailing geographic location, the material dated, its stratigraphic position or setting, the dating technique, the dating result, errors and calibration, and comments pertinent to its interpretation, are included in the accompanying table. It is anticipated that this dataset will be a useful resource for Quaternary research in the UK and Ireland and is therefore available to download as a shapefile and/or PDF file. The map is presented at a scale of 1:2,700,000, designed to be printed at A2 size.

  • 24.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björck, Svante
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lif, Arne
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koyi, Hemin
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Major earthquake at the Pleistocene-Holocene transition in Lake Vattern, southern Sweden2014In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 42, no 5, p. 379-382Article in journal (Refereed)
    Abstract [en]

    Lake Vattern, Sweden, is within a graben that formed through rifting along the boundary between two Precambrian terrains. Geophysical mapping and geological coring show that substantial tectonic movements along the Lake Vattern graben occurred at the very onset of the Holocene. This is evident from deformation structures in the soft sediment accumulated on the lake floor. Our interpretation of these structures suggests as much as 13 m of vertical tectonic displacements along sections of a >80-km-long fault system. If these large displacements are from one tectonic event, Lake Vattern must have had an earthquake with seismic moment magnitudes to 7.5. In addition, our geophysical mapping shows large landslides along sections of the steep lake shores. Pollen analysis of sediment infillings of some of the most prominent sediment deformation structures places this major seismic event at the Younger Dryas-Preboreal transition, ca. 11.5 ka. We suggest that this event is mainly related to the rapid release of ice-sheet load following the deglaciation. This paleoseismic event in Lake Vattern ranks among the larger known intraplate tectonic events in Scandinavia and attests to the significance of glacio-isostatic unloading.

  • 25.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Bo
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Weidner, Elizabeth
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Bathymetric properties of the Baltic Sea2019In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 15, no 4, p. 905-924Article in journal (Refereed)
    Abstract [en]

    Baltic Sea bathymetric properties are analysed here using the newly released digital bathymetric model (DBM) by the European Marine Observation and Data Network (EMODnet). The analyses include hypsometry, volume, descriptive depth statistics, and kilometre-scale seafloor ruggedness, i.e. terrain heterogeneity, for the Baltic Sea as a whole as well as for 17 sub-basins defined by the Baltic Marine Environment Protection Commission (HELCOM). We compare the new EMODnet DBM with IOWTOPO the previously most widely used DBM of the Baltic Se aproduced by the Leibniz-Institut fur Ostseeforschung Warnemiinde (IOW), which has served as the primary gridded bathymetric resource in physical and environmental studies for nearly two decades. The area of deep water exchange between the Bothnian Sea and the Northern Baltic Proper across the Aland Sea is specifically analysed in terms of depths and locations of critical bathymetric sills. The EMODnet DBM provides a bathymetric sill depth of 88 m at the northern side of the Aland Sea and 60 m at the southern side, differing from previously identified sill depths of 100 and 70 m, respectively. High-resolution multibeam bathymetry acquired from this deep water exchange path, where vigorous bottom currents interacted with the seafloor, allows us to assess what presently available DBMs are missing in terms of physical characterization of the seafloor. Our study highlights the need for continued work towards complete high-resolution mapping of the Baltic Sea seafloor.

  • 26. Jones, R. S.
    et al.
    Mackintosh, A. N.
    Norton, K. P.
    Golledge, N. R.
    Fogwill, C. J.
    Kubik, P. W.
    Christl, M.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rapid Holocene thinning of an East Antarctic outlet glacier driven by marine ice sheet instability2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, article id 8910Article in journal (Refereed)
    Abstract [en]

    Outlet glaciers grounded on a bed that deepens inland and extends below sea level are potentially vulnerable to 'marine ice sheet instability'. This instability, which may lead to runaway ice loss, has been simulated in models, but its consequences have not been directly observed in geological records. Here we provide new surface-exposure ages from an outlet of the East Antarctic Ice Sheet that reveal rapid glacier thinning occurred approximately 7,000 years ago, in the absence of large environmental changes. Glacier thinning persisted for more than two and a half centuries, resulting in hundreds of metres of ice loss. Numerical simulations indicate that ice surface drawdown accelerated when the otherwise steadily retreating glacier encountered a bedrock trough. Together, the geological reconstruction and numerical simulations suggest that centennial-scale glacier thinning arose from unstable grounding line retreat. Capturing these instability processes in ice sheet models is important for predicting Antarctica's future contribution to sea level change.

  • 27.
    Kylander, Malin E.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Martinez-Cortizas, A.
    Bindler, Richard
    Kaal, Joeri
    Sjöström, Jenny K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hansson, Sophia V.
    Silva-Sanchez, Noemi
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gallagher, Kerry
    Rydberg, Johan
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rauch, Sebastien
    Mineral dust as a driver of carbon accumulation in northern latitudes2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6876Article in journal (Refereed)
    Abstract [en]

    Peatlands in northern latitudes sequester one third of the world's soil organic carbon. Mineral dusts can affect the primary productivity of terrestrial systems through nutrient transport but this process has not yet been documented in these peat-rich regions. Here we analysed organic and inorganic fractions of an 8900-year-old sequence from Store Mosse (the Great Bog) in southern Sweden. Between 5420 and 4550 cal yr BP, we observe a seven-fold increase in net peat-accumulation rates corresponding to a maximum carbon-burial rate of 150 g C m(-2) yr(-1) -more than six times the global average. This high peat accumulation event occurs in parallel with a distinct change in the character of the dust deposited on the bog, which moves from being dominated by clay minerals to less weathered, phosphate and feldspar minerals. We hypothesize that this shift boosted nutrient input to the bog and stimulated ecosystem productivity. This study shows that diffuse sources and dust dynamics in northern temperate latitudes, often overlooked by the dust community in favour of arid and semi-arid regions, can be important drivers of peatland carbon accumulation and by extension, global climate, warranting further consideration in predictions of future climate variability.

  • 28.
    Kylander, Malin E.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Martinez-Cortizas, Antonio
    Bindler, Richard
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rauch, Sebastien
    Potentials and problems of building detailed dust records using peat archives: An example from Store Mosse (the Great Bog), Sweden2016In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 190, p. 156-174Article in journal (Refereed)
    Abstract [en]

    Mineral dust deposition is a process often overlooked in northern mid-latitudes, despite its potential effects on ecosystems. These areas are often peat-rich, providing ample material for the reconstruction of past changes in atmospheric deposition. The highly organic (up to 99% in some cases) matrix of atmospherically fed mires, however, makes studying the actual dust particles (grain size, mineralogy) challenging. Here we explore some of the potentials and problems of using geochemical data from conservative, lithogenic elements (Al, Ga, Rb, Sc, Y, Zr, Th, Ti and REE) to build detailed dust records by using an example from the 8900-yr peat sequence from Store Mosse (the Great Bog), which is the largest mire complex in the boreo-nemoral region of southern Sweden. The four dust events recorded at this site were elementally distinct, suggesting different dominant mineral hosts. The oldest and longest event (6385-5300 cal yr BP) sees a clear signal of clay input but with increasing contributions of mica, feldspar and middle-REE- rich phosphate minerals over time. These clays are likely transported from a long-distance source (< 100 km). While dust deposition was reduced during the second event (5300-4370 cal yr BP), this is the most distinct in terms of its source character with [Eu/Eu*] UCC revealing the input of plagioclase feldspar from a local source, possibly active during this stormier period. The third (2380- 2200 cal yr BP) and fourth (1275-1080 cal yr BP) events are much shorter in duration and the presence of clays and heavy minerals is inferred. Elemental mass accumulation rates reflect these changes in mineralogy where the relative importance of the four dust events varies by element. The broad changes in major mineral hosts, grain size, source location and approximated net dust deposition rates observed in the earlier dust events of longer duration agree well with paleoclimatic changes observed in northern Europe. The two most recent dust events are much shorter in duration, which in combination with evidence of their local and regional character, may explain why they have not been seen elsewhere.

  • 29.
    Muschitiello, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lea, James M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nick, Faezeh M.
    Brunnberg, Lars
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Macleod, Alison
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Timing of the first drainage of the Baltic Ice Lake synchronous with the onset of Greenland Stadial 12016In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 45, no 2, p. 322-334Article in journal (Refereed)
    Abstract [en]

    Glacial varves can give significant insights into recession and melting rates of decaying ice sheets. Moreover, varve chronologies can provide an independent means of comparison to other annually resolved climatic archives, which ultimately help to assess the timing and response of an ice sheet to changes across rapid climate transitions. Here we report a composite 1257-year-long varve chronology from southeastern Sweden spanning the regional late AllerOd-late Younger Dryas pollen zone. The chronology was correlated to the Greenland Ice-Core Chronology 2005 using the time-synchronous Vedde Ash volcanic marker, which can be found in both successions. For the first time, this enables secure placement of the Lateglacial Swedish varve chronology in absolute time. Geochemical analysis from new varve successions indicate a marked change in sedimentation regime accompanied by an interruption of ice-rafted debris deposition synchronous with the onset of Greenland Stadial 1 (GS-1; 12846years before AD 1950). With the support of a simple ice-flow/calving model, we suggest that slowdown of sediment transfer can be explained by ice-sheet margin stabilization/advance in response to a significant drop of the Baltic Ice Lake level. A reassessment of chronological evidence from central-western and southern Sweden further supports the hypothesis of synchronicity between the first (penultimate) catastrophic drainage of the Baltic Ice Lake and the start of GS-1 in Greenland ice-cores. Our results may therefore provide the first chronologically robust evidence linking continental meltwater forcing to rapid atmosphere-ocean circulation changes in the North Atlantic.

  • 30.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geotechnical and sedimentary evidence for thick-grounded ice in southern Lake Vättern during deglaciation2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 2, p. 355-366Article in journal (Refereed)
    Abstract [en]

    A 74-meter Late Pleistocene to Holocene sedimentary sequence was recovered from southern Lake Vattern in the autumn of 2012. At approximate to 54m below the lake floor, shear strength and high-resolution bulk density measurements suggest the presence of an unconformity in the varved proglacial clays. Incremental load consolidation tests reveal highly overconsolidated sediments below this level. Preconsolidation pressures for the underlying sediments are between 1250 and 2100kPa, up to approximate to 1700kPa more than the current in-situ effective stress. The highly overconsolidated sediments indicate either substantial erosion (the removal of 215-360m of sediment), or consolidation under a large grounded ice mass sitting up to 230m above paleo-lake level. Glaciotectonic deformation in underlying sediments supports the interpretation of a grounded ice mass. It is likely that this horizon is either contemporaneous with or older than the Levene moraine, formed between 13.4 and 13.8ka. In the approximate to 30m of overlying proglacial clays, there is no further evidence for grounded ice, indicating that any ice advance to southern Lake Vattern during the Younger Dryas would have been limited to an extremely thin ice tongue.

  • 31.
    Preto, Pedro
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Näslund, Jens-Ove
    Sundberg, Jan
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geothermal evidence for groundwater flow through Quaternary sediments overlying bedrock aquifers below Lake V?ttern, Sweden2019In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 141, no 2, p. 106-120Article in journal (Refereed)
    Abstract [en]

    Groundwater discharge into lakes is an important component of the fluid and nutrient budgets, and a possible route for contaminant transport. However, groundwater flow beneath lakes is difficult to investigate due to the need for drilling deep boreholes. In 2012, a 2,000 m deep borehole was drilled in Lake Vättern, the second largest lake in Sweden. A continuous temperature profile was collected from the borehole. The geothermal gradient in the upper 180 m is highly non-linear, and not controlled by variability in the measured thermal properties of the sediments and rocks. The anomalous temperature profile is best explained by fluid flow into the borehole and subsequent vertical flow of warm waters towards the lake floor. Combining the temperature profile with stratigraphic information from drilling logs and seismic data, we find that fluid flow into the borehole occurs in glacial and glaciofluvial sediments deposited on top of a large sandstone aquifer (the Visingsö Group). The warm waters flowing through the glacial and glaciofluvial sediments are likely sourced from the underlying Visingsö Group sandstones. There is no evidence for substantial vertical migration of these waters through the overlying glacial and postglacial sediments. We speculate that they escape either along lake margins where overlying sediments become thinner, or along faults that are known to exist in the deeper basin.These results highlight an important hydraulic transport pathway between recognised regional aquifers and Lake Vättern. Further work is needed to evaluate the significance of groundwater discharge on the water and nutrient budget of the lake.

  • 32. Shackleton, Calvin
    et al.
    Patton, Henry
    Hubbard, Alun
    Winsborrow, Monica
    Kingslake, Jonathan
    Esteves, Mariana
    Andreassen, Karin
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Subglacial water storage and drainage beneath the Fennoscandian and Barents Sea ice sheets2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 201, p. 13-28Article in journal (Refereed)
    Abstract [en]

    Subglacial hydrology modulates how ice sheets flow, respond to climate, and deliver meltwater, sediment and nutrients to proglacial and marine environments. Here, we investigate the development of subglacial lakes and drainage networks beneath the Fennoscandian and Barents Sea ice sheets over the Late Weichselian. Utilizing an established coupled climate/ice flow model, we calculate high-resolution, spatio-temporal changes in subglacial hydraulic potential from ice sheet build-up (similar to 37 ka BP) to complete deglaciation (similar to 10 ka BP). Our analysis predicts up to 3500 potential subglacial lakes, the largest of which was 658 km(2), and over 70% of which had surface areas <10 km(2), comparable with subglacial lake size distributions beneath the Antarctic Ice Sheet. Asynchronous evolution of the Fennoscandian Ice Sheet into the flatter relief of northeast Europe affected patterns of subglacial drainage, with up to 100 km(3) more water impounded within subglacial lakes during ice build-up compared to retreat. Furthermore, we observe frequent fill/drain cycles within clusters of subglacial lakes at the onset zones and margins of ice streams that would have affected their dynamics. Our results resonate with mapping of large subglacial channel networks indicative of high-discharge meltwater drainage through the Gulf of Bothnia and central Barents Sea. By tracking the migration of meltwater drainage outlets during deglaciation, we constrain locations most susceptible to focussed discharge, including the western continental shelf-break where subglacial sediment delivery led to the development of major trough mouth fans. Maps of hydraulic potential minima that persist throughout the Late Weichselian reveal potential sites for preserved subglacial lake sediments, thereby defining useful targets for further field investigation.

  • 33. Simkins, Lauren M.
    et al.
    Anderson, John B.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gonnermann, Helge M.
    Prothro, Lindsay O.
    Halberstadt, Anna Ruth W.
    Stearns, Leigh A.
    Pollard, David
    DeConto, Robert M.
    Anatomy of a meltwater drainage system beneath the ancestral East Antarctic ice sheet2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 9, p. 691-697Article in journal (Refereed)
    Abstract [en]

    Subglacial hydrology is critical to understand the behaviour of ice sheets, yet active meltwater drainage beneath contemporary ice sheets is rarely accessible to direct observation. Using geophysical and sedimentological data from the deglaciated western Ross Sea, we identify a palaeo-subglacial hydrological system active beneath an area formerly covered by the East Antarctic ice sheet. A long channel network repeatedly delivered meltwater to an ice stream grounding line and was a persistent pathway for episodic meltwater drainage events. Embayments within grounding-line landforms coincide with the location of subglacial channels, marking reduced sedimentation and restricted landform growth. Consequently, channelized drainage at the grounding line influenced the degree to which these landforms could provide stability feedbacks to the ice stream. The channel network was connected to upstream subglacial lakes in an area of geologically recent rifting and volcanism, where elevated heat flux would have produced sufficient basal melting to fill the lakes over decades to several centuries; this timescale is consistent with our estimates of the frequency of drainage events at the retreating grounding line. Based on these data, we hypothesize that ice stream dynamics in this region were sensitive to the underlying hydrological system.

  • 34. Simkins, Lauren M.
    et al.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, John B.
    Diagnosing ice sheet grounding line stability from landform morphology2018In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 12, no 8, p. 2707-2726Article in journal (Refereed)
    Abstract [en]

    The resilience of a marine-based ice sheet is strongly governed by the stability of its grounding lines, which are in turn sensitive to ocean-induced melting, calving, and flotation of the ice margin. Since the grounding line is also a sedimentary environment, the constructional landforms that are built here may reflect elements of the processes governing this dynamic and potentially vulnerable environment. Here we analyse a large dataset (n = 6275) of grounding line landforms mapped on the western Ross Sea continental shelf from high-resolution geophysical data. The population is divided into two distinct morphotypes by their morphological properties: recessional moraines (consistently narrow, closely spaced, low amplitude, symmetric, and straight) and grounding zone wedges (broad, widely spaced, higher amplitude, asymmetric, sinuous, and highly variable). Landform morphotypes cluster with alike forms that transition abruptly between morphotypes both spatially and within a retreat sequence. Their form and distribution are largely independent of water depth, bed slope, and position relative to glacial troughs. Similarly, we find no conclusive evidence for morphology being determined by the presence or absence of an ice shelf. Instead, grounding zone wedge construction is favoured by a higher sediment flux and a longer-held grounding position. We propose two endmember modes of grounding line retreat: (1) an irregular mode, characterised by grounding zone wedges with longer standstills and accompanied by larger-magnitude retreat events, and (2) a steady mode, characterised by moraine sequences that instead represent more frequent but smaller-magnitude retreat events. We suggest that while sediment accumulation and progradation may prolong the stability of a grounding line position, progressive development of sinuosity in the grounding line due to spatially variable sediment delivery likely destabilises the grounding position by enhanced ablation, triggering large-magnitude retreat events. Here, the concept of stability is multifaceted and paradoxical, and neither mode can be characterised as marking fast or slow retreat. Diagnosing grounding line stability based on landform products should be considered for a wider geographic range, yet this large dataset of landforms prompts the need to better understand the sensitivity of marine-based grounding lines to processes and feedbacks governing retreat and what stability means in the context of future grounding line behaviour.

  • 35.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ananyev, Roman
    Chernykh, Denis
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Regional deglaciation and postglacial lake development as reflected in a 74m sedimentary record from Lake Vättern, southern Sweden2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 2, p. 336-354Article in journal (Refereed)
    Abstract [en]

    The withdrawal of the Late Weichselian ice sheet and rapid isostatic uplift in southern Scandinavia led to the entrainment of large volumes of melt water within the proglacial Baltic Ice Lake (BIL). The eventual western outpost of BIL, Lake Vattern, has been a focal point for studying the dynamic retreat history of the Late Weichselian ice sheet in south central Sweden. This part of the deglacial history is described from an abundance of terrestrial studies, but, to date, no complimentary long sediment cores from Lake Vattern have been available. Here, we present the results from a unique, 74m borehole in southern Lake Vattern that recovered a Late Pleistocene to Holocene sedimentary sequence. Physical and chemical analyses of the sediment and pore water, together with geophysical mapping, reveal glacial as well as postglacial imprints implying an oscillating ice sheet margin, evidence for neotectonic activity and one or more marine incursions into the lake during deglaciation. We attribute the glaciotectonic deformation of the sediments at 54m below the lake floor to an ice readvance that likely occurred at the same time or before the advance that formed the Levene moraine (approximate to 13.8-13.4cal.kaBP). After this event, potential readvances were likely restricted to a more northerly position in the basin. We identify the final drainage of the BIL, but find evidence for an earlier marine incursion into the Vattern basin (approximate to 13.0cal.kaBP), indicating water exchange between the North Atlantic and the Baltic Ice Lake during the late Allerod.

  • 36.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björck, Svante
    Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A chronology of environmental changes in the Lake Vättern basin from deglaciation to its final isolation2018In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 47, no 2, p. 609-624Article in journal (Refereed)
    Abstract [en]

    During and after deglaciation, Lake Vättern developed from a proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL), into a brackish water body connecting the North Sea and the Baltic Sea, and finally into an isolated freshwater lake. Here we present geochemical and mineralogical data from a 70‐m composite sediment core recovered in southern Lake Vättern. Together with a radiocarbon age model of this core, we are able to delineate the character and timing of the different lake stages. In addition to a common mineralogical background signature seen throughout the sediment core, the proglacial sediments bear a calcite imprint representing ice‐sheet transported material from the limestone bedrock that borders the lake basin in the northeast. The proglacial fresh to brackish water transition is dated to 11 480±290 cal. a BP and is in close agreement with other regional chronologies. The brackish period lasted c. 300 years and was followed by a c. 1600 year freshwater period before the Vättern basin became isolated from the Initial Littorina Sea. Decreasing detrital input, increasing δ13C values and the appearance of diatoms in the upper 15 m of the sediment succession are interpreted as an overall increase in biological productivity. This mode of sedimentation continues until the present and is interpreted to mark the final isolation of the lake at 9530±50 cal. a BP. Consequently, the isolation of Lake Vättern was not an outcome of the Ancylus Lake regression, but rather because of ongoing continental uplift in the early Littorina period.

  • 37.
    Wohlfarth, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Watson, Jenny
    Whitehouse, Nicola J.
    Hasseldala-a key site for Last Termination climate events in northern Europe2017In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 46, no 2, p. 143-161Article in journal (Refereed)
    Abstract [en]

    The Last Termination (19 000-11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hasseldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (> 14.1-9.5 cal. ka BP) is one of the few chronologically well-constrained, multi- proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hasseldala's multi-proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5-11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hasseldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.

1 - 37 of 37
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