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Late Quaternary Biostratigraphy and Paleoceanography of the central Arctic Ocean
Stockholm University, Faculty of Science, Department of Geological Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The central Arctic Ocean is one of the least explored deep sea regions and long biostratigraphic sediment records are sparse. The main focus of this thesis is the Arctic Ocean foraminiferal record and its application to reconstruct paleoceanographic variations and summer sea ice cover changes between late Quaternary interglacial periods. One of the studied cores was retrieved from the central Lomonosov Ridge Intra Basin. This core contains a relatively high-resolution biostratigraphic record spanning Marine Isotope Stages (MIS) 1–3, although with a hiatus encompassing the Last Glacial Maximum. Radiocarbon age calibrations in this core show a decreasing trend of high marine reservoir ages of about 1400 years during the last deglaciation to 700 years in the late Holocene. The cores from the Lomonosov Ridge off Greenland and the Morris Jesup Rise contain preserved calcareous microfossils further back in time than most previously studied central Arctic Ocean cores. The calcium content estimated by X-ray fluorescence scanning of these cores shows a distinct pattern of calcium rich intervals coinciding with peaks in foraminiferal abundance in the sediment record of MIS 1–7. The calcium peaks originate from material accumulated during interglacials, primarily through detrital carbonate and dolomite input from the decaying North American ice sheet and secondarily from biogenic material. Intervals of calcareous benthic foraminifera are found in pre MIS 7 sediments on both the southern Lomonosov Ridge and Morris Jesup Rise. Their assemblage composition and stable carbon isotope data suggest increased primary production and decreased summer sea ice cover compared to the Holocene central Arctic Ocean. This is also suggested for an interval of high abundance of the subpolar planktic foraminifera Turborotalita quinqueloba on the southern Lomonosov Ridge with a proposed MIS 11 age.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University , 2011. , 32 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 345
Keyword [en]
Arctic Ocean, Quaternary, biostratigraphy, foraminifera, paleoceanography
National Category
Other Earth and Related Environmental Sciences
Research subject
Marine Geoscience
Identifiers
URN: urn:nbn:se:su:diva-57245ISBN: 978-91-7447-311-7OAI: oai:DiVA.org:su-57245DiVA: diva2:414857
Public defence
2011-06-10, Ahlmansalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted.

Available from: 2011-05-12 Created: 2011-05-04 Last updated: 2014-03-28Bibliographically approved
List of papers
1. Quaternary Arctic Ocean sea ice variations and deep water isolation times
Open this publication in new window or tab >>Quaternary Arctic Ocean sea ice variations and deep water isolation times
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2010 (English)In: Quaternary Science Reviews, ISSN 0277-3791, Vol. 29, no 25-26, 3430-3441 p.Article in journal (Refereed) Published
Abstract [en]

A short sediment core retrieved from a local depression forming an intra basin on the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Marine reservoir ages of 1400 years or more, at least during the last deglaciation, seem plausible from calibration of the radiocarbon ages using modeled reservoir corrections from previous studies in combination with the microfossil abundance record of the studied core. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Late Glacial to the Holocene, suggesting circulation and ventilation changes.

National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-30891 (URN)10.1016/j.quascirev.2010.06.011 (DOI)000284724400007 ()
Available from: 2009-10-30 Created: 2009-10-30 Last updated: 2011-11-21Bibliographically approved
2. Biogenic and detrital rich intervals in central arctic ocean cores identified using x ray fluorescence scanning
Open this publication in new window or tab >>Biogenic and detrital rich intervals in central arctic ocean cores identified using x ray fluorescence scanning
2013 (English)In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 32, 18386- p.Article in journal (Refereed) Published
Abstract [en]

X-ray fluorescence (XRF) scanning of sediment cores from the Lomonosov Ridge and the Morris Jesup Rise reveals a distinct pattern of Ca intensity peaks through Marine Isotope Stages (MIS) 1 to 7. Downcore of MIS 7, the Ca signal is more irregular and near the detection limit. Virtually all major peaks in Ca coincide with a high abundance of calcareous microfossils; this is particularly conspicuous in the cores from the central Arctic Ocean. However, the recorded Ca signal is generally caused by a combination of biogenic and detrital carbonate, and in areas influenced by input from the Canadian Arctic, detrital carbonates may effectively mask the foraminiferal carbonates. Despite this, there is a strong correlation between XRF-detected Ca content and foraminiferal abundance. We propose that in the Arctic Ocean north of Greenland a common palaeoceanographic mechanism is controlling Ca-rich ice-rafted debris (IRD) and foraminiferal abundance. Previous studies have shown that glacial periods are characterized by foraminfer-barren sediments. This implies that the Ca-rich IRD intervals with abundant foraminifera were most likely deposited during interglacial periods when glaciers left in the Canadian Arctic Archipelago were still active and delivered a large amount of icebergs. At the same time, conditions were favourable for planktic foraminifera, resulting in a strong covariance between these proxies. Therefore, we suggest that the XRF scanner's capability to efficiently map Ca concentrations in sediment cores makes it possible to systematically examine large numbers of cores from different regions to investigate the palaeoceanographic reasons for the calcareous microfossils' spatial and temporal variability.

Keyword
Foraminifera, Arctic Ocean, IRD, calcareous microfossils, XRF scanning
National Category
Oceanography, Hydrology, Water Resources Ecology
Identifiers
urn:nbn:se:su:diva-88337 (URN)10.3402/polar.v32i0.18386 (DOI)000314828200001 ()
Note

AuthorCount:3;

Available from: 2013-03-18 Created: 2013-03-12 Last updated: 2014-03-28Bibliographically approved
3. Late Quaternary benthic foraminiferal assemblages from the central Arctic Ocean
Open this publication in new window or tab >>Late Quaternary benthic foraminiferal assemblages from the central Arctic Ocean
(English)Article in journal (Refereed) Submitted
Abstract [en]

Sediment cores retrieved from the Morris Jesup Rise and the southern Lomonosov Ridge north off Greenland reveal an extended microfossil record compared to most other cores recovered from the central Arctic Ocean. The identified benthic foraminifera can be divided into six assemblages, all of which are dominated by the most common species Cassidulina neoteretis. This species is observed in surface sediments throughout the central Arctic Ocean at water depth under the influence of the Arctic Intermediate Water suggesting that this condition prevailed for a long time and also show that is an important factor for assemblage composition. The important accessory species in the top two assemblages, Oridorsalis tener, suggests oligotroph conditions and probable high sea ice cover during the Marine Isotope Stages (MIS) 1 to 5.1. The occurrence of the phytodetrital exploiting species Epistominella exigua characterizes the assemblages 3 to 6 (MIS 5.5 and older). This species is not present in recent central Arctic Ocean sediments and has been used as biostratigraphic marker for MIS 5.5 as a unique event. This study shows that E. exigua rather has its last occurrence in this time interval and is continuously found in older sediments. For the environmental conditions during this time period the presence of E. exigua implies higher primary production in the surface waters and with that lesser summer sea ice compared to present day conditions. While the abundance of agglutinated specimens increases downcore a complete switch as described from most other central Arctic Ocean cores during MIS 7 to 9 cannot be confirmed.

Research subject
Geology
Identifiers
urn:nbn:se:su:diva-56910 (URN)
Available from: 2011-04-29 Created: 2011-04-29 Last updated: 2011-05-05Bibliographically approved

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