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  • 1. Jahn, A.
    et al.
    Aksenov, Y.
    de Cuevas, B. A.
    de Steur, L.
    Hakkinen, S.
    Hansen, E.
    Herbaut, C.
    Houssais, M. -N
    Karcher, M.
    Kauker, F.
    Lique, C.
    Nguyen, A.
    Pemberton, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Worthen, D.
    Zhang, J.
    Arctic Ocean freshwater: How robust are model simulations?2012Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, s. C00D16-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Arctic freshwater (FW) has been the focus of many modeling studies, due to the potential impact of Arctic FW on the deep water formation in the North Atlantic. A comparison of the hindcasts from ten ocean-sea ice models shows that the simulation of the Arctic FW budget is quite different in the investigated models. While they agree on the general sink and source terms of the Arctic FW budget, the long-term means as well as the variability of the FW export vary among models. The best model-to-model agreement is found for the interannual and seasonal variability of the solid FW export and the solid FW storage, which also agree well with observations. For the interannual and seasonal variability of the liquid FW export, the agreement among models is better for the Canadian Arctic Archipelago (CAA) than for Fram Strait. The reason for this is that models are more consistent in simulating volume flux anomalies than salinity anomalies and volume-flux anomalies dominate the liquid FW export variability in the CAA but not in Fram Strait. The seasonal cycle of the liquid FW export generally shows a better agreement among models than the interannual variability, and compared to observations the models capture the seasonality of the liquid FW export rather well. In order to improve future simulations of the Arctic FW budget, the simulation of the salinity field needs to be improved, so that model results on the variability of the liquid FW export and storage become more robust. Citation: Jahn, A., et al. (2012), Arctic Ocean freshwater: How robust are model simulations?, J. Geophys. Res., 117, C00D16, doi: 10.1029/2012JC007907.

  • 2.
    Mårtensson, Sebastian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Meier, H. E. Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Pemberton, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Haapala, J.
    Ridged sea ice characteristics in the arctic from a coupled multicategory sea ice model2012Inngår i: Journal of Geophysical Research: Oceans, ISSN 2169-9291, Vol. 117, nr C8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, a multicategory sea ice model with explicit ice classes for ridged and rafted ice was used to examine the evolution of deformed ice during the period 1980-2002. The results show that (1) ridged ice comprises roughly 45-60% of Arctic sea ice volume and 25-45% of the sea ice area, (2) most of the perennial ice consists of ridged ice, and (3) ridged ice exhibits a small seasonal variability. Our results also show an increase in mean ridged ice thickness of 4-6 cm yr(-1) during the summer in an area north of the Canadian Archipelago and a corresponding decrease in the East Siberian Sea and Nansen Basin. At the same time, Arctic sea ice age has been observed to decline and ice drift speed to increase during the simulation period. We connect these findings with a modeled regional increase in the production rate of ridged ice. Comparison of the multicategory model and a two category reference model shows a substantially increased ice production rate due to a more frequent occurrence of leads, resulting in an ice thickness increase of up to 0.8 m. Differences in ice physics between the multicategory and reference models also affect the freshwater content. The sum of liquid and solid freshwater content in the entire Arctic Ocean is about 10% lower and net precipitation (P-E) is about 7% lower as compared to the reference model.

  • 3.
    Pemberton, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Freshwater processes and water mass transformation in the Arctic Ocean2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis explores freshwater-related processes and water mass transformation in the Arctic Ocean. Knowledge of these processes is important from both a local and a global perspective. Globally, because the export of cold and low saline water and sea ice might influence the North Atlantic and global meridional overturning circulation. Locally, because freshwater processes affect the vertical stratification and permit favorable conditions for the ice cover.

    Models of different complexity are the main tools of the present work. A part of the material considers how these models can be used to examine the key processes governing freshwater balance. Additionally, the freshwater budgets amongst 10 different ocean general circulation models (OGCMs) are compared and robust features and weaknesses identified.

    A large part considers the freshwater processes governing the stratification with an emphasis on the low saline upper parts. The interactions between freshwater sources and sinks are studied in an OGCM using passive tracers. It is found that the composition, pathways and shelf-basin exchange of low saline water primarily involve processes linked to Siberian runoff, Pacific water and sea-ice melting and formation. Motivated by observed changes and paleorecords the sensitivity of the stratification is further explored in freshwater perturbation experiments with an OGCM. The response yields a deeper halocline for decreasing freshwater input, in line with a theoretical model.

    The final part focuses on a new framework for analyzing water mass transformations. In the framework volume, heat and salt budgets are computed in salinity-temperature space. Using different OGCMs it is shown how surface and interior processes transform inflowing waters towards colder and fresher waters and how the halocline renewal rate can be estimated. Limiting cases for the water mass transformation balance are identified by separating contributions from surface, internal and boundary fluxes.

    Fulltekst (pdf)
    fulltext
  • 4.
    Pemberton, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Hieronymus, Magnus
    Meier, H. E. Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Arctic Ocean Water Mass Transformation in S-T Coordinates2015Inngår i: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 45, nr 4, s. 1025-1050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, watermass transformations in the Arctic Ocean are studied using a recently developed salinity-temperature (S-T) framework. The framework allows the water mass transformations to be succinctly quantified by computing the surface and internal diffusive fluxes in S-T coordinates. This study shows how the method can be applied to a specific oceanic region, in this case the Arctic Ocean, by including the advective exchange of water masses across the boundaries of the region. Based on a simulation with a global ocean circulation model, the authors examine the importance of various parameterized mixing processes and surface fluxes for the transformation of water across isohaline and isothermal surfaces in the ArcticOcean. The model-based results reveal a broadly realistic Arctic Ocean where the inflowing Atlantic and Pacific waters are primarily cooled and freshened before exiting back to the North Atlantic. In the model, the water mass transformation in the T direction is primarily accomplished by the surface heat flux. However, the surface freshwater flux plays a minor role in the transformation of water toward lower salinities, which is mainly driven by a downgradient mixing of salt in the interior ocean. Near the freezing line, the seasonal melt and growth of sea ice influences the transformation pattern.

  • 5.
    Pemberton, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Meier, H. E. Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Arctic Ocean freshwater composition, pathways and transformations from a passive tracer simulation2014Inngår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 66, artikkel-id 23988Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Freshwater (FW) induced transformations in the upper Arctic Ocean were studied using a coupled regional sea ice-ocean model driven by winds and thermodynamic forcing from a reanalysis of data during the period 1948-2011, focusing on the mean state during 1968-2011. Using passive tracers to mark a number of FW sources and sinks, their mean composition, pathways and export were examined. The distribution of the simulated FW height reproduced the known features of the Arctic Ocean and volume-integrated FW content matched climatological estimates reasonably well. Input from Eurasian rivers and extraction by sea-ice formation dominate the composition of the Arctic FW content whilst Pacific water increases in importance in the Canadian Basin. Though pathways generally agreed with previous studies the locus of the Eurasian runoff shelf-basin transport centred at the Alpha-Mendeleyev ridge, shifting the Pacific-Atlantic front eastwards. A strong coupling between tracers representing Eurasian runoff and sea-ice formation showed how water modified on the shelf spreads across the Arctic and mainly exits through the Fram Strait. Transformation to salinity dependent coordinates showed how Atlantic water is modified by both low-salinity shelf and Pacific waters in an estuary-like overturning producing water masses of intermediate salinity that are exported to the Nordic Seas. A total halocline renewal rate of 1.0 Sv, including both shelf-basin exchange and cross-isohaline flux, was estimated from the transports: both components were of equal magnitude. The model’s halocline shelf-basin exchange is dominated by runoff and sea-ice processes at the western shelves (the Barents and Kara seas) and Pacific water at the eastern shelves (the Laptev, East Siberian and Chukchi seas).

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