Göran Björk
University of Gothenburg, Dept of Marine sciences, Faculty Member
This large‐scale quasi‐synoptic study gives a comprehensive picture of sea‐air CO2 fluxes during the melt season in the central and outer Laptev Sea (LS) and East Siberian Sea (ESS). During a 7 week cruise we compiled a continuous record... more
This large‐scale quasi‐synoptic study gives a comprehensive picture of sea‐air CO2 fluxes during the melt season in the central and outer Laptev Sea (LS) and East Siberian Sea (ESS). During a 7 week cruise we compiled a continuous record of both surface water and air CO2 concentrations, in total 76,892 measurements. Overall, the central and outer parts of the ESAS constituted a sink for CO2, and we estimate a median uptake of 9.4 g C m−2 yr−1 or 6.6 Tg C yr−1. Our results suggest that while the ESS and shelf break waters adjacent to the LS and ESS are net autotrophic systems, the LS is a net heterotrophic system. CO2 sea‐air fluxes for the LS were 4.7 g C m−2 yr−1, and for the ESS we estimate an uptake of 7.2 g C m−2 yr−1. Isotopic composition of dissolved inorganic carbon (δ13CDIC and δ13CCO2) in the water column indicates that the LS is depleted in δ13CDIC compared to the Arctic Ocean (ArcO) and ESS with an offset of 0.5‰ which can be explained by mixing of δ13CDIC‐depleted riveri...
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During the LOMROG-2007 icebreaker expedition to the area where the Lomonosov Ridge attaches to the Greenland shelf, we observed a well defined signal in water mass properties of clear CBDW origin. The major part of CBDW passes the... more
During the LOMROG-2007 icebreaker expedition to the area where the Lomonosov Ridge attaches to the Greenland shelf, we observed a well defined signal in water mass properties of clear CBDW origin. The major part of CBDW passes the Lomonosov Ridge at the 1870 m deep channel near the North Pole (88 25' N, 150 E) as was discovered during the Beringia/Hotrax 2005 exploration of the sill area. During the LOMROG expedition we observed the signal of CBDW along the Amundsen Basin side of the Lomonosov Ridge slope north of Greenland and further along the Greenland shelf towards east and south. The signal with Canadian Basin properties is clearly seen in the TS structure as well as in the oxygen, silicate and CFC signals around 2000 m depth. No indication of a deep overflow across the Lomonosov Ridge at the channel just north of Greenland was seen.
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The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed due to logistical difficulties, even though the importance of the Arctic Ocean for global climate is widely recognized. The cold waters of the... more
The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed due to logistical difficulties, even though the importance of the Arctic Ocean for global climate is widely recognized. The cold waters of the high latitudes have high solubility of gases resulting in high concentrations of carbon dioxide (CO2) and thus a resulting relative low pH. The distribution of CO2, its variability in time and space, as well as its sources, are not known in detail. The Arctic Ocean has wide shelf areas where a number of processes impact the CO2 cycling. These comprise extensive biological activity, both high primary productivity and an active microbial loop within the surface sediment, uptake of CO2 from the atmosphere driven by the increased solubility caused by cooling of the waters flowing in from the Atlantic and Pacific Oceans, and input of total alkalinity and dissolved inorganic and organic carbon by the river runoff. On top of this we have increasing uptake of atmospheric CO2 resulting from the rising atmospheric concentration caused by burning of fossil fuel and deforestation, the so-called anthropogenic CO2. The waters on most shelves flow off into the deep Arctic basins where they penetrate different depth layers depending on their density. Some shelf water has very high density as a result of brine production during sea ice formation, and this water can at places penetrate to several km depths in the central basin while entraining surrounding waters. However, most waters penetrate the upper few hundred meters, i.e., the waters shallower than the Atlantic Layer. In this contribution we utilize data collected during IPY and earlier programs and assess the biochemical production and consumption of CO2 in the shelf seas as well as the air-sea interaction, compute how this transformation impact the acidity of the waters, and illustrate how this signal is exported into the deep central basin. We show that the cold waters of the Arctic shelves has very variable partial pressure of CO2 (pCO2) in the summer; generally lower than atmospheric levels (under-saturated) in the surface waters with high primary productivity, but with over-saturated pCO2 in some surface waters, especially close to the coast and in the river mouths, and with generally over-saturated bottom waters. The high pCO2 bottom waters get its signal from organic matter (both marine and terrestrial) that decays at the sediment surface and its signature reveal that it is brine enriched from sea ice production. The density of this brine enriched water makes it flow out into the deep basin at a depth range of 50 to 250 m. This water with its high pCO2 has a pH minimum that is enough to make it corrosive to most forms of calcium carbonate minerals. Utilizing CFC concentrations we conclude that this corrosive volume has grown since preindustrial times and will further grow to a level where it reaches the surface by the year 2050.
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General dynamical features of East Greenland Current (EGC) are synthesized from a survey conducted by the icebreaker Oden during the Swedish Arctic Ocean Expedition 2002. The data includes hydrography and ADCP observations in eight... more
General dynamical features of East Greenland Current (EGC) are synthesized from a survey conducted by the icebreaker Oden during the Swedish Arctic Ocean Expedition 2002. The data includes hydrography and ADCP observations in eight transects of the EGC, from the Fram Strait in the north to the Denmark Strait in the south. The survey reveals a strong confinement of the low-saline polar water in the EGC to the continental slope/shelf --- a feature of relevance for the overall stability of the thermohaline circulation in the Arctic Ocean. The southward transport of liquid freshwater in the EGC was found to vary dramatically between transects: from peak values on the order of 0.06 Sverdrup to virtually zero. The dynamical origin of the observed alongstream pulsations in freshwater transport is briefly discussed from a theoretical standpoint, emphasizing the potential for freshwater leakage into the deep-water producing areas in the Greenland Sea.
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Research Interests: Earth Sciences, Environmental Science, Oceanography, Carbon Dioxide, Sea Ice, and 15 moreBiological Sciences, Seasonality, Environmental Sciences, Ocean acidification, Atmospheric Pressure, Biogeosciences, Methane, Primary Production, Marine Environment, Pacific ocean, Calcium Carbonate, Organic Matter, Dissolved Inorganic Carbon, Nutrient Concentration, and Biogeochemical Cycle
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The circulation pathways and subsurface cooling and freshening of warm deep water on the central Amundsen Sea shelf are deduced from hydrographic transects and four subsurface moorings. The Amundsen Sea continental shelf is intersected by... more
The circulation pathways and subsurface cooling and freshening of warm deep water on the central Amundsen Sea shelf are deduced from hydrographic transects and four subsurface moorings. The Amundsen Sea continental shelf is intersected by the Dotson trough (DT), leading from the outer shelf to the deep basins on the inner shelf. During the measurement period, warm deep water was observed to flow southward on the eastern side of DT in approximate geostrophic balance. A northward outflow from the shelf was also observed along the bottom in the western side of DT. Estimates of the flow rate suggest that up to one-third of the inflowing warm deep water leaves the shelf area below the thermocline in this deep outflow. The deep current was 1.2°C colder and 0.3 psu fresher than the inflow, but still warm, salty, and dense compared to the overlying water mass. The temperature and salinity properties suggest that the cooling and freshening process is induced by subsurface melting of glacial ...
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ABSTRACT Hydrographic observations from four icebreaker expeditions to the Arctic Ocean between 1991 and 2001 show evidence of changes in the deep waters of the Arctic Ocean. The deepest waters show 300-1000 m thick homogenous bottom... more
ABSTRACT Hydrographic observations from four icebreaker expeditions to the Arctic Ocean between 1991 and 2001 show evidence of changes in the deep waters of the Arctic Ocean. The deepest waters show 300-1000 m thick homogenous bottom layers, characterized by slightly warmer temperatures compared to ambient, overlying water masses, indicating that they may have formed by convection induced by geothermal heat supplied from Earth's interior. The layers are present in the central parts of the deep basins, away from continental slopes and ocean ridges. The observations also suggest relatively large changes in the deep waters of the Amundsen Basin between 1991 and 2001, with warmer water being present in 2001 over the entire deep-water column.
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The thinning and acceleration of the West Antarctic Ice Sheet has been attributed to basal melting induced by intrusions of relatively warm salty water across the continental shelf. A hydrographic section including lowered acoustic... more
The thinning and acceleration of the West Antarctic Ice Sheet has been attributed to basal melting induced by intrusions of relatively warm salty water across the continental shelf. A hydrographic section including lowered acoustic Doppler current profiler measurements showing such an inflow in the channel leading to the Getz and Dotson Ice Shelves is presented here. The flow rate was 0.3–0.4 Sv (1 Sv ≡ 106 m3 s−1), and the subsurface heat loss was estimated to be 1.2–1.6 TW. Assuming that the inflow persists throughout the year, it corresponds to an ice melt of 110–130 km3 yr−1, which exceeds recent estimates of the net ice glacier ice volume loss in the Amundsen Sea. The results also show a 100–150-m-thick intermediate water mass consisting of Circumpolar Deep Water that has been modified (cooled and freshened) by subsurface melting of ice shelves and/or icebergs. This water mass has not previously been reported in the region, possibly because of the paucity of historical data.
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. Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along... more
. Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along the Alaskan coast, as Alaskan Coastal Water. A central pathway exhibits intermediate salinity and nutrient concentrations, while the most nutrient-rich water enters Bering Strait on its western side. Towards the Arctic Ocean the flow of these water masses is subject to strong topographic steering within the Chukchi Sea with volume transports modulated by the wind field. In this contribution we use data from several sections crossing Herald Canyon collected in 2008 and 2014 together with numerical modeling to investigate the circulation and transport in the western part of the Chukchi Sea. We find that a substantial fraction of water from the Chukchi Sea enters the East Siberian Sea south of Wrangel Island and circulates in an anticyclonic direction around the island. This water then contributes to the high nutrient waters of Herald Canyon. The bottom of the canyon has the highest nutrient concentrations, likely as a result of addition from the degradation of organic matter at the sediment surface in the East Siberian Sea. The flux of nutrients (nitrate, phosphate, and silicate) and dissolved inorganic carbon in Bering Summer Water and Winter Water is computed by combining hydrographic and nutrient observations with geostrophic transports referenced to LADCP and surface drift data. Even if there are some general similarities between the years, there are differences in both the temperature-salinity and nutrient characteristics. To assess these differences, and also to get a wider temporal and spatial view, numerical modeling results are applied. According to model results, high frequency variability dominates the flow in Herald Canyon. This leads us to conclude that this region needs to be monitored over a longer time frame to deduce the temporal variability and potential trends.
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The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian land masses. The presently shallow…
Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high... more
Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker <i>Oden</i>, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180° E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140° E, while it appears in the Makarov Basin at 150° E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to ∼ 34....
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Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model... more
Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOC<sub>ter</sub> and POC<sub>ter</sub>) supplied to the shelf. Rivers supply on average 8.5 Tg C yr<sup>−1</sup> dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr<sup>−1</sup> DOC<sub>ter</sub> and POC<sub>ter</sub> respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ<sup>13</sup>C<sub>DOC</sub>) in shelf waters, we estimate that only some 20 % of the riverine DOC<sub>ter</sub...
Recent geological and geophysical data suggest that a one-kilometre thick ice shelf extended over the glacial Arctic Ocean during Marine Isotope Stage 6, about 140 000 years ago. Here, we theoretically analyse the development and... more
Recent geological and geophysical data suggest that a one-kilometre thick ice shelf extended over the glacial Arctic Ocean during Marine Isotope Stage 6, about 140 000 years ago. Here, we theoretically analyse the development and equilibrium features of such an ice shelf, using scaling analyses and a one-dimensional ice-sheet–ice-shelf model. We find that the dynamically most consistent scenario is an ice shelf with a nearly uniform thickness that covers the entire Arctic Ocean. Further, the ice shelf have two regions with distinctly different dynamics: a vast interior region covering the central Arctic Ocean and an exit region towards the Fram Strait. In the interior region, which is effectively dammed by the Fram Strait constriction, there are strong back stresses and the mean ice-shelf thickness is controlled primarily by the horizontally-integrated mass balance. A narrow transitions zone is found near the continental grounding line, in which the ice-shelf thickness ...
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The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow ( ∼ 53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted... more
The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow ( ∼ 53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9–11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic–Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, w...
The Lomonosov Ridge represents a major topographical feature in the Arctic Ocean which has a large effect on the water circulation and the distribution of water properties. This study presents detailed bathymetric survey data along with... more
The Lomonosov Ridge represents a major topographical feature in the Arctic Ocean which has a large effect on the water circulation and the distribution of water properties. This study presents detailed bathymetric survey data along with hydrographic data at two deep passages across the ridge: A southern passage (80–81° N) where the ridge crest meets the Siberian continental slope and a northern passage around 84.5° N. The southern channel is characterized by smooth and flat bathymetry around 1600–1700 m with a sill depth slightly shallower than 1700 m. A hydrographic section across the channel reveals an eastward flow with Amundsen Basin properties in the southern part and a westward flow of Makarov Basin properties in the northern part. The northern passage includes an approximately 72 km long and 33 km wide trough which forms an intra basin in the Lomonosov Ridge morphology (the Oden Trough). The eastern side of Oden Tr...
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Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high... more
Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, July to September 2014, show the distribution of such nutrient rich cold bottom waters along the continental margin from about 140 to 180° E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140° E while it appears in the Makarov Basin at 150° E to intensify further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient rich water is found at salinities up to ~ ...
High-resolution MODIS thermal infrared satellite data are used to infer spatial and temporal characteristics of 16 prominent coastal polynya regions over the entire Arctic basin. Thin-ice thickness distributions (≤ 20 cm)... more
High-resolution MODIS thermal infrared satellite data are used to infer spatial and temporal characteristics of 16 prominent coastal polynya regions over the entire Arctic basin. Thin-ice thickness distributions (≤ 20 cm) are calculated from MODIS ice-surface temperatures, combined with ECMWF ERA-Interim atmospheric reanalysis data in an energy balance model for 13 winter-seasons (2002/2003 to 2014/2015; November to March). From all available swath-data, (quasi-) daily thin-ice thickness composites are computed in order to derive quantities such as polynya area and total thermodynamic (i.e. potential) ice production. A gap-filling approach is applied to account for cloud and data gaps in the MODIS composites. All polynya regions combined cover an average thin-ice area (POLA) of 184.3 ± 35.6 × 10<sup>3</sup> km<sup>2</sup> in winter. This allows for an average total wintertime accumulated ice production...
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The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making... more
The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (∼140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.
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ABSTRACT [1] A time-dependent, 1-D coupled ice-ocean model is used to quantify the impact of ocean stratification on the Arctic ice cover. The model results show that the ice growth during winter equals the ice melt in summer for areas... more
ABSTRACT [1] A time-dependent, 1-D coupled ice-ocean model is used to quantify the impact of ocean stratification on the Arctic ice cover. The model results show that the ice growth during winter equals the ice melt in summer for areas with a well-developed cold halocline layer (CHL), provided that the initial ice thickness is around 3 m, while thinner initial ice thickness results in net growth. Areas with weak salt stratification can have a negative annual thickness change irrespective of the initial ice thickness and are thus dependent on ice import in order to remain ice covered. The model results also show that ocean stratification is mostly important for ice-thickness development during the growing season. Areas with weak stratification have an ocean heat flux up to 8 W m−2 reaching the ice during the growing season, while areas with a CHL have an average of about 0.7 W m−2. In the extreme area, north of Svalbard, the ocean heat fluxes are typically around 25 W m−2 but can be up to 400 W m−2 during the initial adjustment, when the warm Atlantic water has direct contact with the ice. A general outcome of the study is that, depending on ocean stratification, the ice cover of Arctic Ocean can be divided into one part with net ice growth (the major part) and another part with net ice melt (mainly in the Nansen Basin).
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ABSTRACT To investigate the impact of ocean stratifications on the ice cover, a one-dimensional numerical model (Björk, 1989) is used to compute oceanic heat flux and ice thickness development, during the ice growth season. The Arctic... more
ABSTRACT To investigate the impact of ocean stratifications on the ice cover, a one-dimensional numerical model (Björk, 1989) is used to compute oceanic heat flux and ice thickness development, during the ice growth season. The Arctic Ocean is divided into six regions according to their stratification of the upper layer. Observed salinity and temperature profiles, from several stations within each region, are used as initial conditions in the model. Observed data come from the NODC data base. Resent observations, from ice tethered profilers (ITṔs) deployed during the IPY period, is also used to increase the spatial coverage. The computations show that the central regions have a largest ice growth, more than 0.7 m, over one growth season, using an initial ice thickness of 2 m. The large ice growth is due to the present cold halocline layer preventing upward mixing of heat from below. The weak stratification in the Nansen Basin enables deeper mixing into the warm Atlantic layer, which reduces the ice growth to a minimum of 0.25 m at some locations. In the Canada Basin the inflow of warm Pacific summer water generates a temperature maximum at 50 m. This heat reservoir is large enough to reduce the ice growth to about 0.55 m, in spite of the strong salinity stratification in the region. The regions with the largest ice growth have correspondingly the lowest annual mean oceanic heat fluxes, around 0.5 W m-2. However some locations in the Nansen and Canada Basins have heat fluxes larger than 1 W m-2. In our investigation we found a net melting over a full year only for one station, located close to the Bering Strait.
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ABSTRACT The biogeochemistry of the Laptev and East Siberian Sea. Iréne Wåhlström1, Leif G. Andersen1, Göran Björk2, Sofia Hjalmarsson1, Sara Jutterström1 1 Department of Chemistry, University of Gothenburg, SE-412 96 Göteborg, Sweden 2... more
ABSTRACT The biogeochemistry of the Laptev and East Siberian Sea. Iréne Wåhlström1, Leif G. Andersen1, Göran Björk2, Sofia Hjalmarsson1, Sara Jutterström1 1 Department of Chemistry, University of Gothenburg, SE-412 96 Göteborg, Sweden 2 Department of Earth Sciences, University of Gothenburg, Box 460, SE-405 30, Göteborg, Sweden, The Siberian shelf seas are a very biogeochemical dynamic region. They receive a lot of river runoff containing nutrients and dissolved and particulate organic matter; exchange waters with the deep Arctic Ocean; exchange gases with the atmosphere and have an extensive biological activity. These processes impact the concentrations of chemical constituents that set the frame for the magnitude of the fluxes. In the summer 2008 we studied the biogeochemistry of the waters in the eastern Laptev Sea, the East Siberian Sea and the western Chukchi Sea during the International Siberian Shelf Study 2008 (ISSS-08). The findings reveal substantial differences from close to the coast and northwards as well as between the western and eastern regions. Close to the coast the signature is influenced by mixing between the river runoff and the seawater, while the outer regions show a more typical marine signature. Overlaying this pattern is the impact by microbial decay of organic matter, in the west dominated by terrestrial OM and in the east by marine OM. The microbial decay results in low oxygen levels, reaching as low as 40 % in the shallow areas. Corresponding author, I. Wåhlström, email: irene.wohlstrom@chem.gu.se
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The sensitivity of the Arctic Ocean ice cover on the atmospheric poleward energy flux, D, is studied using a coupled column model of the ocean, ice, and atmosphere. In the model, the ice cover is described by a thickness distribution and... more
The sensitivity of the Arctic Ocean ice cover on the atmospheric poleward energy flux, D, is studied using a coupled column model of the ocean, ice, and atmosphere. In the model, the ice cover is described by a thickness distribution and the atmosphere is a simple two stream grey body, in radiative equilibrium. It is shown that the thickness distribution in combination with the albedo function gives a strong nonlinear response to positive perturbations of D. The response on D is sensitive to the albedo parameterization and the shape of the thickness distribution, controlled by ridging and divergence. An increase of about 9 W m-2 from a standard value of D=103 W m-2 has a dramatic effect, reducing the ice thickness with more than 2 m and generates a large open water fraction during summer. The reduction of ice thickness is characterized by a clear transition between two regimes, going from a regime where first year ice survives the next summer melt period, to a seasonal ice regime wh...
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The interannual variation of the Arctic Ocean ice thickness during the period 1954-1990 is investigated using a coupled ocean-ice-atmosphere column model. The model is forced by poleward energy flux in the atmosphere from NCEP/NCAR... more
The interannual variation of the Arctic Ocean ice thickness during the period 1954-1990 is investigated using a coupled ocean-ice-atmosphere column model. The model is forced by poleward energy flux in the atmosphere from NCEP/NCAR reanalysis data, cloudiness, and precipitation observed at the Russian North Pole drift stations, and ice export from satellite observations. During the period 1977-1986 the ice thickness decreased from 3.2 m down to 2.0 m. Increased ice melt caused by large poleward energy flux in summer, and less ice growth due to increased cloudiness and poleward energy flux in winter are the main effects that cause the decrease of the ice thickness. Variations in precipitation and ice export are of less importance. A sensitivity study show that the NCEP/NCAR data is accurate enough with respect to stochastical errors to ensure that the thinning is not caused by forcing errors.
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Research Interests: Image Analysis, Heat Exchanger, Algorithm, Image Classification, Numerical Simulation, and 13 moreMicrowave Imaging, Synthetic Aperture Radar, Geomatic Engineering, Simulation Methods, Air Temperature, Coastal Zone, Size, Numerical Model, Correlation coefficient, Large Scale, Ground Truth, Radar Imaging, and Contextual Information
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The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents transport warm dense water... more
The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents transport warm dense water onto the shelf, channeled by bathymetric troughs leading to the deep inner basins. A hydrographic mooring equipped with an upward-looking ADCP has been placed in one of these troughs on the central Amundsen shelf. The two years (2010/11) of mooring data are here used to characterize the inflow of warm deep water to the deep shelf basins. During both years, the warm layer thickness and temperature peaked in austral fall. The along-trough velocity is dominated by strong fluctuations that do not vary in the vertical. These fluctuations are correlated with the local wind, with eastward wind over the shelf and shelf break giving flow toward the ice shelves. In addition, there is a persistent flow of dense lower Circumpolar Deep Water (CDW) toward the ice s...
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The central basins of the Arctic Ocean, below the surface mixed layer and remote from peripheral boundary currents, comprise an extremely low energy oceanic environment. Water masses having distinctly different Θ–S characteristics are... more
The central basins of the Arctic Ocean, below the surface mixed layer and remote from peripheral boundary currents, comprise an extremely low energy oceanic environment. Water masses having distinctly different Θ–S characteristics are organised throughout the central basins in extensive layers, consistent with occurrence of double-diffusive convection. In the Eurasian Basin, these structures can be explained by invoking formation along
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The observed vertical nutrient distribution including a maximum at about 100 m depth in the Arctic Ocean is investigated using a one-dimensional time-dependent circulation model together with a simple biological model. The circulation... more
The observed vertical nutrient distribution including a maximum at about 100 m depth in the Arctic Ocean is investigated using a one-dimensional time-dependent circulation model together with a simple biological model. The circulation model includes a shelf-forced circulation. This is thought to take place in a box from which the outflow is specified regarding temperature and volume flux at different salinities. It has earlier been shown that the circulation model is able to reproduce the observed mean salinity and temperature stratification in the Arctic Ocean. Before introducing nutrients in the model a test is performed using the conservative tracer delta18(18O/16O ratio) as one extra state variable in order to verify the circulation model. It is shown that the field measurements can be simulated. The result is, however, rather sensitive to the tracer concentration in the Bering Strait inflow. The nutrients nitrate, phosphate, and silicate are then treated by coupling a simple biological model to the circulation model. The biological model describes some overall effects of production, sinking, and decomposition of organic matter. First a standard case of the biological model is presented. This is followed by some modified cases. It is shown that the observed nutrient distribution including the maximum can be generated. The available nutrient data from the arctic Ocean are not sufficient to decide which among the cases is the most likely to occur. One case is, however, chosen as the best case. A nutrient budget and estimates of the magnitudes of the new production are presented for this case.
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ABSTRACT We use passive tracers in a one-dimensional numerical model of the Arctic Ocean to determine the residence time in the mixed layer and the cold halocline. When run to a steady state, the model successfully reproduces most of the... more
ABSTRACT We use passive tracers in a one-dimensional numerical model of the Arctic Ocean to determine the residence time in the mixed layer and the cold halocline. When run to a steady state, the model successfully reproduces most of the observed distribution of salinity and temperature in the Arctic above the Atlantic layer. Comparison of model-calculated tritium concentrations with observational data also indicates that the transient properties are correct. An important component of the model is the implementation of a ``shelf circulation&#39;&#39; of about 0.8 Sv that simulates the observed production and interleaving of cold, highly saline shelf waters. We use the model to derive bulk residence times, which are about 25 years in the mixed layer and about 100 years in the halocline. These values are higher than those published in the literature. We explain how the model residence time is related to different tracer ages by generating age distributions with the model. It is shown that the weighted mean of these distributions corresponds well with published tracer age data. The model dynamics that correctly reproduce Arctic mixed-layer and cold halocline vertical structure in salinity, temperature, density, and various tracers also appear to simulate the natural processes that filter out interannual fluctuations in the freshwater influx from runoff and Bering Strait flow. Under these conditions, the period of the variation must be over 30 years to get 50% of the signal through to Fram Strait. In accord with other investigations, this would suggest that short-term fluctuations in Arctic river runoff are not the direct cause of freshwater anomalies in the northern North Atlantic.