ADCP-referenced geostrophic velocity and transport in the West Spitsbergen Current

During the summer of 2000 and 2002 (June-July) the West Spitsbergen Current (WSC) was investigated by the Institute of Oceanology, Polish Academy of Sciences. CTD and current measurements by a vessel-mounted Acoustic Doppler Current Profiler (ADCP) were performed along three transects perpendicular to the WSC main stream and covering the region from 76°30' N to 78°20' N and from 02°30' E to 15° E. In general, the geostrophic, baroclinic flow patterns and the ADCP-measured currents were found to be in good agreement but measured current velocities were significantly higher than calculated values. This fact supports earlier observations that the barotropic component is dominant in the WSC. Since ADCP has a better spatial resolution than CTD records, the West Spitsbergen Current could be investigated and described in much greater detail than before. The main stream of Atlantic Water is topographically steered by the continental slope (isobars 800-2000 m) and the complex, multistream structure of the West Spitsbergen Current is clearly visible. The absolutely referenced total geostrophic transport is about three times higher than the estimated value assuming the level of no motion lies at 1000 m

Atlantic Water Pathways Along the North-Western Svalbard Shelf Mapped Using Vessel-Mounted Current Profilers

A large amount of warm Atlantic water (AW) enters the Arctic as a boundary current through Fram Strait (West Spitsbergen Current [WSC]) and is the major oceanic heat source to the Arctic Ocean. Along the north‐western Svalbard shelf, the WSC splits into the shallow Svalbard Branch, the Yermak Branch that follows the slope of the Yermak Plateau, and the Yermak Pass Branch flowing across the plateau. The WSC has previously been studied using moorings, dedicated oceanographic transects, and models. In this study, we mapped the circulation patterns and AW flow around Svalbard using Vessel‐Mounted Acoustic Doppler Current Profiler data from multiple surveys during four consecutive summers (2014–2017). Despite the scattered nature of this compiled data set, persistent circulation patterns could be discerned. Spatial interpolation showed a meandering boundary current west of Svalbard and a more homogeneous AW flow, centered around the 1,000‐m isobath north of Svalbard. In all summers, we observed a northward jet between 79 and 80°N and the 1,000‐ and 500‐m isobaths, before the WSC divided into the three branches. North of Svalbard, the shallow Svalbard Branch reunited with the Yermak Pass Branch between 10 and 15°E and a part of the AW circulated within Hinlopen Trench. The calculated volume transport of 2 Sv in the upper 500 m compares well with model results and previous observations. Our results further show that the Yermak Pass Branch can be as important as the Svalbard Branch in transporting AW across the Yermak Plateau during summer.publishedVersio

From pole to pole : 33 years of physical oceanography onboard R/V Polarstern

Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available at doi: 10.1594/PANGAEA.860066. During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data -the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.Peer reviewe

Sensitivity of ocean hydrography and fluxes across Fram Strait in the Regional Arctic System Model

2018 Ocean Sciences Meeting, AGUThe Arctic has experienced some of the most extreme climate changes currently occurring anywhere on Earth, including a warming trend. One of the key indicators of such decadal changes has been the decrease of the sea ice cover, driven by atmospheric forcing and the inflow of warm waters from the sub-polar oceans. While Earth System models (ESMs) are in broad agreement with such changes, they are limited in representing some critical high-latitude processes. Those include processes controlling the inflow, accumulation and distribution of heat in the upper ocean and its interaction with the sea ice cover. Such ESM limitations are likely due to a combination of coarse resolution, inadequate parameterizations, or under-represented processes, and they affect model skill in representing and predicting polar climate. To better understand some of these limitations, a series of sensitivity experiments are performed using the Regional Arctic System Model (RASM). RASM consists of the atmosphere, ocean, sea ice, land hydrology and runoff routing components, coupled through the flux coupler. The ocean and sea ice configurations include the horizontal resolution of 1/12o (~9km) or 1/48o (~2.4 km) and 45 or 60 vertical levels. We focus on the oceanic volume and property fluxes across Fram Strait and analyze their sensitivity to altered horizontal and vertical resolution as well as to parameterizations of air-ice-ocean coupling. Next, we compare model output against moored and hydrographic observations in the Fram Strait region. Our analyses suggest that both surface momentum coupling and model resolution influence the upper ocean thermohaline structure and fluxes at Fram Strait. The role of mesoscale eddies in the recirculation within and exchanges through Fram Strait will be quantified. Suggestions for a limited observational monitoring approach will be provided. Finally, comparisons with observations will be summarized to guide improved simulations of such exchanges

Atlantic Water Pathways Along the North-Western Svalbard Shelf Mapped Using Vessel-Mounted Current Profilers

A large amount of warm Atlantic water (AW) enters the Arctic as a boundary current through Fram Strait (West Spitsbergen Current [WSC]) and is the major oceanic heat source to the Arctic Ocean. Along the north‐western Svalbard shelf, the WSC splits into the shallow Svalbard Branch, the Yermak Branch that follows the slope of the Yermak Plateau, and the Yermak Pass Branch flowing across the plateau. The WSC has previously been studied using moorings, dedicated oceanographic transects, and models. In this study, we mapped the circulation patterns and AW flow around Svalbard using Vessel‐Mounted Acoustic Doppler Current Profiler data from multiple surveys during four consecutive summers (2014–2017). Despite the scattered nature of this compiled data set, persistent circulation patterns could be discerned. Spatial interpolation showed a meandering boundary current west of Svalbard and a more homogeneous AW flow, centered around the 1,000‐m isobath north of Svalbard. In all summers, we observed a northward jet between 79 and 80°N and the 1,000‐ and 500‐m isobaths, before the WSC divided into the three branches. North of Svalbard, the shallow Svalbard Branch reunited with the Yermak Pass Branch between 10 and 15°E and a part of the AW circulated within Hinlopen Trench. The calculated volume transport of 2 Sv in the upper 500 m compares well with model results and previous observations. Our results further show that the Yermak Pass Branch can be as important as the Svalbard Branch in transporting AW across the Yermak Plateau during summer

Atlantic Water Pathways Along the North-Western Svalbard Shelf Mapped Using Vessel-Mounted Current Profilers

A large amount of warm Atlantic water (AW) enters the Arctic as a boundary current through Fram Strait (West Spitsbergen Current [WSC]) and is the major oceanic heat source to the Arctic Ocean. Along the north‐western Svalbard shelf, the WSC splits into the shallow Svalbard Branch, the Yermak Branch that follows the slope of the Yermak Plateau, and the Yermak Pass Branch flowing across the plateau. The WSC has previously been studied using moorings, dedicated oceanographic transects, and models. In this study, we mapped the circulation patterns and AW flow around Svalbard using Vessel‐Mounted Acoustic Doppler Current Profiler data from multiple surveys during four consecutive summers (2014–2017). Despite the scattered nature of this compiled data set, persistent circulation patterns could be discerned. Spatial interpolation showed a meandering boundary current west of Svalbard and a more homogeneous AW flow, centered around the 1,000‐m isobath north of Svalbard. In all summers, we observed a northward jet between 79 and 80°N and the 1,000‐ and 500‐m isobaths, before the WSC divided into the three branches. North of Svalbard, the shallow Svalbard Branch reunited with the Yermak Pass Branch between 10 and 15°E and a part of the AW circulated within Hinlopen Trench. The calculated volume transport of 2 Sv in the upper 500 m compares well with model results and previous observations. Our results further show that the Yermak Pass Branch can be as important as the Svalbard Branch in transporting AW across the Yermak Plateau during summer

The Arctic Circumpolar Boundary Current

We present high?resolution simulations and observational data as evidence of a fast current flowing along the shelf break of the Siberian and Alaskan shelves in the Arctic Ocean. Thus far, the Arctic Circumpolar Boundary Current (ACBC) has been seen as comprising two branches: the Fram Strait and Barents Sea Branches (FSB and BSB, respectively). Here we describe a new third branch, the Arctic Shelf Break Branch (ASBB). We show that the forcing mechanism for the ASBB is a combination of buoyancy loss and non?local wind, creating high pressure upstream in the Barents Sea. The potential vorticity influx through the St. Anna Trough dictates the cyclonic direction of flow of the ASBB, which is the most energetic large?scale circulation structure in the Arctic Ocean. It plays a substantial role in transporting Arctic halocline waters and exhibits a robust seasonal cycle with a summer minimum and winter maximum. The simulations show the continuity of the FSB all the way around the Arctic shelves and the uninterrupted ASBB between the St. Anna Trough and the western Fram Strait. The BSB flows continuously along the Siberian shelf as far as the Chukchi Plateau, where it partly diverges from the continental slope into the ocean interior. The Alaskan Shelf break Current (ASC) is the analog of the ASBB in the Canadian Arctic. The ASC is forced by the local winds and high upstream pressure in Bering Strait, caused by the drop in sea surface height between the Pacific and Arctic Oceans

A review of Arctic-Subarctic ocean linkages: past changes, mechanisms and future projections

International audienceArctic Ocean gateway fluxes play a crucial role in linking the Arctic with the global ocean and affecting climate and marine ecosystems. We reviewed past studies on Arctic-Subarctic ocean linkages and examined their changes and driving mechanisms. Our review highlights that radical changes occurred in the inflows and outflows of the Arctic Ocean during the 2010s. Specifically, the Pacific inflow temperature in the Bering Strait and Atlantic inflow temperature in the Fram Strait hit record highs, while the Pacific inflow salinity in the Bering Strait and Arctic outflow salinity in the Davis and Fram straits hit record lows. Both the ocean heat convergence fromlower latitudes to the Arctic and the hydrological cycle connecting the Arctic with Subarctic seas were stronger in 2000–2020 than in 1980–2000. CMIP6 models project a continuing increase inpoleward ocean heat convergence in the 21st century, mainly due to warming of inflow waters. They also predict an increase in freshwater input to the Arctic Ocean, with the largest increase in freshwater export expected to occur in the Fram Strait due to both increased ocean volume export and decreased salinity. Fram Strait sea ice volume export hit a record low in the 2010s and is projected to continue to decrease along with Arctic sea ice decline. We quantitatively attribute the variability of the volume, heat and freshwater transports in the Arctic gateways to forcing within and outside the Arctic based on dedicated numerical simulations and emphasize the importance of both origins in driving the variabilit