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  • 1
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    Impact of Cyclonic Wind Anomalies Caused by Massive Winter Sea Ice Retreat in the Barents Sea on Atlantic Water Transport Toward the Arctic: A Model Study (2023)
    Details
    Publication Date: 2023-12-05
    Description: The Arctic is warming much faster than the global average. This is known as Arctic Amplification and is caused by feedbacks in the local climate system. In this study, we explore a previously proposed hypothesis that an associated wind feedback in the Barents Sea could play an important role by increasing the warm water inflow into the Barents Sea. We find that the strong recent decrease in Barents Sea winter sea ice cover causes enhanced ocean‐atmosphere heat flux and a local air temperature increase, thus a reduction in sea level pressure and a local cyclonic wind anomaly with eastward winds in the Barents Sea Opening. By investigating various reanalysis products and performing high‐resolution perturbation experiments with the ocean and sea ice model FESOM2.1, we studied the impact of cyclonic atmospheric circulation changes on the warm Atlantic Water import into the Arctic via the Barents Sea and Fram Strait. We found that the observed wind changes do not significantly affect the warm water transport into the Barents Sea, which rejects the wind‐feedback hypothesis. At the same time, the cyclonic wind anomalies in the Barents Sea increase the amount of Atlantic Water recirculating westwards in Fram Strait by a downslope shift of the West Spitsbergen Current, and thus reduce Atlantic Water reaching the Arctic basin via Fram Strait. The resulting warm‐water anomaly in the Greenland Sea Gyre drives a local anticyclonic circulation anomaly.
    Description: Plain Language Summary: The Barents Sea has been experiencing a rapid decrease in its winter sea ice extent during the last 30 years. The loss of sea ice creates new areas where, in winter, the relatively warm ocean loses heat to the cold atmosphere. As warm air rises, the warming reduces the sea level air pressure, changing the atmospheric circulation to develop a local anticlockwise wind system centered over the northern Barents Sea. The associated eastward winds in the Barents Sea Opening and southeastward winds in Fram Strait affect how warm water from the North Atlantic moves toward the Arctic. There has been a long debate on whether this wind anomaly can increase the warm Atlantic Water transport into the Barents Sea and thus cause a positive feedback mechanism for further reducing the sea ice through melting. We find that the observed atmospheric circulation changes have no significant impact on the Barents Sea warm water inflow and thus reject the wind feedback as a strong player in contributing to Arctic Amplification. However, strong anomalous southeastward winds in Fram Strait and the northern Nordic Seas cause a southward shift of the warm Atlantic Water recirculation and reduce its flow toward the Arctic.
    Description: Key Points: A hypothesis that a wind feedback contributes to Arctic Amplification is rejected by performing dedicated wind perturbation simulations. Winter sea ice retreat in the northern Barents Sea causes anomalous cyclonic winds by locally enhancing ocean heat loss. Anomalous cyclonic winds result in less Atlantic Water transport through Fram Strait.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: North‐German Supercomputing Alliance
    Description: https://github.com/FESOM/fesom2
    Description: https://doi.org/10.7265/N5K072F8
    Description: https://doi.org/10.5065/D6HH6H41
    Description: https://doi.org/10.5065/D6WH2N0S
    Description: https://github.com/FESOM/pyfesom2
    Description: https://doi.org/10.5281/zenodo.7458143
    Keywords: ddc:551 ; Barents Sea ; Arctic Amplification ; feedback ; Atlantic water ; modeling ; Fram Strait
    Language: English
    Type: doc-type:article
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  • 2
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    The Deep‐Water Plume in the Northwestern Weddell Sea, Antarctica: Mean State, Seasonal Cycle and Interannual Variability Influenced by Climate Modes (2023)
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    Publication Date: 2023-06-21
    Description: We provide an updated estimate of the annual‐mean, seasonal cycle and interannual variability of the transports and properties of the Weddell Sea Bottom Water (WSBW) plume in the northwestern Weddell Sea. For this we used a densely instrumented mooring array deployed across the continental slope between January 2017 and January 2019. We found that the annual‐mean WSBW transport is 3.4 ± 1.5 Sv, corresponding to a cross‐section area of 35 km2 and a maximum thickness of 203 m. The annual mean transport‐weighted properties of WSBW are −0.99°C (Θ), 34.803 g/kg (SA) and 28.44 kg/m3 (γn). The WSBW is characterized by 3 bottom‐intensified velocity cores, which display seasonal variations in flow speed and transport different varieties of WSBW. The seasonal peak of WSBW transport and density is reached in May (4.7 Sv, 28.443 kg m−3) while the minimum values are observed in February (2.8 Sv, 28.435 kg m−3). The coldest WSBW is found between March and May, and the warmest between August and October. The density decrease of WSBW observed in the austral autumn of 2018 can be explained by warmer ambient waters being entrained during the formation of WSBW. This was enabled by the weakening of the along‐shore winds associated with a positive Southern Annular Mode index, reinforced by a La Niña event in early 2018. The synchronous decrease of total WSBW transport and volume between September 2018 and February 2019 indicates a reduction in the export of the dense precursors of WSBW from the Weddell Sea continental shelf.
    Description: Plain Language Summary: The Meridional Overturning Circulation (MOC) redistributes heat and carbon dioxide in the world ocean. Thus, it plays an important role in the regulation of our planet's climate. The Weddell Sea is the main contributor to the deep branch of the MOC in the Southern Hemisphere. Despite the importance of this contribution, uncertainties still remain associated to the plume of dense waters transported along the continental slope of the Weddell Sea. To reduce these uncertainties, we analyzed the most densely instrumented mooring array deployed across the continental slope in the northwestern Weddell Sea. We found that this plume flows faster close to the seafloor and that it presents important seasonal and interannual variability. The Weddell Sea Bottom Water interannual variability is influenced by changes in the along‐shore winds driven by the phase of two important climate modes, the Southern Annular Mode and the El Niño‐Southern Oscillation, but also by changes in the export of the dense precursors of WSBW in its formation areas. Increasing our knowledge on the along‐slope plume variability and properties is important to better understand the causes behind the variability of the MOC observed further downstream.
    Description: Key Points: The Weddell Sea Bottom Water (WSBW) plume presents 3 velocity cores and a clear seasonal cycle, with maximum transports and densities in May and minimum in February. A +SAM, reinforced by a ‐ENSO, favors the warming of WSBW via a wind‐driven warming of the ambient waters entrained during its formation. We observed a marked decrease in WSBW density and transports between September 2018 and February 2019 compared to the previous year.
    Description: EU Horizon 2020 Research and Innovation Program
    Description: German Research Foundation
    Description: Alfred Wegener Institute Helmholtz‐Center
    Description: https://doi.org/10.5281/zenodo.7500163
    Keywords: ddc:551.46 ; Weddell Sea ; WSBW ; Meridional Overturning Circulation ; SAM ; ENSO ; deep‐water plume
    Language: English
    Type: doc-type:article
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  • 3
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    Structure and Seasonal Variability of the Arctic Boundary Current North of Severnaya Zemlya (2023)
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    Publication Date: 2023-11-13
    Description: We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using seven oceanographic moorings, deployed across the continental slope north of Severnaya Zemlya in 2015–2018. Transports and individual water masses were quantified based on temperature and salinity recorders and current profilers. Our results were compared with observations from the northeast Svalbard and the central Laptev Sea continental slopes to evaluate the hydrographic transformation along the ABC pathway. The highest velocities (〉0.30 m s〈sup〉−1〈/sup〉) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 m s〈sup〉−1〈/sup〉 in the deep basin. The ABC showed seasonal variability with velocities two times higher in winter than in summer. Compared to upstream conditions in Svalbard, water mass distribution changed significantly within 20 km of the shelf edge due to mixing with‐ and intrusion of shelf waters. The ABC transported 4.15 ± 0.3 Sv in the depth range 50–1,000 m, where 0.88 ± 0.1, 1.5 ± 0.2, 0.61 ± 0.1 and 1.0 ± 0.15 Sv corresponded to Atlantic Water (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW). 62–70% of transport was constrained to within 30–40 km of the shelf edge, and beyond 84 km, transport increases were estimated to be 0.54 Sv. Seasonality of TAW derived from local shelf‐processes and advection of seasonal‐variable Fram Strait waters, while BSBW transport variability was dominated by temperature changes with maximum transport coinciding with minimum temperatures. Further Barents Sea warming will likely reduce TAW and BSBW transport leading to warmer conditions along the ABC pathway.
    Description: Plain Language Summary: We assessed the structure and seasonal variability of the flow and water masses of the Arctic Boundary Current (ABC) in the region north of Severnaya Zemlya. This current is important in the Arctic Ocean as it transports relatively warm and saline waters along the Eurasian Arctic continental slope. We quantified the flow, transport and hydrographic variability of the ABC. Compared to observations from upstream, our results indicate that the water masses away from the shelf break maintained the hydrographic characteristics from upstream. In contrast, the water masses near the shelf break were significantly cooled and freshened due to intrusion of‐ and mixing with shelf waters. The water masses near the shelf break showed a seasonal signal in volume transport and temperature which derives from local shelf processes, advection of seasonal‐variable waters along the ABC pathway and the seasonal cooling of the Barents Sea. If the warming trend in the Barents Sea continues, warmer waters are expected to be advected eastward along the Eurasian continental slope by the ABC.
    Description: Key Points: We quantify the Arctic Boundary Current (ABC) transport north of Severnaya Zemlya with a 2015–2018 mooring array. Hydrographic changes along the ABC pathway are most prominent at the continental slope due to the interaction with shelf water. Seasonality of water masses from the shelf sea was observed in transport, temperature and off‐shelf excursions within the ABC.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: EC Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: Russian Science Foundation http://dx.doi.org/10.13039/501100006769
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.pangaea.de/10.1594/PANGAEA.951363
    Description: https://doi.pangaea.de/10.1594/PANGAEA.951394
    Description: https://doi.pangaea.de/10.1594/PANGAEA.951394
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954244
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954249
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954299
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954352
    Keywords: ddc:551.48 ; Arctic Boundary Current ; seasonal transport variability ; water mass transport ; along‐slope current
    Language: English
    Type: doc-type:article
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  • 4
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    Coherent Seasonal Acceleration of the Weddell Sea Boundary Current System Driven by Upstream Winds (2021)
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    Publication Date: 2021-10-13
    Description: The Weddell Sea is of global importance in the formation of dense bottom waters associated with sea ice formation and ocean-ice sheet interaction occurring on the shelf areas. In this context, the Weddell Sea boundary current system (BCS) presents a major conduit for transporting relatively warm water to the Weddell Sea ice shelves and for exporting some modified form of Wedell Sea deep and bottom waters into the open ocean. This study investigates the downstream evolution of the structure and the seasonality of the BCS along the Weddell Sea continental slope, combining ocean data collected for the past two decades at three study locations. The interannual-mean geostrophic flow, which follows planetary potential vorticity contours, shifts from being surface intensified to bottom intensified along stream. The shift occurs due to the densification of water masses and the decreasing surface stress that occurs westward, toward the Antarctic Peninsula. A coherent along-slope seasonal acceleration of the barotropic flow exists, with maximum speed in austral autumn and minimum speed in austral summer. The barotropic flow significantly contributes to the seasonal variability in bottom velocity along the tip of the Antarctic Peninsula. Our analysis suggests that the winds on the eastern/northeastern side of the gyre determines the seasonal acceleration of the barotropic flow. In turn, they might control the export of Weddell Sea Bottom Water on seasonal time scales. The processes controlling the baroclinic seasonality of the flow need further investigation.
    Keywords: 551.46 ; Southern Ocean ; Weddell Sea ; Antarctic slope current ; surface stress ; flow strength ; teleconnection
    Language: English
    Type: map
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  • 5
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    FRIS Revisited in 2018: On the Circulation and Water Masses at the Filchner and Ronne Ice Shelves in the Southern Weddell Sea (2021)
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    Publication Date: 2021-09-29
    Description: The Filchner‐Ronne Ice Shelf (FRIS) is characterized by moderate basal melt rates due to the near‐freezing waters that dominate the wide southern Weddell Sea continental shelf. We revisited the region in austral summer 2018 with detailed hydrographic and noble gas surveys along FRIS. The FRIS front was characterized by High Salinity Shelf Water (HSSW) in Ronne Depression, Ice Shelf Water (ISW) on its eastern flank, and an inflow of modified Warm Deep Water (mWDW) entering through Central Trough. Filchner Trough was dominated by Ronne HSSW‐sourced ISW, likely forced by a recently intensified circulation beneath FRIS due to enhanced sea ice production in the Ronne polynya since 2015. Glacial meltwater fractions and tracer‐based water mass dating indicate two separate ISW outflow cores, one hugging the Berkner slope after a two‐year travel time, and the other located in the central Filchner Trough following a ∼six year‐long transit through the FRIS cavity. Historical measurements indicate the presence of two distinct modes, in which water masses in Filchner Trough were dominated by either Ronne HSSW‐derived ISW (Ronne‐mode) or more locally derived Berkner‐HSSW (Berkner‐mode). While the dominance of these modes has alternated on interannual time scales, ocean densities in Filchner Trough have remained remarkably stable since the first surveys in 1980. Indeed, geostrophic velocities indicated outflowing ISW‐cores along the trough's western flank and onto Berkner Bank, which suggests that Ronne‐ISW preconditions Berkner‐HSSW production. The negligible density difference between Berkner‐ and Ronne‐mode waters indicates that each contributes cold dense shelf waters to protect FRIS against inflowing mWDW.
    Description: Plain Language Summary: We visited the largest floating Antarctic ice shelf in the southern Weddell Sea in 2018 with an icebreaker expedition, and measured ocean temperature, salinity, meltwater content, and other parameters in front of the FRIS. We found that the ocean conditions were still dominated by the very cold and dense waters needed to protect the ice shelf from inflowing warm waters from the deep ocean. We compared the 2018 conditions with earlier surveys since the 1980s and concluded that, in spite of climate change and in contrast to other Antarctic regions, the water masses on the southern Weddell Sea shelf remained relatively stable overall. We found that most of the stations we visited near the Filchner Ice Shelf edge were dominated by cold ISW, which forms when water masses interact with the underside of the shelf ice. Our measurements helped improve our understanding regarding the currents and water masses on the southern Weddell Sea continental shelf.
    Description: Key Points: Hydrographic status update with the first comprehensive CTD survey along the entire FRIS front since 1995. Strong and stable presence of High Salinity Shelf Water in Ronne Depression over decades. Dominance of Ronne‐sourced Ice Shelf Water in Filchner Trough in 2018 points to intensified sub‐FRIS circulation.
    Description: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) http://dx.doi.org/10.13039/501100003207
    Keywords: 551.46 ; Ocean circulation ; ocean‐ice shelf interaction ; water masses ; Weddell Sea ; Filcher and Ronne shelves
    Type: map
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