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  • 1
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    Winter storms accelerate the demise of sea ice in the Atlantic sector of the Arctic Ocean (2019)
    In:  EPIC3Scientific Reports, 9(1), ISSN: 2045-2322
    Details
    Publication Date: 2020-07-07
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Sea Ice Mass Balance Buoys (IMBs): Introduction to working group and Data Processing Intercomparison Study (2016)
    In:  EPIC3AGU Fall Meeting 2016, San Francisco, USA, 2016-12-12-2016-12-17
    Details
    Publication Date: 2016-12-13
    Description: IMBs are autonomous instruments able to continuously monitor the growth and melt of sea ice and its snow cover at a single point on an ice floe. Complementing field expeditions, remote sensing observations and modelling studies, this in-situ data is crucial to assess the mass balance and seasonal evolution of sea ice and snow in the polar oceans. Established subtypes of IMBs combine coarse-resolution temperature profiles through air, snow, ice and ocean with ultrasonic pingers to detect snow accumulation and ice thermodynamic growth. Recent technological advancements enable the use of high-resolution temperature chains, which are also able to identify the surrounding medium through a „heating cycle“. The temperature change during this heating cycle provides additional information on the internal properties and processes of the ice. However, a unified data processing technique to reliably and accurately determine sea ice thickness and snow depth from this kind of data is still missing, and an unambiguous interpretation remains a challenge. Following the need to improve techniques for remotely measuring sea ice mass balance, an international IMB working group has recently been established. The main goals are 1) to coordinate IMB deployments, 2) to enhance current IMB data processing and –interpretation techniques, and 3) to provide standardized IMB data products to a broader community. We present results from an intercomparison study, which compares different techniques of IMB data processing, with a focus on the automatic calculation of sea ice thickness and snow depth in selected IMB datasets from the Arctic and Antarctic. The results of a number of existing algorithms are evaluated, and validated against reference datasets from manual inspection and co-deployed instruments. Finally, recommendations with respect to the manifold challenges of IMB data processing and -interpretation are highlighted.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 3
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    Influence of the meridional shifts of the Kuroshio and the Oyashio Extensions on the atmospheric circulation (2011)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 24 (2011): 762-777, doi:10.1175/2010JCLI3731.1.
    Description: The meridional shifts of the Oyashio Extension (OE) and of the Kuroshio Extension (KE), as derived from high-resolution monthly sea surface temperature (SST) anomalies in 1982–2008 and historical temperature profiles in 1979–2007, respectively, are shown based on lagged regression analysis to significantly influence the large-scale atmospheric circulation. The signals are independent from the ENSO teleconnections, which were removed by seasonally varying, asymmetric regression onto the first three principal components of the tropical Pacific SST anomalies. The response to the meridional shifts of the OE front is equivalent barotropic and broadly resembles the North Pacific Oscillation/western Pacific pattern in a positive phase for a northward frontal displacement. The response may reach 35 m at 250 hPa for a typical OE shift, a strong sensitivity since the associated SST anomaly is 0.5 K. However, the amplitude, but not the pattern or statistical significance, strongly depends on the lag and an assumed 2-month atmospheric response time. The response is stronger during fall and winter and when the front is displaced southward. The response to the northward KE shifts primarily consists of a high centered in the northwestern North Pacific and hemispheric teleconnections. The response is also equivalent barotropic, except near Kamchatka, where it tilts slightly westward with height. The typical amplitude is half as large as that associated with OE shifts.
    Description: This work was supported in part by the L’Institut universitaire de France (CF), the WHOI Heyman fellowship, and the NASAGrant withAwardNNX09AF35G(Y.-O. K), and grants through NOAA’s Climate Variability and Predictability Program (MAA).
    Keywords: Atmospheric circulation ; Currents
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020 (2021)
    EGU
    In:  EPIC3EGU General Assembly, online, 2021Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020 , EGU
    Details
    Publication Date: 2022-07-05
    Description: The Atlantic Water (AW) inflow through Fram Strait, largest oceanic heat source to the Arctic Ocean, undergoes substantial modifications in the Western Nansen Basin (WNB). Evaluation of the Mercator system in the WNB, using 1,500 independent temperature‐salinity profiles and five years of mooring data, highlighted its performance in representing realistic AW inflow and hydrographic properties. In particular, favorable comparisons with mooring time‐series documenting deep winter mixed layers and changes in AW properties led us to examine winter conditions in the WNB over the 2007–2020 period. The model helped describe the interannual variations of winter mixed layers and documented several processes at stake in modifying AW beyond winter convection: trough outflows and lateral exchange through vigorous eddies. Recently modified AW, either via local convection or trough outflows, were identified as homogeneous layers of low buoyancy frequency. Over the 2007–2020 period, two winters stood out with extreme deep mixed layers in areas that used to be ice‐covered: 2017/18 over the northern Yermak Plateau‐Sofia Deep; 2012/13 on the continental slope northeast of Svalbard with the coldest and freshest modified AW of the 12‐year time series. The northern Yermak Plateau‐Sofia Deep and continental slope areas became “Marginal Convection Zones” in 2011 with, from then on, occasionally ice‐free conditions, 50‐m‐ocean temperatures always above 0 °C and highly variable mixed layer depths and ocean‐to‐atmosphere heat fluxes. In the WNB where observations require considerable efforts and resources, the Mercator system proved to be a good tool to assess Atlantic Water modifications in winter.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
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    Changes in Atlantic Water circulation patterns and volume transports North of Svalbard over the last 12 years (2008-2020) (2021)
    EGU
    In:  EPIC3EGU General Assembly, online, 2022Changes in Atlantic Water circulation patterns and volume transports North of Svalbard over the last 12 years (2008-2020) , EGU
    Details
    Publication Date: 2022-07-05
    Description: Atlantic Water (AW) enters the Arctic through Fram Strait as the West Spitsbergen Current (WSC). When reaching the south of Yermak Plateau, the WSC splits into the Svalbard, Yermak Pass and Yermak Branches. Downstream of Yermak Plateau, AW pathways remain unclear and uncertainties persist on how AW branches eventually merge and contribute to the boundary current along the continental slope. We took advantage of the good performance of the 1/12° Mercator Ocean model in the Western Nansen Basin (WNB) to examine the AW circulation and volume transports in the area. The model showed that the circulation changed in 2008-2020. The Yermak Branch strengthened over the northern Yermak Plateau, feeding the Return Yermak Branch along the eastern flank of the Plateau. West of Yermak Plateau, the Transpolar Drift likely shifted westward while AW recirculations progressed further north. Downstream of the Yermak Plateau, an offshore current developed above the 3800 m isobath, fed by waters from the Yermak Plateau tip. East of 18°E, enhanced mesoscale activity from the boundary current injected additional AW basin-ward, further contributing to the offshore circulation. A recurrent anticyclonic circulation in Sofia Deep developed, which also occasionally fed the western part of the offshore flow. The intensification of the circulation coincided with an overall warming in the upper WNB (0-1000 m), consistent with the progression of AW. This regional description of the changing circulation provides a background for the interpretation of upcoming observations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 6
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    Changes in Freshwater Distribution and Pathways in the Arctic Ocean Since 2007 in the Mercator Ocean Global Operational System (2022)
    In:  EPIC3Journal of Geophysical Research: Oceans, 127(6), ISSN: 2169-9275
    Details
    Publication Date: 2022-07-13
    Description: Low-salinity waters in the upper Arctic Ocean, referred to as “freshwaters”, are cold and play a major role in isolating the sea ice cover from the heat stored in the salty Atlantic Waters (AW) underneath. We examined changes in Arctic freshwater distribution and circulation since 2007 using the 1/12° global Mercator Ocean operational model. We first evaluated model simulations over the upper water column in the Arctic Ocean, using nearly 20,000 independent in situ temperature-salinity profiles over the 2007–2020 period. Simulated hydrographic properties and water mass distributions were in good agreement with observations. Comparison with long-term mooring data in the Bering Strait and Beaufort Gyre highlighted the model's capabilities for reproducing the interannual evolution of Pacific Water properties. Taking advantage of the good performance of the model, we examined the interannual evolution of the freshwater distribution and circulation over 2007–2020. The Beaufort Gyre is the major freshwater reservoir across the full Arctic Ocean. After 2012 the gyre extended northward and increased the freshwater content in the Makarov Basin, near the North Pole. Coincidentally, the freshwater content decreased along the East Siberian slope, along with the AW shoaling, and the Transpolar Drift moved from the Lomonosov Ridge to align with the Mendeleev Ridge. We found that these changes in freshwater distribution were followed in 2015 by a marked change in the export of freshwater from the Arctic Ocean with a reduction in Fram Strait (−30%) and an increase in the western Canadian Archipelago (+16%).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 7
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    Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020 (2022)
    In:  EPIC3Journal of Geophysical Research: Oceans, ISSN: 2169-9275
    Details
    Publication Date: 2022-08-16
    Description: The evolution of halocline waters in the Makarov Basin and along the East Siberian continental slope is examined by combining drifting platform observations, shipborne hydrographic data, and simulations from a global operational physical model from 2007 to 2020. From 2012 onwards, relatively shallow and cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian continental slope. Their eastward extent abruptly shifted from 155°E to 170°E in early 2012, stabilized at 170°E until the end of 2015, then gradually advanced to reach the western Chukchi Sea in 2017. Such eastward progression led to a strengthening of the associated boundary current and to the shedding of mesoscale eddies of cold Atlantic-derived waters into the lower halocline of the Makarov Basin in September 2015 and near the East Siberian continental slope in November 2017. Additionally, active mixing between upwelled Atlantic Water and shelf water formed dense warm water supplying the Makarov Basin lower halocline. The increasing contribution from Atlantic-derived waters into the lower halocline along the East Siberian continental slope and in the Makarov Basin led to a weakening of the halocline, which is characteristic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime may now extend toward the Amerasian Basin.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
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    Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020 (2022)
    In:  EPIC3EGU General Assembly, Vienna, 2022Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020
    Details
    Publication Date: 2022-10-04
    Description: The Makarov Basin halocline receives contributions from diverse water masses of Atlantic, Pacific, and East Siberian Sea origin. Changes in surface circulation (e.g., in the Transpolar Drift and Beaufort Gyre) have been documented since the 2000s, while the upper ocean column in the Makarov Basin has received little attention. The evolution of the upper and lower halocline in the Makarov Basin and along the East Siberian Sea slope was examined combining drifting platforms observations, shipborne hydrographic data, and modelled fields from a global operational physical model. In 2015, the upper halocline in the Makarov Basin was warmer, fresher, and thicker compared to 2008 and 2017, likely resulting from the particularly westward extension of the Beaufort Gyre that year. From 2012-onwards, cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian slope, with a sharp shift from 155 to 170°E above the 1000 m isobath in winter 2011-2012, followed by a progressive eastward motion after winter 2015-2016 and reached the western Chukchi Sea in 2017. In parallel, an active mixing between upwelled Atlantic water and shelf water along the slope, formed dense warm water which also supplied the Makarov Basin lower halocline. The progressive weakening of the halocline, together with shallower Atlantic Waters, is emblematic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime now may extend toward the Amerasian Basin.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 9
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    Influence of the decadal variability of the Kuroshio Extension on the atmospheric circulation in the cold season (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 29 (2016): 2123-2144, doi:10.1175/JCLI-D-15-0511.1.
    Description: The atmospheric response to the Kuroshio Extension (KE) variability during 1979–2012 is investigated using a KE index derived from sea surface height measurements and an eddy-resolving ocean general circulation model hindcast. When the index is positive, the KE is in the stable state, strengthened and shifted northward, with lower eddy kinetic energy, and the Kuroshio–Oyashio Extension (KOE) region is anomalously warm. The reverse holds when the index is negative. Regression analysis shows that there is a coherent atmospheric response to the decadal KE fluctuations between October and January. The KOE warming generates an upward surface heat flux that leads to local ascending motions and a northeastward shift of the zones of maximum baroclinicity, eddy heat and moisture fluxes, and the storm track. The atmospheric response consists of an equivalent barotropic large-scale signal, with a downstream high and a low over the Arctic. The heating and transient eddy anomalies excite stationary Rossby waves that propagate the signal poleward and eastward. There is a warming typically exceeding 0.6 K at 900 hPa over eastern Asia and western United States, which reduces the snow cover by 4%–6%. One month later, in November–February, a high appears over northwestern Europe, and the hemispheric teleconnection bears some similarity with the Arctic Oscillation. Composite analysis shows that the atmospheric response primarily occurs during the stable state of the KE, while no evidence of a significant large-scale atmospheric response is found in the unstable state. Arguments are given to explain this strong asymmetry.
    Description: This research has received funding from the European Union 7th Framework Program (FP7 2007–2013) under Grant Agreement 308299 (NACLIM), from NSF Grant AGS CLD 1035423, and from Agence Nationale de la Recherche under the reference ANR 2011 Blanc SIMI 5-6 014 01.
    Description: 2016-09-23
    Repository Name: Woods Hole Open Access Server
    Type: Article
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