The distribution of water masses and their circulation on the western Chukchi Sea shelf are investigated using shipboard data from the Russian-American Long Term Census of the Arctic (RUSALCA) program. Eleven hydrographic/velocity transects were occupied during September of that year, including a number of sections in the vicinity of Wrangel Island and Herald canyon, an area with historically few measurements. We focus on four water masses: Alaskan coastal water (ACW), summer Bering Sea water (BSW), Siberian coastal water (SCW), and remnant Pacific winter water (RWW). In some respects the spatial distributions of these water masses were similar to the patterns found in the historical World Ocean Database, but there were significant differences. Most notably, the ACW and BSW were transposed in Bering Strait, and the ACW was diverted from its normal coastal pathway northwestward through Herald Canyon. It is argued that this was the result of atmospheric forcing. September 2009 was characterized by an abnormally deep Aleutian Low and the presence of the Siberian High, which is normally absent this time of year. This resulted in strong northerly winds during the month, and mooring data from the RUSALCA program reveal that the ACW and BSW were transposed in Bering Strait for a significant portion of the month. Using an idealized numerical model we show that the Ekman response to the wind can cause such a transposition, and that the consequences of this will persist on the shelf long after the winds subside. This can explain the anomalous presence of ACW in Herald Canyon during the RUSALCA survey.

The relationship between patterns of benthic fauna and zooplankton in the Chukchi Sea and physical forcing.

The Iceland Greenland Seas Project (IGP) is a coordinated atmosphere–ocean research program investigating climate processes in the source region of the densest waters of the Atlantic meridional overturning circulation. During February and March 2018, a field campaign was executed over the Iceland and southern Greenland Seas that utilized a range of observing platforms to investigate critical processes in the region, including a research vessel, a research aircraft, moorings, sea gliders, floats, and a meteorological buoy. A remarkable feature of the field campaign was the highly coordinated deployment of the observing platforms, whereby the research vessel and aircraft tracks were planned in concert to allow simultaneous sampling of the atmosphere, the ocean, and their interactions. This joint planning was supported by tailor-made convection-permitting weather forecasts and novel diagnostics from an ensemble prediction system. The scientific aims of the IGP are to characterize the atmospheric forcing and the ocean response of coupled processes; in particular, cold-air outbreaks in the vicinity of the marginal ice zone and their triggering of oceanic heat loss, and the role of freshwater in the generation of dense water masses. The campaign observed the life cycle of a long-lasting cold-air outbreak over the Iceland Sea and the development of a cold-air outbreak over the Greenland Sea. Repeated profiling revealed the immediate impact on the ocean, while a comprehensive hydrographic survey provided a rare picture of these subpolar seas in winter. A joint atmosphere–ocean approach is also being used in the analysis phase, with coupled observational analysis and coordinated numerical modeling activities underway.

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The Kara and Laptev seas receive about one half of total freshwater runoff to the Arctic Ocean from the ob, Yenisei, and Lena rivers. Discharges of these large rivers form freshened surface water masses over wide areas in these seas. these water masses, i.e., the ob-Yenisei and Lena river plumes, generate an eastward buoyancy boundary current that accounts for the large-scale zonal freshwater transport along the Siberian part in the Arctic ocean. in this study we investigate spreading of the ob-Yenisei plume from the Kara Sea to the Laptev Sea through the Vilkitsky Strait and of the Lena plume from the Laptev Sea to the east-Siberian Sea through the Laptev and Sannikov straits during ice-free season. Large horizontal density gradient between freshened plume water and salty ambient sea water is the main driver of these processes, however, their intensity strongly depends on local wind forcing. the ob-Yenisei plume is spreading to the Laptev Sea in a narrow alongshore current which is induced by strong and long-term southwesterly winds. Under other wind forcing the plume does not reach the Vilkitsky Strait. the Lena plume is almost constantly spreading to the east-Siberian Sea as a large-scale surface water mass which intensity is governed by eastward ekman transport and is prone to large synoptic variability. The Ob, Yenisei and Lena rivers contribute large volumes of freshwater discharge into the Kara (~ 1,500 km 3 annually from the Ob and Yenisei rivers) and Laptev (~ 800 km 3 annually from the Lena River) seas that account for approximately one half of the total river runoff into the Arctic Ocean 1-3. Most of the continental runoff to the Kara and Laptev seas is discharged during ice-free period in June-September and forms sea-wide Ob-Yenisei and Lena river plumes which are among the largest freshwater reservoirs in the Arctic Ocean 4-6. River plumes are freshened surface-advected water masses, which seasonally form a relatively thin surface layer, compared to ambient saline sea. As a result, dynamics of river plumes is buoyancy-driven and wind-driven 7-12 , which is also true for large Ob-Yenisei and Lena plumes 3,13-18. It was previously investigated, that in the absence of strong wind forcing the Coriolis force and large salinity gradient between river plumes and ambient shelf water induce a baroclinic flow along the coast, which was previously addressed in many studies 7,19-21. This flow can be favored or impeded by local wind forcing. The associated eastward freshwater transport along large segments of northern shores of Eurasia and North America is an important part of large-scale freshwater transport pathways in the Arctic Ocean 22-27. Eastward alongshore spreading of the Ob-Yenisei and Lena plumes as a buoyancy-driven boundary current was described as a part of the Siberian Coastal Current (SCC) 22 which is the Eurasian branch of the Riverine Coastal Domain (RCD) 26. However, only few previous studies specifically addressed spreading of these river plumes from their source sea to an eastward sea, i.e., ...