Sea Surface Salinity (SSS) anomalies and near-surface thermohaline stratification are key parameters to improve our understanding of sea-ice retreat and formation in polar regions. Since 2010, the remote sensing salinity missions ESA SMOS (Soil Moisture and Ocean Salinity) and NASA SMAP (Soil Moisture Active Passive) offer unprecedented SSS observations globally (SSS_SMOS and SSS_SMAP respectively). In this study, we compare these observations with in-situ salinity observations (SSS_in-situ) made during the NASA Salinity Field Campaign SASSIE (Salinity and Stratification at Sea-Ice Edge) during the fall of 2022. The SASSIE SSS_in-situ were collected by 9 different platforms: CastAway and Underway CTD, Wave Gliders, Thermosalinograph, Snake-salinity, SWIFT drifters, UpTempO buoys, Jet-SSP and ALTO and ALAMO profilers. Because satellite SSS retrievals are impacted by land and sea-ice contaminations, cold temperatures, and surface roughness, mean differences, RMSD and STD between satellite SSS and SSS_in-situ are examined as a function of distance from the coast and sea-ice edge, sea surface temperature (SST) and wind speed. We find that SSS_SMOS and SSS_SMAP are well correlated (0.66 and 0.78 respectively) with similar RMSD when compared with SSSin-situ. Close to the coast (0–150 km), SSS_SMAP compare better with SSSin-situ with RMSD (<2 g/kg) lower than that from SSS_SMOS. Near the sea-ice edge (0–150 km), SSS_SMOS compare better with SSS_in-situ with RMSD (<2.5 g/kg) lower than that from SSS_SMAP. In cold water (SST<1.5°C) and low wind speed conditions (< 7 m/s), both SSS_SMOS and SSS_SMAP are consistent with each other. The RMSD between SSS_SMAP and SSS_in-situ decreases considerably (<1 g/kg) when SST >1.5°C, while the RMSD between SSS_SMOS and SSS_in-situ shows less dependence on SST.

There are many challenges associated with obtaining high-fidelity sea ice concentration (SIC) information, and products that rely solely on passive microwave measurements often struggle to represent conditions at low concentration, especially within the marginal ice zone and during periods of active melt. Here, we present a newly gridded SIC product for the Alaskan Arctic, generated with data from the National Weather Service Alaska Sea Ice Program (hereafter referred to as ASIP), that synthesizes a variety of satellite SIC and in situ observations from 2007–present. These SIC fields have been primarily used for operational purposes and have not yet been gridded or independently validated. In this study, we first grid the ASIP product into 0.05° resolution in both latitude and longitude (hereafter referred to as gridded ASIP, or grASIP). We then perform extensive intercomparison with an international database of ship-based in situ SIC observations, supplemented with observations from saildrones. Additionally, an intercomparison between three ice products is performed: (i) grASIP, (ii) a high-resolution passive microwave product (AMSR2), and (iii) a product available from the National Snow and Ice Data Center (MASIE) that originates from the US National Ice Center (USNIC) operational IMS product. This intercomparison demonstrates that all products perform similarly when compared to in situ observations generally, but grASIP outperforms the other products during periods of active melt and in low-SIC regions. Furthermore, we show that the similarity in performance among products is partly due to the deficiencies in the in situ observations' geographical distribution, as most in situ observations are far from the ice edge in locations where all products agree. We find that the grASIP ice edge is generally farther south than both the AMSR2 and MASIE ice edges by an average of approximately 50 km in winter and 175 km in summer for grASIP vs. AMSR2 and 10 km in winter and 40 km in summer for grASIP vs. MASIE.

In order to quantify pelagic-benthic coupling on high-latitude shelves, it is imperative to identify the different physical mechanisms by which phytoplankton are exported to the sediments. In June–July 2023, a field program documented the evolution of an under-ice phytoplankton bloom on the northeast Chukchi shelf. Here, we use in situ data from the cruise, a simple numerical model, historical water column data, and ocean reanalysis fields to characterize the physical setting and describe the dynamically driven vertical export of chlorophyll associated with the bloom. A water mass front separating cold, high-nutrient winter water in the north and warmer summer waters to the south—roughly coincident with the ice edge—supported a baroclinic jet which is part of the Central Channel flow branch that veers eastward toward Barrow Canyon. A plume of high chlorophyll fluorescence extending from the near-surface bloom in the winter water downwards along the front was measured throughout the cruise. Using a passive tracer to represent phytoplankton in the model, it was demonstrated that the plume is the result of subduction due to baroclinic instability of the frontal jet. This process, in concert with the gravitational sinking, pumps the chlorophyll downwards an order of magnitude faster than gravitational sinking alone. Particle tracking using the ocean reanalysis fields reveals that a substantial portion of the chlorophyll away from the front is advected off of the northeast Chukchi shelf before reaching the bottom. This highlights the importance of the frontal subduction process for delivering carbon to the sea floor.

The flow of Pacific-origin water across the Chukchi Sea shelf impacts the regional ecosystem in profound ways, yet the two current branches on the eastern shelf that carry the water from Bering Strait to Barrow Canyon — the Alaskan Coastal Current (ACC) and Central Channel (CC) Branch — have not been clearly distinguished or quantified. In this study we use an extensive collection of repeat hydrographic sections occupied at three locations on the Chukchi shelf, together with data from a climatology of shipboard velocity data, to accomplish this. The data were collected predominantly between 2010 and 2020 during the warm months of the year as part of the Distributed Biological Observatory and Arctic Observing Network. The mean sections show that mass is balanced for both currents at the three locations: Bering Strait, Point Hope, and Barrow Canyon. The overall mean ACC transport is 0.34 ± 0.04 Sv, and that of the CC Branch is 0.86 ± 0.11 Sv. The dominant hydrographic variability at Bering Strait is seasonal, but this becomes less evident to the north. At Barrow Canyon, the dominant hydrographic signal is associated with year-to-year variations in sea-ice melt. Farther south there is pronounced mesoscale variability: an empirical orthogonal function analysis at Bering Strait and Point Hope reveals a distinct ACC mode and CC Branch mode in hydrography and baroclinic transport, where the former is wind-driven. Finally, the northward evolution in properties of the two currents is investigated. The poleward increase in salinity of the ACC can be explained by lateral mixing alone, but solar heating together with wind mixing play a large role in the temperature evolution. This same atmospheric forcing also impacts the northward evolution of the CC Branch.

Understanding the variability of the Atlantic Meridional Overturning Circulation is essential for better predictions of our changing climate. Here we present an updated time series (August 2014 to June 2020) from the Overturning in the Subpolar North Atlantic Program. The 6-year time series allows us to observe the seasonality of the subpolar overturning and meridional heat and freshwater transports. The overturning peaks in late spring and reaches a minimum in early winter, with a peak-to-trough range of 9.0 Sv. The overturning seasonal timing can be explained by winter transformation and the export of dense water, modulated by a seasonally varying Ekman transport. Furthermore, over 55% of the total meridional freshwater transport variability can be explained by its seasonality, largely owing to overturning dynamics. Our results provide the first observational analysis of seasonality in the subpolar North Atlantic overturning and highlight its important contribution to the total overturning variability observed to date.

Arctic-origin and Greenland meltwaters circulate cyclonically in the boundary current system encircling the Labrador Sea. The ability of this freshwater to penetrate the interior basin has important consequences for dense water formation and the lower limb of the Atlantic Meridional Overturning Circulation. However, the precise mechanisms by which the freshwater is transported offshore, and the magnitude of this flux, remain uncertain. Here, we investigate wind-driven upwelling northwest of Cape Farewell using 4 years of high-resolution data from the Overturning in the Subpolar North Atlantic Program west Greenland mooring array, deployed from September 2014–2018, along with Argo, shipboard, and atmospheric reanalysis data. A total of 49 upwelling events were identified corresponding to enhanced northwesterly winds, followed by reduced along-stream flow of the boundary current and anomalously dense water present on the outer shelf. The events occur during the development stage of forward Greenland tip jets. During the storms, a cross-stream Ekman cell develops that transports freshwater offshore in the surface layer and warm, saline, Atlantic-origin waters onshore at depth. The net fluxes of heat and freshwater for a representative storm are computed. Using a one-dimensional mixing model, it is shown that the freshwater input resulting from the locus of winter storms could significantly limit the wintertime development of the mixed layer and hence the production of Labrador Sea Water in the southeastern part of the basin.