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.