As Arctic temperatures rise at twice the global rate, sea ice is diminishing more quickly than models can predict. Processes that dictate Arctic cloud formation and impacts on the atmospheric energy budget are poorly understood, yet crucial for evaluating the rapidly changing Arctic. In parallel, warmer temperatures afford conditions favorable for productivity of microorganisms that can effectively serve as ice nucleating particles (INPs). Yet the sources of marine biologically derived INPs remain largely unknown due to limited observations. Here we show, for the first time, how biologically derived INPs were likely transported hundreds of kilometers from deep Bering Strait waters and upwelled to the Arctic Ocean surface to become airborne, a process dependent upon a summertime phytoplankton bloom, bacterial respiration, ocean dynamics, and wind‐driven mixing. Given projected enhancement in marine productivity, combined oceanic and atmospheric transport mechanisms may play a crucial role in provision of INPs from blooms to the Arctic atmosphere.

Synoptic and historical shipboard data, spanning the period 1981–2017, are used to investigate the seasonal evolution of water masses on the northeastern Chukchi shelf and quantify the circulation patterns and their impact on nutrient distributions. We find that Alaskan coastal water extends to Barrow Canyon along the coastal pathway, with peak presence in September, while the Pacific Winter Water (WW) continually drains off the shelf through the summer. The depth‐averaged circulation under light winds is characterized by a strong Alaskan Coastal Current (ACC) and northward flow through Central Channel. A portion of the Central Channel flow recirculates anticyclonically to join the ACC, while the remainder progresses northeastward to Hanna Shoal where it bifurcates around both sides of the shoal. All of the branches converge southeast of the shoal and eventually join the ACC. The wind‐forced response has two regimes: In the coastal region the circulation depends on wind direction, while on the interior shelf the circulation is sensitive to wind stress curl. In the most common wind‐forced state—northeasterly winds and anticyclonic wind stress curl—the ACC reverses, the Central Channel flow penetrates farther north, and there is mass exchange between the interior and coastal regions. In September and October, the region southeast of Hanna Shoal is characterized by elevated amounts of WW, a shallower pycnocline, and higher concentrations of nitrate. Sustained late‐season phytoplankton growth spurred by this pooling of nutrients could result in enhanced vertical export of carbon to the seafloor, contributing to the maintenance of benthic hotspots in this region.

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.

Upper-ocean turbulence is central to the exchanges of heat, momentum, and gasses across the air/sea interface, and therefore plays a large role in weather and climate. Current understanding of upper-ocean mixing is lacking, often leading models to misrepresent mixed-layer depths and sea surface temperature. In part, progress has been limited due to the difficulty of measuring turbulence from fixed moorings which can simultaneously measure surface fluxes and upper-ocean stratification over long time periods. Here we introduce a direct wavenumber method for measuring Turbulent Kinetic Energy (TKE) dissipation rates, ϵ, from long-enduring moorings using pulse-coherent ADCPs. We discuss optimal programming of the ADCPs, a robust mechanical design for use on a mooring to maximize data return, and data processing techniques including phase-ambiguity unwrapping, spectral analysis, and a correction for instrument response. The method was used in the Salinity Processes Upper-ocean Regional Study (SPURS) to collect two year-long data sets. We find the mooring-derived TKE dissipation rates compare favorably to estimates made nearby from a microstructure shear probe mounted to a glider during its two separate two-week missions for (10−8) ≤ ϵ ≤ (10−5) m2 s−3. Periods of disagreement between turbulence estimates from the two platforms coincide with differences in vertical temperature profiles, which may indicate that barrier layers can substantially modulate upper-ocean turbulence over horizontal scales of 1-10 km. We also find that dissipation estimates from two different moorings at 12.5 m, and at 7 m are in agreement with the surface buoyancy flux during periods of strong nighttime convection, consistent with classic boundary layer theory.

Among the organisms that spread into and flourish in Arctic waters with rising temperatures and sea ice loss are toxic algae, a group of harmful algal bloom species that produce potent biotoxins. Alexandrium catenella, a cyst-forming dinoflagellate that causes paralytic shellfish poisoning worldwide, has been a significant threat to human health in southeastern Alaska for centuries. It is known to be transported into Arctic regions in waters transiting northward through the Bering Strait, yet there is little recognition of this organism as a human health concern north of the Strait. Here, we describe an exceptionally large A. catenella benthic cyst bed and hydrographic conditions across the Chukchi Sea that support germination and development of recurrent, locally originating and self-seeding blooms. Two prominent cyst accumulation zones result from deposition promoted by weak circulation. Cyst concentrations are among the highest reported globally for this species, and the cyst bed is at least 6× larger in area than any other. These extraordinary accumulations are attributed to repeated inputs from advected southern blooms and to localized cyst formation and deposition. Over the past two decades, warming has likely increased the magnitude of the germination flux twofold and advanced the timing of cell inoculation into the euphotic zone by 20 d. Conditions are also now favorable for bloom development in surface waters. The region is poised to support annually recurrent A. catenella blooms that are massive in scale, posing a significant and worrisome threat to public and ecosystem health in Alaskan Arctic communities where economies are subsistence based.