In the Arctic Ocean ice algae constitute a key ecosystem component and the ice algal spring bloom a critical event in the annual production cycle. The bulk of ice algal biomass is usually found in the bottom few cm of the sea ice and dominated by pennate diatoms attached to the ice matrix. Here we report a red tide of the phototrophic ciliate Mesodinium rubrum located at the ice–water interface of newly formed pack ice of the high Arctic in early spring. These planktonic ciliates are not able to attach to the ice. Based on observations and theory of fluid dynamics, we propose that convection caused by brine rejection in growing sea ice enabled M. rubrum to bloom at the ice–water interface despite the relative flow between water and ice. We argue that red tides of M. rubrum are more likely to occur under the thinning Arctic sea ice regime.

Arctic Ocean freshwater content increased in the 2000s. Since variations in freshwater input into the North Atlantic Ocean can modify its properties, monitoring the freshwater export from the Arctic Ocean to southern latitudes is critical. The Arctic Outflow Observatory in Fram Strait has collected continuous ocean measurements from moored platforms since 1997. Here new and improved records of freshwater transport from the mooring array are presented until 2015, showing that, since the last documented record in 2009, the freshwater export was substantially larger from 2010 to 2013. The increase was mostly due to increased southward flow, and secondly due to low salinities. While sea level pressure gradient across the strait explains seasonal variability, it does not explain the observed freshwater anomaly. The cumulative freshwater anomaly between 2010 and 2014 amounted to 3,684 km³, representing a significant external source of freshwater to the North Atlantic.

The fine spatial resolution of laser altimeters makes them potentially valuable to oceanography studying features at mesoscale, close to land, and in the marginal ice zone. To fulfill this promise, we must understand laser sea state bias (SSB). SSB occurs in the measurement of sea surface height in the presence of waves when the altimeter observations are preferentially influenced by particular parts (e.g., wave troughs) of the wave-covered surface. Radar altimeters have received considerable attention relating radar SSB to wave properties and wind speed. Comparatively, little attention has been devoted to the SSB of laser altimeters, and the studies of laser SSB which have been done have led to indeterminate or ambiguous results even as to sign. Here, we find that to make changes in satellite dynamic ocean topography (DOT) from the Ice, Clouds, and Land Elevation Satellite (ICESat) period, 2004–2009, to the CryoSat-2 period, 2011–2015, consistent with hydrography plus ocean bottom pressure in the subarctic Greenland and Norwegian seas, we need to correct the ICESat DOT for SSB. On average, ICESat SSB is –18% of significant wave height in excess of 1.7 m.

A budget of meteoric water (MW = river runoff, net precipitation minus evaporation, and glacial meltwater) over four regions of the Arctic Ocean is constructed using a simple box model, regional precipitation-evaporation estimates from reanalysis data sets, and estimates of import and export fluxes derived from the literature with a focus on the 2003–2008 period. The budget indicates an approximate/slightly positive balance between MW imports and exports (i.e., no change in storage); thus, the observed total freshwater increase observed during this time period likely resulted primarily from changes in non-MW freshwater components (i.e., increases in sea ice melt or Pacific water and/or a decrease in ice export). Further, our analysis indicates that the MW increase observed in the Canada Basin resulted from a spatial redistribution of MW over the Arctic Ocean. Mean residence times for MW were estimated for the Western Arctic (5–7 years), Eastern Arctic (3–4 years), and Lincoln Sea (1–2 years). The MW content over the Siberian shelves was estimated (~14,000 km³) based on a residence time of 3.5 years. The MW content over the entire Arctic Ocean was estimated to be ≥ 44,000 km³. The MW export through Fram Strait consisted mostly of water from the Eastern Arctic (3237 ± 1370 km³ yr^-1) whereas the export through the Canadian Archipelago was nearly equally derived from both the Western Arctic (1182 ± 534 km³ yr^-1) and Lincoln Sea (972 ± 391 km³ yr^-1).

It is typically stated that the Pacific-to-Arctic oceanic flow through the Bering Strait (important for Arctic heat, freshwater, and nutrient budgets) is driven by local wind and a (poorly defined) far-field "pressure head" forcing, related to sea surface height differences between the Pacific and the Arctic. Using monthly, Arctic-wide, ocean bottom pressure satellite data and in situ mooring data from the Bering Strait from 2002 to 2016, we discover the spatial structure of this pressure head forcing, finding that the Bering Strait throughflow variability is dominantly driven from the Arctic, specifically by sea level change in the East Siberian Sea (ESS), in turn related to westward winds along the Arctic coasts. In the (comparatively calm) summer, this explains approximately two thirds of the Bering Strait variability. In winter, local wind variability dominates the total flow, but the pressure head term, while still correlated with the ESS-dominated sea level pattern, is now more strongly related to Bering Sea Shelf sea level variability.