The Arctic Ocean has experienced rapid warming and sea ice loss in recent decades, becoming the first open-ocean basin to experience widespread aragonite undersaturation [saturation state of aragonite (Ω _arag ) < 1]. However, its trend toward long-term ocean acidification and the underlying mechanisms remain undocumented. Here, we report rapid acidification there, with rates three to four times higher than in other ocean basins, and attribute it to changing sea ice coverage on a decadal time scale. Sea ice melt exposes seawater to the atmosphere and promotes rapid uptake of atmospheric carbon dioxide, lowering its alkalinity and buffer capacity and thus leading to sharp declines in pH and Ω _arag . We predict a further decrease in pH, particularly at higher latitudes where sea ice retreat is active, whereas Arctic warming may counteract decreases in Ω _arag in the future.

This article focuses on the interaction between the Ob‐ and Yenisei‐dominated parts of the large Ob‐Yenisei buoyant plume formed in the southern part of the Kara Sea during ice‐free periods. It was shown that certain wind forcing and river discharge conditions cause the formation of a specific structure of the Ob‐Yenisei plume with significantly different properties of the Ob‐ and Yenisei‐dominated water masses. Under these conditions, the Yenisei runoff generates a narrow coastal current propagating northward from the Yenisei Gulf along the Taymyr Peninsula, which is isolated by the Ob‐dominated water mass from ambient sea water. As a result, the low‐salinity Yenisei‐dominated water mass occupies a relatively small area, while more saline Ob‐dominated water mass spreads over a wide area between the Gulf of Ob and the Taymyr Peninsula. The formation of the “isolation” configuration of the Ob‐Yenisei plume described above is presumed to be caused by the eastward Ekman transport and the resulting downwelling flow of the Ob‐dominated waters under the low‐saline and warm Yenisei‐dominated waters along the Taymyr Peninsula. Based on satellite imagery, wind reanalysis, and river discharge data collected and derived for the period of 2005–2011, it was estimated that the “isolation” configuration is regularly formed during late summer and autumn when the Ob discharge to the Kara Sea exceeds the Yenisei discharge and the local atmospheric circulation is dominated by the northerly wind regime. Assessment of the frequency and duration of the occurrence of the “isolation” configuration showed their synoptic time scale and significant interannual variability.

This paper presents the results of long-term in situ and satellite measurements at shelf areas adjacent to the estuaries of the small rivers of the Russian coast of the Black Sea (Mezyb, Pshada,...

Studies have been performed on a transect along 130°30′ E from the Lena River delta (71°60′ N) to the continental slope and adjacent deepwater area (78°22′ N) of the Laptev Sea in September 2015. The structure of phytoplankton communities has distinct latitudinal zoning. The southern part of the shelf (southward of 73°10′ N), the most desalinated by riverine discharge, houses a phytoplankton community with a biomass of 175–840 mg/m², domination of freshwater Aulacoseira diatoms, and significant contribution of green algae (both in abundance and biomass). The northern border for the distribution range of the southern complex of phytoplankton species lies between the 8 and 18 psu isohalines (~73°10′ N). The continental slope and deepwater areas of the Laptev Sea (north of 77°30′ N), with a salinity of >27 psu in the upper mixed layer, are populated by the community prevalently composed of Chaetoceros and Rhizosolenia diatoms, very abundant in the Arctic, and dinoflagellates. The phytoplankton number in this area fall in the range of 430–1100 × 10⁶ cell/m², and the biomass, in the range of 3600 mg/m². A moderate desalinating impact of the Lena River discharge is observed in the outer shelf area between 73°20′ and 77°30′ N; the salinity in the upper mixed layer is 18–24 psu. The phytocenosis in this area has a mosaic spatial structure with between-station variation in the shares of different alga groups in the community, cell number of 117–1200 × 10⁶ cells/m², and a biomass of 1600–3600 mg/m². As is shown, local inflow of “fresh” nutrients to the euphotic layer in the fall season leads to mass growth of diatoms.

Observations and predictions show that consequences of climate warming such as declining summer sea ice cover, melting glaciers, thawing permafrost, and increased river runoff to the Arctic Ocean will likely modify processes relevant to the freshwater and carbon budget, which in turn affect high-latitude marine ecosystems. There is a knowledge gap in terms of understanding the seasonal variability of biogeochemical characteristics in coastal environments, first of all due to a lack of winter data. More data are also needed on the biogeochemical composition of different environmental media, i.e., sediments, snow, and ice. The aim of this work was to assess the current biogeochemical regime of a fjord system exposed to coastal runoff and glacial melting and discuss the possible consequences connected with climate warming. We used data from five expeditions to the Templefjord, West Spitsbergen, obtained in different seasons (February 2011, September 2011, March 2014, June 2015, and June 2017). In all the expeditions, the distributions of dissolved oxygen, nutrients, and carbonate system parameters in the water column were studied. The principal environmental media, i.e., seawater, bottom sediments, river water, sea ice, river ice, glacier ice, and snow, were sampled. The collected data allowed us to describe seasonal dynamics in the water column and to estimate the concentrations of the parameters under study in different environmental media. Our observations revealed the glacial and river footprints in the water column biogeochemistry; the glacial influence can be traced both in summer and in winter season. The results demonstrated the significant influence of coastal runoff and melted glacier water on the carbonate system and nutrient regime in the Templefjord, and can be extrapolated to other Arctic fjord systems.

Abiotic characteristics of the waters in the Bransfield Strait were studied in a section from the South Shetland Islands to the Antarctic Peninsula. The Bransfield Current was recorded northeastward flowing along the archipelago with a speed of 20–47 cm/s. It is marked by the water temperature and salinity in the core (2.7°C and 34.18%). The depth of the lower boundary of the euphotic layer varies from 40 m near the South Shetland Islands to 80 m on the shelf of the Antarctic Peninsula. The oxygen content and parameters of the carbonate system indicate the predominance of production over destructive processes in the surface layer of the central part of the Strait during the period under study. A countercurrent from the Weddell Sea was recorded on the shelf of the Antarctic Peninsula, which is distinguished by the oxygen saturation (90%) and silica content (74 µM). Four water masses were identified in the region under studied: Antarctic Surface Water, Circumpolar Deep Water, modified water of the north-western Weddell Sea shelf, and Bottom Bransfield Water.