Climate warming is amplified in the land-sea system of the East Siberian Arctic, which also holds large pools of vulnerable carbon in permafrost. This coastal area is strongly influenced by sediment and carbon transport from both its large rivers and extensive erosion of Pleistocene permafrost along its coastline. This study is investigating the coastal fate of the sediment and organic carbon delivered to the Buor-Khaya Gulf, which is the first recipient of the overwhelming fluvial discharge from the Lena River and is additionally receiving large input from extensive erosion of the coastal ice-complex (permafrost a.k.a. Yedoma; loess soil with high organic carbon content). Both water column suspended particulate matter (SPM) and surface sediments were sampled at about 250 oceanographic stations in the Gulf in this multi-year effort, including one winter campaign, and analyzed for the distribution and sorting of sediment size, organic carbon content, and stable carbon isotope signals. The composition of the surface sediment suggests an overwhelmingly terrestrial contribution from both river and coastal erosion. The objective of this paper is to improve our understanding of the seasonal (i.e., winter vs summer) and interannual variability of these coastal sedimentation processes and the dynamics of organic carbon (OC) distribution in both the water column SPM and the surface sediments of the Buor-Khaya Gulf. Based on data collected during several years in the period 2000–2008, two different sedimentation regimes were revealed for the Buor-Khaya Gulf, the relative importance of each at a given time depend on hydrometeorological conditions, the Lena River water discharge and sea-ice regime: Type 1 erosion-accumulation and Type 2 accumulation. The Type 1 erosion-accumulation sedimentation regime is typical (2000–2006) for the ice-free period of the year (here considered in detail for August 2005). Under such conditions terrigenous sources of SPM and particulate organic carbon (POC) stem predominantly from river discharge, thermal erosion of coastal ice-complex and remobilized bottom sediments. The Type 2 accumulation sedimentation regime develops under ice-covered conditions, and only occasionally during the ice-free period (August 2008). In Type 2 winter, combined terrigenous and marine-biogenic SPM and POC sources are dominating due to relatively low overall terrigenous input (April 2007). In Type 2 summer, river alluvium becomes the major SPM and POC source (August 2008). The water column SPM and POC loadings vary by more than a factor of two between the two regimes. This study underscores the necessity of multi-year investigations to better understand the functioning of the primary recipient of terrestrially expulsed matter in the East Siberian Arctic.

The first full transarctic section of ²²⁸Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the transpolar drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased ²²⁸Ra input is attributed to stronger wave action on shelves resulting from a longer ice‐free season. A concomitant decrease in the ²²⁸Th/²²⁸Ra ratio likely results from more rapid transit of surface waters depleted in ²²⁸Th by scavenging over the shelf. The ²²⁸Ra activities observed in intermediate waters (<1,500 m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15–18 years, in good agreement with estimates based on SF₆ and ¹²⁹I/²³⁶U. The ²²⁸Th excess below the mixed layer up to 1,500 m depth can complement ²³⁴Th and ²¹⁰Po as tracers of export production, after correction for the inherent excess resulting from the similarity of ²²⁸Ra and ²²⁸Th decay times. We show with a Th/Ra profile model that the ²²⁸Th/²²⁸Ra ratio below 1,500 m is inappropriate for this purpose because it is a delicate balance between horizontal supply of ²²⁸Ra and vertical flux of particulate ²²⁸Th. The accumulation of ²²⁶Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of ²³⁰Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov‐Canada Basin, in good agreement with previous estimates using other tracers.

The paper provides information about a complex of geological studies in Chaun Bay in the East Siberian Sea during cruise 60 of the R/V Akademik Oparin in October 2020. Preliminary results of the scientific expedition are discussed.

Chaun Bay, located on the fringe of the East Siberian Sea, has been described since the mid-20th century to support a unique marine ecosystem that is atypical for the local Siberian Arctic. Here we use ship-board physical, biogeochemical and geological measurements taken in October 2020, along with hydrographic observations taken from land-fast ice in April 2023, to demonstrate that these warm-water biological communities are supported by hydrothermal submarine groundwater discharge that delivers heat, salinity, nutrients, and trace elements to the bay. We identify a cyclonic eddy that mixes the warm nutrient-rich groundwater with oxygen-rich surface water, resulting in a water mass within Chaun Bay that has similar physical and chemical properties to the highly productive waters of the North Pacific and Southern Chukchi Sea. The bay showed elevated concentrations of chlorophyll-a and zooplankton, and the abundance and species diversity of epibenthos significantly exceeded values observed elsewhere in the East Siberian Sea. The benthic communities contained a number of boreal species that are not typically found in the Arctic Ocean. We also observed Thysanoessa krill populations, a pelagic species generally considered an expatriate in Arctic waters.

On the basis of perennial studies, the features of formations of suspended particulate matter fields were revealed depending on the evolution of synoptic processes and the river runoff. The...