ALBERT

Description: The Terrestrial Multidisciplinary distributed Observatories for the Study of the Arctic Connections (T-MOSAiC) 2021 permafrost thaw data set provides standardized measurements for permafrost thaw and the linked parameters snow depth, vegetation height, water level and soil texture as suggested by Boike et al., 2021. It contains measurements from eight circumpolar permafrost sites where data was obtained using the myThaw app which is based on the user-friendly, multiparameter protocol for standardized monitoring of permafrost thaw for the year 2021. The data set contains detailed metadata for each site including data on the timing of data collection, geographical coordinates and land surface characteristics (vegetation, ground surface and water features).

Description: The Lena River Delta in Northern Yakutia forms one of the largest deltas in the Arctic and its catchment area (2 430 000 km2) is one of the largest in the whole of Eurasia. The study site is one of the coldest and driest places on Earth, with a mean annual air temperatures of about -13 °C, a large annual air temperature range of about 44 °C and summer precipitation usually less than 150 mm. Permafrost plays a major role for storage and release of water to rivers and surface and subsurface water bodies. Very cold continuous permafrost of about −8.6°C underlays the area between about 400 and 600 m below the surface and since 2006 the permafrost has warmed more than 1°C at 10.7 m. Roughly half of the land surface is dominated by wet surfaces, such as polygons, thermokarst lakes and ponds. Ponds are generally well mixed and experience high water temperatures up to 23°C during the summer and therefore are hotspots for biological activity and CO2 emission. Compared to the gaseous emissions, however, the lateral export of dissolved carbon from the polygonal tundra was negligible due to the small volumes of runoff. The ponds in the study area freeze completely in winter, whereas the deeper thermokarst lakes do not freeze to the bottom. These deep thermokarst lakes are thermally stratified during winter and reach maximum water temperatures of up to 19°C during summer. There are distinct differences in the zooplankton community between ponds and lakes, depending on their hydrological and chemical characteristics. Most productive ecosystems are thermokarst ponds with a high abundance of zooplankton and biomass. The summer water balance at the catchment scale was found to be mainly controlled by vertical fluxes (precipitation and evapotranspiration). Overall, the long-term summer storage (precipitation minus evapotranspiration) in the polygonal tundra from 1958-2011 is reasonably balanced with an average surplus of 5 mm. But it is also characterized by high inter-annual variability due to changes in precipitation. During negative water balance years where evapotranspiration exceeds precipitation, shallow water bodies dry out. This indicates that the extent of wetlands and water bodies will shift with changes in vertical water fluxes as well as permafrost warming and thaw.

Description: Enhanced permafrost warming and increased Arctic river discharges have heightened concern about the input of terrigenous matter into Arctic coastal waters. We used optical operational satellite data from the ocean colour sensor MERIS (Medium-Resolution Imaging Spectrometer) aboard the ENVISAT satellite mission for synoptic monitoring of the pathways of terrigenous matter on the shallow Laptev Sea shelf. Despite the high cloud coverage in summer that is inherent to this Arctic region, time series from MERIS satellite data from 2006 on to 2011 could be acquired and were processed using the Case-2 Regional Processor (C2R) for optically complex surface waters installed in the open-source software ESA BEAM-VISAT. Since optical remote sensing using ocean colour satellite data has seen little application in Siberian Arctic coastal and shelf waters, we assess the applicability of the calculated MERIS C2R parameters with surface water sampling data from the Russian–German ship expeditions LENA2008, LENA2010 and TRANSDRIFT-XVII taking place in August 2008 and August and September 2010 in the southern Laptev Sea. The shallow Siberian shelf waters are optically not comparable to the deeper, more transparent waters of the Arctic Ocean. The inner-shelf waters are characterized by low transparencies, due to turbid river water input, terrestrial input by coastal erosion, resuspension events and, therefore, high background concentrations of suspended particulate matter and coloured dissolved organic matter. We compared the field-based measurements with the satellite data that are closest in time. The match-up analyses related to LENA2008 and LENA2010 expedition data show the technical limits of matching in optically highly heterogeneous and dynamic shallow inner-shelf waters. The match-up analyses using the data from the marine TRANSDRIFT expedition were constrained by several days' difference between a match-up pair of satellite-derived and in situ parameters but are also based on the more stable hydrodynamic conditions of the deeper inner- and the outer-shelf waters. The relationship of satellite-derived turbidity-related parameters versus in situ suspended matter from TRANSDRIFT data shows that the backscattering coefficient C2R_bb_spm can be used to derive a Laptev-Sea-adapted SPM algorithm. Satellite-derived Chl a estimates are highly overestimated by a minimum factor of 10 if applied to the inner-shelf region due to elevated concentrations of terrestrial organic matter. To evaluate the applicability of ocean colour remote sensing, we include the visual analysis of lateral hydrographical features. The mapped turbidity-related MERIS C2R parameters show that the Laptev Sea is dominated by resuspension above submarine shallow banks and by frontal instabilities such as frontal meanders with amplitudes up to 30 km and eddies and filaments with horizontal scales up to 100 km that prevail throughout the sea-ice-free season. The widespread turbidity above submarine shallow banks indicates inner-shelf vertical mixing that seems frequently to reach down to submarine depths of a minimum of 10 m. The resuspension events and the frontal meanders, filaments and eddies indicate enhanced vertical mixing being widespread on the inner shelf. It is a new finding for the Laptev Sea that numerous frontal instabilities are made visible, and how highly time-dependent and turbulent the Laptev Sea shelf is. The meanders, filaments and eddies revealed by the ocean colour parameters indicate the lateral transportation pathways of terrestrial and living biological material in surface waters.

Description: Enhanced permafrost warming and increased arctic river discharges have heightened concern about the input of terrigenous matter into Arctic coastal waters. The IPY project 'ocOC- from Ocean Colour to Organic Carbon' (2008-2010) uses Ocean Colour (OC) data for synoptic monitoring of the input of terrigenous Organic Carbon (OC) from fluvial and coastal sources into Arctic coastal waters. Every late summer, Russian-German ship expeditions take part in the southern Laptev Sea (Arctic Siberia, Russia). The multi-year expedition data are the base for understanding the optico-chemico properties of the coastal waters. The coastal waters are characterized by low transparencies, resuspension events and high cDOM concentrations. The Laptev Sea Region has become an ESA CoastColour investigation site to support the use of the ground data. Ocean Colour MERIS data from 2008 on to 2010 are processed using the VISAT Beam Case2Regional Processor (C2R). The expedition data show that Siberian Arctic coastal waters are highly specific in terms of high cDOM background concentrations. Therefore, all remote sensing chlorophyll products are overestimated by an order of magnitude due to the high cDOM concentrations. The optical C2R parameters such as absorption, attenuation and the first attenuation depth are of immediate value to show the hydrographic dynamics of the Laptev Sea coastal waters