ALBERT

Description: Arctic permafrost coasts are eroding at rates similar or greater than temperate coasts and release large quantities of organic carbon and nitrogen previously stored in permafrost. Estimates of organic carbon fluxes from ice-rich permafrost coasts of the Laptev Sea, where data is scarce, differ widely with estimates varying by two orders or magnitude. Here, we used high resolution datasets on coastal erosion, cryostratigraphy, organic carbon and geomorphology from the Bykovsky Peninsula, in the southern Laptev Sea, to compute below ground organic carbon and nitrogen pools and fluxes of organic carbon from the coast for the current period and the next hundred years. Frozen deposits of the peninsula contain 141.6 Tg of organic carbon, a number 27% lower than what it would contain if the surface had not been affected by permafrost thaw in the past. An additional 44.0 Tg of organic carbon is contained under the peninsula below current sea level. The current fluxes of organic carbon from the peninsula are estimated at 0.058 Tg C a-1 and future fluxes at 0.067 Tg C a-1, or even at 0.085 Tg C a-1 if below sea level organic carbon stocks are included in the calculation. Extrapolation of these measurements to the entire Yedoma coast of the Laptev Sea gives an maximum annual flux of organic carbon from coastal erosion of 6.95 Tg C a-1, which ranges between the previously published minimum and maximum estimations for the same area.s

Description: The transition from onshore to offshore permafrost during periods of low relative sea level rise is often the result of coastal retreat. Along the Laptev Sea coastline, ice-rich syngenetic permafrost is particularly susceptible to erosion due to changing climate, and coastal retreat floods about 10 km2 of permafrost each year. Changes to permafrost immediately after flooding provide an opportunity to study the mechanism of submarine permafrost degradation in general. Recent studies have drawn a link between observed methane release on the Laptev Sea shelf and surmised permafrost degradation. We combine direct observations of permafrost and methane to investigate the possibility of methane release from permafrost as a source. Our studies focus on a site in Buor Khaya Bay in the central Laptev Sea, for which coastal retreat rates have been studied. Following geophysical reconnaissance, we drilled a 52 m deep core in the near-shore zone of the eastern shore of Buor Khaya Bay and measured the permafrost temperature in the resulting borehole. Comparison of the submarine permafrost temperature to temperatures on land reveal warming of permafrost by 8 to 10 °C over a period of less than a millennium. During this time, the top of the ice-bearing permafrost (IBPF) degraded from 0 to 28.8 m b.s.l. at the borehole site, a mean degradation rate of almost 3 cm per year. Geoelectric resistivity measurements corroborate this observation and show a decline of the IBPF with increasing distance from shore. Similar to many other Siberian locations, the deeper permafrost at the study site contained less organic carbon by orders of magnitude when compared to the overlying syngenetic ice complex deposits. The same held true for methane concentrations in the frozen permafrost. Our data suggest that these comparatively low concentrations of methane are oxidized in the sediment column upon thawing. Analyses of the sediment and pore water chemistry demonstrate that sea water is probably advected to the IBPF, which contributes to permafrost degradation and provides sulfate for methane oxidation at the top of the thawing permafrost.

Description: The intensity of thermo-erosion in the coastal zone of the Laptev Sea region mirrors the strong seasonality of exogenous hydro-meteorological conditions, mainly the presence or absence of sea ice and large temperature amplitudes. Permafrost, and in particular the widespread presence of syngenetic ground ice, both above and below sea level, constitute endogenous local conditions that make this coastline highly susceptible to currently observed warming and the associated extension of the open water season on the East Siberian arctic shelf. Although the general magnitude of erosion dynamics along Ice Complex coasts has been investigated, substantial information about local, regional, seasonal, and inter-annual variations still remain unknown. Monitoring capabilities could be increased by using the large areal coverage of historical records, accompanied by new acquisitions of contemporary high and very high resolution remote sensing data. Based on topographic reference measurements during field campaigns, we derived digital elevation models for subsequent orthorectification, in order to enable consistent distance and area measurements. A distinction was made between two related processes that work together, but with temporal and quantitative differences. Cliff top erosion (thermo-denudation) and cliff bottom erosion (thermo-abrasion) have different impacts on the volume of land loss and subsequent mass displacements. For a geographically broad baseline of well-distributed key areas, a proportional relationship of both processes on a multi-decadal long-term scale was observed, at site-specific average rates of -1.8 to -3.4 m/yr on Muostakh Island off the coast of Tiksi and along the continental coast of the Dmitriy Laptev Strait, respectively. However, short-term observations over the recent past revealed not only that erosion rates were 1.6 times more rapid on average, but also responded differently in terms of thermo-denudation and abrasion towards environmental forcings. This response was evaluated using the Normalized Difference Thermo-erosion Index (NDTI), whose value domain differentiates either marine or atmospherically driven erosion regimes, and may additionally indicate near-surface ground ice conditions. Seasonal observations on Muostakh, where the most rapid long-term rates of -9.6 m a-1 have been measured, revealed the existence of a thermo-erosional cycle, during which rates of either thermo-denudation or abrasion are overtaken by the respective opposite process. The frequency of this recurring pattern is also likely to have increased, at least since 2005, when the summer sea ice free period in the southern central Laptev Sea was above average and the sum of positive daily average surface air temperatures in Tiksi reached new all-time maxima. This is necessarily accompanied by larger short-term fluctuations of NDTI, causing coastal cliff morphologies to change more often, resulting in more effective volumetric erosion.

Description: Of major concern in periglacial research is the question of how arctic permafrost landscapes react to climate change. Warming and thawing of ice-rich permafrost may result in substantial hydrological, geomorphological, ecological, and biogeochemical feedbacks which may have local to global impacts. While numerous studies have investigated thermokarst as one main process of permafrost degradation, data is sparse on thermal erosion, another widespread process of permafrost degradation. Siberian coastal lowlands underlain by ice-rich permafrost often feature streams, valleys, and valley networks that have formed under the influence of thermal erosion, but systematic regional studies have been lacking. We present an inventory of streams and valleys in three ice-rich lowland areas adjacent to the Laptev Sea using GIS-based analysis of remote sensing data, elevation models, and field investigations. The calculated total stream length is 4,153 km in the Cape Mamontov Klyk area, 1,541 km in the Lena River Delta area, and 2,047 km in the Buor Khaya Peninsula area; valley densities are 1.8, 0.9, and 1.0 km/km², respectively. Strong variations in the morphology and spatial distribution of streams and valleys are observed and can be attributed to differences in the size and relief characteristics of the study areas as well as to their predominant cryolithological properties, which are also influenced by previous degradation of the study areas by thermokarst. Based on the results, the evolution of different valley types in continuous ice-rich permafrost landscapes is discussed. The current valley pattern is largely the result of the late Holocene evolution of the hydrological system that is strongly connected to the degradation of ice-rich permafrost by thermal erosion.

Description: The estimation of the carbon pool stored in arctic permafrost and its biogeochemical characteristics are essential topics in today’s permafrost research. While the uppermost cryosoil horizons are well-studied and already recorded in the Northern Circumpolar Soil Carbon Database (NCSCD) there are still large uncertainties concerning the quality and distribution of deep (i.e. up to decameters) organic carbon stocks. Well-exposed permafrost sections along the arctic sea coast and river banks in northern Yakutia are excellent objects to study permafrost organic carbon characteristics in connection with cryolithogy, cryostratigraphy and past periglacial landscape dynamics. Organic carbon occurs in permafrost as large tree trunks, peat inclusions, twigs and root fragments, other solid plant remains, and finely distributed plant detritus, but also as fossil mammal remains, insects, aquatic zooplankton and -benthos, and soil microorganisms, and finally its decomposition and metabolic products in terms of particulate and dissolved organic matter. These different kinds of fossil organic matter were formed, deposited, frozen, thawed and partly degraded, and sometimes refrozen, under different paleoclimatic and paleogeographical conditions of the Quaternary past. Therefore, the deep permafrost organic carbon pool is far from homogeneous and strongly linked to depositional and permafrost dynamics as well as the ecological and climatic history. The archive of specific biogeochemical and cryolithological features of frozen ground is recorded in permafrost sequences of about the last 200.000 years in northern Yakutia. We present the variabilites of the spatial distribution of organic carbon and organic matter qualities between different stratigraphical units, between correlated stratigraphical units of several sites, and even within stratigraphic units at the same site. Especially the coverage and composition of the widely distributed late Pleistocene Yedoma horizons and its thermokarst-affected derivatives in alas depressions are of interest to climate modeling, microbiology or biochemistry. There are significant differences to former estimates of the area, thickness of the relevant frozen deposits, ground ice content and finally in organic carbon content that lead to a reassessment of the deep permafrost carbon pools of the northern high latitude Yedoma region.