ALBERT

Description: Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007–2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged.

Description: Permafrost ground is one of the largest repositories of terrestrial organic carbon and might become or already is a carbon source in response to ongoing global warming. With this study of syngenetically frozen, ice-rich and organic carbon (OC)-bearing Yedoma and associated alas deposits in central Yakutia (Republic of Sakha), we aimed to assess the local sediment deposition regime and its impact on permafrost carbon storage. For this purpose, we investigated the Yukechi alas area (61.76495°N, 130.46664°E), which is a thermokarst landscape degrading into Yedoma in central Yakutia. We retrieved two sediment cores (Yedoma upland, 22.35m deep, and alas basin, 19.80m deep) in 2015 and analyzed the biogeochemistry, sedimentology, radiocarbon dates and stable isotope geochemistry. The laboratory analyses of both cores revealed very low total OC (TOC) contents (〈 0.1 wt %) for a 12m section in each core, whereas the remaining sections ranged from 0.1 wt% to 2.4 wt% TOC. The core sections holding very little to no detectable OC consisted of coarser sandy material were estimated to be between 39 000 and 18 000 BP (years before present) in age. For this period, we assume the deposition of organic-poor material. Pore water stable isotope data from the Yedoma core indicated a continuously frozen state except for the surface sample, thereby ruling out Holocene reworking. In consequence, we see evidence that no strong organic matter (OM) decomposition took place in the sediments of the Yedoma core until today. The alas core from an adjacent thermokarst basin was strongly disturbed by lake development and permafrost thaw. Similar to the Yedoma core, some sections of the alas core were also OC poor (〈 0.1 wt %) in 17 out of 28 samples. The Yedoma deposition was likely influenced by fluvial regimes in nearby streams and the Lena River shifting with climate. With its coarse sediments with low OC content (OC mean of 5.27 kg m-3), the Yedoma deposits in the Yukechi area differ from other Yedoma sites in North Yakutia that were generally characterized by silty sediments with higher OC contents (OC mean of 19 kg m-3 for the non-icewedge sediment). Therefore, we conclude that sedimentary composition and deposition regimes of Yedoma may differ considerably within the Yedoma domain. The resulting heterogeneity should be taken into account for future upscaling approaches on the Yedoma carbon stock. The alas core, strongly affected by extensive thawing processes during the Holocene, indicates a possible future pathway of ground subsidence and further OC decomposition for thawing central Yakutian Yedoma deposits.

Description: Yedoma Ice Complex is a type of permafrost characterized by high ice content and carbon content of approx. 2 wt%. The high ice content makes it very vulnerable to thawing in terms of global warming. Previously stored organic material becomes available for microbial decomposition, releasing carbon into the atmosphere. But Yedoma deposits might be more heterogenous than previously thought. This is indicated by findings from the Yukechi Alas landscape in Central Yakutia where Yedoma deposits with a lack of carbon for several meters are found. Analysis reveals shifts in regional sedimentary processes as a plausible solution to the found heterogenity, making it important to further investigate the composition of Yedoma Ice Complex deposits throughout the arctic. Such heterogenity may change the proposed amount of carbon stored in those deposits but may as well have effects on thaw behaviour and vulnerability to climate warming. Therefore, more information is needed on the scope of such regional influences in order to increase knowledge about the effects of thawing Yedoma on climate change.

Description: Permafrost thaw leads to thermokarst lake formation and talik growth tens of meters deep, enabling microbial decomposition of formerly frozen organic matter (OM). We analyzed two 17-m-long thermokarst lake sediment cores taken in Central Yakutia, Russia. One core was from an Alas lake in a Holocene thermokarst basin that underwent multiple lake generations, and the second core from a young Yedoma upland lake (formed ca. 70 years ago) whose sediments have thawed for the first time since deposition. This comparison provides a glance into OM fate in thawing Yedoma deposits. We analyzed total organic carbon (TOC) and dissolved organic carbon (DOC) content, n-alkanes concentrations, and bacterial and archaeal membrane markers. Furthermore, we conducted one-year-long incubations (4 °C, dark) and measured anaerobic carbon dioxide (CO2) and methane (CH4) production. The sediments from both cores contained little TOC (0.7±0.4 wt%), but DOC values were relatively high, with highest values in the frozen Yedoma lake sediments (1620 mg L-1). Cumulative GHG production after one year was highest in the Yedoma lake sediments (226±212 μg CO2-C gdw-1, 28±36 μg CH4-C gdw-1) and 3 and 1.5 times lower in the Alas lake sediments, respectively (75±76 μg CO2-C gdw-1, 19±29 μg CH4-C gdw-1). The highest CO2 production in the frozen Yedoma lake sediments likely results from decomposition of readily bioavailable OM, while highest CH4 production in the non-frozen top sediments of this core suggests that methanogenic communities established upon thaw. The lower GHG production in the non-frozen Alas lake sediments resulted from advanced OM decomposition during Holocene talik development. Furthermore, we found that drivers of CO2 and CH4 production differ following thaw. Our results suggest that GHG production from TOC-poor mineral deposits, which are widespread throughout the Arctic, can be substantial. Therefore, our novel data are relevant for vast ice-rich permafrost deposits vulnerable to thermokarst formation.

Description: The dataset presents the radiocarbon ages (with standard deviation ±) from thermokarst lake sediment cores from the Yukechi Alas, Siberia. The sediment cores were taken from an alas lake (YUK15-YU-L7) and a yedoma lake (YUK15-YU-L15). Raw, calibrated and rounded calibrated ages are presented. Measurements were carried out in the AWI MICADAS Laboratory in Bremerhaven. Calibrations were performed according to Stuiver et al. (2017) using CALIB 7.1 software and the IntCal13 calibration curve.

Description: These data are laboratory results for carbon characteristics (TOC, TC, TN, C/N ratio, stable carbon isotope ratio, radiocarbon ages from bulk organic material), sediment characteristics (mass specific magnetic susceptibility (4.65 kHz & 0.465 kHz), grain size measurements 〈 1 mm) and ice characteristics (sample mass (wet), sample mass (dry), absolute ice content, stable oxygen and hydrogen isotope ratios of pore ice, pH and conductivity of pore ice). Two cores were analyzed: Yedoma core YED1 N 61.75967° / E 130.47438°; h = 218 m asl total length: 22,35 m (recovery 21,13 m) ice wedge included from ~7,14 to ~9,5 m Alas core Alas1 drilled in the drained part of a thermokarst lake basin N 61.76490° / E 130.46503° total length: 19,80 m (recovery 11,14 m) unfrozen conditions from ~1,6 to ~7,5 m Both cores were drilled in March 2015 from dry land surface in a joint expedition of the ERC PETA-Carb poject and the DFG project UL426/1-1 "Short and long-term thermokarst dynamics due to climate changes and human impacts in Central Yakutia, Siberia (2013-2016)". The sample names are compiled as [campaign]-[core] [drive] [depth (top)] - [depth (bottom)]. Age calibration was done with Calib7.10. Grain size percentages were calculated using GRADISTAT (Blott and Pye, 2001). Missing carbon isotope and C/N ratio values are a result of carbon and/or nitrogen contents below detection limit (0.1 wt%). Missing ice characteristics values are a result of dry and/or fine material obstructing the pore ice/water extraction.

Description: This file presents the detailed description of two deep permafrost cores from the Yukechi Alas landscape in Central Yakutia, Russia. These data were recorded during subsampling of the cores and are based on visual and haptic impression. The core "YED1" is a Yedoma permafrost core. Core was obtained during field work in March 2015.