Paleodynamics and organic carbon characteristics in a thermokarst affected landscape in West Alaska

Global warming will continue to warm the Arctic resulting in the degradation of permafrost soils which leads to large-scale ground subsidence. Vast regions of the Arctic are covered with ice-rich silts, known as yedoma, containing large ice wedges. The formation of thermokarst lakes is one of the most important forms of permafrost degradation. Consequently, large amounts of previously freeze-locked organic carbon (OC) can be mobilized and released, which is of global significance for the carbon cycle. The aim of this research was to reconstruct the late Quaternary depositional environment and organic carbon characteristics of a thermokarst affected landscape, to better understand the processes involved in thermokarst development and identify the vulnerability of the organic carbon. Fieldwork was conducted on Baldwin Peninsula during the summer expedition in 2016 in West Alaska. Yedoma and drained thermokarst lake basin (DTLB) exposures were sampled and a thermokarst lake core was taken. Sedimentological and biochemical parameters, as well as lipid biomarkers were analyzed. A land cover classification map was made from the peninsula using Landsat imagery and a digital terrain model. By extrapolation of the field data, an estimation of the OC quantity on the peninsula and the loss since the Late Pleistocene was made. Yedoma deposition started > 50 cal ka BP whereas the DTLB deposits and thermokarst lake sediments originate from the Holocene. The grain size distributions show that the yedoma and DTLB deposits accumulated in a dominantly aeolian, stable regime. Yedoma was deposited in a drier and colder climate than the DTLB, as indicated by the lower BIT index (mean BIT: 0.94 for yedoma and 1.00 for DTLB) and MBT index. About 53 Mt of OC is stored in the frozen deposits on Baldwin Peninsula and it is estimated that the net loss since the Late Pleistocene is 3 Mt OC. The frozen DTLB deposits contain the largest share of OC (36 Mt, 70%). However, the yedoma deposits contain the most labile OC, as has been shown by the CPI (mean: 11.6 for yedoma and 8.8 for DTLB). This OC has been freeze-locked and not or barely altered by microbial degradation. The OC is terrestrially derived for the yedoma and DTLB deposits. The thermokarst lake shows a lacustrine input (mean δ13C -28.5‰). Because of the high ice content of the deposits on the Baldwin Peninsula, the deposits are highly susceptible and vulnerable to permafrost thaw. The high quality of the stored OC in the yedoma deposits makes these carbon pools an important source for microbial alteration. This poses an important input of carbon to the carbon cycle

IPA Action Group Reports - The Yedoma Region: A Synthesis of Circum-Arctic Distribution and Thickness

The Yedoma Action Group aimed to synthesize existing information and generate new data products on the circum-arctic distribution of Yedoma permafrost. , Due to their very high excess ice content, Yedoma deposits are especially prone to degradation under projected future climate scenarios in Siberia, Alaska and the Yukon. Thawing of organic rich Yedoma releases greenhouse gases, which is contributing to climate change. Recently, we finalised the last deliverables by guest editing a special issue in the open access journal Frontier in Earth Science entitled “Yedoma Permafrost Landscapes as Past Archives, Present and Future Change Areas” (https://www.frontiersin.org/research-topics/15964/yedoma-permafrost-landscapes-as-past-archives-present-and-future-change-areas

Organic carbon characteristics in yedoma and thermokarst deposits on Baldwin Peninsula, West-Alaska

As Arctic warming continues and permafrost thaws, more soil and sedimentary organic carbon (OC) will be decomposed in northern high latitudes. Still, uncertainties remain in the quantity and quality of OC stored in different deposit types of permafrost landscapes. This study presents OC data from deep permafrost and lake deposits on the Baldwin Peninsula which is located in the southern portion of the continuous permafrost zone in West-Alaska. Sediment samples from yedoma and drained thermokarst lake basin (DTLB) deposits as well as thermokarst lake sediments were analyzed for cryostratigraphical and biogeochemical parameters and their lipid biomarker composition to identify the size and quality of belowground OC pools in ice-rich permafrost on Baldwin Peninsula. We provide the first detailed characterization of yedoma deposits on Baldwin Peninsula. We show that three quarters of soil organic carbon in the frozen deposits of the study region (total of 68 Mt) is stored in DTLB deposits (52 Mt) and one quarter in the frozen yedoma deposits (16 Mt). The lake sediments contain a relatively small OC pool (4 Mt), but have the highest volumetric OC content(93 kg m-3) compared to the DTLB (35 kg m-3) and yedoma deposits (8 kg m-3), largely due to differences in the ground ice content. The biomarker analysis indicates that the OC in both yedoma and DTLB deposits is mainly of terrestrial origin. Nevertheless, the relatively high carbon preference index of plant leaf waxes in combination with a lack of degradation trend with depth in the yedoma deposits indicates that OC stored in yedoma is less degraded than that stored in DTLB deposits. This suggests that OC in yedoma has a higher potential for decomposition upon thaw, despite the relatively small size of this pool. These findings highlight the importance of molecular OC analysis for determining the potential future greenhouse gas emissions from thawing permafrost, especially because this area close to the discontinuous permafrost boundary is projected to thaw substantially within the 21st century

Organic carbon stored in a thermokarst affected landscape on Baldwin Peninsula, Alaska

As Arctic warming continues and permafrost degrades, more organic carbon (OC) will be decomposed in high northern latitudes. Still, uncertainties remain in the quality and quantity of OC stored in permafrost. This study presents OC data from permafrost deposits on the Baldwin Peninsula, West-Alaska. We analyzed cryostratigraphical, biogeochemical and biomarker parameters of yedoma- and drained thermokarst lake basin (DTLB) deposits as well as thermokarst lake sediments to identify the size and quality of OC pools in ice-rich permafrost. Here we show that two thirds of soil OC in this region are stored in frozen DTLB deposits and that the lake sediments have the highest volumetric OC content. The n-alkane distribution shows, however, that OC stored in yedoma is of higher quality than that stored in DTLB deposits. These findings highlight the importance of molecular OC analysis for determining the potential future greenhouse gas emissions from thawing permafrost

Soil carbon and nitrogen stocks in Arctic river deltas: New data for three Northwest Alaskan deltas

Arctic river deltas are dynamic and rapidly changing permafrost environments in a warming Arctic. Our study presents new data on permafrost carbon and nitrogen stocks from 26 soil permafrost cores collected from the Noatak, Kobuk and Selawik river deltas in Western Alaska. We analyzed 318 samples for total carbon (TC) and total nitrogen (TN). Average landscape-scale carbon storage is 50.1 ± 7.8 kg C (both organic and inorganic) and 2.4 ± 0.3 kg N m-2 (0-200 cm). This totals 67 ± 11 Mt C and 3.3 ± 0.6 Mt N in the first two meters of soil in the Noatak, Kobuk and Selawik deltas combined. Our findings demonstrate that Arctic river deltas are important regions of permafrost soil carbon storage and need to be considered in panarctic permafrost carbon estimations

More than one third of the organic carbon exposed by the world’s largest thaw slump (Batagay, Siberia) is not directly available for mineralization but geochemically stabilized

Mineral-organic carbon (OC) interactions account for 30 – 80 % of the total permafrost OC pool. Quantifying the nature and controls of mineral-OC interactions is necessary to better assess permafrost-carbon-climate feedbacks. This is particularly true for ice-rich environments that are impacted by rapid thaw and the development of thermokarst landforms. Retrogressive thaw slumps are amongst the most dynamic forms of slope thermokarst and they expand through the years due to the ablation of an ice-rich headwall. These phenomena are important to consider in the permafrost carbon budget since they expose deep OC sometimes tens of thousands of years old that would not have re-entered the modern carbon cycle if these disturbances had not occurred. Here, we analyzed sediment samples collected from the headwall of the Batagay megaslump, East Siberia, locally reaching 55 m high. The series of discontinuous deposits comprises also older sediment up to ~650 ka old. We present total element concentrations, mineralogy, and mineral-OC interactions in the different stratigraphic units. The mineralogy in the deposits is very similar across the sedimentary series. Our data show that up to 34 ± 8 % of the total OC pool is stabilized by mineral-OC interactions. For most of the analyzed samples, associations to poorly crystalline iron oxides do not have a significant role in OC stabilization. Hypothesizing a retreat rate of 26000 m²/yr and constant thickness of stratigraphic units within the headwall, we provide a first order estimate of ~2 × 10^7 kg of OC is exported annually downslope of the headwall, with ~ 38 % being geochemically stabilized by complexation with metals or associations to poorly crystalline iron oxides. These data support that more than one third of the organic carbon exposed by this massive thaw slump is not directly available for mineralization, but rather stabilized geochemically

Heterogeneity of Yedoma Ice Complex deposits due to regional genesis processes

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

A Third of Organic Carbon Is Mineral Bound in Permafrost Sediments Exposed by the World's Largest Thaw Slump, Batagay, Siberia

Organic carbon (OC) in permafrost interacts with the mineral fraction of soil and sediments, representing < 1% to ~80% of the total OC pool. Quantifying the nature and controls of mineral-OC interactions is therefore crucial for realistic assessments of permafrost-carbon-climate feedbacks, especially in ice-rich regions facing rapid thaw and the development of thermo-erosion landforms. Here, we analyzed sediment samples from the Batagay megaslump in East Siberia, and we present total element concentrations , mineralogy, and mineral-OC interactions in its different stratigraphic units. Our findings indicate that up to 34 ± 8% of the OC pool interacts with mineral surfaces or elements. Interglacial deposits exhibit enhanced OC-mineral interactions, where OC has undergone greater microbial transformation and has likely low degradability. We provide a first-order estimate of ~12,000 tons of OC mobilized annually downslope of the headwall (i.e., the approximate mass of 30 large aircrafts), with a maximum of 38% interacting with OC via complexation with metals or associations to poorly crystalline iron oxides. These data imply that over one-third of the OC exposed by the slump is not readily available for mineralization, potentially leading to prolonged OC residence time in soil and sediments under stable physicochemical conditions

Organic carbon characteristics in ice-rich permafrost in alas and Yedoma deposits, central Yakutia, Siberia

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