Alfred Wegener Institute for Polar and Marine Research
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Enhanced response of soil respiration to experimental warming upon thermokarst formation
Get PDFAs global temperatures continue to rise, a key uncertainty of terrestrial carbon (C)–climate feedback is the rate of C loss upon abrupt permafrost thaw. This type of thawing—termed thermokarst—may in turn accelerate or dampen the response of microbial degradation of soil organic matter and carbon dioxide (CO2) release to climate warming. However, such impacts have not yet been explored in experimental studies. Here, by experimentally warming three thermo-erosion gullies in an upland thermokarst site combined with incubating soils from five additional thermokarst-impacted sites on the Tibetan Plateau, we investigate how warming responses of soil CO2 release would change upon upland thermokarst formation. Our results show that warming-induced increase in soil CO2 release is ~5.5 times higher in thermokarst features than the adjacent non-thermokarst landforms. This larger warming response is associated with the lower substrate quality and higher abundance of microbial functional genes for recalcitrant C degradation in thermokarst-affected soils. Taken together, our study provides experimental evidence that warming-associated soil CO2 loss becomes stronger upon abrupt permafrost thaw, which could exacerbate the positive soil C–climate feedback in permafrost-affected regions
Socioecological dynamics of diverse global permafrost-agroecosystems under environmental change
Get PDFPermafrost-agroecosystems include all cultivation and pastoral activities in areas underlain by
permafrost. These systems support local livelihoods and food production and are rarely considered
in global agricultural studies but may become more relevant as climate change is increasing
opportunities for food production in high latitude and mountainous areas. The exact locations
and amount of agricultural production in areas containing permafrost are currently unknown,
therefore we provide an overview of countries where both permafrost and agricultural activities
are present. We highlight the socioecological diversity and complexities of permafrostagroecosystems
through seven case studies: (1) crop cultivation in Alaska, USA; (2) Indigenous
food systems and crop cultivation in the Northwest Territories, Canada; (3) horse and cattle
husbandry and Indigenous hay production in the Sakha Republic, Russia; (4) mobile pastoralism
and husbandry in Mongolia; (5) yak pastoralism in the Central Himalaya, Nepal; (6) berry picking and
reindeer herding in northern Fennoscandia; and (7) reindeer herding in northwest Russia. We
discuss regional knowledge gaps associated with permafrost and make recommendations to policy
makers and land users for adapting to changing permafrost environments. A better understanding
of permafrost-agroecosystems is needed to help sustainably manage and develop these systems
considering rapidly changing climate, environments, economies, and industries
Predicting September Arctic Sea Ice: A Multi-Model Seasonal Skill Comparison
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This study quantifies the state-of-the-art in the rapidly growing field of seasonal Arctic sea ice prediction. A novel multi-model dataset of retrospective seasonal predictions of September Arctic sea ice is created and analyzed, consisting of community contributions from 17 statistical models and 17 dynamical models. Prediction skill is compared over the period 2001–2020 for predictions of Pan-Arctic sea ice extent (SIE), regional SIE, and local sea ice concentration (SIC) initialized on June 1, July 1, August 1, and September 1. This diverse set of statistical and dynamical models can individually predict linearly detrended Pan-Arctic SIE anomalies with skill, and a multi-model median prediction has correlation coefficients of 0.79, 0.86, 0.92, and 0.99 at these respective initialization times. Regional SIE predictions have similar skill to Pan-Arctic predictions in the Alaskan and Siberian regions, whereas regional skill is lower in the Canadian, Atlantic, and Central Arctic sectors. The skill of dynamical and statistical models is generally comparable for Pan-Arctic SIE, whereas dynamical models outperform their statistical counterparts for regional and local predictions. The prediction systems are found to provide the most value added relative to basic reference forecasts in the extreme SIE years of 1996, 2007, and 2012. SIE prediction errors do not show clear trends over time, suggesting that there has been minimal change in inherent sea ice predictability over the satellite era. Overall, this study demonstrates that there are bright prospects for skillful operational predictions of September sea ice at least three months in advance.</jats:p
Impact of increased resolution on Arctic Ocean simulations in Ocean Model Intercomparison Project phase 2 (OMIP-2)
Get PDFAbstract. This study evaluates the impact of increasing resolution on Arctic Ocean simulations using five pairs of matched low- and high-resolution models within the OMIP-2 (Ocean Model Intercomparison Project phase 2) framework. The primary objective is to assess whether a higher resolution can mitigate typical biases in low-resolution models and improve the representation of key climate-relevant variables. We reveal that increasing the horizontal resolution contributes to a reduction in biases in mean temperature and salinity and improves the simulation of the Atlantic water layer and its decadal warming events. A higher resolution also leads to better agreement with observed surface mixed-layer depth, cold halocline base depth and Arctic gateway transports in the Fram and Davis straits. However, the simulation of the mean state and temporal changes in Arctic freshwater content does not show improvement with increased resolution. Not all models achieve improvements for all analyzed ocean variables when spatial resolution is increased so it is crucial to recognize that model numerics and parameterizations also play an important role in faithful simulations. Overall, a higher resolution shows promise in improving the simulation of key Arctic Ocean features and processes, but efforts in model development are required to achieve more accurate representations across all climate-relevant variables.
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Selective Sorting and Degradation of Permafrost Organic Matter in the Nearshore Zone of Herschel Island (Yukon, Canada)
Get PDFAbstractErosion of permafrost coasts due to climate warming releases large quantities of organic carbon (OC) into the Arctic Ocean. While burial of permafrost OC in marine sediments potentially limits degradation, resuspension of sediments in the nearshore zone potentially enhances degradation and greenhouse gas production, adding to the “permafrost carbon feedback.” Recent studies, focusing on bulk sediments, suggest that permafrost OC derived from coastal erosion is predominantly deposited close to shore. However, bulk approaches disregard sorting processes in the coastal zone, which strongly influence the OC distribution and fate. We studied soils and sediments along a transect from the fast‐eroding shoreline of Herschel Island—Qikiqtaruk (Yukon, Canada) to a depositional basin offshore. Sample material was fractionated by density (1.8 g cm−3) and size (63 μm), separating loose OC from mineral‐associated OC. Each fraction was analyzed for element content (TOC, TN), carbon isotopes (δ13C, Δ14C), molecular biomarkers (n‐alkanes, n‐alkanoic acids, lignin phenols, cutin acids), and mineral surface area. The OC partitioning between fractions changes considerably along the transect, highlighting the importance of hydrodynamic sorting in the nearshore zone. Additionally, OC and biomarker loadings decrease along the land‐ocean transect, indicating significant loss of OC during transport. However, molecular proxies for degradation show contrasting trends, suggesting that OC losses are not always well reflected in its degradation state. This study, using fraction partitioning that crosses land‐ocean boundaries in a way not done before, aids to disentangle sorting processes from degradation patterns, and provides quantitative insight into losses of thawed and eroded permafrost OC.</jats:p
News from the Klondike Goldfields (Canada) - first results of the AWI expedition Klondike 2023
Get PDFOver the last 25 years, Canadian scientists have studied the permafrost environmental archives in the Klondike Goldfields south of Dawson City. In 2023, a small Canadian-German team visiting this area to sample mining exposures in the Klondike area. The goal was to conduct studies on ground ice (ice wedges and pore ice) and frozen sediments to reconstruct past landscape and climate conditions. Detailed profiles were sampled at three sites at Little Blanche Creek, Whitman Gulch and Bear Creek. Ice wedges were described in terms of their size, the color of ice, internal structure, existence and form of gas bubbles and were sampled by chain saw as blocks. The frozen sediment was cleaned, and ice, sediment and cryostructures were described, followed by sediment sampling with an axe and hammer. Separately, sediment cores were collected with a battery driven drill for biomarker studies. In our presentation, we present the first results of new field and laboratory studies. This concerns age determinations, sediment data, stable isotopes and hydrochemistry of the ground ice. We expect new knowledge regarding the reconstruction of Late Quaternary environment of Central Yukon
NITROGEN SLIGHTLY REDUCES GHG PRODUCTION FROM INCUBATED PEAT SAMPLES
Get PDFPeatland soils are projected to respond to rising global temperatures with an increase in microbial respiration rates. At the same time, nutrients that were previously bound in undecomposed organic matter will increasingly become available to the decomposer microbial communities. The pathway and magnitude of response in respiration rates to a changing nutrient status remains an open question, especially given that these ecosystems are typically limited in nutrients like nitrogen.
In my ongoing Master thesis, I investigate the effects of adding nitrate and ammonium to incubated peat samples from Siikaneva bog in boreal Finland. While the site itself is not affected by permafrost, this study provides an analogue for the future of peatlands at the edge of the permafrost zone. Preliminary results from 190 days of incubation indicate that carbon dioxide production was reduced by ammonia additions. Data on methane production were less conclusive, but also point to an average reduction of total C respiration. Samples from above and below the water table exhibit different trajectories, which may be an expression of different microbial communities: most prominently, a complete lack of methanogenenis in the surface samples.
In summary, this implies that the peatland carbon sink is not endangered by nutrient release
Erratum for Brüwer et al., “In situ cell division and mortality rates of SAR11, SAR86, Bacteroidetes, and Aurantivirga during phytoplankton blooms reveal differences in population controls”
Get PDFDrivers of heterogeneity in tundra vegetation productivity on the Yamal Peninsula, Siberia, Russia
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The direction and magnitude of tundra vegetation productivity trends inferred from the normalized difference vegetation index (NDVI) have exhibited spatiotemporal heterogeneity over recent decades. This study examined the spatial and temporal drivers of Moderate Resolution Imaging Spectroradiometer Max NDVI (a proxy for peak growing season aboveground biomass) and time-integrated (TI)-NDVI (a proxy for total growing season productivity) on the Yamal Peninsula, Siberia, Russia between 2001 and 2018. A suite of remotely-sensed environmental drivers and machine learning methods were employed to analyze this region with varying climatological conditions, landscapes, and vegetation communities to provide insight into the heterogeneity observed across the Arctic. Summer warmth index, the timing of snowmelt, and physiognomic vegetation unit best explained the spatial distribution of Max and TI-NDVI on the Yamal Peninsula, with the highest mean Max and TI-NDVI occurring where summer temperatures were higher, snowmelt occurred earlier, and erect shrub and wetland vegetation communities were dominant. Max and TI-NDVI temporal trends were positive across the majority of the Peninsula (57.4% [5.0% significant] and 97.6% [13.9% significant], respectively) between 2001 and 2018. Max and TI-NDVI trends had variable relationships with environmental drivers and were primarily influenced by coastal-inland gradients in summer warmth and soil moisture. Both Max and TI-NDVI were negatively impacted by human modification, highlighting how human disturbances are becoming an increasingly important driver of Arctic vegetation dynamics. These findings provide insight into the potential future of Arctic regions experiencing warming, moisture regime shifts, and human modification, and demonstrate the usefulness of considering multiple NDVI metrics to disentangle the effects of individual drivers across heterogeneous landscapes. Further, the spatial heterogeneity in the direction and magnitude of interannual covariation between Max NDVI, TI-NDVI, and climatic drivers highlights the difficulty in generalizing the effects of individual drivers on Arctic vegetation productivity across large regions.</jats:p
PANABIO: a point-referenced PAN-Arctic data collection of benthic BIOtas
Get PDFProfound environmental changes, such as drastic sea-ice decline, leave large-scale ecological footprints on the distribution and composition of marine biota in the Arctic. Currently, the impact of such stressors is not sufficiently understood due to the lack of pan-Arctic data that allow for estimating ecological baselines as well as modelling current and forecast potential changes in benthic biodiversity and ecosystem functioning. Here, we introduce the PAN-Arctic data collection of benthic BIOtas (PANABIO) and discuss its timeliness, potential, and details of its further development. The data collection contains individual datasets with records (presence, counts, abundance, or biomass) of benthic fauna, usually at genus level or species level, which were identified in field samples obtained at point-referenced locations (stations) by means of grabs, towed gear, or seabed imaging. The data cover the entire pan-Arctic realm, i.e.The central Arctic Ocean, Chukchi Sea, East Siberian Sea, Laptev Sea, Kara Sea, Barents Sea (including the White Sea), Svalbard waters, Greenland Sea, Norwegian Sea, Canadian Archipelago, Beaufort Sea, and Bering Sea as well as some adjacent sub-Arctic regions (Sea of Japan, Gulf of Okhotsk). Currently (as of 14 December 2023), PANABIO includes 27 datasets with a total of 126ĝ€¯388 records of 2978 taxa collected from 11ĝ€¯555 samples taken at 10ĝ€¯596 stations during 1095 cruises between 1800 and 2014. These numbers will increase with more data becoming available over time through contributions from PANABIO users. The data collection is available in a PostgreSQL-based data warehouse that can be accessed and queried through an open-Access front-end web service at https://critterbase.awi.de/panabio (last access: 27 February 2024). A snapshot of the current data collection and its 27 individual datasets is also available from the data publisher PANGAEA (10.1594/PANGAEA.963640, Piepenburg et al., 2023)