Alfred Wegener Institute for Polar and Marine Research
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DARTS: Multi-year database of AI-detected retrogressive thaw slumps in the circum-arctic permafrost region
Get PDFRetrogressive Thaw Slumps (RTS) are widespread mass-wasting hillslope failures triggered by thawing permafrost. While regional studies have provided insights into the spatial distribution and dynamics of RTS, a consistent and unbiased quantification and monitoring remains unsolved at pan-arctic scales. We present the Database of AI-detected Arctic RTS footprints (DARTS), comprising ~43,000 individual footprints of active RTS or active areas within larger RTS landforms. DARTS spans ~1.6 million km2 from 2018–2023, with at least annual coverage from 2021–2023 across a ~900,000 km2 region. The database is freely available in two processing levels: sub-annual and annually aggregated polygon footprints including spatial and tabular metadata. DARTS uses a highly automated workflow based on deep learning segmentation of PlanetScope multi-spectral satellite imagery (3–5 m resolution) and elevation data. Validation against different regional RTS datasets yielded F1 scores ranging from 0.263 to 0.700, with higher accuracy in areas of intense RTS activity. DARTS provides a valuable resource for systematically mapping, quantifying, and analyzing active hillslope thermokarst distribution and changes over time across the circum-arctic permafrost region
Life cycle of the seabird digenean Gymnophallus minor (Gymnophallidae) in the Arctic
Get PDFGymnophallidae is one of the digenean families featuring bivalves as first intermediate hosts. However, the exact bivalve host species remain unknown for most members of this family. Gymnophallids have been one of the targets in our continuous efforts to reveal the diversity of digeneans in the higher north. Here, we focus on Gymnophallus minor, which we found in eiders from various locations in the Arctic and sub-Arctic. Sexual adults (maritae) of G. minor can be easily identified because they have a distinctive character: the roughly equal size of the pharynx and the ventral sucker. We also matched them, using DNA markers, with the intramolluscan stages (sporocysts, cercariae, and metacercariae) from the bivalve Liocyma fluctuosa collected on Spitsbergen. Taken together, we compile the first data on the life cycle of G. minor and discuss them in the context of other gymnophallids
Assessment of continuous flow analysis (CFA) for high-precision profiles of water isotopes in snow cores
Get PDFIn order to derive climatic information from stable water isotopes of the very recent past, the signal-to-noise ratio in climate reconstructions from ice cores has to be improved. To this end, understanding of the formation and preservation of the climate signal in stable water isotopes at the surface is required, which in turn requires a substantial number of snow surface profiles. However, due to its high porosity and poor stability surface, snow has been rarely measured; i.e., climate records from firn and ice cores often start at several meter depths, and the few discrete samplings of surface snow required large effort. Here we present a new setup to efficiently measure stable water isotopes in snow profiles utilizing a continuous flow analysis (CFA) system enabling measuring multiple snow cores in a reasonable time and with high quality. The CFA setup is described, and a systematic assessment of the mixing of the isotope signal due to the setup is conducted. We systematically determine the mixing length at different parts of the system. We measure and analyze six snow cores from Kohnen station, Antarctica, and find the largest contribution to mixing to originate in the percolation of meltwater on top of the melt head. In comparison to discrete measurements, we show that our CFA system is able to reasonably analyze highly porous snow cores for stable water isotopes. Still, for future developments we recommend improving the melt head with respect to the strong percolation
Characteristics and Seasonality of Particulate and Dissolved Organic Matter Discharged by the Lena River to the Arctic Coast
Get PDFPermafrost is considered to be a resting titan, exceptionally vulnerable to the impact of ongoing climate change. Warming temperatures intensify permafrost thawing, leading to the release of previously stored and frozen organic matter (OM) back into the active biogeochemical cycle. Once released from permafrost, OM eventually appears in lakes, streams and rivers, which carry their waters into larger water bodies. In this study, I aimed to investigate particulate and dissolved organic carbon (POC and DOC) discharged by the one of largest Arctic rivers—the Lena River—into the Arctic Ocean. While writing this work, I was deeply curious and focused on the major question: what is the composition and fate of organic matter that the Lena River transports across the continent, through its delta, to the Arctic coast?
This thesis was written to resolve this research curiosity as a part of the German–British scientific research project “Changing Arctic Carbon cycle in the COastal Ocean Near-shore (CACOON)”. The main body of this thesis comprises three manuscripts, each focusing on specific research themes.
The first manuscript, a scientific publication titled “Particulate organic matter in the Lena River and its delta: from the permafrost catchment to the Arctic Ocean,” was published in the journal Biogeosciences (DOI: https://doi.org/10.5194/bg-20-1423-2023). Here, the dynamics of POC were studied in the Lena River delta and compared with those in the river’s main stem using C isotopic composition to define the sources of organic matter. This study reveals that total suspended matter and POC concentrations decreased by 70 % during transit from the main stem to the delta and Arctic Ocean. Dual-carbon (D14C and d13C) isotope mixing model analyses revealed a dominant phytoplankton contribution to deltaic POC and also demonstrated an additional input of permafrost-derived OM. These results highlight the importance of deltaic and estuarine processes in shaping OM dynamics in Arctic nearshore zones.
The second manuscript “Dissolved and Particulate Organic Carbon Characteristics in Summer and Winter Waters of the Lena Delta” was submitted to Permafrost and Periglacial Processes journal. It aimed to identify sources and seasonality of organic C at the Lena delta. C isotopes (∆14C and d13C) were measured in DOC and POC along a 140 km transect of the Lena delta. The study showed that DOC concentrations in the Lena delta were unexpectedly higher in winter than in summer. Isotopic analyses revealed that winter DOC showed a greater contribution of older C compared to summer DOC. These findings provide valuable insights into carbon dynamics in the largest Arctic delta, contributing to the understanding of how climate warming affects the critical interface between land and ocean.
Finally, the third manuscript “Exploring the mysteries of GDGTs in the Arctic: Insights from the Lena Delta and Laptev Sea Nearshore” is a draft focused on glycerol dialkyl glycerol tetraethers (GDGTs) —biomarkers used as proxies for environmental conditions. Isoprenoidal (isoGDGT), hydroxylated (OH-GDGT), branched (brGDGT), and H-shaped brGDGTs (H-brGDGTs) were extracted from POC to analyse their distribution in the Lena delta in winter and summer and along a transect to the Laptev Sea (only in summer). The result showed that IsoGDGT and OH-GDGT reflected marine influence - salinity and water temperatures. BrGDGTs, largely soil-derived, were more concentrated in winter, indicating higher terrestrial input, whereas summer levels reflected dilution by vegetation and aquatic microorganisms. H-brGDGTs, associated with peat, showed enhanced deposition near the coast, likely due to flocculation in saline waters. Additionally, this study highlighted the unique geochemical signature of Arctic river systems such as brGDGT signature with the dominance of 6-methyl isomers (IIIa’, IIa’) and the predominance of 5-methyl isomers (IIIa, IIa). These findings reveal how temperature, salinity, and organic matter sources shape the distribution of GDGTs in Arctic riverine and coastal systems.
Supporting the findings of my research, I added three published and co-authored manuscripts to the appendix of this thesis. First, the paper “Organic matter characteristics of a rapidly eroding permafrost cliff in NE Siberia” by Haugk et al. (2022) demonstrates how permafrost thaw and coastal erosion mobilize significant quantities of organic carbon and nitrogen, driving changes in the biogeochemistry of Arctic nearshore waters. Second, “Degrading permafrost river catchments and their impact on the Arctic Ocean nearshore processes” by Mann et al. (2022) explores the transformations and ecological impacts of permafrost-derived organic matter as it is transported from land to the ocean, highlighting its role in shaping nearshore ecosystem dynamics. Third, “Seasonal nitrogen fluxes of the Lena River Delta” by Sanders et al. (2022) expands on these insights by examining the broader implications of these processes for Arctic carbon fluxes and nutrient cycling, emphasizing the importance of nearshore zones as hotspots of change under ongoing climate warming.
Overall, this thesis provides comprehensive and multifaceted research on dissolved and particulate organic carbon in the Lena delta, including their origin, transformation during transport from the source to the Arctic nearshore zone, and seasonal changes
Mean ocean temperature change and decomposition of the benthic δ18O record over the past 4.5 million years
Get PDFWe use a recent reconstruction of global mean sea surface temperature change relative to preindustrial (ΔGMSST) over the last 4.5 Myr together with independent proxy-based reconstructions of bottom water (ΔBWT) or deep-ocean (ΔDOT) temperatures to infer changes in mean ocean temperature (ΔMOT). Three independent lines of evidence show that the ratio of ΔMOT / ΔGMSST, which is a measure of ocean heat storage efficiency (HSE), increased from ∼ 0.5 to ∼ 1 during the Middle Pleistocene Transition (MPT, 1.5–0.9 Ma), indicating an increase in ocean heat uptake (OHU) at this time. The first line of evidence comes from global climate models; the second from proxy-based reconstructions of ΔBWT, ΔMOT, and ΔGMSST; and the third from decomposing a global mean benthic δ18O stack (δ18Ob) into its temperature (δ18OT) and seawater (δ18Osw) components. Regarding the latter, we also find that further corrections in benthic δ18O, probably due to some combination of a long-term diagenetic overprint and to the carbonate ion effect, are necessary to explain reconstructed Pliocene sea-level highstands inferred from δ18Osw. We develop a simple conceptual model that invokes an increase in OHU and HSE during the MPT in response to changes in deep-ocean circulation driven largely by surface forcing of the Southern Ocean. Our model accounts for heat uptake and temperature in the non-polar upper ocean (0–2000 m) that is mainly due to wind-driven ventilation, while changes in the deeper ocean (> 2000 m) in both polar and non-polar waters occur due to high-latitude deepwater formation. We propose that deepwater formation was substantially reduced prior to the MPT, effectively decreasing HSE. We attribute these changes in deepwater formation across the MPT to long-term cooling which caused a change starting ∼ 1.5 Ma from a highly stratified Southern Ocean due to warm SSTs and reduced sea-ice extent to a Southern Ocean which, due to colder SSTs and increased sea-ice extent, had a greater vertical exchange of water masses
Guiding Light: Mechanisms and Adjustments of Environmental Light Interpretation with Insights from Platynereis dumerilii and Other Selected Examples
Get PDFAnimals possess many light-sensitive molecules. They exist as dedicated photoreceptors, or as byproducts of biochemical reactions. Their numbers are often high even in species that live in environments that humans would consider dark, as well as in species that are considered comparably simple (e.g., worms, cnidarians). But why are there so many photoreceptors? We provide some considerations on this question. Light conveys a significant amount of information to animals, through complex spectral and intensity changes, often specific to the spatial and temporal ecological niches a species inhabits. We discuss that the large number of opsins and cryptochromes, often also present outside the eyes and partially co-expressed, represent adaptation mechanisms to the highly complex light environment within a given niche. While theoretical, it is a plausible hypothesis given that most experimentally tested opsins and cryptochromes have been shown to be functional photoreceptors. The example of lunar and solar timing of the marine annelid Platynereis dumerilii provides insight on how animals use the biochemical and cellular properties of different photoreceptors to decode solar versus lunar light, and their different adaptations in Drosophila melanogaster. We suggest that the future understanding of biological processes will strongly benefit from comparative lab and field work on the same species, and provide a first example for such work in P. dumerilii. Finally, we point out that work on animal light detection systems and their adaptability is crucial to understand the impact of anthropogenic changes on species and ecosystems
The excess of qualitative interviews and the feminist anticolonial reimaginings of research methods
No full textMelt pond CO2 dynamics and fluxes with the atmosphere in the central Arctic Ocean during the summer-to-autumn transition
Get PDFMelt ponds are a common feature of the Arctic sea-ice environment during summer, and they play an important role in the exchange of heat and water vapor between the ocean and the atmosphere. We report the results of a time-series study of the CO2 dynamics within melt ponds (and nearby lead) and related fluxes with the atmosphere during the summer-to-autumn transition in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. In late summer 2020, low-salinity meltwater was distributed throughout the melt ponds, and undersaturation of pCO2 in the meltwater drove a net influx of CO2 from the atmosphere.The meltwater layer subsequently thinned due to seawater influx, and a strong gradient in salinity and low-pCO2 water was observed at the interface between meltwater and seawater at the beginning of September. Mixing between meltwater and underlying seawater drives a significant drawdown of pCO2 as a result of the non-linearities in carbonate chemistry. By the middle of September, the strong stratification within the meltwater had dissipated. Subsequent freezing then began, and cooling and wind-induced drifting of ice floes caused mixing and an influx of seawater through the bottom of the melt pond. The pCO2 in the melt pond reached 300 matm as a result of exchanging melt pond water with the underlying seawater. However, gas exchange was impeded by the formation of impermeable freshwater ice on the surface of the melt pond, and the net flux of CO2 was nearly zero into the pond, which was no longer a sink for atmospheric CO2. Overall, the melt ponds in this Arctic sea-ice area (both melt ponds and lead water) act as moderate sinks for atmospheric CO
Carbon Cycle of Arctic Lagoons - Greenhouse Gas Production During the Transition from Terrestrial to Marine Permafrost
Get PDFPermafrost, defined as ground that has been frozen for more than two consecutive years,
underlies 15% of the land area of the Northern Hemisphere, storing vast amounts of organic
carbon accumulated over millennia. Over 30% of global coastlines are shaped by
permafrost, which is particularly sensitive to climate change. The rapid reduction in sea ice,
rising air and sea temperatures, and more intense storm activity amplify erosion along these
ice-rich coasts, leading to land loss of up to 25 meters per year at the Beaufort Sea. Coastal
erosion taps lakes and drained lake basins formed during permafrost thaw, transforming
them into so-called thermokarst lagoons. These lagoons serve as transition zones between
terrestrial and subsea permafrost. Entering seawater accelerates thawing, making
previously frozen or lacustrine organic carbon available for microorganisms to decompose
into greenhouse gases (GHGs) such as carbon dioxide and methane, which contributes to
further climate warming. So far, only a few studies have focused on the geology and
evolution of these Arctic lagoons, and little is known about the role of thermokarst lagoons
in the permafrost carbon cycle. To address this research gap, the key research questions of
this thesis are:
• What is the spatial pan-Arctic extent of thermokarst lagoons, how are they
distributed and how can they be classified according to their development stages?
• What is the effect of increasing seawater influence on GHG production and microbial
community composition?
• Does GHG production of inundated Arctic coastal lowlands differ between
landscape features and regions?
To answer these research questions, a combination of remote sensing and laboratory
analyses was conducted. High-resolution satellite imagery and geographic information
system tools were used for mapping and classifying thermokarst lagoons, providing a pan-
Arctic context. The effect of seawater inundation on GHG production in thawed permafrost
sediments was studied through four long-term anaerobic incubation experiments (at 4°C
for up to 415 days) using permafrost, active layer, thermokarst lake, and lagoon sediment
from three distinct Arctic coastal regions under various saline conditions to simulate
increasing seawater influence. Microbial analyses were conducted before and after two of
the experiments to understand how microorganisms respond to changing seawater
influence.
Along the Arctic coast between the Taimyr Peninsula (Siberia) and the Tuktoyaktuk
Peninsula (Canada), 520 lagoons originating from former lakes and lake basins were
identified and mapped with remote sensing and cover an area of 3,457 km², which is only a fraction of the area occupied by thermokarst lakes. Based on their connectivity to the sea,
the lagoons were categorized into five classes, with the majority (55%) in early transition
stages (very low and low connected).
Incubation studies consistently revealed that under the prevailing brackish conditions,
methane production is highest in these low-connected lagoons and decreases during the
ongoing transition into a marine environment. Due to the higher global warming potential
of methane, the climate impact of these low-connected lagoons is up to 18 times greater than
that of open lagoons, where CO₂ is the dominant GHG produced. The microbial diversity
is found to be higher in lagoon sediments than in terrestrial sediments, underlining the
uniqueness of these transitional systems. However, the shift from terrestrial to marine
conditions involves changes in oxygen availability and salinity, both of which disrupt the
initial terrestrial microbial community, leading to a decrease in GHG production in the short
term. Over time, as salt-tolerant, anaerobic microbial communities establish, CO₂
production increases, reaching levels as high as eight times those found in terrestrial
permafrost.
Combining data from all incubation experiments revealed that GHG production varies
significantly during the transition from newly thawed terrestrial permafrost to established
lagoons. GHG production is highest in lagoon sediments compared to the terrestrial
landscape features (permafrost, active layer, lake). Although regional variations in GHG
production exist, they are less pronounced than the variations between different landscape
features. The combination of incubation and mapping results enabled the first rough
estimate of potential carbon release from all mapped pan-Arctic lagoons, showing that, on
average, 3 Tg CO₂eq could be released per year from all mapped thermokarst lagoons by
2100.
In conclusion, these results show that, while the total thermokarst lagoon area is
relatively small (3,457 km²), thermokarst lagoons release more than four times the CO₂-
equivalent per unit area compared to thermokarst lakes, and even more than gradually
thawing permafrost. This indicates that thermokarst lagoons are hotspots of carbon cycling
and may play a more significant role in the carbon budget of rapidly thawing Arctic
landscapes than previously anticipated. This role may become even more critical, as current
climate scenarios suggest accelerating permafrost coastal erosion and rising sea levels. The
incubation experiments were useful for understanding the impact of changing salinities on
microbial dynamics and GHG production in seawater-inundated terrestrial and lagoon
sediments, but it is not possible to reproduce all processes occurring in natural
environments. To confirm and verify the presented incubation results, in situ measurements
of GHG fluxes during the land-sea transition are needed