Collapsing permafrost coasts in the Arctic

Arctic warming is exposing permafrost coastlines, which account for 34% of the Earth’s coasts, to rapid thaw and erosion. Coastal erosion rates as high as 25 m yr-1 together with the large amount of organic matter frozen in permafrost are resulting in an annual release of 14.0 Tg (10^12 gram) particulate organic carbon into the nearshore zone. The nearshore zone is the primary recipient of higher fluxes of carbon and nutrients from thawing permafrost. We highlight the crucial role the nearshore zone plays in Arctic biogeochemical cycling, as here the fate of the released material is determined to: (1) degrade into greenhouse gases, (2) fuel marine primary production, (3) be buried in nearshore sediments or (4) be transported offshore. With Arctic warming, coastal erosion fluxes have the potential to increase by an order of magnitude until 2100. Such increases would result in drastic impacts on global carbon fluxes and their climate feedbacks, on nearshore food webs and on local communities, whose survival still relies on marine biological resources. Quantifying the potential impacts of increasing erosion on coastal ecosystems is crucial for food security of northern residents living in Arctic coastal communities. We need to know how the traditional hunting and fishing grounds might be impacted by high loads of sediment and nutrients released from eroding coasts, and to what extent coastal retreat will lead to a loss of natural habitat. Quantifying fluxes of organic carbon and nutrients is required, both in nearshore deposits and in the water column by sediment coring and systematic oceanographic monitoring. Ultimately, this will allow us to assess the transport and degradation pathways of sediment and organic matter derived from erosion. We need to follow the complete pathway, which is multi-directional including atmospheric release, lateral transport, transitional retention in the food web, and ultimate burial in seafloor sediments. We present numbers of multi-year dissolved organic matter (DOM) fluxes from coastal erosion into the nearshore zone of the southern Canadian Beaufort Sea. We further explore removal and degradation patterns of DOM based on oceanographic monitoring of coastal waters. Ultimately, we present accumulation rates and biogeochemical properties of marine sediment sequences drilled off the Yukon coast to track the pathways of the eroded material

Contribution of Retrogressive Thaw Slumps to the Near Shore Carbon Budget along the Yukon Coast, Canada

The mechanism of carbon dioxide and methane release to the atmosphere in permafrost regions is not solely restricted to the progressive thawing of the upper part of the ground by warmer air temperatures. Organic carbon and nutrients are released to streams, rivers or coasts by abrupt processes such as thermokarst, thermal erosion and simply river bank or coastal erosion. Thermo-erosion, as a mechanism of rapid permafrost thaw, reshapes Arctic coasts and has a clear impact on the mobilization and distribution of carbon and nitrogen in permafrost terrains. Retrogressive thaw slumps are one specific and highly dynamic landform, which results from thermo-erosion of ice-rich permafrost and leads to the displacement of large volumes of sediments. Studies reporting on the occurrence and evolution of retrogressive thaw slumps over the Arctic show that in varied Arctic areas, slumps have increased over the last decades. While the processes responsible for the initiation of retrogressive thaw slumps are well defined, little research has been done on a regional scale to define the terrains on which they occur, and to measure the volumes of sediments eroded through their development. There are currently no estimates of the contribution of these permafrost degradation landforms to the carbon budget, therefore thermo-erosional features are not yet accounted in the carbon models. With this study, we highlight the important contribution of retrogressive thaw slumps to the nearshore carbon cycle in the eastern part of the Beaufort Sea by 1) calculating the amount of sediments eroded through the development of RTSs, 2) estimating the amount of carbon mobilized and potentially transported from the land to the nearshore zone of the Beaufort Sea. We used a large set of high-resolution multispectral satellite images from 2011 (GeoEye-1 and WorldView-2) we manually digitized coastal retrogressive thaw slumps along a 235 km coastline. We gathered additional observations during fieldwork in July and August 2015 on the current development stage of retrogressive thaw slumps and classified them between active and stable. We extrapolated the eroded surfaces using a digital elevation model. Based on available literature on carbon stocks in the area, we estimated the amounts of mobilized particulate organic carbon and nitrogen. This model allowed us to measure the contribution of retrogressive thaw slumps to the near shore carbon budget in the area

The Way of Carbon - Composition and Transport of Organic Carbon in the Nearshore Zone of Herschel Island, Qikiqtaruk

Arctic permafrost coasts are greatly impacted by global climate change. Warming permafrost, decreasing sea ice extent and increasing sea temperature lead to greater coastal erosion. The carbon stored in the permafrost is then released into the nearshore zone, where it degrades, potentially leading to the release of greenhouse gas emissions (GHG) into the atmosphere. Yet, the exact pathways of organic carbon (OC) in the nearshore zone are not completely understood. In order to fill this gap, we collected dissolved and particulate OC (DOC, POC) samples in the nearshore zone of Herschel Island, Qikiqtaruk. The sampling was repeatedly carried out along a transect over a period of two weeks during the open water season in summer 2022. Water samples were collected at the surface and at several water depths. Subsequently, water samples were filtered through 47μm fiberglass filters and examined in the laboratory for suspended particulate matter, DOC, and POC. When possible, Van Veen Grab samples and short cores were taken at each sample location. The upper six centimeters of the short cores as well as the grab samples were analyzed for grain size, mercury, carbon and nitrogen content. In addition to the water sampling, temperature, conductivity, salinity, and turbidity were measured at each sampling location with CTD and turbidity meter. Initial data shows a gradient in temperature and turbidity in the water column, especially at the beginning of the sampling period, which coincided with the sea ice breakup. Hereby, values for Turbidity range from 3.81 to 205.00 FNU. The amount of DOC and POC in the water samples will give an indication on the variability of geochemical properties in the water column over time. This will allow us to determine and quantify the link between these properties and environmental forcing. Keywords: Coastal Erosion, Carbon Pathways, Sediment Transport, Permafrost Coas

Drivers of Turbidity and Its Seasonal Variability at Herschel Island Qikiqtaruk (Western Canadian Arctic)

The Arctic is greatly affected by climate change. Increasing air temperatures drive permafrost thaw and an increase in coastal erosion and river discharge. This results in a greater input of sediment and organic matter into nearshore waters, impacting ecosystems by reducing light transmission through the water column and altering biogeochemistry. This potentially results in impacts on the subsistence economy of local people as well as the climate due to the transformation of suspended organic matter into greenhouse gases. Even though the impacts of increased suspended sediment concentrations and turbidity in the Arctic nearshore zone are well-studied, the mechanisms underpinning this increase are largely unknown. Wave energy and tides drive the level of turbidity in the temperate and tropical parts of the world, and this is generally assumed to also be the case in the Arctic. However, the tidal range is considerably lower in the Arctic, and processes related to the occurrence of permafrost have the potential to greatly contribute to nearshore turbidity. In this study, we use high-resolution satellite imagery alongside in situ and ERA5 reanalysis data of ocean and climate variables in order to identify the drivers of nearshore turbidity, along with its seasonality in the nearshore waters of Herschel Island Qikiqtaruk, in the western Canadian Arctic. Nearshore turbidity correlates well to wind direction, wind speed, significant wave height, and wave period. Nearshore turbidity is superiorly correlated to wind speed at the Beaufort Shelf compared to in situ measurements at Herschel Island Qikiqtaruk, showing that nearshore turbidity, albeit being of limited spatial extent, is influenced by large-scale weather and ocean phenomenons. We show that, in contrast to the temperate and tropical ocean, freshly eroded material is the predominant driver of nearshore turbidity in the Arctic, rather than resuspension, which is caused by the vulnerability of permafrost coasts to thermo-erosion

Factors Influencing the Spatial and Temporal Occurrence of Thermo-erosional Landforms along the Yukon Coast, Canada

Processes associated with permafrost degradation in the arctic coastal zone are highly dynamic and account for significant amounts of organic carbon released to the Arctic Ocean. Thermo-erosion, as a mechanism of rapid permafrost thaw, reshapes arctic landscapes and has a clear impact on the mobilization and distribution of carbon and nitrogen in permafrost terrains. However, few studies report on the diversity of thermo-erosional landforms or assess the factors involved in their development. This study highlights the diversity of thermo-erosional drainage pathways -- including gullies and valleys -- and specific thermokarst features such as retrogressive thaw slumps and active layer detachments, and determines the prevailing factors accounting for their distribution and driving their expansion over the last 60 years along the Yukon coast. With the software OrthoEngine from PCI Geomatica we used a large set of high resolution satellite images from 2011 (GeoEye-1 and WorldView-2) for geocoding aerial photographs from the 1950s. The aerial photographs come from the National Air Photo Library, Canada. This dataset allowed us to manually digitize and classify thermo-erosional gullies, valleys, retrogressive thaw slumps and active layer detachments for the 1950s and 2011 using ArcGIS 10.3. We gathered additional observations during fieldwork in July and August 2015 on gully and valley morphologies, and on the current development stage of retrogressive thaw slumps. Based on remote sensing, we calculated and compared the surface area occupied by slumps in 1950s and in 2011 as well as the types, number and lengths of thermo-erosional drainage pathways over the same period. We coupled these information with additional datasets related to climate, geology and topography, and performed multivariate statistical analyses using the software R. Over this time span, we observed an important spatial heterogeneity in the landform dynamics among the different geological units. The number and the surface area of retrogressive thaw slumps increased on average. We did not detect a specific increase in the length of thermo-erosional drainage pathways over the whole area, however, in some specific geological units they decreased in length due to important coastal erosion. This dataset will be complemented by soil organic carbon data collected across several thermo-erosional landforms during fieldwork conducted in 2015 in order to understand the processes of carbon mobilization within specific thermo-erosional landforms

Coastal Changes on the Pan-Arctic Sale – Update of the Arctic Coastal Dynamics Database

One third of all coastlines worldwide consist of permafrost. Many of these permafrost coasts are presently exposed to greater environmental forcing as a consequence of climate change, such as a lengthening of the open water season, intensified storms, and higher water and air temperatures. As a result, increasing erosion rates are currently reported from various sites across the Arctic. It is crucial to synthetize these data on Arctic shoreline dynamics in order to improve our understanding on present coastal dynamics on the pan-Arctic scale. A first synthesis product was released in form of the Arctic Coastal Dynamics databse in 2012, which included data published until 2009 (Lantuit et al., 2012). Since then, numerous publications and data products were published on short and long term changes of Arctic coasts across a wide range of study sites. We made an extensive literature review of publications released within the last 10 years and updated the shoreline change data section in the Arctic Coastal Dynamics database. While in 2009 for one percent of the Arctic shoreline data on coastal dynamics was available, the addition of new data leads to a broader data coverage, which is mainly the effect of the greater availability of remotely sensed products for analyses conducted in these remote regions. Further, the additional data allow us to update the current mean rate of Arctic shoreline change

Eastern Beringia and beyond: Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada

Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry, and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2 cal ka BP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean δ18O of −29.1‰); this, together with low dexcess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island icethrust moraine was accompanied by alluvial, proluvial, and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until ~11 cal ka BP during a period of low glacio-eustatic sea level. The late glacial–Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2 cal ka BP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet, ocean, and permafrost that have existed since the Late Wisconsinan

Timing and drivers of mid- to late Holocene ice-wedge polygon development in the Western Canadian Arctic

Ice-wedge polygon formation and development from low-centred to high-centred types are thought to be either linear processes acting on long time-scales or rapid shifts between different regimes. We analyzed six sediment cores from three ice-wedge polygons on the Yukon Coastal Plain to examine the timing and drivers of these dynamics. All sites developed from shallow lakes or submerged polygon environments to low-centred polygons before rapid degradation and drying during the last century. We found that ice-wedge polygon initiation was linked to moderate climatic cooling during the mid-Holocene combined with drainage of lakes. The further conversion to high-centred polygons appeared to have been a rapid process linked to modern climatic warming. Continued warming may thus lead to increasing ice-wedge melt on larger scales and subsequent degradation of ice-wedge polygons, especially if paired with increasing geomorphic disturbances caused by thermokarst and thermo-erosion

Contribution of Coastal Retrogressive Thaw Slumps to the Nearshore Organic Carbon budget along the Yukon Coast

We describe the evolution of coastal retrogressive thaw slumps (RTSs) between 1952 and 2011 along the Yukon Coast, Canada, and provide the first estimate of the contribution of RTSs to the nearshore organic carbon budget in this area. We 1) monitor the evolution of RTSs during the periods 1952-1972 and 1972-2011; 2) calculate the volume of material eroded and stocks of organic carbon (OC) mobilized through slumping – including soil organic carbon (SOC) and dissolved organic carbon (DOC) – and 3) measure the OC fluxes mobilized through slumping between 1972 and 2011. We identified RTSs using high-resolution satellite imagery from 2011 and geocoded aerial photographs from 1952 and 1972. To estimate the volume of eroded material, we applied a spline interpolation on an airborne LiDAR dataset acquired in July 2013. We inferred the stocks of mobilized SOC and DOC from existing related literature. Our results show a 73% increase in the number of RTSs between 1952 and 2011. In the study area, RTSs displaced at least 8600*103 m^3 of material, with 53% of ice. We estimated that slumping mobilized 81900*10^3 kg of SOC and 156*10^3 kg of DOC. Since 1972, 17% of the RTSs have displaced 8.6*103 m^3/yr of material, with an average OC flux of 82.5*10^3 kg/yr. This flux represents 0.3% of the OC flux released from coastal retreat; however RTSs have a strong impact on the transformation of OC in the coastal fringe