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1. Shoreface erosion counters blue carbon accumulation in transgressive barrier-island systems

   https://doi.org/10.1038/s41467-023-42942-8  

   Barksdale, Mary Bryan; Hein, Christopher J.; Kirwan, Matthew L. (December 2023, Nature Communications)

   Abstract Landward migration of coastal ecosystems in response to sea-level rise is altering coastal carbon dynamics. Although such landscapes rapidly accumulate soil carbon, barrier-island migration jeopardizes long-term storage through burial and exposure of organic-rich backbarrier deposits along the lower beach and shoreface. Here, we quantify the carbon flux associated with the seaside erosion of backbarrier lagoon and peat deposits along the Virginia Atlantic Coast. Barrier transgression leads to the release of approximately 26.1 Gg of organic carbon annually. Recent (1994–2017 C.E.) erosion rates exceed annual soil carbon accumulation rates (1984–2020) in adjacent backbarrier ecosystems by approximately 30%. Additionally, shoreface erosion of thick lagoon sediments accounts for >80% of total carbon losses, despite containing lower carbon densities than overlying salt marsh peat. Together, these results emphasize the impermanence of carbon stored in coastal environments and suggest that existing landscape-scale carbon budgets may overstate the magnitude of the coastal carbon sink. 

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2. Erosion of coastal archaeological sites on Santa Rosa Island, California

   Christopher S. Jazwa Kerri N. Johnson (October 2018, Western North American naturalist)

   The damage and loss of coastal archaeological sites from shoreline transgression and other near-coastal processes is common around the world. It negatively impacts our ability to address important research questions including those about the colonization of the New World, which likely occurred along the Pacific Coast. Differences in geomorphic context, annual weather patterns, topography, vegetation, bedrock, and land-use history lead to distinct localized patterns of erosion even within small geographic regions. We assessed near-coastal erosion on Santa Rosa Island, California, by monitoring annual change at 16 controlled points on 11 archaeological sites from 2013 to 2017 and by comparing it to the local geomorphic context and annual weather patterns. Overall, erosion through this period was greatest on the northwest coast of the island, which is directly in the path of prevailing winds and most winter storms, and least on the more protected west and south coasts. The 2016–2017 winter was the rainiest and had the most annual erosion in general; however, erosion at sites along gulley walls was lowest that year. By monitoring annual erosion and weather and associating them with variations in erosional processes, we can better understand threats to valuable cultural resources and take appropriate steps for mitigating their losses and the loss of archaeological data. 

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3. Heading for the hills: climate-driven community relocations in the Solomon Islands and Alaska provide insight for a 1.5 °C future

   https://doi.org/10.1007/s10113-017-1256-8  

   Albert, Simon; Bronen, Robin; Tooler, Nixon; Leon, Javier; Yee, Douglas; Ash, Jillian; Boseto, David; Grinham, Alistair (November 2017, Regional Environmental Change)

   Whilst future air temperature thresholds have become the centrepiece of international climate negotiations, even the most ambitious target of 1.5 °C will result in significant sea-level rise and associated impacts on human populations globally. Of additional concern in Arctic regions is declining sea ice and warming permafrost which can increasingly expose coastal areas to erosion particularly through exposure to wave action due to storm activity. Regional variability over the past two decades provides insight into the coastal and human responses to anticipated future rates of sea-level rise under 1.5 °C scenarios. Exceeding 1.5 °C will generate sea-level rise scenarios beyond that currently experienced and substantially increase the proportion of the global population impacted. Despite these dire challenges, there has been limited analysis of how, where and why communities will relocate inland in response. Here, we present case studies of local responses to coastal erosion driven by sealevel rise and warming in remote indigenous communities of the Solomon Islands and Alaska, USA, respectively. In both the Solomon Islands and the USA, there is no national government agency that has the organisational and technical capacity and resourcestofacilitateacommunity-widerelocation.IntheSolomonIslands,communitieshavebeenabletodrawonflexibleland tenure regimes to rapidly adapt to coastal erosion through relocations. These relocations have led to ad hoc fragmentation of communitiesintosmallerhamlets.Government-supportedrelocationinitiativesinbothcountrieshavebeenlesssuccessfulinthe short term due to limitations of land tenure, lacking relocation governance framework, financial support and complex planning processes.Theseexperiences fromthe Solomon Islands and USA demonstrate the urgentneedtocreatea relocation governance framework that protects people’s human rights. 

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4. Permafrost thaw subsidence, sea-level rise, and erosion are transforming Alaska’s Arctic coastal zone

   https://doi.org/10.1073/pnas.2409411121  

   Creel, Roger; Guimond, Julia; Jones, Benjamin_M; Nielsen, David_M; Bristol, Emily; Tweedie, Craig_E; Overduin, Pier_Paul (December 2024, Proceedings of the National Academy of Sciences)

   Arctic shorelines are vulnerable to climate change impacts as sea level rises, permafrost thaws, storms intensify, and sea ice thins. Seventy-five years of aerial and satellite observations have established coastal erosion as an increasing Arctic hazard. However, other hazards at play—for instance, the cumulative impact that sea-level rise and permafrost thaw subsidence will have on permafrost shorelines—have received less attention, preventing assessments of these processes’ impacts compared to and combined with coastal erosion. Alaska’s Arctic Coastal Plain (ACP) is ideal for such assessments because of the high-density observations of topography, coastal retreat rates, and permafrost characteristics, and importance to Indigenous communities and oilfield infrastructure. Here, we produce 21st-century projections of Arctic shoreline position that include erosion, permafrost subsidence, and sea-level rise. Focusing on the ACP, we merge 5 m topography, satellite-derived coastal lake depth estimates, and empirical assessments of land subsidence due to permafrost thaw with projections of coastal erosion and sea-level rise for medium and high emissions scenarios from the Intergovernmental Panel on Climate Change’s AR6 Report. We find that by 2100, erosion and inundation will together transform the ACP, leading to 6-8x more land loss than coastal erosion alone and disturbing 8-11x more organic carbon. Without mitigating measures, by 2100, coastal change could damage 40 to 65% of infrastructure in present-day ACP coastal villages and 10 to 20% of oilfield infrastructure. Our findings highlight the risks that compounding climate hazards pose to coastal communities and underscore the need for adaptive planning for Arctic coastlines in the 21st century. 

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5. The Role of Thermal Denudation in Erosion of Ice-Rich Permafrost Coasts in an Enclosed Bay (Gulf of Kruzenstern, Western Yamal, Russia)

   https://doi.org/10.3389/feart.2020.566227  

   Baranskaya, Alisa; Novikova, Anna; Shabanova, Natalya; Belova, Nataliya; Maznev, Stepan; Ogorodov, Stanislav; Jones, Benjamin M. (January 2021, Frontiers in Earth Science)

   null (Ed.)

   Coastal erosion in the Arctic has numerous internal and external environmental drivers. Internal drivers include sediment composition, permafrost properties and exposure which contribute to its spatial variability, while changing hydrometeorological conditions act as external drivers and determine the temporal evolution of shoreline retreat. To reveal the relative role of these factors, we investigated patterns of coastal dynamics in an enclosed bay in the southwestern Kara Sea, Russia, namely the Gulf of Kruzenstern, which is protected from open-sea waves by the Sharapovy Koshki Islands. Using multitemporal satellite imagery, we calculated decadal-scale retreat rates for erosional segments of the coastal plain from 1964 to 2019. In the field, we studied and described Quaternary sediments and massive ground-ice beds outcropping in the coastal bluffs. Using data from regional hydrometeorological stations and climate reanalysis (ERA), we estimated changes in the air thawing index, sea ice-free period duration, wind-wave energy and total hydrometeorological stress for the Gulf of Kruzenstern, and compared it to Kharasavey and Marre-Sale open-sea segments north and south of the gulf to understand how the hydrometeorological forcing changes in an enclosed bay. The calculated average shoreline retreat rates along the Gulf in 1964–2010 were 0.5 ± 0.2 m yr −1 ; the highest erosion of up to 1.7 ± 0.2 m yr −1 was typical for segments containing outcrops of massive ground-ice beds and facing to the northwest. These retreat rates, driven by intensive thermal denudation, are comparable to long-term rates measured along open-sea sites known from literature. As a result of recent air temperature and sea ice-free period increases, average erosion rates rose to 0.9 ± 0.7 m yr −1 in 2010–2019, with extremes of up to 2.4 ± 0.7 m yr −1 . The increased mean decadal-scale erosion rates were also associated with higher spatial variability in erosion patterns. Analysis of the air thawing index, wave energy potential and their total effect showed that inside the Gulf of Kruzenstern, 85% of coastal erosion is attributable to thermal denudation associated with the air thawing index, if we suppose that at open-sea locations, the input of wave energy and air thawing index is equal. Our findings highlight the importance of permafrost degradation and thermal denudation on increases in ice-rich permafrost bluff erosion in the Arctic. 

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