Session ITS1.7/GM2

ITS1.7/GM2 | Sandy solutions for coasts / Arctic coastal processes

Sandy solutions for coasts / Arctic coastal processes

Co-organized by BG4

Convener: Michel Riksen | Co-conveners: Zuzanna Swirad, Maria Ansine Jensen, Juul Limpens, Gregor Luetzenburg, Anna Irrgang

Orals

| Fri, 28 Apr, 16:15–18:00 (CEST)

Room N1

Posters on site

| Attendance Fri, 28 Apr, 14:00–15:45 (CEST)

Hall X3

This session is a compilation of two independent sessions: ITS1.7 ‘Sandy solutions for coastal safety, measurements and modelling’ and GM7.3 ‘Arctic coastal processes’.

Future projections show that coastal regions are among the most vulnerable ecosystems on our planet. From nearshore to dunes, the coastal system provides ecosystem services such as water supply and storage, recreation, biodiversity and flood protection, all of which can be considered of critical importance for human well-being. Climate change, sea level rise and anthropogenic impacts can affect these services by altering topography and habitat development. Flexible nature-based solutions have been proposed to promote resilience against climate change and safeguard coastal services for current and future generations. For this session we aim to bring together experts from varying disciplines focused on measuring, modelling and designing nature-based solutions in a changing world. This includes but is not limited to topics related to coastal morphology, sediment and vegetation dynamics, hydrology, and anthropogenic impacts.

Decreasing extent and duration of sea ice cover, changes in storm patterns as well as rising sea surface and air temperatures impact coastal processes in the Arctic. Wave overtopping, flooding and coastal erosion pose risks to societies and infrastructure located at the coast. There is a pressing need to understand the rates and mechanisms of coastal change to better predict future trajectories under the changing climate. In this session, we invite contributions from a range of disciplines and across time scales on local to pan-Arctic studies related to coastal processes in the Arctic. Those can include observational (satellite and instrumental) data, historical data, geological records and proxy data, model simulations as well as forecasts, for the past, present and future rates and drivers of Arctic coastal change. The common denominator of these studies will be their focus on a better understanding of short- to long-term mechanisms and feedbacks that drive Arctic coastal changes, and their impact on coastal communities and infrastructure, at local to global scales.

Orals: Fri, 28 Apr | Room N1

Chairpersons: Michel Riksen, Zuzanna Swirad, Maria Ansine Jensen

16:15–16:25

EGU23-67

ECS

On-site presentation

A global analysis of how human infrastructure squeezes sandy coasts

Eva Lansu, Valérie Reijers, Solveig Höfer, Arjen Luijendijk, Max Rietkerk, Martin Wassen, Evert Jan Lammerts, and Tjisse van der Heide

Coastal ecosystems provide vital services, including water storage, carbon sequestration, biodiversity, and coastal protection. Human disturbances, however, cause massive losses. The most direct impact is habitat destruction through infrastructure development, restricting the space available to coastal ecosystems and impeding their capacity to adapt to sea level rise by landward retreat – a phenomenon called ‘coastal squeeze’. While shoreline retreat is intensively studied, coastal congestion through infrastructure remains unquantified. Here we calculated the distance to the nearest human-made structure along 263,900 transects worldwide to show that infrastructure occurs at a 560-meter median distance from the shoreline. Moreover, we find that 18% of global sandy shores harbour less than 100 m of infrastructure-free space, and that 14-17% of the unimpacted space may drown by 2100 according to sea level rise projections. Further analyses show that population density and gross domestic product explain 40-44% of observed squeeze variation, emphasizing the intensifying pressure imposed as countries develop and populations expand. Encouragingly, we find that nature reserves relieve squeezing by 3-5 times, illustrating their effectiveness. Yet, at present only 16% of world’s sandy shores has a protected status. We therefore argue that expansion of nature reserves could be key to preserving coastal resilience to sea level rise.

How to cite: Lansu, E., Reijers, V., Höfer, S., Luijendijk, A., Rietkerk, M., Wassen, M., Lammerts, E. J., and van der Heide, T.: A global analysis of how human infrastructure squeezes sandy coasts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-67, https://doi.org/10.5194/egusphere-egu23-67, 2023.

16:25–16:35

EGU23-1076

ECS

On-site presentation

Response of dune-building grasses to summer precipitation

Jan-Markus Homberger, Aaron Lynch, Juul Limpens, and Michel Riksen

Coastal ecosystems are vulnerable to climate change, with rising sea levels and increased anthropogenic pressure constraining space for natural processes. Nature based solutions using sediments rather than hard surfaces in coastal defense may offer an alternative that both creates new habitats and offer a flexible protection against flooding.

In contrast to hard infrastructure, the topography of dunes depends on the highly dynamic processes of wind and waves and the resistance to them offered by dune vegetation. Perennial grass species such as marram grass (Ammophila arenaria) and sand couch (Elytrigia juncea) play a key-role for topographic stability and the development and shape of coastal dune forms. This is usually attributed to their dense cover which effectively traps sand as well as their positive growth response to burial by sediments. Therefore, species like marram grass have been used as ecosystem engineers in both past and recent coastal dune restoration projects.

Whether this solution will be applicable in the future depends on climate change. Coastal vegetation is vulnerable to climate change due to its susceptibility to changes in growing conditions (e.g. Temperature, Precipitation). Especially at the dry-beach section where the influence of groundwater is limited, a change in growing season precipitation could potentially affect the cover of dune grasses. Past research was already able to establish a general link between dune development and growth in function of precipitation. However, to this date direct responses of dune vegetation to precipitation has not been quantified.

We explored the response of dune building grasses to summer precipitation and its implication for the future dune building in a two-step approach. We used a greenhouse-experiment to derive species growth relationships with water availability for marram grass and sand couch. In a second step we used these relationships to explore the impact of potential changes in summer precipitation on the growth of these species. We found that both marram grass and sand couch were equally sensitive to changes in water availability and responded positively to an increase in it. Comparing soil moisture from the field to the greenhouse, showed that field water availability tended to be on the lower end of ranges in the greenhouse. This suggests that dune vegetation in the field is susceptible to drought effects. Exploring these results further using climate scenarios, we found that plant growth was increased by 1.3 % (experimental period) – 1.8 % (extrapolated) under the most recent RCP 4.5 IPCC projection and by 9.6 – 13 % for an extremely wet year. In contrast, for an extremely dry year plant growth could decrease by 6.2 – 8.2 %.

While changes of < 2 % in plant growth might have limited implications for dune development and stability, years of extreme climate conditions show a bigger range in plant growth (- 8 % - + 13 %) which is more likely to also have direct consequences for dune growth and development. Incorporating these relationships between plant growth and climate in models of coastal dune development should improve predictions of climate change impacts.

How to cite: Homberger, J.-M., Lynch, A., Limpens, J., and Riksen, M.: Response of dune-building grasses to summer precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1076, https://doi.org/10.5194/egusphere-egu23-1076, 2023.

16:35–16:45

EGU23-2771

ECS

On-site presentation

Recreation impact on establishment of dune building species

Sasja van Rosmalen, Jan-Markus Homberger, Michel Riksen, and Juul Limpens

Sandy shores serve a multitude of purposes; they protect the inland from flooding, support a high biodiversity, and are recreation hotspots. To what extent these functions can coexist or are mutually exclusive is unclear, especially given increasing stressors such as rising sea levels and urbanization. Knowledge on the trade-offs between these functions is important when designing these areas and nature-based solutions to ensure the desired results. We investigated the effect of recreational pressure on the establishment of two common dune building grass species (Ammophila arenaria and Elytrigia juncea). We conducted a field introduction experiment with seeds and rhizomes of both species along increasing distance to a beach entrance. We established a total of 300 plots, following a randomised block design with 4 factorial treatments (species * type diaspore) and 60 replicates for two beaches on the Dutch barrier Island of Terschelling. Plant material was collected from the wild, using local genetic material. Plant seeds were left in their husk to mimic natural dispersal. Plots were georeferenced by means of Real Time Kinematic and left unmarked to enable undisturbed recreation.

Recreation pressure was assessed by counting the number of people at different beach sections, confirming that anthropogenic pressure increased with distance to the beach entrance. Establishment success was monitored by counting the number of emerged seeds and sprouted rhizomes per plot at regular intervals across the growing season. To control for drivers other than recreation pressure, we also monitored environmental variables, such as the change in beach level. Preliminary results suggest that environmental factors such as erosion and burial are limiting the establishment success for all treatments. Moreover, a positive effect of distance from the entrance on the establishment success of both species can be observed. This is especially clear within the first 100 meters. The strongest effect seems to be for Ammophila arenaria. These preliminary results indicate that both sediment dynamics and recreational pressure play a role in the new establishment of these species on the upper beach. This means that the impact of both should be considered when designing sandy coastal areas.

How to cite: van Rosmalen, S., Homberger, J.-M., Riksen, M., and Limpens, J.: Recreation impact on establishment of dune building species, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2771, https://doi.org/10.5194/egusphere-egu23-2771, 2023.

16:45–16:55

EGU23-4119

On-site presentation

Morphological changes in a planted coastal dune field: measurements and modelling

Glenn Strypsteen and Pieter Rauwoens

In front of the traditional dike at Oosteroever, Belgium, a new 120x20 m² artificial dune with planted marram grass of different densities and patterns was built in January 2021. This man-made dune was constructed to reduce the local aeolian sand nuisance on the dike. The complex interaction between aeolian sand transport and vegetation will ensure future morphological development of a dune body strengthening the local coastal protection. For an optimal design of these planted dunes, a fundamental knowledge of morphological changes is required. This study is twofold: 1) Investigate dune growth by exploring a multi-monthly field dataset of wind characteristics and high-resolution topographic data, 2) Development and assessment of the AeoLiS model for simulation of this new planted coastal dune field. The performance of AeoLiS is analyzed by comparing observed and simulated results of erosion and deposition patterns and cross-shore bed level changes. The total volume of sand in the dune has increased significantly since the plantation of marram grass, resulting in 15 m³ m^-1 due to aeolian sand transport from the surrounding beach. Most dune growth occurred during the first year. Dune growth during the second year was less pronounced and was attributed to the influence of supply limitations, vegetation characteristics, and sediment erosion by wind and storm events. The results of the model simulations demonstrate that AeoLiS can replicate the spatial patterns and profile development inside the artificial dune area to some extent. However, to adequately account for the interaction between vegetation and aeolian sand transport, the model's treatment of vegetation dynamics needs to be improved.

How to cite: Strypsteen, G. and Rauwoens, P.: Morphological changes in a planted coastal dune field: measurements and modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4119, https://doi.org/10.5194/egusphere-egu23-4119, 2023.

16:55–17:05

EGU23-15297

ECS

Virtual presentation

Decision-Making on Nature-Based Solutions for Multifunctional Coastal Climate Adaptation

Haye Geukes, Alexander Van Oudenhoven, and Peter Van Bodegom

Nature-based solutions (NbS) are fast becoming the norm for multifunctional climate adaptation to the combined challenges of increased sea-level rise, coastal population densities, and erosion of sandy shores worldwide, delivering functions such as flood prevention, recreation, and biodiversity benefits. However, it remains a challenge to the research field to inform decision-makers well on the outcomes and trade-offs of designing, planning, and managing the multifunctional NbS. This study set out to identify the information requirements by decision-makers on NbS for coastal climate adaptation. Using the Sand Motor in The Netherlands as a case study, we applied a policy science framework to distinguish four stages of decision-making to quantitatively analyse the content of functions and indicators utilized per stage in public policy documents. These stages are the ambition, political, bureaucratic, and provisioning processes. This study is the first comprehensive empirical investigation distinguishing these crucial stages of decision-making to analyse NbS information requirements. Our results show, most notably, that as the project developed through the decision-making stages, the content of the functions and indicators changed from abstract to concrete. And, with it, the content of the information required shifted significantly. These results suggest that it is crucial for academic researchers to recognize the decision-making process their information will be used in and adapt its content and level of abstraction accordingly to increase its uptake in decision-making. This study lays the groundwork for future research into the multiple dimensions of NbS decision-making and for the increased understanding of the information requirements on evaluation and trade-offs in planning, designing, and managing NbS, to increase the ability of NbS to deliver multifunctional coastal climate adaptation for sandy shores worldwide.

How to cite: Geukes, H., Van Oudenhoven, A., and Van Bodegom, P.: Decision-Making on Nature-Based Solutions for Multifunctional Coastal Climate Adaptation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15297, https://doi.org/10.5194/egusphere-egu23-15297, 2023.

17:05–17:10

5-minute convener introduction

17:10–17:20

EGU23-1493

Highlight

On-site presentation

Ice-rich permafrost coastline erosion processes

Brian Moorman, Andrew Clark, and Dustin Whalen

Around the Arctic Ocean there are many stretches of coastline composed of ice-rich sediments. With the dramatic climatic, oceanic and terrestrial changes that are currently underway, there is considerable concern over the stability of these coasts and how they impact coastal communities. Unfortunately, there is still relatively little research that has been done the processes at work in these environments. Being able to effectively model coastal erosion in a permafrost setting is highly desirable. With the complexity that ice-rich permafrost conditions add to the coastal setting, modelling erosion involves a more detailed understanding of the physical and thermal conditions as well as the sedimentological and wave action processes. This research examines the rate and character of coastal erosion of ice-rich terrain and role that re-sedimentation has on the shallow water energy balance in preserving sub-bottom massive ice. It also addresses it implications to secondary sea bottom disturbance as the water depth increases.

The study area was Peninsula Point which is approximately 10 km west of Tuktoyaktuk, Northwest Territories, Canada. The massive ice and retrogressive thaw flows at this location are some of the more dramatic examples of the impact of ice-rich permafrost on coastal processes in the Arctic. Through a three decade long program of remote sensing, geophysical and ground-based monitoring, long-term changes were investigated. The character of coastal retreat above, and below, the waterline in an area where a massive ice body extends to depths below sea level were revealed. Airphoto, satellite imagery and drone data revealed the complexity of erosion with the retreating headwall of retrogressive thaw flow more rapidly eroding the landscape than the observed lateral changes of the waterline. Ground-penetrating radar (GPR) imaged the top and base of the massive ice body as well as providing a delineation of the subsurface sedimentary architecture. In winter, the GPR was pulled behind a snowmobile along transects on land, across the shoreline and out onto the near shore area of the Beaufort Sea. This provided the stratigraphic continuity between the terrestrial and sub-sea settings. The roles of erosion, re-sedimentation and shallow-water thermodynamics in the degradation and preservation of massive ground ice were revealed. The results of this study demonstrate how coastal erosion is much more complex that just the inland movement of the waterline.

How to cite: Moorman, B., Clark, A., and Whalen, D.: Ice-rich permafrost coastline erosion processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1493, https://doi.org/10.5194/egusphere-egu23-1493, 2023.

17:20–17:30

EGU23-11651

ECS

On-site presentation

Procedure for examining long-term Arctic shoreline displacement from multispectral satellite data

Tua Nylén, Carlos Gonzales-Inca, and Mikel Calle Navarro

The Arctic coast is facing rapid, irreversible changes mainly caused by Climate Warming, e.g., melting sea ice, permafrost thaw, glacial retreat, land uplift and sea level rise. These processes are leading to fundamental changes in the ecosystem structure and functioning, negatively impacting biological and human communities. Under this complex setting, more knowledge is needed to identify the hotspots of shoreline displacement at an Arctic scale. Thus, the goal of this study was to develop and describe a procedure for mapping long-term shoreline displacement in the Arctic that can provide local communities and environmental managers better opportunities to adapt to further coastal changes. Therefore, the procedure will need to be transferrable to diverse environments and able to handle pan-Arctic analyses at a 30-meter spatial resolution. In this study, the procedure was developed using two test areas: Tanafjorden in the low Arctic mainland Norway and Kongsfjorden in the high Arctic Svalbard. The presentation introduces the final procedure and validation results, and discusses its applicability to pan-Arctic shoreline displacement analyses.

The procedure was calibrated in the surroundings of Tanafjorden. It was built on a 40-year time-series of open Landsat and Sentinel multispectral satellite images, taken during the Arctic summer. Supervised random forest classification was used to identify land and water pixels, utilizing information from multiple infrared bands and spectral indices. Mountain shadow pixels were treated as their own class and then merged to the land class. Open spatial data were used for limiting the area-of-interest and for automated creation of training data. In total over 700 individual images were first classified separately to account for local environmental conditions and transient illumination conditions. Images were then summarized over 5-year time-steps. The classification results were examined against an independent validation dataset of 2000 land cover observations and manually digitized shoreline, and the supervised classification results were compared to single-band classifications based on Otsu’s thresholding. The final procedure was then validated in the Kongsfjorden environment. The process was built on Google Earth Engine’s image collections and cloud computing infrastructure to minimize computing times.

The results indicate that it is possible to transform open satellite imagery into 40-year pan-Arctic shoreline displacement information, with a 30-meter resolution and an overall accuracy of more than 95 %. Data fusion is needed in most processing steps: to limit the area-of-interest, save computing power and reduce errors, provide information that complements multispectral satellite data and reduce the impact of short-term atmospheric and water-level effects. Summarizing dozens of images efficiently removes data gaps and the impact of noise, but this efficiency is sensitive to the number of summarized images. The single-image classification approach is flexible and seems to make the procedure transferable to different locations. Cloud image collections are needed to remove the bottleneck of reading and writing satellite data, and potentially allows the promising procedure to be applied at a pan-Arctic scale in the future.

How to cite: Nylén, T., Gonzales-Inca, C., and Calle Navarro, M.: Procedure for examining long-term Arctic shoreline displacement from multispectral satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11651, https://doi.org/10.5194/egusphere-egu23-11651, 2023.

17:30–17:40

EGU23-14578

ECS

Highlight

On-site presentation

Pan-Arctic remotely sensed observation of coastal settlements - recent updates

Rodrigue Tanguy, Annett Bartsch, Barbara Widhalm, Clemens von Baeckmann, Aleksandra Efimova, and Goncalo Vieira

Rapid and unprecedented warming of high latitudes exposes Arctic coastal communities to greater vulnerability as they observe their territory changing through general permafrost degradation, episodes of flooding and accelerated coastal erosion threatening their infrastructure and livelihood. Local information is known for infrastructures mapping and coastal changes but consistency in the measurement is lacking as well as spatial coverage for large coastal areas. The need of a consistent circumpolar dataset is primordial in order to map risks and mitigate impacts for arctic coastal communities. Machine learning methods with Sentinel 1/2 imagery allow the circumpolar mapping of arctic coastal settlements (Bartsch et al. 2021a). Validation of recent updates are supported by high-resolution data from the Pleiades satellites, aerial and drone imagery.

This study is part of the ESA EO4PAC project which aims to provide a range of satellite derived information, including coastal erosion/accretion and infrastructure in the proximity, for the next generation of the Arctic Coastal Dynamic Database (ACD; Lantuit, et al. 2012). Previous results highlight the detection of 50% more human presence information than in OpenStreetMap especially in Russia with recent expansion of infrastructures related to expanding oil and gas industry. Recent updates of the SACHI dataset (Bartsch et al. 2021b) will be presented including additional attributes for roads and their validation. A preliminary categorization of settlements with respect to permafrost degradation (based on Permafrost_cci records) and coastal erosion based on the current ACD will be presented.

Bartsch, A., G. Pointner, I. Nitze, A. Efimova, D. Jakober, S. Ley, E. Högström, G. Grosse, P. Schweitzer (2021a): Expanding infrastructure and growing anthropogenic impacts along Arctic coasts. Environmental Research Letters. https://doi.org/10.1088/1748-9326/ac3176

Bartsch, Annett, Pointner, Georg, & Nitze, Ingmar. (2021b). Sentinel-1/2 derived Arctic Coastal Human Impact dataset (SACHI) (Version 1) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.4925911

Lantuit, Hugues; Overduin, Pier Paul; Couture, Nicole; Wetterich, Sebastian; Are, Felix; Atkinson, David; Brown, Jerry; Cherkashov, Georgy A; Drozdov, Dimitry S; Forbes, Donald Lawrence; Graves-Gaylord, Allison; Grigoriev, Mikhail N; Hubberten, Hans-Wolfgang; Jordan, James; Jorgenson, M Torre; Ødegård, Rune Strand; Ogorodov, Stanislav; Pollard, Wayne H; Rachold, Volker; Sedenko, Sergey; Solomon, Steve; Steenhuisen, Frits; Streletskaya, Irina; Vasiliev, Alexander (2012): The Arctic Coastal Dynamics Database: A New Classification Scheme and Statistics on Arctic Permafrost Coastlines. Estuaries and Coasts, 35(2), 383-400, https://doi.org/10.1007/s12237-010-9362-6

How to cite: Tanguy, R., Bartsch, A., Widhalm, B., von Baeckmann, C., Efimova, A., and Vieira, G.: Pan-Arctic remotely sensed observation of coastal settlements - recent updates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14578, https://doi.org/10.5194/egusphere-egu23-14578, 2023.

17:40–17:50

EGU23-12412

ECS

On-site presentation

Glacier decay boosts formation of new Arctic coastal environments – lessons learned from Svalbard

Jan Kavan and Mateusz Strzelecki

The consequences of accelerating climatic warming on Arctic landscape evolution are far-reaching. In Svalbard, glaciers are rapidly retreating after the Little Ice Age, which leads to exposing new coastal landscapes from marine-terminating glaciers. Precise quantification of these changes was limited until the complete dataset of Svalbard glacier outlines from 1930’s was made available. Here, we analyse the new Svalbard glacier change inventory data and demonstrate that glacier retreat was responsible for a major shift from marine-terminating towards land-terminating glaciers in the last century. This retreat also led to the formation of 922.9 km of new coastline since 1930’s (representing increase of 16.37% in coastline length) creating pristine landscapes governed by paraglacial processes and sediment-rich nearshore fjord environments. Recent palaeogeographical reconstructions suggest that such a mode of coastal evolution was dominant over the extended periods of the Holocene. Transitions from marine-terminating to land-based glaciers had significant implications for fjord circulation, biological production, state of marine ecosystems, biogeochemical cycles between land and seas, and CO₂ budget in coastal waters. Still ongoing climate warming with associated further glacier retreat may lead to more coasts to be exposed in the future. Moreover, glacier retreat will likely cause collapse of Hornbreen-Hambergbreen glacier bridge leading to separation of Sørkappland and rest of Spitsbergen with severe consequences for regional ocean circulation and climate dynamics.

New bays, new straits, new peninsulas and new islands, that have appeared in the last decades of unprecedented warming and associated decay of marine-terminating glaciers in the Arctic are predominantely uncharted and unexplored territories which foreshadow ice-free Arctic and other cold regions of the warmer future. The importance of transdisciplinary research exploring those deglaciated oases has never been more important than at present.

Acknowledgement: The research leading to these results has received funding from the Norwegian Financial Mechanism 2014-2021: SVELTA - Svalbard Delta Systems Under Warming Climate (UMO-2020/37/K/ST10/02852) based at the University of Wroclaw.

How to cite: Kavan, J. and Strzelecki, M.: Glacier decay boosts formation of new Arctic coastal environments – lessons learned from Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12412, https://doi.org/10.5194/egusphere-egu23-12412, 2023.

17:50–18:00

EGU23-4579

On-site presentation

Morphodynamic evolution of paraglacial spit complexes on a tide-influenced Arctic fjord delta (Dicksonfjorden, Svalbard)

Kyungsik Choi, Dohyeong Kim, Joohee Jo, Seungyeon Sohn, and Seung-Il Nam

Recent global warming triggered pronounced geomorphic changes such as coastal retreat and delta progradation along the coastlines of the Arctic regions. Coastal morphodynamics and associated sediment transport at the Arctic fjord head remain relatively unexplored due to the logistically limited accessibility to the field area, especially at short-term temporal scales. A repeat survey using an unmanned aerial vehicle (UAV)-assisted photogrammetry was conducted to quantify the annual morphodynamics of gravel spit complexes developed on the tidal delta plain of the deglaciated Dicksonfjorden, Svalbard of the Arctic. Results show that the spit morpho-dynamics vary in time and space with an overall downfjord increase in the growth and migration rate of the spits. The youngest spits elongated 22 m yr− 1 and migrated landward 4.3 m yr− 1 between 2015 and 2019, marking the most pronounced spit morphodynamics documented to date in the Svalbard fjord systems. The spit morphodynamics is driven primarily by longshore drift and, to a lesser degree, by overwash processes. Gravels constituting the spits originate from the unconsolidated debris-flow deposits of old alluvial fans, which locally retreat 0.5 m yr− 1. The growth of the spit complexes is also fed by snow meltwater discharge on the alluvial fans, accounting for a downfjord imbrication of angular gravel layers that are intercalated with interlaminated sands and muds on the landward sides of the spits. The breached spits at the most upfjord location have remained stationary during the study period and presumably since the 1930s. Rapid delta progradation combined with an isostatic rebound after the Little Ice Age (LIA) has decreased spit morphodynamics on the tidal delta plain upfjord in Dicksonfjorden with infrequent and insignificant wave influence. The sparse distribution of the isolated spits signifies the intermittent spit development, which is constrained by the proximity to the protruded alluvial fans. The spit complexes in Dicksonfjorden highlight that climate change accelerates coastal geomorphic changes at the fjord head by enhancing wave intensity and regulating episodic sediment delivery that led to the downfjord shift in the locus of wave shoaling.

How to cite: Choi, K., Kim, D., Jo, J., Sohn, S., and Nam, S.-I.: Morphodynamic evolution of paraglacial spit complexes on a tide-influenced Arctic fjord delta (Dicksonfjorden, Svalbard), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4579, https://doi.org/10.5194/egusphere-egu23-4579, 2023.

Posters on site: Fri, 28 Apr, 14:00–15:45 | Hall X3

Chairpersons: Michel Riksen, Maria Ansine Jensen, Jan-Markus Homberger

X3.1

EGU23-4673

Restoring Piping Plover Habitat and Building Coastal Resilience with Nature-based Solutions in Atlantic Canada

Jennie Graham, Danika vanProosdij, Kirsten Ellis, Tony Bowron, and Jubin Thomas

Located in north-eastern Canada near Shippagan, New Brunswick, the Shippagan Gully Conservation Offsetting Project is leveraging salt marsh creation and sand motor techniques to create Piping Plover habitat while increasing resiliency of the Chaisson Office Spit and surrounding communities to climate change. The spit has been altered by more than a century of human activity and is increasingly impacted by climate change and sea-level rise. The project, which employs a holistic approach to improve marine navigation through the Gully and install nature-based solutions for coastal protection and habitat creation, is the first sand motor in Atlantic Canada and the most northern created marsh with sill to date. Extensive modeling was undertaken by NRC prior to the commencement of baseline data collection and design in 2017. Several monitoring and research initiatives are associated with the project, including a fifteen-year monitoring program (regulatory requirement), five-year post-graduate scientific research program, and a 3-year research project which will augment and build on the NRC-led Nature-Based Infrastructure for Coastal Resilience project. Construction began on the sand motor in 2020, with the marsh and marsh sill scheduled to be built in winter 2023 from on-site materials and planted in spring 2023. The final stages of the implementation will include dune and wetland restoration following the removal of old infrastructure, returning nearly the entire spit to a more natural state and restoring natural processes. The first two years of monitoring following the sand motor implementation have shown a shift in conditions to those more closely matching a nearby control site, as well as the first successful nesting and fledging of Piping Plover (Federally Endangered Species) on the site in over 20 years. The project is the result of a collaborative effort that includes federal and provincial government departments, private industry, academia, and environmental NGOs.

How to cite: Graham, J., vanProosdij, D., Ellis, K., Bowron, T., and Thomas, J.: Restoring Piping Plover Habitat and Building Coastal Resilience with Nature-based Solutions in Atlantic Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4673, https://doi.org/10.5194/egusphere-egu23-4673, 2023.

X3.2

EGU23-13052

ECS

Sea ice, wind waves and coastal erosion in Hornsund, Svalbard

Zuzanna Swirad, Mateusz Moskalik, Agnieszka Herman, Malin Johansson, and Gareth Rees

Increasing water levels at the shore can cause coastal erosion, wave overtopping and flooding that threaten communities and infrastructure. More frequent, longer and more severe storm events observed in the North Atlantic sector of the Arctic bring more energetic waves to beaches of western Svalbard. Decreasing extent and duration of the sea ice cover increases potential fetch which makes the waves higher and longer. At the shore, the number of ice-free days per year has increased and coasts that were protected from waves by ice are becoming exposed perennially or over longer time. Modelling suggests that in future the sea ice will continue to decrease while the storminess will further increase. Better understanding the role of sea ice conditions and nearshore wave transformations on wave energy at the Arctic shores is needed to predict coastal hazards under changing climate.

In this study we focus on wave energy delivery to the shores of Hornsund, a ~300 km² fjord of south-western Spitsbergen, Svalbard, and particularly to Isbjornhamna bay in northern Hornsund, where the Polish Polar Station infrastructure is located. We monitor continuously nearshore wind wave conditions and the state of the shore ice, and seasonally the wave run-up and beach morphology. We use three nested SWAN (Simulating WAves Nearshore) models that take low-resolution global wind and wave models and nearshore bathymetry to reconstruct wind wave conditions in the nearshore (~15 m depth) Isbjornhamna. Finally, we use Sentinel-1 SAR data to reconstruct sea ice conditions in Hornsund area which need be incorporated into the wave model. Here we show how our monitoring and modelling scheme facilitates the comprehensive understanding of the nearshore and coastal processes in Isbjornhamna.

How to cite: Swirad, Z., Moskalik, M., Herman, A., Johansson, M., and Rees, G.: Sea ice, wind waves and coastal erosion in Hornsund, Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13052, https://doi.org/10.5194/egusphere-egu23-13052, 2023.

X3.3

EGU23-14978

ECS

Cross-Shelf Transport, Composition and Degradation of Terrestrial Permafrost Organic Matter at the Sediment-Water Interface in the Laptev and East Siberian Seas

Lina Madaj, Kirsi Keskitalo, Örjan Gustafsson, Tommaso Tesi, Igor Semiletov, Oleg Dudarev, Jannik Martens, Negar Haghipour, Lisa Bröder, and Jorien Vonk

The ongoing rise of atmospheric temperatures and sea level is exacerbating Arctic coastal permafrost thaw which leads to increased coastal erosion and input of permafrost soils into the Arctic Ocean. Permafrost soils hold vast amounts of organic carbon (OC) which is released into the coastal waters upon thawing. The fate of this OC with regards to its transport and degradation pathways is not yet fully understood - it could either be degraded within the water column and released into the atmosphere as CO2 or it could be buried at the sea floor. When settling onto the seafloor sediment-water interactions become crucial in the OC degradation process. These so-called flocculation layers at the sediment-water interface hold a high potential for sediment re-suspension and therefore represent an environment favouring the degradation of OC thus preventing burial. Yet, there is little data available from these flocculation (i.e. nepheloid) layers, particularly in the Arctic shelf seas.

To improve our understanding of OC degradation within these flocculation layers, we analysed samples from the flocculation layer and from the underlying surface sediments for organic geochemical parameters (TOC, C/N values, δ13C, Δ14C, sediment surface area). Samples within this study were collected along two cross-shelf transects in the Laptev and in the East Siberian Sea during ISSS-2020 expedition in late summer (Sept-Oct) of 2020 onboard R/V Akademik Msistlav Keldysh. First results show variations in OC composition in both shelf seas between the flocculation and surface sediment layers and also with increasing water depth and distance from shore, further emphasizing the degradation potential of this particular layer. With the collected data, we want to gain new insights into how transport and degradation processes of terrestrial OC vary across the vast Siberian shelves.

How to cite: Madaj, L., Keskitalo, K., Gustafsson, Ö., Tesi, T., Semiletov, I., Dudarev, O., Martens, J., Haghipour, N., Bröder, L., and Vonk, J.: Cross-Shelf Transport, Composition and Degradation of Terrestrial Permafrost Organic Matter at the Sediment-Water Interface in the Laptev and East Siberian Seas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14978, https://doi.org/10.5194/egusphere-egu23-14978, 2023.

X3.4

EGU23-7877

ECS

Early melt-season nutrient and inorganic carbon sediment-water fluxes in the Bering and Chukchi Seas

Lauren Barrett, Penny Vlahos, and Doug Hammond

The Bering and Chukchi Seas are important oceanic regions of carbon sequestration, owing to enhanced gas solubility in cold surface waters and the rapid uptake of carbon dioxide (CO₂) during intense spring blooms. The biogeochemical impacts of decreasing sea ice extent and earlier onset of spring ice melt in this region are yet uncertain. As these marginal seas of the western Arctic Ocean are quite shallow, mostly <60m depth, there is extensive interaction across air-sea-sediment boundaries, but the transformations and fluxes of inorganic carbon in Bering and Chukchi Sea sediments have not been directly quantified. In May-June 2021, we collected water column samples at 14 stations and sediment cores at 5 stations spanning the eastern Bering Sea and southern and eastern Chukchi Sea. Duplicate cores were incubated for several days at in situ temperature, and core-top water was sampled to estimate inorganic carbon and nutrient fluxes. The stations spanned a range of surface ice coverage history, from greater than one month to less than one day of ice-free conditions. In the Chukchi Sea, salinity-normalized bottom water nutrient and dissolved inorganic carbon (DIC) concentrations increased northward, indicating a net input of remineralization products, although effluxes of these parameters from the sediments decreased northward. Moving northward in the Chukchi Sea, the surface water had greater sea ice concentrations, inhibiting surface productivity and air-sea exchange. This may have reduced the rain of labile carbon to the seafloor, resulting in the decreased benthic remineralization. The combination of increasing northward ice coverage and the northward flow of nutrient and IC-rich Pacific-sourced waters influences the bottom-water concentration of remineralization products and sediment-water fluxes. We expect our northeastern Chukchi Sea flux observations are representative of baseline low wintertime sediment-water flux conditions, while the more southerly stations represent at least one month post-ice melt benthic fluxes when surface water productivity is high and the air-water-sediment system openly interacts. We note that some duplicate core measurements were highly heterogeneous, especially in the Bering Sea, illustrating the dynamic nature of this macrofauna-dominated benthic environment and the range of possible fluxes under different rates of bioturbation. While these observations may serve as a seasonal reference, they may also demonstrate how sedimentary fluxes will evolve under future conditions that are expected when sea ice retreats earlier in the season. Here we present our sediment-water flux and water column DIC and nutrient measurements and place them in context with previous work in the region.

How to cite: Barrett, L., Vlahos, P., and Hammond, D.: Early melt-season nutrient and inorganic carbon sediment-water fluxes in the Bering and Chukchi Seas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7877, https://doi.org/10.5194/egusphere-egu23-7877, 2023.

X3.5

EGU23-9832

Beach ridge formation and landward migration along the isostatically rising coastlines of Hudson Bay

Jens Ehn, Kaushik Gupta, Arijit Reeves, and Anirban Mukhodpadhyay

While most global coasts suffer from a loss of landmass due to sea-level rise and coastal transgression, the Arctic and Sub-Arctic coastlines of Hudson Bay and James Bay witness a reverse phenomenon due to post-glacial rebound. The carbon-rich peatlands Hudson Bay Lowland, that emerged from the retraction of the Tyrell Sea, are witnessing the highest rate of vertical upliftment on the planet. The continual reshaping of the coastline by multiple physical forcings is readily visible by the contiguous and recurrent pattern of raised beach ridges imprinted on the rising land far from the present-day coastline. These beach ridges, formed through the interplay of coastal sea ice dynamics and then preserved above sea-level by uplift, hold back terrestrial runoff and are thus critical to the extensive wetland-saltmarsh ecosystems that provide important habitats for waterfowl and wildlife. This study examines the intricate process behind the formation and modification of these geomorphological units using remote sensing techniques. The study includes the use of various remote sensing products to determine ice duration (Canadian Ice Service- Ice Charts), change detection of ridge dimensions and vectors (Landsat Images), elevation (SRTM and ICESat-2), rate of vertical upliftment (glacial isostasy models) and ice motion in the nearshore zone (GOES). Remote sensing observations reveal that the beach ridges originate offshore on mudflats due to ice scouring and gradually, pushed by sea ice, move shoreward, and often merge and build up existing ridges but sometimes initiating a new beach ridge sequence. The current study documents the impact of changing ice regime on the landward movement of beach ridges on the tidal flats. We find that the seaward point of origin on the tidal flats, and the rate at which the ridges expand and finally merge with the coastline vary greatly across the coastline. The slope of the coast and the dynamics of the sea ice in the nearshore zone are key factors leading to this variability.

How to cite: Ehn, J., Gupta, K., Reeves, A., and Mukhodpadhyay, A.: Beach ridge formation and landward migration along the isostatically rising coastlines of Hudson Bay, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9832, https://doi.org/10.5194/egusphere-egu23-9832, 2023.

X3.6

EGU23-15893

Small-scale nature-based solutions for protection of sandy coasts

Caroline Hallin, Emanuel Schmidt, and Björn Almström

Nature-based solutions (NBS) are promising methods to enhance biodiversity and adapt to climate change in coastal areas. However, upscaling NBS to replace conventional methods requires knowledge about their performance from multiple perspectives, e.g., biodiversity, coastal safety, and economy. In recent years, great efforts have been put into researching NBS pilots of sandy solutions. Some of the most prominent examples are found in the Netherlands, e.g., the Sandmotor, the Hondsbossche Dunes, and the Prince Hendrik Sand dike. These are examples of large-scale interventions with nourished sand volumes of hundreds of thousands to millions of cubic meters. In contrast, this study focuses on small-scale NBS pilots of sandy solutions with nourishment volumes of hundreds to thousands of cubic meters. Two NBS pilots in Sweden are described and analysed, and the advantages and disadvantages of small-scale NBS are discussed in relation to larger-scale interventions.

The first pilot was installed in 2018 in the Furusund navigational fairway in the Stockholm Archipelago. A few hundred cubic meters of sand was nourished to a beach subject to erosion due to ship-generated waves. The nourishment protects an eroding bluff and prevents the loss of forest areas with high nature values. Compared to hard solutions, e.g., a rock revetment, the small-scale beach nourishment supplies sand to a small sandy beach down-drift used for recreational purposes. Since the implementation, a significant part of the nourishment has already been eroded, and the expected lifetime of this intervention is in the order of a few years.

The second pilot was installed at Fortuna beach, located in the narrow sound between Sweden and Denmark. The area has a low-energy wave climate, and the nourishment was designed to protect a beach in front of a residential area from storm erosion recurring with decadal frequency. The beach and dune area were nourished with approximately 3000 m³ of sediment. The area has limited offshore sand resources that can be extracted without adverse environmental impact. Therefore, the beneficial use of sediment dredged from local marinas and a mixture of sand and seaweed from nearby beach clean-ups was used to carry out the project. Within a year after the nourishment, a storm with a recurrence period of approximately 5-20 years hit the coast, but the dune volume still exceeded the volume before the measures.

Experiences from the small-scale sandy solutions are that the limited extent of the interventions facilitates financing and permitting processes, which can be a bottleneck in upscaling NBS. The limited volume of nourishments makes it easier for beneficial use of dredged material, which in many cases is viewed as a waste rather than a resource. Both the volume and timing can be adapted to nearby dredging operations, thus reducing the cost of maintenance of small marinas with a high cultural value. The short lifetime and low safety level of small-scale NBS can be a disadvantage but allow for more flexibility, and no-regret solutions compatible with adaptive pathway approaches to climate change adaptation.

How to cite: Hallin, C., Schmidt, E., and Almström, B.: Small-scale nature-based solutions for protection of sandy coasts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15893, https://doi.org/10.5194/egusphere-egu23-15893, 2023.

X3.7

EGU23-14844

ECS

A framework for assessing the space needed for dune-based coastal adaption at multiple time scales.

Rut Romero-Martín, Herminia Valdemoro, Rosh Ranasinghe, and Jose A. Jiménez

Under current conditions, the Spanish Mediterranean coast is already presenting hotspots of extreme exposure to coastal hazards and recurrent damage, making it necessary to adopt disruptive adaptation strategies as opposed to the classic expectation of full protection. This situation is expected to worsen under the effect of sea level rise, which will increase existing erosion rates, with some areas being fully eroded due to the lack of accommodation space to allow natural adaptation to the new conditions.

In this context, nature-based solutions (NBS) are becoming one of the main type of measures to be favored in order to be more climate-resilient and thus support EU policy priorities. Although research on the effectiveness of most nature-based coastal protection methods is still limited, some of them such as dune systems and sand banks have been classified as essential for future coastal defense.

In highly-developed coastal zones, which are the most at risk, the lack of the sufficient space limits the viability of using NBS as they cannot be accommodated. Thus, the existence of accommodation space is the required condition to permit the beach migration and rebuilding under SLR, otherwise will progressively decline and ultimately disappear. It has to be stressed that the accommodation space is a relative concept, being related to the expected magnitude of the shoreline retreat at a given time horizon under a given climate forcing scenario.

Within this context, this work presents a regional-scale framework to assess the accommodation space needed to adopt dune-based NBS planning as a coastal adaptation strategy, by integrating predictions of accommodation space needed to cope with coastal hazards under current and IPCC AR6 climate scenarios and for different time horizons relevant for planning purposes (up to 2100), and to enable dune development. The hazards considered are (i) long-term (decadal scale) coastline evolution; (ii) storm-induced erosion; (iii) SLR-induced erosion; (iv) permanent inundation due to SLR; and (v) storm-induced flooding. The framework applies to the Catalan coast, a 600 km long stretch of the Spanish Mediterranean coastline.

This work was supported by the Spanish Agency of Research in the framework of the CoastSpace project, TED2021-130001B-C21 (MCIN/AEI/10.13039/501100011033).

How to cite: Romero-Martín, R., Valdemoro, H., Ranasinghe, R., and Jiménez, J. A.: A framework for assessing the space needed for dune-based coastal adaption at multiple time scales., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14844, https://doi.org/10.5194/egusphere-egu23-14844, 2023.