Arctic Continental Shelf Research Articles

The marine methane cycle in the Canadian Arctic Archipelago during summer.

In the Arctic Ocean, methane concentrations surpassing global averages are prevalent, especially along sub-Arctic and Arctic continental shelf margins. Despite elevated dissolved methane levels, the Arctic Ocean exhibits minimal methane fluxes to the atmosphere, indicating a potential role of water column oxidation in methane processing. During the Northwest Passage Project in the summer of 2019, we integrated thermohaline, chemical, and biological data with in-situ and in-vitro methane data in Canadian Arctic Archipelago (CAA) waters. Elevated in-situ dissolved methane was prominent in near-surface Pacific waters (between 2 and 7m), particularly in meltwater regions, with av. concentrations of 5.8±2.5 nM within the upper 30m. While methane oxidation constants were generally low (av. 0.006±0.002 d-1), surface waters in Wellington Channel and Croker Bay exhibited higher rates (av. 0.01±0.0004 d-1), associated with Pacific-origin microbial taxa like Oleispira and Aurantivirga. Deeper layers (>200m) displayed lower methane concentrations (av. 3.1±1.1 nM) and oxidation rates (av. 0.005±0.001 d-1). Sea ice showed elevated dissolved methane concentrations (av. 9.2±5 nM). Waters in the western CAA exhibited a 25% increase in methane concentrations compared to ice-free areas. The overall picture suggested supersaturation of in-situ methane in shallow waters (between 2 and 50m), coupled with faster oxidation rates in meltwater and Pacific dominant layers, suggesting rapid seasonal cycling of methane and prevention of the methane migration into the atmosphere.

Seismic Imaging of the Arctic Subsea Permafrost Using a Least-Squares Reverse Time Migration Method

High-resolution seismic imaging allows for the better interpretation of subsurface geological structures. In this study, we employ least-squares reverse time migration (LSRTM) as a seismic imaging method to delineate the subsurface geological structures from the field dataset for understanding the status of Arctic subsea permafrost structures, which is pertinent to global warming issues. The subsea permafrost structures in the Arctic continental shelf, located just below the seafloor at a shallow water depth, have an abnormally high P-wave velocity. These structural conditions create internal multiples and noise in seismic data, making it challenging to perform seismic imaging and construct a seismic P-wave velocity model using conventional methods. LSRTM offers a promising approach by addressing these challenges through linearized inverse problems, aiming to achieve high-resolution, subsurface imaging by optimizing the misfit between the predicted and the observed seismic data. Synthetic experiments, encompassing various subsea permafrost structures and seismic survey configurations, were conducted to investigate the feasibility of LSRTM for imaging the Arctic subsea permafrost from the acquired seismic field dataset, and the possibility of the seismic imaging of the subsea permafrost was confirmed through these synthetic numerical experiments. Furthermore, we applied the LSRTM method to the seismic data acquired in the Canadian Beaufort Sea (CBS) and generated a seismic image depicting the subsea permafrost structures in the Arctic region.

Arctic Continental-Shelf Sediment Dynamics.

Sediments covering Arctic continental shelves are uniquely impacted by ice processes. Delivery of sediments is generally limited to the summer, when rivers are ice free, permafrost bluffs are thawing, and sea ice is undergoing its seasonal retreat. Once delivered to the coastal zone, sediments follow complex pathways to their final depocenters-for example, fluvial sediments may experience enhanced seaward advection in the spring due to routing under nearshore sea ice; during the open-water season, boundary-layer transport may be altered by strong stratification in the ocean due to ice melt; during the fall storm season, sediments may be entrained into sea ice through the production of anchor ice and frazil; and in the winter, large ice keels more than 20 m tall plow the seafloor (sometimes to seabed depths of 1-2 m), creating a type of physical mixing that dwarfs the decimeter-scale mixing from bioturbation observed in lower-latitude shelf systems. This review summarizes the work done on subtidal sediment dynamics over the last 50 years in Arctic shelf systems backed by soft-sediment coastlines and suggests directions for future sediment studies in a changing Arctic. Reduced sea ice, increased wave energy, and increased sediment supply from bluffs (and possibly rivers) will likely alter marine sediment dynamics in the Arctic now and into the future.

Chromosome-level genome assembly and annotation of the cold-water species Ophiura sarsii

The cold-water species Ophiura sarsii, a brittle star, is a key echinoderm in the Arctic continental shelf region, highly sensitive to climate change. However, the absence of a high-quality genome has hindered a thorough understanding of its adaptive evolution. In this study, we reported the first chromosome-level genome assembly of O. sarsii. The genome assembly totalled 1.57 Gb, encompassing 19 chromosomes with a GC content of 37.11% and a scaffold N50 length of 78.03 Mb. The Benchmarking Universal Single-Copy Orthologs (BUSCO) assessment yielded a completeness estimate of 93.5% for this assembly. We predicted a total of 27,099 protein-coding genes, with 25,079 functionally annotated. The genome was comprised of 58.09% transposable elements. This chromosome-level genome of O. sarsii contributes to our understanding of the origin and evolution of marine organisms.

Glacial isostatic adjustment reduces past and future Arctic subsea permafrost

Sea-level rise submerges terrestrial permafrost in the Arctic, turning it into subsea permafrost. Subsea permafrost underlies ~ 1.8 million km2 of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial-interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for glacial isostatic adjustment (GIA), which deviates local sea level from the global mean due to changes in ice and ocean loading. Here we incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects as well as deformation related to Northern Hemisphere ice sheets. Additionally, we extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change’s sixth assessment report. We find that subsea permafrost is preserved under a low emissions scenario but mostly disappears under a high emissions scenario.

Biogeochemical investigations of methane seepage at the ultraslow-spreading Arctic mid-ocean ridge: Svyatogor ridge, Fram Strait

The Arctic continental shelves are important reservoirs of methane stored in gas hydrates and deeper geological formations. However, little is known about methane dynamics in deeper oceanic settings such as mid-ocean ridges, mainly due to operational challenges related to their remoteness. This study investigates a recently discovered methane seepage environment at Svyatogor Ridge, a sediment-covered transform fault on the western flank of the Arctic mid-ocean ridge west of Svalbard. Svyatogor Ridge was previously hypothesized to host deep gas hydrates and active fluid flow systems, which is a unique combination for this setting and requires geochemical evidence. Based on sediment and foraminiferal geochemistry, we demonstrate that Svyatogor Ridge hosts a shallow methane cycle with anaerobic oxidation of microbial methane, sustaining chemosynthetic communities at the seafloor. Our geochemical datasets also suggest that methane fluxes were higher in the past than today and long-lasting, with episodes of intense methane oxidation recorded in pre-Holocene sediments. Methane seepage is still ongoing at this location, although no evidence exists that methane is reaching the sea surface. The results provide the first evidence of a methane seepage environment ever reported from the ultra-slow spreading Arctic mid-ocean ridge, thus calling for a reevaluation of the role of this type of ridge in the ocean methane cycle.

Biodegradation of Ancient Organic Carbon Fuels Seabed Methane Emission at the Arctic Continental Shelves

AbstractThis study explores the carbon stability in the Arctic permafrost following the sea‐level transgression since the Last Glacial Maximum (LGM). The Arctic permafrost stores a significant amount of organic carbon sequestered as frozen particulate organic carbon, solid methane hydrate and free methane gas. Post‐LGM sea‐level transgression resulted in ocean water, which is up to 20°C warmer compared to the average annual air mass, inundating, and thawing the permafrost. This study develops a one‐dimensional multiphase flow, multicomponent transport numerical model and apply it to investigate the coupled thermal, hydraulic, microbial, and chemical processes occurring in the thawing subsea permafrost. Results show that microbial methane is produced and vented to the seawater immediately upon the flooding of the Arctic continental shelves. This microbial methane is generated by the biodegradation of the previously frozen organic carbon. The maximum seabed methane flux is predicted in the shallow water where the sediment has been warmed up, but the remaining amount of organic carbon is still high. It is less likely to cause seabed methane emission by methane hydrate dissociation. Such a situation only happens when there is a very shallow (∼200 m depth) intra‐permafrost methane hydrate, the occurrence of which is limited. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change.

The Role of Coastal Yedoma Deposits and Continental Shelf Sediments in the Arctic Ocean Silicon Cycle

AbstractThe availability of silicon (Si) in the ocean plays an important role in regulating biogeochemical and ecological processes. The Si budget of the Arctic Ocean appears balanced, with inputs equivalent to outputs, though it is unclear how a changing climate might aggravate this balance. In this study, we focus on Si cycling in Arctic coastal areas and continental shelf sediments to better constrain the Arctic Ocean Si budget. We provide the first estimate of amorphous Si (ASi) loading from erosion of coastal Yedoma deposits (30–90 Gmol yr−1), demonstrating comparable rates to particulate Si loading from rivers (10–90 Gmol yr−1). We found a positive relationship between surface sediment ASi and organic matter content on continental shelves. Combining these values with published Arctic shelf sediment properties and burial rates we estimate 70 Gmol Si yr−1 is buried on Arctic continental shelves, equivalent to 4.5% of all Si inputs to the Arctic Ocean. Sediment dissolved Si fluxes increased with distance from river mouths along cruise transects of shelf regions influenced by major rivers in the Laptev and East Siberian seas. On an annual basis, we estimate that Arctic shelf sediments recycle approximately up to twice as much DSi (680 Gmol Si) as is loaded from rivers (340–500 Gmol Si).

Russia, the USA and the Arctic. Part 2. Conflicts and the new arms race

The article is devoted to the analysis of the primary background issues for the growth of the conflict potential of the US-Russia relations in the Arctic region. The author focuses on the competition for control over the Arctic continental shelf. The Arctic Council has been paralyzed since the start of a special emergency operation. The confrontation in the Northern Sea Route between Russia and the USA, advocating «freedom of navigation», is considered. The article analyses doctrinal documents of Russia and the United States and evaluates the military history of the Arctic region and the arms race launched by NATO in the Arctic. Russian defense response is briefly described.

Technology and the construction of oceanic space: Bathymetry and the Arctic continental shelf dispute

How did the Arctic seabed become a political space despite its almost complete inaccessibility to humans? While we can explain the causes of this in geopolitical and economic terms, theorizing the process is more difficult. This article argues that spatial constructions of the Arctic seabed emerge from the interaction among human actors, technologies, and the material environment. This interaction generates representations which are then fed into the overall process of spatializing the seabed. By highlighting the role of technology, this paper offers a way of relating human agency and materiality in the construction of oceanic space. The case study of bathymetry in the ongoing disputes over the Arctic continental shelf illustrates how technological and scientific advancements are embedded into global politics and themselves cause evolutions in the spatial construction of the seabed.

Results and prospects of geological mapping of the Arctic shelf of Russia

The results of compiling the sets of the State Geological Map at a scale of 1:1,000,000 for the Arctic continental shelf of Russia are analyzed. Results are summed up, and the main problems of geological mapping are outlined. The results of geological and geophysical studies of the Arctic Ocean are of great importance for deciphering the geological evolution. The Arctic shelf is the widest shelf in the world, while the spreading ocean basin is one of the narrowest and is characterized by anomalous structural features. The main problems of geological mapping include identification the sedimentary cover/folded basement boundary, interpretation the geodynamic evolution of the shelf and adjacent ocean, determining the rates of sedimentation and stratigraphic subdivision of the sedimentary cover due to a small number of key boreholes. It is promising to further study problem areas with unclear features of geological structure as well as small-scale mapping in areas of industrial development on the Arctic continental shelf.

Rapid seafloor changes associated with the degradation of Arctic submarine permafrost

SignificanceTemperature increases in Arctic regions have focused attention on permafrost degradation on land, whereas little is known about the dynamics of extensive glacial-age permafrost bodies now submerged under the vast Arctic Continental shelves. Repeated high-resolution bathymetric surveys show that extraordinarily rapid morphologic changes are occurring at the edge of the continental slope of the Canadian Beaufort Sea along what was once the seaward limit of relict Pleistocene permafrost. How widespread similar changes are on the Arctic shelves is unknown, as this is one of the first areas in the Arctic subjected to multiple multibeam bathymetric surveys. Rapid morphologic changes associated with active submarine permafrost thawing may be an important process in sculpturing the seafloor in other submarine permafrost settings.

Physical drivers of sediment-water interaction on the Beaufort Sea shelf

Climate change is causing sea ice loss on Arctic continental shelves, resulting in increases of shelf-derived materials to the Arctic Ocean. Sediment-water interaction can chemically transform water as it moves across the shelf, enriching shelf waters in nutrients and carbon, which can impact primary productivity and greenhouse gas cycling. However, the drivers of sediment-water interaction in the Arctic Ocean are poorly understood. In this study, we use radium isotope measurements and physical data from a cruise to the Beaufort shelf in late-October-November 2018 to investigate the impact of storm events and winter water formation on sediment-water interaction. In response to winter water formation, radium-228 and 228Ra/226Ra increased in shelf bottom waters, with both indicative of enhanced sediment-water exchange. Ammonium, an important nutrient for phytoplankton growth with a known sediment source, also increased during this time period. Our results suggest that processes related to ice formation, together with wind effects, have the ability to drive dissolved constituents from sediment porewaters into the water column. The spatial variability in chemical constituents and water mass ages based on short-lived Ra isotopes suggest that these sediment-water interaction events are episodic in nature, and that storm-driven mesoscale water column features can drive local exchange with the benthos.

Monitoring Alaskan Arctic Shelf Ecosystems Through Collaborative Observation Networks

Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, information-rich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes.

Arctic geothermal structures inferred from Curie-point depths and their geodynamic implications

We applied the modified centroid method with a fractal magnetization model on a new magnetic anomaly grid for the Circum-Arctic area (CAMP) to obtain the first high-resolution Arctic Curie-point model and to infer geothermal structure. The shallowest Curie-point depths, found in the oceanic domain, reveal the cooling pattern of oceanic lithosphere and asymmetric mantle thermal activities across spreading ridges. The Cretaceous High Arctic large igneous province (HALIP), the most prominent magmatic feature in the Arctic, shows slightly lower heat flow and higher thermal conductivities than the surrounding area, indicating a complete cooling of the HALIP, but HALIP also has shallow Curie-point depths. We attribute this contradiction to the high titanium content of HALIP that lowers the Curie temperature. Therefore, Curie-point depths constrain well the boundary of the HALIP. On the Arctic continental shelves, the largest Curie-point depths are found in deep sedimentary basins, where lower crust eclogitization was previously interpreted. Furthermore, we found that this positive correlation between large Curie-point depths and large sediment thickness is prevalent for global continental margin sedimentary basins.

Possible future scenarios for two major Arctic Gateways connecting Subarctic and Arctic marine systems: I. Climate and physical–chemical oceanography

AbstractWe review recent trends and projected future physical and chemical changes under climate change in transition zones between Arctic and Subarctic regions with a focus on the two major inflow gateways to the Arctic, one in the Pacific (i.e. Bering Sea, Bering Strait, and the Chukchi Sea) and the other in the Atlantic (i.e. Fram Strait and the Barents Sea). Sea-ice coverage in the gateways has been disappearing during the last few decades. Projected higher air and sea temperatures in these gateways in the future will further reduce sea ice, and cause its later formation and earlier retreat. An intensification of the hydrological cycle will result in less snow, more rain, and increased river runoff. Ocean temperatures are projected to increase, leading to higher heat fluxes through the gateways. Increased upwelling at the Arctic continental shelf is expected as sea ice retreats. The pH of the water will decline as more atmospheric CO2 is absorbed. Long-term surface nutrient levels in the gateways will likely decrease due to increased stratification and reduced vertical mixing. Some effects of these environmental changes on humans in Arctic coastal communities are also presented.

Mg/Ca ratios in ostracode genera Sarsicytheridea and Paracyprideis: A potential paleotemperature proxy for Arctic and subarctic continental shelf and slope waters

We evaluate the potential utility of Mg/Ca in the ostracode genera Sarsicytheridea and Paracyprideis as a paleotemperature proxy for continental shelf and upper slope waters of the Arctic Ocean and adjacent seas. Using sediment core-top and surface sediment samples, shells of three species, S. bradii, S. punctillata, and P. pseudopunctillata, were analyzed from Arctic Ocean sites in water depth from 7 to 200 m and bottom-water temperatures (BWT) of −1.5 °C to 12 °C. Mg/Ca values range from 4 to 9 mmol/mol. These results are in excellent agreement with the range of Mg/Ca obtained in a previous study (Ingram, 1998) of shells of Sarsicytheridea from the sub-polar North Atlantic Ocean region with BWT ranging from 1 to 11.4 °C. Unlike this study of Sarsicytheridea, and work on the Arctic ostracode marine genus Krithe showing strong correlations between Mg/Ca and BWT, analysis of Mg/Ca in this study are not correlated with BWT below 0 °C. We hypothesize that this primarily has to do with uncertainty regarding the actual ambient BWT at the time of shell secretion. As with many continental shelf sites, individual sites used in the study have large interannual and seasonal variations in BWT (≥5–8 °C). Thus, there is difficulty in assigning a shell secretion temperature and assessing the utility of Sarsicytheridea Mg/Ca ratios as a paleotemperature proxy below 0 °C. The calibration of Mg/Ca results from temperatures above 0 °C justifies continued evaluation of this potential paleothermometer for Arctic continental shelf and upper slope environments.

Actual legal situation and international controversy concerning the continental shelf in the arctic zone

The proposed article briefly presents the prehistory of these problems, the established approaches to determining the legal status of the Arctic continental shelf, so the importance of resolving existing differences between the Arctic states The authors of the article note that the motivation of the Russian Federation according to determination and legal protection of their external borders of the continental shelf in the Arctic is inspired by the growth of the scientific researches and the conduction of various kinds of expeditions, not only by the Arctic states, but also by leading European and Asian countries (Germany, China, etc.), to search for evidence in order to review the existing maritime borders. In conclusion, the article notes that only the peaceful settlement of disputes, compliance with the rules of International Law and observation of the concluded interstate agreements are the key to global stability, because the clash of interests in the Arctic can lead to unpredictable consequences for many states and doesn't exclude the occurrence of military conflicts.

The Importance of Benthic Nutrient Fluxes in Supporting Primary Production in the Laptev and East Siberian Shelf Seas

AbstractThis study presents an assessment of benthic nutrient regeneration and its role for the nutrient budget of the outer Laptev and East Siberian shelf sea. Porewater profiles of the major nutrients dissolved silica (DSi), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphate (DIP) as well as total dissolved iron (DFe) were evaluated with a one‐dimensional reaction transport model to derive net reaction rates and benthic nutrient fluxes from shelf and slope 16 stations. Integrated over the shelf area the benthic fluxes of DSi, DIN, and DIP were found to be 7.1, 1.2, and 0.5 Gmol/year in the Laptev Sea and 29.8, 9.5, and 2.8 Gmol/year in East Siberian Sea, respectively. A comparison of the ratios of the benthic nutrient fluxes with marine and riverine inputs and Arctic plankton stoichiometry indicate substantial benthic nitrogen loss likely due to denitrification relative to DIP and DSi. Our benthic flux estimation is likely a low estimate of benthic nutrient fluxes considering potentially higher regeneration rates of nutrients from more productive, bioturbated near‐shore sediments. The estimate emphasizes the role of benthic nutrient fluxes by returning nutrients with a fundamentally different stoichiometry to bottom waters from that of Arctic marine phytoplankton, riverine sources, and open water inflow. With a simple box model, we provide a snapshot of today's nutrient budget in the two seas and estimate that about 10%–20% of nutrients required by primary production are derived from sediments. This proportion is expected to increase for a future warmer Arctic continental shelf in response to increasing primary production.

Widespread surface waterpCO2 undersaturation during ice-melt season in an Arctic continental shelf sea (Hudson Bay, Canada)

Estimating sea–air CO2 fluxes in coastal seas remains a source of uncertainty in global carbon budgets because processes like primary production, upwelling, water mixing, and freshwater inputs produce high spatial and temporal variability of CO2 partial pressure (pCO2). As a result, improving our pCO2 baseline observations in these regions is important, especially in sub-Arctic and Arctic seas that are experiencing strong impacts of climate change. Here, we show the patterns and main processes controlling seawater pCO2 and sea–air CO2 fluxes in Hudson Bay during the 2018 spring and early summer seasons. We observed spatially limited pCO2 supersaturation (relative to the atmosphere) near river mouths and beneath sea ice and widespread undersaturated pCO2 in offshore and ice-melt-influenced waters. pCO2 was highly correlated with salinity and temperature, with a limited but statistically significant relationship with chlorophyll a and fluorescent dissolved organic matter. Hudson Bay on average was undersaturated with respect to atmospheric CO2, which we attribute mainly to the dominance of sea-ice meltwater. We calculated an average net CO2 flux of about –5mmol CO2 m–2 day–1 (–3.3 Tg C) during the spring and early summer seasons (92 days). Combining this result with extrapolated estimates for late summer and fall seasons, we estimate the annual CO2 flux of Hudson Bay during the open water season (184 days) to be –7.2 Tg C. Our findings indicate that the bay on average is a weaker CO2 sink than most other Arctic seas, emphasizing the importance of properly accounting for seasonal variability in the Arctic coastal shelves to obtain reliable sea–air CO2 exchange budgets.