Alfred Wegener Institute for Polar and Marine Research
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A Topography‐Aware Eddy Parameterization Improves Warm Water Transport Across the Cape Darnley Continental Slope
Get PDFAbstract The onshore transport of warm Circumpolar Deep Water determines the properties of Antarctic shelf waters and drives the melting of the Antarctic ice shelves. The largest net onshore transport of CDW coincides with regions of dense water export, such as the Cape Darnley region in the East Antarctic, one of the major sources of Antarctic Bottom Water. In an eddy‐resolving regional ocean model of the Cape Darnley region, the winter downslope flow of dense water produces an eddy‐driven transport of warm modified Circumpolar Deep Water across the shelf break. At coarse resolution typical for climate models, this warm water transport is absent and needs to be parameterized. The Gent and McWilliams/Redi (GM/Redi) scheme improves the simulated hydrographic fields and recovers a transport of warm water across the shelf break. With high constant GM/Redi coefficients that improve the mean hydrography the most, however, the on‐shelf transport of warm water is overestimated. This is because the dynamical suppression of eddy‐driven transports across sloping bottom topography is not considered in the GM/Redi scheme. Therefore, we implement a topography‐aware version of the GM/Redi scheme that reduces the coefficients over steep continental slopes, representing the eddy‐suppressive effect of sloping bottom topography. The topography‐aware GM/Redi scheme outperforms the traditional version by simultaneously improving the mean hydrographic fields and the cross‐slope warm water transports. Eddy parameterizations remain important for the representation of onshore tracer transports and shelf water masses in ocean models provided they incorporate regional and local physics as in our example of a topography‐aware scheme.
Plain Language Summary Eddies—ocean whirls with length scales of tens to hundreds of kilometers—transport warm water across the Antarctic continental slope and onto the shelf, where they contribute to the melting of Antarctic ice masses. In a high‐resolution regional model of the Cape Darnley region in East Antarctica, eddies form when dense water flows from the shelf into the deep ocean. These eddies then carry warm water shoreward across the shelf break. However, in coarse‐resolution climate models, eddies are not resolved, resulting in the absence of warm water transport toward the shelf. To address this, we activate an additional scheme in the model that represents eddy fluxes at coarse resolution. This scheme can restore the missing transport and is most effective when it accounts for the slope of the ocean floor.
Key Points In a regional ocean model, the downslope flow of dense water in the Cape Darnley region produces an eddy‐driven onshore warm water transport At coarse resolution, the onshore transport of warm water is absent but can be restored by employing a classical eddy parameterization The parameterization is most effective when it is modified to consider the suppressive effect of sloping bottom topograph
Effect of Sea Water Inundation on CO2 and CH4 Production of Thawing Coastal Permafrost Near Utqiaġvik, Alaska
Get PDFRising sea levels and changing marine dynamics are increasing the inundation of previously terrestrial permafrost, accelerating thaw and altering microbial carbon cycling. On the Arctic Coastal Plain of Alaska, permafrost features like drained lake basins (DLBs) and uplands (ULs), offer distinct redox conditions and formation histories that may influence the carbon cycling response to sea water inundation. This study investigates changes in CO2 and CH4 production during potential seawater inundation using ex situ anaerobic incubations of soils from a DLB and a UL near Utqiaġvik, Alaska. Results showed that CO2 and CH4 production was, respectively, up to 2.2 and 3.3 times higher in the DLB site than in the UL site with the salt‐less control treatment. The addition of artificial sea water inhibited CH4 production at both sites. CO2 production increased in the active and permafrost layers of the UL site, decreased in surface layers of both sites, and remained unaffected by saltwater treatments in the permafrost layers of the DLB site, likely due the presence of marine sediments in the DLB. Carbon availability, microbial adaptation, and electron acceptors are potential factors for the CO2 and CH4 response. Overall, the results of this study showed that anaerobic CO2 production responded differently to sea water at different landscape positions and formation histories while CH4 was inhibited independently of the landscape position. Those results highlight the need to consider local hydrology and landscape history in future GHG projections for coastal permafrost
Adjusting the management of the Antarctic krill fishery to meet the challenges of the 21st century
Get PDFAntarctic krill (Euphausia superba) is the central prey species in the Southern Ocean food web, supporting the largest and fastest-growing fishery in the region, managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Climate change is threatening krill populations and their predators, while current catch limits do not take into account climate variability or krill population dynamics. In 2024, CCAMLR was unable to renew its spatial catch limits, highlighting the urgent need for improved management of the krill fishery to prevent any harm to the Southern Ocean ecosystem. To address this, we propose a management framework that integrates variability in krill recruitment and key pathways between spawning and nursery areas-a krill stock hypothesis-to inform decisions on catch limits and conservation measures. Implementing this approach will require targeted data collection, which we propose can be achieved through a multisector collaborative network that combines traditional and new technologies, including the use of fishing vessels as data collection platforms. We use case studies to demonstrate how fisheries can contribute to data collection while promoting sustainable management. A major challenge in this effort is securing long-term funding for data collection, which is critical for managing climate-sensitive populations of high commercial interest. We therefore recommend using the industry as a source of funding, research platform and data provider, alongside national research funding opportunities. Given the fundamental role of krill in the Southern Ocean ecosystem, its decline would have cascading effects on predators and essential ecosystem services
Large driftwood accumulations along arctic coastlines and rivers
Get PDFDriftwood deposits along Arctic coastlines play key ecological roles and serve as indicators of past environmental conditions. Yet, there is a lack of knowledge regarding large-scale distribution patterns, which are important to assess its ecological and geomorphic impacts and carbon stocks. Here, we present a systematic mapping of Arctic driftwood in the North American low Arctic using PlanetScope nano-satellite imagery. We identify 19,717 driftwood deposits covering 22,960,000 m2 . Driftwood accumulates in clusters near major river deltas, strongly correlating with boreal forest cover within river catchments. Accumulation declines sharply beyond 200 km from river mouths, challenging current narratives of predominantly long-range redistribution. We compare the performance of driftwood-mapping using PlanetScope imagery with sub-metre aerial imagery. Our method underestimates the total driftwood area by 23.18% but captures large deposits with high accuracy (-4.28% bias). Our assessment highlights the abundance of driftwood on Arctic coastlines and forms a baseline for exploring its temporal variability across large regions, its role in coastal erosion mitigation, and its importance as a carbon sink
Morphomolecular studies of Ceratocorys species (Dinophyceae, Gonyaulacales, Protoceratiaceae) reveal that Ceratocorys armata, C. gourretii, and C. horrida are conspecific and should be considered formae of C. horrida
No full textCeratocorys armata, C. gourretii, and C. horrida have historically been treated as distinct species based on morphology. Both field samples and cultured strains, however, exhibit continuous morphological variation and intergradations between these taxa. Here, strains from Viet Nam, Japan (Pacific Ocean), and France (Mediterranean Sea, Atlantic Ocean) were analyzed using integrated morphomolecular approaches. Cultured strains revealed morphological intergradations from C. horrida to C. armata and from C. armata to C. gourretii. Phylogenetic analysis based on the ITS1-5.8S-ITS2 rDNA region sequences and the SSU (18S) and LSU (28S) nuclear rDNA gene sequences confirmed the genetic identity of these three taxa for these markers. The ITS2 secondary structure comparisons-including C. malayensis from Viet Nam and Malaysia-further supported their conspecificity, while validating C. malayensis as a distinct species. Based on these data, we have proposed to treat them as formae: C. horrida f. horrida, C. horrida f. armata, and C. horrida f. gourretii. Furthermore, our results indicated that C. malayensis strains from Viet Nam are non-toxic. We have also provided morphological descriptions and illustrations of C. bipes and C. magna, two species rarely reported in the Asia-Pacific region, enhancing the taxonomic clarity of the genus
Preface to the Annals of Glaciology Collection ‘Sea Ice Across Temporal and Spatial Scales’
Get PDFAnnals of Glaciology Collection ‘Sea Ice Across Temporal and Spatial Scales’ contains 21 timely
contributions about sea-ice properties and processes, considering its variability and change on
various temporal and spatial scales, from the micro- to the global scale. These are most relevant
given the rapid retreat of Arctic and Antarctic sea ice. Many of the included papers were also
presented at the International Glaciology Society’s International Symposium on Sea Ice Across
Temporal and Spatial Scales, which took place in Bremerhaven, Germany, in June 2023
Relationship of physical and mechanical properties of sea ice during the freeze-up season in Nansen Basin
Get PDFSea-ice properties, such as porosity and strength, can have significant spatial variability at small scales. Quantifying this variability may give better estimates of the ice properties and their interrelation. Additionally, correlating in situ ice strength measurements and ice properties, including porosity, may improve understanding of the factors influencing ice strength. This paper presents measurements of sea-ice properties and strength on first- and second-year sea ice during the GoNorth expedition to the Arctic Ocean in October 2022. In situ borehole indentation measurements were co-located with measurements of physical properties, and the meter-scale variability of the physical properties and strength was investigated. Bulk density values found from hydrostatic weighing were 911 ± 5 kg m−3 for first-year and 904 ± 5 kg m−3 for second-year ice, with significantly less uncertainty than density values from the mass/volume method or from freeboard/draft measurements. The second-year ice was relatively saline, with a mean bulk salinity of 3.1 ± 0.5, and the ice was desalinated in the upper and lower 0.2 m. The bulk gas fraction in the second-year ice was 2.5 ± 0.5 %, similar to the first-year ice gas fraction of 2.8 ± 0.5 %. Gas fractions up to 6.5 % were observed in the second-year ice without any obvious correlation with the brine fraction. The second-year ice had larger spatial variability in thickness, porosity, grain structure, and ice strength compared to the first-year ice. Variability in bulk density and gas fraction were similar for first- and second-year ice, as the larger variability was mostly seen below the upper 0.4 m of the second-year ice. The borehole strength was 26.0 ± 4.4 MPa for first-year and 41.0 ± 12.1 MPa for second-year ice. There were indications that the total microporosity at indentation depth was related to in situ borehole strength (
= 0.82), and that brine volume was the most influential parameter. The relative variability in the local microporosity in the second-year ice (0.43) was greater than the relative variability in borehole strength (0.27), while the opposite was true for the first-year ice (0.09 versus 0.17)
Arctic Ocean Dynamical Downscaling Data for Understanding Past and Future Climate Change
Get PDFThe Arctic is one of Earth’s regions highly susceptible to climate change. However, in situ long-term observations used for climate research are relatively sparse in the Arctic Ocean, and current climate models exhibit notable biases in Arctic Ocean simulations. Here, we present an Arctic Ocean dynamical downscaling dataset, obtained from the global ocean-sea ice model FESOM2 with a regionally refined horizonal resolution of 4.5 km in the Arctic region, which is driven by bias-corrected surface forcings derived from a climate model. The dataset includes 115 years (1900–2014) of historical simulations and two 86-year future projection simulations (2015–2100) for the SSP2-4.5 and SSP5-8.5 scenarios. The historical simulations demonstrate substantially reduced biases in temperature, salinity and sea-ice thickness compared to CMIP6 climate models. Common biases in the representation of the Atlantic Water layer found in climate model simulations are also markedly reduced in the dataset. Serving as a crucial long-term data source for climate change assessments and scientific research for the Arctic Ocean, this dataset provides valuable information for the scientific community
Genomic comparison of the temperate coral Astrangia poculata with tropical corals yields insights into winter quiescence, innate immunity, and sexual reproduction
Get PDFFacultatively symbiotic corals provide important experimental models to explore the establishment, maintenance, and breakdown of the mutualism between corals and members of the algal family Symbiodiniaceae. Here, we report the de novo chromosome-scale genome assembly and annotation of the facultatively symbiotic, temperate coral Astrangia poculata. Though widespread segmental/tandem duplications of genomic regions were detected, we did not find strong evidence of a whole-genome duplication event. Comparison of the gene arrangement between As. poculata and the tropical coral Acropora millepora revealed considerable conserved colinearity despite ∼415 million years of divergence. Gene families related to sperm hyperactivation and innate immunity, including lectins, were found to contain more genes in Ac. millepora relative to As. poculata. Sperm hyperactivation in Ac. millepora is expected given the extreme requirements of gamete competition during mass spawning events in tropical corals, while lectins are important in the establishment of coral–algal symbiosis. By contrast, gene families involved in sleep promotion, feeding suppression, and circadian sleep/wake cycle processes were expanded in As. poculata. These expanded gene families may play a role in As. poculata's ability to enter a dormancy-like state (winter quiescence) to survive freezing temperatures at the northern edges of the species' range