Alfred Wegener Institute for Polar and Marine Research
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Polychaete community distribution: the challenge of predicting functional and taxonomic patterns using bioregionalization approaches
Get PDFThe extended Weddell Sea (WS) shelf region, including the Antarctic Peninsula, is increasingly threatened by effects of climate change. In order to establish conservation strategies and forecast the benthic diversity under changing environmental conditions, it is crucial to understand the benthic community composition, distribution and their relationships to abiotic drivers. However, the limited accessibility in such remote areas results in scarce biological data, forcing the use of environmental surrogates, used for defining habitats (Jerosch et al. 2018), to identify infauna distribution. Polychaetes are a dominant faunal group in the WS soft-bottom ecosystems, contributing up to 50% to the total macrobenthic abundance (Säring et al. 2022), with a high functional diversity. However, their distribution patterns, particularly in relation to ecological drivers in the WS are poorly understood.
Here, we describe polychaete communities including their taxonomy and functional identity at the Antarctic Peninsula and the Filchner Trough region related to sea-ice cover and benthic food regimes. We further present the attempt to fit their distribution to bioregionalization based on environmental parameters. We used point data of fauna, sediment (grain size, TOC, TN, pigment content) and of the water column (temperature, salinity, chlorophyll a) from three expeditions (PS81, PS96, PS118) with the RV Polarstern, ice-cover data (2010–2019) extracted from remote sensing imagery, as well as nine environmental raster data sets (e.g. sea-ice cover, TOC, current speed). We observed 34 polychaete families that were grouped into 14 functional groups based on categories. Using cluster analysis we identified 6 taxonomic and 5 functional community types. Ice-cover variation and TOC were identified as the best suitable environmental parameters explaining the variation of both taxonomic (39%) and functional (45%) community compositions. Although the four bioregions defined by the k-means cluster algorithm could not explain the complex distribution patterns of the taxonomic or of the functional communities, we could highlight potentially vulnerable areas across the WS, e.g. the Filchner Trough region with heterogenous community compositions. We assume that the different resolution of input data, and insufficient fauna data density compared to vast survey areas were limiting factors to run reliable models combining biological and physical information. Our findings underscore the relevance of filling spatial gaps of infauna sampling and environmental data to apply advanced models, in order to specify reliable conservation strategies for vulnerable areas
The Expedition PS140 of the Research Vessel POLARSTERN to the Cooperation Sea and Davis Sea in 2023/2024
Get PDFTowards semi-quantification of DOM: isomer separation with LC-FT-ICR-MS combined with a post-column infusion of standard.
Get PDF10.1039/D4AN00119
Probabilistic multi-parameter Backus-Gilbert method - Application to density inversion
Get PDFWe present an adaptation of the Backus–Gilbert method that enables (i) the incorporation of arbitrary prior knowledge and (ii) the solution of multiparameter inverse problems, providing a tunable balance between spatial resolution, inference errors and interparameter trade-offs. This yields a powerful approach for solving a class of inverse problems where the forward relation is linear or weakly nonlinear. The method rests on a probabilistic reformulation of Backus–Gilbert inversion and the solution of an optimization problem that maximizes deltaness while minimizing interparameter trade-offs. Applying the theory to multimode surface wave dispersion data collected by distributed acoustic sensing on the Northeast Greenland Ice Stream, we show that density in the firn layer may be constrained directly and without the need for scaling relations to depths of around ten metres, provided that dispersion data up to at least the third overtone of Rayleigh waves are available in the 10–50 Hz frequency band. The limiting factor that prevents the resolution of density at greater depth is data quality. Hence, progress on the direct inference of density could be made by repeated experiments or higher signal-to-noise ratios that would require better coupling and shielding of fibre-optic cables from wind and temperature fluctuations
An analysis of air-sea gas exchange for the entire MOSAiC Arctic drift
Get PDFSea ice cover influences the generation of surface ocean turbulence in ways that sometimes enhance, but mostly inhibit air-water gas exchange. Inhibition happens as ice cover reduces wind fetch, enhancement occurs when haline convection or sea ice drift creates additional surface turbulence. We used the bulk turbulence relationships within the Wave Age Gas Transfer model to estimate air-sea gas transfer velocity (kWAGT), based on sea ice cover and turbulence conditions in the ice-ocean boundary layer, throughout a year-long (2019–2020) ice drift campaign in the central Arctic Ocean. During the drift, sea ice cover averaged >97%, with a minimum of 58%, and boundary layer shear played a dominant role in the turbulence budget. Modeled turbulent kinetic energy dissipation was compared against 167 in-situ profiles of ocean dissipation to evaluate model performance and explore related processes. The modeled dissipation and observed dissipation profiles, averaged over 0–4 m depth, agreed within 1% of each other, with a mean dissipation of 5.8 × 10-7 W kg-1. Examining individual dissipation estimates by surface conditions, however, revealed poorest agreement in leads, especially leads covered by thin ice, which the model cannot detect. Dissipation from the model was used to produce a time series of kWAGT, revealing an average velocity of 0.034 m d-1 or 1% of the global average for the open ocean. Comparison with a widely used wind speed parameterization for gas exchange showed that wind speed scaling would overestimate k during 92% of the drift by 3.5 times on average, demonstrating how fetch limitation can suppress gas exchange, even as open water increases. These results suggest that photic zone processes, under-ice blooms, and attendant cycling of CO2 and O2 as well as CH4 can remain isolated from the atmosphere for an entire annual cycle in the central Arctic
An Assessment of CO2 Storage and Sea‐Air Fluxes for the Atlantic Ocean and Mediterranean Sea Between 1985 and 2018
Get PDFAs part of the second phase of the Regional Carbon Cycle Assessment and Processes project (RECCAP2), we present an assessment of the carbon cycle of the Atlantic Ocean, including the Mediterranean Sea, between 1985 and 2018 using global ocean biogeochemical models (GOBMs) and estimates based on surface ocean carbon dioxide (CO2) partial pressure (pCO2 products) and ocean interior dissolved inorganic carbon observations. Estimates of the basin-wide long-term mean net annual CO2 uptake based on GOBMs and pCO2 products are in reasonable agreement (−0.47 ± 0.15 PgC yr−1 and −0.36 ± 0.06 PgC yr−1, respectively), with the higher uptake in the GOBM-based estimates likely being a consequence of a deficit in the representation of natural outgassing of land derived carbon. In the GOBMs, the CO2 uptake increases with time at rates close to what one would expect from the atmospheric CO2 increase, but pCO2 products estimate a rate twice as fast. The largest disagreement in the CO2 flux between GOBMs and pCO2 products is found north of 50°N, coinciding with the largest disagreement in the seasonal cycle and interannual variability. The mean accumulation rate of anthropogenic CO2 (Cant) over 1994–2007 in the Atlantic Ocean is 0.52 ± 0.11 PgC yr−1 according to the GOBMs, 28% ± 20% lower than that derived from observations. Around 70% of this Cant is taken up from the atmosphere, while the remainder is imported from the Southern Ocean through lateral transport
A large-scale transcontinental river system crossed West Antarctica during the Eocene
Get PDFExtensive ice coverage largely prevents investigations of Antarctica’s unglaciated past. Knowledge about environmental and tectonic development before large-scale glaciation, however, is important for understanding the transition into the modern icehouse world. We report geochronological and sedimentological data from a drill core from the Amundsen Sea shelf, providing insights into tectonic and topographic conditions during the Eocene (~44 to 34 million years ago), shortly before major ice sheet buildup. Our findings reveal the Eocene as a transition period from >40 million years of relative tectonic quiescence toward reactivation of the West Antarctic Rift System, coinciding with incipient volcanism, rise of the Transantarctic Mountains, and renewed sedimentation under temperate climate conditions. The recovered sediments were deposited in a coastal-estuarine swamp environment at the outlet of a >1500-km-long transcontinental river system, draining from the rising Transantarctic Mountains into the Amundsen Sea. Much of West Antarctica hence lied above sea level, but low topographic relief combined with low elevation inhibited widespread ice sheet formation.</jats:p
Distribution of Arnoux's beaked whales (Berardius arnuxii)
Get PDFArnoux's beaked whales (Berardius arnuxii) are generally considered to be uncommon to rare, and likely to prefer deep oceanic waters of the Southern Hemisphere. During many top-predator surveys in the Southern Ocean since 1988 we did not sight the species. However, in April 2022 we encountered three groups in the marginal sea-ice zone of the Weddell Sea. This study provides detailed descriptions of the sighted animals and their environment and report on unpublished sightings of this species from 1986 to 1998. A search of published information on the distribution of the species revealed 108 documented sightings with a total of 1,125 individuals. In combination these sources of information for the Southern Ocean, suggest a frequent occurrence in ice-covered waters, often close to the continental coast and edges of fast ice and ice-shelves. North of 60 S, in the temperate regions of the Southern Hemisphere, the species was also regularly sighted near continents, even far inshore, in fjords surrounded by land
Publisher Correction: Projected poleward migration of the Southern Ocean CO2 sink region under high emissions
Get PDFCorrection to: Communications Earth & Environmenthttps://doi.org/10.1038/s43247-024-01382-y, published online 02 May 2024 The original version of this article omitted one of the affiliations of the corresponding author “Precious Mongwe”. The missing affiliation “National Institute for Theoretical and Computational Sciences (Nitec), Cape Town, South Africa” has been added. In the original version of this article, several reference numbers were incorrect. Specifically: In the section “Results”, subsection “Mechanisms of air-sea CO2 fluxes in the present climate”, third paragraph, references in the sentence starting “Some studies have linked this temperature bias to discrepancies”, were incorrectly given as “40,41”, whereas “40” is correct. In the section “Discussion”, second paragraph, references in the sentence starting “Relatively low model skill” were incorrectly given as “35, 47–49” following “biases in sea ice” whereas “36, 47–49” is correct; as “38,40” following “impact on heat fluxes”, whereas “38,40” is correct; and as “37,50” following “the AMOC”, whereas “37” is correct. In the section “Discussion”, last paragraph, the reference in the sentence starting “On the other hand, anthropogenic ice sheet melt in Antarctica” was incorrectly given as “41”, whereas “58” is correct. In the following sentence, starting “Moreover, ice sheet melt”, references were incorrectly given as “38,41”, whereas “58,59” is correct. In the section “Methods”, subsection “Earth System Models”, first sentence, the reference following “climate scenario” was incorrectly given as “59”, whereas “60” is correct. In the section “Methods”, subsection “Observation-based pCO2 -products”, first sentence, the reference following “Sea-Flux dataset” was incorrectly given as “60”, whereas “61” is correct; in the following sentence, references were incorrectly given as “61” following “CMEMS-LSCE-FFNN”, whereas “62” is correct; as “63” following “CSIR-ML6”, whereas “63” is correct; as “63” following “Jena-MLS”, whereas “64” is correct; as “64” following “JMA-MLR”, whereas “59” is correct; as “65” following “MPI-SOMFFN” whereas “65” is correct; and as “66” following “NIES-FNN” whereas “67” is correct. In the sentence starting “All methods use”, the reference following “SOCAT version 2020 or later” was incorrectly given as “66” whereas 68 is correct. In the sentence starting “Further, we use”, the reference following “World Ocean Atlas” was incorrectly given as “67”, whereas “69” is correct. In the next sentence starting “We use a monthly”, the references following “mixed layer depth by” were incorrectly given as “68,69”, whereas just “70” is correct. In the next sentence starting “Lastly, we use DIC”, the reference following “dissolved inorganic carbon dataset” was incorrectly given as “41”, whereas “71” is correct. In the section “Methods”, subsection “DIC decomposition”, first sentence, references following “(i.e., primary production and respiration)” were incorrectly given as “70,71”, whereas “72,73” is correct; in the next sentence starting “DIC is consumed”, references following “as regenerated DIC” were incorrectly given as “70,72”, whereas “72,74” is correct; in the sentence starting “In this study, we decompose”, references following “regenerated following” were incorrectly given as “70,72”, whereas “72,74” is correct; in the following sentence starting “Regenerated DIC”, the reference following “(Eq. 8)” was incorrectly given as “72”, whereas “73” is correct; in the following sentence starting “Since our analysis is focussed”, references following “air-sea exchange is complete (Cdis)” were incorrectly given as “70,73–75”, whereas “72,74–75” is correct. These reference errors have been corrected in the HTML and PDF versions of the article. In addition, the original version of this Article omitted a reference ‘Olsen, A. et al. GLODAPv2.2019—an update of GLODAPv2. Earth Syst. Sci. Data11, 1437–1461, https://doi.org/10.5194/essd-11-1437-2019 (2019). This has been added as reference 77
The deglacial history of 79N glacier and the Northeast Greenland Ice Stream
Get PDFThe Northeast Greenland Ice Stream (NEGIS) is the main artery for ice discharge from the northeast sector of the Greenland Ice Sheet (GrIS) to the North Atlantic. Understanding the past, present and future stability of the NEGIS with respect to atmospheric and oceanic forcing is of global importance as it drains around 17% of the GrIS and has a sea-level equivalent of 1.6 m. This paper reconstructs the deglacial and Holocene history of Nioghalvfjerdsbræ (or 79N Glacier); a major outlet of the NEGIS. At high elevation (>900 m asl) autochthonous blockfield, a lack of glacially moulded bedrock and pre LGM exposure ages point to a complex exposure/burial history extending back over half a million years. However, post Marine Isotope Stage 12, enhanced glacial erosion led to fjord incision and plateaux abandonment. Between 900 and 600 m asl the terrain is largely unmodified by glacial scour but post LGM erratics indicate the advection of cold-based ice through the fjord. In contrast, below ∼600 m asl Nioghalvfjerdsfjorden exhibits a geomorphological signal indicative of a warm-based ice stream operating during the last glacial cycle. Dated ice marginal landforms and terrain along the fjord walls show initial thinning rates were slow between ∼23 and 10 ka, but post-10 ka it is evident that Nioghalvfjerdsfjorden deglaciated extremely quickly with complete fjord deglaciation below ∼500 m asl between 10.0 and 8.5 ka. Both increasing air and ocean temperatures were pivotal in driving surface lowering and submarine melt during deglaciation, but the final withdrawal of ice through Nioghalvfjerdsfjorden was facilitated by the action of marine ice sheet instability. Our estimates show that thinning and retreat rates reached a maximum of 5.29 ma−1 and 613 ma−1, respectively, as the ice margin withdrew westwards. This would place the Early Holocene disintegration of this outlet of the NEGIS at the upper bounds of contemporary thinning and retreat rates seen both in Greenland and Antarctica. Combined with recent evidence of ice stream shutdown during the Holocene, as well as predictions of changing ice flow dynamics within downstream sections of the NEGIS catchment, this suggests that significant re-organisation of the terminal zone of the ice stream is imminent over the next century