Alfred Wegener Institute for Polar and Marine Research
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The Alexandrium tamarense species complex in Kuwait’s waters (Arabian/Persian Gulf, northern Indian Ocean) with the description of Alexandrium arabiense sp. nov
No full textExtraordinary bloom of toxin-producing phytoplankton enhanced by strong retention on the offshore Patagonian shelf
Get PDFAbstract. The extensive Patagonian continental shelf in the Atlantic Ocean is renowned for its high productivity associated with nutrient-rich waters that fertilize massive phytoplankton blooms, especially along the shelf-break frontal system. Growing evidence reflects this ecosystem as a hotspot for harmful algal blooms (HABs). Whether these HABs reach coastal areas or are exported to the adjacent ocean basin by energetic edge currents remains unexplored. During two oceanographic cruises in spring 2021, a bloom of dinoflagellates of the Amphidomataceae family was sampled over the outer shelf with a 10 d interval, at stations 40 km apart. The bloom was first sampled on 16 November, with 32 ×106 cells L−1, and was still persistent on 25 November, with 14 ×106 cells L−1. The magnitude of this bloom is a global record for this group so far reported in the literature. The toxin azaspiracid-2 (AZA-2) was detected in both stages of the bloom, with values up to 2122 pg L−1. The most likely source of AZA-2 was Azadinium spinosum ribotype B. The bloom developed in vertically stable waters (60 m mixed layer depth) with elevated chlorophyll concentration. Water retention and the presence of fronts induced by horizontal stirring controlled the persistence and trajectory of the bloom in a localized area over the continental shelf, as evidenced by analysis of geostrophic surface currents, Lyapunov coefficients, and particle advection modelling. These findings underscore the importance of monitoring HABs in offshore environments and the need to understand biophysical interactions that govern bloom taxa assemblages and transport pathways.
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Preliminary paleoenvironmental analysis and luminescence dating of upper Middle Pleistocene permafrost deposits of the Ulakhan Sular Formation, Adycha River, east Siberia
Get PDFUlakhan Sular provides one of the largest natural stratigraphic sections through ancient permafrost deposits in the Batagay-Betenkes region of the Yana Uplands of western Beringia, but their depositional environment, age, and paleoenvironmental significance are uncertain. To address these uncertainties, we report the results of reconnaissance observations of the stratigraphy, sedimentology, paleosols and soil-like bodies, plant and insect macrofossils, and geochronology of the permafrost deposits at the stratotype section of the Ulakhan Sular Formation. Sedimentologically, this formation is dominated by well-sorted, fine to very fine sand that contains fluvial, aeolian, and permafrost sedimentary structures consistent with deposition near the paleo-Adycha River. The fluvio-aeolian deposits have similarities and differences to periglacial fluvio-aeolian and aeolian deposits in modern arctic regions of Canada and Greenland, and Pleistocene deposits in Alaska, China, and northwest Europe. The remarkable thickness of aeolian deposits (∼50 m) at Ulakhan Sular is attributed to abundant local sand sources, ample accommodation space, and intensive aeolian transport and deposition. Optically stimulated luminescence dating of quartz sand and post-infrared-infrared dating of K-feldspar sand suggests deposition of the Ulakhan Sular Formation during late Marine Oxygen Isotope Stage (MIS) 6 or MIS 5. The aeolian sand-sheet deposits are correlated with other cold-climate aeolian sand and silt (loess) deposits in Beringia and southern Siberia, indicating a regional episode of aeolian sand transport and deposition at a similar time to glaciation by the Eastern Siberian Ice Sheet
Past Ocean surface density from planktonic foraminifera calcite &delta 18O
Get PDFAbstract. Density of seawater is a critical property that controls ocean dynamics. Previous works suggest the use of the δ18O calcite of foraminifera as a potential proxy for paleodensity. However, potential quantitative reconstructions were limited to the tropical and subtropical surface ocean and without an explicit estimate of the uncertainty in calibration model parameters. We developed the use of the δ18Oc of planktonic foraminifera as a surface paleodensity proxy for the whole ocean using Bayesian regression models calibrated to annual surface density. Predictive performance of the models improves when we account for inter-species specific differences. We investigate the additional uncertainties that could be introduced by potential evolution of the δ18Oc-density relationship with time (from the last glacial maximum (LGM) to the preindustrial (PI)) through the combination of past isotope enabled climate model simulations and a foraminiferal growth module. We demonstrate that additional uncertainties are weak globally, except for the Nordic Seas region. We applied our Bayesian regression model to LGM and Late Holocene (LH) δ18Oc foraminifera databases to reconstruct annual surface density during these periods. We observe stronger LGM density value changes at low latitudes compared to mid latitudes. These results will be used to evaluate numerical climate models in their ability to simulate ocean surface density during the extreme climatic period of the LGM. The new calibration has great potential to be applied to other past periods and to reconstruct the past temporal evolution of ocean surface density.
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The land–ocean Arctic carbon cycle
No full textAnthropogenic climate warming is amplified in the Arctic, impacting the Arctic carbon cycle and its role in regulating climate and global biogeochemical cycles. In this Review, we provide a quantitative and comprehensive overview of the present-day Arctic carbon cycle across the land–ocean continuum. Terrestrial soil stocks total 877 ± 16 Pg C, with upper marine sediments containing 82 ± 35 Pg C. Overall, the integrated Arctic system is a carbon sink, driven by oceanic uptake of CO2 (127 ± 36 Tg C year−1) and organic carbon burial in shelf sea sediments (112 ± 41 Tg C year–1). Terrestrial systems, including inland waters and disturbance, are a net source of CH4 (38 (21, 53) Tg C year–1) and CO2 (12 (–606, 661) Tg C year–1). The Arctic carbon sink will likely weaken under continued warming, owing to factors such as increased coastal erosion, outgassing of riverine organic carbon and enhanced nearshore carbon turnover lowering shelf sediment burial. Arctic greening and increases in terrestrial carbon sinks will be substantially offset by increases in soil respiration, disturbance from extreme events and enhanced emissions from inland waters. Future research should prioritize enhanced coverage of small catchments and nearshore regions, and inclusion of non-linear responses in biogeochemical models
Effect of temperature and trace metal exposure on early life stages of European flat oysters and Pacific oysters
Get PDFOcean warming and metal pollution pose a threat to coastal ecosystems worldwide. In the German Bight, efforts to restore biogenic reefs using the native European flat oyster (Ostrea edulis) face challenges due to environmental conditions and potential pollutants of the North Sea. Besides O. edulis, the non-native Pacific oyster (Crassostrea gigas) inhabits the North Sea. Larval stages of bivalves are known to be sensitive to pollution. In this study, we investigate the effect of the trace metals copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in combination with water temperatures of 18° and 24°C on the embryo-larval development of C. gigas and acute mortality of C. gigas and O. edulis D-larvae. This multi-stressor approach revealed that Cu was the most toxic metal, regardless of temperature, species or life stage. While elevated temperatures mitigated the negative effects of metal exposure on embryo-larval development, larval mortality was species- and metal-dependent at the tested temperatures. O. edulis D-larvae demonstrated a greater absolute tolerance to metal exposure at both temperatures, but a species comparison showed that O. edulis D-larvae had lower relative tolerance to the combined stress of warming and metal exposure than C. gigas. Based on the resulting toxicity thresholds, an environmental risk assessment for Cu was conducted to identify potentially hazardous areas for O. edulis restoration to be included in future habitat suitability studies and site selection for restoration. The identified areas may also indicate problematic environmental conditions for larval stages of other invertebrate species or fish
Unpacking plastic credits: Challenges to effective and just global plastics governance
Get PDFPlastic credits are marketed as an innovative solution to plastic pollution, yet they mirror the well-documented shortcomings of carbon credits and overlook the unique material complexities of plastics. Effective plastics governance must avoid fragmented, loophole-prone, and inequitable approaches to plastic pollution
Representation of Arctic Winter Atmospheric Boundary Layer Stability Over Sea Ice in CMIP6 Models
Get PDFAbstractThe Arctic winter atmospheric boundary layer often features strong and persistent low‐level stability (LLS), which arises from longwave radiative cooling of the surface during the polar night. This stable stratification results in a positive lapse rate feedback, which is a major contributor to Arctic amplification. A second state, with cloudy conditions, weaker stability, and near‐zero net surface longwave flux is also observed. Previous work has shown that many CMIP5 models fail to appropriately partition water between liquid and ice phases in mixed‐phase clouds, leading to a lack of this cloudy state. In this study, we assess the representation of the Arctic winter atmospheric boundary layer over sea ice in global climate models contributing to the latest phase of the Coupled Model Intercomparison Project (CMIP6). We compare boundary layer process relationships in these models to those in surface‐based and radiosonde observations collected during the MOSAiC (2019–2020) and SHEBA (1997–1998) expeditions, and by North Pole drifting stations (1955–1991). The majority of CMIP6 models fail to realistically represent the cloudy state over winter Arctic sea ice. Despite this, CMIP6 multimodel mean LLS falls within the observational range, and models mostly capture the observed dependence of LLS on near‐surface air temperature and wind speed. CMIP6 models predict a decline in winter LLS with Arctic warming, with mean stability falling below zero by 2100 under the SSP2‐4.5 scenario. Our results highlight the failure to accurately simulate mixed‐phase clouds as an important limitation on representing a realistic Arctic winter boundary layer in many CMIP6 models.</jats:p
Multi-year dynamics of harmful algae in Disko Bay, West Greenland
Get PDFHarmful algal blooms (HABs) increasingly affect Arctic coastal ecosystems, due to hydrographic and bathymetric conditions that support the accumulation of cells and cysts, and coupled with increasing temperatures, extensive bloom events can be easily triggered. However, various harmful algae species have been reported in the past and it is unclear which are most threatening in Greenlandic waters, a region that vitally depend on its fisheries. Here, we explore the diversity and succession of harmful algae by metabarcoding at a multi-year station in Greenlandic coastal waters, offering a comprehensive analysis of species dynamics over time. Dinoflagellates, diatoms and haptophytes, known for their toxin production and potential negative effects on ecosystems and food webs, were regularly detected across years and throughout all sampled months. Yet, results also indicate significant interannual variability in harmful algal occurrences, with high abundances of Alexandrium and increasing abundances of Aureococcus, Prymnesium, and Pseudo-nitzschia. Through a boosted regression tree analysis of the ecological drivers of HABs in Arctic waters, we identified an important role of climate-induced environmental variables such as temperature, salinity, and the number of ice-free days year-1. These findings provide critical baseline data for understanding the future risks of HABs in the Arctic and underscore the importance of ongoing, high-resolution monitoring