Alfred Wegener Institute for Polar and Marine Research
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Future Arctic: how will increasing coastal erosion shape nearshore planktonic food webs?
Get PDFArctic regimes. Currently, warming accelerates the erosion of permafrost coasts and the associated discharge of sediment, carbon, and nutrients into the Arctic Ocean. However, the impacts of coastal erosion on planktonic food webs remain understudied. We aimed to (1) understand how coastal erosion impacts nearshore carbon, nutrient, and light regimes; (2) investigate the effects on primary production and energy transfer; and (3) predict how increased erosion will impact the productivity of consumers, and the overall food web interactions. We found that sediment discharge increases turbidity (darkening). This darkening is expected to hamper phytoplankton productivity, while additional carbon input will provide bacteria with direct energy sources, and shift the balance between basal autotrophic and heterotrophic production. Since the heterotrophic pathway has a lower efficiency, its dominance might negatively affect mesozooplankton. Increased Arctic coastal erosion might therefore influence planktonic food webs by changing mechanisms of energy mobilization and transfer to higher trophic levels
Coupling ecological concepts with an ocean-colour model: Parameterisation and forward modelling
Get PDFIn the first part of this paper series (Sun et al., 2023), we developed an ecological model that partitions the total chlorophyll-a concentration (Chl-a) into three phytoplankton size classes (PSCs), pico-, nano-, and microplankton. The parameters of this model are controlled by sea surface temperature (SST), intended to capture shifts in phytoplankton size structure independently of variations in total Chl-a. In this second part of the series, we present an Ocean Colour Modelling Framework (OCMF), building on the classical Case-1 assumption, that explicitly incorporates our ecological model. The OCMF assumes the presence of the three PSCs and the existence of an independent background of non-algal particles. The framework assumes each phytoplankton group resides in a distinct optical environment, assigning chlorophyll-specific inherent optical properties to each group, both directly (phytoplankton) and indirectly (non-algal particulate and dissolved substances). The OCMF is parameterised, validated, and assessed using a large global dataset of inherent and apparent optical properties. We use the OCMF to explore the influence of variations in temperature and Chl-a on phytoplankton size structure and its resulting effects on ocean colour. We also discuss applications of the OCMF, such as its potential for inverse modelling and phytoplankton climate trend detection, which will be explored further in subsequent papers
Late Quaternary permafrost dynamics of the Beringian land bridge - Sediment and ground-ice studies on the Baldwin Peninsula (West Alaska) during spring and summer 2024
Get PDFIn order to investigate the late Pleistocene permafrost, landscape, and climate dynamics on the eastern side of the Beringian land bridge in the spring and summer of 2024, during the expedition “West Alaska 2024,” field studies were carried out on the Baldwin Peninsula. Holocene thermokarst and cover deposits (MIS 1), late Pleistocene Yedoma Ice Complex deposits (MIS 3/2), and older interglacial and glaciofluvial deposits (likely MIS 5e and older) were investigated. This research complements and connects earlier studies across Beringia, i.e., in north-eastern Siberia, on the Seward Peninsula, near Fairbanks, and in the Klondike.
Frozen sediments and ground ice (ice wedges and intra-sedimental pore and segregated ice) were sampled and described. First analyses of the ice content were carried out during the expedition. Analyses of stable water isotopes of ground ice, stable carbon and nitrogen isotopes of organic matter, age determination (radiocarbon and optically and infrared stimulated luminescence), determination of organic matter composition, analysis of biomarkers, sediment properties, and studies of paleoecology are currently in progress.
Our poster will present field data (permafrost profiles, sediment, and ground ice properties) and first laboratory results from the expedition near Kotzebue on the Baldwin Peninsula. The external conditions during the two phases of the expedition were excellent. We used snowmobiles in spring, as well as boats and four-wheeled vehicles to reach the outcrops in summer. In Kotzebue, we had very good conditions for sample processing and initial laboratory work, including freezer capacity to keep all the samples frozen
Expeditions to Antarctica: ANT-Land 2023/24 NEUMAYER STATION III, Kohnen Station and Field Campaigns
Get PDFDistribution of organic-walled dinoflagellate cysts in surface sediments of San Matías Gulf (North Patagonian Shelf, Argentina): a seed bank for potential harmful algal blooms
Get PDFIn the southwestern Atlantic Ocean, the San Matías Gulf (SMG) is a semi-enclosed coastal ecosystem (40.5°-42.5°S; 63.5°-65.5°W) with considerably greater depths (up to 190 m) than the adjacent continental shelf (~70 m). A thermohaline frontal system develops in a latitudinal position around 41.8°S from spring to summer leading to high biological productivity in this relevant area for fisheries. In this study, twelve surface sediment samples from the SMG were analyzed for the determination of species and distribution of organic-walled dinoflagellate cysts (dinocysts) in relation to physico-chemical conditions (grain-size of sediments, water column stability, spring sea-surface temperature, salinity, and nitrate concentration). Thirty different taxa of dinocysts were recorded, of which twenty-eight were identified to species level. The strong dominance of Operculodinium centrocarpum (cyst of Protoceratium reticulatum, a yessotoxin producer in the Argentine Sea) accompanied by minor abundances of other phototrophic and heterotrophic taxa characterized all assemblages. Cysts of Alexandrium catenella, which is known as a saxitoxin-producing species in the gulf, were also recorded across sites. The highest absolute abundances of dinocysts occurred at the inner gulf, north of the latitudinal front. For this area we argue that multi-year fluxes of phototrophic dinocysts to the silty bottom are enhanced by the great production of vegetative cells in the seasonally stratified water column, the encystment strategies of the dominant species and the particular physical oceanographic characteristics. Although densities of both phototrophic and heterotrophic cysts were lower in the coarser sediments near the mouth of the gulf, the relative abundances of heterotrophic cysts were higher. The preference of heterotrophic species reflects higher nitrate concentrations, which increase the primary production and thus food availability for heterotrophs.</jats:p
Organic carbon, mercury, and sediment characteristics along a land–shore transect in Arctic Alaska
Get PDFClimate warming in the Arctic results in thawing permafrost and associated processes like thermokarst, especially in ice-rich permafrost regions. Since permafrost soils are one of the largest organic carbon reservoirs of the world, their thawing leads to the release of greenhouse gases due to increasing microbial activity with rising soil temperature, further exacerbating climate warming. To enhance the predictions of potential future impacts of permafrost thaw, a detailed assessment of changes in soil characteristics in response to thermokarst processes in permafrost landscapes is needed, which we investigated in this study in an Arctic coastal lowland. We analysed six sediment cores from the Arctic Coastal Plain of northern Alaska, each representing a different landscape feature along a gradient from upland to thermokarst lake and drained basin to thermokarst lagoon in various development stages. For the analysis, a multiproxy approach was used, including sedimentological (grain size, bulk density, ice content), biogeochemical (total organic carbon (TOC), TOC density (TOCvol), total nitrogen (TN), stable carbon isotopes (δ13C), TOC/TN ratio, mercury (Hg)), and lipid biomarker (n-alkanes, n-alkanols, and their ratios) parameters. We found that a semi-drained state of thermokarst lakes features the lowest OC content, and TOC and TN are generally higher in unfrozen deposits, hinting at a more intact state of organic matter. Indicated by the average chain length (ACL), δ13C, Paq, and Pwax, we found a stronger influence of aquatic organic matter (OM) in the OM composition in the soils covered by water compared to those not covered by water. Moreover, the results of the δ13C, TOC/TN ratio, and CPI indicate that the saline deposits contain stronger degraded OM than the deposits not influenced by saltwater. Additionally, we found positive correlations between the TOC and TOCvol and the Hg content in the deposits. The results indicate that thermokarst-influenced deposits tend to accumulate Hg during thawed periods and thus contain more Hg than the upland permafrost deposits that have not been impacted by lake formation. Our findings offer valuable insights into the dynamics of carbon storage and vulnerability to decomposition in coastal permafrost landscapes, reflecting the interplay of environmental factors, landform characteristics, and climate change impacts on Arctic permafrost environments
Depuration kinetics of trinitrotoluene (TNT) and its metabolites in exposed blue mussels (Mytilus edulis L.)
Get PDFExplosives released by dumped warfare material pose a threat to the marine environment and can enter the marine food web. 2,4,6-Trinitrotoluene (TNT) is one of the most used explosives in munitions and is, therefore, of special interest. To test the uptake, depuration, and potential biotransformation of TNT, common blue mussels (Mytilus edulis) from the German North Sea were exposed to different TNT concentrations in two laboratory experiments (first experiment, 48-h exposure to TNT concentrations of 0, 0.625, 1.25, and 2.5 mg/L; second experiment, 24-h exposure to 0 and 5 mg/L deuterated TNT) followed by recovery phases in clean artificial seawater (first experiment, 60-h recovery; second experiment, 12-h recovery). Water samples and mussel soft bodies were analyzed for TNT and its metabolites 2-amino-4,6-dinitrotoluene (2-ADNT), 4-amino-2,6-dinitrotoluene (4-ADNT), and 2,4-diamino-6-nitrotoluene (2,4-DANT) using Gas Chromatography – Tandem Mass Spectrometry (GC-MS/MS) techniques. The results showed a continuous uptake of dissolved TNT during exposure and a rapid depuration during the recovery phase, independent of the original TNT exposure concentrations. Furthermore, evidence for the biotransformation of TNT is shown by the presence of labelled ADNTs both in mussel soft bodies analyzed within the recovery phase and in water sampled during the recovery phase. Overall, 57% to 76% of the measured concentration was biotransformed within the first 4 h after the exposure.</jats:p
Seasonal vertical migration of large polar copepods reinterpreted as a dispersal mechanism throughout the water column
Get PDFSeasonal vertical migration of large lipid-rich copepods is often described as a mass descent of animals when primary production ceases, with important implications for mesopelagic food webs and global carbon sequestration. This view ignores the existence of surface-resident individuals, but here we show that non-migrants can form a substantial part of the populations of polar migrant species. In the Central Arctic Ocean, the biomass-dominant Calanus hyperboreus was evenly distributed throughout the water column from November 2019 to March 2020, with ~20% of subadults and adult females remaining in the upper 200 m and ~41% migrating to 1000–2000 m. These vertical positions aligned with differences in the copepods’ cholesterol content, which can enhance the tissue density at higher temperatures. Gonad development and the vertical distribution of their offspring indicate that both non-migrant and migrant females contribute to the population recruitment. We reinterpret copepod seasonal migration as a bet-hedging strategy that balances nutritional benefits near the surface with survival benefits at depth, and thereby contributes to the species’ resilience under climatic change
More realistic plankton simulation models will improve projections of ocean ecosystem responses to global change
Get PDFPlankton models form the core of marine ecosystem simulators, with uses from regional resource and ecosystem management to climate change projections. In this Perspective, we suggest that stronger alignment of models with empirical knowledge about plankton physiology, diversity and trophic roles will improve model utility and the reliability of their outputs regarding biodiversity, ecophysiology, trophic dynamics and biogeochemistry. We recommend key steps to resolve the disconnect between empirical research and simulation models accounting for well-established plankton processes with an aim to increase the utility of such models for applied uses. A central challenge is characterizing the complexity of plankton diversity and activity in ways that are amenable to model incorporation. We argue that experts in empirical science are best placed to advise the development of next-generation models to address these challenges, and we propose a series of actions to achieve that engagement, including involvement of these experts in the design and exploitation of plankton digital twins
Plankton communities today and tomorrow—potential impacts of multiple global change drivers and marine heatwaves
Get PDFIn the context of global change, marine organisms are subjected not only to gradual changes in abiotic parameters, but also to an increasing number of extreme events, such as heatwaves. However, we still know little about the influence of heatwaves on the structure of marine communities, and experimental studies are needed to test the impact of heatwaves alone and in combination with other environmental drivers. Here, we conducted a mesocosm experiment to assess the potential impact of heatwaves on plankton communities, which we did under ambient and future environmental conditions. To simulate future environmental conditions, we simultaneously manipulated temperature and pH based on IPCC predictions for 2100, and dissolved N : P ratios based on the conditions expected in European coastal zones. While we did not observe any effects of simulated heatwaves on phytoplankton abundances, we identified that future environmental conditions may favor smaller phytoplankton species and that additional heatwaves may especially favor small phytoflagellates and coccolithophores. We also observed that future environmental conditions may reduce the abundances and modify the species composition of bacterioplankton, microzooplankton, and mesozooplankton, and that heatwaves may exacerbate these effects. Using a unique approach to examine the potential impacts of heatwaves under current and future environmental conditions on a natural multi-trophic marine plankton community, we show that the combination of multiple global change drivers has the potential to perturb the entire basis of marine food webs