Alfred Wegener Institute for Polar and Marine Research
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Winners and losers of Atlantification: The degree of ocean warming affects the structure of Arctic microbial communities
Get PDFPresentation held at the ASLO Aquatic Sciences Meeting 2023
Constraints on simulated past Arctic amplification and lapse rate feedback from observations
Get PDFAbstract. The Arctic has warmed more rapidly than the global mean during the past few decades. The lapse rate feedback (LRF) has been identified as being a large contributor to the Arctic amplification (AA) of climate change. This particular feedback arises from the vertically non-uniform warming of the troposphere, which in the Arctic emerges as strong near-surface and muted free-tropospheric warming. Stable stratification and meridional energy transport are two characteristic processes that are evoked as causes for this vertical warming structure. Our aim is to constrain these governing processes by making use of detailed observations in combination with the large climate model ensemble of the sixth Coupled Model Intercomparison Project (CMIP6). We build on the result that CMIP6 models show a large spread in AA and Arctic LRF, which are positively correlated for the historical period of 1951–2014. Thus, we present process-oriented constraints by linking characteristics of the current climate to historical climate simulations. In particular, we compare a large consortium of present-day observations to co-located model data from subsets that show a weak and strong simulated AA and Arctic LRF in the past. Our analyses suggest that the vertical temperature structure of the Arctic boundary layer is more realistically depicted in climate models with weak (w) AA and Arctic LRF (CMIP6/w) in the past. In particular, CMIP6/w models show stronger inversions in the present climate for boreal autumn and winter and over sea ice, which is more consistent with the observations. These results are based on observations from the year-long Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in the central Arctic, long-term measurements at the Utqiaġvik site in Alaska, USA, and dropsonde temperature profiling from aircraft campaigns in the Fram Strait. In addition, the atmospheric energy transport from lower latitudes that can further mediate the warming structure in the free troposphere is more realistically represented by CMIP6/w models. In particular, CMIP6/w models systemically simulate a weaker Arctic atmospheric energy transport convergence in the present climate for boreal autumn and winter, which is more consistent with fifth generation reanalysis of the European Centre for Medium-Range Weather Forecasts (ERA5). We further show a positive relationship between the magnitude of the present-day transport convergence and the strength of past AA. With respect to the Arctic LRF, we find links between the changes in transport pathways that drive vertical warming structures and local differences in the LRF. This highlights the mediating influence of advection on the Arctic LRF and motivates deeper studies to explicitly link spatial patterns of Arctic feedbacks to changes in the large-scale circulation.
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Marine primary producers in a darker future: a meta‐analysis of light effects on pelagic and benthic autotrophs
Get PDFThe availability of underwater light, as primary energy source for all aquatic photoautotrophs, is (and will further be) altered by changing precipitation, water turbidity, mixing depth, and terrestrial input of chromophoric dissolved organic matter (CDOM). While experimental manipulations of CDOM input and turbidity are frequent, they often involve multiple interdependent changes (light, nutrients, C-supply). To create a baseline for the expected effects of light reduction alone, we performed a weighted meta-analysis on 240 published experiments (from 108 studies yielding 2500 effect sizes) that directly reduced light availability and measured marine autotroph responses. Across all organisms, habitats, and response variables, reduced light led to an average 23% reduction in biomass-related performance, whereas the effect sizes on physiological performance did not significantly differ from zero. Especially, pigment content increased with reduced light, which indicated a strong physiological plasticity in response to diminished light. This acclimation potential was also indicated by light reduction effects minimized if the experiments lasted longer. Nevertheless, the performance (especially biomass accrual) was reduced the more the less light intensity remained available. Light reduction effects were also more negative at higher temperatures if ambient light conditions were poor. Macrophytes or benthic systems were more negatively affected by light reduction than microalgae or plankton systems, especially in physiological responses were microalgae and plankton showed slightly positive responses. Otherwise, the effect magnitudes remained surprisingly consistent across habitats and aspects of experimental design. Therefore, the strong observed log–linear relationship between remaining light and autotrophic performance can be used as a baseline to predict marine primary production in future light climate
Carbon storage, Carbon degradation and sediment transport mechanisms in a changing coastal thermokarst landscape - Case study for a land - near shore transect in the Teshekpuk Lake Region, Alaska, USA
Get PDFOne impact of climate change is the rapid warming of the Arctic, resulting in the thawing of permafrost and associated processes like thermokarst. This leads to the development of thermokarst features, like thermokarst lakes, thermokarst lagoons, and drained thermokarst lake basins. Since permafrost is one of the largest climate sensitive carbon reservoirs of the world, its thaw can possibly lead to the release of substantial amounts of greenhouse gases, thus further exacerbating climate warming. To predict future impacts of permafrost thaw it is of interest to understand how the characteristics of the soils change with a changing permafrost landscape. The aim of this master thesis is the comparison of different landscape features in a dynamic coastal thermokarst landscape, focusing on three main objectives: (1) the quantification and characterization of organic carbon, (2) the sedimentological and depositional characterization, and (3) the quantification of the mercury content in the profiles. The analysis involves six cores, ranging from 12 to 219 cm in length, from six different landscape units within a land-sea transect in Alaska. A multi-proxy approach, including a hydrochemical, a geochronological, a sedimentological, a biogeochemical, and a bio-marker analysis was used to analyse the samples in the laboratory. The results show variations in the total organic carbon (TOC) content within the profiles and across the different landforms. The highest TOC contents were measured in the sediments of the drained thermokarst lake basin and the thermokarst lake. Sites influenced by saltwater have significantly lower TOC contents than the sites not influenced by saltwater, with the semi-drained lagoon and the marine deposits showing the lowest TOC contents. The biomarker analysis indicates a higher level of organic matter degradation in saltwater influenced soil profiles and fresh undegraded organic matter in the thermokarst lake and drained thermokarst lake basin deposits. Moreover, it shows a varying degree of aquatic influence on the source of organic matter in the deposits of the different landscape units. Additionally, the biomarker indices (average chain length, Paq, Pwax) reveal significant differences between the saltwater influenced deposits and the deposits not influenced by saltwater, as well as between the unfrozen and frozen profiles. The sedimentological and depositional characterization shows different characteristics of the grain size distribution across the different soil profiles, with coarser grain sizes in the upland permafrost deposits and finer lacustrine deposits in the thermokarst deposits. The analysis of the profile of the semi-drained lagoon shows deposits similar to upland permafrost samples in the deeper layers and to thermokarst deposits in the upper layer. The quantification of mercury in the soil samples shows higher contents in the thermokarst deposits compared to the upland VII permafrost profile, with the highest mean mercury content in the thermokarst lake deposits, indicating an increased accumulation of mercury with higher input of organic matter and with permafrost thaw
Potential geographic shifts in the coral reef ecosystem under climate change
Get PDFThe coral reefs are the most diverse marine ecosystem in the world. Considering its contribution as a natural resource for humanity and global biodiversity, it is critical to understand its response to climatic change. To date, no global predictions have been made about potential ecosystem changes in relation to its inhabiting species. Predicting changes in species' climatic suitability under increasing temperature and comparing them among species would be the first step in understanding the geographic and taxonomic coherence and discrepancies that may occur within the ecosystem. Using 57 species-specific global climate suitability models (of corals, molluscs, fish, crustaceans, and polychaetes) under present and future climate scenarios (RCP 4.5 and 8.5), we compared the potential coherence and differences and their cumulative impact on the ecosystem in warm, cold, shallow, and deep waters. Under the climatic scenarios, nearly 90% of 30 warm-water species were predicted to lose their suitability in the parts of the Indo-west Pacific, the Coast of Northern Australia, the South China Sea, the Caribbean Sea, and the Gulf of Mexico, resulting in the overall southward shift in their distributions. In contrast, a mixed response occurred in 27 cold-water species, with most northern temperate/boreal ones increasing their suitability in the Arctic Ocean and the Arctic species declining overall. We noticed that irrespective of their taxonomic group, the species with wider distribution ranges (thermal and geographic) had larger predicted gains in their suitability than their stenothermal counterparts, suggesting an increase of generalist species and a decline of specialist (endemic) species of the ecosystem under a warming climate. Our coherent projections of species' climatic suitability in warm and cold habitats of the tropics, temperate, boreal, and the Arctic, represent significant taxonomic groups of the ecosystem. This might indicate mass extinction risk (local– in the tropics and northern temperate regions, and overall– in the Arctic) in native habitats and a high species turnover across the ecosystem under a warming climate. This may also destabilise predator–prey dynamics in the ecosystem, especially if foraging specialists dominate coral food webs and adversely affect the associated countries. Our global projections highlight the regions of species’ potential loss and gain; stakeholders could use the information to protect biodiversity and maintain human well-being
Heat hardening enhances metabolite-driven thermoprotection in the Mediterranean mussel Mytilus galloprovincialis
Get PDFIntroduction: Temperature affects organisms’ metabolism and ecological performance. Owing to climate change, sea warming constituting a severe source of environmental stress for marine organisms, since it increases at alarming rates. Rapid warming can exceed resilience of marine organisms leading to fitness loss and mortality. However, organisms can improve their thermal tolerance when briefly exposed to sublethal thermal stress (heat hardening), thus generating heat tolerant phenotypes. Methods: We investigated the “stress memory” effect caused by heat hardening on M. galloprovincialis metabolite profile of in order to identify the underlying biochemical mechanisms, which enhance mussels’ thermal tolerance. Results: The heat hardening led to accumulation of amino acids (e.g., leucine, isoleucine and valine), including osmolytes and cytoprotective agents with antioxidant and anti-inflammatory properties that can contribute to thermal protection of the mussels. Moreover, proteolysis was inhibited and protein turnover regulated by the heat hardening. Heat stress alters the metabolic profile of heat stressed mussels, benefiting the heat-hardened individuals in increasing their heat tolerance compared to the non-heat-hardened ones. Discussion: These findings provide new insights in the metabolic mechanisms that may reinforce mussels’ tolerance against thermal stress providing both natural protection and potential manipulative tools (e.g., in aquaculture) against the devastating climate change effects on marine organisms
Validation of Nadir SWH and Its Variance Characteristics from CFOSAT in China’s Offshore Waters
Get PDFThe offshore waters of China are a typical monsoon−affected area where the significant wave height (SWH) is strongly influenced by the different seasonal mean flow in winter and summer. However, limited in situ validations of the SWH have been performed on the China–France Oceanography Satellite (CFOSAT) in these waters. This study focused on validating CFOSAT nadir SWH data with SWH data from in situ buoy observations for China’s offshore waters and the Haiyang−2B (HY−2B) satellite, from July 2019 to December 2021. The validation against the buoy data showed that the relative absolute error has a seasonal cycle, varying in a narrow range near 35%. The RMSE of the CFOSAT nadir SWH was 0.29 m when compared against in situ observations, and CFOSAT was found to be more likely to overestimate the SWH under calm sea conditions. The sea−surface winds play a key role in calm sea conditions. The spatial distributions of the CFOSAT and HY−2B seasonal SWHs were similar, with a two−year mean SWH−field correlation coefficient of 0.98. Moreover, the coherence between the two satellites’ SWH variance increased with SWH magnitude. Our study indicates that, in such typical monsoon−influenced waters, attention should be given to the influence of sea conditions on the accuracy of CFOSAT SWH, particularly in studies that combine data from multiple, long−duration space−based sensors
Greenland Ice Sheet Ice Slab Expansion and Thickening
Get PDFWe use airborne accumulation radar data acquired over the Greenland Ice Sheet between 2002 and 2018 to identify changes in ice slab extent and thickness. We show that ice slabs several meters thick were already present at least as early as 2002. Between 2012 and 2018, they expanded by 13,400–17,600 (Formula presented.) inland, or 37%–44%. Our results document that the extremely warm summer of 2012 produced near-surface ice layers at higher elevations, enabling ice slabs to develop with only moderate melting in the following summers. With repeat flights along a transect in southwest Greenland, we show that moderate melting primarily causes slab thickening through uniform accretion on top of the ice slabs, while large melting events can also trigger localized accretion below existing ice slabs
AlgaeTraits: a trait database for (European) seaweeds
Get PDFThe analysis of biological and ecological traits has a long history in evolutionary and ecological
research. However, trait data are often scattered and standardised terminology that transcends taxonomic and
biogeographical context are generally missing. As part of the development of a global trait database of marine
species, we collated trait information for European seaweeds and structured the data within the standardised
framework of the World Register of Marine Species (WoRMS). We collected 45 175 trait records for 21 biolog-
ically and ecologically relevant traits of seaweeds. This resulted in a trait database for 1745 European seaweed
species of which more than half (56 %) of the records were documented at the species level, while the remaining
44 % were documented at a higher taxonomic level and subsequently inherited at lower levels. The trait database
for European seaweeds will serve as a foundation for future research on diversity and evolution of seaweeds and
their responses to global changes. The data will contribute to developing detailed trait-based ecosystem models
and will be an important tool to inform marine conservation policies. The data are publicly accessible through
the AlgaeTraits portal, https://doi.org/10.14284/574 (AlgaeTraits, 2022)
The impact of spatially varying ice sheet basal conditions on sliding at glacial time scales
Get PDFSpatially variable basal conditions are thought to govern how ice sheets behave at glacial time scales (>1000 years) and responsible for changes in dynamics between the core and peripheral regions of the Laurentide and Fennoscandian ice sheets. Basal motion is accomplished via the deformation of unconsolidated sediments, or via sliding of the ice over an undeformable bed. We present an ice sheet sliding module for the Parallel Ice Sheet Model (PISM) that takes into account changes in sediment cover and incorporates surface meltwater. This model routes meltwater, produced at the surface and base of the ice sheet, toward the margin of the ice sheet. Basal sliding is accomplished through the deformation of water saturated sediments, or sliding at the ice-bed interface. In areas with continuous, water saturated sediments, sliding is almost always accomplished through sediment deformation. In areas with incomplete cover, sliding has a stronger dependence on the supply of water. We find that the addition of surface meltwater to the base is a more important factor for ice sheet evolution than the style of sliding. In a glacial cycle simulation, our model causes a more rapid buildup of the Laurentide Ice Sheet