Alfred Wegener Institute for Polar and Marine Research
Electronic Publication Information CenterNot a member yet
52828 research outputs found
Sort by
Atlantic Water warming increases melt below Northeast Greenland's last floating ice tongue
No full textDo we need non-Boussinesq effects in an ocean general circulation model for climate simulations?
Get PDFThe Boussinesq approximation is commonly made in ocean general circulation models (OGCMs). As a consequence, the model ocean is incompressible and conserves volume, but not mass. It has been argued that these consequence introduce errors at the noise level of coarse OGCMs, but that non-Boussinesq modeling is preferable simply for tidiness. Here, we use the height-pressure coordinate isomorphism implemented in the MITgcm to construct a non-Boussinesq OGCM and revisit the differences between Boussinesq and non-Boussinesq models at a resolution comparable to IPCC climate models. Subtleties such as the choice of a proper equation of state that includes the effect of pressure on heat capacity, but also the use of mass as a convenient alternative to pressure coordinates are discussed
From snow accumulation to snow depth distributions by quantifying meteoric ice fractions in the Weddell Sea
Get PDFYear-round snow cover is a characteristic of the entire Antarctic sea ice cover, which has significant implications for the energy and mass budgets of sea ice, e.g., by preventing surface melt in summer and enhancing sea ice growth through extensive snow ice formation. However, substantial observational gaps in the seasonal cycle of Antarctic sea ice and its snow cover limit the understanding of important processes in the ice-covered Southern Ocean. They also introduce large uncertainties in satellite remote sensing applications and climate studies. Here we present results from 10 years of autonomous snow observations from Snow Buoys in the Weddell Sea. To distinguish between actual snow depth and potential snow ice thickness within the accumulated snowpack, a one-dimensional thermodynamic sea ice model is applied along the drift trajectories of the buoys. The results show that potential snow ice formation, with an average maximum thickness of 35cm, was detected along 41% of the total track length of the analyzed Snow Buoy tracks, which corresponds to about one-quarter of the snow accumulation. In addition, we simulate the evolution of internal snow properties along the drift trajectories with the more complex SNOWPACK model, which results in superimposed ice thicknesses between 0 and 14cm on top of the snow ice layer. These estimates will provide an important reference dataset for both snow depth and meteoric ice rates in the Southern Ocean
Extensive palaeo-surfaces beneath the Evans–Rutford region of the West Antarctic Ice Sheet control modern and past ice flow
Get PDFThe subglacial landscape of Antarctica records and influences the behaviour of its overlying ice sheet. However, in many places, the evolution of the landscape and its control on ice sheet behaviour have not been investigated in detail. Using recently released radio-echo sounding data, we investigate the subglacial landscape of the Evans–Rutford region of West Antarctica. Following quantitative analysis of the landscape morphology under ice-loaded and ice-unloaded conditions, we identify 10 flat surfaces distributed across the region. Across these 10 surfaces, we identify two distinct populations based on clustering of elevations, which potentially represent remnants of regionally coherent pre-glacial surfaces underlying the West Antarctic Ice Sheet (WAIS). The surfaces are bounded by deeply incised glacial troughs, some of which have potential tectonic controls. We assess two hypotheses for the evolution of the regional landscape: (1) passive-margin evolution associated with the break-up of the Gondwana supercontinent or (2) an extensive planation surface that may have been uplifted in association with either the West Antarctic Rift System or cessation of subduction at the base of the Antarctic Peninsula. We suggest that passive-margin evolution is the most likely of these two mechanisms, with the erosion of glacial troughs adjacent to, and incising, the flat surfaces likely having coincided with the growth of the WAIS. These flat surfaces also demonstrate similarities to other identified surfaces, indicating that a similar formational process may have been acting more widely around the Weddell Sea embayment. The subsequent fluctuations of ice flow, basal thermal regime, and erosion patterns of the WAIS are therefore controlled by the regional tectonic structures
Effects of bottom‐up factors on growth and toxin content of a harmful algae bloom dinoflagellate
Get PDFThe toxin-producing dinoflagellate Alexandrium pseudogonyaulax has become increasingly abundant in northern European waters, replacing other Alexandrium species. A. pseudogonyaulax produces goniodomins and lytic substances, which can be cytotoxic toward other organisms, including fish, but we still know little about the environmental conditions influencing its growth and toxicity. Here, we investigated the impacts of different nitrogen sources and light intensities, common bottom-up drivers of bloom formation, on the growth and toxin content of three A. pseudogonyaulax strains isolated from the Danish Limfjord. While the growth rates were significantly influenced by nitrogen source and light intensity, the intracellular toxin contents only showed strong differences between the exponential and stationary growth phases. Moreover, the photophysiological response of A. pseudogonyaulax showed little variation across varying light intensities, while light-harvesting pigments were significantly more abundant under low light conditions. This study additionally highlights considerable physiological variability between strains, emphasizing the importance of conducting laboratory experiments with several algal strains. A high physiological plasticity toward changing abiotic parameters points to a long-term establishment of A. pseudogonyaulax in northern European waters
Decomposition of physical processes controlling EASM precipitation changes during the mid-Piacenzian: new insights into data–model integration
Get PDFThe mid-Piacenzian warm period (MPWP, ~3.264–3.025 Ma) has gained widespread interest due to its partial analogy with future climate. However, quantitative data–model comparison of East Asian Summer Monsoon (EASM) precipitation during the MPWP is relatively rare, especially due to problems in decoding the imprint of physical processes to climate signals in the records. In this study, pollen-based precipitation records are reconstructed and compared to the multi-model ensemble mean of the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). We find spatially consistent precipitation increase in most simulations but a spatially divergent change in MPWP records. We reconcile proxy data and simulation by decomposing physical processes that control precipitation. Our results 1) reveal thermodynamic control of an overall enhancement of EASM precipitation and 2) highlight a distinct control of thermodynamic and dynamical processes on increases of tropical and subtropical EASM precipitation, reflecting the two pathways of water vapor supply that enhance EASM precipitation, respectively
Long‐term shifts in phenology, thermal niche, population size, and their interactions in marine pelagic copepods
Get PDFUnder climatic warming many species shift their seasonal timing of life cycle events (phenology) and seasonal abundance distribution, but whether they maintain the same thermal niche is still poorly understood. Here, we studied multidecadal trends in abundance and phenology of seven major copepod species across three stations (Stonehaven (SH), Helgoland Roads (HR), and Plymouth L4) on the North–West European shelf, spanning ~ 6.5° of latitude. All seven species consistently occupied colder temperatures at the northern station compared to the southerly station, but they maintained the same realized thermal niche over years. Expected phenological shifts (i.e., earlier when warmer) in some stations were obscured possibly by the long-term drop of copepod density in spring–summer, which may be due to a variation in the food/predators abundance. The ongoing spring–summer declines in abundance (~ 50%) of many North Atlantic pelagic species over the last five decades, as found in recent studies, may have also influenced the metrics of seasonal timing. To separate the seasonal timing of life events from that of seasonal abundance distribution, we used a time series of egg production rate (EPR) of Calanus helgolandicus at L4, and found that this shifted later into the summer–autumn over the last 30 yr of warming, coincident with declining spring–summer food and increasing predator abundance. Overall, direct temperature effects do appear to influence the seasonal timing of the copepods, but to explain impacts at individual stations or long-term trends in population size or phenology, understanding the changing balance of food and predators appears to be critical
Short and decadal impacts of seafloor physical perturbation on the abundances of Lebensspuren ‘traces of life’ in the Peru Basin manganese nodule province
Get PDFInterest in deep-sea mining for polymetallic nodules as an alternative source to onshore mines for various high-technology metals has risen in recent years, as demands and costs have increased. The need for studies to assess its short- and long-term consequences on polymetallic nodule ecosystems is therefore also increasingly prescient. Recent image-based expedition studies have described the temporal impacts on epi-/megafauna seafloor communities across these ecosystems at particular points in time. However, these studies have failed to capture information on large infauna within the sediments or give information on potential transient and temporally limited users of these areas, such as mobile surface deposit feeders or fauna responding to bloom events or food fall depositions. This study uses data from the Peru Basin polymetallic nodule province, where the seafloor was previously disturbed with a plough harrow in 1989 and with an epibenthic sled (EBS) in 2015, to simulate two contrasting possible impact forms of mining disturbance. To try and address the shortfall on information on transient epifauna and infauna use of these various disturbed and undisturbed areas of nodule-rich seafloor, images collected 6 months after the 2015 disturbance event were inspected and all Lebensspuren, ‘traces of life’, were characterized by type (epi- or infauna tracemakers, as well as forming fauna species where possible), along with whether they occurred on undisturbed seafloor or regions disturbed in 1989 or 2015. The results show that epi- and endobenthic Lebensspuren were at least 50% less abundant across both the ploughed and EBS disturbed seafloors. This indicates that even 26 years after disturbance, sediment use by fauna may remain depressed across these areas
Was ist so spannend an alter Luft?
Get PDFEiskerne sind ein einmaliger Zugang zur Atmosphäre vergangener Zeiten. Aber was ist daran so spannend? Eines der ungelösten Probleme bei der Erforschung des Klimas der Vergangenheit ist wie es vor ca. 1.5 Millionen Jahren (für Geologen: im mittleren Pleistozän) dazu kam, dass sich der wiederkehrende Wechsel der Kalt- und Warmzeiten von 40 Tausend auf 100 Tausend Jahre vergrößerte. Das europäische Projekt Beyond EPICA – Oldest Ice will dem auf den Grund gehen. Dazu soll in der Antarktis der ersten Eiskern erbohrt werden, mit dem uralte Lufteinschlüsse an die Oberfläche gebracht werden, die diesen Zeitraum kontinuierlich abdecken.
In Episode 149 gibt Olaf Eisen, Professor für Glaziologie am Alfred-Wegener-Institut und der Universität Bremen, in seinem Vortrag einen Einblick in die Motivation für das Projekt und die bisherige Reise zu einem neuen Eiskern