Alfred Wegener Institute for Polar and Marine Research
Electronic Publication Information CenterNot a member yet
52828 research outputs found
Sort by
Introducing a glacier forefield monitoring site network to understand succession in the Northern Limestone Alps
Get PDFAbstract. Since the end of the Little Ice Age (ca. 1855), glaciers retreated in the Alps, leaving new ground for genuine primary succession. The patterns and processes of glacier forefield succession have been studied globally for decades. Surprisingly, no such analysis exists from the Northern Limestone Alps. We therefore initiated a monitoring scheme with permanent plots to study plant succession and vegetation assembly at four forefields, namely the Hallstätter Glacier, Großer Gosau Glacier (both at Dachstein massif, Austria), Watzmann Glacier, and Blaueis (both at Berchtesgaden National Park, Germany), which is abbreviated as the BDGF (Berchtesgaden-Dachstein Glacier Forefield) platform. The aim of the long-term research envisaged and performed in this platform is to get a better understanding of the vegetation succession and community assembly in the glacier forefield development of the Northern Limestone Alps, using a multidisciplinary approach. Here, we introduce the basic characteristics of the BDGF platform; i.e. we describe the monitoring network, the observational design, and the methodological approaches. We present the baseline vegetation characteristics, and we outline the studies already initiated or to be performed in the near future. The methodology encompasses a chronosequence approach, where plots, using a frequency grid frame of 1 m × 1 m, are placed in specific successional stages (related to age classes since deglaciation). We show that, as expected, species richness and cover increase with age. Unexpectedly, though, these processes seem to be much slower than what has been observed in the Central Alps on siliceous substrates. We suggest that this could be due to the geological substrate, i.e. its chemistry as well as its karstic conditions, but also due to the morphology of the terrain, which hardly enables species colonization from above (i.e. following gravity) but mainly from below
An Assessment of Uncertainty in the ECCO Global Ocean‐Sea Ice State Estimate Due To Atmospheric Forcing Uncertainty
Get PDFAbstract The Estimating the Circulation and Climate of the Ocean (ECCO) state estimate is the result of adjusting a set of controls comprising atmospheric forcings, initial conditions, and mixing parameters to reduce model‐data misfits. Despite this, uncertainties remain in the solution. Among others, small amplitude perturbations to the optimized controls may yield differences in the estimated state without notably increasing the misfits, providing distinct but equally acceptable solutions to the inverse problem. We focus on the impact of uncertainty in the atmospheric controls via ensemble perturbation. Our multivariate empirical orthogonal function (EOF) approach to construct the ensemble perturbations accounts for the covariance of control variables. Furthermore, it provides new insights into the space‐time characteristics of ECCO's atmospheric adjustments. The two leading EOFs of these adjustments show a seasonal cycle dominated by high‐latitude adjustments and a decadal component. Removing the time‐mean of the adjustments results in large model‐data misfits and thus unacceptable estimates. Ensemble perturbations in time‐varying adjustments incur uneven uncertainties in oceanic metrics, for example, in global meridional heat transport (0.03 PW), the Atlantic meridional overturning circulation at 26°N (0.7 Sv), or ocean heat uptake (15 ZJ). These are an order of magnitude smaller than the uncertainty evaluated via ocean reanalysis intercomparisons and forward perturbation ensembles. The relatively weak impacts result from the relatively small amplitude of estimated atmospheric uncertainty in the ECCO release, out of sufficient consideration of a massive set of observational constraints. Future work should assess the impact of other sources of uncertainties.
Plain Language Summary Ocean reanalysis and state estimation seeks to bring an ocean model into consistency with available observations via data assimilation, providing a complete reconstruction of the time‐evolving ocean state to support forecasting efforts and climate research. Uncertainty remains in the resulting products, however, arising from uncertainties in the underlying model, applied atmospheric forcings, assimilated data constraints, and assimilation method. Whilst computational challenges prevent comprehensive uncertainty quantification, this information is valuable for all applications (e.g., forecast initialization; robust climate change detection). To address this issue, we have sought to provide the first uncertainty estimate for the latest release of the ECCO global ocean and sea ice state estimate, spanning the period 1992–2017. Using an ensemble perturbation approach, we explore the impact of uncertainties in applied atmospheric forcings. Our ensemble design is advantageous in accounting for the joint variations between different atmospheric variables and in providing new insights into the space‐time characteristics of adjustments made to these terms as part of the ECCO data assimilation procedure, highlighting the relative role of time‐mean and time‐variable adjustments. Our perturbed ensemble yields distinct solutions to the inverse problem with moderate changes in climate‐relevant metrics, including ocean meridional overturning circulation, heat transport and heat uptake.
Key Points Using a perturbed ensemble we explore the impact of uncertainty in atmospheric forcings on the ECCO ocean and sea ice state estimate The ensemble yields alternative estimated solutions (with acceptable model‐data misfits) if time‐meanforcing adjustments are retained These alternative solutions are accompanied by moderate changes in climate relevant metrics, including ocean overturning and heat uptak
Integrating molecular methods and biophysical modeling to assess functional connectivity between marine protected areas
Get PDFAbstract
Marine protected area (MPA) networks are important for supporting biodiversity, enhancing ecosystem resilience, and facilitating species recovery. For the effectiveness of conservation and restoration, functional connectivity plays a vital role. The dispersal, movement, and successful establishment of organisms between suitable habitats and MPAs ensure long‐term sustainability of the populations. Despite its importance, functional connectivity is rarely integrated into restoration planning, which limits the effectiveness of species reintroductions, habitat connectivity, and adaptation to environmental changes. In this study, we applied an integrative approach combining molecular detections (environmental DNA [eDNA] and meroplankton metabarcoding) with biophysical modeling to explore the functional connectivity between two Natura 2000 MPAs in the North Sea: Borkum Reef Ground (BRG) and Sylt Outer Reef (SOR). We focused on the European flat oyster (
Ostrea edulis
), a reef‐building species that once provided vast reef habitats but is now functionally extinct in the German Bight and is therefore the subject of recent restoration measures at BRG. Our results showed partial but informative correspondence between molecular detections of oyster genetic traces and the modeled larval pathways during the June–July 2022 sampling period. We further explored larval dispersal across entire spawning seasons in 2022 and 2023. Connectivity between BRG and SOR was highly dependent on larval drift depth. Surface‐drifting larvae showed strong interannual variability, with 3% reaching SOR in 2022 when northwesterly winds dominated, increasing to 22% in 2023 under westerly and southwesterly winds. Larvae drifting at depth, however, exhibited near‐zero connectivity, leading to high self‐recruitment rates, with over 25% settling near the original restoration sites. Our results demonstrate that wind‐driven currents are a key driver of interannual variability in larval retention and dispersal. Additionally, they highlight the role of biological traits, such as vertical positioning and pelagic larval duration, in shaping connectivity between MPAs and oyster restoration sites. These findings emphasize the need to integrate connectivity assessments into MPA management and the restoration planning of reef‐building benthic species. The interdisciplinary approach presented here provides a quantitative framework for assessing connectivity under species‐ and site‐specific conditions, offering a transferable tool to evaluate the restoration potential of other species and enhance the functional network between MPAs.
</jats:p
Identification and expression of circadian clock genes in the European flat oyster Ostrea edulis
Get PDFCircadian clocks enable organisms to synchronize their biological processes to environmental daily cycles, thereby increasing species fitness. Components of the molecular clock are conserved across many taxa, though their structure and function can vary. In this study, we aim to investigate the circadian clock of the European flat oyster Ostrea edulis, an endangered species with a pivotal role in biogenic reef ecosystems. Phylogenetic and protein domain analyses were performed to identify orthologues of core clock and clock-associated genes (OeClock, OeBmal1, OePeriod, OeTimeless, OeCryptochrome2, OeRev-erb, OeRor, OeDoubletime, OeClockWorkOrange, OeShaggy), a gene related to melatonin synthesis (OeHiomt) and genes involved in light perception (OeCryptochrome1, OeOpsin4). As a functional output of the clock, we observed daily and circadian rhythms in valve behaviour recorded under light:dark and constant dark conditions. In parallel, gene expression analyses in two tissues under similar light regimes revealed tissue-specific rhythms, suggesting the presence of a functional and plastic endogenous circadian system in O. edulis. These findings offer a first molecular work for deeper exploration of the circadian clock functioning in O. edulis, providing essential resources to investigate its evolutionary adaptation to cyclic environments, and inform restoration and conservation strategies of this threatened species
Mapping encounters between Antarctic krill fishing vessels and air-breathing krill predators using acoustic data from the fishery
Get PDFAntarctic krill is a keystone species in the Antarctic marine ecosystem and the target of a growing fishery. Given the ecological importance of krill, concerns have been raised about potential negative impacts of fishing on the Southern Ocean ecosystem. Resource-efficient approaches to fisheries monitoring are particularly valuable in this context due to the high costs associated with data collection in Antarctica. In this study, we trained a segmentation model (U-Net) to extract dives of air-breathing krill predators from more than 30,000 h of active acoustic data collected by three krill fishing vessels over six years. We were able to characterize the temporal and spatial dynamics of predator-vessel co-occurrences, which aligned well with the findings from more costly tracking studies. For example, we found that encounters with whales consistently peaked in autumn around the Antarctic Peninsula, when whales are building up fat reserves for their migration to breeding grounds. We also demonstrated that protection measures, introduced to protect breeding penguins at the Antarctic Peninsula, have simply shifted penguin-vessel encounters to the South Orkney Islands, where the affected colonies are not currently monitored. Our approach, results, and application example demonstrate how acoustic data from fishing vessels can provide important information to support fisheries management. As a by-product of fishing operations, these data are cost-effective, offering unique temporal and spatial coverage and providing a useful basis for rapid, low-level assessments of the fishery's interaction with the wider ecosystem. This is particularly important given the unpredictable dynamics of krill fishery management decision-making
Closing the Plio-Pleistocene 13C cycle in the 405 kyr periodicity by isotopic signatures of geological sources
Get PDFThe 13C cycle of the Plio-Pleistocene, as recorded in δ13C of benthic foraminifera, has power in periodicities related to the long eccentricity cycle of 405 kyr that is missing in corresponding climate records (e.g. δ18O). Using a global carbon cycle model, I show in an inverse approach that the long eccentricity in δ13C might have been caused by variations in the isotopic signature of geological sources, namely of the weathered carbonate rock (δ13Crock) or of volcanically released CO2 (δ13Cv). This closure of the 13C cycle in these periodicities also explains the offset in atmospheric δ13CO2 seen between the Penultimate Glacial Maximum (PGM) and the Last Glacial Maximum (LGM). The necessary isotopic signatures in δ13Crock or δ13Cv, which align my simulations with reconstructions of the 13C cycle on orbital timescales, have the most power in the obliquity band (41 kyr), suggesting that land ice dynamics are the ultimate cause for these suggested variations. Since the Asian monsoon as reconstructed from speleothems also has an obliquity-related component and since precipitation (or runoff) is one main driver for local weathering rates, it is possible that these proposed changes in weathering are indeed, at least partly, connected to the monsoon as previously suggested. Alternatively, the suggested impact of land ice or sea level on volcanic activity might also be influential for the 13C cycle. This indirect influence of ice sheets on the long eccentricity cycle in δ13C implies that these processes might not have been responsible for the 405 kyr periodicity found in times of the pre-Pliocene parts of the Cenozoic that have been largely ice-free in the Northern Hemisphere
Precession-driven low-latitude hydrological cycle paced by shifting perihelion
Get PDFPalaeoclimate proxies reveal a significant precessional impact on the low-latitude hydrological cycle. Classical theory suggests that precession modulates the interhemisphere summer insolation difference and hence controls the meridional displacement of the Intertropical Convergence Zone (ITCZ). Accordingly, low-latitude precipitation variations are expected to be in phase (for the Northern Hemisphere) or anti-phase (for the Southern Hemisphere) with the Northern Hemisphere summer insolation. However, increasing numbers of proxies, particularly those that are absolutely dated, reveal that variations in terrestrial precipitation at different low latitudes follow distinct precession rhythms that are very often out of phase with hemispheric summer insolation. The mechanism underlying such spatial–temporal complexity remains elusive. In this study, we performed theoretical analysis, climate simulations, and synthesis of geological records to hypothesise that the low-latitude hydrological cycle is paced by shifting perihelion rather than by the hemispheric summer insolation. More specifically, precession of the Earth’s rotation axis shifts the season and latitude of perihelion. Here, the latitude of perihelion is introduced as the latitude of Earth’s subsolar point during perihelion, which is the location where the most intense solar radiation is concentrated. At the time of perihelion, intense solar radiation heats the land faster than the ocean due to differing thermal inertia. This thermodynamically moves the tropical convection from the ocean to the land, contributing to enhancing the terrestrial precipitation around the perihelion latitude. As the precessional phase changes, perihelion moves toward different latitudes, causing asynchronous maximums in terrestrial precipitation at different latitudes. Perihelion can occur in any season; therefore, the insolation in individual seasons is equally important in shaping the orbital-scale climate changes at low latitudes. This offers new insight into the Milankovitch theory, which highlights summer insolation’s role in shaping orbital-scale climate change
Fitted Fv/Fm temperature response curves: applying lessons from plant ecophysiology to acute thermal stress experiments in coral holobionts
Get PDFMaximum photochemical efficiency, Fv/Fm, is the preferred metric for quantifying the loss of photosystem II (PSII) function in photosynthetic algal symbionts (Symbiodiniaceae) of reef-building corals exposed to heat stress, particularly at the early stages of coral bleaching. Loss of PSII function can be quantified as the temperature at which a holobiont loses 50% of maximum photochemical efficiency (50% effective dose, or ED50) when exposed to a range of experimental temperatures. Here, we demonstrate that dose–response curves can be substantially more informative about a coral’s stress response by including ED5 (5% effective dose), ED95 (95% effective dose), and decline width (ED95–ED5) values in summary statistics. These parameters are commonly used in plant ecophysiology and can be extracted from fitted Fv/Fm temperature response curves. This suite of metrics provides a broader understanding of the loss of PSII function in acute thermal stress experiments in corals and could enhance comparability among coral and plant studies
Microplastics in Antarctica - A plastic legacy in the Antarctic snow?
Get PDFMicroplastic pollution in remote inland Antarctica is largely unknown. This study explored the plastic footprint of snow from remote Antarctic camps: Union Glacier, Schanz Glacier and the South Pole. Refined automated FTIR techniques enabled interrogation of microplastics (including fibres) to a lower detection limit of 11 μm in Antarctic snow for the first time. Microplastics were pervasive (73–3099 MP L−1). The majority (95 %) measured <50 μm, indicating that previous microplastic reports in Antarctica may be underestimated, due to analytical restrictions. Plastic polymer composition and concentration did not vary significantly between sites, with dominant polymers being polyamide (PA), polyethylene terephthalate (PET), polyethylene (PE) and synthetic rubber. Results indicate that even in the earth's most remote regions, humans are leaving a plastic legacy in the snow, illustrating the importance of remote, cryospheric regions as critical study sites for determining temporal fluxes in microplastic pollution