Alfred Wegener Institute for Polar and Marine Research
Electronic Publication Information CenterNot a member yet
52828 research outputs found
Sort by
Globally consistent estimates of high-resolution Antarctic ice mass balance and spatially resolved glacial isostatic adjustment
Get PDFA detailed understanding of how the Antarctic ice sheet (AIS) responds to a warming climate is needed because it will most likely increase the rate of global mean sea level rise. Time-variable satellite gravimetry, realized by the Gravity Recovery and Climate Experiment (GRACE) and Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) missions, is directly sensitive to AIS mass changes. However, gravimetric mass balances are subject to two major limitations. First, the usual correction of the glacial isostatic adjustment (GIA) effect by modelling results is a dominant source of uncertainty. Second, satellite gravimetry allows for a resolution of a few hundred kilometres only, which is insufficient to thoroughly explore causes of AIS imbalance. We have overcome both limitations by the first global inversion of data from GRACE and GRACE-FO, satellite altimetry (CryoSat-2), regional climate modelling (RACMO2), and firn densification modelling (IMAU-FDM). The inversion spatially resolves GIA in Antarctica independently from GIA modelling jointly with changes of ice mass and firn air content at 50km resolution. We find an AIS mass balance of -144±27Gta-1 from January 2011 to December 2020. This estimate is the same, within uncertainties, as the statistical analysis of 23 different mass balances evaluated in the Ice sheet Mass Balance Inter-comparison Exercise (IMBIE; ). The co-estimated GIA corresponds to an integrated mass effect of 86±21Gta-1 over Antarctica, and it fits better with global navigation satellite system (GNSS) results than other GIA predictions. From propagating covariances to integrals, we find a correlation coefficient of -0.97 between the AIS mass balance and the GIA estimate. Sensitivity tests with alternative input data sets lead to results within assessed uncertainties
Overview of the MOSAiC expedition: Ecosystem
Get PDFThe international and interdisciplinary sea-ice drift expedition “The Multidisciplinary drifting Observatory for the Study of Arctic Climate” (MOSAiC) was conducted from October 2019 to September 2020. The aim of MOSAiC was to study the interconnected physical, chemical, and biological characteristics and processes from the atmosphere to the deep sea of the central Arctic system. The ecosystem team addressed current knowledge gaps and explored unknown biological properties over a complete seasonal cycle focusing on three major research areas: biodiversity, biogeochemical cycles, and linkages to the environment. In addition to the measurements of core properties along a complete seasonal cycle, dedicated projects covered specific processes and habitats, or organisms on higher taxonomic or temporal resolution in specific time windows. A wide range of sampling instruments and approaches, including sea-ice coring, lead sampling with pumps, rosette-based water sampling, plankton nets, remotely operated vehicles, and acoustic buoys, was applied to address the science objectives. Further, a broad range of process-related measurements to address, for example, productivity patterns, seasonal migrations, and diversity shifts, were made both in situ and onboard RV Polarstern. This article provides a detailed overview of the sampling approaches used to address the three main science objectives. It highlights the core sampling program and provides examples of habitat- or process-specific sampling. The initial results presented include high biological activities in wintertime and the discovery of biological hotspots in underexplored habitats. The unique interconnectivity of the coordinated sampling efforts also revealed insights into cross-disciplinary interactions like the impact of biota on Arctic cloud formation. This overview further presents both lessons learned from conducting such a demanding field campaign and an outlook on spin-off projects to be conducted over the next years.</jats:p
Assessment of Hygroscopic Behavior of Arctic Aerosol by Contemporary Lidar and Radiosonde Observations
Get PDFThis study presents the hygroscopic properties of aerosols from the Arctic free troposphere by means of contemporary lidar and radiosonde observations only. It investigates the period from the Arctic Haze in spring towards the summer season in 2021. Therefore, a one-parameter growth curve model is applied to lidar data from the Koldewey Aerosol Raman Lidar (AWIPEV in Ny-Ålesund, Svalbard) and simultaneous radiosonde measurements. Hygroscopic growth depends on different factors like aerosol diameter and chemical composition. To detangle this dependency, three trends in hygroscopicity are additionally investigated by classifying the aerosol first by its dry color ratio, and then by its season and altitude. Generally, we found a complex altitude dependence with the least hygroscopic particles in the middle of the troposphere. The most hygroscopic aerosol is located in the upper free troposphere. A hypothesis based on prior lifting of the particles is given. The expected trend with aerosol diameter is not observed, which draws attention to the complex dependence of hygroscopic growth on geographical region and altitude, and to the development of backscatter with the aerosol size itself. In a seasonal overview, two different modes of stronger or weaker hygroscopic particles are additionally observed. Furthermore, two special days are discussed using the Mie theory. They show, on the one hand, the complexity of analyzing hygroscopic growth by means of lidar data, but on the other hand, they demonstrate that it is in fact measurable with this approach. For these two case studies, we calculated that the aerosol effective radius increased from 0.16μm (dry) to 0.18μm (wet) and from 0.28μm to 0.32μm for the second case
Can animal grazing help to reduce permafrost thaw?
Get PDFLarge herbivorous animals were identified to globally affect soil and vegetation conditions. In the Arctic, intensive animal activity excerts impacts on permafrost that might help to stabilize thaw-vulnerable deposits and counteract vegetation changes associated with global warming. Exploiting such mechanisms on a local scale would help to (re-)establish animal- and herding-based livelihoods while stabilizing ground for infrastructure and being climatically beneficial
Future Antarctic Climate: Storylines of Midlatitude Jet Strengthening and Shift Emergent from CMIP6
Get PDFA main source of regional climate change uncertainty is the large disparity across models in simulating the atmospheric circulation response to global warming. Using the latest suite of global climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), a storyline approach is adopted to derive physically plausible scenarios of Antarctic climate change for 2070–99, according to Shared Socioeconomic Pathway SSP5-8.5. These storylines correspond to differences in the simulated amount of seasonal sea ice loss and either (i) the delay in the summertime stratospheric polar vortex (SPV) breakdown or (ii) wintertime SPV strengthening, which together constitute robust drivers of the response pattern to future climate change. Such changes combined are known to exert a strong control over the Southern Hemisphere midlatitude jet stream, which we quantify as collectively explaining up to 70% of the variance in jet response in summer and 35% in winter. For summer, the expected strengthening and displacement of the tropospheric jet stream varies between a;1 and 2 m s21 increase and;28–48 poleward shift, respectively, across storylines. In both seasons, a larger strengthening of the jet is correlated with less Antarctic warming. By contrast, the response in precipitation is more consistent but still strongly attenuated by large-scale dynamics. We find that an increase in high-latitude precipitation around Antarctica is more pronounced for storylines characterized by a greater poleward jet shift, particularly in summer. Our results highlight the usefulness of the storyline approach in illustrating model uncertainty and understanding the processes that determine the spread in projected Antarctic regional climate response. SIGNIFICANCE STATEMENT: Uncertainty in future climate predictions for the Antarctic is dominated by the unknown response of the large-scale (global) atmospheric circulation. In characterizing such uncertainty, plausible outcomes of climate response (storylines) are generated from the organization of model projections according to the amount of simulated seasonal sea ice loss and the delay in summertime breakdown/winter strengthening of the stratospheric westerly circulation (polar vortex). The intensity and location of the tropospheric jet stream is strongly dependent on both factors, which strongly influences the near-surface climate response over Antarctica. We find that the simulated amount that Antarctic air temperatures increase by in the future (to the end of the century) is intrinsically related to the projected intensification of the Southern Hemisphere tropospheric jet, varying by a factor of 2 or more across storylines for summer. Storylines with greater jet strengthening are associated with less Antarctic warming (reduced poleward advection of air masses from lower latitudes). Similar differences are found for changes in jet position, which we note has a much stronger control on mid- to high-latitude precipitation response. This includes both an enhanced wetting response around Antarctica and drying response farther equatorward, for storylines characterized by a greater poleward jet shift
Kelp forest community structure and demography in Kongsfjorden (Svalbard) across 25 years of Arctic warming
No full textThe Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience
a continuous increase in seawater temperature and glacial melt while sea-ice
cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species
diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen)
in order to identify potential changes over time. In 2021, we repeated the earlier studies
by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0,
2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae
between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2
at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the
depth transect in 2021 was not significantly different compared to 2012/2013, the
digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed
into an Alaria esculenta-dominated
kelp forest. Consequently, a pronounced shift
in kelp forest structure occurred over time as we demonstrate that biomass allocation
to thallus parts is kelp species-specific.
Over the past decade, kelp demography
changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp
individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth
limits of all dominant brown algae declined noticeably over the last 25 years while the
red algal flora abundance remained unchanged at depth. We propose that the major
factor driving the observed changes in the macroalgal community are alterations in
underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance
since 2012 and 2017, respectively. As a consequence, the interplay between
kelp forest retreat to lower depth levels caused by coastal darkening and potential
macroalgal biomass gain with increasing temperatures will possibly intensify in the
future with unforeseen consequences for melting Arctic coasts and fjord ecosystem
services. The Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience
a continuous increase in seawater temperature and glacial melt while sea-ice
cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species
diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen)
in order to identify potential changes over time. In 2021, we repeated the earlier studies
by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0,
2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae
between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2
at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the
depth transect in 2021 was not significantly different compared to 2012/2013, the
digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed
into an Alaria esculenta-dominated
kelp forest. Consequently, a pronounced shift
in kelp forest structure occurred over time as we demonstrate that biomass allocation
to thallus parts is kelp species-specific.
Over the past decade, kelp demography
changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp
individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth
limits of all dominant brown algae declined noticeably over the last 25 years while the
red algal flora abundance remained unchanged at depth. We propose that the major
factor driving the observed changes in the macroalgal community are alterations in
underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance
since 2012 and 2017, respectively. As a consequence, the interplay between
kelp forest retreat to lower depth levels caused by coastal darkening and potential
macroalgal biomass gain with increasing temperatures will possibly intensify in the
future with unforeseen consequences for melting Arctic coasts and fjord ecosystem
services
Stepwise Subduction Observed at a Front in the Marginal Ice Zone in Fram Strait
Get PDFAt high latitudes, submesoscale dynamics act on scales of (Formula presented.) (100 m–1 km) and are associated with the breakdown of geostrophic balance, vertical velocities, and energy cascading to small scales. Submesoscale features such as fronts, filaments, and eddies are ubiquitous in marginal ice zones forced by the large horizontal density gradients. In July 2020, we identified multiple fronts and filaments using a towed undulating vehicle near the sea ice edge in central Fram Strait, the oceanic gateway to the Arctic Ocean between Greenland and Svalbard. Sea ice covered the entire study region 1–2 weeks earlier, and a stratified meltwater layer was present. We observed a front between warm and saline Atlantic Water (AW) and cold and fresh Polar Water (PW) at 30–85 m depth, where we identified a subsurface maximum in chlorophyll fluorescence and other biogeochemical properties extending along the tilted isopycnals down to 75 m, indicating subduction of AW (mixed with meltwater) that had previously occurred. The meltwater layer also featured multiple shallow fronts, one of which exhibited high velocities and a subsurface maximum in chlorophyll fluorescence, possibly indicating subduction of PW below the meltwater layer. The fronts at different depth levels suggest a stepwise subduction process near the ice edge, where water subducts from the surface below the meltwater and then further down along subsurface fronts. The submesoscale features were part of a larger-scale mesoscale pattern in the marginal ice zone. As sea ice continuously retreats, such features may become more common in the Arctic Ocean
Basal melt rate of the 79 North Glacier, Northeast Greenland, and its connection to the Atlantic Water circulation in the Nordic Seas
No full textOverview: quasi-Lagrangian observations of Arctic air mass transformations – introduction and initial results of the HALO–(AC)3 aircraft campaign
Get PDFGlobal warming is amplified in the Arctic. However, numerical models struggle to represent key processes
that determine Arctic weather and climate. To collect data that help to constrain the models, the HALO–
(AC)3 aircraft campaign was conducted over the Norwegian and Greenland seas, the Fram Strait, and the central Arctic Ocean in March and April 2022. The campaign focused on one specific challenge posed by the models, namely the reasonable representation of transformations of air masses during their meridional transport into and out of the Arctic via northward moist- and warm-air intrusions (WAIs) and southward marine cold-air outbreaks (CAOs). Observations were made over areas of open ocean, the marginal sea ice zone, and the central Arctic sea ice. Two low-flying and one long-range, high-altitude research aircraft were flown in colocated formation whenever possible. To follow the air mass transformations, a quasi-Lagrangian flight strategy using trajectory calculations was realized, enabling us to sample the same moving-air parcels twice along their trajectories. Seven distinct WAI and 12 CAO cases were probed. From the quasi-Lagrangian measurements, we have quantified the diabatic heating/cooling and moistening/drying of the transported air masses. During CAOs, maximum values of 3Kh^-1 warming and 0.3 g kg^-1 h^-1 moistening were obtained below 1 km altitude. From the observations of WAIs, diabatic cooling rates of up to 0.4Kh^-1 and a moisture loss of up to 0.1 g kg^-1 h^-1 from the ground to about 5.5 km altitude were derived. Furthermore, the development of cloud macrophysical (cloud-top height and horizontal cloud cover) and microphysical (liquid water path, precipitation, and ice index) properties along the southward pathways of the air masses were documented during CAOs, and the moisture budget during a specific WAI event was estimated. In addition, we discuss the statistical frequency of occurrence of the different thermodynamic phases of Arctic low-level clouds, the interaction of Arctic cirrus clouds with sea ice and water vapor, and the characteristics of microphysical and chemical properties of Arctic aerosol particles. Finally, we provide a proof of concept to measure mesoscale divergence and subsidence in the Arctic using data from dropsondes released during the flights