Alfred Wegener Institute for Polar and Marine Research
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Hierarchical Modelling of Species Communities (HMSC) of benthic species, Potter Cove, King George Island, Antarctica
Get PDFUnderstanding the distribution and coexistence patterns of (benthic) species in Antarctic ecosystems is crucial for the estimation of present and future carbon turnover, ecosystem management, and conservation. Spatial and predictive modeling of environmental and biological data becomes more and more important at remote places to understand and to observe the ecological response to global climate change. In our study, we use the Hierarchical Modelling of Species Communities (HMSC) to model the distribution and coexistence of benthic species based on ecological data. The approach implements a Bayesian framework with Gibbs 'Markov chain Monte Carlo' sampling, and enables to assess the influence of phylogenetic information on species distribution patterns. The HMSC at Potter Cove, West Antarctic Peninsula (WAP), includes a variety of environmental variables, such as water temperature, salinity, bathymetry, distance to the glacier, sediment grain size, suspended particulate matter, and current velocity, among others. As a result, we present habitats for selected benthic communities in prediction maps, and we provide the species composition and spatial variability within the study area. We identify the environmental variables with the highest impact on the benthic community distribution, pinpointing the critical ecological factors in times of climate change. And we learn about the species coexistence patterns, the role of species interactions, and phylogenetic relationships in shaping community structures. The application of HMSC at Potter Cove contributes to the estimation of coastal blue carbon at the WAP, and thus to better coastal conservation planning for Polar regions
Using AI-based numerical weather prediction models for climate applications
No full textState-of-the-art AI-based numerical weather prediction models (AI-NWP) produce forecasts that are comparable or even outperform conventional forecasting systems while being orders of magnitude faster. Since climate projections are obtained by simulating the long-term evolution of weather states with appropriate forcing, the use of AI-NWP models for climate modeling is a promising avenue that has received little attention so far. We present two applications of AI-NWP models for climate modeling: (i) downscaling and (ii) weather forecasting initialised from climate projection data. Both applications use ERA5-pre-trained AI-NWP models without fine-tuning for the tasks or for the input data. For downscaling, we use low-resolution CMIP6 simulation data as initial condition and obtain high-resolution, bias corrected output fields by performing short-term forecasting with the existing model; see Fig. 1 for an example. Our results show a remarkable robustness of AI-NWP to unseen states from historical and climate simulations of different resolutions. For AI-based weather forecasting in future climates, we obtain almost unchanged RMSE scores in a 2o warmer climate although a more detailed analysis shows a cold bias in the forecasts. We believe that differences between climate model results and AI-NWP forecasts have the potential to provide insights into the physics and deficiencies of both climate models (e.g. for short time scales) and AI-NWP models (on long time scales). Based on our results, we discuss how existing AI-NWP models can be extended for climate projections, e.g. to sample extreme weather events, and hence help with adaptation to climate change
Tibetan terrestrial and aquatic ecosystems collapsed with cryosphere loss inferred from sedimentary ancient metagenomics
Get PDFGlacier and permafrost shrinkage and land-use intensification threaten mountain wildlife and affect nature conservation strategies. Here, we present paleometagenomic records of terrestrial and aquatic taxa from the southeastern Tibetan Plateau covering the last 18,000 years to help understand the complex alpine ecosystem dynamics. We infer that steppe-meadow became woodland at 14 ka (cal BP) controlled by cryosphere loss, further driving a herbivore change from wild yak to deer. These findings weaken the hypothesis of top-down control by large herbivores in the terrestrial ecosystem. We find a turnover in the aquatic communities at 14 ka, transitioning from glacier-related (blue-green) algae to abundant nonglacier-preferring picocyanobacteria, macrophytes, fish, and otters. There is no evidence for substantial effects of livestock herding in either ecosystem. Using network analysis, we assess the stress-gradient hypothesis and reveal that root hemiparasitic and cushion plants are keystone taxa. With ongoing cryosphere loss, the protection of their habitats is likely to be of conservation benefit on the Tibetan Plateau
No respite from permafrost-thaw impacts in the absence of a global tipping point
Get PDFArctic permafrost, the largest non-seasonal component of Earth’s cryosphere, contains a substantial climate-sensitive carbon pool. The existence of a global tipping point, a warming threshold beyond which permafrost thaw would accelerate and become self-perpetuating, remains debated. Here we provide an integrative Perspective on this question, suggesting that despite several permafrost-thaw feedbacks driving rapid thaw and irreversible ground-ice loss at local to regional scales, the accumulated response of Arctic permafrost to climate warming remains quasilinear. We argue that in the absence of a global tipping point there is no safety margin within which permafrost loss would be acceptable. Instead, each increment of global warming subjects more land areas underlain by permafrost to thaw, causing detrimental local impacts and global feedbacks
Direct and indirect cumulative effects of temperature, nutrients, and light on phytoplankton growth
Get PDFTemperature and resource availability are pivotal factors influencing phytoplankton community structures. Numerous prior studies demonstrated their significant influence on phytoplankton stoichiometry, cell size, and growth rates. The growth rate, serving as a reflection of an organism's success within its environment, is linked to stoichiometry and cell size. Consequently, alterations in abiotic conditions affecting cell size or stoichiometry also exert indirect effects on growth. However, such results have their limitations, as most studies used a limited number of factors and factor levels which gives us limited insights into how phytoplankton respond to environmental conditions, directly and indirectly. Here, we tested for the generality of patterns found in other studies, using a combined multiple-factor gradient design and two single species with different size characteristics. We used a structural equation model (SEM) that allowed us to investigate the direct cumulative effects of temperature and resource availability (i.e., light, N and P) on phytoplankton growth, as well as their indirect effects on growth through changes in cell size and cell stoichiometry. Our results mostly support the results reported in previous research thus some effects can be identified as dominant effects. We identified rising temperature as the dominant driver for cell size reduction and increase in growth, and nutrient availability (i.e., N and P) as dominant factor for changes in cellular stoichiometry. However, indirect effects of temperature and resources (i.e., light and nutrients) on species' growth rates through cell size and cell stoichiometry differed across the two species suggesting different strategies to acclimate to its environment
Properties of Cirrus Cloud Observed over Koror, Palau (7.3°N, 134.5°E), in Tropical Western Pacific Region
Get PDFThis study presented an analysis of the geometric and optical properties of cirrus clouds with data produced by Compact Cloud-Aerosol Lidar (ComCAL) over Koror, Palau (7.3°N, 134.5°E), in the Tropical Western Pacific region. The lidar measurement dataset covers April 2018 to May 2019 and includes data collected during March, July and August 2022. The results show that cirrus clouds occur approximately 47.9% of the lidar sampling time, predominantly between altitudes of 15 and 18 km. Seasonal variations in cirrus top height closely align with those of the cold point tropopause. Most cirrus clouds exhibit low cloud optical depth (COD < 0.1), with an annual mean depolarization ratio of 31 ± 19%. Convective-forming cirrus clouds during the summer monsoon season exhibit a larger size by notably lower values in terms of color ratio. Extremely thin cirrus clouds (COD < 0.005) constituting 1.6% of total cirrus occurrences are frequently observed at 1–2 km above the cold point, particularly during winter and summer, suggesting significant stratosphere–troposphere exchange. The coldest and highest tropopause over Palau is persistent during winter, and related to the pathway of tropospheric air entering the stratosphere through the cold trap. In summer, the extremely thin cirrus above the cold point is likely correlated with equatorial Kelvin waves induced by western Pacific monsoon convection
Atmospheric blocking slows ocean-driven melting of Greenland’s largest glacier tongue
No full textMass loss from the Greenland ice sheet has contributed to global sea-level rise over the past 20 years. Yet direct observations from the 79 North Glacier (79NG) calving front reveal decreasing Atlantic Intermediate Water (AIW) temperatures below the ice tongue from 2018 to 2021, leading to reduced ocean heat transport. This is linked to a concurrent decrease in basal melt and thinning rates at the grounding line. The origin of this AIW cooling is traced to a slowdown of the large-scale ocean circulation in the Nordic Seas, driven by European atmospheric blocking that strengthens cold air advection from the central Arctic through the Fram Strait. Blocking has driven major ocean cooling events over the last 50 years and will remain crucial in affecting Northeast Greenland's glaciers
The Cumulative Effect of Wintertime Weather Systems on the Ocean Mixed‐Layer Stable Isotope Composition in the Iceland and Greenland Seas
Get PDFThe Iceland and Greenland Seas are characterized by strong heat fluxes from the ocean to the
atmosphere during wintertime. Here we characterize the atmospheric signal of this strong evaporation in terms of water vapor isotopes and investigate if such a signal can have a cumulative imprint on the ocean mixed‐layer. Observations include continuous water vapor isotope measurements, event‐based precipitation samples, and
sea-water samples taken at various depths from the research vessel Alliance during the Iceland‐Greenland Seas Project cruise in February and March 2018. In conjunction with a simulation from a regional, isotope‐enabled atmospheric model, we find that the predominant atmospheric isotope signature during predominant marine
cold‐air outbreak conditions is−129.8 ±16.6‰ for δ2H and −18.10 ±2.87‰ for δ18O, with a d‐excess of 15.1±7.9‰, indicating enhanced non‐equilibrium fractionation compared to the global average. During events of warm‐air intrusion from mid‐latitudes, near‐surface vapor becomes saturated and the vapor d‐excess approaches equilibrium or becomes negative. Similarly, precipitation d‐excess is lower and thus closer to equilibrium conditions during warm‐air intrusions. There are indications that an evaporation signal of waters exiting the Nordic Seas through Denmark Strait could be locally enhanced over seasons to years, as supported by simple model calculations. Our findings thus suggest that evaporation signals could be transferred into the ocean isotope composition in this region, potentially enabling mass‐balance constraints in isotope‐enabled coupled ocean‐atmosphere models
Inland Summer Speedup at Zachariæ Isstrøm, Northeast Greenland, Driven by Subglacial Hydrology
Get PDFThe Northeast Greenland Ice Stream (NEGIS) has experienced substantial dynamic thinning in recent years. Here, we examine the evolving behavior of NEGIS, with focus on summer speedup at Zachariae Isstrøm, one of the NEGIS outlet glaciers, which has exhibited rapid retreat and acceleration, indicative of its vulnerability to changing climate conditions. Through a combination of Sentinel-1 data, in-situ GPS observations, and numerical ice flow modeling from 2007, we investigate the mechanisms driving short-term changes. Our analysis reveals a summer speedup in ice flow both near the terminus and inland, with satellite data detecting changes up to 60 km inland, while GPS data capture changes up to 190 km inland along the glacier center line. We attribute this summer speedup to variations in subglacial hydrology, where surface meltwater runoff influences basal friction over the melt season. Incorporating subglacial hydrology into numerical models makes it possible to replicate observed ice velocity patterns
Biocalcification in porcelaneous foraminifera
Get PDFLiving organisms control the formation of mineral skeletons and other structures through
biomineralization. Major phylogenetic groups usually consistently follow a single
biomineralization pathway. Foraminifera, which are very efficient marine calcifiers, making
a substantial contribution to global carbonate production and global carbon sequestration,
are regarded as an exception. This phylum has been commonly thought to follow two
contrasting models of either in situ “mineralization of extracellular matrix” attributed to
hyaline rotaliid shells, or “mineralization within intracellular vesicles” attributed to
porcelaneous miliolid shells. Our previous results on rotaliids along with those on miliolids in
this paper question such a wide divergence of biomineralization pathways within the same
phylum of Foraminifera. We found that both groups produced calcareous shells via the
intravesicular formation of unstable mineral precursors (Mg-rich amorphous calcium
carbonates) supplied by endocytosed seawater and deposited at the site of new wall
formation within the organic matrix. Precipitation of high-Mg calcitic mesocrystals took place
in situ and formed a dense, chaotic meshwork of needle-like crystallites. We did not observe
deposition of calcified needles that had already precipitated in the transported vesicles,
which challenges the previous model of miliolid mineralization. Hence, Foraminifera utilize
less divergent calcification pathways, following the recently discovered biomineralization
principles. Mesocrystalline chamber walls are therefore apparently created by accumulating
and assembling particles of pre-formed liquid amorphous mineral phase within the
extracellular organic matrix enclosed in a biologically controlled privileged space by active
pseudopodial structures. Both calcification pathways evolved independently in the Paleozoic
and are well-conserved in two clades that represent different chamber formation modes