Alfred Wegener Institute for Polar and Marine Research
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Unraveling boreal forest composition and drivers across scales in eastern Siberia
Get PDFThe Siberian boreal forest is the largest continuous forest region on Earth and plays a crucial role in regulating global climate. However, the distribution and environmental processes behind this ecosystem are still not well understood. Here, we first develop Sentinel-2-based classified maps to show forest-type distribution in five regions along a southwest-northeast transect in eastern Siberia. Then, we constrain the environmental factors of the forest-type distribution based on a multivariate analysis of bioclimatic variables, topography, and ground-surface temperatur at the local and regional scales. Furthermore, we identify potential versus realized forest-type niches and their applicability to other sites. Our results show that mean annual temperature and mean summer and winter temperatures are the most influential predictors of forest-type distribution. Furthermore, we show that topography, specifically slope, provides an additional but smaller impact at the local scale. We find that the filling of climatic environmental niches by forest types decreases with geographic distance, but that the filling of topographic niches varies from one site to another. Our findings suggest that boreal forests in eastern Siberia are driven by current climate and topographical factors, but that there remains a portion of the variability that cannot be fully accounted for by these factors alone. While we hypothesize that this unexplained variance may be linked to legacies of the Late Glacial, further evidence is needed to substantiate this claim. Such results are crucial to understanding and predicting the response of boreal forests to ongoing climate change and rising temperatures
Life in a warmer world
Get PDFWhile the global mean temperature indicates that human activities are altering the climate, the local implications of these changes are much less explored. This presentation aims to bridge that gap by discussing recent developments in climate modelling, including storylines, that provide a more tangible understanding of climate change impacts at the local level. Through these insights, we aim to enhance our comprehension of the real-world consequences of a warming planet, thereby supporting adaptation and mitigation
DNA metabarcoding reveals a diverse, omnivorous diet of Arctic amphipods during the polar night, with jellyfish and fish as major prey
Get PDFIntroduction: Currently, Arctic marine ecosystems are witnessing the most rapid physical changes worldwide, leading to shifts in pelagic and benthic communities and food web structure, concomitant with the introduction of boreal species. Gelatinous zooplankton or jellyfish represent one particular group of which several boreal species are prone to undergo significant poleward range expansions and population increases in the Arctic in the course of the ongoing changes. Historically, jellyfish were considered a trophic dead-end, but an increasing number of studies using modern tools have highlighted their role as major prey items in marine food webs. In this study, we aimed to verify the role of jellyfish and other metazoans as food sources in the Arctic polar night food web, when pelagic resources are limited. Methods: We identified the diet of different bentho-pelagic amphipod species in the Atlantifying Kongsfjorden (West Svalbard) during the polar night. We regularly sampled lysianassoid and gammarid amphipods using baited traps and hand nets over a period of one month during the polar night and identified their diet spectrum by applying DNA metabarcoding (COI) to their stomach contents. Results: We demonstrate that all investigated species are omnivorous. Fish species including polar cod and snailfish, likely in the shape of carrion, played an important role in the diet of the scavengers Orchomenella minuta and Anonyx sarsi. Predation and potential scavenging on jellyfish contributed to the diet of all four investigated species, particularly for the species Gammarus setosus and G. oceanicus, as evidenced by high read abundances and high frequencies of occurrence. Besides jellyfish, crustaceans and macroalgae were important components of the diet of the two Gammarus species. Discussion: The diverse jellyfish community present in Kongsfjorden in the polar night is clearly being utilized as a food source, either through pelagic feeding or feeding on jelly-falls, albeit to a different extent in the local amphipod community. These findings provide novel insights into the Arctic food web during the polar night and represent the first evidence of feeding on natural (non-experimental) jelly-falls
Revealing the profound influence of diapause on gene expression: Insights from the annual transcriptome of the copepod Calanus finmarchicus
Get PDFAnnual rhythms are observed in living organisms with numerous ecological implications. In the zooplanktonic copepod Calanus finmarchicus, such rhythms are crucial
regarding its phenology, body lipid accumulation, and global carbon storage. Climate change drives annual biological rhythms out of phase with the prevailing environmental conditions with yet unknown but potentially catastrophic consequences. However, the molecular dynamics underlying phenology are still poorly described. In a rhythmic analysis of C. finmarchicus annual gene expression, results reveal that more than 90% of the transcriptome shows significant annual rhythms, with abrupt and dramatic upheaval between the active and diapause life cycle states. This work explores the implication of the circadian clock in the annual timing, which may control epigenetic mechanisms to profoundly modulate gene expression in response to calendar time. Results also suggest an increased light sensitivity during diapause that would ensure the photoperiodic entrainment of the endogenous annual clock
Allelochemicals determine competition and grazing control in Alexandrium catenella
Get PDFThe production of allelochemicals by the toxigenic dinoflagellate Alexandrium catenella is one of the suggested mechanisms to facilitate its bloom formation and persistence by outcompeting other phototrophic protists and reducing grazing pressure. In Southern California, toxic events caused by A. catenella and paralytic shellfish toxins (PSTs) regularly impact coastal ecosystems; however, the trophic interactions and mechanisms promoting this species in a food web context are still not fully understood. In the present study, we combined a dynamical mathematical model with laboratory experiments to investigate potential toxic and allelochemical effects of an A. catenella strain isolated off the coast of Los Angeles, Southern California, on competitors and a common zooplankton consumer. Experiments were conducted using three toxigenic strains of A. catenella, comparing the new Californian isolate (Alex Cal) to two strains previously described from the North Sea, a lytic (Alex2) and non-lytic (Alex5) strain, testing for donor density-dependent effects on two phytoplankton species (Rhodomonas salina, Tetraselmis sp.) and on the rotifer Brachionus plicatilis. Bioassays revealed a steep decline in competitor and consumer populations with increasing Alex Cal concentrations, indicating an intermediate lytic activity compared to the North Sea strains (lytic Alex2 and non-lytic Alex5). The rotifer fed and grew well on the PST- toxic, but non-lytic Alex5 strain, while its survival significantly decreased with increasing concentrations of the two lytic strains Alex Cal and Alex 2, indicating that negative effects on the rotifer were mediated by allelochemicals rather than PST-toxins. Mixed culture experiments including both competitors and consumers demonstrated that the intensity of allelochemical effects not only depended on the A. catenella density but also on the target density. Negative effects on grazers were alleviated by co-occurring competitors with a lower sensitivity to allelochemicals, thus reducing harmful compounds and allowing grazing control on the dinoflagellate to come into effect again. Results from mixed culture experiments were supported by the mathematical approach used in this study which was calibrated with data from simple monoculture growth, pairwise competition and predator-prey experiments, demonstrating the applicability of this model approach to predict the outcome of more complex food web dynamics at the community level
Detection and Exclusion of False-Positive Molecular Formula Assignments via Mass Error Distributions in UHR Mass Spectra of Natural Organic Matter
Get PDFUltrahigh resolution mass spectrometry (UHRMS) routinely detects and identifies thousands of mass peaks in complex mixtures, such as natural organic matter (NOM) and petroleum. The assignment of several chemically plausible molecular formulas (MFs) for a single accurate mass still poses a major problem for the reliable interpretation of NOM composition in a biogeochemical context. Applying sensible chemical rules for MF validation is often insufficient to eliminate multiple assignments (MultiAs)─especially for mass peaks with low abundance or if ample heteroatoms or isotopes are included - and requires manual inspection or expert judgment. Here, we present a new approach based on mass error distributions for the identification of true and false assignments among MultiAs. To this end, we used the mass error in millidalton (mDa), which was superior to the commonly used relative mass error in ppm. We developed an automatic workflow to group MultiAs based on their shared formula units and Kendrick mass defect values and to evaluate the mass error distribution. In this way, the number of valid assignments of chlorinated disinfection byproducts was increased by 8-fold as compared to only applying 37Cl/35Cl isotope ratio filters. Likewise, phosphorus-containing MFs can be differentiated against chlorine-containing MFs with high confidence. Further, false assignments of highly aromatic sulfur-containing MFs (“black sulfur”) to sodium adducts in negative ionization mode can be excluded by applying our approach. Overall, MFs for mass peaks that are close to the detection limit or where naturally occurring isotopes are rare (e.g., 15N) or absent (e.g., P and F) can now be validated, substantially increasing the reliability of MF assignments and broadening the applicability of UHRMS analysis to even more complex samples and processes
Constraining glacial ocean carbon cycle – A multi-model study
Get PDFThe ocean contained a larger carbon content at the Last Glacial Maximum (LGM, ~21kyr before present) compared to the late Holocene, making a considerable contribution to the deglacial atmospheric CO2 rise of about 90 ppm. Yet, there’s no consensus on the mechanisms controlling the glacial-interglacial changes in oceanic carbon storage due to uncertainties and sparseness of proxy data. Numerical simulations have been widely used to quantify the impact of key factors, such as changes in sea surface temperatures, ocean circulation and biological production, on glacial ocean carbon sequestration. However, the robustness of these findings is subject to further testing due to the differences in process representation, parameterization, model architecture, or external forcing employed by models.
Towards further constraining the LGM ocean carbon cycle, we conducted a multi-model comparison with three comprehensive Earth System Models (Alfred Wegener Institute Earth System Model, AWI-ESM; Community Earth System Model, CESM; Max Planck Institute Earth System Model, MPI-ESM) and one Earth system Model of Intermediate Complexity (CLIMBER-X). We carried out three coordinated experiments with each model: 1) PI (the pre-industrial control simulation), 2) LGM-PMIP (following PMIP4 LGM protocol) and 3) LGM-LowCO2 (as LGM-PMIP, but with boosted alkalinity inventory to lower atmospheric CO2 to about 190 ppm. All experiments were conducted with the prognostic CO2 for the carbon cycle, considering only the atmosphere and ocean reservoirs, and prescribed CO2 for radiative forcing.
All models consistently show that applying the PMIP4 LGM boundary conditions alone leads to only a 5-40 ppm decrease in atmospheric CO2. Globally, the glacial CO2 drawdown in LGM-PMIP is mainly controlled by the enhanced solubility pump. The spatial distribution of the increased glacial DIC depends on the ocean circulation state in each model. In MPI-ESM and CLIMBER-X, the shallower and weaker AMOC facilitates carbon storage in the deep Atlantic. An LGM atmospheric CO2 of 190 ppm can be achieved by boosting alkalinity by 5-8% in scenario LGM-LowCO2. In all models, boosting LGM alkalinity inventory increases DIC in the bottom water. However, comparison to proxy data reveals that the models lack respired carbon, particularly in the deep Pacific. This suggests a need to enhance the glacial biological carbon pump in the models.</jats:p
Late Cenomanian Plenus event in the Western Interior Seaway
No full textThe Late Cenomanian Plenus Cold Event is one of the most enigmatic paleoclimate episodes in Earth history with potential to inform understanding of global climate system variability under greenhouse warming conditions, as well as internal feedback pathways that modulate such variability. Following an interpreted massive addition of volcanic CO2 to the atmosphere and warming that led to a major ocean anoxic event (OAE2), there was a brief interval of cooling recorded in oxygen isotopes and biogeographic data. Here we present evidence that cooling was absent or muted within the Western Interior Seaway (WIS). Clumped isotope data from the basin suggest persistent extreme warmth during the Late Cenomanian, macroinvertebrate fossil assemblages do not record a decrease in temperature, and changes in other paleoceanographic proxies do not correlate temporally with Plenus interval signals from other locales. Using select proxy data to guide construction of GCM model simulations, we explore possible hypotheses to explain these observations. Our results suggest that the paleogeographic configuration of the basin and its gateways to adjoining oceans, which evolved in association with changing pCO2 and sea level, influenced winter sea ice formation at the northern aperture of the seaway, water mass circulation, salinity, temperature, and water column stratification. We propose that northward advection of warm Tethyan water muted expression of Plenus cooling in the seaway. Understanding the unique character of the Western Interior paleoceanographic record provides critical input for the development of robust models of ancient Earth System dynamics and should aid predictions of future climate system dynamics
Transition from a mixotrophic/heterotrophic protist community during the dark winter to a photoautotrophic spring community in surface waters of Disko Bay, Greenland
Get PDFUnicellular eukaryotic plankton communities (protists) are the major basis of the marine food web. The spring bloom is especially important, because of its high biomass. However, it is poorly described how the protist community composition in Arctic surface waters develops from winter to spring. We show that mixotrophic and parasitic organisms are prominent in the dark winter period. The transition period toward the spring bloom event was characterized by a high relative abundance of mixotrophic dinoflagellates, while centric diatoms and the haptophyte Phaeocystis pouchetii dominated the successive phototrophic spring bloom event during the study. The data shows a continuous community shift from winter to spring, and not just a dormant spring community waiting for the right environmental conditions. The spring bloom initiation commenced while sea ice was still scattering and absorbing the sunlight, inhibiting its penetration into the water column. The initial increase in fluorescence was detected relatively deep in the water column at ~55 m depth at the halocline, at which the photosynthetic cells accumulated, while a thick layer of snow and sea ice was still obstructing sunlight penetration of the surface water. This suggests that water column stratification and a complex interplay of abiotic factors eventually promote the spring bloom initiation