Alfred Wegener Institute for Polar and Marine Research
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Deciphering the Neurotoxic Effects of Karenia selliformis
Get PDFKarenia selliformis is a globally recognized dinoflagellate associated with harmful algal blooms and massive fish kills along southern Chilean coasts. Its toxicity varies with environmental factors and genetic diversity. While K. selliformis is traditionally linked to neurotoxins like gymnodimines (GYMs), analysis of the strain CREAN-KS02 from Chile’s Aysén Region (43° S) revealed no presence of toxins associated with this genus, such as gymnodimines, brevetoxins, or brevenal. Given the high toxicity and impact on marine life, our study aimed to functionally characterize the neurotoxic metabolites in the exudate of K. selliformis cultures. Cytotoxicity was evaluated using a Neuro-2a cell-based assay (CBA), determining an IC50 of 2.41 ± 0.02 μg mL−1. The incubation of Neuro-2a cells with the bioactive lipophilic extract obtained from the exudate of K. selliformis and the ouabain/veratridine couple showed activation of voltage-gated ion channels. Electrophysiological recordings on cultured mouse hippocampal neurons showed that the extract increased cell excitability in a dose-dependent manner, modulating action potential firing and exhibiting an opposed effect to tetrodotoxin. These findings indicate the presence of excitatory neurotoxic compounds affecting mammalian cells. This study provides the first mechanistic evidence of K. selliformis toxicity and highlights potential risks associated with its proliferation in marine environments
The Two Arctic Wintertime Boundary Layer States: Disentangling the Role of Cloud and Wind Regimes in Reanalysis and Observations During <scp>MOSAiC</scp>
Get PDFABSTRACTThe wintertime central Arctic atmosphere comprises a radiatively clear and a radiatively opaque state, which are linked to synoptic forcing and mixed‐phase clouds. Weather and climate models often lack process representations surrounding these states, but prior work mostly treated the problem as an aggregate of synoptic conditions, resulting in partially overlapping biases. Here, we disaggregate the Arctic states and confront ERA5 reanalysis with observations from the MOSAiC campaign over the central Arctic sea ice during winter 2019/2020. Low‐level winds and liquid water path (LWP) are combined to derive different synoptic classes. Results show that the clear state is primarily formed by weak/moderate winds and the absence of liquid‐bearing clouds, while strong winds and enhanced LWP primarily form the radiatively opaque state. ERA5 struggles to reproduce these basic statistics, shows too weak sensitivity of thermal radiation to synoptic forcing, and overestimates thermal radiation for similar LWP amounts. The latter is caused by a warm bias, which has a pronounced inversion structure and is largest in clear and calm conditions. Under strong synoptic forcing, the warm bias is constant with height and discrepancies in mixed‐phase cloud altitude appear. Separating synoptic conditions is regarded as useful for process‐oriented evaluation of the Arctic troposphere in models.</jats:p
Closing the Plio-Pleistocene 13C cycle in the 405-kyr periodicity by isotopic signatures of geological sources
Get PDFTo unravel which processes are responsible for changes in atmospheric CO2 the carbon isotopes are useful helpers widely applied in the past. This study helps to better understand long-term changes in 13C, which has also consequences for the interpretation of atmospheric δ13CO2 measured together with CO2 in ice cores.
The 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 that the long eccentricity cycle 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 peridicities also explains the offset in atmospheric δ13CO2 seen between the penultimate and the last glacial maximum. The necessary isotopic signatures in δ13Crock or δ13Cv which align my simulations with reconstructions of the 13C cycle on orbital timscales have 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 has also an obliquity-related component 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 ice-free times of the pre-Pliocene parts of the Cenozoic.
See preprint (https://doi.org/10.5194/cp-2024-63) for details
Dominant control of temperature on (sub-)tropical soil carbon turnover
Get PDFCarbon storage in soils is important in regulating atmospheric carbon dioxide (CO2). However, the sensitivity of the soil-carbon turnover time (τ_soil) to temperature and hydrology forcing is not fully understood. Here, we use radiocarbon dating of plant-derived lipids in conjunction with reconstructions of temperature and rainfall from an eastern Mediterranean sediment core receiving terrigenous material from the Nile River watershed to investigate τ_soil in subtropical and tropical areas during the last 18,000 years. We find that τ_soil was reduced by an order of magnitude over the last deglaciation and that temperature was the major driver of these changes while the impact of hydroclimate was relatively small. We conclude that increased CO2 efflux from soils into the atmosphere constituted a positive feedback to global warming. However, simulated glacial-to-interglacial changes in a dynamic global vegetation model underestimate our data-based reconstructions of soil-carbon turnover times suggesting that this climate feedback is underestimated
On the path to cosmopolitanism: the continuing geographic expansion of Caprella mutica (Crustacea, Amphipoda)
Get PDFHuman activities have been transporting caprellid amphipods (or “skeleton shrimps”) across the oceans for many decades. As a result, some caprellid amphipods now are among the most widespread non-indigenous species in many different coastal regions of the world. The global spread of these species is still ongoing in some cases, such as that of the successful invader Caprella mutica Schurin, 1935. Here, we report on the arrival of C. mutica in South America and modelled its environmental niche based on its current global distribution in order to evaluate future expansion risks. The species distribution model confirmed high occupancy probabilities for already invaded areas of Europe and North America with generally lower probabilities in the southern hemisphere and mean sea surface temperature as best predictor. Further, the model suggested that our discovery of C. mutica in northern Chile was made in a region that is less favorable for this species, while occupancy probabilities increased further south. Given the invasion history of C. mutica in other marine regions of the world and the more favorable oceanographic conditions, a further spread of this invader southwards along the South American Pacific coast seems very likely
Governing Processes of Structure‐Borne Snowdrifts: A Case Study at Neumayer Station III
No full textThe genesis of snowdrifts and its governing processes are not fully understood. In Antarctica, understanding snow movement is crucial for assessing ice sheet mass balance and tackling logistical challenges related to human infrastructure. So far, extensive research has focused on snow‐wind interactions on flat terrain, emphasizing the crucial roles of flow turbulence and snow properties. This work expands an existing Eulerian‐ Lagrangian model by incorporating buildings to simulate snowdrifts around complex structures, using advanced saltation physics. The German Antarctic research station Neumayer III is used as a test site. This development brings new levels of interaction between snow particles and larger structures, making the simulations more representative of real‐world conditions. Specifically, numerical simulations were conducted to test the influence of six parameters on snowdrift formation, namely: wind force, snowbed cohesion, particle diameter, precipitation rate and building height and shape. Results show that the size of snowdrifts is mostly affected by wind force, preferential deposition and snowbed cohesion, while fine features of the building shape control their form. Nevertheless, significant uncertainties remain regarding the interaction of these parameters, highlighting the need for further research to improve modeling frameworks. This study demonstrates that our model is wellsuited for engineering applications, guiding optimal designs for buildings and infrastructure in snow‐affected environments
Long-term changes of wildfire regimes in eastern Siberia: an evaluation based on lake sediment indicators and individual-based modeling
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Genomes of the Caribbean reef-building corals Colpophyllia natans, Dendrogyra cylindrus, and Siderastrea siderea
Get PDFCoral populations worldwide are declining rapidly due to elevated ocean temperatures and other human impacts. The Caribbean harbors a high number of threatened, endangered, and critically endangered coral species compared to reefs of the larger Indo-Pacific. The reef corals of the Caribbean are also long diverged from their Pacific counterparts and may have evolved different survival strategies. Most genomic resources have been developed for Pacific coral species which may impede our ability to study the changes in genetic composition of Caribbean reef communities in response to global change. To help fill the gap in genomic resources, we used PacBio HiFi sequencing to generate the first genome assemblies for three Caribbean, reef-building corals, Colpophyllia natans, Dendrogyra cylindrus, and Siderastrea siderea. We also explore the genomic novelties that shape scleractinian genomes. Notably, we find abundant gene duplications of all classes (e.g., tandem and segmental), especially in S. siderea. This species has one of the largest genomes of any scleractinian coral (822Mb) which seems to be driven by repetitive content and gene family expansion and diversification. As the genome size of S. siderea was double the size expected of stony corals, we also evaluated the possibility of an ancient whole genome duplication using Ks tests and found no evidence of such an event in the species. By presenting these genome assemblies, we hope to develop a better understanding of coral evolution as a whole and to enable researchers to further investigate the population genetics and diversity of these three species.</jats:p
Assessing planimetric and volumetric coastal changes on Herschel Island Qikiqtaruk, Yukon, Canada
Get PDFPermafrost coasts in the Arctic are extremely vulnerable to the effects of global climate change. The increase in sea temperature, the decrease in sea ice extent and longer open-water seasons lead to higher coastal erosion. These erosion rates are among the highest worldwide. This results in significant land loss, both planimetric and volumetric, and leads to a notable reshaping of the coastline. Coastal erosion rates are usually reported in 2 dimensions and focus on the shoreline movement. Few studies have attempted to compute the volumes eroded by coastal retreat. The goal of this study is to connect planimetric and volumetric coastal erosion measurements and to serve as an update of coastal erosion rates in the most recent years on Herschel Island Qikiqtaruk (HIQ) in the Western Canadian Beaufort Sea. LiDAR-derived high-resolution digital elevation models (DEMs) were used to compute volumetric data for the years 2013 and 2023. For the planimetric changes we used digitized coastlines derived from satellite imagery in 2000, 2011 and 2022. Our preliminary results show that the average planimetric erosion ranges between -0.71 and -0.74 [m^2/(m*a)] for the observed periods 2000-2011 and 2011-2022. The volumetric erosion along the entire coastline of Herschel Island Qikiqtaruk experiences a drastic coastal retreat with average values of -33.18 [m^3/(m*a)] whereas the highest values occur along the northwestern, northern and northeastern coastlines of HIQ. This increase can have large implications on the near-shore ecosystems of the island and extensive impacts for the settlement on Herschel Island Qikiqtaruk in the future