Alfred Wegener Institute for Polar and Marine Research
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A circadian clock drives behavioral activity in Antarctic krill (Euphausia superba) and provides a potential mechanism for seasonal timing
Get PDFAntarctic krill is a species with fundamental importance for the Southern Ocean ecosystem. Their large biomass and synchronized movements, like diel vertical migration (DVM), significantly impact ecosystem structure and the biological carbon pump. Despite decades of research, the mechanistic basis of DVM remains unclear. Circadian clocks help organisms anticipate daily environmental changes, optimizing adaptation. In this study, we used a recently developed activity monitor to record swimming activity of individual, wild-caught krill under various light conditions and across different seasons. Our data demonstrate how the krill circadian clock, in combination with light, drives a distinct bimodal pattern of swimming activity, which could facilitate ecologically important behavioral patterns, such as DVM. Rapid damping and flexible synchronization of krill activity indicate that the krill clock is adapted to a life at high latitudes and seasonal activity recordings suggest a clock-based mechanism for the timing of seasonal processes. Our findings advance our understanding of biological timing and high-latitude adaptation in this key species.
The Southern Ocean is home to whales, seals, seabirds and other iconic wildlife. All of these animals depend either directly, or indirectly, on a small marine prey species known as Antarctic krill, which thrives in the harsh conditions of the Southern Ocean. At night, large swarms of krill move towards the water surface to feed on plankton before returning to the depths during the day to avoid whales, fish and other predators. This synchronized movement influences the structure of the ecosystem in a number of ways by transporting carbon and influencing predator-prey interactions. Researchers have observed the movements of krill swarms for many decades, but the processes controlling this swimming behavior remained unknown, in part, due to a lack of tools that can track the movements of individual krill. Do the krill simply respond to light and other external cues, or do they also have internal biological clocks that can maintain the observed rhythms even without such cues? In 2024, researchers developed a new monitor known as AMAZE, which can record the swimming activity of individual krill in tanks of seawater. Hüppe et al. – including many of the researchers involved in the 2024 work – have now used this technique to trace the movement of individual wild-caught krill under different light conditions and seasons. Hüppe et al. captured krill from the Southern Ocean on a commercial fishing boat and transferred them into a tank on the vessel for experiments. Observations revealed that the krill were most active at night, matching their natural patterns of migration in the wild. These patterns of nighttime activity adjusted to the changing length of the night over the seasons. Furthermore, the krill maintained a daily rhythm of activity even when they were kept in constant darkness for several days. These findings suggest that an internal biological clock, in combination with light cues, regulates the swimming patterns of krill and helps them adapt to daily and seasonal changes in their environment. Understanding these internal rhythms will be key to assessing how well krill may cope with rapid changes in their environment due to climate change, which are particularly pronounced in polar regions
A new habitat map of the Lena Delta in Arctic Siberia based on field and remote sensing datasets
Get PDFThe Lena Delta is the largest river delta in the Arctic (about 30 000 km2) and prone to rapid changes due to climate warming, associated cryosphere loss, and ecological shifts. The delta is characterized by ice-rich permafrost landscapes and consists of geologically and geomorphologically diverse terraces covered with tundra vegetation and of active floodplains, featuring approximately 6500 km of channels and over 30 000 lakes. Because of its broad landscape and habitat diversity, the delta is a biodiversity hotspot with high numbers of nesting and breeding migratory birds, fish, caribou, and other mammals and was designated a State Nature Reserve in 1995. Characterizing plant composition, aboveground biomass, and application of field spectroscopy was a major focus of a 2018 expedition to the delta. These field data collections were linked to Sentinel-2 satellite data to upscale local patterns in land cover and associated habitats to the entire delta. Here, we describe multiple field datasets collected in the Lena Delta during summer 2018 including foliage projective cover (Shevtsova et al., 2025, https://doi.org/10.1594/PANGAEA.935875), aboveground biomass (Shevtsova et al., 2023, https://doi.org/10.1594/PANGAEA.956067; Shevtsova et al., 2023, https://doi.org/10.1594/PANGAEA.935923), and hyperspectral field measurements (Runge et al., 2022, https://doi.org/10.1594/PANGAEA.945982). We further describe a detailed Sentinel-2 satellite image-based classification of habitats for the central Lena Delta (Landgraf et al., 2025a, https://doi.org/10.1594/PANGAEA.945057; Landgraf et al., 2025b, https://doi.org/10.1594/PANGAEA.945056; Landgraf et al., 2025c, https://doi.org/10.1594/PANGAEA.945055; Landgraf et al., 2025d, https://doi.org/10.1594/PANGAEA.945054), an upscaled classification for the entire Lena Delta (Lisovski et al., 2022, https://doi.org/10.1594/PANGAEA.946407), and the test data set for accuracy assessment (Heim et al., 2025, https://doi.org/10.5281/zenodo.14731823) and a synthesis product for disturbance regimes (Heim and Lisovski, 2023, https://doi.org/10.5281/zenodo.7575691) in the delta that is based on the classification, the described datasets, and field expertise. We present context and detailed methods of these openly available datasets and show how their combined use can improve our understanding of the rapidly changing Arctic tundra system. The new Lena Delta habitat classification represents a first baseline against which future observations can be compared. The link between such detailed habitat classifications and disturbance regime may provide a better understanding of how Arctic lowland landscapes will respond to climate change and how this will impact land surface processes
Climate‐Dependency of Impact of Increased Carbon Dioxide on African Monsoon Rainfall: Insights From Model Simulations
Get PDFPrevious studies on future scenarios identified two key effects of increasing CO2 on the African summer monsoon (ASM): Rising CO2 leads to an enhancement in moisture supply, favoring an increase in
ASM precipitation (the thermodynamic effect). However, it also results in a weakening in mean atmospheric
flow, thus facilitating a dryness across the ASM region (the dynamic effect). Therefore, the ultimate change in
ASM precipitation stems from the balance of both the thermodynamic and dynamic effects. This study further
examines the impact of rising CO2 on ASM rainfall, by taking into account various climate states. Our results
suggest that an increase in CO2 during warm interglacial periods has a stronger influence from thermodynamic
factors than from dynamic factors, resulting in an enhancement in ASM rainfall. In contrast, if CO2 increases
under cold glacial climate backgrounds, its dynamic impact dominates a reduction of rainfall in most ASM
region
Precession Controls on Climate and Water Isotope Signals in Northern Africa
Get PDFPrecessional forcing is a key driver of quaternary climate change. Based on 24 experiments covering a full precession cycle, this study explores spatio‐temporal variations of both climate and isotope signals in Northern Africa. We find a synchronous phasing of precipitation variations with solar radiation levels and an asynchronous timing of surface air temperature changes across different sub‐regions of Northern Africa. Based on daily precipitation, our results reveal earlier onset and withdrawal, as well as a shorter duration of the West Africa summer monsoon (WASM) at minimum precession compared to maximum precession. The onset of the WASM is controlled by the intensity of the Sahara Heat Low, while the monsoon termination is linked to subtropical solar radiation and interhemispheric thermo contrast. Using a novel scale‐flux tracing technique, we
find that, precipitation during minimum precession is more influenced by evaporation from warmer and more humid regions compared to maximum precession. Additionally, certain inland areas of Northern Africa exhibit positive temporal isotope‐precipitation gradients, violating the “amount effect.” This phenomenon mainly occurs during precession phases associated with Green Sahara periods. The isotope composition changes in such places primarily reflect changes in upstream rainfall quantity, rather than changes in local precipitation as is inferred from present day analogs. Conversely, the “amount effect” remains applicable during dry periods in Africa when the Sahara desert is present. This suggests that isotope‐based reconstruction of past precipitation variations during Green Sahara periods over Northern Africa needs to be taken with caution
Postglacial bioweathering, soil nutrient cycling, and podzolization from palaeometagenomics of plants, fungi, and bacteria
Get PDFWarming-induced glacier retreat exposes bare rocks and glacial sediments, facilitating the establishment of soils. The dynamic interplay between climate, vegetation cover, and soil formation is poorly understood as time-series data are lacking. Here, we present postglacial soil formation during the past 23,000 years inferred from ancient DNA shotgun analyses of Lake Lama sediments targeting plants, soil-associated fungi, and bacteria showing postmortem damage signatures that verify their ancient origin. In the Late Glacial, we reveal basaltic weathering with high abundances of lichens, carbon, and arsenic cyclers, shifting to mycorrhizae domination and N cycling in the Holocene. We reconstruct podzolization starting with spruce forest migration in the Holocene, resulting in soil acidification and increased iron cycling. Our reconstruction of soil formation also contributes basic knowledge for the design of carbon-capture strategies using basalt weathering
Eiszeiten in der jüngeren Vergangenheit: Welche Rolle spielte die Sonne im Vergleich zu anderen Prozessen?
Get PDFDie Sonneneinstrahlung auf der Erde läßt sich zu jedem Ort und jeden Tag rückwirkend über die vergangenen Millionen von Jahre berechnen. Hierbei spielen die zeitlichen Veränderungen in drei der orbitalen Parameter eine zentrale Rolle:
- Die Exzentrizität der Erdbahn um die Sonne mit eine Periode von 100.000 Jahren.
- Die Neigung der Erdachse bezüglich der Umlaufbahn (41.000 Jahre).
- Die Präzession sowohl der Erdachse als auch der elliptischen Erdbahn (21.000 Jahre).
In den Klimarekonstruktionen findet sich ein Wechsel in der Periode der Eiszeiten von ca 41.000 Jahren zu ca 100.000 Jahren während der vergangenen 1 Million Jahre, der jedoch nicht in den Sonnneneinstrahlung selbst zu finden ist. Rückkopplungen im Klimasystem sind vermutlich verantwortlich für diese Veränderungen. Zu den wichtigsten Prozessen zählen hier die Konzentration von CO2 in der Erdatmosphäre und der Albedo von großen Landeisschilden. Wie all diese Prozesse interagiert haben können, um die beobachteten Klimaänderungen zu erklären, wird in diesem Vortrag beleuchtet. Schlussendlich wird gezeigt, welchen Erkenntnisse hierbei von 1,5 Millionen Jahre alten Daten von einem in diesen Tagen neugebohrten Eiskern in der Antarktis zu erwarten sind
Anthropogenic stressors that favour nuisance species. A study from environmental DNA in marine plankton samples
Get PDFAnthropogenic stressors reduce marine biodiversity. Tolerant species may develop in altered areas where they occupy niches that native species are unable to use. Species of biosecurity concern, like invasive aliens or harmful microalgae, are especially successful in disturbed areas. Here, we employed multiple regression approach to investigate the relationship between the proportion of planktonic stages of invasives and anthropogenic stressors. Planktonic species were inventoried from environmental DNA on water samples from the Bay of Biscay. Key findings were that the proportion of invasives was associated with port and touristic activities that are vectors for biological invaders, and with industrial pollution, likely for their tolerance to disturbed environments. The proportion of toxic algae was correlated with port activity, reinforcing the role of maritime traffic as a vector of harmful microalgae. An increase of nuisance species is expected under the current growth of pollution in the ocean. Promoting awareness of biological invasions among maritime sectors and tourists, and controlling pollution, seem priorities for environmental conservation in this region and elsewhere
Reconstruction of Holocene and Last Interglacial vegetation dynamics and wildfire activity in southern Siberia
Get PDFAbstract. Wildfires are a rapidly increasing threat to boreal forests. While our understanding of the drivers behind wildfires and their environmental impact is growing, it is mostly limited to the observational period. Here we focus on the boreal forests of southern Siberia and exploit a U–Th-dated stalagmite from Botovskaya Cave, located in the upper Lena region of southern Siberia, to document wildfire activity and vegetation dynamics during parts of two warm periods: the Last Interglacial (LIG; specifically part of the Last Interglacial maximum between 124.1 and 118.8 ka) and the Holocene (10–0 ka). Our record is based on levoglucosan (Lev), a biomarker sensitive to biomass burning, and on lignin oxidation products (LOPs) that discriminate between open and closed forest and hard- or softwood vegetation. In addition, we used carbonate carbon stable isotope ratios (δ13C), which reflect a dominant control of the host rock, to evaluate soil respiration and local infiltration changes. Our LOP data suggest that, during the Last Interglacial, the region around Botovskaya Cave was characterised by open forest, which by ca. 121.5 ka underwent a transition from fire-resistant hardwood to fire-prone softwood. The Lev record indicates that fire activity was high and increased towards the end of Last Interglacial just before 119 ka. In contrast, the Holocene was characterised by a closed-forest environment with mixed hard- and softwood vegetation. Holocene fire activity varied but at a much lower level than during the Last Interglacial. We attribute the changes in wildfire activity during the intervals of interest to the interplay between vegetation and climate. The open forests of the Last Interglacial were more likely to ignite than their closed Holocene equivalents, and their flammability was aided by warmer and drier summers and a stronger seasonal temperature contrast due to the increase in seasonal insolation difference compared to the Holocene. Our comparison of the last two interglacial intervals suggests that, with increasing global temperatures, the boreal forest of southern Siberia may become progressively more vulnerable to higher wildfire activity.
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Cryptic diversity within the Gonyaulax spinifera species complex, its relation to the cyst‐defined species Spiniferites bentorii, S. mirabilis and S. membranaceus, with the description of Gonyaulax carbonell‐mooreae sp. nov. (Gonyaulacales, Dinophyceae)
No full textAbstractThe fossil dinoflagellates Spiniferites bentorii, S. mirabilis, and S. membranaceus are known to inhabit recent sediments and are often used to reconstruct past sea‐surface conditions. However, information on their corresponding motile cells has been rare. We isolated single cysts resembling these fossil species from China and France to yield Gonyaulax spinifera‐like cells. Gonyaulax strains were also established from Viet Nam and South Korea by isolating single cells. Both cysts and cells were examined by light and scanning electron microscopy, and their LSU rRNA genes were sequenced. A new Gonyaulax species, G. carbonell‐mooreae, was obtained from S. bentorii‐like cysts and considered the equivalent of Spiniferites bullatus, dating back to the Campanian. Gonyaulax kunsanensis was related to S. mirabilis‐like cysts. A typical S. membranaceus cyst from France yielded cells resembling G. lewisiae but shared only 75% similarity in LSU rRNA gene sequence with those from South Korea. Molecular phylogeny revealed that the pronounced apical boss is systematically significant, whereas the presence of intergonal processes is insignificant. Two ASVs of 18S rRNA V4 region were respectively identified as G. kunsanensis and G. lewisiae from the Tara Oceans metabarcoding data. Gonyaulax kunsanensis has a wide distribution in the Pacific, Indian, and Atlantic Oceans, but G. lewisiae has a restricted distribution. One strain of G. kunsanensis was examined for yessotoxin content using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS), but no detectable amounts of toxins were observed. Our results uncover the hidden diversity within the G. spinifera species complex and stress the significance of cyst morphology in the taxonomy of Gonyaulax.</jats:p