Alfred Wegener Institute for Polar and Marine Research
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Evolution of the Antarctic ice sheet since its inception 34 million years ago and using this knowledge for advancing numerical model simulations
No full textThe Antarctic Ice Sheet (AIS) is thought to diminish considerably over coming decades and centuries – largely because warm deep waters increasingly reach its ice margins with many hinterland ice sheet portions grounded way below modern sea level, together leading to accelerating and irreversible retreat. So, are we currently witnessing the fate of an ice sheet associated with severe consequences for global coastal communities? Finding better answers to this question requires robust multi-proxy continental data evidence from times that were warmer and CO2-richer than today. Such sediment records, however, are rare and challenging to obtain, and associated continental drilling campaigns only feasible within large multinational consortiums. Some extensive Antarctic field campaigns, however, were recently realized, are about to be accomplished, or at planning stage. This presentation will introduce these campaigns and highlight how their results combined with novel coupled modeling techniques will eventually allow for significant new insights into AIS’ long-term evolution and, with this, for better predicting its behavior to conditions anticipated for the foreseeable future
Sedimentary relations: cultures of access and the matter of shallow seabed coring
Get PDFContemporary cultural geographies have increasingly addressed subterranean and deep spaces through questions of access to earthly materials and the politics of resource extraction. This article engages with these themes through an investigation into the ‘doings’ or practices of seabed access. It does so by following the embodied and material experiences of two human geographers, an artist, a scientific coordinator and a microbiologist, who together undertook a day trip to learn shallow sediment coring in the Wadden Sea mudflats of Northern Germany. Stemming from a research project concerned with the accessibility of the seabed in international waters (how society can access its ‘common heritage’), we examine how taking samples from even the most accessible type of seabed – a shallow coastal mudflat within national waters that is not covered by seawater during low tide – presents a myriad of considerations, challenges and complications. We argue these are vital in examining the cultures of access – the embodied and material limits that define and shape participation in environments in which you and I have rights. These considerations, challenges and complications ranged from physical strength and balance requirements to an understanding of tidal movements, access to simple but specific equipment, appropriate clothing and private transport. We use ethnographic reflections and our photographic engagements to consider sedimentary relations: how we can and do relate to the seabed. </jats:p
A new dinoflagellate Gonyaulax pospelovana with resting cysts resembling Spiniferites delicatus and its biogeography and ecology revealed by DNA metabarcoding
No full textExtant species of the dinoflagellate genus Gonyaulax are capable of producing resting cysts morphologically similar to different cyst-based genera, and their cyst-theca relationships are far from resolved. Here we have carried out germination experiments on several living cysts that resemble Spiniferites delicatus from the subtropical regions of China and Mexico. Both cyst and theca morphology were examined by light and scanning electron microscopy. A new species, Gonyaulax pospelovana, is described, characterized by a cingulum displacement and an overhang of twice its width, and two short antapical spines. The cysts of G. pospelovana had a granular surface and gonal processes with petaloid tips. Maximum likelihood and Bayesian inference analyses based on LSU and SSU rRNA gene sequences revealed that strains identified as G. pospelovana were monophyletic, forming a sister clade to Gonyaulax ellegaardiae and several presumable strains of Gonyaulax spinifera. One Chinese strain and two Mexican strains of G. pospelovana were examined for yessotoxin production using LC-MS/MS, but were not found to produce a detectable amount of toxins. Metabarcoding targeting the 18S V4 rRNA gene was performed on monthly collected samples in Xiamen Bay, China. A ZOTU (zero-radius operational taxonomic units) was detected that was consistent with G. pospelovana. Its maximum abundance was recorded in summer. Additionally, an OTU was identified as G. pospelovana from the Tara Oceans metabarcoding data, which occurred in the Indian and Pacific oceans at temperatures ranging from 28°C to 31°C, suggesting that it is a warm water species
The stable sulfur isotope and abundance fluxes of reduced inorganic sulfur and organic sulfur phases recorded in the Permian-Triassic transition of the Meishan type section
Get PDFSulfur cycle fluxes implicated in the Permian-Triassic mass extinction have traditionally been studied by the sulfur phase abundances in sedimentary rocks and the stable sulfur isotopic value (δ34S) of seawater sulfate inferred from mineral sulfate analyses. This information might be complemented by studies of the reduced inorganic sulfur and organic sulfur produced following bacterial sulfate reduction. To explore this potential the δ34S and concentration analyses of total reduced inorganic sulfur (TRIS) and organic sulfur – separately in the forms of kerogen (Ker) and individual organosulfur compounds, specifically dibenzothiophenes (DBTs) – has been conducted on sediments across the Late Permian to Early Triassic marine type section of Meishan-1 (South China). The relatively steady δ34S profiles (e.g., < 5 ‰ variation) of all sulfur phases measured through much of the late Permian were indicative of a primary seawater sulfate control, but other biogeochemical modulators caused prominent δ34S fluctuations of TRIS and DBT adjacent to the extinction event. The late Triassic δ34STRIS profile of Meishan-1 displayed a notable 34S enrichment (+15 ‰ increase) in bed 22–24 sediments concomitant with lower δ34SDBT values (−7 ‰ decrease), whereas co-eval δ34SKerS values remained relatively constant. The contrasting δ34SDBT and δ34SKerS data suggests the dynamic behavior of specific diagenetic sulfurisation processes may be resolved by the δ34S of discrete organic sulfur compounds (i.e., dibenzothiophenes, DBTs), but dissipated by the sulfurisation collective represented by the bulk kerogen fraction. The inverse isotopic trend observed between DBT and TRIS resulted in negative Δδ34SDBT-TRIS values identifying an organic sulfurisation pathway(s) with an unusual preference over pyrite (FeS2) for the lighter stable sulfur isotope. A redox control of the δ34SDBTs and δ34STRIS deviations in the bed 22–24 extinction interval was confirmed by coincident variation in TRIS/(TRIS + KerS) and pyrite (Py) and highly reactive (HR) iron ratios (FePy/FeHR). The iron (Fe) speciation data indicated a transition to ferruginous conditions, ruling out Fe2+ limitation as a factor in the bias against 34S evident in DBT formation. The 34S depletion of the DBTs promoted by the ferruginous setting may arise from the rapid and irreversible reaction of organic substrates with labile sulfur anions (e.g. HS-) or be supported by an especially localised sediment–water depositional microenvironment. Our study highlights the potential of incorporating stable sulfur isotope analytics of reduced and organic sulfur phases, particularly of specific organic compounds, into a holistic assessment of the dynamic sulfur biochemical periods of Earth's past
A Synoptic Scale Perspective of Solar Forcing on Extreme Precipitation and Floods Over Europe During Summer
Get PDFThe relationship between total solar irradiance (TSI) forcing and summer extreme precipitation and flood frequency over western Europe is investigated from a synoptic-scale perspective, with a focus on the role of Rossby wave packets (RWPs). Utilizing observational, model, and proxy data, we reveal a significant increase in RWP frequency along a zonal band centered around 50°N, extending from North America to western Europe, during periods of low TSI. This anomaly in RWP frequency is consistent with a significant increase in the frequency of extreme precipitation events recorded over western Europe. Sensitivity experiments conducted with a state-of-the-art chemistry-climate model corroborate our findings based on observational data. Additionally, a flood record from western Europe demonstrates a significant increase in flood frequency during low TSI years, a relationship that persists across timescales. We argue that the frequency patterns associated with TSI forcing presented in this study are robust and, therefore, valuable for estimating the frequency of extreme precipitation events over western Europe under various solar irradiance scenarios. Moreover, our findings indicate that the North Atlantic sector is more responsive to changes in solar forcing during the boreal summer than previously thought, with this effect manifesting primarily on synoptic timescales rather than the long-term climatological mean
Ice-free period too long for Southern and Western Hudson Bay polar bear populations if global warming exceeds 1.6 to 2.6 °C
Get PDFHudson Bay has warmed over 1 °C in the last 30 years. Coincident with this warming, seasonal patterns have shifted, with the spring sea ice melting earlier and the fall freeze-up occurring later, leading to a month longer of ice-free conditions. This extended ice-free period presents a significant challenge for polar bears, as it restricts their hunting opportunities for seals and their ability to accumulate the necessary body weight for successful reproduction. Drawing on the latest insights from CMIP6, our updated projections of the ice-free period indicate a more spatially detailed and alarming outlook for polar bear survival. Limiting global warming to 2 °C above pre-industrial levels may prevent the ice-free period from exceeding 183 days in both western and southern Hudson Bay, providing some optimism for adult polar bear survival. However, with longer ice-free periods already substantially impacting recruitment, extirpation for polar bears in this region may already be inevitable
SISALv3: a global speleothem stable isotope and trace element database
Get PDFPalaeoclimate information on multiple climate variables at different spatiotemporal scales is becoming increasingly important to understand environmental and societal responses to climate change. A lack of high-quality reconstructions of past hydroclimate has recently been identified as a critical research gap. Speleothems, with their precise chronologies, widespread distribution, and ability to record changes in local to regional hydroclimate variability, are an ideal source of such information. Here, we present a new version of the Speleothem Isotopes Synthesis and AnaLysis database (SISALv3), which has been expanded to include trace element ratios and Sr isotopes as additional, hydroclimate-sensitive geochemical proxies. The oxygen and carbon isotope data included in previous versions of the database have been substantially expanded. SISALv3 contains speleothem data from 365 sites from across the globe, including 95 Mg/Ca, 85 Sr/Ca, 52 Ba/Ca, 25 U/Ca, 29 P/Ca, and 14 Sr-isotope records. The database also has increased spatiotemporal coverage for stable oxygen (892) and carbon (620) isotope records compared with SISALv2 (which consists of 673 and 430 stable oxygen and carbon records, respectively). Additional meta information has been added to improve the machine-readability and filtering of data. Standardized chronologies are included for all new entities along with the originally published chronologies. Thus, the SISALv3 database constitutes a unique resource of speleothem palaeoclimate information that allows regional to global palaeoclimate analyses based on multiple geochemical proxies, permitting more robust interpretations of past hydroclimate and comparisons with isotope-enabled climate models and other Earth system and hydrological models. The database can be accessed at 10.5287/ora-2nanwp4rk (Kaushal et al., 2024)
Frazil ice changes winter biogeochemical processes in the Lena River
Get PDFThe ice-covered period of large Arctic rivers is shortening. To what extent will this affect biogeochemical processing of nutrients? Here we reveal, with silicon isotopes (δ30Si), a key winter pathway for nutrients under river ice. During colder winter phases in the Lena River catchment, conditions are met for frazil ice accumulation, which creates microzones. These are conducive to a lengthened reaction time for biogeochemical processes under ice. The heavier δ30Si values (3.5 ± 0.5 ‰) in river water reflect that 39 ± 11% of the Lena River discharge went through these microzones. Freezing-driven amorphous silica precipitation concomitant to increased ammonium concentration and changes in dissolved organic carbon aromaticity in Lena River water support microbially mediated processing of nutrients in the microzones. Upon warming, suppressing loci for winter intra-river nitrogen processing is likely to modify the balance between N2O production and consumption, a greenhouse gas with a large global warming potential
Cold-water coral energy reserves and calcification in contrasting fjord environments
Get PDFThe relationship between energy reserves of cold-water corals (CWCs) and their physiological performance remains largely unknown. In addition, it is poorly understood how the energy allocation to different metabolic processes might change with projected decreasing food supply to the deep sea in the future. This study explores the temporal and spatial variations of total energy reserves (proteins, carbohydrates and lipids) of the CWC Desmophyllum dianthus and their correlation with its calcification rate. We took advantage of distinct horizontal and vertical physico-chemical gradients in Comau Fjord (Chile) and examined the changes in energy reserves over one year in an in situ reciprocal transplantation experiment (20 m vs. 300 m and fjord head vs. mouth). Total energy reserves correlated positively with calcification rates. The fast-growing deep corals had higher and less variable energy reserves, while the slower-growing shallow corals showed pronounced seasonal changes in energy reserves. Novel deep corals (transplanted from shallow) were able to quickly increase both their calcification rates and energy reserves to similar levels as native deep corals. Our study shows the importance of energy reserves in sustaining CWC growth in spite of aragonite undersaturated conditions (deep corals) in the present, and potentially also future ocean