Alfred Wegener Institute for Polar and Marine Research
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Phylogenetic analysis of the toxigenic genus Amphidinium (Amphidiniales, Dinophyceae) revealed an unexpectedly high diversity in the Asia–Pacific region
No full textThe dinoflagellate genus Amphidinium encompasses several toxic species known to cause harmful algal blooms. Despite their ecological significance, the diversity within this genus may be underestimated due to the morphological similarities among species. In this study, we established 82 strains of Amphidinium by isolating single cells from the Asia–Pacific region. We examined their morphology using light and transmission electron microscopy. Additionally, we obtained partial sequences of the large subunit ribosomal (LSU) DNA and/or internal transcribed spacer regions for all strains. Furthermore, DNA metabarcoding targeting the LSU D1-D2 region was employed to detect species in the Bohai Sea, Yellow Sea, Mediterranean Sea, and Red Sea, where strain data is limited. The 82 strains were classified into 13 Amphidinium species. Among these were four undescribed species, provisionally named Amphidinium sp. 1 to Amphidinium sp. 4, as well as A. cupulatisquama, A. fijiensis, A. gibbosum, A. massartii, A. operculatum, A. pseudomassartii, A. thermaeum, A. tomasii, and A. trulla, based on both morphological and molecular analyses. DNA metabarcoding detected nine Amphidinium species. While Amphidinium gibbosum and A. tomasii are confined to tropical and warm subtropical waters, the other species exhibit a broader distribution. Molecular phylogenetic analysis revealed two distinct clades within the genus Amphidinium. Species in clade A, including A. uduigamense, A. stirisquamtum, A. operculatum, Amphidinium sp. 1, and Amphidinium sp. 2, share a characteristic sulcus that originates in the posterior one-third of the hypocone. In contrast, species in clade B are characterized by a sulcus that originates in the anterior or middle part of the cell. Additionally, amphidinol analysis was conducted on ten strains of five Amphidinium species using liquid chromatography-tandem mass spectrometry (LC-MS/MS), but amphidinols were below the detection limit. However, one strain of A. massartii produces a new amphidinol variant with a molecular mass of 1402.7 Da (34.47 fg cell−1) and hemolysis assays suggest the potential presence of novel amphidinols or related compounds in A. operculatum. Our findings underscore the significant diversity and potential risk posed by Amphidinium species in the Asia–Pacific region and beyond
Increased light‐enhanced dark respiration under warming suggests intensified metabolic coupling in an Arctic diatom
Get PDFJustification for high-ascent attainment for balloon radiosonde soundings at GRUAN and other sites
Get PDFWe assess and illustrate the benefits of high altitude
attainment of balloon-borne radiosonde soundings,
up to and beyond 10 hPa level compared to, for example,
30 hPa, at operational stations and at sites of the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN). We first discuss technical challenges and the possible solutions for balloon soundings at these higher altitudes. Then, we assess the role of high-ascent radiosonde measurements in climate monitoring and various process studies, contributions to satellite calibration and validation, and impacts on numerical weather prediction systems. The analysis herein shows that the extra costs and technical challenges involved in consistent attainment of high ascents are more than outweighed by the benefits for a broad variety of
real-time and delayed-mode applications. Consistent attainment of high ascents should therefore be pursued across the GRUAN network and the broader observational network
Global biome changes over the last 21 000 years inferred from model–data comparisons
Get PDFAbstract. We present a global megabiome reconstruction for 43 time slices at 500-year intervals throughout the last 21 000 years based on an updated, and thus currently the most extensive, global taxonomically and temporally standardized fossil pollen dataset of 3455 records. The evaluation with modern potential natural vegetation distributions yields an agreement of ∼ 80 %, suggesting a high reliability of the pollen-based megabiome reconstruction. We compare the reconstruction with an ensemble of six biomized simulations derived from transient Earth system models (ESMs). Overall, the global spatiotemporal patterns of megabiomes estimated by both the simulation ensemble and the reconstructions are generally consistent. Specifically, they reveal a global shift from open glacial non-forest megabiomes to Holocene forest megabiomes since the Last Glacial Maximum (LGM), in line with the general climate warming trend and continental ice-sheet retreat. The shift to a global megabiome distribution generally similar to today's took place during the early Holocene; furthermore, the reconstructions reveal that enhanced anthropogenic disturbances since the late Holocene have not altered broad-scale megabiome patterns. However, certain data–model deviations are evident in specific regions and periods, which could be attributed to systematic climate biases in ESMs or biases in the pollen-based biomization method. For example, at a global scale over the last 21 000 years, the largest deviations between the reconstructions and the simulation ensemble are observed during the LGM and the early deglaciation. These discrepancies are probably attributed to the ESM systematic summer cold biases that overestimate tundra in periglacial regions and to the challenging identification of steppes and tundra from the Tibetan Plateau pollen records. Moderate deviations during the Holocene mainly occur in non-forest megabiomes in the Mediterranean and northern Africa, with increasing discrepancies over time. These deviations may result from the underestimation of woody plant functional type (PFT) cover in simulations due to systematic biases, such as overly warm summers with dry winters in the Mediterranean, and the overrepresentation of woody taxa in reconstructions, misclassifying deserts as savanna in northern Africa. Overall, our reconstruction, with its relatively high temporal and spatial resolution, serves as a robust dataset for evaluating ESM-based paleo-megabiome simulations and provides potential clues for improving systematic model biases
Coastal Erosion as a Major Sediment Source in the Inner Gulf of Thailand: Implications for Carbon Dynamics in Tropical Coastal Ocean Systems
Get PDFAbstract Coastal erosion is an increasingly dominant sediment source in marginal seas, particularly in low‐lying areas affected by deltaic subsidence and sediment deficits from upstream water management. However, its role in sediment and organic carbon (OC) dynamics remains to be estimated. Our analyses of the inner Gulf of Thailand (IGoT) revealed that riverine sediment fluxes decreased from 6.6 to 5.4 Mt/yr after 1975, while sediment accumulation within the IGoT increased from 20.8 to 29.5 Mt/yr. The observed trend indicates major sediment contributions from coastal erosion, particularly from mangrove deposits. This process destabilizes coastal ecosystems and accelerates OC decomposition, that is, a low burial efficiency (16.8 ± 5.5%) leads to CO 2 release. Extrapolating these findings globally, mangrove loss could release ∼175 Tg/yr CO 2 . As coastal erosion intensifies under sea‐level rise and human land‐use practices, preserving coastal ecosystems is critical for mitigating blue carbon loss and maintaining coastal stability and resilience.
Plain Language Summary Coastal areas are increasingly eroding due to rising sea levels, reduced riverine sediment supply, and deltaic subsidence. The impact on global and regional carbon dynamics remains poorly resolved although the carbon cycle is closely tied to a changing climate and human land‐use practices. In the inner Gulf of Thailand, riverine sediment discharge has decreased from 6.6 to 5.4 Mt/yr since 1975 because of upstream river damming and field irrigation management. However, the total sediment accumulation within the inner gulf is much higher than the river input and has also increased from 20.8 to 29.5 Mt/yr during the same time. This discrepancy indicates that coastal erosion, especially of mangrove deposits, is now a major source of sediment and organic carbon. However, the organic carbon freshly from eroded coastal mangrove deposits decomposes significantly, releasing carbon dioxide into the atmosphere. Based on these findings, global mangrove loss could emit around 175 million tons carbon dioxide per year. As sea level rises and human land‐use practices intensify, protecting coastal ecosystems is crucial to prevent further carbon loss and maintain stable shorelines.
Key Points Since 1975, sediment accumulation in the inner Gulf of Thailand (IGoT) increased from 20.8 to 29.5 Mt/yr but riverine fluxes decreased from 6.6 to 5.4 Mt/yr Coastal erosion contributes significantly to IGoT sediment accumulation but the eroded coastal organic carbon has a low burial efficiency (16.8 ± 5.5%) Global mangrove loss could contribute ∼175 Tg/yr CO 2 , making preserving coastal ecosystems critically importan
The Polarstern Atlantic Transect as a concept for shipboard training on ocean science
Get PDFAbstract The significance of global marine education in ocean science and management is critical, especially in regions with weak infrastructure and economies. Therefore, knowledge generation as basis to establish and maintain essential research infrastructure, expertise, and management systems is crucial. In this context, we present the Polarstern Atlantic Transect Training (PSATT) as a versatile and proven shipboard training programme. This training is suitable for medium (50-100 m length, duration of at least5 days) and large (>100 m length, duration of > 14 days) research vessels, by scaling the modular nature of the educational concept. This programme can be adjusted to cater for vessels of various sizes and cruise durations, making it a valuable blueprint for similar marine education initiatives at sea. As a result, this tested concept provides an effective and adaptable framework for training at sea; it hasbeen conducted four times on board the research vessel (RV) Polarstern in 2015, 2016, 2019 and 2022 and trained so far 97 scholars on board. In this paper, we present a straightforward yet efficient framework for training at sea, designed to be inclusive, intercultural and international, as well as transdisciplinary and operational on research vessels. This approach aims to contribute to the development of skilled professionals in the field of ocean science and management
Deep-sea nematode community changes over two decades at HAUSGARTEN observatory (Fram Strait, Arctic Ocean)
Get PDFOver the past 2 decades, deep-sea nematode communities in the Arctic Ocean have undergone significant changes in structure and diversity, likely linked to shifting organic matter input and environmental conditions. Free-living nematodes were collected in 2000, 2004, 2009, 2014 and 2019 at 3 stations along a bathymetric transect (1300, 2500, 4000 m) at the Long-Term Ecological Research (LTER) observatory HAUSGARTEN, a region of the Arctic Ocean undergoing rapid environmental change. Nematodes were identified to genus level and their biomass size distribution was calculated. Sedimentary food indicators, i.e. chloroplastic pigments (phytodetritus) and bacterial abundance/biomass, were analysed as explanatory variables. Food availability changed over time, with initial chlorophyll a decline at shallower depths, followed by increasing total pigment concentrations and bacterial biomass at greater depths, especially at 4000 m. Nematode abundances declined significantly across all depths, most notably by ~75% at 1300 m. Multivariate analyses revealed progressive and significant shifts in community composition, influenced primarily by depth and with clear separation between early (2000) and late (2019) samples. Alpha diversity (EG(50), J ‘, H ‘(log2)) declined over time, remaining highest at 1300 m. Beta diversity based on genus exchange ratios showed high genus turnover (29-77%) and changes in dominance (12-55%), suggesting a combination of immigration and replacement of rare genera. Our findings indicate that long-term warming in surface waters and an accompanying shift in productivity are potentially reshaping deep-sea nematode communities, particularly at bathyal depths. This study highlights the value of sustained long-term time-series for understanding deep-sea benthic responses to climate change
Comparison of sedimentary ancient DNA (sedaDNA) extraction and shotgun metagenomic library preparation techniques
No full textSedimentary ancient DNA (sedaDNA) is an emerging field, increasingly being applied to the study of past aquatic ecosystems. However, several sedaDNA extraction methods from deep-ocean sediment matrices and sequencing library preparation have recently been developed, which may complexify results comparison and interpretations. We present a sedaDNA interlaboratory comparison study to assess the impact of extraction and library preparation protocols on metagenomic results. We applied three extraction protocols to four samples from two sediment cores from the Northern Antarctic Peninsula: (1) a ‘combined’ protocol using ethylenediaminetetraacetic acid (EDTA) and silica-in-solution to isolate DNA, (2) a high-guanidine protocol involving long cold centrifugation to remove polymerase chain reaction (PCR) inhibitors, and (3) a commercial kit, the DNeasy PowerSoil Pro Kit. We also compared two library preparation protocols, both optimised versions from Meyer and Kircher (2010). Using a blind approach relying on k-mer similarity assessment, greater variability was observed between individual samples than between protocols. An in-depth analysis of eukaryotic and (highly abundant) diatom community composition revealed that all protocols recovered eukaryotic sedaDNA, with minor differences between extraction and library protocols on sequence composition. However, the different DNA extraction and library preparations influenced the DNA read length, potentially resulting in selective targeting of organisms with variable sedaDNA preservation. This study highlights the importance of selection and standardisation of protocols to ensure reproducibility and comparability of past ecosystem reconstructions, particularly at lower taxonomic levels, e.g. diatoms. Although complete standardisation across research projects is challenging, this study shows that data remain reasonably comparable when processed consistently
Carbon drawdown by algal blooms during Antarctic Cold Reversal from sedimentary ancient DNA
Get PDFThe Southern Ocean plays a crucial role in the global carbon budget. One key interval for understanding this role is the Antarctic Cold Reversal (14,700–12,700 calibrated (cal) yr BP)—a Southern Hemisphere-specific cooling event that temporarily reversed the deglacial trend of warming and rising atmospheric CO₂. Modelling studies propose that the atmospheric CO₂ plateau during the Antarctic Cold Reversal is related to increased marine productivity. However, proxy constraints on the primary producer community are limited to the subset of groups that leave a fossil record. Here we applied ancient DNA shotgun metagenomics to samples from a marine sediment core to characterize the composition of the marine ecosystem across all trophic levels, finding that the haptophyte algae Phaeocystis antarctica was the dominant primary producer during the event. Independent proxy evidence from the same record points to high productivity in response to enhanced sea-ice seasonality caused by the cooling. Post Antarctic Cold Reversal, abrupt Phaeocystis community loss shows how sensitive this ecosystem is to warming, potentially representing a key tipping element. As an analogy for present warming, it highlights the importance of regions with high seasonal sea-ice variability and Phaeocystis dominance, such as the Ross Sea, in stabilizing atmospheric CO₂ content
