Alfred Wegener Institute for Polar and Marine Research
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Trophic ecology of Angolan cold-water coral reefs (SE Atlantic) based on stable isotope analyses
Get PDFCold-water coral (CWC) reefs of the Angolan margin (SE Atlantic) are dominated by Desmophyllum pertusum and support a diverse community of associated fauna, despite hypoxic conditions. In this study, we use carbon and nitrogen stable isotope analyses (δ13C and δ15N) to decipher the trophic network of this relatively unknown CWC province. Although fresh phytodetritus is available to the reef, δ15N signatures indicate that CWCs (12.90 ± 1.00 ‰) sit two trophic levels above Suspended Particulate Organic Matter (SPOM) (4.23 ± 1.64 ‰) suggesting that CWCs are highly reliant on an intermediate food source, which may be zooplankton. Echinoderms and the polychaete Eunice norvegica occupy the same trophic guild, with high δ13C signatures (-14.00 ± 1.08 ‰) pointing to a predatory feeding behavior on CWCs and sponges, although detrital feeding on 13C enriched particles might also be important for this group. Sponges presented the highest δ15N values (20.20 ± 1.87 ‰), which could be due to the role of the sponge holobiont and bacterial food in driving intense nitrogen cycling processes in sponges’ tissue, helping to cope with the hypoxic conditions of the reef. Our study provides first insights to understand trophic interactions of CWC reefs under low-oxygen conditions
Impact of Local Iron Enrichment on the Small Benthic Biota in the deep Arctic Ocean
Get PDFThis study assesses the impact of local iron enrichment on the small benthic biota (bacteria, meiofauna) at the deep seafloor. To evaluate the hypothesis that abundance, distribution, and diversity of the small benthic biota varies in relation to a local input of structural steel at the seabed, we analyzed sediment samples and the associated infauna along a short transect (~1.5 m in length) with increasing distance to an iron source, i.e., corroding steel weights (30 cm in length and width, and 6 cm in height) of a free-falling observational platform (bottom-lander), lying on the seafloor for approximately seven years. Bacterial and meiofaunal densities and biomasses in iron-enriched sediments were significantly lower than those in unaffected sediments. Moreover, bacterial and nematode community structure between iron-enriched sediments and unaffected sediments differed strongly; taxonomic richness as well as diversity was lowest closest to the iron source. The presence of iron fostered the establishment of specialized iron oxidizers and other chemolithoautotrophic bacterial members, which were rare or absent in the unaffected sediments, within which opportunistic heterotrophs predominated. Nematodes comprised >90% of the total metazoan meiofauna and were therefore studied in more detail. A total of 26 genera from 16 families occurred in iron-enriched sediments (three genera were found exclusively in these sediments), while 65 genera from 27 families occurred in the unaffected sediments (39 genera and 12 families were found exclusively in these sediments). Nematode genera number (S), estimated genera richness (EG(51)) and heterogeneity (H’(log2)) were significantly lower in iron-enriched sediments than in unaffected sediments. Our results confirm that the local enrichment of deep-sea sediments by metallic and corroding structures (e.g., by ship hulls, containers, scientific equipment) strongly affects the diversity of the small benthic biota at short distances from these sources
Controls on Lithium Incorporation and Isotopic Fractionation in Large Benthic Foraminifera
Get PDFThe lithium (Li) isotopic composition of carbonates is considered to be a reliable archive of past seawater Li isotopic compositions, which are useful as a tracer of silicate weathering. However, δ7Li values have been shown to be dependent on either pH or DIC in two studies using similar species of large, benthic foraminifera from the genus Amphistegina. To resolve this issue, we conducted culture experiments on Amphistegina lessonii in decoupled pH–DIC conditions, under two different light treatments, and with normal or Li-enriched seawater. The δ7Li values and Li/Ca ratios in the foraminifera tests were analysed by ion microprobe and LA-ICP-MS, respectively. No links between either the pH or DIC and δ7Li or Li/Ca values were observed for any of the treatments, and growth rates also did not seem to influence the Li incorporation or isotopic fractionation, contrary to observations from inorganic carbonate-precipitation experiments. Overall, these findings appear to support the use of Li isotopes in large benthic foraminifera to reconstruct past seawater chemistry and to infer changes in chemical weathering during carbon-cycle perturbations.
Keywords: δ7Li; Li/Ca; lithium; large benthic foraminifera; culture experiments; pH; DIC; geochemical proxie
Bericht aus dem AWI - 17. Nationales GCOS Treffen, 01.03.2023, Bremerhaven
Get PDFReporting for the German GCO
Changes in deep Pacific circulation and carbon storage during the Pliocene-Pleistocene transition
No full textThe global climate has been gradually cooling over the Cenozoic and is punctuated by the intensification of Northern Hemisphere Glaciation (NHG) from the latest Pliocene to earliest Pleistocene (∼3.1–2.5 millions of years ago, Ma). A decline of atmospheric CO2 is supposed as a prerequisite for the NHG, but the associated carbon-cycle processes remain elusive. Here we combine foraminiferal records of neodymium isotope and boron-calcium ratio, and simulations of an Earth system model, to investigate changes in the water-mass composition and carbonate-ion concentration of the deep Pacific Ocean during the NHG. Our proxy records have revealed a significant expansion of southern-sourced waters with increased respired carbon storage into the deep Pacific during the NHG. These changes may be explained by strengthened deep-water formation and biological-pump efficiency in the Southern Ocean due to Antarctic sea-ice growth, as suggested by our model experiments and evidence from the Sub-Antarctic region. These results provide key clues for quantifying the role of the dissolved inorganic carbon content of deep Pacific waters in modulating atmospheric CO2 during the NHG
Detailed visualization of settlement and early development in Leptastrea purpurea reveals distinct bio-optical features
Get PDFSexually produced juvenile scleractinian corals play a key role in the adaptation process of coral reefs, as they are considered to possess an innate plasticity and thus can adjust to changing environmental parameters within a certain range. In this study we investigated in detail the early life stages of the brooding species Leptastrea purpurea to identify, categorize and visualize the critical steps of the complex transformation process from a swimming coral larva to a sessile coral recruit and later to a coral colony. For that, we performed settlement experiments using previously known cues: cycloprodigiosin (CYPRO) and crustose coralline algae (CCA) as well as novel cues: crude extracts of Pseudoalteromonas espejiana and P. piscicida to identify a general, cue-independent settlement pathway. We monitored the development of L. purpurea over 12 months using bright field and fluorescence microscopy. Also we identified the fluorescence signals of L. purpurea with confocal microscopy at four crucial development steps: (A) swimming larva, (B) metamorphosing larva, (C) coral recruit and (D) adult coral. Our methodological approach allowed us to observe an ontogenetic shift of fluorescence signals which provokes the hypothesis that certain fluorescence patterns might be connected to distinct sequential functions in the early life cycle of scleractinian corals. Our observations showed great similarities to the early development of other brooding and spawning corals, making L. purpurea a prospective candidate to be used as a model organism for coral research. Furthermore, our in-depth picture series provides a robust monitoring reference for coral nurseries or field applications and demonstrates the potential of fluorescence as an indicator to instantly determine the growth stage of a developing coral recruit.</jats:p
Interdisciplinary observations of the under-ice environment using a remotely operated vehicle
Get PDFImproving our understanding of the climate and ecosystem of the sea-ice covered Arctic Ocean was a key objective during MOSAiC. We aimed for a better understanding of the linkages of physical and biological processes at the interface between sea ice and ocean. To enhance the quantification of these linkages, year-round observations of physical, biological, and chemical parameters are needed. We operated a remotely operated vehicle (ROV) equipped with an interdisciplinary sensor platform to simultaneously measure these parameters underneath the drifting sea ice. These observations were made synchronous in time and place enabling a description of their spatial and temporal variability. Overall, we completed more than 80 surveys covering all seasons and various sea ice and surface conditions. We focused on optical parameters, sea-ice bottom topography, and upper ocean physical and biological oceanography. In addition, visual documentation of the under-ice environment was performed, nets for zooplankton were towed, and the ROV was used for instrument deployment and maintenance. Here, we present all ROV sensor data, allowing for a comprehensive picture of the under-ice environment. We are inviting discussions on further collaboration in data analyses and usage, in particular co-location and merging with other datasets from MOSAiC and other (also future) projects
Comparison of two rapid automated analysis tools for large FTIR microplastic datasets
Get PDFAbstractOne of the biggest issues in microplastic (MP, plastic items <5 mm) research is the lack of standardisation and harmonisation in all fields, reaching from sampling methodology to sample purification, analytical methods and data analysis. This hampers comparability as well as reproducibility among studies. Concerning chemical analysis of MPs, Fourier-transform infrared (FTIR) spectroscocopy is one of the most powerful tools. Here, focal plane array (FPA) based micro-FTIR (µFTIR) imaging allows for rapid measurement and identification without manual preselection of putative MP and therefore enables large sample throughputs with high spatial resolution. The resulting huge datasets necessitate automated algorithms for data analysis in a reasonable time frame. Although solutions are available, little is known about the comparability or the level of reliability of their output. For the first time, within our study, we compare two well-established and frequently applied data analysis algorithms in regard to results in abundance, polymer composition and size distributions of MP (11–500 µm) derived from selected environmental water samples: (a) the siMPle analysis tool (systematic identification of MicroPlastics in the environment) in combination with MPAPP (MicroPlastic Automated Particle/fibre analysis Pipeline) and (b) the BPF (Bayreuth Particle Finder). The results of our comparison show an overall good accordance but also indicate discrepancies concerning certain polymer types/clusters as well as the smallest MP size classes. Our study further demonstrates that a detailed comparison of MP algorithms is an essential prerequisite for a better comparability of MP data.</jats:p
Optical remote sensing (Sentinel-3 OLCI) used to monitor dissolved organic carbon in the Lena River, Russia
Get PDFIn the past decades the Arctic has experienced stronger temperature increases than any other region globally. Shifts in hydrological regimes and accelerated permafrost thawing have been observed and are likely to increase mobilization of organic carbon and its transport through rivers into the Arctic Ocean. In order to better quantify changes to the carbon cycle, Arctic rivers such as the Lena River in Siberia need to be monitored closely. Since 2018, a sampling program provides frequent in situ observations of dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) of the Lena River. Here, we utilize this ground truth dataset and aim to test the potential of frequent satellite observations to spatially and temporally complement and expand these observations. We explored all available overpasses (~3250) of the Ocean and Land Colour Instrument (OLCI) on Sentinel-3 within the ice-free periods (May – October) for four years (2018 to 2021) to develop a new retrieval scheme to derive concentrations of DOC. OLCI observations with a spatial resolution of ~300 m were corrected for atmospheric effects using the Polymer algorithm. The results of this study show that using this new retrieval, remotely sensed DOC concentrations agree well with in situ DOC concentrations (MAPD=10.89%, RMSE=1.55 mg L−1, r²=0.92, n=489). The high revisit frequency and wide swath of OLCI allow it to capture the entire range of DOC concentrations and their seasonal variability. Estimated satellite-derived DOC export fluxes integrated over the ice-free periods of 2018 to 2021 show a high interannual variability and agree well with flux estimates from in situ data (RMSD=0.186 Tg C, MAPD=4.05%). In addition, 10-day OLCI composites covering the entire Lena River catchment revealed increasing DOC concentration and local sources of DOC along the Lena from south to north. We conclude that moderate resolution satellite imagers such as OLCI are very capable of observing DOC concentrations in large/wide rivers such as the Lena River despite the relatively coarse spatial resolution. The global coverage of remote sensing offers the expansion to more rivers in order to improve our understanding of the land-ocean carbon fluxes in a changing climate