Trophic ecology of Angolan cold-water coral reefs (SE Atlantic) based on stable isotope analyses

Cold-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

Cold-water coral carbonate mounds as unique palaeo-archives: the Plio-Pleistocene Challenger Mound record (NE Atlantic)

Through the interplay of a stabilising cold-water coral framework and a dynamic sedimentary environment, cold-water coral carbonate mounds create distinctive centres of bio-geological accumulation in often complex (continental margin) settings. The IODP Expedition 307 drilling of the Challenger Mound (eastern Porcupine Seabight; NE Atlantic) not only retrieved the first complete developmental history of a coral carbonate mound, it also exposed a unique, Early-Pleistocene sedimentary sequence of exceptional resolution along the mid-latitudinal NE Atlantic margin.In this study, a comprehensive assessment of the Challenger Mound as an archive of Quaternary palaeo-environmental change and long-term coral carbonate mound development is presented. New and existing environmental proxy records, including clay mineralogy, planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts, planktonic foraminifer oxygen isotopes and siliciclastic particle-size, are thereby discussed within a refined chronostratigraphic and climatic context.Overall, the development of the Challenger Mound shows a strong affinity to the Plio-Pleistocene evolution of the Northern Hemisphere climate system, albeit not being completely in phase with it. The two major oceanographic and climatic transitions of the Plio-Pleistocene – the Late Pliocene/Early Pleistocene intensification of continental ice-sheet development and the mid-Pleistocene transition to the more extremely variable and more extensively glaciated late Quaternary – mark two major thresholds in Challenger Mound development: its Late Pliocene (>2.74 Ma) origin and its Middle–Late Pleistocene to recent decline. Distinct surface-water perturbations (i.e. water-mass/polar front migrations, productivity changes, melt-water pulses) are identified throughout the sequence, which can be linked to the intensity and extent of ice development on the nearby British–Irish Isles since the earliest Pleistocene. Glaciation-induced shifts in surface-water primary productivity are thereby proposed to fundamentally control cold-water coral growth, which in turn influences on-mound sediment accumulation and, hence, coral carbonate mound development throughout the Pleistocene. As local factors, such as proximal ice-sheet dynamics and on-mound changes in cold-water coral density, significantly affected the development of the Challenger Mound, they can potentially explain the nature of its palaeo-record and its offsets with the periodicities of global climate variability. On the other hand, owing to this unique setting, a regionally exceptional, high-resolution palaeo-record of Early Pleistocene (ca 2.6 to 2.1 Ma) environmental change (including early British–Irish ice-sheet development), broadly in phase with the 41 ka-paced global climate system, is preserved in the lower Challenger Mound. All in all, the Challenger Mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic (continental margin) environments

COLD-WATER Coral carbonate mounds as palaeo-archives : the Plio-Pleistocene sediment record from the Challenger Mound (NE Atlantic)

International audienc