High-resolution records of environmental change in cold-water coral reefs: geochemical evidence recorded in the skeleton of the marine bivalve Acestaexcavata

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The current rise in atmospheric pCO2 and temperature is a serious threat for marine calcifiers in deep sea ecosystems. Among these, cold-water coral (CWC) ecosystems appear to be under particular risk due to their position in cold and deep waters close to the limit of carbonate saturation. One factor poorly explored for the growth of CWC reefs is seasonality. Moreover, to date geochemical research on CWC is mainly focused on framework building corals as environmental archives for which severe vital effects are known. Here, we explore a promising alternative model organism, the large clam Acesta excavata, as a new environmental archive for CWC reef ecosystems. A series of geochemical proxies already established in other marine biogenic carbonates will be applied with a suite of analytical methods and different sampling techniques. In addition, the geochemical data will be calibrated for the first time to high-resolution in situ oceanographic data (logged via >1 year lander deployments at the sample sites). This integrated approach aims to: (1) identify and evaluate potential vital effects of A. excavata, (2) assess A. excavata as paleoceanographic archive for geochemical proxies and age chronometers, (3) resolve temporal and spatial variations of seasonality in CWC reefs off Norway (Trondheimsfjord (Leksa Reef) and off-shore Sula Reef) and Mauretania (BandaMounds), and finally (4) address the role of seasonality in the context of shifts in CWC reef occurrencesat high and low latitudes on glacial/ interglacial time scales.