Long-term environmental controls on cold-water corals off the Angolan margin

Cold-water corals (CWCs) were found thriving under hypoxic conditions (0.5 – 1.5ml/L) within the oxygen minimum zone (OMZ) off the Angolan margin (Hebbeln et al., 2020). Geological records reveal the consistent occurrence of CWC at least over the last 50 kyr BP, although the beginning of local coral colonization cannot precisely be determined. Here, we reconstructed the bottom-water conditions from marine sediments core GeoB20911 in order to identify the most critical physical-chemical parameters having controlled the development of CWC off the Angola margin. Our results show that the prolific period of corals coincides with enhanced bottom-water hydrodynamics and increased temperature (Fig. 1). Vigorous bottom current, normally associated with internal wave propagations and nepheloid layer, increases the lateral transport of food to corals. The combination of high food supply and warmer thermocline created the ideal condition for regional coral proliferation by increasing their growth rates as documented in cultured experiments (Büscher et al., 2017). Interestingly, our results show a decline of the bottom-water oxygenation in the course of the last 50kyr BP without any negative impact on CWC occurrence. We speculate that local CWC is able to develop under hypoxic conditions as long as an elevated amount of fresh and high-quality food is available to compensate for such deleterious conditions