Spatial linkages between coral proxies of terrestrial runoff across a large embayment in Madagascar
1Department of Marine Geology, Royal Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands
2School of Earth and Environment, The University of Western Australia and the UWA Oceans Institute, 35 Stirling Highway, Crawley WA 6009, Australia and the Australian Institute of Marine Science, 39 Fairway, Nedlands WA 6009, Australia
3University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics (IBED), Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands
4Department of Biological Sciences, Macquarie University, Sydney NSW, Australia
5Wildlife Conservation Society (WCS), B. P. 8500 Soavimbahoaka, Antananarivo 101, Madagascar
*now at: Unidad Académica de Sistemas Arrecifales, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Apdo. Postal 1152, Cancún, Quintana Roo 77500, Mexico
Abstract. Coral cores provide vital climate reconstructions for site-specific temporal variability in river flow and sediment load. Yet, their ability to record spatial differences across multiple catchments is relatively unknown. Here, we investigate spatial linkages between four coral proxies of terrestrial runoff and their relationships between sites. Coral cores were drilled in and around Antongil Bay, the largest bay in Madagascar, and individually analysed for fifteen years of continuous luminescence (G / B), Ba / Ca, δ18Osw and δ13C data. Each coral core was drilled close to individual river mouths (≥ 7 km), and proxy data were compared to modelled river discharge and sediment runoff data for the three corresponding catchments. A reasonable agreement between terrestrial runoff proxies with modelled river discharge and sediment yield was observed. Some inconsistencies between proxy and modelled data are likely linked to proxy behaviour, watershed size and local environmental physiochemical parameters. In general, the further a coral resided from its river source, the weaker the proxy relationship was with modelled data and other corals, due to mixing gradients and currents. Nevertheless, we demonstrate that two coral Ba / Ca and luminescence (G / B) records influenced by the same watershed are reproducible. Furthermore, a strong Ba / Ca relationship was observed between two cores from distant watersheds, with baseline averages in agreement with modelled sediment runoff data. As humic acids behave conservatively in the water column, luminescence (G / B) data gave the highest regional correlations between cores, and showed the most consistent relationship with site specific modelled discharge. No statistical relationship was observed between cores in terms of interannual δ18Osw and δ13C, meaning corals were recording a localised signal at their respective sites, confounded by vital effects. Comparing proxy baseline averages and mean seasonal cycles provided a good overview of the runoff dynamics of the bay system.