Abstract

Three cores from the scleractinian coral Montastraea faveolata and one core from the scleractinian coral Siderastrea siderea from the Belize barrier and atoll reef complex, Central America, were analyzed with regard to sclerochronology (skeletal extension rates) and stable isotope geochemistry (δ18O and δ13C). The core material covers the time span from 1815 to 2000. The four coral time series were compared with available instrumental climate data, such as sea surface temperatures (GISST), cloud cover (GHCN), and precipitation (COADS). Skeletal extension rates measured in the cores average 8.5–14 mm/year in M. faveolata and 8 mm/year in S. siderea. No systematic correlations between extension rates and instrumental climate data were detected. Annual variation in oxygen isotopes is 0.6– 0.8‰, which accounts for monthly averages of sea-surface water temperature fluctuations of 3–4°C. In three cores from the Belize shelf and barrier reef, negative correlations of δ18O with the GISST 2.3b data were observed. Time series analyses of the oxygen isotope data in these three cores revealed a decadal periodicity (10–15 years), which are attributed here to the influence of the Atlantic sea surface temperature (SST) dipole variation. Three- to six-year periodicities, indicative of the El Niño Southern Oscillation (ENSO), in the same data are only weakly developed. Carbon isotopes of shallow-water corals also exhibit negative correlations with the GISST data. It is speculated that warmer years were characterized by increased cloud cover leading to reduced photosynthesis rates in the corals. Indeed, there is a negative correlation between δ13C and historic cloud-cover data. Carbon isotopes in the Belize shelf and barrier reef cores further exhibit general trends towards lighter values in time indicating the uptake of fossil fuel CO2 in the coral skeletons. A proxy data time series from a core from the restricted Turneffe Atoll lagoon differs from those of the Belize shelf and barrier reef cores, and there are fewer systematic correlations with historical climate and proxy data. This is probably a consequence of the strong influence of local environmental factors, which obliterate broader scale environmental parameters. First analyses of oxygen isotopes in fossil (Holocene) coral cores of M. faveolata indicate higher SSTs around 7,000 ybp in Belize as compared to older, younger, and modern samples.

You do not currently have access to this article.