Corals in Estuarine Environments: Their Response to Environmental Changes and Application in Reconstructing Past Environmental Variability

Abstract

Corals represent a vast and detailed archive of past environmental changes in regions where instrumental data are limited and where our knowledge of multidecadal climate variability is incomplete. In estuarine areas, coral skeletal records provide an opportunity to monitor anthropogenic impacts as well as to investigate natural environmental variability through a range of time scales, from seasonal to millennial. This paper analyzes the status of the field of coral sclerochronology (layer analysis) and geochemistry as it relates to the recovery of past records of environmental variability in estuarine settings. Coral biology, density band formation, and factors affecting the uptake of isotopic and elemental signals in the coral skeleton are explored, as they constitute important aspects in understanding corals as environmental proxies. Density bands in coral skeletons, commonly used for first-order dating, are a reliable proxy for long-term seasonal variability and to identify periods of environmental stress. The stable isotopic composition of coral carbonate has been employed to reconstruct sea-surface temperatures and salinities (delta O-18), insolation changes (delta C-13), pH variability (delta B-11), and water quality (delta N-15), while changes in the elemental composition of corals constitute robust proxies for sea surface temperature (Sr/Ca) and riverine discharge (Ba/Ca). Additionally, changes in the trace concentration of metals, such as Pb, Cd, Al, Mn and Zn, have been used to monitor pollutants entering estuaries from urban areas and to reconstruct past changes in water quality. However, there is still controversy about the degree to which biological parameters such as metabolism and calcification rate influence the final isotopic and elemental composition of the coral lattice. As a result, a multi-proxy approach to coral-based paleoclimatology has emerged, both from the need to better understand the influences controlling coral environmental records and from recent advances in the analytical techniques for measuring the composition of coral skeletons. PU - SPRINGER PI - DORDRECHT PA - PO BOX 17, 3300 AA DORDRECHT, NETHERLANDS