Understanding the impact of the growth rate on the incorporation of trace element and heavy metal in coral skeleton and its implication for environmental paleo-reconstructions

Dr Not, Christelle Aurelie   (Principal Investigator (PI))

18

2016-08-01

90000

Understanding the impact of the growth rate on the incorporation of trace element and heavy metal in coral skeleton and its implication for environmental paleo-reconstructions

Corals, Environmental reconstruction, Growth rate, Heavy metals, Trace element

Earth Sciences,Environmental Studies and Science

Physical Sciences (P)

201602173004

Dr. Stephen S.F. Hui Trust Fund

2015

Completed

Long-lived massive corals can contribute to the monitoring of coral reef environments through measurable growth records in the annual density patterns; these can provide an historical perspective against which to assess environmental changes, and can help to establish limits of coral growth. Trace elements and heavy metals content of corals skeleton have been used to estimate long-term variability in coral reefs environments, allowing unnatural changes to be distinguished from natural variability. However, an understanding of coral growth processes and trace element and heavy metals incorporation within coral skeleton is an essential pre-requisite for proper interpretation of studies of geochemical tracers in corals. In this study we proposed to measure trace elements, magnesium (Mg), strontium (Sr), barium (Ba) and heavy metals as cadmium (Cd), zinc (Zn), copper (Cu), lead (Pb) and aluminum (Al) in coral skeleton and observe the relation between their variability and the growth rate in two of the most common coral species of Hong Kong marine waters, Platygyra and Porites. Trace elements and heavy metals content in coral has been an important tool for paleoenvironmental reconstruction, since elemental shell chemistry represent the chemistry of the surrounding water at the specific time of the calcification. For example, the correlation between Sr/Ca and ambient temperature have been used to reconstruct paleo temperature (Gagan et al, 2012), Ba/Ca content in coral skeleton has been linked to the intensity of rainfall (Lewis et al., 2007) and high Pb/Ca and Cd/Ca content have been interpreted as an evidence of heavy metal coastal contamination (Al-rousan et a., 2007). Some studies have demonstrated the sensitivity of the incorporation of Sr to variable growth rates and their influence on temperature reconstruction on Porites (de Villiers et al., 1994; Gagan et al., 2012). In addition, it is important to note that trace element and metal uptakes by corals have been shown to species specific and location specific highlighting the importance of understanding coral growth characteristics in interpreting geochemical tracers in coral skeletons for each species studied. By measuring trace element and heavy metals content in two different corals species and comparing their content with their growth rate we aim to: 1. Determine the difference of trace element and heavy metals incorporation between two distinct coral species, Platygyra and Porites. 2. Understand the influence of growth rate in the incorporation of Mg, Sr, Ba, Cd, Zn, Cu, Al and Pb. 3. Estimate the potential of trace elements content as paleo proxies for temperature, salinity or dissolved oxygen reconstruction. 4. Estimate the potential of heavy metals content as proxy for their marine environment content. 5. Evaluate the temporal variability of the environmental parameter reconstructed.