Oil spill recorded by skeletal δ~(13)C of Porites corals in Weizhou Island, Beibu Gulf, Northern South China Sea

摘要

Oil, is one kind of natural product of biological origin which is depleted in C-13. Coral skeletal delta C-13 is an important archive of environmental and climatic change. However, few studies have been conducted on the effect of oil spill on the coral skeletal delta C-13 at present. This kind of research is useful for us to obtain environmental and climatic information from coral skeletal delta C-13. In this study, two continuously growing Porites corals (W1 and W3), aged 22 and 31 years (1994-2015 and 1985-2015), respectively, were collected from the fringing reef of Weizhou Island in October 2015, coral skeletal delta C-13 and delta O-18 were analyzed. Besides, seawater was collected during an oil spill in 28 January 2018, and was used for delta(CDIC)-C-13 (delta C-13 values of DIC) analysis. The purpose is to explore the potential impact of oil spills on delta(CDIC)-C-13 and coral delta C-13. delta(CDIC)-C-13 value during oil spill was significantly lower than that of normal seawater (Delta delta C-13 approximate to -2.38 parts per thousand). Coral delta C-13 of both two coral colonies showed lower values since 2008 (average value of delta C-13 before and after 2008 change from -2.04 +/- 0.48 parts per thousand to -3.33 +/- 0.55 parts per thousand parts per thousand and -1.77 +/- 0.49 parts per thousand to -2.88 +/- 0.54 parts per thousand of W1 and W3 respectively), especially, several abrupt negative shifts in 2008, 2009, 2011, 2012 and 2014 when oil spills occurred (extent of delta 13C variation were W:-3.08 parts per thousand, -1.82 parts per thousand, -1.82 parts per thousand, -1.53 parts per thousand, -1.37 parts per thousand; W3:-3.27 parts per thousand, -1.8 parts per thousand, -1.91 parts per thousand, -1.21 parts per thousand, -1.13 parts per thousand respectively). Our results clearly show that degradation of oil by microorganisms when oil spill occurs should render a decrease in the C-13/C-12 ratio of the seawater dissolved inorganic carbon (DIC) which is the ultimate carbon source of coral calcification