ZINC, LEAD, AND CADMIUM CONCENTRATIONS IN LIVING (STAINED) BENTHIC FORAMINIFERAL CALCITE ACROSS A CONTAMINATION GRADIENT IN LAKE MACQUARIE, AUSTRALIA

A north-south gradient in trace metal contaminants within the sediments of Lake Macquarie, a saline coastal estuary in southeastern Australia, makes an excellent environment to examine the influence of ambient chemistry on microfaunal inhabitants. Through an understanding of modern ecological and biogeochemical relationships, the ubiquitous fossil record of foraminifera has been used extensively to assess modern and ancient marine environmental conditions in a wide variety of settings. The objective of this study is to examine the relationship between ambient trace metal contaminants and incorporation of these elements into cosmopolitan calcareous benthic foraminiferal tests. Individual foraminiferal test chambers of Ammonia aoteana, Elphidium advenum, Quinqueloculina seminula, and Spirillina vivipara were ablated using a high-resolution LA-ICP-MS at the Australian National University. Comparisons of Zn, Pb, and Cd concentrations in ambient sediment with those incorporated in the carbonate tests of these species revealed positive linear relationships with robust R² values. Comparisons of chamber variability within individual tests revealed that for S. vivipara and E. advenum, the chambers analyzed (5 to 6 per individual) yielded similar Zn, Pb, and Ca values. However, for Q. seminula and A. aoteana Zn, Pb, and Cd of the innermost (older) chambers had a much closer correlation with those of ambient sediments. Linear relationships between Cd concentration within the sediment and Cd/Ca ratios in the inner most ablated chamber of A. aoteana yielded a Pearson’s R² value of 0.79. The relationship between Zn concentrations within the sediment and Zn/Ca ratios in both the inner chambers of A. aoteana and Q. seminula had R² values of 0.83 and 0.71 respectively. Lead concentration within the sediment plotted versus Pb/Ca ratios in E. advenum and S. vivipara had R² values of 0.73 and 0.81. Inner chambers of A. aoteana and Q. seminula yielded R² values of 0.80 and 0.91 respectively. These robust linear relationships between foraminiferal calcite and ambient sediment concentrations provide the means to quantitatively detect and monitor bioavailable contaminants in the modern realm, and to assess the history of pollution in shallow marine habitats by analyzing fossil specimens.