Great Barrier Reef Coral and Halimeda Cd/Ca Ratios: Holocene Paleochemical Records

大堡礁珊瑚礁发育的模式和时间 过去的大堡礁（澳大利亚昆士兰州大陆架） 全新世的10,000年可能是由 地表水营养盐浓度和季节性上升流 密封水平上升驱动的模式。 生物礁 由沉积的文石板的积累而形成， 无暗礁水域中的石灰质绿色藻类Halimeda 外架后面的植物也可以通过营养物质来控制 富集事件。 没有直接的古- 营养水平，以检验这些假设。 然而，海水中溶解的镉水平与 与磷酸盐，一种必需的限制性营养素的关系。 镉是结合在珊瑚文石的比例， 海水与文石中主要阳离子钙的比例， 精确测量珊瑚中Cd/Ca比值的技术 已开发出微量的文石， 应用于研究季节性和年度地表水变化， 主要存在于加拉帕戈斯的珊瑚中。 Cd/Ca的效用 在珊瑚和Halimeda中进行的营养测量 然而，大堡礁的历史尚不清楚， 本可行性研究提出了几个目标， 大堡礁珊瑚中的镉钙比例 Halimeda作为海洋条件的记录者， 全新世时期的地区。 这些目标包括：（1） 确定陆地影响可能影响的程度 测量大堡礁珊瑚中的Cd/Ca信号;（2） 调整和验证样品处理和分析方案 用于与Halimeda文石;和（3）记录 现代和底层微量元素信号和解释 在Halimeda文石的关系， 环境

The pattern and timing of coral reef development in the Great Barrier Reef (Queensland shelf, Australia) during the past 10,000 y of the Holocene may have been controlled by changing surface water nutrient concentrations and seasonal upwelling patterns as driven by rising seal level. The bioherms developed by accumulation of the aragonite plates deposited by the calcareous green algae Halimeda in the reefless tract behind the outer shelf may also be controlled by nutrient enrichment events. There are no direct records of paleo- nutrient levels available with which to test these hypotheses. However, dissolved cadmium levels in seawater correlate well with those of phosphate, an essential limiting nutrient. Cadmium is incorporated in coral aragonite in proportion to its seawater ratio to calcium, the major cation in aragonite, and techniques to accurately measure Cd/Ca ratios in coral aragonite at the trace levels found have been developed and applied to study seasonal and annual surface water variability, primarily in corals from the Galapagos. The utility of Cd/Ca measurements in coral and Halimeda for determining the nutrient history of the Great Barrier Reef is not yet known, however, this feasibility study addresses several objectives to define how cadmium-calcium ratios in Great Barrier Reef coral and Halimeda act as recorders of oceanographic conditions in that region during the Holocene. These objectives involve: (1) defining the degree to which terrestrial influences may affect measured Cd/Ca signals in Great Barrier Reef corals; (2) adapting and verifying sample handling and analytical protocols for use with Halimeda aragonite; and (3) documenting the modern and down-core trace element signals and preservational states in Halimeda aragonite in relationship to their environment.