Description:
The decrease in seawater pH (ocean acidification) caused by absorption of anthropogenic atmospheric CO2 leads to a reduction in the aragonite saturation state (ΩAR). Studies indicate that calcifying marine organisms respond to reduced ΩAR with decreased calcification rates. In particular, calcification rates in reef-building corals may have slowed by 10% over the last 150 years, with predictions to slow another 15-30% by the end of century. We cannot fully evaluate or address this threat to ocean biota without a highly precise, sensitive and direct method for measuring calcification rates. Existing methods for measuring calcification rates are not ideal. The most common measures changes in total alkalinity by titration followed by using assumptions and equations to calculate the change in [Ca+2]. Measuring skeletal incorporation of radioactive Ca+2 is hazardous and difficult to use for field/community studies. Direct measurement of [Ca+2] is possible with ion selective electrodes (ISE). Calcium ISEs are common in clinical applications, but are not widely used in seawater because of calibration difficulties, drift, and low sensitivity. Measurements of [Ca+2] by complexometric titrations are laborious and lack the sensitivity or precision needed. To advance, the field needs a quick and simple method to measure [Ca+2] with a precision of ±5 µM. Major issues to address are: high background [Ca+2] in seawater (~10.2 mM); interference from other ions (e.g. Mg); and relatively small [Ca+2] changes during laboratory incubations or diel cycles due to calcification (~0.050 mM). It will take a novel new technology or analytical method to achieve this goal.