Validation of the B/Ca proxy for surface seawater pH and application to measure anthropogenic ocean acidification

Arguably, a better knowledge of past natural fluctuations in the earth?s climate and its relation to greenhouse gases will enhance the ability to constrain future impacts on ocean and atmospheric chemistry, and thus global climate change related to anthropogenic additions of CO2. Particular concern exists regarding the potential impact of ocean acidification on marine calcifiers such as corals, pteropods, foraminifers and calcareous algae. The actual extent of ocean acidification since the industrial revolution is still poorly quantified. In this project, researchers at the Lamont Doherty Earth Observatory of Columbia University will study the robustness of a proposed B/Ca paleoproxy through a combination of experimental laboratory cultures and a high-resolution sediment core from the Gulf of Mexico. A pilot study has shown that this proxy has the potential to reflect glacial/interglacial changes of surface seawater pH and atmospheric pCO2. However, the incorporation of boron into planktonic foraminifer shells also seems to be affected by temperature, and salinity variations change the seawater boron concentration. Because pH, temperature and salinity change in unison in the ocean, quantification of the respective effects on B/Ca can only be quantified in the laboratory, were parameters can be singled out. The first step of the proposed research is therefore the proxy validation under controlled conditions in the laboratory. If the quality of the B/Ca proxy is confirmed in laboratory culture and effects can be quantified, B/Ca could have several advantages over the boron isotope/paleo-pH proxy: B/Ca analyses are much faster, require less sample material, and the proxy may not be affected by dissolution in the sediment. In terms of broader impacts, it is clear that the acid-base state of seawater is of fundamental importance to all subdisciplines of oceanography and to a wide variety of global environmental research disciplines. The project will feature multiple inter-institutional collaborations and will provide for the training and support of a graduate student.