Scales of pH variability on Pacific coral reefs reconstructed from skeletal boron and boron isotopes

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

The decreased vitality of coral reef ecosystems is often cited as one of the most prominent costs associated with the progressive oceanic uptake of fossil fuel carbon dioxide and the consequent ocean acidification. Yet, despite the prominent concerns, it is presently unknown whether and how regional oceanographically-induced pH variability is actually manifested at the site of coral calcification. This uncertainty requires comprehensive monitoring of diverse reef systems. As a complementary approach to in situ monitoring installations, a research team from the Scripps Institution of Oceanography will make use of the known changes in Pacific ocean/atmosphere variability of the late 20th century as a retrospective monitoring system. In effect, the system of measurements from this targeted network of coral samples will provide a direct comparison to hindcast expectations of the pH variability forced by oceanographic change. These results of this project will allow a direct assessment of the extent to which massive corals in various oceanographic settings were actually sensitive to historical changes in regional pH. The project will serve as the doctoral research of a student who broadens participation of severely underrepresented groups. The project will also be used as a platform for public outreach through SIO Birch Aquarium exhibits. The research team will measure coral skeletal chemistry in existing coral cores from locations that represent very different geographic poles of historical Pacific basin-wide changes. Specifically, they will apply the boron isotopic proxy for pH, in conjunction with a suite of other skeletal tracers that might be sensitive to perturbations in seawater carbon chemistry, to generate seasonally-resolved records of environmental changes. Two of the study sites, Palmyra and Moorea, feature on going, multi-year in situ pH sensor installations. Accordingly, the research team will collect and analyze the most recent coral growth at these locations, which will provide the best available means for field calibration of the skeletal proxies. In general, the assessment of the scale of pH variability manifested at the site of calcification--and, especially, its relationship with oceanographic perturbations--is essential for establishing the proper perspective for projections of future anthropogenic effects on reef carbon chemistry.