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Coral reefs are a vital part of our earth ecosystems and millions of people depend on coral reefs to provide their primary food source: fish. However, these ecosystems are threatened by pollution, warming temperatures, and ocean acidification In earth’s history coral reefs have already faced higher atmospheric CO2 and lower pH values than today, however, because this has been over longer steady state time periods, the negative geochemical feedback from rock weathering prevented the ocean from becoming undersaturated in aragonite. With the fast changes in the uptake of CO2 by the atmosphere and the ocean that we observe today the ocean becomes undersaturated in aragonite and the calcium carbonate production in marine organisms, such as corals, decreases. Previous research has shown that by the time atmospheric CO2 reaches 520 ppm coral reefs will dissolve more then they will be able to build, leading to a net loss of coral reefs worldwide.
In spite of the climate emergency that is ocean acidification only a few ship track and station based measurements of pH exist that go back just a few decades. Corals cores provide the opportunity to retrieve high resolution paleoclimatic signals that date back to preindustrial times, making it possible to analyze the development of the oceans pH, sea surface temperature and sea surface salinity.
So far a majority of studies have focused on the reconstruction of historical pH data in the Chinese sea and at the Great Barrier Reef but have neglected open ocean conditions in the pacific and the Atlantic.
The OASIS project (of the working group Coral Climatology at the ZMT under Dr. Henry Wu) will analyze coral cores from different ocean basins to study the development of the pH since the preindustrial time and link it to the CO2 uptake of the ocean as well as to environmental changes. With several coral cores from each region we will be able to reconstruct seasonal changes in sea surface temperature and sea surface salinity, seasonal to yearly changes in pH as well as an estimation of the carbon uptake of the ocean, making it possible to predict future developments. In the course of the three years of this PhD project I will focus on the Caribbean as my region of interest. Because of limited access to coral cores for different regions we will work on the first spatially distributed pH reconstructions of the ocean.