My main interest is focussed on the understanding and reconstruction of past marine carbonate chemistry. Specifically, I seek to validate and apply the boron isotope proxy for past seawater pH. The methods used for the validation work are culture experiments with living planktic foraminifers, as well as observations on planktic and benthic foraminifers from coretop sediments, and now also bamboo corals. Specifically I studied the influence of symbiont photosynthesis on the pH recorded by planktic foraminifers (Hönisch et al., 2003) and scleractinian corals (Hönisch et al., 2004). The boron isotopic composition of symbiont-bearing planktic foraminifers also changes with foraminiferal shell size, as it appears that larger individuals spend relatively more time closer to the seasurface where light levels are higher and symbiont photosynthesis is stronger (Hönisch and Hemming, 2004). In the latter study we also describe a significant post-depositional dissolution effect on the boron isotopic composition in foraminifera shells. Although these side effects are significant, the detailed knowledge of these proxy limitations now allows us to carefully select sample material for paleoreconstructions. I am currently applying the boron isotope proxy to reconstruct ocean acidification across the Paleocene/Eocene Thermal Maximum.
The B/Ca proxy for marine carbonate chemistry is fairly new and we continue to test it in culture experiments Allen et al., 2011, Allen et al., 2012), where we can control environmental conditions. I am also particularly interested in testing proxy relationships of times when the minor and trace element composition of seawater was different from today.
Some of my projects include:
- Testing Geochemical proxy relationships under variable paleo-seawater chemical conditions
- Reconstructing surface ocean acidification at the PETM
- Validating the boron isotope proxy in deep-sea corals and tracing anthropogenic CO2 invasion