Karim Lakhani, PhD

Using foraminiferal oxygen isotope data from the global tropics, I (with the help of my co-authors) investigated the calcification habitat for planktonic foraminifera. These freely floating microorganisms are very useful for paleoceanographic study, as long as we understand the depths at which they live and calcify. This work builds on previous global studies of surface-dwelling foraminifera (MARGO project and Malevich et al. 2019) and extends it to subsurface-dwelling foraminifera (G. tumida, N. dutertrei, and P. obliquiloculata). We present this new dataset and attempt to characterize trends in the calcification depth under various assumptions. Using a novel TP metric, we show that G. tumida has a calcification habitat independent of the thermocline depth, while N. dutertrei and P. obliquiloculata have calcification habitats that depend on the thermocline depth. This interactive Tableau visualization summarizes the main findings.

With the species depth data, we can attempt to determine the depth of the thermocline with just these foraminiferal data. I (with the help of my co-authors) do this by assuming a form of the thermocline based on oceanographic principles and fitting parameters to the oxygen isotope data. This is done with enough flexibility to accommodate differences in the thermocline profile regionally in the Pacific Ocean (allowing the surface mixed layer to be shallow or deep, etc.). With this method, I analyze previously published data as well as generate new data for the Western, Central and Eastern Pacific to investigate thermocline changes during the Last Glacial Maximum.

Placeholder — to be filled in with a summary of the later parts of the thesis.