Publications

Core-top Constraints on the Ecology and Paleothermometry of Planktic Foraminifera in the Indian Ocean

Using a new database of 115 core tops from the Indian Ocean, we refine the living depths and Mg/Ca relationships for four species of planktic foraminifera. Using a combination of multivariate regression techniques and Bayesian factor analysis, we systematically test whether multivariate calibrations accounting for non-thermal influences on Mg/Ca sufficiently improve model fit and performance over classic "temperature-only" models. For surface-dwelling species, the temperature-only models were the best fits to the data, while more data is required for the subsurface-dwelling species.

Elevated Shallow Water Salinity in the Deglacial Indian Ocean was Sourced from the Deep

We reconstructed upper ocean temperature and salinity in the southeast Indian Ocean: one of the largest source regions of Subantarctic Mode Water in the global ocean. We find that at the onset of the Last Deglaciation, mode water salinity sharply rose by >2 PSU. We argue this salt originated in the deep glacial ocean, and explore the implications of this previously overlooked salt source on the recovery of the Atlantic overturning circulation at the end of the Last Ice Age.

An Inconsistent ENSO Response to Northern Hemisphere Stadials over the Last Deglaciation

Trace element analysis of individual foraminiferal shells provides a look at past subsurface temperature variability in the equatorial Pacific, an indicator of El Niño-Southern Oscillation (ENSO) intensity. We find that ENSO was most intense during Heinrich Stadial 1, likely amplified by meltwater-induced changes to ocean and atmospheric circulation. Interestingly, we do not observe a similar intensification during the Younger Dryas, suggesting that meltwater's remote influence over millennial-scale ENSO variability may be mediated by tropical Pacific mean state.

Characterizing the Stable Oxygen Isotope Composition of the Southeast Indian Ocean

New seawater observations from the southeast Indian Ocean suggest surface δ¹⁸O – salinity relationships are determined by both the water cycle and ocean mixing between subtropical and subpolar water masses. These relationships provide key insights into water mass interconnectivity throughout the water column of the Indo-Australian basin.

Tools of the Trade: Taking the Temperature of Ancient Oceans with Foraminiferal Mg/Ca

To understand past climate change, we need information on a crucial ingredient of Earth's climate system—ocean temperatures. However, without thermometers (or oceanographers) to take the ocean’s temperature hundreds, thousands, or millions of years ago, the only way we can piece together the thermal history of the oceans is through "proxy observations". One common tool I use: the Mg/Ca ratio of foraminiferal calcite.

Neodymium Isotope Evidence for coupled Southern Ocean Circulation and Antarctic Climate throughout the last 118,000 Years

Neodymium isotopes and sediment grain size analyses show that changes in deep Indian Ocean circulation and water mass provenance co-occured with changes in Antarctic climate change over the last 118,000 years. We suggest that the expansion of sea ice during the inception of the Last Ice Age stratified the deep ocean and prevented newer Atlantic-sourced deep waters from entering the Indian basin, increasing the proportion of older, Pacific-sourced deep waters.

Discerning Changes in High-Frequency Climate Variability using Geochemical Populations of Individual Foraminifera

We developed a new individual foraminiferal analysis (IFA) proxy system model, QUANTIFA, that combines methods for assessing IFA detection sensitivity with analytical tools for processing and interpreting IFA data. We apply this model to previously published datasets to show how QUANTIFA can be used to standardize and streamline single-shell reconstructions of climate variability.