I study past changes in Earth's climate to further our understanding of forcings, responses, and feedbacks in the climate system. I use a combination of isotope geochemistry and numerical modelling to reconstruct and understand these changes. Some of my active research projects, and selected publications, are listed below.
Volcanic forcing of climate
Volcanic eruptions provide one of the major natural forcings of climate, and thus past eruptions are opportunities to study how the climate responds to external forcing. Our best records of past volcanic events come from sulfate peaks in ice cores, but many of the key attributes that determine the climate forcing associated with an eruption are hidden. I have been developing new techniques to measure sulfur isotopes in ice cores to reconstruct the climate forcing potential of unidentified past eruptions.
Ocean carbon cycling in the Last Glacial Maximum & deglaciation
The end of the last ice age between 20 and 10 thousand years ago marks the largest, most recent natural perturbation to the carbon cycle, with atmospheric CO2 concentrations rising by 90 ppm. The ocean played a key role in this transition, but the exact mechanisms remain elusive. I have been using geochemical tracers (e.g. radiocarbon and boron isotopes) in marine calcifying organisms such as foraminifera and deep-sea corals to reconstruct when and how carbon moved from the ocean to the atmosphere.
Sea ice, circulation, and carbon dynamics in the Southern Ocean
The Southern Ocean plays a crucial role in setting the large scale global overturning circulation. Furthermore, the unique dynamics and biogeochemistry of this region contribute to its importance on glacial-interglacial carbon cycling. My research combines geochemical records from deep sea corals with dynamical models of this important region and highlights the importance that Southern Ocean sea ice has on circulation and carbon cycling on glacial-interglacial to centennial timescales.
The sequence of climate events resulting in the last deglaciation
The demise of the Laurentide and other major Northern Hemisphere ice sheets at the end of the last ice age and the concommitant rise in atmospheric CO2 was the result of a complex interplay of feedbacks and responses to forcings. Studying the sequence of events that led to this extreme change in climate allows us to investigate key processes and identify tipping points in the climate system. I have been working on improving marine chronologies over this time period, as well as synthesizing data for comparison to climate model simulations of the last deglaciation through the PMIP4 effort.
Ivanovic et al., 2018. Acceleration of northern ice sheet melt induces AMOC slowdown and northern cooling in simulations of the early last deglaciation. Paleoceanography and Paleoclimatology. 33: 807-824.
Weathering and its role in climate
The weathering of rocks on Earth's surface is intimately linked to the global carbon cycle, and as such it plays a key role regulating Earth's climate. However, whether weathering is a source or sink of CO2 to the ocean-atmosphere system depends on the rock that is being weathered, the source of acidity in the water, and the timescale being considered. Isotope measurements are ideal for distinguishing between different weathering sources, and can be used with an inverse model to determine weathering budgets in individual catchments or globally. My work on riverine sulfur isotopes has shown that the global weathering of pyrite has been previously underestimated, and thus that the CO2 weathering sink is likely overestimated.
Kemeny et al., 2021. Sulfate sulfur isotopes and major ion chemistry reveal that pyrite oxidation counteracts CO2 drawdown from silicate weathering in the Langtang-Trisuli-Narayani River system, Nepal Himalaya. Geochimica et Cosmochimica Acta, 294, pp.43-69.