Research Projects

Research

My research investigates the connections between marine chemistry (notably carbon cycling) and climate variability on a variety of timescales—from the ice ages to today.

This work can be broken down into two areas of interest:

    • Changes in the ocean’s role was a source or sink of atmospheric CO2 on geologic timescales (Paleoceanography)
    • The importance (or not) of marine biogeochemistry on modern air-sea partitioning of CO2 (Marine biogeochemistry)

Paleoceanography

Extreme climate variability
– Evidence that long-term ENSO variability is insensitive to atmospheric CO2 (Rafter and Charles 2012)
– Seawater radiocarbon records decadal variability of the North Pacific Gyre Oscillation (NPGO)

Seawater carbon chemistry since the Last Glacial Maximum (LGM)
– Validating the benthic foraminifera proxy for seawater radiocarbon (14C) (Rafter et al. 2018 in CP)
– Reconstructing the flux of geologic carbon to the ocean (Rafter et al. 2019 in GRL)
– Quantifying the “alteration” of foraminifera test 14C—”frosty” vs. “glassy” benthic foraminifera 14C from Eastern Tropical North Pacific sediments (UCI Senior Thesis of Alan Yue; funded by UCI UROP grant)
– What is the influence of geologic carbon on seawater pH and atmospheric CO2 after the last ice age? (Rafter, Hain, Gray, and Rae In Prep; NSF proposal to be re-submitted)
– Deep-sea changes in 14C since the last ice age (Rafter and DeVries, underway)

Changes in marine nutrient consumption on ice age timescales
– 1 million year record of Eastern Equatorial Pacific nitrate consumption (Rafter and Charles 2012 in Paleoceeanography)
– Validating the foraminifera-bound N isotope proxy along the equatorial Pacific (Rafter et al. In Prep; funded by NSF; poster available upon request)
– A 5 million year rise in marine nitrate d15N and the implications for high latitude nutrient consumption and low latitude denitrification (Rafter et al. in prep; funded by NSF; poster available upon request)
– 5 million year record of Eastern Equatorial Pacific nitrate consumption (Rafter et al. in prep; funded by NSF; poster available upon request)
– Improved iron and N cycle model and increased Southern Ocean stratification as—a partial driver of ice age atmospheric CO2 variability (Rafter, Sigman, Martinez-Garcia, Studer, et al. In Prep)

Marine biogeochemistry

– Identifying Tropical Pacific subsurface nitrate characteristics and their origin (Rafter et al. 2012)
– Pacific-wide nitrate characteristics and their origin (Rafter et al. 2013)
– Equatorial Pacific nitrate uptake dynamics via the first time series of nitrate N isotopes (Rafter and Sigman 2016)
– The importance of iron recycling for nitrate consumption and the efficiency of the biological carbon pump in iron-limited waters (Rafter et al. 2017)
– Quantifying the subsurface source of surface ocean nitrate and a new estimate of new primary production (Rafter; In Prep, but feel free to ask for the code!)
– Using an array of neural networks to estimate the global marine nitrate N isotope composition (Rafter et al. 2019 in Biogeosciences)
– Using the Community Earth System Model to estimate elemental cycling in the upper ocean and its contribution to carbon export (Rafter, Martiny, and Moore In Prep)
– The influence of dynamic nutrient stoichiometry on carbon export (Moore, Rafter, and Martiny In Prep.)