The Biological Pump During the Last Glacial Maximum and Early Deglaciation

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An important unanswered question in climate science is what caused the increase of atmospheric carbon dioxide (CO2) concentrations during the last deglaciation. During the height of the last ice age, 20,000 years ago, climate was cold and CO2 concentrations were low, around 180 parts per million (ppm). Subsequently CO2 concentrations rose to about 280 ppm causing the climate to warm, ice sheets to melt and sea levels to rise. The last deglaciation was the last time in Earth's history when global climate warmed substantially, comparable to the warming projected for the coming centuries. Currently interactions between climate and the carbon cycle are not well understood, with possible implications for the accuracy of future climate projections. This project it will contribute to a better understanding of Earth's coupled climate-carbon cycle system. Previous research suggests that the carbon that was missing in the atmosphere during the ice age may have been stored somewhere in the ocean, but at present it is not clear where it was, how it got there, or what mechanisms may have controlled its outgassing from the ocean to the atmosphere during the deglaciation. This project will synthesize carbon isotope data from ocean sediments and combine them with detailed model simulations in order to better understand the ocean's circulation and carbon cycle during the early part of the last deglaciation from 20,000 to 13,000 years before the present. The data synthesis will be accomplished through an international collaborative project (OC3: Ocean Circulation and Carbon Cycling). A newly developed global climate model that includes three-dimensional ocean physics, biogeochemical cycles, isotopes of carbon and nitrogen, and sediments will be constrained by the OC3 carbon isotope synthesis and other existing paleoceanographic datasets such as a recent synthesis of nitrogen isotope data and an ongoing radiocarbon compilation. The goal is to reconstruct quantitatively how ocean carbon storage was affected by different processes, such as the biological pump, sea ice cover, ocean circulation, stratification, iron fertilization, sea level and sediment interactions. The project has the potential to improve our understanding of the deglacial ocean circulation, its carbon cycling, and it may provide explanations for the rise in atmospheric CO2. Funding supports a postdoctoral researcher, and provides research opportunities for undergraduate students.