Changes in the North Pacific Ocean biological pump over the last glacial-interglacial cycle

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Carbon dioxide (CO2) is a major greenhouse gas which exerts a significant control on global climatic conditions. Between past glacial (cold) and interglacial (warm) periods atmospheric concentrations of CO2 decreased by 80-100 ppm while within glacial periods concentrations varied by up to 60 ppm. Of interest to palaeoclimatologists are the controls and processes which result in these large changes in CO2. One mechanism which has been proposed to explain a large proportion of these changes is the marine biological pump in which variations in surface water biological productivity lead to greater or lower amounts of atmospheric CO2 being draw down out of the atmosphere and stored within the deep ocean. Recent investigations into the role of the marine biological pump have focused on the Antarctic and Subantarctic waters of the Southern Ocean. However, while some climate models suggest that changes in the Southern Ocean may explain all of the past changes in atmospheric CO2, evidence from marine sediment cores and other climate models suggest that the Southern Ocean is actually only able to explain a proportion of the observed CO2 changes. As such, there is a need to examine the role of the biological pump in other locations. The research within the proposed fellowship aims to develop a better understanding of the mechanisms and processes which controlled past and potentially future changes in atmospheric CO2 by investigating changes in the North Pacific Ocean biological pump over the last glacial cycle (from 131,000 years ago to the current day). This will primarily be achieved by analysing the isotopic composition of diatoms, unicellular siliceous algae, within a series of sediment cores spread across the North Pacific Ocean. Analysis of diatom isotopes is a comparatively novel technique and has not yet been widely applied to many marine samples, particularly outside of the Southern Ocean. Results from these analyses, though, will provide key information on past changes in surface water biological productivity, nutrient utilisation and changes in the stability of the water column in the North Pacific Ocean. This, in turn, will enable an insight into the spatial and temporal changes in the North Pacific Ocean biological pump over the last 131,000 years and the possible role of the pump in changing global atmospheric concentrations of CO2 over both long and short timescales. By combining the results of this research with other mechanisms which may also control atmospheric concentrations of CO2 over similar timescales, such as the Southern Ocean biological pump and the terrestrial biosphere, a more detailed understanding will be obtained with regards to the internal mechanisms that influence the global climate over long, glacial-interglacial, and shorter, millennial, timescales. This information will be valuable both to palaeoceanographers and palaeoclimatologists attempting to understand past global climatic changes. In addition, the research will provide an essential framework for the development of more accurate climate models to investigate both past and future climate change scenarios.