Thesis

Calcification and growth of the marine coccolithophorid Emiliania huxleyi in response to elevated partial pressure of carbon dioxide and low phosphate concentration

Anthropogenic input may double atmospheric carbon dioxide (C02) by the year 2100. Elevating the carbon dioxide concentration in ocean surface waters alters the carbonate system, lowers the carbonate ion (C03-2) concentration and consequently the saturation state of CaC03. These conditions may impact both the production of CaC03 as well as its persistence in the water column. Laboratory experiments simulating these conditions of elevated pC02 and reduced C03 -2 concentration have been shown to reduce CaC03 production in many marine organisms, including the marine coccolithophorid Emiliania hu.xleyi. Coccolith formation in E. huxleyi increases under phosphorus limitation, demonstrating that factors other than carbonate chemistry can alter CaC03 production in these algae. As a consequence, investigations predicting net carbon flux may require close consideration of factors such as nutrient levels. This investigation focuses on E. huxleyi, grown in a closed system under initial conditions simulating present day and projected atmospheric C02 levels ( -360 and -780!-latm, respectively) and minimal (0.6!-lmol r1) phosphate loading. We found that the elevated pC02 caused a reduction in net calcification owing to a combination of reduced calcification per cell and an observed a "fertilization effect" that caused a proliferation of non-calcified cells. Any enhanced calcification due to phosphate limitation was offset by the effect of elevated pC02• If this shift is representative of natural populations, then there is the potential for a drastic reduction in surface ocean carbonate production by this ubiquitous alga. Furthermore, the decrease in CaC03 may reduce the flux of particulate organic carbon (POC) and particulate inorganic carbon (PIC) to the deep sea.

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