The effect of coccolithophores and non-calcifying phytoplankton on the marine dissolved inorganic carbonate system

Weston, Keith (1997) The effect of coccolithophores and non-calcifying phytoplankton on the marine dissolved inorganic carbonate system. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Recent interest in the global climate system has focused attention on the oceanic carbon cycle due to its role in the 'Greenhouse Effect'. Calcifying pelagic micro-algae, i.e. coccolithophores, represent an important component of the oceanic carbon cycle due to the vast blooms which occur in many parts if the world's oceans. The dynamics of the production of both organic and inorganic carbon in coccolithophore blooms have important implications for the carbon cycle. It has been proposed that coccolithophores may decrease the flux of carbon dioxide across the air-sea interface relative to non-calcifying phytoplankton. In this study the effect of a high-calcifying strain of the coccolithophore, Emiliania huxleyi, on the dissolved inorganic carbonate system was compared to a low-calcifying strain of E. huxleyi and the non-calcifying chrysophyte, Isochrysis galbana. In the high-calcifying strain of E. huxleyi the uptake of ¹⁴C-labelled dissolved inorganic carbon showed a greater rate of calcification relative to photosynthesis in lag and exponential growth phase than in stationary phase. This caused a decreased rate of PCO₂ uptake relative to total dissolved inorganic carbon (C_T) uptake, relative to low-calcifying E. huxleyi and I. galbana. The dissolved inorganic carbonate system was determined from pH and one point alkalinity titrations. The relationship between PCO₂ and C_T was represented by the homogenous buffer factor (β). The buffer factor was lower in high-calcifying E. huxleyi cultures (β = 0.17-7.12) than for I. galbana and low-calcifying E. huxleyi cultures (β = 6.92-13.50). A net increase in PCO₂ was also noted for certain high-calcifying E. huxleyi cultures as C_T was declining.

Field studies, in nutrient adjusted experimental enclosures, were undertaken to measure changes in photosynthetic and calcification parameters in conjunction with measurements of the dissolved inorganic carbonate system. β measured in E. huxleyi dominated blooms and a mixed E. huxleyi and diatom bloom ranged from -0.27-4.25 and 6.80-7.59 respectively, in agreement to those calculated in culture. An increase in PCO₂ was detected during an E. huxleyi dominated bloom, coincident with the minimum value of β (-0.27). Rates of calcification to photosynthesis, from derived from ¹⁴C uptake rates, showed an average ratio of 0.4 in E. huxleyi dominated blooms, which increased to a maximum of 1.2 concurrent with the minimum value of β.