Phytoplankton productivity in the North Pacific ocean since 1900 and implications for absorption of anthropogenic CO2

Paul G. Falkowski and Cara Wilson

Nature 358: 741-743, 1992.

Abstract

The world's carbon budget has not been in steady state since the beginning of the Industrial Revolution. At present, carbon dioxide released by anthropogenic activities adds about 71.2 gigatons (Gt) C/yr to the atmosphere, of which about 2 Gt C/yr is thought to be sequestered in the oceans. In the steady state, phytoplankton fix about 35-50 Gt C/yr, representing a significant component of the natural cycle. If ocean productivity were changing, these biological processes could have a significant influence on anthropogenic CO2 levels by drawing down the CO2 concentration in surface waters and increasing the concentration gradient along the air-sea interface. The question of productivity changes is unresolved however. Venrick et al. reported that phytoplankton chlorophyll concentration had roughly doubled in the central North Pacific gyre between 1965 and 1985. Here we use historical records of Secchi depth data to investigate whether such dramatic changes in phytoplankton biomass have occurred throughout the North Pacific ocean during this century. We find that, although very minor changes may have occurred in this basin over the past 70 years, they are too small to have a significant impact on the rise in anthropogenic CO2 concentrations.

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