THE DIRECT RADIATIVE IMPACT OF COCCOLITHOPHORE BLOOMS ON BASIN-SCALE CLIMATE

• Main Authors: M. Gondwe, W. Klaassen, W. Gieskes, H. De Baar
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.568.626; http://dissertations.ub.rug.nl/FILES/faculties/science/2004/m.gondwe/c2.pdf

The water-leaving radiance, defined as radiation from the sun reflected off particles in water and exiting the ocean surface back into the atmosphere and space, is often used to derive ocean-colour information from remotely sensed data. However, it is in itself a measure of the amount of solar irradiance reflected by oceanic constituents and, therefore, not available to the Earth's heat reservoir (changes in which can affect the Earth's energy balance and climate). A strong influence on the water-leaving radiance is observed from coccolithophore blooms, owing to the highly reflective calcareous platelets or coccoliths covering these marine algae. We analysed remotely sensed water-leaving radiances (1998-1999) over the N. Atlantic, where the blooms are spatially and temporally most abundant, and found that the direct radiative forcing of climate between 402-565 nm (the major range of optical influence) by coccolithophores in this ocean is negligible (-0.05 W m-2 mean annually). To put this in perspective, the global mean annual radiative forcing of highly scattering sulphate aerosol particles in the present day climate has been estimated at-0.4 W m-2, while that combined for the greenhouse gases carbon dioxide, methane, nitrous oxide and halocarbons has been estimated at +2.43 W m-2. The radiative forcing of the stratospheric ozone hole has been estimated at-0.15 W m-2 while that of tropospheric ozone has been estimated at +0.35 W m-2, producing a net forcing of +0.2 W m-2 [IPCC, 2001]. Comparatively, the mean annual solar radiation received at the Earth's surface ranges from 80 W m-2 over the Arctic to 280 W m-2 over the Sahara desert, where cloud cover is negligible. 2.2