Boyd¹, P.W., S.C. Doney^2#, J. Kleypas² and J.K. Moore^2*

¹NIWA Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand, Tel: 64-3-479-5249, E-mail: Pboyd@alkali.otago.ac.nz, ²Climate and Global Dynamics, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, USA, ^#Present Address Department of Chemistry and Geochemistry, Woods Hole Oceanographic Institute, Woods Hole, MA 02543-1057, USA, ^*Present Address Ocean Ecosystem Dynamics and Biogeochemistry, Department of Earth System Science, Rowland Hall 279, University of California at Irvine, Irvine, CA 92697-3100

Modelling regional responses by marine pelagic ecosystems to global climate change

Marine biota play an important role in the Earth’s climate by regulating atmospheric CO₂ levels on decadal to millennial time-scales. Current coupled ocean-atmosphere model (COAM) projections of future oceanic anthropogenic carbon uptake suggest reduced rates due to surface warming, enhanced stratification, and slowed thermohaline overturning. Such models rely on simple, bulk biogeochemical parameterisations, whereas recent ocean observations indicate that floristic shifts may be induced by climate variability, are widespread, complex, and directly impact biogeochemical cycles. Moreover, projected changes in ocean physics occur on regional scales, similar to the scales observed for the response of algal community structure to natural interannual climate variability. We present a strategy to incorporate ecosystem function in COAM’s and to evaluate the results in relation to region-specific ecosystem dynamics using a template of oceanic biogeographical provinces. Illustrative simulations for nitrogen fixers with an off-line multi-species, functional group model suggest significant changes by the end of this century in ecosystem structure on regional scales mainly due to increased stratification and temperature, and to a lesser extent decreased subsurface nutrient concentrations. Some of the largest regional impacts are caused by shifts in the areal extent of biomes.