AGU Journal Highlights -- March 19, 2008

1. Higher CO₂ boosts phytoplankton in Antarctic waters

Oceanographers and climatologists are intensely studying how the ocean acts as a source or a sink of carbon dioxide (CO₂). Under normal conditions, highly productive areas of the ocean are carbon sinks: Biological activity traps atmospheric CO₂ within organic particles that fall to the ocean floor when organisms die. The efficiency of this “biological C pump” is known to depend on the productivity and species composition of phytoplankton, yet almost no information is currently available on how CO₂ concentrations may affect these parameters. The results of Tortell et al. show that elevated CO₂ concentrations increase phytoplankton productivity in the Ross Sea, Antarctica, and promote the growth of larger diatom chains. These chains are prolific bloom formers with very high capacities to export organic carbon to sediments. The authors expect that as ocean CO₂ levels rise, similar blooms may be found in regions subject to natural ion fertilization, through upwelling of deep waters, windblown input, island effects, or melting sea ice.

Title: CO₂ sensitivity of Southern Ocean phytoplankton

Authors: Philippe D. Tortell: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, Canada; also at Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada;

Christopher D. Payne and Yingyu Li: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, Canada;

Scarlett Trimborn and Björn Rost: Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany;

Walker O. Smith: Virginia Institute of Marine Sciences, Gloucester Point, Virginia, U.S.A.;

Christina Riesselman and Robert B. Dunbar: Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.;

Pete Sedwick: Bermuda Institute of Ocean Sciences, Inc., St. George's, Bermuda;

Giacomo R. DiTullio: Hollings Marine Laboratory, University of Charleston, Charleston, South Carolina, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL032583, 2008; http://dx.doi.org/10.1029/2007GL032583

2. Stabilizing climate requires near-zero carbon emissions

Current international climate mitigation efforts aim to cap levels of greenhouse gases in the atmosphere to avoid dangerous interference in the climate system. Nonetheless, stable greenhouse gas concentrations do not equate to stable global climate. Simulations show that human-induced climate warming will continue for many centuries, even after atmospheric carbon dioxide is kept level. To study how future warming could be avoided, Matthews and Caldeira use an Earth system model to assess emission requirements for global temperature stabilization within the next several centuries. They find that a single pulse of carbon released into the atmosphere increases globally averaged surface temperature by an amount that remains approximately constant for several centuries, even in the absence of additional emissions. Further, holding the climate constant at a given global temperature requires near-zero future carbon emissions. These results suggest that future greenhouse gas emissions by humans would need to be eliminated in order to hold global temperatures steady. As a consequence, any future emissions will commit the climate system to warming that is essentially irreversible on centennial timescales.