Abstract (ACCEPTED) for:
ASLO Summer Meeting 2005 (ASLO=American Society for Limnology and
Oceanography), June 19-24, Santiago de Compostela, Spain, invited talk, session SS25
(Identification and Quantification of Major Feed-backs of Ocean Biology to Climate
Change), Thursday, 23 June 2005, 17:30
Heinze, C., Geophysical Institute of the University of Bergen and Bjerknes Centre for
Climate Research, Bergen, Norway, Heinze@gfi.uib.no
Marine biological carbon cycle climate feedbacks – do they matter or not?
Internal forcing of the climate system by anthropogenic carbon dioxide emissions
modifies the physical and chemical marine environment among other factors through
changes in: hydrography, velocity field, mixing, sea ice, pH value, and land-ocean
transfer of matter. Over the last two decades, a controversy among oceanographers has
persisted on the extent to which marine biology can modify anthropogenic carbon dioxide
uptake by the oceans. Early ocean carbon cycle models were a-biotic and used constant
alkalinity (e.g. Maier-Reimer and Hasselmann, 1987). Then marine biological research
started to justify itself on the background of the excess greenhouse gas threat. Heavy
criticisms for this were issued at the beginning of the Joint Ocean Global Flux Study
program (e.g. Broecker, 1991). Still, the quantitative significance of biological processes
for the kinetics of anthropogenic carbon dioxide uptake must be proven. Recently, a
series of additional feedback processes has emerged, mainly on the background of the
previously often overlooked oceanic acidification due to anthropogenic carbon dioxide
buffering (e.g., Caldeira and Wickett, 2003). Ph induced changes of oceanic plankton
may potentially feed back on the remineralization depth of marine biogenic particles, the
species composition among primary as well as secondary producers, the alkalinity
inventory, possibly the Redfield ratios and thus on the carbon budget. At present, these
feedbacks pose more question than they can answer. Furthermore, the mode of an
expected ocean circulation change in a warmer climate is not known. Model experiments
show a parallel drawdown of global biological production and atmospheric carbon
dioxide concentration with a slowing down of ocean overturning. At the colder climate of
the last glacial maximum, the ocean circulation was also more sluggish than today but
probably in a different pattern than expected for a warmer climate. The reason of the
substantial glacial-interglacial carbon dioxide variations in the atmosphere and the
ocean’s role in these are not yet clarified. In view of the existing uncertainties, upper or
lower limits for the potential of biological feedbacks on the carbon dioxide climate
forcing cannot be assessed conclusively. An attempt is made to face the well established
facts with the uncertainties in order to neither underestimate nor overestimate biological
ocean carbon cycle climate feedbacks.
Broecker, W. S., 1991, Keeping global change honest, Global Biogeochemical Cycles, 5,
191-192.
Caldeira, K., and M. E. Wickett, 2003, Anthropogenic carbon and ocean pH, Nature, 425,
p. 365.
Maier-Reimer, E., and K. Hasselmann, 1987, Transport and storage of CO2 in the ocean an inorganic ocean-circulation carbon cycle model, Climate Dynamics, 2, 63-90.