the atmosphere at lower rates (in the global total) set by the concentrations established
at depth over the whole interval that the water has been sequestered, that is up to
thousands of years. Thus, return to the atmosphere represents the pre-industrial
atmospheric levels. Adding to that non-equilibrium effect, the CO 2 evasion now must
work to push the gas into the atmosphere against a reduced concentration gradient,
because there is more in the atmosphere. So, until a new equilibrium is established,
probably a 3000–6000-year delay, some of the fossil-fuel CO 2 will move quickly into
the ocean.
(^) However, the CO 2 concentration at the evasion sites is not the same as that at the
invasion sites – it is higher. While water moves along at depth, carbon is added from
respiratory oxidation of organic matter sinking into it all along the route of deep-water
flow. We assume that factors affecting primary-production rates probably have not
changed much over 200 years, so there probably has been no large change in this
biological sequestration during the industrial build-up. It is taken to be a large but
constant term in the overall exchange. The current consensus (IPCC 2007) for the
overall budget (Fig. 16.9) puts the biological contribution at about 11 GtC yr−1. That
is a large enough component of the budget that, if it does vary, it could account for
major shifts in the overall input–output balance for labile carbon in the ocean.
“Labile” in this context means not fixed into rock, but free to come and go between
gaseous and dissolved carbonate pools and organic matter.
Fig. 16.9 Approximate global ocean reservoir sizes of labile, combined carbon (in
gigatonnes carbon, GtC), and contributions of different processes to transfers of CO 2
to and from the ocean and among carbon-bearing constituents in the ocean. Rates in
italics are per year. Abbreviations: GPP, gross primary production; NPP, net primary
production; AR, autotrophic respiration; HR, heterotrophic respiration; DIC,
dissolved inorganic carbon; DOC, dissolved organic carbon.
Data from Sarmiento and Gruber (2006), IPCC (2007), and Emerson and Hedges (2008).