Effects of ocean acidification on pelagic organisms and ecosystems - Ocean Acidification - page 112

Atmospheric CO 2

Climate

Ocean acidification Ocean warming

Seawater
CO 2

Temperature Mixing,

stratification

Circulation Atmospheric

deposition

Carbonate
chemistry

Light Nutrients

Pelagic ecosystems

Rain ratio
(CaCO 3 /POC)

Stoichiometry
(Si/C/N/P/Fe)

C-partitioning
(POC-DOC-TEP)

Nutrient utilization
efficiency

Carbon sinks & sources

Figure 6.1 Schematic representation of the environmental changes affecting pelagic ecosystems and possible feedbacks to the global carbon cycle
(POC, particulate organic carbon; DOC, dissolved organic carbon; TEP, transparent exopolymeric particles).

Table 6.6 Biotic responses to ocean acidii cation and their feedback potential to the global carbon cycle. Responses are characterized
with regard to feedback sign, sensitivity, capacity, and longevity using best guesses (±0 for negligible, + for low, ++ for moderate,
and +++ for high). Empty boxes indicate missing information/understanding (adapted from Riebesell et al. 2009 ).

Process Sign of feedback Sensitivity Capacity Longevity

+ 1 + 1

Calcii cation Negative +

Ballast effect Positive +++ +++

++ 1 ? 2 Extracellular organic matter prod. Negative +++

++ 1 Stoichiometry Negative ++ ++

++ 1 ? 2 Nitrogen i xation Negative +

1 Available information mainly based on short-term perturbation experiments.
2 Potential for adaptation currently unknown.

CO 2 - (and pH)-dependent ecological processes,
which may drive these biogeochemical feedbacks.
In Chapter 12 Gehlen et al. use a variety of experi-
mental data and ocean models to explore the poten-
tial magnitude of these feedbacks and their
quantitative impacts on the climate system.
As discussed in the sections above, changes in the
carbonate chemistry of the surface ocean have the
potential to inl uence the physiology and growth of
various members of the pelagic ecosystem, and to
affect the ecological and trophic dynamics which
govern the exchange of energy and cycling of nutri-

ents through the marine food web. For the purposes
of the present discussion, the following changes
will be considered: changes in cellular carbon
processing, changes in phytoplankton species
assemblage composition, and changes in biological
nitrogen cycling.

6.5.1 Changes in cellular carbon processing

Marine pelagic organisms mediate the transforma-
tion of inorganic carbon into organic and inorganic
particulate forms, and into a large dissolved organic