Geoscience Reference
In-Depth Information
the role of marine biota in controlling its cycle is
given in Chapter 11. Impacts of ocean acidii cation
on DMS emissions and implications for climate
feedbacks are still largely unknown. Published
studies report contrasting results. Potential effects
have so far not been included in coupled climate-
marine biogeochemistry models.
given plankton functional type, nor potential for
acclimation and adaptation. The increase in func-
tional types in an effort to better capture ecosys-
tem complexity is limited by the lack of available
data to constrain model parameterizations. The
evaluation of the impacts of ocean acidii cation
and climate change might well require the devel-
opment of a new generation of ecosystem models
( Follows
et al.
2007 ; Barton
et al.
2010 ) or optimali-
ty-based adaptive models (Bruggeman and
Kooijman 2007 ; Pahlow
et al.
2008 ).
Elemental cycles are tightly coupled through
reactions involved in organic matter synthesis and
remineralization. One has just begun to evaluate
how changes in one cycle spread to another as
exemplii ed by studies linking changes in the export
efi ciency of the biological pump either mediated
by CaCO
3
production (Hofmann and Schellnhuber
2009) or export stoichiometry (Oschlies
et al.
2008 )
to ocean oxygen inventory and the nitrogen cycle.
Clearly, the study of biogeochemical impacts of
ocean acidii cation, its interaction with climate
change, and feedbacks to the earth system are at an
early stage.
12.5
Conclusion and perspectives
This chapter has addressed biogeochemical impacts
for which experimental evidence is available and
which, with the exception of atmospheric trace
gases, have been addressed in model studies. As a
result, we have largely focused on the C and N
cycles. It is likely that other major cycles also will be
affected by ocean acidii cation either directly (Fe;
Shi
et al.
2010 ; Breitbarth
et al.
2010 ) or indirectly
through changes in elemental ratios of export pro-
duction (P and Si; Hutchins
et al.
2009 and refer-
ences therein). At present, however, experimental
evidence is too sparse, and often contradictory, to
allow inferences of biogeochemical consequences
across the whole spectrum of elements.
Not surprisingly, early research efforts on the
impacts of ocean acidii cation focused on marine
calcii cation. Because of its seemingly straightfor-
ward incorporation into biogeochemical models
and the negative feedback to atmospheric CO
2
lev-
els associated with its decrease, this particular
impact was rapidly implemented in global ocean
biogeochemical models. Ocean acidii cation
research is a i eld of rapidly expanding knowledge,
and recent evidence suggests that the response of
marine calcii ers to changes in carbonate chemis-
try is more complex than originally expected.
Within-species and between-species variability, as
well as processes such as acclimatization and
adaptation, challenge the approaches currently
used in biogeochemical modelling. These mostly
rely on the representation of a limited number of
plankton groups, to which major biogeochemical
functions are assigned, e.g. CaCO
3
production,
biogenic silica formation and N
2
i xation. If envi-
ronmental conditions (irradiance, temperature,
nutrients) cross a critical threshold for a given plank-
ton functional type, it disappears from the model
world. There is no shift between species within a
12.6 Acknowledgements
We acknowledge i nancial support from grant
GOCE-511176 (EU FP6 RTP project CARBOOCEAN)
and grant 211384 (EU FP7 RTP project EPOCA) pro-
vided by the European Commission.
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