Geoscience Reference
In-Depth Information
3.6 Biological production and nutrient changes
The functioning of ocean ecosystems depends strongly upon climate conditions, including
near-surface density stratification, ocean circulation, temperature, salinity, wind field, and
composition of the atmosphere, including concentrations of CO
2
, N
2
O, O
2
, dimethyl sulfide
(DMS), and sulfate aerosol. Feedbacks are very complex because they involve physical con-
ditions and responses. Warmer water could lead to higher photosynthetic uptake of CO
2
, but
stratification increase could lead to lower nutrient levels in the euphotic zone. Sulfate aero-
sol particles are responsible for globally averaged temperatures being lower than would be
expected from the GHG levels alone. The aerosols scatter and absorb radiation and act as
cloud condensation nuclei (CCN), reducing precipitation efficiency, likely to result in a re-
duction of the annual mean net radiation at the top of the atmosphere.
Large uncertainties about this remain. However, the influence of climate conditions on
ocean productivity is well documented through long time-series of observations. These in-
clude the Continuous Plankton Recorder (CPR) in the North Atlantic, displaying close cor-
relation between different phytoplankton species and the NAO (Beaugrand
et al
.,
2009
).
Nutrient supply to the ocean has changed through increased nitrate release from the
land due to use of fertilizers and nitrogen deposition from the air in polluted areas. The
nitrogen cycle is 'accelerated' with an increase in NO
X
and nitrite oxide emissions driven
by human actions: increased fertilizer use, agriculture, and fossil fuel combustion. Dust de-
position provides an important source of micronutrients like iron, zinc, and others which
could change the biological production pattern, and enhance photosynthetic carbon fixation.
A warmer climate may lead to a decrease in dust deposition. This would provide for a posit-
ivefeedback, decreasing photosynthesis andtheuptake ofCO
2
.Changes inplankton species
composition and regional shifting of high production zones due to changing climate could
lead to further feedbacks. An increase in plankton blooms is indicated for high northern lat-
itudes.
