Ocean Science
www.ocean-sci.net
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2
2
2006
10.5194/os-2-267-2006
http://www.ocean-sci.net/2/267/2006/
http://www.ocean-sci.net/2/267/2006/os-2-267-2006.html
http://www.ocean-sci.net/2/267/2006/os-2-267-2006.pdf
267
279
2006-12-06
Mechanisms controlling primary and new production in a global ecosystem model – Part II: The role of the upper ocean short-term periodic and episodic mixing events
E. E. Popova
ekp@noc.soton.ac.uk
A. C. Coward
G. A. Nurser
B. de Cuevas
T. R. Anderson
National Oceanographic Centre, Southampton, UK
The use of 6 h, daily, weekly and monthly atmospheric forcing resulted in dramatically
different predictions of plankton productivity in a global 3-D coupled physical-biogeochemical
model.
<br><br>
Resolving the diurnal cycle of atmospheric variability by use of 6 h forcing,
and hence also diurnal variability in UML depth, produced the largest
difference, reducing predicted global primary and new production by 25% and
10% respectively relative to that predicted with daily and weekly forcing.
This decrease varied regionally, being a 30% reduction in equatorial areas
primarily because of increased light limitation resulting from deepening of the
mixed layer overnight as well as enhanced storm activity, and 25% at moderate
and high latitudes primarily due to increased grazing pressure resulting from
late winter stratification events. Mini-blooms of phytoplankton and zooplankton
occur in the model during these events, leading to zooplankton populations being
sufficiently well developed to suppress the progress of phytoplankton blooms. A
10% increase in primary production was predicted in the peripheries of the
oligotrophic gyres due to increased storm-induced nutrient supply end enhanced
winter production during the short term stratification events that are resolved
in the run forced by 6 h meteorological fields.
<br><br>
By resolving the diurnal cycle, model performance was significantly improved with respect to several
common problems: underestimated primary production in the oligotrophic gyres; overestimated primary
production in the Southern Ocean; overestimated magnitude of the spring bloom in the subarctic Pacific Ocean,
and overestimated primary production in equatorial areas. The result of using 6 h forcing on predicted ecosystem
dynamics was profound, the effects persisting far beyond the hourly timescale, and having major consequences for
predicted global and new production on an annual basis.
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