Mechanisms controlling primary and new production in a global ecosystemmodel – Part II: The role of the upper ocean short-term periodic and episodic mixing events

[摘要] The use of 6 h, daily, weekly and monthly atmospheric forcing resulted in dramaticallydifferent predictions of plankton productivity in a global 3-D coupled physical-biogeochemicalmodel.

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 areasprimarily because of increased light limitation resulting from deepening of themixed layer overnight as well as enhanced storm activity, and 25% at moderateand high latitudes primarily due to increased grazing pressure resulting fromlate winter stratification events. Mini-blooms of phytoplankton and zooplanktonoccur in the model during these events, leading to zooplankton populations beingsufficiently well developed to suppress the progress of phytoplankton blooms. A10% increase in primary production was predicted in the peripheries of theoligotrophic gyres due to increased storm-induced nutrient supply end enhancedwinter production during the short term stratification events that are resolvedin the run forced by 6 h meteorological fields.

By resolving the diurnal cycle, model performance was significantly improved with respect to severalcommon problems: underestimated primary production in the oligotrophic gyres; overestimated primaryproduction 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 ecosystemdynamics was profound, the effects persisting far beyond the hourly timescale, and having major consequences forpredicted global and new production on an annual basis.

[学科分类] 海洋学与技术