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

• Main Authors: Popova, E.E., Coward, A.C., Nurser, G.A., de Cuevas, B., Anderson, T.R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2006
• Subjects: Southern Ocean; Pacific; Subarctic
• Online Access: https://eprints.soton.ac.uk/43920/; http://www.ocean-sci.net/2/267/2006/os-2-267-2006.pdf

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. 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 thatare resolved in the run forced by 6 h meteorological fields. 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.