Marine Ecosystem Model Group

Figure: Schematic diagram of physical-biological processes at 30 yeas ago and present
Upper figure indicate the 30 years ago status. In this period, active winter mixing supplied iron from mesopelagic layer to upper layer, and massive phytoplankton blooming occurred and zooplankton biomass was high. Lower figure indicate present status. Iron supply was decreased due to diminished winter mixing, and phytoplankton productively decreased and zooplankton biomass was low.
To improve the accuracy of numerical model for forecasting the future global scale warming, this group has been conducting a process study to understand in the lower trophic level in relation to climatic events in the Ocean. This group observed linear decrease of dissolved oxygen (DO) in winter subsurface for the 30 years in the Oyashio. The DO decrease implied diminishing of water exchange between subsurface and surface in the Oyashio water. In the Oyashio, decrease in surface salinity was observed for the 30 years and it might have increased stratification, resulting in attenuation of vertical water mixing. Net community production (NCP) estimated from the phosphate consumption from February through August, decreased in the Oyashio for the same periods. Decreases in average spring diatom abundance and Chl-a concentration were consistent with the multi-decadal decreasing trend of NCP. Total spring zooplankton biomass, presumably dominated by Neocalanus copepods also decreased.@The attenuation of winter vertical water mixing might limit iron entrainment from subsurface to surface reduced winter-summer NPC, and zooplankton biomass for these 3 decades in the Oyashio.

Figure: 3-D NEMURO, our coupled ecosystem-biogeochemical model, has 16 compartments: two phytoplankton, three zooplankton, four nutrients, three particles, dissolved matter and carbon system.

To predict the effects of global warming on ecosystem dynamics and the effects of those changes in ecosystem dynamics on biogeochemical cycles and oceanic CO2 uptake, development of new, coupled ecosystem-biogeochemical models that explicitly represent phytoplankton and recycling of nutrients is necessary. The ecosystem model, NEMURO (North pacific Ecosystem Model Used for Regional Oceanography) in the Modeling Workshop in the North Pacific Marine Science Organization (PICES) was developed, and it was coupled with a three-dimensional ocean model (horizontal resolution, 1 x 1 degrees) including nutrient and carbon cycles (3-D NEMURO). Using 3-D NEMURO, the role of seasonal vertical migration of copepods, an important zooplankton, in the subarctic marine ecosystem was discussed (Aita et al., 2003).
Figure: CFC-11 inventories (mol/m2) and comparison of the CFC-11 concentrations (pmol/kg) from observation and model with potential density (solid line) along the Greenwich Meridian (AJAX) in the South Atlantic (1983). Shaded area is a range of 13 models from Dutay et al. [2002].
Simulation of uptake of oceanic chlorofluorocarbons (CFCs) using an eddy-resolving high resolution model (1/10 x 1/10 degrees) on the Earth Simulator was conducted to understand effects of mesoscale eddies on the CFCs distribution. The model successfully reproduces the horizontal distribution of CFC-11 inventory. The model's estimate of global CFC-11 inventory for 1994 is 5.1 x 108 mol, which is within the 5.5 } 1.2 x 108 moles estimated from WOCE (World Ocean Circulation Experiment) CFC-11 concentrations (Willey et al., 2004). Our results demonstrate that global models with super high resolution are useful for studying local distributions such as those observed on single cruises, which cannot be resolved by coarser models.