Sensitivity tests for Improvement of Chlorophyll Simulation with NEMO-TOPAZ
NEMO-TOPAZ well represents the major biogeochemical variables; however, chlorophyll was over-estimated (CTL). Chlorophyll generally represents the amount of phytoplankton, and the growth of phytoplankton is largely affected by the trace amount of iron in iron-limited regions. The model takes into account the amount of iron deposition supplied from the atmosphere to seawater, desorption parameter relating to the supply process of iron from particulates in the ocean to seawater, and scavenging parameter being removed from seawater after being absorbed to particles for impact of iron. Iron deposition of NEMO-TOPAZ was over-diagnosed compared to the other biogeochemistry model NEMO-PISCES; however when these data were changed to reduced iron in the NEMO-PISCES model, the concentration of chlorophyll improved (PFE; Equatorial Pacific RSME reduced by 59% compared to CTL).
As a result of adjusting parameters affecting the concentration of iron in seawater, scavenging of iron had a large impact on reducing the concentration of iron in seawater (PFE_S1.5; Equatorial Pacific RSME reduced by 65% compared to CTL). However, these results demonstrate an increase in silicate in seawater, which can be caused by a reduction of phytoplankton that decreased consumption of nutrients. This error was somewhat improved when the dissolution coefficient related to silicate removal was reduced (PFE_S1.5_D0.5), as chlorophyll errors did along with it. However, various sensitivity experiments such as adjusting the plankton rate related to silicate consumption should be conducted in addition to improving over-simulated silicate and chlorophyll that are still in presence.
This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMI (KMI2018-03513). The main calculations were performed by using the supercomputing resource of the Korea Meteorological Administration (National Center for Meteorological Supercomputer)