Physical and biogeochemical controls of the phytoplankton seasonal cycle in the Indian Ocean: A modeling study

Abstract

A three-dimensional primitive equation model Océan Parallélisé (OPA) was coupled to the biogeochemical model Pelagic Interaction Scheme for Carbon and Ecosystem Studies to simulate the ocean circulation and the marine biological productivity through the biogeochemical cycles of carbon and the main nutrients (P, N, Si, Fe). We focus on surface phytoplankton dynamics in the Indian Ocean extending from 30°S to 30°N and from 30°E to 120°E. The seasonal cycle of phytoplankton over the Indian Ocean is generally characterized by two blooms, one during the summer monsoon, the other one during the winter monsoon. Based on the method proposed by Lévy et al. (2007), different biogeochemical provinces can be defined during the summer and winter monsoons. The model performed relatively well by simulating the main features of the cumulated increase in chlorophyll, and the time of the bloom onsets is consistent with data. It also reproduced quite well the main biogeochemical provinces in good agreement with data in most of the Arabian Sea (except in the central part), the Bay of Bengal, and in the convergence zone south of the equator. The analysis of the modeled biogeochemical processes has shown that during the blooms onset periods, the most limiting nutrient was nitrogen except some areas around India and the eastern part of the Bay of Bengal where the ecosystem tends toward silicate limitation. These limitations change during the blooms development. The model also highlighted a variety of the critical physical processes (horizontal and vertical advection, turbulent diffusion, mixed layer depth) involved in each biogeochemical province bloom dynamics.

PISCES-v2: an ocean biogeochemical model for carbon and ecosystem studies

“…In the latter region, mesoscale and submesoscale processes have been shown to be of critical importance (Lee et al, 2000;Kawamiya, 2001;Hood et al, 2003). A model study, using PISCES coupled to a higher resolution version of NEMO, has been shown to simulate chlorophyll distribution in much better agreement with the observations (Koné et al, 2009). Chlorophyll concentrations are high in the eastern boundary upwelling systems.…”

Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

“…The main reason for this discrepancy is linked to the coarse resolution of both the atmosphere (LMDZ) and ocean (OPA) general circulation models that force the biogeochemical model, and that precludes a good representation of coastal upwelling zones. Indeed, a similar version of the PISCES model, coupled to OPA at 0.5 • resolution and forced by reanalysis products has been compared to the same data set over the 1990-1999 period and it reproduced nicely the distribution, the seasonality and the magnitude of surface chlorophyll changes (Koné et al, 2009). …”

Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

“…The NEMO-PISCES coupled biophysical model has been successfully applied to various studies in the Indian Ocean (e.g., Koné et al, 2009;Resplandy et al, 2009;Currie et al, 2013;Keerthi et al, 2016), including the Arabian Sea OMZ (Resplandy et al, 2011(Resplandy et al, , 2012. A more detailed model description is provided in the manuals for NEMO and PISCES, available online at http://www.nemo-ocean.eu/ About-NEMO/Reference-manuals.…”