Biogeochemical impact of tropical instability waves in the equatorial Pacific

Abstract

[1] Tropical Instability Waves (TIW) have been suggested to fertilize the equatorial Pacific in iron leading to enhanced ecosystem productivity. Using a coupled dynamical -biogeochemical model, we show that contrary to this suggestion, TIWs induce a decrease of iron concentration by 10% at the equator and by about 3% over the Wyrtki box [90°W -180, 5°N-5°S]. Chlorophyll decreases by 10% at the equator and 1% over the Wyrtki box. This leads to a decrease of new production up to 10% at the equator (4% over the Wyrtki box). TIW-induced horizontal advection exports iron-rich equatorial water to the north, but also brings iron-depleted water to the equator leading to a net decrease in iron. Additional iron decrease is caused by TIW-induced iron vertical diffusion. These two mechanisms are partly counter balanced by a decrease of iron biological uptake, driven by lower phytoplankton concentrations, and to a lesser extent by TIW-induced iron vertical advection.

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

“…PISCES has been used to analyze intraseasonal (Gorgues et al, 2005;) to interannual and decadal timescales (Raynaud et al, 2006;Rodgers et al, 2008). PISCES is part of the Institut Pierre et Simon Laplace (IPSL) and CEntre National de Recherche en Météorologie (CNRM) Earth system models which contribute to the different Intergovernmental Panel on Climate Change (IPCC)-related activities including the Climate Model Intercomparison Project (CMIP5) modeling component .…”

SMOSSea Surface Salinity signals of tropical instability waves

“…They are also larger during La Niña conditions when the cold tongue and the related current shear are more intense than those during a normal year. TIWs are found to play important roles in mixing and cross-equator transport of sea water [Jochum and Murtugudde, 2006;Menkes et al, 2006], the modulation of the heat budget of the ocean mixed layer [Swenson and Hansen, 1999;Vialard et al, 2003], air-sea coupling [Liu et al, 2000;Yu and Liu, 2003], and marine biogeochemistry [Boutin et al, 1999;Gorgues et al, 2005;Evans et al, 2009].…”

The influence of salinity on tropical Atlantic instability waves

“…They are also stronger and last longer in the Pacific than the Atlantic Ocean due to the stronger equatorial current shear and density gradients in the Pacific [e.g., Chelton et al, 2000]. TIWs are important to ocean dynamics such as eddy-mean flow interaction and mixed-layer processes [e.g., Baturin and Niiler, 1997;Grodsky et al, 2005;Jochum and Murtugudde, 2006;Menkes et al, 2006;Kim et al, 2007], ocean-atmosphere interactions [Hayes et al, 1989;Xie et al, 1998;Liu et al, 2000;Chelton et al, 2001;Yu and Liu, 2003;Pezzi et al, 2004], and marine biogeochemistry [e.g., Feely et al, 1994;Strutton et al, 2001;McCain et al, 2002;Gorgues et al, 2005;Evans et al, 2009].…”