Interannual Variation in Phytoplankton Primary Production at A Global Scale

Cecile Rousseaux,Watson Gregg

doi:10.3390/rs6010001

Abstract

We used the NASA Ocean Biogeochemical Model (NOBM) combined with remote sensing data via assimilation to evaluate the contribution of four phytoplankton groups to the total primary production. First, we assessed the contribution of each phytoplankton groups to the total primary production at a global scale for the period 1998–2011. Globally, diatoms contributed the most to the total phytoplankton production (~50%, the equivalent of ~20 PgC∙y−1). Coccolithophores and chlorophytes each contributed ~20% (~7 PgC∙y−1) of the total primary production and cyanobacteria represented about 10% (~4 PgC∙y−1) of the total primary production. Primary production by diatoms was highest in the high latitudes (>40°) and in major upwelling systems (Equatorial Pacific and Benguela system). We then assessed interannual variability of this group-specific primary production over the period 1998–2011. Globally the annual relative contribution of each phytoplankton groups to the total primary production varied by maximum 4% (1–2 PgC∙y−1). We assessed the effects of climate variability on group-specific primary production using global (i.e., Multivariate El Niño Index, MEI) and “regional” climate indices (e.g., Southern Annular Mode (SAM), Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO)). Most interannual variability occurred in the Equatorial Pacific and was associated with climate variability as indicated by significant correlation (p < 0.05) between the MEI and the group-specific primary production from all groups except coccolithophores. In the Atlantic, climate variability as indicated by NAO was significantly correlated to the primary production of 2 out of the 4 groups in the North Central Atlantic (diatoms/cyanobacteria) and in the North Atlantic (chlorophytes and coccolithophores). We found that climate variability as indicated by SAM had only a limited effect on group-specific primary production in the Southern Ocean. These results provide a modeling and data assimilation perspective to phytoplankton partitioning of primary production and contribute to our understanding of the dynamics of the carbon cycle in the oceans at a global scale.

Highlights

Phytoplankton is responsible for over half of the net primary production on Earth [1]
Primary production by diatoms was highest in the high latitudes (>40°) and in major upwelling systems (Equatorial Pacific and Benguela system)
We found that climate variability as indicated by Southern Annular Mode (SAM) had only a limited effect on group-specific primary production in the Southern Ocean

Summary

Introduction

Phytoplankton is responsible for over half of the net primary production on Earth [1]. In this paper we explicitly compare NOBM total primary production with a commonly used satellite-derived method that has the advantage of public availability and heritage, the Vertically-Integrated Production Model [24] (data downloaded from www.science.oregonstate.edu). The purpose of this comparison is not to validate per se because there are many other models and we are not attributing an assessment of the quality of this particular one. We improve our knowledge of group-specific primary production by highlighting the strengths and weaknesses of our approach

Climatology of Primary Production and Comparison with VGPM

Interannual Variability

Experimental Section

Conclusions