Global primary productivity and the role of climate modes of variability

Phytoplankton are a unique group of organisms, mostly due to their exclusive capacity to photosynthesise inorganic matter into highly energetic organic compounds. Consequently phytoplankton growth, i.e., primary productivity, fuels almost all life in the global ocean and plays a crucial role in biogeochemical cycles and climate processes. Although it is commonly known that phytoplankton primary productivity is highly variable at intra-annual scales, inter-annual patterns of variability have only relatively recently been observed with the advent of remote sensing technology. Satellite instruments detect and estimate chlorophyll, a molecule present in all phytoplankton, and primary productivity rates, at a global scale. Here, we use remote sensing products to assess net primary productivity and surface chlorophyll-a patterns of variability from intra- to multi-annual, and global to regional scales, and evaluate its physical forcing mechanisms. We aim to assess the connections between large-scale climate variability and inter- and multi-annual phytoplankton patterns of variability via empirical analysis of satellite derived Chl and various geophysical parameters. The main methodology utilised to this end is the Empirical Orthogonal Function (EOF) for detecting standing signals and its extended form to isolate propagating features. Our findings include a much higher percentage of NPP variability at seasonal scales (~90%) than previously acknowledged, an anomalous change of 90 Pg.C (Pg = 1015g) in the last decade coupled to the classic El Niño - Southern Oscillation (ENSO) regional climate phenomenon, and an extra 18 Pg.C fixed in the ocean which can be attributed to the influence of the past decade's trend found in a controversial second main mode of variability. Further, we use extended EOF (EEOF) to isolate and analyse propagating features of surface chlorophyll-a across the global ocean and link them to regional climate modes of variability. We then focus on the Tropical and South Pacific regions, characterizing the seasonal atmosphere and ocean dynamics and isolating the regional propagating inter-annual features. Finally, we assess the influence of the East Australian Current on regional remotely sensed chlorophyll, and investigate the role of large-scale regional climate modes of variability on chlorophyll patterns.