Does eddy-eddy interaction control surface phytoplankton distribution and carbon export in the North Pacific Subtropical Gyre?

Lionel Guidi (1) , Paulo H. R. Calil , Solange Duhamel (2) , Karin M. Bjoerkman , Scott C. Doney (3) , George A. Jackson (4) , Binglin Li , Matthew J. Church , Sasha Tozzi , Zbigniew S. Kolber , Kelvin J. Richards (5) , Allison A. Fong , Ricardo M. Letelier , Gabriel Gorsky (6) , Lars Stemmann (6) , David M. Karl

1 Department of Oceanography
2 LMGEM - Laboratoire de MicrobiologiE de Géochimie et d'Ecologie Marines
3 WHOI - Woods Hole Oceanographic Institution
4 Department of Oceanography [College Station]
5 IPRC - International Pacific Research Center
6 LOV - Laboratoire d'océanographie de Villefranche

In the North Pacific Subtropical Gyre (NPSG), the regular occurrence of summer phytoplankton blooms contributes to marine ecosystem productivity and the annual carbon export. The mechanisms underlying the formation, maintenance, and decay of these blooms remain largely unknown; nitrogen fixation, episodic vertical mixing of nutrients, and meso- (<100 km) and submesoscale (<10 km) physical processes are all hypothesized to contribute to bloom dynamics. In addition, zones of convergence in the ocean's surface layers are known to generate downwelling and/or converging currents that affect plankton distributions. It has been difficult to quantify the importance of these convergence zones in the export flux of particulate organic carbon (POC) in the open ocean. Here we use two high-resolution ocean transects across a pair of mesoscale eddies in the vicinity of Station ALOHA (22 degrees 45'N, 158 degrees 00'W) to show that horizontal turbulent stirring may have been a dominant control on the spatial distribution of the nitrogen fixing cyanobacterium Trichodesmium spp. Fast repetition rate fluorometry measurements suggested that this distribution stimulated new primary production; this conclusion was not confirmed by C-14-based measurements, possibly because of different sampling scales for the two methods. Our observations of particle size distributions along the two transects showed that stretching by the mesoscale eddy field produced submesoscale features that mediated POC export via frontogenetically generated downwelling currents. This study highlights the need to combine high-resolution biogeochemical and physical data sets to understand the links between Trichodesmium spp. surface distribution and POC export in the NPSG at the submesoscale level.

Domaines: Océanographie

Lionel Guidi, Paulo H. R. Calil, Solange Duhamel, Karin M. Bjoerkman, Scott C. Doney, et al.. Does eddy-eddy interaction control surface phytoplankton distribution and carbon export in the North Pacific Subtropical Gyre?. Journal of Geophysical Research: Biogeosciences, 2012, 117, ⟨10.1029/2012JG001984⟩. ⟨hal-03502664⟩