Summary of Abstract Submission

Abstract Submission No. IO50-02-0007PresentationOral

NITROGEN FIXATION AND SHALLOW RECYCLING OF NITROGEN IN THE EASTERN INDIAN OCEAN

Anya Waite*1, Eric J. Raes2, Peter A. Thompson3, Nick Hardman-Mountford3

1 Alfred Wegener Institute for Polar and Marine Research, Germany
2 The University of Western Australia, Australia
3 CSIRO, Australia

ABSTRACT :

Over the last five years, we have shown that nitrogen fixation is a key source of new nitrogen towards the N budget in the eastern Indian Ocean. This data aids towards the current knowledge gap of the biogeochemical dynamics that drive air-sea fluxes of N2 and CO2 in the Indian Ocean. In our work we show how different diazotrophic communities impact N2 fixation rates along a latitudinal gradient from the colder and more saline subtropical waters in the south-eastern Indian Ocean (34˚S) to the warmer and fresher waters in the Timor Sea (12˚S). We are the first to (1) quantify N2 fixation rates along the entire west coast of Australia and (2) estimate a first-order regional transfer of low δ15N, derived from N2 fixation, into higher trophic levels. The analysis of the physical and biogeochemical data from four voyages conducted in 2010, 2011, 2012 and 2013 has allowed us to sketch an understanding of the biogeochemical components that control primary productivity and the adjacent fixation of CO2 in this region. In our analysis we provide a conceptual understanding how NO3- in the photic zone could be derived from new nitrogen through N2-fixation. We conclude with the hypothesis that nitrogen injected through N2 fixation can be recycled within the photic zone as NH4+, and sequentially oxidized to nitrite and nitrate in shallow low dissolved oxygen (DO) layers. Here we present a review and synthesis of our recent work and speculate on regional, and possibly global, impacts.