M176/2 Time-series study of biological N2 fixation in the North Atlantic

Figure 1: Water sampling from CTD. Photo: Linbin Zhou

It is a great honor to join the scientific cruise M176/2, a part of the International GEOTRACES Program as a process study. The aim of this cruise is to conduct a detailed geochemical study of the hydrothermal plume at deep (~2500m) close to the sea floor at the Rainbow Vent in the North Atlantic. But to our biology guys, we care more about the phytoplankton diversity and their activities in the upper sunlit ocean (up 200m).

About me, a postdoctoral researcher supported by both GEOMAR (Germany) and XIAMEN University (China), focus on the Nitrogen fixing microorganisms (Diazotrophs), important species which convert N2 gas to bioavailable New Nitrogen and support the productivity in the oligotrophic ocean (Figure 2). Despite their Importance, a mechanistic understanding of what controls the distribution of diazotrophs and associated N2 fixation rates in the current ocean is still lacking, presenting a major barrier to making accurate projections. To address this, I conduct N2 fixation rate incubations, and DNA sampling for the analysis of the abundances of key diazotrophic phylotypes in this cruise. These efforts are also accompanied by a diverse range of ancillary environmental parameters, alongside several nutrient amendment experiments directly testing the response of N2 fixation rates to supply of potentially limiting nutrients (Iron and Phosphate).

Figure 2. Overview of the importance of nitrogen fixation in the ocean (from Sohm et al., 2011).

Now the cruise is about to coming to the end, and I have obtained more than fifteen days’ sample sets at nearly the same station around the sea area of Rainbow Vent. I regarding this as a Time-series study of biological N2 fixation, and the dynamic changes of hydrology and nutrients inputs (like N, Fe and P) during this period are supposed to affect the diazotrophs abundance, composition and their activities, leading to major switches of nutrient (Fe and/or P) limitation.

Finally, this is the first time I attending a German research cruise and the first time to the Atlantic Ocean. People in the METEOR are nice and always willing to help. I am really enjoyed this fantastic cruise.

Reference: Sohm, J. A. Webb, E. A. Capone, D. G. Emerging patterns of marine nitrogen fixation. 2011, Nat. Rev. Microbiol. 9(7): 499-508.

Leave a Reply

Your email address will not be published. Required fields are marked *