VAHINE - Understanding the nitrogen cycle in the Pacific Ocean

VAriability of vertical and tropHIc transfer of fixed N2 in the south wEst Pacific and potential impact on the biological carbon pump

 

ResponsiblesSophie Bonnet & Thierry Moutin

 

The aim of the VAHINE project is to study the fate of fixed nitrogen in the oceanic pelagic food web and its potential impact on carbon export. The field campaign of VAHINE took place in the South West Pacific (New Caledonia) in Jan.-Feb. 2013, involving 16 scientists from France, Israel, Germany and the USA. This project is funded by INSU-LEFE, GOPS, IRD and ANR-JCJC (PI : Sophie Bonnet, IRD/MIO Noumea/Marseille)

The ocean provides many provisioning services, such as food, employment, water, energy. It also provides regulating services. The most important one is the regulation of climate. The ocean absorbs 2 Petagramms (10^15 g) of carbon annually, representing 1/3 of the annual anthropogenic inputs of CO2 to the atmosphere (IPCC, 2001).

The availability of nitrogen is one of the main factors controlling primary productivity and carbon sequestration by the ocean. Biological N2 fixation by diazotrophic organisms (or N2-fixing organisms) constitutes one of the major sources of ‘new’ nitrogen for the surface ocean with a net input estimated at 100-200 Teragramms.yr-1 (10^12 g).

A critical question that remains unanswered so far is the fate of nitrogen newly fixed by diazotrophs in oceanic food webs. The objective of VAHINE is to answer this central question !

 

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An oceanographic cruise

The VAHINE team
On the way to the mesocosms!
Samples taken
Mesocosms at sea
Mesocosms at sea