Nitrous oxide distribution, production and sea-air exchange in the eastern Caribbean basin

I report results of studies on nitrous oxide (N2O) spatial distribution, production, and sea-air exchange in the Eastern Caribbean Basin. I present evidence for a significant latitudinal gradient in the surface production and fluxes of N2O as determined during cruise ORIPEX VI aboard the University of Puerto Rico research vessel RN Chapman. A detailed analysis of the possible forces that affect temporal N2O variability at the Caribbean Time Series Station (CaTS), occupied for a period of 38 months (1998--2002), is presented where particular attention was focused on the Caribbean mixed layer waters. Nitrous oxide fluxes during cruise ORIPEX VI averaged 1.9 +/- 0.9 mumol m-2 d-1 (n = 12) ranging from 0.5 to 2.6 mumol m-2 d-1. Higher N2O fluxes, up to 248.3 mumol m-2 d-1, were computed for the southern coastal upwelling zone. Ammonium oxidation rates (AOR) were assessed using chlorate as a specific metabolic inhibitor of nitrite reduction. Ammonium oxidation rates off Punta Esmeralda in the coastal upwelling ranged from 16.5 to 64.8 mumol m-3 d-1 with an overall mean of 39.6 +/- 18.9 mumol m-3 d-1. Near-surface AORs in open ocean stations ranged from 0.7 to 21.5 mumol m-3 d-1 with an overall mean of 7.19 +/- 8.1 mumol m-3 d-1. I estimated N2O production in the near-surface layer assuming a 0.30% yield of N2O from AOR. The estimates ranged between 0.2 and 6.4 mumol m-2 d-1 averaging 2.1 +/- 2.4 mumol m-2 d-1 . Results indicate that, on a global ocean perspective, the Caribbean sea may account for 2.4% of the total global ocean N2O flux. Mixed layer N2O concentration at CaTS ranged from 5.02 nM to 7.44 nM and estimates of sea-air N2O flux averaged 0.74 +/- 0.99 mumol m-2 d-1. Ammonium oxidation rate in the mixed layer ranged from 0.2 +/- 0.1 mumol m-3 d-1 to 23.4 +/- 4.3 mumol m-3 d-1. I conclude that N2O dynamics in the Caribbean mixed layer respond to: (1) in-situ production from ammonium oxidation, (2) Orinoco River water intrusion with the subsequent production and accumulation of N2O and (3) entrainment of deep and cold N2O rich water from below the mixed layer during the spring-summer seasons.