Interannual Variability of Methane and Nitrous Oxide in the North Pacific Subtropical Gyre

The temporal variability of two important greenhouse gases, methane (CH4) and nitrous oxide (N2O), is reported for the upper water column at Station ALOHA in the North Pacific Subtropical Gyre. Measured concentrations of N2O conform to predicted values with an increase in saturation during the summer period. In contrast, CH4 is less predictable and shows an approximate 2 year transition from a state of oversaturation in surface waters to equilibrium values in 2015, implying a change in net CH4 production. The decrease in CH4 followed on from fluctuations in phosphate concentrations supporting the hypothesized link between microbial metabolism of phosphorus and the global biogeochemical cycle of CH4. At this current time, future trends in the net CH4 production in the North Pacific Subtropical Gyre are uncertain and specifically whether the surface ocean will be a net source or sink for CH4.