Oxygen and Nitrate New Production and Remineralization in the North Atlantic Subtropical Gyre

New estimates are obtained of oxygen utilization rates on isopycnal surfaces in the North Atlantic subtropical gyre thermocline based on tritium inventories (2.4-3.5 mol m -2 yr -1) and 228Ra measurements (8.5 _+ 0.8 mol m -2 yr-l). Arguments are given for why the tritium inventory oxygen utilization rate estimate may be too low. The 228Ra results are combined with recent estimates of oxygen utilization within the thermocline (Jenkins, 1987) as well as estimates of oxygen production in the mixed layer (Spitzer and Jenkins, 1989; Musgrave et al., 1988), to suggest a tentative overall oxygen balance for the whole water column. The new production of oxygen in the surface ocean (--•4.6 _+ 1.6 mol m -2 yr -1) appears to be lower than the estimated utilization within the thermocline (--•8.5 + 2 l _ 0.8 mol myr), suggesting that there may be a net lateral import of organic matter into the thermocline equivalent to a new production of--•3.9 -+ 1.8 mol m -2 yr -1. The nitrogen balance is consistent with these results. An estimate for the total nitrogen remineralization rate in the thermocline is obtained from the oxygen utilization rate by using an -O2:N Redfield ratio of 9.1 _+ 0.4 for remineralization (Minster and Boulahdid, 1987), giving a nitrogen remineralization rate of--•0.93 -+ 0.10 mol m -2 yr -I . Subtracting off the estimated lateral export of nitrate of--•0.51 + 0.21 mol m -2 yr -I , which is presumed tobe balanced by a lateral import of dissolved organic nitrogen (Rintoul and Wunsch, 1990), gives a nitrate flux into the surface of--•0.42 _+ 0.23 mol m -2 yr -1, which is comparable to the estimate of 0.6 -+ 0.2 mol m -2 yr -I obtained by Jenkins (1988) near Bermuda s well as the 100-m particulate nitrogen flux of 0.33 mol m -2 yr -1 obtained Altabet (1989) near Bermuda.