Oxygen utilization rates in North Atlantic subtropical gyre and primary production in oligotrophic systems

Abstract

If the observed distribution of dissolved oxygen in deep oceans below the euphotic zone is in stationary and steady state, then it can be assumed that the in situ consumption of oxygen is balanced by ‘ventilation’, or, in other words, physical transport of oxygen from regions of higher dissolved oxygen and ultimately the sea surface. It follows, therefore, that measurement or determination of those physical transport processes, coupled with observation of the oxygen distribution will lead to an estimate of the net oxygen utilization rate (OUR). The character of such an estimate is that it is a space and time average over scales governed by the nature (space and time scales) of the transport processes, the scale of the oxygen distribution, and the climatologic nature of the system. As such, one obtains an average which is characteristically of the order of 10⁸ s, 10⁸ cm or more, that is large compared with scales of biological variability. I report here some new determinations of oxygen utilization rates determined by tritium dating in the North Atlantic subtropical gyre, compare them with other and previous estimates, and discuss their implications regarding primary production and nutrient cycling in an oligotrophic system.