Abstract
Net community production (NCP), an analog of carbon export out of the surface ocean, is often estimated using budgets of dissolved oxygen. Accurate estimates of oxygen-based NCP, especially in dynamic coastal regions, require constraints on vertical transport of water with O-2 out of equilibrium with the atmosphere, nonsteady state change in the oxygen inventory, heating/cooling-driven O-2 disequilibrium, and the rate of bubble injection from wave activity. The latter two are typically evaluated by using discrete measurements of the O-2/Ar ratio in lieu of O-2 only. Because sophisticated sampling and measurement techniques are required to make these measurements, they are often limited in spatiotemporal resolution. However, high-resolution estimates of NCP may be useful in determining small-scale patchiness in export. In this study, we calculated high-resolution NCP in coastal Southern California using dissolved oxygen measurements made by an autonomous buoyancy-driven Slocum glider and an empirical relationship derived using discrete measurements of O-2/Ar in the surface mixed layer to remove the influence of bubble injection, which accounted for approximately one fourth of the O-2 supersaturation observed. Using estimates of vertical transport from wind speed-based parameterizations, previously validated using a Be-7 budget, we were able to correct for the physical biases to the signal, which are known to significantly influence dissolved oxygen budgets in this region. Our results agree well with previously published NCP estimates for the study area but also reveal higher-frequency variability that discrete sampling was unable to resolve, suggesting that this approach may be useful in other regions with well-constrained vertical transport rates.
Plain Language Summary The ocean takes up carbon dioxide from the atmosphere through a process referred to as the biological pump. Carbon export refers to the amount of carbon removed by this process and is therefore an important quantity in determining the ocean's role as a sink for atmospheric carbon dioxide and significantly influences ocean chemistry. Carbon export is often estimated using budgets of oxygen in the surface ocean because oxygen is affected by the same processes. However, bubbles introduced through wave activity can bias oxygen budgets if not accounted for using precise measurements, which are often made in low spatiotemporal resolution and thus can miss patchy, high-productivity events believed to contribute significantly to carbon export. In this study, we use an autonomous underwater vehicle to estimate carbon export with high resolution in coastal California. The results agree with more precise but lower-resolution measurements, implying that the vehicle-based approach may be useful for estimating carbon export in similar regions that may be dominated by undersampled, high-productivity events.