Diurnal and Seasonal Variability of Near‐Surface Oxygen in the Strait of Georgia. Issue 4 (5th April 2019)

• Record Type: Journal Article
• Authors: Wang, Chuning; Pawlowicz, Rich; Sastri, Akash R.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 4(2019)
• Page Start: 2418
• Page End: 2439
• Publication Date: 2019-04-05
• Subjects: dissolved oxygen -- Strait of Georgia -- primary productivity -- air‐sea gas flux; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2018JC014766
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Dissolved oxygen ( O 2 ) concentrations in waters of the ocean surface mixed layer are generally close to thermodynamic equilibrium with atmospheric concentrations. However, near‐surface O 2 levels are also affected by other processes, including primary productivity, and thus measurements of near‐surface O 2 can in theory be used to estimate productivity. Here we discuss variations in near‐surface O 2 concentrations in the Strait of Georgia by examining a variety of data sets, focusing primarily on ferry‐based measurements over a 3‐year period (2015–2017). Both diurnal, seasonal, and interannual variations are quantified, and various fluxes into and out of the surface waters are estimated so that the degree to the measured oxygen variations representing biological activity can be assessed. On average, advective and vertical transport makes only a small negative contribution, while other budget terms show a strong seasonal cycle, lowest in winter, peaking in spring and slowly dropping to winter level during summer and autumn. For most of the year, the air‐sea flux is the largest term, but the storage term is important during the spring blooms. Diurnal variations of 5–10% saturation in measured oxygen levels must therefore largely reflect diurnal cycles in productivity and respiration. We estimate respiration effects from the rate of decay of O 2 at night, which yields an average respiration rate of 459 mmol·m −2 ·day −1 . This value is almost an order of magnitude larger than the other budget terms we have discussed, suggesting that a future focus on diurnal variations might provide most insight into biological processes in the Strait. Key Points: Near‐surface dissolved oxygen in the Strait of Georgia shows significant seasonal and diurnal variations Seasonal oxygen budgets in the top 50 m is dominated by the storage term, air‐sea flux, and biological production Diurnal oxygen variation suggests gross productivity is significantly larger than net community productivity in the Strait of Georgia