Abstract
Abstract. We present three years of Apparent Oxygen Utilization Rates (AOUR) estimated from oxygen and tracer data collected over the ocean thermocline at monthly resolution between 2003 and 2006 at the Bermuda Atlantic Time-series Study (BATS) site. We estimate water ages by calculating a transit time distribution from tritium and helium-3 data. The vertically integrated AOUR over the upper 500 m, which is a regional estimate of export, during the three years is 3.1 ± 0.5 mol O2 m−2 yr−1. This is comparable to previous AOUR-based estimates of export production at the BATS site but is several times larger than export estimates derived from sediment traps or 234Th fluxes. We compare AOUR determined in this study to AOUR measured in the 1980s and show AOUR is significantly greater today than decades earlier because of changes in AOU, rather than changes in ventilation rates. The changes in AOU are likely a methodological artefact associated with problems with early oxygen measurements.
Highlights
A number of papers have been published in the scientific literature suggesting that the oxygen content in the ocean is decreasing (Keeling et al, 2010; Stramma et al, 2008, 2010; Whitney et al, 2007)
We present Apparent Oxygen Utilization Rates (AOUR) as determined from T and 3He ages, calculated using transit time distributions, at the Bermuda Atlantic Time-series Study (BATS) site, a typical subtropical oligotrophic gyre location
What is the cause for this increase in AOUR with time? When we look at the AOUR in terms of its two components – apparent oxygen utilization (AOU) and τ (Fig. 7b and c), we see that τ is the same, within errors, in the two time periods but that AOU was significantly lower in 1977–1987 than in 2003–2006
Summary
A number of papers have been published in the scientific literature suggesting that the oxygen content in the ocean is decreasing (Keeling et al, 2010; Stramma et al, 2008, 2010; Whitney et al, 2007). This decrease, both predicted in models (Bopp et al, 2002; Matear and Hirst, 2003; Plattner et al, 2001) and seen in data (Stramma et al, 2008, 2010; Whitney et al, 2007), is due to the ocean becoming warmer and more stratified. Futhermore, diagnosing the magnitude of oxygen sinks within the water column is key to developing our understanding of the relevant biogeochemical dynamics
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