Hourly oxygen and total gas tension measurements at the Southern Ocean Time Series site reveal winter ventilation and spring net community production

Abstract

[1] Using a moored instrument package at 35 m depth at the Southern Ocean Time Series (SOTS) site near 46 56 0 S 142 15 0 E from September 2010 to April 2011 (219 days), we obtained the first Southern Ocean Time Series of dissolved oxygen (from an optode sensor) and nitrogen (from a total gas tension sensor). Nitrogen was consistently supersaturated (100.8%-102.9%), while oxygen was highly subsaturated in early spring (as low as 93.5%) and reached supersaturation (maximum 104.9%) during only 37 days in early summer. The low oxygen levels in spring illustrate the importance of deep mixing in the Subantarctic Zone in ventilating the upper limb of the global overturning circulation. Using nitrogen as a proxy for physical processes, we isolated biological contributions to the oxygen time series to obtain net community production (NCP). Almost all NCP occurred in spring in the presence of deep mixed layers, with only small additional contributions in summer after water column stratification. The temperature and salinity time series also revealed distinct parcels of water. Rapid changes at their interfaces generated unrealistic NCP events in the standard calculation model, which were removed, while still retaining NCP contributions from each parcel. NCP totaled 2.2 6 1.2 mol O 2 m 22 over the deployment, within the range of previous estimates from low temporal resolution techniques. Examination of errors revealed particular sensitivity to entrainment, suggesting more rigorous understanding of this process is required, e.g., via profiling instruments.Citation: Weeding, B., and T. W. Trull (2014), Hourly oxygen and total gas tension measurements at the Southern Ocean Time Series site reveal winter ventilation and spring net community production,

Biological and physical controls on N2, O2, and CO2 distributions in contrasting Southern Ocean surface waters

“…In some cases (e.g., ~11,000 km cruise track distance), strong N 2 supersaturation was associated with recent warming of the mixed layer and decreased gas solubility. The maximum ΔN 2 values we observed are significantly higher than those reported previously for midlatitude oceanic regions [ Emerson et al , ; McNeil et al , ; Vagle et al , ], including recent observations from the Sub‐Antarctic zone of the Southern Ocean [ Weeding and Trull , ], where ΔN 2 did not exceed ~ +3% during an observation period of 7 months. Our observations may be indicative of a persistently high ΔN 2 signal across large areas of the Southern Ocean, driven by high regional wind speeds and strong changes in atmospheric pressure.…”

Impact of recently upwelled water on productivity investigated using in situ and incubation‐based methods in Monterey Bay

“…In this study, we used K z profiles obtained during the cruise to parameterize the vertical flux of [ ] B out of the mixed layer. In many other studies, K z is estimated based on past measurements, which can induce a factor of 10 uncertainty into the vertical flux, and is sometimes the largest source of error in estimates of NOP [ Hamme and Emerson , ; Giesbrecht et al ., ; Jonsson et al ., ; Cassar et al ., ; Weeding and Trull , ]. For each CTD cast that was immediately preceded by microstructure profiles, we calculated the vertical biological gradient, from a linear regression of the measured [ ] B profile from the base of the mixed layer to 10 m below the mixed layer (Figure b).…”

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

“…In this study, we used profiles obtained during the cruise to parameterize the vertical flux of [O 2 ] out of the mixed layer. In many other studies, is estimated based on past measurements, which can induce a factor of 10 uncertainty into the vertical O 2 flux, and is sometimes the largest source of error in estimates of NOP (Hamme and Emerson, 2006;Giesbrecht et al, 2012;Jonsson et al, 2013;Cassar et al, 2014;Weeding and Trull, 2014 profile from the base of the mixed layer to 10 m below the mixed layer (Figure 4-1b). We derived from air-sea equilibrium has 17 ∆ ≃ 8 per meg (Reuer et al, 2007;Stanley et al, 2010), and O 2 that is purely biological in origin has 17 ∆ ≃ 293 per meg with = 0.5179.…”