Using dissolved oxygen concentrations to determine mixed layer depths in the Bellingshausen Sea

Abstract

Abstract. Concentrations of oxygen (O 2) and other dissolved gases in the oceanic mixed layer are often used to calculate air-sea gas exchange fluxes. The mixed layer depth (z mix ) may be defined using criteria based on temperature or density differences to a reference depth near the ocean surface. However, temperature criteria fail in regions with strong haloclines such as the Southern Ocean where heat, freshwater and momentum fluxes interact to establish mixed layers. Moreover, the time scales of airsea exchange differ for gases and heat, so that z mix defined using oxygen may be different than z mix defined using temperature or density. Here, we propose to define an O 2 -based mixed layer depth, z mix (O 2 ), as the depth where the relative difference between the O 2 concentration and a reference value at a depth equivalent to 10 dbar equals 0.5 %. This definition was established by analysis of O 2 profiles from the Bellingshausen Sea (west of the Antarctic Peninsula) and corroborated by visual inspection. Comparisons of z mix (O 2 ) with z mix based on potential temperature differences, i.e., z mix (0.2 • C) and z mix (0.5 • C), and potential density differences, i.e., z mix (0.03 kg m −3 ) and z mix (0.125 kg m −3 ), showed that z mix (O 2 ) closely follows z mix (0.03 kg m −3 ). Further comparisons with published z mix climatologies and z mix derived from World Ocean Atlas 2005 data were also performed. To establish z mix for use with biological production estimates in the absence of O 2 profiles, we suggest using z mix (0.03 kg m −3 ), which is also the basis for the climatology by de Boyer Montégut et al. (2004).

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

“…As a result, Ar is commonly used as an abiotic analogue for ; Ar responds similarly to physical forcings but has no biological flux [ Craig and Hayward , ; Spitzer and Jenkins , ]. To calculate net biological production of , investigators must correct for the effect of physical processes because in many environments the physical and biological fluxes of are similar in magnitude in the mixed layer [ Emerson , ; Hamme and Emerson , ; Castro‐Morales and Kaiser , ; Giesbrecht et al ., ]. Physical processes that affect include air‐sea gas exchange, vertical mixing/entrainment, and lateral advection.…”

An organic carbon budget for coastal Southern California determined by estimates of vertical nutrient flux, net community production and export

“…In this study, we model the euphotic zone as a 1-dimensional, two-box system with one box defined from the surface to the base of the mixed layer (ML box) and one box from the mixed layer depth (MLD) to the base of the euphotic zone (BML box; Figure 2). Oxygen mixed layer depths were determined as the depth at which the oxygen concentration was 0.5% different from the surface concentration (Castro-Morales and Kaiser, 2012) and ranged between 10m and 35m. Euphotic depths were typically between 35m and 65m, with the exception of Up-8 and Up-15 (30m and 70m).…”

The effect of the NAO on sea level and on mass changes in the Mediterranean Sea

“…The mass loss from land is redistributed over the ocean as an equilibrium response. The derived gravity coefficients were processed identically to the GRACE_RL04 data, using the same destriping and Gaussian smoothing algorithms, as well as using an iterative procedure to estimate the leaked signals using mapped data from the simulated gravity coefficients over land [Chambers and Bonin, 2012].…”