Estimating net community production in the Southern Ocean based on atmospheric potential oxygen and satellite ocean color data

Abstract

[1] The seasonal cycle of atmospheric potential oxygen (APO $ O 2 + 1.1 CO 2 ) reflects three seasonally varying ocean processes: 1) thermal in-and outgassing, 2) mixed layer net community production (NCP) and 3) deep water ventilation. Previous studies have isolated the net biological seasonal signal (i.e., the sum of NCP and ventilation), after using air-sea heat flux data to estimate the thermal signal. In this study, we resolve all three components of the APO seasonal cycle using a methodology in which the ventilation signal is estimated based on atmospheric N 2 O data, the thermal signal is estimated based on heat flux or atmospheric Ar/N 2 data, and the production signal is inferred as a residual. The isolation of the NCP signal in APO allows for direct comparison to estimates of NCP based on satellite ocean color data, after translating the latter into an atmospheric signal using an atmospheric transport model. When applied to ocean color data using algorithms specially adapted to the Southern Ocean and APO data at three southern monitoring sites, these two independent methods converge on a similar phase and amplitude of the seasonal NCP signal in APO and yield an estimate of annual mean NCP south of 50°S of 0.8-1.2 Pg C/yr, with corresponding annual mean NPP of $3 Pg C/yr and a mean growing season f ratio of $0.33. These results are supported by ocean biogeochemistry model simulations, in which air-sea O 2 and N 2 O fluxes are resolved into component thermal, ventilation and (for O 2 ) NCP contributions.

On the processes controlling the seasonal cycles of the air–sea fluxes of O₂ and N₂O: A modelling study

“…This confirms the close relationship between N 2 O production and O 2 consumption. Furthermore, the recent findings of Nevison et al (2012), using the same model results presented here, confirmed that the typical signature of the ratio between N 2 O production and O 2 consumption taking place in certain water masses can propagate not only to the corresponding fluxes (driven by ventilation only) but also up to the corresponding atmospheric measurements of these gases when vented out of the ocean surface. The values also match the findings reported by Lueker et al (2003) derived from atmospheric observations.…”

Exploring causes of interannual variability in the seasonal cycles of tropospheric nitrous oxide

“…The thermal cycles of N 2 O and CFC-12 were estimated from the modeled O 2 thermal cycles by scaling by the ratio of the temperature derivative of the respective solubility coefficients (Nevison et al, 2005). The thermal signal in N 2 O is uncertain by ± ∼1 month in phase and ± ∼30% in amplitude (Nevison et al, 2011).…”

Development of a new high precision continuous measuring system for atmospheric O₂/N₂ and Ar/N₂ and its application to the observation in Tsukuba, Japan

“…Keeling et al, 1993;Nevison et al, 2012). Because the atmospheric d(Ar/N 2 ) variation is caused mainly by the thermally driven airÁsea Ar and N 2 fluxes, the thermal components of the seasonal APO cycle can be estimated from the simultaneously measured seasonal d(Ar/N 2 ) cycle (e.g.…”

“…Therefore, a concurrently observed Ar/N 2 , along with O 2 /N 2 , can be used to estimate the contribution of the airÁsea heat fluxes to atmospheric potential oxygen (APO 0O 2 '1.1)CO 2 ), which is a conservative variable for terrestrial biospheric activities and is an indicator of airÁsea O 2 fluxes (Stephens et al, 1998). Such an estimation is useful for not only deriving the contribution of marine biological activities, including the effects of ventilation of deep water with depleted O 2 from the seasonal APO (Battle et al, 2003;Blaine 2005;Nevison et al, 2012), but also for *Corresponding author. email: s-ishidoya@aist.go.jp Tellus B 2014.…”