Carbon dioxide and oxygen fluxes in the Southern Ocean: Mechanisms of interannual variability

Verdy, Ariane; Dutkiewicz, Stephanie; Follows, Michael J.; Marshall, John; Czaja, Arnaud

doi:10.1029/2006gb002916

Cited by 64 publications

(69 citation statements)

References 26 publications

(43 reference statements)

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“…Such patterns have been previously reported at mid-latitudes of the Southern Ocean in conjunction with changes in SAM (Hall and Visbeck, 2002;Lovenduski and Gruber, 2005;Morrow et al, 2007). Figure 7 shows that low wind speed years are in general associated with positive phases of SAM, although not as clear during the 1993-1998 period, possibly related to ENSO and SAM interactions (Verdy et al, 2006(Verdy et al, , 2007.…”

Section: Inter-annual Sst and Pco 2 Variationsmentioning

confidence: 57%

“…don (1996) and Hamilton (2006), grid nodes from the Reynolds et al (2002) sea surface temperature monthly climatology (squares), and the grid nodes of the Kalnay et al (1996) National Centers for Environmental Prediction daily wind speeds (circles). Quéré et al, 2007;Lenton and Matear, 2007;Lovenduski et al, 2007;Verdy et al, 2007). Due to the relative scarcity of pCO 2 field data in the Southern Ocean, the inter-annual variability of air-sea CO 2 fluxes has seldom been investigated from a purely observational based approach.…”

Section: Introductionmentioning

confidence: 99%

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Inter-annual variability of the carbon dioxide oceanic sink south of Tasmania

et al. 2008

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Abstract.We compiled a large data-set from 22 cruises spanning from 1991 to 2003, of the partial pressure of CO 2 (pCO 2 ) in surface waters over the continental shelf (CS) and adjacent open ocean (43 • to 46 • S; 145 • to 150 • E), south of Tasmania. Climatological seasonal cycles of pCO 2 in the CS, the subtropical zone (STZ) and the subAntarctic zone (SAZ) are described and used to determine monthly pCO 2 anomalies. These are used in combination with monthly anomalies of sea surface temperature (SST) to investigate inter-annual variations of SST and pCO 2 . Monthly anomalies of SST (as intense as 2 • C) are apparent in the CS, STZ and SAZ, and are indicative of strong inter-annual variability that seems to be related to large-scale coupled atmosphere-ocean oscillations. Anomalies of pCO 2 normalized to a constant temperature are negatively related to SST anomalies. A reduced winter-time vertical input of dissolved inorganic carbon (DIC) during phases of positive SST anomalies, related to a poleward shift of westerly winds, and a concomitant local decrease in wind stress is the likely cause of the negative relationship between pCO 2 and SST anomalies. The observed pattern is an increase of the sink for atmospheric CO 2 associated with positive SST anomalies, although strongly modulated by interannual variability of wind speed. Assuming that phases of positive SST anomalies are indicative of the future evolution of regional ocean biogeochemistry under global warming, we show using a purely observational based approach that some provinces of the Southern Ocean could provide a potential negative feedback on increasing atmospheric CO 2 .

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Section: Inter-annual Sst and Pco 2 Variationsmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Inter-annual variability of the carbon dioxide oceanic sink south of Tasmania

et al. 2008

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“…Moore and Abbott, 2000;Sambrotto and Mace, 2000;Trull et al, 2001a). Inter-annual variability in O 2 in upper layers of the Southern Ocean have also been related to changes in the entrainment of deeper waters into the mixed layer due to the mixed layer depth variability (Matear et al, 2000;Verdy et al, 2007;Sabine et al, 2008;Sallée et al, 2012). Although some studies found long-term decreases in O 2 due to circulation in deep waters of the Weddell Sea (van Heuven et al, 2014) and for the first 1000 m of the global ocean (Helm et al, 2011) , since part of the changes in AOU with time reflect changes in circulation that we cannot separate from those in remineralisation.…”

Section: Changes In the Carbon Systemmentioning

confidence: 99%

“…Circulation and biological processes drive the redistribution of dissolved inorganic carbon (DIC) that ultimately affects the capacity of the waters to uptake more CO 2 . The uptake of CO 2 by the Southern Ocean presents strong spatiotemporal variability (Lenton et al, 2013), and this can lead to conflicting results for observational studies, models and atmospheric inversions, depending on the methodology used (Verdy et al, 2007;Lenton et al, 2012;Fay et al, 2014). Quantifying long-term changes in the carbon system is difficult due to the scarcity of data Kouketsu and Murata, 2014;Fay et al, 2014) and the influence of biological processes.…”

Section: Introductionmentioning

confidence: 99%

Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

et al. 2017

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Abstract. Biogeochemical change in the water masses of the Southern Ocean, south of Tasmania, was assessed for the 16-year period between 1995 and 2011 using data from four summer repeats of the WOCE-JGOFS-CLIVAR-GO-SHIP (Key et al., 2015;Olsen et al., 2016) SR03 hydrographic section (at ∼ 140 • E). Changes in temperature, salinity, oxygen, and nutrients were used to disentangle the effect of solubility, biology, circulation and anthropogenic carbon (C ANT ) uptake on the variability of dissolved inorganic carbon (DIC) for eight water mass layers defined by neutral surfaces (γ n ). C ANT was estimated using an improved back-calculation method. Warming (∼ 0.0352 ± 0.0170 • C yr −1 ) of Subtropical Central Water (STCW) and Antarctic Surface Water (AASW) layers decreased their gas solubility, and accordingly DIC concentrations increased less rapidly than expected from equilibration with rising atmospheric CO 2 (∼ 0.86 ± 0.16 µmol kg −1 yr −1 versus ∼ 1 ± 0.12 µmol kg −1 yr −1 ). An increase in apparent oxygen utilisation (AOU) occurred in these layers due to either remineralisation of organic matter or intensification of upwelling. The range of estimates for the increases in C ANT were 0.71 ± 0.08 to 0.93 ± 0.08 µmol kg −1 yr −1 for STCW and 0.35 ± 0.14 to 0.65 ± 0.21 µmol kg −1 yr −1 for AASW, with the lower values in each water mass obtained by assigning all the AOU change to remineralisation. DIC increases in the Sub-Antarctic Mode Water (SAMW, 1.10 ± 0.14 µmol kg −1 yr −1 ) and Antarctic Intermediate Water (AAIW, 0.40 ± 0.15 µmol kg −1 yr −1 ) layers were similar to the calculated C ANT trends. For SAMW, the C ANT increase tracked rising atmospheric CO 2 . As a consequence of the general DIC increase, decreases in total pH (pH T ) and aragonite saturation ( Ar ) were found in most water masses, with the upper ocean and the SAMW layer presenting the largest trends for pH T decrease (∼ −0.0031 ± 0.0004 yr −1 ). DIC increases in deep and bottom layers (∼ 0.24 ± 0.04 µmol kg −1 yr −1 ) resulted from the advection of old deep waters to resupply increased upwelling, as corroborated by increasing silicate (∼ 0.21 ± 0.07 µmol kg −1 yr −1 ), which also reached the upper layers near the Antarctic Divergence (∼ 0.36 ± 0.06 µmol kg −1 yr −1 ) and was accompanied by an increase in salinity. The observed changes in DIC over the 16-year span caused a shoaling (∼ 340 m) of the aragonite saturation depth (ASD, Ar = 1) within Upper Circumpolar Deep Water that followed the upwelling path of this layer. From all our results, we conclude a scenario of increased transport of deep waters into the section and enhanced upwelling at high latitudes for the period between 1995 and 2011 linked to strong westerly winds. Although enhanced upwelling lowered the capacity of the AASW layer to uptake atmospheric CO 2 , it did not limit that of the newly forming SAMW and AAIW, which exhibited C ANT storage rates (∼ 0.41 ± 0.20 mol m −2 yr −1 ) twice that of the upper layers.

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“…Previous definitions of z mix in the Southern Ocean have used criteria based on physical properties of the water column, such as potential temperature or density (Cisewski et al, 2008;Dong et al, 2008;Gordon and Huber, 1990;Rintoul and Trull, 2001;Verdy et al, 2007). However, temperature and salinity do not always show the same stratification, leading to water column structures such as temperature inversions (i.e., abrupt changes in the temperature profile due to intrusions of water masses), barrier layers (as a result of temperature inversions and at locations where the halocline is shallower than the thermocline) and density-compensated profiles (de Boyer Montégut et al, 2004;Rintoul and Trull, 2001).…”

Section: K Castro-morales and J Kaiser: Using Dissolved Oxygen Concmentioning

confidence: 99%

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

Castro-Morales

Kaiser

2012

Ocean Sci.

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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).

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Carbon dioxide and oxygen fluxes in the Southern Ocean: Mechanisms of interannual variability

Cited by 64 publications

References 26 publications

Inter-annual variability of the carbon dioxide oceanic sink south of Tasmania

Inter-annual variability of the carbon dioxide oceanic sink south of Tasmania

Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

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

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