The temperature‐ballast hypothesis explains carbon export efficiency observations in the Southern Ocean

Britten, Gregory L.; Wakamatsu, Lael; Primeau, François

doi:10.1002/2016gl072378

Cited by 19 publications

(35 citation statements)

References 26 publications

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“…Our results agree with recent analysis which indicate that silica‐induced ballasting is a key process to take into account for the estimation of carbon export in the Southern Ocean (Britten et al, ). It is still not clear, however, what drives an inverse relationship between export efficiency and primary productivity in this region (assuming that this relationship is not entirely driven by an statistical artifact).…”

Section: Discussionsupporting

confidence: 93%

Assessment of Export Efficiency Equations in the Southern Ocean Applied to Satellite‐Based Net Primary Production

et al. 2018

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Carbon export efficiency (e‐ratio) is defined as the fraction of organic carbon fixed through net primary production (NPP) that is exported out of the surface productive layer of the ocean. Recent observations for the Southern Ocean suggest a negative e‐ratio versus NPP relationship, and a reduced dependency of export efficiency on temperature, different than in the global domain. In this study, we complement information from a passive satellite sensor with novel space‐based lidar observations of ocean particulate backscattering to infer NPP over the entire annual cycle, and estimate Southern Ocean export rates from five different empirical models of export efficiency. Inferred Southern Ocean NPP falls within the range of previous studies, with a mean estimate of 15.8 (± 3.9) Pg C yr−1 for the region south of 30 °S during the 2005–2016 period. We find that an export efficiency model that accounts for silica(Si)‐ballasting, which is constrained by observations with a negative e‐ratio versus NPP relationship, shows the best agreement with in situ‐based estimates of annual net community production (annual export of 2.7 ± 0.6 Pg C yr−1 south of 30 °S). By contrast, models based on the analysis of global observations with a positive e‐ratio versus NPP relationship predict annually integrated export rates that are ∼ 33% higher than the Si‐dependent model. Our results suggest that accounting for Si‐induced ballasting is important for the estimation of carbon export in the Southern Ocean.

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Section: Discussionsupporting

confidence: 93%

Assessment of Export Efficiency Equations in the Southern Ocean Applied to Satellite‐Based Net Primary Production

et al. 2018

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“…Subregions of the p compilation are also well described by lognormals, whose moments sort according to oceanographic intuition, indicating that the lognormal is a general and robust feature of large‐scale p variability. In agreement with recent models for the relationship between f and

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(Britten et al, ; Laws et al, ; Maiti et al, ), we posit a statistical scaling relationship between f and p , noting that it is the only relationship mapping one lognormal into another (Campbell, ); we then demonstrate that the moments of the two distributions should be linearly related via this scaling relationship. We then find agreement between two independent approaches to estimate the scaling relationship's parameters—one an out‐of‐sample test utilizing the log‐means of p and f from three open ocean time series stations, and the other subregioning the p and f data into three biomes, following Banse ().…”

Section: Introductionsupporting

confidence: 90%

Can Rates of Ocean Primary Production and Biological Carbon Export Be Related Through Their Probability Distributions?

Cael

Bisson

Follett

2018

Global Biogeochemical Cycles

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We describe the basis of a theory for interpreting measurements of two key biogeochemical fluxes—primary production by phytoplankton (p, μg C · L−1 · day−1) and biological carbon export from the surface ocean by sinking particles (f, mg C · m−2 · day−1)—in terms of their probability distributions. Given that p and f are mechanistically linked but variable and effectively measured on different scales, we hypothesize that a quantitative relationship emerges between collections of the two measurements. Motivated by the many subprocesses driving production and export, we take as a null model that large‐scale distributions of p and f are lognormal. We then show that compilations of p and f measurements are consistent with this hypothesis. The compilation of p measurements is extensive enough to subregion by biome, basin, depth, or season; these subsets are also well described by lognormals, whose log‐moments sort predictably. Informed by the lognormality of both p and f we infer a statistical scaling relationship between the two quantities and derive a linear relationship between the log‐moments of their distributions. We find agreement between two independent estimates of the slope and intercept of this line and show that the distribution of f measurements is consistent with predictions made from the moments of the p distribution. These results illustrate the utility of a distributional approach to biogeochemical fluxes. We close by describing potential uses and challenges for the further development of such an approach.

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“…Equation (24) also highlights the fact that a multitude of factors may confound the dependence of ef on temperature (including varying MLD, light attenuation, and availability of nutrients and light). This again may explain some of the conflicting observations recently reported in the literature (e.g., Maiti et al, 2013); the effect of temperature may be masked by changes in community composition (Britten et al, 2017;Henson et al, 2015). One therefore needs to account or correct for the multitude of confounding factors when predicting the effect of a given environmental condition (e.g., temperature, mineral ballast, and NPP) on the export ratio.…”

Section: Resultsmentioning

confidence: 48%

A mechanistic model of an upper bound on oceanic carbon export as a function of mixed layer depth and temperature

Cassar

2017

Biogeosciences

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Abstract. Export production reflects the amount of organic matter transferred from the ocean surface to depth through biological processes. This export is in large part controlled by nutrient and light availability, which are conditioned by mixed layer depth (MLD). In this study, building on Sverdrup's critical depth hypothesis, we derive a mechanistic model of an upper bound on carbon export based on the metabolic balance between photosynthesis and respiration as a function of MLD and temperature. We find that the upper bound is a positively skewed bell-shaped function of MLD. Specifically, the upper bound increases with deepening mixed layers down to a critical depth, beyond which a long tail of decreasing carbon export is associated with increasing heterotrophic activity and decreasing light availability. We also show that in cold regions the upper bound on carbon export decreases with increasing temperature when mixed layers are deep, but increases with temperature when mixed layers are shallow. A meta-analysis shows that our model envelopes field estimates of carbon export from the mixed layer. When compared to satellite export production estimates, our model indicates that export production in some regions of the Southern Ocean, particularly the subantarctic zone, is likely limited by light for a significant portion of the growing season.

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The temperature‐ballast hypothesis explains carbon export efficiency observations in the Southern Ocean

Cited by 19 publications

References 26 publications

Assessment of Export Efficiency Equations in the Southern Ocean Applied to Satellite‐Based Net Primary Production

Assessment of Export Efficiency Equations in the Southern Ocean Applied to Satellite‐Based Net Primary Production

Can Rates of Ocean Primary Production and Biological Carbon Export Be Related Through Their Probability Distributions?

A mechanistic model of an upper bound on oceanic carbon export as a function of mixed layer depth and temperature

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