A novel estimate of ocean oxygen utilisation points to a reduced rate of respiration in the ocean interior

Duteil, Olaf; Koeve, Wolfgang; Oschlies, Andreas; Bianchi, Daniele; Galbraith, Eric D.; Kriest, Iris; Matear, Richard J.

doi:10.5194/bg-10-7723-2013

Cited by 53 publications

(84 citation statements)

References 41 publications

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“…This includes the Modular Ocean Model version 5, a sea ice module, static land and ice sheets, and a module of Biogeochemistry with Light, Iron, Nutrients and Gases (BLINGv1.5) 5 (Galbraith et al, 2010). Unlike BLINGv0, BLINGv1.5 allows for variable stoichiometry and calculates the mass balance of phytoplankton in order to prevent unrealistic bloom magnitudes at high latitudes, reducing the magnitude of disequilibrium O 2 , which was very high in BLINGv0 (Duteil et al, 2013;Tagliabue et al, 2016).…”

Section: Model Descriptionmentioning

confidence: 99%

“…Dissolved O 2 can potentially serve as a better metric of DIC soft , given the relatively small variations in the O 2 :C of respiration compared to the relatively high variability in C:P (Martiny et al, 2013). But Apparent Oxygen Utilization (AOU), typically taken as a measure (Ito et al, 2004;Duteil et al, 2013). Thus, despite being conceptually simple, DIC soft can be difficult to quantify observationally.…”

Section: Introductionmentioning

confidence: 99%

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The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

Eggleston

Galbraith

2017

Preprint

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Abstract. Ocean dissolved inorganic carbon (DIC) storage can be conceptualized as the sum of four components: saturation (DIC sat ), disequilibrium (DIC dis ), carbonate (DIC carb ) and soft tissue (DIC soft ). Among these, DIC dis and DIC soft have the potential for large changes that are relatively difficult to predict. Here we explore changes in DIC soft and DIC dis in a large suite of simulations with a complex coupled climate-biogeochemical model, driven by changes in orbital forcing, ice sheets and the radiative effect of CO 2 . Both DIC dis and DIC soft vary over a range of 40 µmol/kg in response to the climate forcing, 5 equivalent to changes in atmospheric CO 2 on the order of 50 ppm for each. We find that, despite the broad range of climate states represented, changes in global DIC soft can be well-approximated by the product of deep ocean ideal age and the global export production flux, while global DIC dis is dominantly controlled by the fraction of the ocean filled by Antarctic Bottom Water (AABW). Because the AABW fraction and ideal age are inversely correlated between the simulations, DIC dis and DIC soft are also inversely correlated. This inverse correlation could be decoupled if changes in deep ocean mixing were to alter ideal 10 age independently of AABW fraction, or if independent ecosystem changes were to alter export and remineralization, thereby modifying DIC soft . As an example of the latter, iron fertilization causes DIC soft to increase, and causes DIC dis to also increase by a similar or greater amount, to a degree that depends on climate state. We propose a simple framework to consider the global contribution of DIC soft + DIC dis to ocean carbon storage as a function of the surface preformed nitrate and DIC dis of dense water formation regions, the global volume fractions ventilated by these regions, and the global nitrate inventory. More 15 extensive sea ice increases DIC dis , and when sea ice becomes very extensive it also causes significant O 2 disequilibrium, which may have contributed to reconstructions of low O 2 in the Southern Ocean during the glacial. Global DIC dis reaches a minimum near modern CO 2 because the AABW fraction reaches a minimum, which may have contributed to preventing further CO 2 rise during interglacial periods.

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Section: Model Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

Eggleston

Galbraith

2017

Preprint

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“…Nonetheless, dissolved oxygen can be conceptualized as including a preformed component, which is the sum of saturation and disequilibrium, and an oxygen utilization component, which is given by the difference between the in situ and preformed O 2 in the ocean interior. Apparent oxygen utilization (AOU), typically taken as a measure of accumulated respiration, can be misleading if the preformed O 2 concentration differed significantly from saturation, i.e., if O 2 dis is significant, as it appears to be in high-latitude regions of dense water formation (Ito et al, 2004;Duteil et al, 2013;Russell and Dickson, 2003). If O 2 dis varies with climate state, it might contribute significantly to past or future oxygen concentrations.…”

mentioning

confidence: 99%

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

Eggleston

Galbraith

2018

Biogeosciences

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Abstract. The complexity of dissolved gas cycling in the ocean presents a challenge for mechanistic understanding and can hinder model intercomparison. One helpful approach is the conceptualization of dissolved gases as the sum of multiple, strictly defined components. Here we decompose dissolved inorganic carbon (DIC) into four components: saturation (DIC sat ), disequilibrium (DIC dis ), carbonate (DIC carb ), and soft tissue (DIC soft ). The cycling of dissolved oxygen is simpler, but can still be aided by considering O 2 , O 2 sat , and O 2 dis . We explore changes in these components within a large suite of simulations with a complex coupled climatebiogeochemical model, driven by changes in astronomical parameters, ice sheets, and radiative forcing, in order to explore the potential importance of the different components to ocean carbon storage on long timescales. We find that both DIC soft and DIC dis vary over a range of 40 µmol kg −1 in response to the climate forcing, equivalent to changes in atmospheric pCO 2 on the order of 50 ppm for each. The most extreme values occur at the coldest and intermediate climate states. We also find significant changes in O 2 disequilibrium, with large increases under cold climate states. We find that, despite the broad range of climate states represented, changes in global DIC soft can be quantitatively approximated by the product of deep ocean ideal age and the global export production flux. In contrast, global DIC dis is dominantly controlled by the fraction of the ocean filled by Antarctic Bottom Water (AABW). Because the AABW fraction and ideal age are inversely correlated among the simulations, DIC dis and DIC soft are also inversely correlated, dampening the overall changes in DIC. This inverse correlation could be decoupled if changes in deep ocean mixing were to alter ideal age independently of AABW fraction, or if independent ecosystem changes were to alter export and remineralization, thereby modifying DIC soft . As an example of the latter, we show that iron fertilization causes both DIC soft and DIC dis to increase and that the relationship between these two components depends on the climate state. We propose a simple framework to consider the global contribution of DIC soft + DIC dis to ocean carbon storage as a function of the surface preformed nitrate and DIC dis of dense water formation regions, the global volume fractions ventilated by these regions, and the global nitrate inventory.

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“…The TMM has been applied to a wide range of problems, including simulating anthropogenic carbon uptake and radiocarbon by the ocean (Graven et al, 2012), simulating noble gases to improve the parameterization of air-sea gas transfer (Nicholson et al, 2011;Liang et al, 2013) and investigate ocean ventilation (Nicholson et al, 2016), studying ocean proxy (Siberlin and Wunsch, 2011) and radiocarbon (Koeve et al, 2015) timescales, investigating the mechanisms controlling nutrient ratios (Weber and Deutsch, 2010), modeling the cycling of particle reactive geochemical tracers Siddall et al, 2008;Vance et al, 2017), estimating respiration in the ocean from oxygen utilization rates (Duteil et al, 2013;Koeve and Kähler, 2016), demonstrating the utility of atmospheric potential oxygen measurements to constrain ocean heat transport , modeling the ocean's CaCO 3 (Koeve et al, 2014) and nitrogen (Kriest and Oschlies, 2015) cycles; studying the impact of the Southern Ocean on global ocean oxygen (Keller et al, 2016), estimating the flux of organic matter (Wilson et al, 2015), and biogeochemical parameter sensitivity (Khatiwala, 2007;Kriest et al, 2010Kriest et al, , 2012 and optimization (Priess et al, 2013b, a;Kriest et al, 2017).…”

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confidence: 99%

Evaluation of the transport matrix method for simulation of ocean biogeochemical tracers

et al. 2017

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Abstract. Conventional integration of Earth system and ocean models can accrue considerable computational expenses, particularly for marine biogeochemical applications. "Offline" numerical schemes in which only the biogeochemical tracers are time stepped and transported using a precomputed circulation field can substantially reduce the burden and are thus an attractive alternative. One such scheme is the "transport matrix method" (TMM), which represents tracer transport as a sequence of sparse matrix-vector products that can be performed efficiently on distributed-memory computers. While the TMM has been used for a variety of geochemical and biogeochemical studies, to date the resulting solutions have not been comprehensively assessed against their "online" counterparts. Here, we present a detailed comparison of the two. It is based on simulations of the state-of-the-art biogeochemical sub-model embedded within the widely used coarse-resolution University of Victoria Earth System Climate Model (UVic ESCM). The default, non-linear advection scheme was first replaced with a linear, third-order upwind-biased advection scheme to satisfy the linearity requirement of the TMM. Transport matrices were extracted from an equilibrium run of the physical model and subsequently used to integrate the biogeochemical model offline to equilibrium. The identical biogeochemical model was also run online. Our simulations show that offline integration introduces some bias to biogeochemical quantities through the omission of the polar filtering used in UVic ESCM and in the offline application of time-dependent forcing fields, with high latitudes showing the largest differences with respect to the online model. Differences in other regions and in the seasonality of nutrients and phytoplankton distributions are found to be relatively minor, giving confidence that the TMM is a reliable tool for offline integration of complex biogeochemical models. Moreover, while UVic ESCM is a serial code, the TMM can be run on a parallel machine with no change to the underlying biogeochemical code, thus providing orders of magnitude speed-up over the online model.

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A novel estimate of ocean oxygen utilisation points to a reduced rate of respiration in the ocean interior

Cited by 53 publications

References 41 publications

The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

Evaluation of the transport matrix method for simulation of ocean biogeochemical tracers

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