Correcting oceanic O<sub>2</sub>/Ar‐net community production estimates for vertical mixing using N<sub>2</sub>O observations

Cassar, Nicolas; Nevison, C. D.; Manizza, Manfredi

doi:10.1002/2014gl062040

Cited by 30 publications

(63 citation statements)

References 77 publications

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“…The greatest difference observed was 1% in the MIZ in the far south of Leg 1, perhaps due to cooling of ice‐melt that can lower Ar concentrations. The high values of biological undersaturation (Figure b) need not have been due to respiration in the SML and instead may reflect supply of low O 2 waters from below that can lead to measured values of O 2 /Ar being less than the O 2 /Ar ratio at saturation with the atmosphere [e.g., Cassar et al ., ]. This would lead to underestimates of biological productivity, as discussed later in section 3.3, and therefore overestimate the contribution of

{Δ O}_{2}^{p h y s}

to the

{Δ O}_{2}^{t o t a l}

supersaturation observed throughout most of the study.…”

Section: Resultsmentioning

confidence: 99%

“…While the MIMS technique provides an alternative estimate of NCP, the calculation of

{Δ O}_{2}^{b i o}

using this method is complicated in high latitude waters due to a number of processes including ice melt, temperature change, and the entrainment of oxygen undersaturated waters into the SML that can lead to underestimates of

{Δ O}_{2}^{b i o}

[e.g., Castro‐Morales et al ., ; Cassar et al ., ; Eveleth et al ., ]. Although these complications do provide challenges to interpretation of the O 2 /Ar signals in our study region, the method does provide an alternative estimate of NCP and addresses different time scales (days to weeks) compared to the seasonal estimates based on carbon and nitrate deficits.…”

Section: Methodsmentioning

confidence: 99%

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Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

Roden

Tilbrook

Trull

et al. 2016

J. Geophys. Res. Oceans

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The carbon cycle of the seasonally ice covered region of the southwest Indian Ocean sector of East Antarctica (30°–80°E, 60°–69°S) was investigated during austral summer (January–March 2006). Large variability in the drivers and timing of carbon cycling dynamics were observed and indicated that the study site was a weak net source of carbon dioxide (CO2) to the atmosphere of 0.8 ± 1.6 g C m−2 during the ice‐free period, with narrow bands of CO2 uptake observed near the continental margin and north of the Southern Antarctic Circumpolar Current Front. Continuous surface measurements of dissolved oxygen and the fugacity of CO2 were combined with net community production estimates from oxygen/argon ratios to show that surface heat gain and photosynthesis were responsible for the majority of observed surface water variability. On seasonal timescales, winter sea‐ice cover reduced the flux of CO2 to the atmosphere in the study area, followed by biologically driven drawdown of CO2 as the ice retreated in spring‐summer highlighting the important role that sea‐ice formation and retreat has on the biogeochemical cycling of the region.

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{Δ O}_{2}^{p h y s}

to the

{Δ O}_{2}^{t o t a l}

supersaturation observed throughout most of the study.…”

Section: Resultsmentioning

confidence: 99%

“…While the MIMS technique provides an alternative estimate of NCP, the calculation of

{Δ O}_{2}^{b i o}

{Δ O}_{2}^{b i o}

Section: Methodsmentioning

confidence: 99%

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

Roden

Tilbrook

Trull

et al. 2016

J. Geophys. Res. Oceans

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“…With an OSSE, one considers a model to be an analog for the real ocean, for which one has the fully resolved state evolution of the system. Earlier ocean OSSEs (Christian et al, 2008;Park et al, 2010;Plancherel et al, 2013;Majkut et al, 2014;Cassar et al, 2014) have tended to focus on one realization of the evolution of the Earth system, and focused on the skill with which different observing strategies can reproduce trends and variability in the ocean through selective sub-sampling of the model output. The target is to test the available skill in reproducing the real-world trends and variability with an incomplete observing system, without any claim to separating the signal associated with the secular trend and natural variability.…”

Section: Implications For Observing System Designmentioning

confidence: 99%

Emergence of multiple ocean ecosystem drivers in a large ensemble suite with an Earth system model

Rodgers

Lin

Frölicher³

2015

Biogeosciences

183

162

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Abstract. Marine ecosystems are increasingly stressed by human-induced changes. Marine ecosystem drivers that contribute to stressing ecosystems -including warming, acidification, deoxygenation and perturbations to biological productivity -can co-occur in space and time, but detecting their trends is complicated by the presence of noise associated with natural variability in the climate system. Here we use large initial-condition ensemble simulations with an Earth system model under a historical/RCP8.5 (representative concentration pathway 8.5) scenario over 1950-2100 to consider emergence characteristics for the four individual and combined drivers. Using a 1-standard-deviation (67 % confidence) threshold of signal to noise to define emergence with a 30-year trend window, we show that ocean acidification emerges much earlier than other drivers, namely during the 20th century over most of the global ocean. For biological productivity, the anthropogenic signal does not emerge from the noise over most of the global ocean before the end of the 21st century. The early emergence pattern for sea surface temperature in low latitudes is reversed from that of subsurface oxygen inventories, where emergence occurs earlier in the Southern Ocean. For the combined multiple-driver field, 41 % of the global ocean exhibits emergence for the 2005-2014 period, and 63 % for the 2075-2084 period. The combined multiple-driver field reveals emergence patterns by the end of this century that are relatively high over much of the Southern Ocean, North Pacific, and Atlantic, but relatively low over the tropics and the South Pacific. For the case of two drivers, the tropics including habitats of coral reefs emerges earliest, with this driven by the joint effects of acidification and warming. It is precisely in the regions with pronounced emergence characteristics where marine ecosystems may be expected to be pushed outside of their comfort zone determined by the degree of natural background variability to which they are adapted. The results underscore the importance of sustained multi-decadal observing systems for monitoring multiple ecosystems drivers.

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“…In this study, we used profiles obtained during the cruise to parameterize the vertical flux of [O 2 ] out of the mixed layer. In many other studies, is estimated based on past measurements, which can induce a factor of 10 uncertainty into the vertical O 2 flux, and is sometimes the largest source of error in estimates of NOP (Hamme and Emerson, 2006;Giesbrecht et al, 2012;Jonsson et al, 2013;Cassar et al, 2014;Weeding and Trull, 2014 profile from the base of the mixed layer to 10 m below the mixed layer (Figure 4-1b). We derived from air-sea equilibrium has 17 ∆ ≃ 8 per meg (Reuer et al, 2007;Stanley et al, 2010), and O 2 that is purely biological in origin has 17 ∆ ≃ 293 per meg with = 0.5179.…”

Section: Calculation Of Nop From O 2 /Ar Mass Balancementioning

confidence: 99%

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

Manning¹

2017

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In this thesis, I use coastal measurements of dissolved O 2 and inert gases to provide insight into the chemical, biological, and physical processes that impact the oceanic cycles of carbon and dissolved gases. Dissolved O 2 concentration and triple isotopic composition trace net and gross biological productivity. The saturation states of inert gases trace physical processes, such as air-water gas exchange, temperature change, and mixing, that affect all gases.First, I developed a field-deployable system that measures Ne, Ar, Kr, and Xe gas ratios in water. It has precision and accuracy of 1 % or better, enables near-continuous measurements, and has much lower cost compared to existing laboratory-based methods. The system will increase the scientific community's access to use dissolved noble gases as environmental tracers.Second, I measured O 2 and five noble gases during a cruise in Monterey Bay, California. I developed a vertical model and found that accurately parameterizing bubble-mediated gas exchange was necessary to accurately simulate the He and Ne measurements. I present the first comparison of multiple gas tracer, incubation, and sediment trap-based productivity estimates in the coastal ocean. Net community production estimated from 15 NO -3 uptake and O 2 /Ar gave equivalent results at steady state. Underway O 2 /Ar measurements revealed submesoscale variability that was not apparent from daily incubations.Third, I quantified productivity by O 2 mass balance and air-water gas exchange by dual tracer ( 3 He/SF 6 ) release during ice melt in the Bras d'Or Lakes, a Canadian estuary. The gas transfer velocity at >90 % ice cover was 6 % of the rate for nearly ice-free conditions. Rates of volumetric gross primary production were similar when the estuary was completely ice-covered and ice-free, and the ecosystem was on average net autotrophic during ice melt and net heterotrophic following ice melt. I present a method for incorporating the isotopic composition of H 2 O into the O 2 isotope-based productivity calculations, which increases the estimated gross primary production in this study by 46-97 %.In summary, I describe a new noble gas analysis system and apply O 2 and inert gas observations in new ways to study chemical, biological, and physical processes in coastal waters.

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Correcting oceanic O₂/Ar‐net community production estimates for vertical mixing using N₂O observations

Cited by 30 publications

References 77 publications

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

Emergence of multiple ocean ecosystem drivers in a large ensemble suite with an Earth system model

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

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Correcting oceanic O2/Ar‐net community production estimates for vertical mixing using N2O observations

Cited by 30 publications

References 77 publications

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

Emergence of multiple ocean ecosystem drivers in a large ensemble suite with an Earth system model

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

Contact Info

Product

Resources

About

Correcting oceanic O₂/Ar‐net community production estimates for vertical mixing using N₂O observations