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Seth G John - One of the best experts on this subject based on the ideXlab platform.
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Biological Uptake and reversible scavenging of zinc in the global ocean
Science, 2018Co-Authors: Thomas C Weber, Seth G John, Alessandro Tagliabue, Tim DevriesAbstract:Zinc (Zn) is a key micronutrient for marine phytoplankton, with a global distribution that is similar to silicic acid. The processes that govern this relationship, despite the very different Biological cycling of Zn and silica, remain poorly understood. Here, we use diagnostic and mechanistic models to show that only a combination of Southern Ocean Biological Uptake and reversible scavenging of Zn onto sinking particles can explain the observations. The distinction between organic and adsorbed Zn can also reconcile the vertical distribution and mass balance of Zn isotopes, which previously appeared at odds. This holistic understanding explains the Zn deficiencies observed throughout the low-latitude ocean and implies a greater sensitivity of the marine Zn cycle to climate-driven changes in organic matter cycling than previously recognized.
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biogeochemical cycling of zn and cd and their stable isotopes in the eastern tropical south pacific
Marine Chemistry, 2017Co-Authors: Seth G John, Joshua Helgoe, Emily TownsendAbstract:Abstract The distribution of Zn and Cd and their stable isotope ratios (δ66Zn and δ114Cd) were measured on samples from the Eastern Subtropical South Pacific Zonal Transect (EPZT), US GEOTRACES section GP16. The broad trends in both δ66Zn and δ114Cd are similar to those observed in other ocean basins, suggesting global similarities in the biogeochemical processes which cycle Zn and Cd. For example, average deep ocean δ66Zn along this transect (+ 0.46‰) are similar to the ~+0.5‰ values observed in the deep North Atlantic and North Pacific. Also similar to other locations, δ66Zn decreases towards the surface ocean. A plume of hydrothermal Zn emanating from the East Pacific Rise is used to calculate hydrothermal end-member δ66Zn as + 0.24‰, which is similar to crustal values and similar to other sources of Zn to the oceans. Average deep-ocean δ114Cd along this transect is + 0.28‰, which is similar to deep-ocean values between + 0.2 and + 0.3 measured elsewhere in the Atlantic, Pacific, and Southern Oceans. δ114Cd increases towards the surface ocean, as observed in other ocean basins, reflecting the preferential Biological Uptake of lighter Cd isotopes. Elsewhere it has been hypothesized that Cd can precipitate in sulfidic microenvironments on sinking particles, affecting seawater Cd concentrations and isotope ratios. However, we don't find evidence of particularly strong CdS precipitation along this transect, despite the fact that the Peru OMZ is one of the most reducing ocean environments worldwide.
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the acceleration of dissolved cobalt s ecological stoichiometry due to Biological Uptake remineralization and scavenging in the atlantic ocean
Biogeosciences, 2016Co-Authors: Mak A Saito, Seth G John, Tim M Conway, Abigail E Noble, Nicholas J Hawco, Benjamin S Twining, Daniel C Ohnemus, Phoebe J Lam, Rod JohnsonAbstract:Abstract. The stoichiometry of Biological components and their influence on dissolved distributions have long been of interest in the study of the oceans. Cobalt has the smallest oceanic inventory of inorganic micronutrients and hence is particularly vulnerable to influence by internal oceanic processes including euphotic zone Uptake, remineralization, and scavenging. Here we observe not only large variations in dCo : P stoichiometry but also the acceleration of those dCo : P ratios in the upper water column in response to several environmental processes. The ecological stoichiometry of total dissolved cobalt (dCo) was examined using data from a US North Atlantic GEOTRACES transect and from a zonal South Atlantic GEOTRACES-compliant transect (GA03/3_e and GAc01) by Redfieldian analysis of its statistical relationships with the macronutrient phosphate. Trends in the dissolved cobalt to phosphate (dCo : P) stoichiometric relationships were evident in the basin-scale vertical structure of cobalt, with positive dCo : P slopes in the euphotic zone and negative slopes found in the ocean interior and in coastal environments. The euphotic positive slopes were often found to accelerate towards the surface and this was interpreted as being due to the combined influence of depleted phosphate, phosphorus-sparing (conserving) mechanisms, increased alkaline phosphatase metalloenzyme production (a zinc or perhaps cobalt enzyme), and biochemical substitution of Co for depleted Zn. Consistent with this, dissolved Zn (dZn) was found to be drawn down to only 2-fold more than dCo, despite being more than 18-fold more abundant in the ocean interior. Particulate cobalt concentrations increased in abundance from the base of the euphotic zone to become ∼ 10 % of the overall cobalt inventory in the upper euphotic zone with high stoichiometric values of ∼ 400 µmol Co mol−1 P. Metaproteomic results from the Bermuda Atlantic Time-series Study (BATS) station found cyanobacterial isoforms of the alkaline phosphatase enzyme to be prevalent in the upper water column, as well as a sulfolipid biosynthesis protein indicative of P sparing. The negative dCo : P relationships in the ocean interior became increasingly vertical with depth, and were consistent with the sum of scavenging and remineralization processes (as shown by their dCo : P vector sums). Attenuation of the remineralization with depth resulted in the increasingly vertical dCo : P relationships. Analysis of particulate Co with particulate Mn and particulate phosphate also showed positive linear relationships below the euphotic zone, consistent with the presence and increased relative influence of Mn oxide particles involved in scavenging. Visualization of dCo : P slopes across an ocean section revealed hotspots of scavenging and remineralization, such as at the hydrothermal vents and below the oxygen minimum zone (OMZ) region, respectively, while that of an estimate of Co* illustrated stoichiometrically depleted values in the mesopelagic and deep ocean due to scavenging. This study provides insights into the coupling between the dissolved and particulate phase that ultimately creates Redfield stoichiometric ratios, demonstrating that the coupling is not an instantaneous process and is influenced by the element inventory and rate of exchange between phases. Cobalt's small water column inventory and the influence of external factors on its biotic stoichiometry can erode its limited inertia and result in an acceleration of the dissolved stoichiometry towards that of the particulate phase in the upper euphotic zone. As human use of cobalt grows exponentially with widespread adoption of lithium ion batteries, there is a potential to affect the limited biogeochemical inertia of cobalt and its resultant ecology in the oceanic euphotic zone.
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biogeochemical cycling of cadmium isotopes along a high resolution section through the north atlantic ocean
Geochimica et Cosmochimica Acta, 2015Co-Authors: Tim M Conway, Seth G JohnAbstract:Abstract Cadmium (Cd) is a bioactive trace element in the oceans, with a nutrient-like distribution that closely matches dissolved phosphate. Seawater-dissolved stable Cd isotope ratios (δ114Cd) are a relatively new parameter, which show much promise for furthering our understanding of the biogeochemical cycling of Cd in the oceans. Here we present a high-resolution paired section of dissolved Cd concentrations and dissolved δ114Cd from 21 open-ocean stations along the US GEOTRACES GA03 transect through the North Atlantic Ocean. Dissolved Cd concentrations along the section are strongly influenced by water-mass distribution and the cycling of Cd. The highest dissolved Cd concentrations (400–540 pmol kg−1) are associated with Antarctic-sourced water masses, whilst Biological Uptake in the surface ocean results in a strong vertical gradient in dissolved Cd towards the surface, reaching as low as 0.03 pmol kg−1 in western surface waters. Dissolved δ114Cd is also characterized by a vertical gradient from ∼+0.2‰ in the deep ocean to +2‰ to +5‰ in the Cd-depleted surface ocean (relative to NIST SRM 3108). This variability in δ114Cd can be ascribed to mixing of Antarctic and North Atlantic water masses, together with fractionation due to in situ Biological Uptake of light Cd in the very surface ocean. Subtle deviations from this overall pattern of dissolved Cd concentration and dissolved δ114Cd are observed within low-oxygen waters off North Africa, where a dissolved Cd deficit relative to phosphate is associated with higher dissolved δ114Cd values. Together with elevated particulate Cd and Ba, this suggests that Cd sulfide precipitation is occurring within the water column of the North Atlantic, constituting a potentially important sink for isotopically light Cd. Additionally, the first measurements of dissolved δ114Cd within a hydrothermal plume at the Mid-Atlantic Ridge show that Cd is scavenged from the dissolved phase, leaving the remnant dissolved Cd isotopically heavier. Constraining the significance of these marine sinks for dissolved Cd is important, not only for our understanding of the marine biogeochemical cycling of Cd in the modern oceans, but also for the successful application of the microfossil Cd/Ca proxy and the development of δ114Cd as a tracer for past-ocean biogeochemical cycling.
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the biogeochemical cycling of zinc and zinc isotopes in the north atlantic ocean
Global Biogeochemical Cycles, 2014Co-Authors: Tim M Conway, Seth G JohnAbstract:Zinc (Zn) is a marine micronutrient, with an overall oceanic distribution mirroring the major macronutrients, especially silicate. Seawater Zn isotope ratios (δ66Zn) are a relatively new oceanographic parameter which may offer insights into the biogeochemical cycling of Zn. To date, the handful of published studies of seawater δ66Zn show the global deep ocean to be both remarkably homogeneous (approximately +0.5‰) and isotopically heavier than the marine sources of Zn (+0.1 to +0.3‰). Here we present the first high-resolution oceanic section of δ66Zn, from the U.S. GEOTRACES GA03 North Atlantic Transect, from Lisbon to Woods Hole. Throughout the surface ocean, Biological Uptake and release of isotopically light Zn, together with scavenging of heavier Zn, leads to large variability in δ66Zn. In the ocean below 1000 m, δ66Zn is generally homogeneous (+0.50 ± 0.14‰; 2 SD), though deviations from +0.5‰ allow us to identify specific sources of Zn. The Mediterranean Outflow is characterized by δ66Zn of +0.1 to +0.3‰, while margin sediments are a source of isotopically light Zn (−0.5 to −0.8‰), which we attribute to release of nonregenerated biogenic Zn. Mid-Atlantic Ridge hydrothermal vents are also a source of light Zn (close to −0.5‰), though Zn is not transported far from the vents. Understanding the biogeochemical cycling of Zn in the modern ocean begins to address the imbalance between the light δ66Zn signature of marine sources and the globally homogeneous deep oceans (δ66Zn of +0.5‰) on long timescales, with overall patterns pointing to sediments as an important sink for isotopically light Zn throughout the oceans.
Tim M Conway - One of the best experts on this subject based on the ideXlab platform.
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the acceleration of dissolved cobalt s ecological stoichiometry due to Biological Uptake remineralization and scavenging in the atlantic ocean
Biogeosciences, 2016Co-Authors: Mak A Saito, Seth G John, Tim M Conway, Abigail E Noble, Nicholas J Hawco, Benjamin S Twining, Daniel C Ohnemus, Phoebe J Lam, Rod JohnsonAbstract:Abstract. The stoichiometry of Biological components and their influence on dissolved distributions have long been of interest in the study of the oceans. Cobalt has the smallest oceanic inventory of inorganic micronutrients and hence is particularly vulnerable to influence by internal oceanic processes including euphotic zone Uptake, remineralization, and scavenging. Here we observe not only large variations in dCo : P stoichiometry but also the acceleration of those dCo : P ratios in the upper water column in response to several environmental processes. The ecological stoichiometry of total dissolved cobalt (dCo) was examined using data from a US North Atlantic GEOTRACES transect and from a zonal South Atlantic GEOTRACES-compliant transect (GA03/3_e and GAc01) by Redfieldian analysis of its statistical relationships with the macronutrient phosphate. Trends in the dissolved cobalt to phosphate (dCo : P) stoichiometric relationships were evident in the basin-scale vertical structure of cobalt, with positive dCo : P slopes in the euphotic zone and negative slopes found in the ocean interior and in coastal environments. The euphotic positive slopes were often found to accelerate towards the surface and this was interpreted as being due to the combined influence of depleted phosphate, phosphorus-sparing (conserving) mechanisms, increased alkaline phosphatase metalloenzyme production (a zinc or perhaps cobalt enzyme), and biochemical substitution of Co for depleted Zn. Consistent with this, dissolved Zn (dZn) was found to be drawn down to only 2-fold more than dCo, despite being more than 18-fold more abundant in the ocean interior. Particulate cobalt concentrations increased in abundance from the base of the euphotic zone to become ∼ 10 % of the overall cobalt inventory in the upper euphotic zone with high stoichiometric values of ∼ 400 µmol Co mol−1 P. Metaproteomic results from the Bermuda Atlantic Time-series Study (BATS) station found cyanobacterial isoforms of the alkaline phosphatase enzyme to be prevalent in the upper water column, as well as a sulfolipid biosynthesis protein indicative of P sparing. The negative dCo : P relationships in the ocean interior became increasingly vertical with depth, and were consistent with the sum of scavenging and remineralization processes (as shown by their dCo : P vector sums). Attenuation of the remineralization with depth resulted in the increasingly vertical dCo : P relationships. Analysis of particulate Co with particulate Mn and particulate phosphate also showed positive linear relationships below the euphotic zone, consistent with the presence and increased relative influence of Mn oxide particles involved in scavenging. Visualization of dCo : P slopes across an ocean section revealed hotspots of scavenging and remineralization, such as at the hydrothermal vents and below the oxygen minimum zone (OMZ) region, respectively, while that of an estimate of Co* illustrated stoichiometrically depleted values in the mesopelagic and deep ocean due to scavenging. This study provides insights into the coupling between the dissolved and particulate phase that ultimately creates Redfield stoichiometric ratios, demonstrating that the coupling is not an instantaneous process and is influenced by the element inventory and rate of exchange between phases. Cobalt's small water column inventory and the influence of external factors on its biotic stoichiometry can erode its limited inertia and result in an acceleration of the dissolved stoichiometry towards that of the particulate phase in the upper euphotic zone. As human use of cobalt grows exponentially with widespread adoption of lithium ion batteries, there is a potential to affect the limited biogeochemical inertia of cobalt and its resultant ecology in the oceanic euphotic zone.
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biogeochemical cycling of cadmium isotopes along a high resolution section through the north atlantic ocean
Geochimica et Cosmochimica Acta, 2015Co-Authors: Tim M Conway, Seth G JohnAbstract:Abstract Cadmium (Cd) is a bioactive trace element in the oceans, with a nutrient-like distribution that closely matches dissolved phosphate. Seawater-dissolved stable Cd isotope ratios (δ114Cd) are a relatively new parameter, which show much promise for furthering our understanding of the biogeochemical cycling of Cd in the oceans. Here we present a high-resolution paired section of dissolved Cd concentrations and dissolved δ114Cd from 21 open-ocean stations along the US GEOTRACES GA03 transect through the North Atlantic Ocean. Dissolved Cd concentrations along the section are strongly influenced by water-mass distribution and the cycling of Cd. The highest dissolved Cd concentrations (400–540 pmol kg−1) are associated with Antarctic-sourced water masses, whilst Biological Uptake in the surface ocean results in a strong vertical gradient in dissolved Cd towards the surface, reaching as low as 0.03 pmol kg−1 in western surface waters. Dissolved δ114Cd is also characterized by a vertical gradient from ∼+0.2‰ in the deep ocean to +2‰ to +5‰ in the Cd-depleted surface ocean (relative to NIST SRM 3108). This variability in δ114Cd can be ascribed to mixing of Antarctic and North Atlantic water masses, together with fractionation due to in situ Biological Uptake of light Cd in the very surface ocean. Subtle deviations from this overall pattern of dissolved Cd concentration and dissolved δ114Cd are observed within low-oxygen waters off North Africa, where a dissolved Cd deficit relative to phosphate is associated with higher dissolved δ114Cd values. Together with elevated particulate Cd and Ba, this suggests that Cd sulfide precipitation is occurring within the water column of the North Atlantic, constituting a potentially important sink for isotopically light Cd. Additionally, the first measurements of dissolved δ114Cd within a hydrothermal plume at the Mid-Atlantic Ridge show that Cd is scavenged from the dissolved phase, leaving the remnant dissolved Cd isotopically heavier. Constraining the significance of these marine sinks for dissolved Cd is important, not only for our understanding of the marine biogeochemical cycling of Cd in the modern oceans, but also for the successful application of the microfossil Cd/Ca proxy and the development of δ114Cd as a tracer for past-ocean biogeochemical cycling.
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the biogeochemical cycling of zinc and zinc isotopes in the north atlantic ocean
Global Biogeochemical Cycles, 2014Co-Authors: Tim M Conway, Seth G JohnAbstract:Zinc (Zn) is a marine micronutrient, with an overall oceanic distribution mirroring the major macronutrients, especially silicate. Seawater Zn isotope ratios (δ66Zn) are a relatively new oceanographic parameter which may offer insights into the biogeochemical cycling of Zn. To date, the handful of published studies of seawater δ66Zn show the global deep ocean to be both remarkably homogeneous (approximately +0.5‰) and isotopically heavier than the marine sources of Zn (+0.1 to +0.3‰). Here we present the first high-resolution oceanic section of δ66Zn, from the U.S. GEOTRACES GA03 North Atlantic Transect, from Lisbon to Woods Hole. Throughout the surface ocean, Biological Uptake and release of isotopically light Zn, together with scavenging of heavier Zn, leads to large variability in δ66Zn. In the ocean below 1000 m, δ66Zn is generally homogeneous (+0.50 ± 0.14‰; 2 SD), though deviations from +0.5‰ allow us to identify specific sources of Zn. The Mediterranean Outflow is characterized by δ66Zn of +0.1 to +0.3‰, while margin sediments are a source of isotopically light Zn (−0.5 to −0.8‰), which we attribute to release of nonregenerated biogenic Zn. Mid-Atlantic Ridge hydrothermal vents are also a source of light Zn (close to −0.5‰), though Zn is not transported far from the vents. Understanding the biogeochemical cycling of Zn in the modern ocean begins to address the imbalance between the light δ66Zn signature of marine sources and the globally homogeneous deep oceans (δ66Zn of +0.5‰) on long timescales, with overall patterns pointing to sediments as an important sink for isotopically light Zn throughout the oceans.
Weijun Cai - One of the best experts on this subject based on the ideXlab platform.
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The Mid-Atlantic Bight Dissolved Inorganic Carbon System Observed in the March 1996 DOE Ocean Margins Program (OMP)—A Baseline Study
'Frontiers Media SA', 2021Co-Authors: Penny Vlahos, Weijun Cai, Ting-hsuan Huang, Douglas W. R. Wallace, Ernie R. Lewis, Chen-tung Arthur ChenAbstract:The United States Department of Energy (DOE)’s Ocean Margins Program (OMP) cruise EN279 in March 1996 provides an important baseline for assessing long-term changes in the carbon cycle and biogeochemistry in the Mid-Atlantic Bight (MAB) as climate and anthropogenic changes have been substantial in this region over the past two decades. The distributions of O2, nutrients, and marine inorganic carbon system parameters are influenced by coastal currents, temperature gradients, and Biological production and respiration. On the cross-shelf direction, pH decreases seaward, but carbonate saturation state (ΩArag) does not exhibit a clear trend. In contrast, ΩArag increases from north to south, while pH has no clear spatial patterns in the along-shelf direction. In order to distinguish between the effects of physical mixing of various water masses and those of Biological activities on the marine inorganic carbon system, we use the potential temperature-salinity diagram to identify water masses, and differences between observations and theoretical mixing concentrations to measure the non-conservative (primarily Biological) effects. Our analysis clearly shows the degree to which ocean margin pH and ΩArag are regulated by Biological activities in addition to water mass mixing, gas exchange, and temperature. The correlations among anomalies in dissolved inorganic carbon, phosphate, nitrate, and apparent oxygen utilization agree with known Biological stoichiometry. Biological Uptake is substantial in nearshore waters and in shelf-slope mixing areas. This work provides valuable baseline information to assess the more recent changes in the marine inorganic carbon system and the status of coastal ocean acidification
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effects of an estuarine plume associated bloom on the carbonate system in the lower reaches of the pearl river estuary and the coastal zone of the northern south china sea
Continental Shelf Research, 2008Co-Authors: Minhan Dai, Weijun Cai, Weidong Zhai, Julie Callahan, Bangqin Huang, Shaoling Shang, Tao Huang, Weifang Chen, Zhaozhang ChenAbstract:Abstract We observed a phytoplankton bloom downstream of a large estuarine plume induced by heavy precipitation during a cruise conducted in the Pearl River estuary and the northern South China Sea in May–June 2001. The plume delivered a significant amount of nutrients into the estuary and the adjacent coastal region, and enhanced stratification stimulating a phytoplankton bloom in the region near and offshore of Hong Kong. A several fold increase (0.2–1.8 μg Chl L −1 ) in biomass (Chl a ) was observed during the bloom. During the bloom event, the surface water phytoplankton community structure significantly shifted from a pico-phytoplankton dominated community to one dominated by micro-phytoplankton (>20 μm). In addition to increased Chl a , we observed a significant drawdown of p CO 2 , Biological Uptake of dissolved inorganic carbon (DIC) and an associated enhancement of dissolved oxygen and pH, demonstrating enhanced photosynthesis during the bloom. During the bloom, we estimated a net DIC drawdown of 100–150 μmol kg −1 and a TAlk increase of 0–50 μmol kg −1 . The mean sea–air CO 2 flux at the peak of the bloom was estimated to be as high as ∼−18 mmol m −2 d −1 . For an average surface water depth of 5 m, a very high apparent Biological CO 2 consumption rate of 70–110 mmol m −2 d −1 was estimated. This value is 2–6 times higher than the estimated air–sea exchange rate.
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riverine inorganic carbon flux and rate of Biological Uptake in the mississippi river plume
Geophysical Research Letters, 2003Co-Authors: Weijun CaiAbstract:[1] Inorganic carbon parameters were studied for the first time in the Mississippi River estuary and plume. Area-integrated Biological Uptake rates (1.5–3 gC m−2 d−1) derived from riverine total dissolved inorganic carbon (DIC) and total alkalinity (TAlk) fluxes as well as that based on the consumptions of DIC and TAlk in the plume are comparable to earlier results of 14C incubation in individual water samples. This rate is among the highest in the estuaries and plumes of the world's largest rivers. Fluvial DIC flux (13.5 × 1012 gC yr−1) indicates a 16% increase in the inorganic carbon flux over the earlier estimate and perhaps an increase in the weathering rate in the Mississippi River basin over the past four decades.
Jacob Opher - One of the best experts on this subject based on the ideXlab platform.
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the biogeochemical impact of glacial meltwater from southwest greenland
Progress in Oceanography, 2019Co-Authors: Katharine R Hendry, Veerle A I Huvenne, Laura F Robinson, Amber L Annett, Marcus P S Badger, Allison W Jacobel, Jacob OpherAbstract:Biogeochemical cycling in high-latitude regions has a disproportionate impact on global nutrient budgets. Here, we introduce a holistic, multi-disciplinary framework for elucidating the influence of glacial meltwaters, shelf currents, and Biological production on biogeochemical cycling in high-latitude continental margins, with a focus on the silica cycle. Our findings highlight the impact of significant glacial discharge on nutrient supply to shelf and slope waters, as well as surface and benthic production in these regions, over a range of timescales from days to thousands of years. Whilst Biological Uptake in fjords and strong diatom activity in coastal waters maintains low dissolved silicon concentrations in surface waters, we find important but spatially heterogeneous additions of particulates into the system, which are transported rapidly away from the shore. We expect the glacially-derived particles – together with biogenic silica tests – to be cycled rapidly through shallow sediments, resulting in a strong benthic flux of dissolved silicon. Entrainment of this benthic silicon into boundary currents may supply an important source of this key nutrient into the Labrador Sea, and is also likely to recirculate back into the deep fjords inshore. This study illustrates how geochemical and oceanographic analyses can be used together to probe further into modern nutrient cycling in this region, as well as the palaeoclimatological approaches to investigating changes in glacial meltwater discharge through time, especially during periods of rapid climatic change in the Late Quaternary.
Xianghui Guo - One of the best experts on this subject based on the ideXlab platform.
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carbonate chemistry in the northern south china sea shelf sea in june 2010
Deep-sea Research Part Ii-topical Studies in Oceanography, 2015Co-Authors: Xianghui Guo, George T F WongAbstract:Abstract The distributions of dissolved inorganic carbon ( C T ), total alkalinity ( A T ) and pH at 25 °C (pH 25 ) were determined in the Northern South China Sea Shelf-sea (NoSoCS) in early June, 2010 during a low flow period. The distributions of the partial pressure of CO 2 ( p CO 2 ), in situ pH, and temperature normalized p CO 2 (N p CO 2 ) were derived from the measured values. The distribution of A T is linearly related to salinity indicating that its distribution is controlled primarily by mixing between the surface water and the subsurface North Pacific Tropical Water. Aside from physical mixing, the distribution of C T is also influenced by its loss through Biological Uptake and CO 2 evasion to the atmosphere. The net community production (NCP) rate in the NoSoCS is estimated to be 10±20 (with a range of 4–13) mmol C m −2 d −1 . Within the NoSoCS, the NCP is elevated in the coastal upwelling area, where it is estimated to reach 30±17 mmol C m −2 d −1 . In addition to temperature, upwelling and Biological Uptake also affect the distribution of the surface p CO 2 and in situ pH. The waters in the NoSoCS are super-saturated with respect to aragonite at all depths as the saturation horizon is at 600–800 m in the open northern South China Sea. Nevertheless, the aragonite saturation state, Ω Ar , in the surface water, which is mostly between 3.3 and 3.5, is already within the range that has been suggested as barely adequate to marginal for the growth of the tropical shallow-water corals. The Ω Ar is linearly related to in situ pH. At the reported rate of pH decrease in the oceans as a result of ocean acidification, Ω Ar might reach a value that is considered “extremely marginal” within several decades and the existence of this type of coral reef ecosystem in the NoSoCS may then be threatened.