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Several studies have suggested that the carbon sink in the Southern Ocean-the ocean's strongest region for the uptake of anthropogenic CO2 -has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002, and by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized., (Copyright © 2015, American Association for the Advancement of Science.)

The past decade has seen a substantial amount of research on air-sea gas exchange and its environmental controls. These studies have significantly advanced the understanding of processes that control gas transfer, led to higher quality field measurements, and improved estimates of the flux of climate-relevant gases between the ocean and atmosphere. This review discusses the fundamental principles of air-sea gas transfer and recent developments in gas transfer theory, parameterizations, and measurement techniques in the context of the exchange of carbon dioxide. However, much of this discussion is applicable to any sparingly soluble, non-reactive gas. We show how the use of global variables of environmental forcing that have recently become available and gas exchange relationships that incorporate the main forcing factors will lead to improved estimates of global and regional air-sea gas fluxes based on better fundamental physical, chemical, and biological foundations.

Using inorganic carbon measurements from an international survey effort in the 1990s and a tracer-based separation technique, we estimate a global oceanic anthropogenic carbon dioxide (CO2) sink for the period from 1800 to 1994 of 118 +/- 19 petagrams of carbon. The oceanic sink accounts for approximately 48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO2 to the atmosphere of about 39 +/- 28 petagrams of carbon for this period. The current fraction of total anthropogenic CO2 emissions stored in the ocean appears to be about one-third of the long-term potential.

A method for preserving natural water samples for dissolved oxygen analysis is recommended. The conventional method of using greased glass stoppers have been found to cause an increase in oxygen concentration by 12% over 1-month period as a result of evaporation of water sample through micro-gaps and concurrent intrusion of air into the water sample bottles. Sealing the sample bottles with water has been found to be the optimal storage method. It permits a 100.2 +/- 0.3% recovery of dissolved oxygen concentration from storage seawater samples over 4 months.

We introduce three new Empirical Seawater Property Estimation Routines (ESPERs) capable of predicting seawater phosphate, nitrate, silicate, oxygen, total titration seawater alkalinity, total hydrogen scale pH (pHT), and total dissolved inorganic carbon (DIC) from up to 16 combinations of seawater property measurements. The routines generate estimates from neural networks (ESPER_NN), locally interpolated regressions (ESPER_LIR), or both (ESPER_Mixed). They require a salinity value and coordinate information, and benefit from additional seawater measurements if available. These routines are intended for seawater property measurement quality control and quality assessment, generating estimates for calculations that require approximate values, original science, and producing biogeochemical property context from a data set. Relative to earlier LIR routines, the updates expand their functionality, including new estimated properties and combinations of predictors, a larger training data product including new cruises from the 2020 Global Data Analysis Project data product release, and the implementation of a first‐principles approach for quantifying the impacts of anthropogenic carbon on DIC and pHT. We show that the new routines perform at least as well as existing routines, and, in some cases, outperform existing approaches, even when limited to the same training data. Given that additional training data has been incorporated into these updated routines, these updates should be considered an improvement over earlier versions. The routines are intended for all ocean depths for the interval from 1980 to ~2030 c.e., and we caution against using the routines to directly quantify surface ocean seasonality or make more distant predictions of DIC or pHT. [ABSTRACT FROM AUTHOR]

The fugacity or partial pressure of CO 2 in surface water (fCO 2w) is a key parameter to determine air-sea CO 2 fluxes and the evolution of ocean acidification. Despite its importance some key physical chemical characteristics are not fully resolved, notably its dependence on temperature. The fCO 2w is mostly measured by autonomous underway systems near in situ sea surface temperature (SST). Subsurface measurements are commonly carried out on individual (discrete) samples at a fixed temperature, normally 20 °C. Here, the underway system observations are compared with co-located discrete observations to determine the consistency of these types of measurements. The co-located discrete fCO 2w at 20 °C and underway fCO 2w measurements at SST are used to infer the temperature dependence of CO 2. In addition, calculated fCO 2w from total alkalinity (TA) and total dissolved inorganic carbon (DIC) are compared with the underway and discrete fCO 2w measurements. For 21 cruises spanning the major ocean basins from 1992 to 2020 a temperature dependence of 4.13 ± 0.01% °C−1 is determined in close agreement with a widely used previous empirical estimate of 4.23 ± 0.02% °C−1 for North Atlantic surface water. The temperature dependency of calculated fCO 2w from TA and DIC using recommended constants is 4.10% °C−1 for 17 cruises where there are co-located measurements of fCO 2w , TA and DIC. • 30 years of surface water CO 2 observations from research cruises show excellent consistency • A temperature dependence of CO 2 fugacity in seawater of 4.13 ± 0.01% °C−1 is determined • The temperature dependence shows good agreement with theoretical estimates [ABSTRACT FROM AUTHOR]

Recent studies based on ocean and atmospheric carbon dioxide (CO2) observations, suggesting that the ocean carbon uptake has been reduced, may help explain the increase in the fraction of anthropogenic CO2 emissions that remain in the atmosphere. is it a response to climate change or a signal of ocean natural variability or both? Regional process analyses are needed to follow the ocean carbon uptake and to enable better attributions of the observed changes. Here, we describe the evolution of the surface ocean CO2 fugacity (fCOoc 2) over the period 1993-2008 in the North Atlantic subpolar gyre (NASPG). This analysis is based primarily on observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) conducted at different seasons in the NASPG between iceland and Canada. The fCOoc 2trends based on DIC and TA data are also compared with direct fCO2 measurements obtained between 2003 and 2007 in the same region. During winters 1993-2003, the fCOoc 2 growth rate was 3.7 (±0.6) μatm y-1, higher than in the atmosphere, 1.8 (±0.1) μatm yr-1. This translates to a reduction of the ocean carbon uptake primarily explained by sea surface warming, up to 0.24 (±0.04) °C yr-1. This warming is a consequence of advection of warm water northward from the North Atlantic into the Irminger basin, which occurred as the North Atlantic Oscillation (NAO) index moved into a negative phase in winter 1995/1996. In winter 2001-2008, the fCOoc. As opposed to the 1990s, this appears to be almost entirely due to changes in seawater carbonate chemistry, the combination of increasing DIC and decreasing of TA. The rapid fCO2 rise was particularly fast, between 5.8 (±1.1) and 7.2 (±1.3) μatm yr-1 depending on the region, more than twice the atmospheric growth rate of 2.1 (±0.2) μatm yr-1, and in the winter of 2007-2008 the area was supersaturated with CO2. As opposed to the 1990s, this appears to be almost entirely due to changes in seawater carbonate chemistry, the combination of increasing DIC and decreasing of TA. The rapid fCOoc 2 increase was not only driven by regional uptake of anthropogenic CO2 but was also likely controlled by a recent increase in convective processes-vertical mixing in the NASPG and cannot be directly associated with NAO variability. The fCOoc 2C increase observed in 2001-2008 leads to a significant drop in pH of -0.069 (±0.007) decade-1. [ABSTRACT FROM AUTHOR]

The interannual variability of net sea-air CO flux for the period 1982-2007 is obtained from a diagnostic model using empirical subannual relationships between climatological CO partial pressure in surface seawater ( pCO) and sea surface temperature (SST), along with interannual changes in SST and wind speed. These optimum subannual relationships show significantly better correlation between pCO and SST than the previous relationships using fixed monthly boundaries. Our diagnostic model yields an interannual variability of ±0.14 PgC yr (1σ) with a 26-year mean of −1.48 PgC yr. The greatest interannual variability is found in the Equatorial Pacific, and significant variability is also found at northern and southern high-latitudes, depending in part, on which wind product is used. We provide an assessment of our approach by applying it to pCO and SST output from a prognostic global biogeochemical ocean model. Our diagnostic approach applied to this model output shows reasonable agreement with the prognostic model net sea-air CO fluxes in terms of magnitude and phase of variability, suggesting that our diagnostic approach can capture much of the observed variability on regional to global scale. A notable exception is that our approach shows significantly less variability than the prognostic model in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Abstract: Air–sea fluxes in the Caribbean Sea are presented based on measurements of partial pressure of CO2 in surface seawater, pCO2sw, from an automated system onboard the cruise ship Explorer of the Seas for 2002 through 2004. The pCO2sw values are used to develop algorithms of pCO2sw based on sea surface temperature (SST) and position. The algorithms are applied to assimilated SST data and remotely sensed winds on a 1° by 1° grid to estimate the fluxes on weekly timescales in the region. The positive relationship between pCO2sw and SST is lower than the isochemical trend suggesting counteracting effects from biological processes. The relationship varies systematically with location with a stronger dependence further south. Furthermore, the southern area shows significantly lower pCO2sw in the fall compared to the spring at the same SST, which is attributed to differences in salinity. The annual algorithms for the entire region show a slight trend between 2002 and 2004 suggesting an increase of pCO2sw over time. This is in accord with the increasing pCO2sw due the invasion of anthropogenic CO2. The annual fluxes of CO2 yield a net invasion of CO2 to the ocean that ranges from −0.04 to −1.2 mol m−2 year−1 over the 3 years. There is a seasonal reversal in the direction of the flux with CO2 entering into the ocean during the winter and an evasion during the summer. Year-to-year differences in flux are primarily caused by temperature anomalies in the late winter and spring period resulting in changes in invasion during these seasons. An analysis of pCO2sw before and after hurricane Frances (September 4–6, 2004), and wind records during the storm suggest a large local enhancement of the flux but minimal influence on annual fluxes in the region. [Copyright &y& Elsevier]

Refined procedures were developed for directly determining carbonate ion concentrations in seawater through measurement of the ultraviolet absorbances of lead carbonate and chloride complexes after addition of divalent lead (Pb(II)) to a seawater sample. Our model algorithm is based on carbonate ion concentrations calculated from measurements of pH and dissolved inorganic carbon (DIC) obtained on a NOAA ocean acidification cruise (GOMECC-2, the second Gulf of Mexico and East Coast Carbon cruise). These calculated carbonate concentrations, in conjunction with Pb(II) absorbance measurements for the same seawater samples, were used to refine previous algorithms based on different chemical-measurement techniques and a limited range of carbonate concentrations. The precision of the spectrophotometric carbonate measurements is affected by the concentration of Pb(II) in the titrated seawater samples. Doubling the concentration of the titrant improved precision relative to previously published procedures but required formulation of a correction for changes in carbonate ion concentration caused by the titrant addition. Minor changes in the new algorithm for the spectrophotometric method produced carbonate ion values (at 25 °C) in excellent agreement with values calculated from paired pH and DIC observations over a carbonate concentration range of 73–258 μmol kg − 1 . This new algorithm, tested on three subsequent research cruises in the Gulf of Mexico, showed a random scatter of residuals and an average offset between measured and calculated carbonate concentrations equal to − 0.92 ± 5.33 μmol kg − 1 . [ABSTRACT FROM AUTHOR]

Abstract: An autonomous multi-parameter flow-through CO2 system has been developed to simultaneously measure surface seawater pH, carbon dioxide fugacity (fCO2), and total dissolved inorganic carbon (DIC). All three measurements are based on spectrophotometric determinations of solution pH at multiple wavelengths using sulfonephthalein indicators. The pH optical cell is machined from a PEEK polymer rod bearing a bore-hole with an optical pathlength of ∼15cm. The fCO2 optical cell consists of Teflon AF 2400 (DuPont) capillary tubing sealed within the bore-hole of a PEEK rod. This Teflon AF tubing is filled with a standard indicator solution with a fixed total alkalinity, and forms a liquid core waveguide (LCW). The LCW functions as both a long pathlength (∼15cm) optical cell and a membrane that equilibrates the internal standard solution with external seawater. fCO2 is then determined by measuring the pH of the internal solution. DIC is measured by determining the pH of standard internal solutions in equilibrium with seawater that has been acidified to convert all forms of DIC to CO2. The system runs repetitive measurement cycles with a sampling frequency of ∼7 samples (21 measurements) per hour. The system was used for underway measurements of sea surface pH, fCO2, and DIC during the CLIVAR/CO2 A16S cruise in the South Atlantic Ocean in 2005. The field precisions were evaluated to be 0.0008 units for pH, 0.9μatm for fCO2, and 2.4μmolkg−1 for DIC. These field precisions are close to those obtained in the laboratory. Direct comparison of our measurements and measurements obtained using established standard methods revealed that the system achieved field agreements of 0.0012±0.0042units for pH, 1.0±2.5μatm for fCO2, and 2.2±6.0μmolkg−1 for DIC. This system integrates spectrophotometric measurements of multiple CO2 parameters into a single package suitable for observations of both seawater and freshwater. [Copyright &y& Elsevier]

A number of workers have recently shown that the thermodynamic constants for the dissociation of carbonic acid in seawater of Mehrbach et al. are more reliable than measurements made on artificial seawater. These studies have largely been confined to looking at the internal consistency of measurements of total alkalinity (TA), total inorganic carbon dioxide (TCO2) and the fugacity of carbon dioxide (fCO2). In this paper, we have examined the field measurements of pH, fCO2, TCO2 and TA on surface and deep waters from the Atlantic, Indian, Southern and Pacific oceans to determine the pK1, pK2 and pK2−pK1. These calculations are possible due to the high precision and accuracy of the field measurements. The values of pK2 and pK2−pK1 over a wide range of temperatures (−1.6–38°C) are in good agreement (within ±0.005) with the results of Mehrbach et al. The measured values of pK1 at 4°C and 20°C are in reasonable agreement (within ±0.01) with all the constants determined in laboratory studies. These results indicate, as suggested by internal consistency tests, that the directly measured values of pK1+pK2 of Mehrbach et al. on real seawater are more reliable than the values determined for artificial seawater. It also indicates that the large differences of pK2−pK1 (0.05 at 20°C) in real and artificial seawater determined by different investigators are mainly due to differences in pK2. These differences may be related to the interactions of boric acid with the carbonate ion.The values of pK2−pK1 determined from the laboratory measurements of Lee et al. and Lueker et al. at low fCO2 agree with the field-derived data to ±0.016 from 5°C to 25°C. The values of pK2−pK1 decrease as the fCO2 or TCO2 increases. This effect is largely related to changes in the pK2 as a function of fCO2 or TCO2. The values of fCO2 calculated from an input of TA and TCO2, which require reliable values of pK2−pK1, also vary with fCO2. The field data at 20°C has been used to determine the effect of changes of TCO2 on pK2 giving an empirical relationship:pK2TCO2=pK2−1.6×10−4(TCO2−2050)which is valid at TCO2>2050 μmol kg−1. This assumes that the other dissociation constants such as KB for boric acid are not affected by changes in TCO2. The slope is in reasonable agreement with the laboratory studies of Lee et al. and Lueker et al. (−1.2×10−4 to −1.9×10−4). This equation eliminates the dependence of the calculated fCO2 on the level of fCO2 or TCO2 in ocean waters (σ=29.7 μatm in fCO2). An input of pH and TCO2 yields values of fCO2 and TA that are in good agreement with the measured values (±22.3 μatm in fCO2 and ±4.3 μmol kg−1 in TA). The cause of the decrease in pK2 at high fCO2 is presently unknown. The observed inconsistencies between the measured and computed fCO2 values may be accounted for by adding the effect of organic acid (∼8 μmol kg−1) to the interpretation of the TA. Further studies are needed to elucidate the chemical reactions responsible for this effect. [Copyright &y& Elsevier]