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Williams, NL, Juranek LW, Feely RA, Johnson KS, Sarmiento JL, Talley LD, Dickson AG, Gray AR, Wanninkhof R, Russell JL, Riser SC, Takeshita Y.  2017.  Calculating surface ocean pCO(2) from biogeochemical Argo floats equipped with pH: An uncertainty analysis. Global Biogeochemical Cycles. 31:591-604.   10.1002/2016gb005541   AbstractWebsite

More than 74 biogeochemical profiling floats that measure water column pH, oxygen, nitrate, fluorescence, and backscattering at 10 day intervals have been deployed throughout the Southern Ocean. Calculating the surface ocean partial pressure of carbon dioxide (pCO(2sw)) from float pH has uncertainty contributions from the pH sensor, the alkalinity estimate, and carbonate system equilibrium constants, resulting in a relative standard uncertainty in pCO(2sw) of 2.7% (or 11 mu atm at pCO(2sw) of 400 mu atm). The calculated pCO(2sw) from several floats spanning a range of oceanographic regimes are compared to existing climatologies. In some locations, such as the subantarctic zone, the float data closely match the climatologies, but in the polar Antarctic zone significantly higher pCO(2sw) are calculated in the wintertime implying a greater air-sea CO2 efflux estimate. Our results based on four representative floats suggest that despite their uncertainty relative to direct measurements, the float data can be used to improve estimates for air-sea carbon flux, as well as to increase knowledge of spatial, seasonal, and interannual variability in this flux. Plain Language Summary The Southern Ocean is a key player in the global flow of carbon, yet it is hard to reach, and there are relatively few measurements there, especially in winter. Measuring the amount of carbon dioxide gas in seawater is key to advancing our understanding of the Southern Ocean. More than 74 robotic floats that use sensors to measure seawater properties have been deployed throughout the Southern Ocean, and each has a lifetime of around 5 years. It is currently not possible to directly measure carbon dioxide gas from these floats; however, it is possible to estimate carbon dioxide from things that the float can measure, like pH, a measure of ocean acidity. Here surface ocean carbon dioxide is estimated from several floats and compared to two ship-based estimates. In some locations, the floats closely match the existing estimates, but in other locations the floats see significantly higher surface ocean carbon dioxide in the wintertime, reinforcing the idea that the Southern Ocean's role in the global carbon cycle needs a closer look. Our results show that despite not measuring carbon dioxide directly, these floats will help scientists learn a lot about the Southern Ocean's part in the global flow of carbon.

Alin, SR, Feely RA, Dickson AG, Hernandez-Ayon JM, Juranek LW, Ohman MD, Goericke R.  2012.  Robust empirical relationships for estimating the carbonate system in the southern California Current System and application to CalCOFI hydrographic cruise data (2005-2011). Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007511   AbstractWebsite

The California Current System (CCS) is expected to experience the ecological impacts of ocean acidification (OA) earlier than most other ocean regions because coastal upwelling brings old, CO2-rich water relatively close to the surface ocean. Historical inorganic carbon measurements are scarce, so the progression of OA in the CCS is unknown. We used a multiple linear regression approach to generate empirical models using oxygen (O-2), temperature (T), salinity (S), and sigma theta (sigma(theta)) as proxy variables to reconstruct pH, carbonate saturation states, carbonate ion concentration ([CO32-]), dissolved inorganic carbon (DIC) concentration, and total alkalinity (TA) in the southern CCS. The calibration data included high-quality measurements of carbon, oxygen, and other hydrographic variables, collected during a cruise from British Columbia to Baja California in May-June 2007. All resulting empirical relationships were robust, with r(2) values >0.92 and low root mean square errors. Estimated and measured carbon chemistry matched very well for independent data sets from the CalCOFI and IMECOCAL programs. Reconstructed CCS pH and saturation states for 2005-2011 reveal a pronounced seasonal cycle and inter-annual variability in the upper water column. Deeper in the water column, conditions are stable throughout the annual cycle, with perennially low pH and saturation states. Over sub-decadal time scales, these empirical models provide a valuable tool for reconstructing carbonate chemistry related to ocean acidification where direct observations are limited. However, progressive increases in anthropogenic CO2 content of southern CCS water masses must be carefully addressed to apply the models over longer time scales.

Turk, D, Zappa CJ, Meinen CS, Christian JR, Ho DT, Dickson AG, McGillis WR.  2010.  Rain impacts on CO2 exchange in the western equatorial Pacific Ocean. Geophysical Research Letters. 37   10.1029/2010gl045520   AbstractWebsite

The ocean plays a major role in the global carbon cycle through the atmosphere-ocean partitioning of atmospheric carbon dioxide. Rain alters the physics and carbon chemistry at the ocean surface to increase the amount of CO(2) taken up by the ocean. This paper presents the results of a preliminary study wherein rain measurements in the western equatorial Pacific are used to determine the enhanced transfer, chemical dilution and deposition effects of rain on air-sea CO(2) exchange. Including these processes, the western equatorial Pacific CO(2) flux is modified from an ocean source of +0.019 mol CO(2) m(-2) yr(-1) to an ocean sink of -0.078 mol CO(2) m(-2) yr(-1). This new understanding of rain effects changes the ocean's role in the global carbon budget, particularly in regions with low winds and high precipitation. Citation: Turk, D., C. J. Zappa, C. S. Meinen, J. R. Christian, D. T. Ho, A. G. Dickson, and W. R. McGillis (2010), Rain impacts on CO(2) exchange in the western equatorial Pacific Ocean, Geophys. Res. Lett., 37, L23610, doi:10.1029/2010GL045520.

Sabine, CL, Feely RA, Millero FJ, Dickson AG, Langdon C, Mecking S, Greeley D.  2008.  Decadal changes in Pacific carbon. Journal of Geophysical Research-Oceans. 113   10.1029/2007jc004577   AbstractWebsite

This paper uses the extended multiple linear regression (eMLR) technique to investigate changes over the last decade in dissolved inorganic carbon (DIC) inventories on a meridional line (P16 along 152 degrees W) up the central Pacific and on a zonal line (P02 along 30 degrees N) across the North Pacific. Maximum changes in the total DIC concentrations along P02 are 15 - 20 mu mol kg(-1) over 10 years, somewhat higher than the similar to 1 mu mol kg(-1) a(-1) increase in DIC expected based on the rate of atmospheric CO(2) increase. The maximum changes of 15 - 20 mu mol kg(-1) along the P16 line over the 14/15-year time frame fit with the expected magnitude of the anthropogenic signal, but there is a deeper than expected penetration of the signal in the North Pacific compared to the South Pacific. The effect of varying circulation on the total DIC change, based on decadal alterations of the apparent oxygen utilization rate, is estimated to be greater than 10 mu mol kg(-1) in the North Pacific, accounting for as much as 80% of the total DIC change in that region. The average anthropogenic CO(2) inventory increase along 30 degrees N between 1994 and 2004 was 0.43 mol m(-2) a(-1), with much higher inventories in the western Pacific. Along P16, the average Northern Hemisphere increase was 0.25 mol m(-2) a(-1) between 1991/1992 and 2006 compared to an average Southern Hemisphere anthropogenic CO(2) inventory increase between 1991 and 2005 of 0.41 mol m(-2) a(-1).