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Carter, BR, Feely RA, Wanninkhof R, Kouketsu S, Sonnerup RE, Pardo PC, Sabine CL, Johnson GC, Sloyan BM, Murata A, Mecking S, Tilbrook B, Speer K, Talley LD, Millero FJ, Wijffels SE, Macdonald AM, Gruber N, Bullister JL.  2019.  Pacific anthropogenic carbon between 1991 and 2017. Global Biogeochemical Cycles. 33:597-617.   10.1029/2018gb006154   AbstractWebsite

We estimate anthropogenic carbon (C-anth) accumulation rates in the Pacific Ocean between 1991 and 2017 from 14 hydrographic sections that have been occupied two to four times over the past few decades, with most sections having been recently measured as part of the Global Ocean Ship-based Hydrographic Investigations Program. The rate of change of C-anth is estimated using a new method that combines the extended multiple linear regression method with improvements to address the challenges of analyzing multiple occupations of sections spaced irregularly in time. The C-anth accumulation rate over the top 1,500 m of the Pacific increased from 8.8 (+/- 1.1, 1 sigma) Pg of carbon per decade between 1995 and 2005 to 11.7 (+/- 1.1) PgC per decade between 2005 and 2015. For the entire Pacific, about half of this decadal increase in the accumulation rate is attributable to the increase in atmospheric CO2, while in the South Pacific subtropical gyre this fraction is closer to one fifth. This suggests a substantial enhancement of the accumulation of C-anth in the South Pacific by circulation variability and implies that a meaningful portion of the reinvigoration of the global CO2 sink that occurred between similar to 2000 and similar to 2010 could be driven by enhanced ocean C-anth uptake and advection into this gyre. Our assessment suggests that the accuracy of C-anth accumulation rate reconstructions along survey lines is limited by the accuracy of the full suite of hydrographic data and that a continuation of repeated surveys is a critical component of future carbon cycle monitoring.

Williams, NL, Juranek LW, Johnson KS, Feely RA, Riser SC, Talley LD, Russell JL, Sarmiento JL, Wanninkhof R.  2016.  Empirical algorithms to estimate water column pH in the Southern Ocean. Geophysical Research Letters. 43:3415-3422.   10.1002/2016gl068539   AbstractWebsite

Empirical algorithms are developed using high-quality GO-SHIP hydrographic measurements of commonly measured parameters (temperature, salinity, pressure, nitrate, and oxygen) that estimate pH in the Pacific sector of the Southern Ocean. The coefficients of determination, R-2, are 0.98 for pH from nitrate (pH(N)) and 0.97 for pH from oxygen (pH(Ox)) with RMS errors of 0.010 and 0.008, respectively. These algorithms are applied to Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) biogeochemical profiling floats, which include novel sensors (pH, nitrate, oxygen, fluorescence, and backscatter). These algorithms are used to estimate pH on floats with no pH sensors and to validate and adjust pH sensor data from floats with pH sensors. The adjusted float data provide, for the first time, seasonal cycles in surface pH on weekly resolution that range from 0.05 to 0.08 on weekly resolution for the Pacific sector of the Southern Ocean.