[1] 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, CO 2 -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 (s q ) as proxy variables to reconstruct pH, carbonate saturation states, carbonate ion concentration ([CO 3 2À ]), 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 CO 2 content of southern CCS water masses must be carefully addressed to apply the models over longer time scales.

[1] We measured gross primary productivity (GPP) in vitro and GPP and net community production (NCP) in situ on four cruises to the Hawaii Ocean Time series (HOT) station ALOHA during [2002][2003]. In vitro GPP, determined by 18 O labeling, yielded integrated production (0-100 m) that was on average 1.5 times the 14 C integrated production. Mean integrated productivity from two winter and two summer cruises was 575 mg C m À2 d À1 and 930 mg C m À2 d À1 , respectively. In situ GPP, determined from the triple-isotope composition of dissolved O 2 , averaged 910 mg C m À2 d À1 in the winter and 1225 mg C m À2 d À1 in the summer/fall, with an uncertainty of ±40%. The NCP/GPP ratio, determined using O 2 /Ar gas ratio and oxygen isotope measurements, was around 0.1 in the summer, close to the canonical f-ratio for the open ocean, indicating station ALOHA is a net autotrophic system during summer months. The consistently higher gross carbon production measured by the in situ method, which integrates production over the $2-week residence time of O 2 in the mixed layer, suggests that aperiodic bursts of production contribute significantly to time-averaged mean productivity at station ALOHA.

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 μatm at pCO 2sw of 400 μatm). 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 CO 2 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.

The continental shelf region off the west coast of North America is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO 2-rich waters. To date, the spatial and temporal distribution of anthropogenic CO 2 (C anth) within the CO 2rich waters is largely unknown. Here we adapt the multiple linear regression approach to utilize the GO-SHIP Repeat Hydrography data from the northeast Pacific to establish an annually updated relationship between C anth and potential density. This relationship was then used with the NOAA Ocean Acidification Program West Coast Ocean Acidification (WCOA) cruise data sets from 2007, 2011, 2012, and 2013 to determine the spatial variations of C anth in the upwelled water. Our results show large spatial differences in C anth in surface waters along the coast, with the lowest values (37-55 µmol kg-1) in strong upwelling regions off southern Oregon and northern California and higher values (51-63 µmol kg-1) to the north and south of this region. Coastal dissolved inorganic carbon concentrations are also elevated due to a natural remineralized component (C bio), which represents carbon accumulated through net respiration in the seawater that has not yet degassed to the atmosphere. Average surface C anth is almost twice the surface remineralized component. In contrast, C anth is only about one third and one fifth of the remineralized component at 50 m and 100 m depth, respectively. Uptake of C anth has caused the aragonite saturation horizon to shoal by approximately 30-50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the shell dissolution of living pteropods. Our data show that the most severe biological impacts occur in the nearshore waters, where corrosive waters are closest to the surface. Since the pre-industrial times, pteropod shell dissolution has, on average, increased approximately 20-25% in both nearshore and offshore waters.

Since the triple isotopic composition of dissolved O(2) ((17)Δ) was introduced as a natural tracer of photosynthetic gross O(2) production (GOP) over 10 years ago, observations of (17)Δ have been used to constrain marine productivity throughout the global ocean. This incubation-independent approach has several advantages: It allows the determination of production free from containment artifacts and reduces logistical hurdles that can make obtaining productivity with traditional incubation-dependent methods difficult. As such, GOP estimates derived from (17)Δ have been used to give insight into potential biases in incubation-based approaches and to evaluate satellite-based estimates of production at the regional scale. With increased use, we have also learned more about the potential biases and uncertainties of this approach, some of which have been addressed by recent method improvements. We recap the major advances the (17)Δ method has brought to improved understanding of biological carbon cycling, from incubation bottles to ocean basins.

[1] We developed a multiple linear regression model to robustly determine aragonite saturation state (W arag ) from observations of temperature and oxygen (R 2 = 0.987, RMS error 0.053), using data collected in the Pacific Northwest region in late May 2007. The seasonal evolution of W arag near central Oregon was evaluated by applying the regression model to a monthly (winter)/bi-weekly (summer) watercolumn hydrographic time-series collected over the shelf and slope in 2007. The W arag predicted by the regression model was less than 1, the thermodynamic calcification/dissolution threshold, over shelf/slope bottom waters throughout the entire 2007 upwelling season (May -November), with the W arag = 1 horizon shoaling to 30 m by late summer. The persistence of water with W arag < 1 on the continental shelf has not been previously noted and could have notable ecological consequences for benthic and pelagic calcifying organisms such as mussels, oysters, abalone, echinoderms, and pteropods.

The carbon system of the western Arctic Ocean is undergoing a rapid transition as sea ice extent and thickness decline. These processes are dynamically forcing the region, with unknown consequences for CO2 fluxes and carbonate mineral saturation states, particularly in the coastal regions where sensitive ecosystems are already under threat from multiple stressors. In October 2011, persistent wind‐driven upwelling occurred in open water along the continental shelf of the Beaufort Sea in the western Arctic Ocean. During this time, cold (<−1.2°C), salty (>32.4) halocline water—supersaturated with respect to atmospheric CO2 (pCO2 > 550 μatm) and undersaturated in aragonite (Ωaragonite < 1.0) was transported onto the Beaufort shelf. A single 10‐day event led to the outgassing of 0.18–0.54 Tg‐C and caused aragonite undersaturations throughout the water column over the shelf. If we assume a conservative estimate of four such upwelling events each year, then the annual flux to the atmosphere would be 0.72–2.16 Tg‐C, which is approximately the total annual sink of CO2 in the Beaufort Sea from primary production. Although a natural process, these upwelling events have likely been exacerbated in recent years by declining sea ice cover and changing atmospheric conditions in the region, and could have significant impacts on regional carbon budgets. As sea ice retreat continues and storms increase in frequency and intensity, further outgassing events and the expansion of waters that are undersaturated in carbonate minerals over the shelf are probable.

We determine rates of gross photosynthetic O2 production (GOP) and net community O2 production (NCP) using the triple oxygen isotope and O2/Ar approach on two spring and two late summer meridional transects of the NE Pacific. Observed GOP and NCP in the subtropical (89 ± 9 and 8.3 ± 1.3 mmol O2 m−2 d−1, respectively) and subarctic (193 ± 16 and 16.3 ± 3.8 mmol O2 m−2 d−1) were in agreement with rates previously determined at time series stations in each region, validating the regional representativeness of these sites. At the transition zone chlorophyll front (TZCF), which migrates seasonally from 32°N in spring to 40°N in summer, GOP and NCPwere elevated by 2–4× compared to adjacent areas. Coincident with the TZCF, increases in surface nitrate concentration and extensive changes in phytoplankton community composition were observed. HPLC pigment data indicated substantial increases in a prymnesiophyte (e.g., coccolithophore) biomarker at the TZCF on a spring and summer cruise, and a diatom biomarker on the spring cruise. Increases in remotely sensed surface particulate inorganic carbon concentration were also observed at the TZCF on all four cruises, indicating that coccolithophore production may contribute to increased productivity at the TZCF. Meridional trends in observed air‐sea CO2 flux on each cruise resembled those of the biologically induced CO2 flux (NCP), but with an overprinting of the response of air‐sea CO2 exchange to summer warming. A simple carbon budget based on regional CO2 flux climatology demonstrates the importance of NCPfor net annual air‐sea CO2uptake, although slow air‐sea equilibration and seasonal solubility effects obscure this term.