The oceanic sink for anthropogenic CO2 from 1994 to 2007.

We quantify the oceanic sink for anthropogenic carbon dioxide (CO2) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression-based method, we find a global increase in the anthropogenic CO2 inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year-1 and represents 31 ± 4% of the global anthropogenic CO2 emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO2, substantial regional differences in storage rate are found, likely owing to climate variability-driven changes in ocean circulation.

On the Frontline: Tracking Ocean Acidification in an Alaskan Shellfish Hatchery.

The invasion of anthropogenic carbon dioxide (CO2) into the ocean is shifting the marine carbonate system such that saturation states of calcium carbonate (CaCO3) minerals are decreasing, and this is having a detrimental impact on early life stages of select shellfish species. The global, secular decrease in CaCO3 saturation states is occurring on top of a backdrop of large natural variability in coastal settings; progressively shifting the envelope of variability and leading to longer and more frequent exposure to adverse conditions. This is a great concern in the State of Alaska, a high-latitude setting vulnerable to rapid changes in the marine carbonate system, where an emerging shellfish industry plans major growth over the coming decades. Currently, the Alutiiq Pride Shellfish Hatchery (APSH) in Seward, Alaska is the only hatchery in the state, and produces many shellfish species with early life stages known to be sensitive to low CaCO3 saturation states. Here we present the first land-based OA measurements made in an Alaskan shellfish hatchery, and detail the trends in the saturation state of aragonite (Ωarag), the more soluble form of CaCO3, over a 10-month period in the APSH seawater supply. These data indicate the largest changes are on the seasonal time scale, with extended periods of sub-optimal Ωarag levels (Ωarag < 1.5) in winter and autumn associated with elevated water column respiration and short-lived runoff events, respectively. The data pinpoint a 5-month window of reprieve with favorable Ωarag conditions above the sub-optimal Ωarag threshold, which under predicted upper-bound CO2 emissions trajectories is estimated to close by 2040. To date, many species in production at APSH remain untested in their response to OA, and the data presented here establish the current conditions at APSH as well as provide a framework for hatchery-based measurements in Alaska. The current and expected conditions seen at APSH are essential to consider for this developing Alaskan industry.

Spectrophotometric measurement of calcium carbonate saturation states in seawater.

Measurements of ocean pH and carbonate ion concentrations in the North Pacific and Arctic Oceans were used to determine calcium carbonate saturation states (Ω(CaCO(3))) from spectrophotometric methods alone. Total carbonate ion concentrations, [CO(3)(2-)](T), were for the first time at sea directly measured using Pb(II) UV absorbance spectra. The basis of the method is given by the following: [formula see text] where (CO(3))ß(1) is the PbCO(3)(0) formation constant, e(i) are molar absorptivity ratios, and R = (250)A/(234)A (ratio of absorbances measured at 250 and 234 nm). On the basis of shipboard and laboratory Pb(II) data and complementary carbon-system measurements, the experimental parameters were determined to be (25 °C) the following: [formula see text]. The resulting mean difference between the shipboard spectrophotometric and conventional determinations of [CO(3)(2-)](T) was ±2.03 µmol kg(-1). The shipboard analytical precision of the Pb(II) method was ∼1.71 µmol kg(-1) (2.28%). Spectrophotometric [CO(3)(2-)](T) and pH(T) were then combined to calculate Ω(CaCO(3)). For the case of aragonite, 95% of the spectrophotometric aragonite saturation states (Ω(Aspec)) were within ±0.06 of the conventionally calculated values (Ω(Acalc)) when 0.5 ≤ Ω(A) ≤ 2.0. When Ω(A) > 2.0, 95% of the Ω(Aspec) values were within ±0.18 of Ω(Acalc). Our shipboard experience indicates that spectrophotometric determinations of [CO(3)(2-)](T) and Ω(CaCO(3)) are straightforward, fast, and precise. The method yields high-quality measurements of two important, rapidly changing aspects of ocean chemistry and offers capabilities suitable for long-term automated in situ monitoring.