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Based on measurements from the WOCE/JGOFS global CO2 survey, the CLIVAR/CO2 Repeat Hydrography Program and the Canadian Line P survey, we have observed an average decrease of 0.34% yr−1 in the saturation state of surface seawater in the Pacific Ocean with respect to aragonite and calcite. The upward migrations of the aragonite and calcite saturation horizons, averaging about 1 to 2 m yr−1, are the direct result of the uptake of anthropogenic CO2 by the oceans and regional changes in circulation and biogeochemical processes. The shoaling of the saturation horizon is regionally variable, with more rapid shoaling in the South Pacific where there is a larger uptake of anthropogenic CO2. In some locations, particularly in the North Pacific Subtropical Gyre and in the California Current, the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon. If CO2 emissions continue as projected over the rest of this century, the resulting changes in the marine carbonate system would mean that many coral reef systems in the Pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole, and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival. Key Points The saturation state of surface waters decreased by an average of 0.34% per year The aragonite and calcite saturation horizons shoal an average of 1‐2 m per yr The shoaling of the saturation horizon is regionally variable

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$118 \\pm 19$petagrams of carbon. The oceanic sink accounts for ~48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO2to the atmosphere of about$39 \\pm 28$petagrams of carbon for this period. The current fraction of total anthropogenic CO2emissions stored in the ocean appears to be about one-third of the long-term potential.

We present measurements of the solubility of Fe(II) and Fe(III) extracted from bulk and size‐fractionated African dust collected in summer trade winds at Barbados, West Indies. Iron solubilities typically ranged from 1% to 3%. Fe(III) dominates the iron solubility over the entire range of particle sizes. At mineral dust concentrations below about 5 ug/m3 Fe(II), believed to be largely derived from anthropogenic and biomass burning sources, becomes increasingly important. Samples containing large soluble iron fractions and high Fe(II)/Fe(III) ratios are associated with South Atlantic back trajectories; the gray coloration of the filters suggests that the source may be biomass burning in southern Africa. In general, much of the variability in Fe solubility is linked to Fe(II) concentration changes. Vanadium is often used as a tracer of anthropogenic impacts. Although many of our samples yielded V/Ti ratios much greater than average crustal abundances, we could find no relationship between the enrichment of V and Fe solubility. Our Fe solubility results are quite similar to those obtained by others despite the fact that the measurements were made in diverse ocean regions and the protocols used were quite different in all cases. This uniformity implies that the factors controlling aerosol iron solubility are largely inherent in the properties of the aerosols themselves and not the procedures used to extract the iron. Our results suggest that dust transport models that focus on the role of iron in ocean biogeochemistry must take into account aerosol origin in order to better model the solubility of iron.

Increasing atmospheric CO₂ over the next 200 years will cause the pH of ocean waters to decrease further. Many recent studies have examined the effect of decreasing pH on calcifying organisms in ocean waters and on other biological processes (photosynthesis, nitrogen fixation, elemental ratios, and community structure). In this review, we examine how pH will change the organic and inorganic speciation of metals in surface ocean waters, and the effect that it will have on the interactions of metals with marine organisms. We consider both kinetic and equilibrium processes. The decrease in concentration of OH⁻ and${\\mathrm{C}\\mathrm{O}}_{3}^{2-}$ions can affect the solubility, adsorption, toxicity, and rates of redox processes of metals in seawater. Future studies are needed to examine how pH affects the interactions of metals complexed to organic ligands and with marine organisms.

The changes in anthropogenic CO2 are evaluated in the South Pacific, along the meridional line P18 (110°W) and the zonal line P06 (32°S), using the extended multiple linear regression (eMLR) method. The structure of the column inventory of anthropogenic CO2 on P18 is similar to the southern section of P16 in the central South Pacific (150°W), but the overall increase is greater by approximately 5–10 μmol kg−1. The value of the anthropogenic CO2 inventory on P18 is in agreement at the crossover point of an earlier evaluation of P06. Subsequent changes in pH due to the increase in anthropogenic CO2 are also evaluated. The change in pH is determined from the changes in anthropogenic CO2 and do not reflect variability in other decadal signals. For both cruise tracks, the average annual change in pH is −0.0016 mol kg−1 yr−1. This value is in good agreement with the average decrease in pH in the North Pacific, at the Hawaii Times Series and the subtropical North Atlantic. The uptake rates of anthropogenic CO2 are within reasonable agreement with similar studies in the South Pacific. There is evidence for greater uptake of anthropogenic CO2 in the western South Pacific and is attributed to the formation of subtropical Mode Water in the region. Key Points Determine the decadal increases in anthropogenic carbon in the South Pacific Determine the decrease in pH from increases in anthropogenic carbon Determine the average rates of increases in anthropogenic carbon

As one of few who have been involved in the equation of state of seawater over the last 40 years, I was invited to review some of the history behind its early development and also the more recent thermodynamic equation of state. The article first reviews early (late 1800s) work by Knudsen and others in defining the concept of salinity. This summary leads into the development of the practical salinity scale. Our studies at the University of Miami Rosenstiel School, along with the work of Alain Poisson's group at Laboratoire de Physique et Chimie, Université Pierre et Marie Curie, and that of Alvin Bradshaw and Karl Schleicher at Woods Hole Oceanographic Institution, were instrumental in deriving the 1980 equation of state (EOS-80) that has been used for 30 years. The fundamental work of Ranier Feistel at Leibniz Institute for Baltic Sea Research led to the development of a Gibbs free energy function that is the backbone of the new thermodynamic equation of state (TEOS-10). It can be used to determine all of the thermodynamic properties of seawater. The salinity input to the TEOS-10 Gibbs function requires knowledge of the absolute salinity of seawater (SA), which is based upon the reference salinity of seawater (SR). The reference salinity is our best estimate of the absolute salinity of the seawater that was used to develop the practical salinity scale (SP), the equation of state, and the other thermodynamic properties of seawater. Reference salinity is related to practical salinity by SR= SP(35.16504/35.000) g kg⁻¹ and absolute salinity is related to reference salinity by SA= SR+ δSA, where δSAis due to the added solutes in seawater in deep waters resulting from the dissolution of CaCO₃(s) and SiO₂(s), CO₂, and nutrients like NO₃ and PO₄ from the oxidation of plant material. The δSAvalues due to the added solutes are estimated from the differences between the measured densities of seawater samples compared with the densities calculated from the TEOS-10 equation of state (Δρ) at the same reference salinity, temperature, and pressure, using δSA= Δρ/0.75179 g kg⁻¹. The values of δSAin the ocean can be estimated for waters at given longitude, latitude, and depth using correlations of δSAand the concentration of Si(OH)₄ in the waters. The SAvalues can then be used to calculate all the thermodynamic properties of seawater in the major oceans using the new TEOS-10. It will be very useful to modelers examining the entropy and enthalpy of seawater.

Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate (CaCO3) particles. Here we estimate the in situ CaCO3 dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO2 on CaCO3 shell-forming species. CaCO3 dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO3 dissolution rate for the global oceans is approximately 0.5 +/- 0.2 petagrams of CaCO3-C per year, which is approximately 45 to 65% of the export production of CaCO3.

The equilibria and rates of reactions of trace metals in natural waters are affected by their speciation or the form of the metal in the solution phase. Many workers have shown, for example, that biological uptake (Anderson and Morel in Limnol Oceanogr 27:789–813, 1982 ), the toxicity (Sunda and Ferguson in Trace metals in seawater, Plenum Press, New York, 1983 ) as well as the solubility (Millero et al. in Mar Chem 50:21–39, 1995 ; Liu and Millero in Geochim Cosmochim Acta 63:3487–3497, 1999 ) are affected by the speciation. For example, Fe(II) and Mn(II) are biologically available for marine organisms, while Fe(III) and Mn(IV) are normally not available. The speciation of metals also affects the rates of oxidation (Millero in Geochim Cosmochim Acta 49:547–553, 1985 , Res Trends Curr Top Sol Chem 1:141–169, 1994 ; Sharma and Millero in Geochim Cosmochim Acta 53:2269–2276, 1989 ; Vazquez et al. in Geophys Res Lett 16:1363–1366, 1989 ) and reduction (Res Trends Curr Top Sol Chem 1:141–169, 1994 ; Millero et al. in Mar Chem 36:71–83, 1991 ) of metals in natural waters. The ionic interactions of metals are controlled by interactions with inorganic (Cl − , OH − , CO 3 2− , etc.) and organic ligands (e.g., Fulvic and Humic acids). The speciation of metals is also affected by the oxidation potential (Eh) and the pH in the solution. In this paper we have developed a Pitzer Model (Pitzer in J Phys Chem 77:268–277, 1973 , Activity coefficients in electrolyte solutions, 2nd edn, CRC Press, Boca Raton, 1991 ) that can be used to determine the speciation of trace metals in seawater and other natural waters. It is based upon the Miami Pitzer Model (Millero and Pierrot in Aquatic Geochem 4:153–199, 1998 ) that has been shown to predict reliable activity coefficients for the major components of seawater. The computer code (Pierrot in Ph.D. Thesis, University of Miami, Miami, Florida, 2002 ) for these calculations is described in detail, in this paper. It has been used in an earlier paper (Millero and Pierrot in Chemistry of marine water and sediments, Springer, Berlin, 2002 ) and more recently used to examine the effect of pH on the speciation of metals in seawater (Millero et al. in Oceanography 22(4):72–85, 2009 ).

Fish have been shown to produce high (10 to 48 mol %) magnesium calcite as part of the physiological mechanisms responsible for maintaining salt and water balance. The importance of this source to the marine carbon cycle is only now being considered. In this paper, we report the first measurements of the solubility of this CaCO3 in seawater. The resulting solubility (pK*sp = 5.89 ± 0.09) is approximately two times higher than aragonite and similar to the high magnesium calcite generated on the Bahamas Banks (pK*sp = 5.90). This high solubility of fish‐produced CaCO3 is a result of the high magnesium content and not a product of micro‐environments created by microbial activity. This material is soluble in near surface waters, contributing to the input of carbonate to surface ocean waters, and may at least partially explain the observed increase in total alkalinity above the aragonite saturation horizon. Key Points First solubility measurements of fish‐produced high Mg calcite Mg calcite is approximately twice as soluble as aragonite Mg calcite contributes to CaCO3 dissolution above aragonite saturation horizon