Ray F. Weiss

Carbon dioxide in water and seawater: the solubility of a non-ideal gas

New measurements of the solubility of carbon dioxide in water and seawater confirm the accuracy of the measurements of Murray and Riley, as opposed to those of Li and Tsui. Corrections for non-ideal behavior in the gas phase and for dissociation in distilled water are required to calculate solubility coefficients from these sets of data. Equations for the solubilities of real gases are presented and discussed. Solubility coefficients for carbon dioxide in water and seawater are calculated for the data of Murray and Riley, and are fitted to equations in temperature and salinity of the form used previously to fit the solubilities of other gases.

Nitrous oxide solubility in water and seawater

Abstract The solubility of nitrous oxide in pure water and seawater has been measured microgasometrically over the range 0–40°C. The data have been corrected for nonideality and are fitted to equations in temperature and salinity of the form used previously to fit the solubilities of other gases. The fitted values have a precision of 0.1% and an estimated accuracy of 0.3%. The nonideal behavior of nitrous oxide—air mixtures is discussed, and the solubility of atmospheric nitrous oxide is presented in parametric form. A similar parametric representation for the solubility of atmospheric carbon dioxide is given in the Appendix.

Chemistry of submarine hydrothermal solutions at 21 °N, East Pacific Rise

Abstract The three hydrothermal fields at 21°N latitude, East Pacific Rise, were resampled and an additional one was discovered. Maximum fluid temperatures observed were within a few degrees of 350°C and these waters had concentrations of Mg and sulfate indistinguishable from zero. One field, NGS, which had active 350°C springs in 1979, was inactive when first located in 1981. However, when a chimney was broken open during sampling, water issued at 273°C and continued to flow for at least five days. The chemical composition strongly suggests that these waters cooled conductively from 350°C in the sealed conduit. The major ion data are consistent with the estimates based on extrapolation of the original measurements made on the hot springs from the Galapagos Spreading Center ( Edmond et al ., 1979a). The fluids have a pH of 3.5 and the sulfide-forming element concentrations show significant inter-field variations. Fe levels range from 0.8 to 2.4 mmoles/kg; the ratio Fe:Mn varies from 0.9 to 2.9 similar to metalliferous sediments on the ridge flanks, but much higher than observed at Galapagos (where sub-surface precipitation of iron sulfides occurs) indicating that the overwhelming proportion of the mass flux from hydrothermal systems occurs at high temperatures. Zn ranges from 40 to 106 μmoles/kg with Cu being substantially lower. Since the ratio of these elements in tholeiites is about unity, there is strong net preferential mobilization of Zn. Lead ranges from 183 to 359 nmoles/kg. Nickel and Be are highly immobile relative to the other trace elements. The abundance of H 2 S is about three times that of the total sulfide-forming cations. These data demonstrate that acid solutions at elevated temperatures can transport substantial amounts of ore-forming elements in the presence of large excesses of sulfide.

Three decades of global methane sources and sinks

Methane is an important greenhouse gas, responsible for about 20% of the warming induced by long-lived greenhouse gases since pre-industrial times. By reacting with hydroxyl radicals, methane reduces the oxidizing capacity of the atmosphere and generates ozone in the troposphere. Although most sources and sinks of methane have been identified, their relative contributions to atmospheric methane levels are highly uncertain. As such, the factors responsible for the observed stabilization of atmospheric methane levels in the early 2000s, and the renewed rise after 2006, remain unclear. Here, we construct decadal budgets for methane sources and sinks between 1980 and 2010, using a combination of atmospheric measurements and results from chemical transport models, ecosystem models, climate chemistry models and inventories of anthropogenic emissions. The resultant budgets suggest that data-driven approaches and ecosystem models overestimate total natural emissions. We build three contrasting emission scenarios-which differ in fossil fuel and microbial emissions-to explain the decadal variability in atmospheric methane levels detected, here and in previous studies, since 1985. Although uncertainties in emission trends do not allow definitive conclusions to be drawn, we show that the observed stabilization of methane levels between 1999 and 2006 can potentially be explained by decreasing-to-stable fossil fuel emissions, combined with stable-to-increasing microbial emissions. We show that a rise in natural wetland emissions and fossil fuel emissions probably accounts for the renewed increase in global methane levels after 2006, although the relative contribution of these two sources remains uncertain.

A history of chemically and radiatively important gases in air deduced from ALE/GAGE/AGAGE

We describe in detail the instrumentation and calibrations used in the Atmospheric Lifetime Experiment (ALE), the Global Atmospheric Gases Experiment (GAGE), and the Advanced Global Atmospheric Gases Experiment (AGAGE) and present a history of the majority of the anthropogenic ozone-depleting and climate-forcing gases in air based on these experiments. Beginning in 1978, these three successive automated high-frequency in situ experiments have documented the long-term behavior of the measured concentrations of these gases over the past 20 years, and show both the evolution of latitudinal gradients and the high-frequency variability due to sources and circulation. We provide estimates of the long-term trends in total chlorine contained in long-lived halocarbons involved in ozone depletion. We summarize interpretations of these measurements using inverse methods to determine trace gas lifetimes and emissions. Finally, we provide a combined observational and modeled reconstruction of the evolution of chlorocarbons by latitude in the atmosphere over the past 60 years which can be used as boundary conditions for interpreting trapped air in glaciers and oceanic measurements of chlorocarbon tracers of the deep oceanic circulation. Some specific conclusions are as follows: (1) International compliance with the Montreal Protocol is so far resulting in chlorofluorocarbon and chlorocarbon mole fractions comparable to target levels; (2) mole fractions of total chlorine contained in long-lived halocarbons (CCl 2 F 2 , CCl 3 F, CH 3 CCl 3 , CCl 4 , CHClF 2 , CCl 2 FCClF 2 , CH 3 Cl, CH 2 Cl 2 , CHCl 3 , CCl 2 =CCl 2 ) in the lower troposphere reached maximum values of about 3.6 ppb in 1993 and are beginning to slowly decrease in the global lower atmosphere; (3) the chlorofluorocarbons have atmospheric lifetimes consistent with destruction in the stratosphere being their principal removal mechanism; (4) multiannual variations in chlorofluorocarbon and chlorocarbon emissions deduced from ALE/GAGE/AGAGE data are consistent approximately with variations estimated independently from industrial production and sales data where available (CCl 2 F 2 (CFC-12) and CCl 2 FCClF 2 (CFC-113) show the greatest discrepancies); (5) the mole fractions of the hydrochlorofluorocarbons and hydrofluorocarbons, which are replacing the regulated halocarbons, are rising very rapidly in the atmosphere, but with the exception of the much longer manufactured CHClF 2 (HCFC-22), they are not yet at levels sufficient to contribute significantly to atmospheric chlorine loading. These replacement species could in the future provide independent estimates of the global weighted-average OH concentration provided their industrial emissions are accurately documented; (6) in the future, analysis of pollution events measured using high-frequency in situ measurements of chlorofluorocarbons and their replacements may enable emission estimates at the regional level, which, together with industrial end-use data, are of sufficient accuracy to be capable of identifying regional noncompliance with the Montreal Protocol.

Atmospheric Trends and Lifetime of CH3CCI3 and Global OH Concentrations.

Determination of the atmospheric concentrations and lifetime of trichloroethane (CH3CCI3) is very important in the context of global change. This halocarbon is involved in depletion of ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH3CCI3 in the total atmosphere is 4.8 � 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmospheres oxidizing capability, shows little change from 1978 to 1994.

Solubilities of chlorofluorocarbons 11 and 12 in water and seawater

The solubilities of dilute mixtures of the chlorofluorocarbons CCl3F (CFC-11) and CCl2F2 (CFC-12) in pure water and seawater over the temperature range 0 to 40°C have been measured by gas chromatography. The data have been fitted to equations in temperature and salinity of the form used previously to fit the solubilities of other gases. The fitted values have an estimated accuracy of ∼1.5% and a relative precision of ∼0.7% for both chlorofluorocarbons. The nonideal behavior of these compounds in dilute air mixtures is discussed, and their solubilities from a water-saturated atmosphere are presented in parametric form.

Thermocline and intermediate water communication between the south Atlantic and Indian oceans

A conductivity-temperature-depth and tracer chemistry section in the southeast South Atlantic in December 1989 and January 1990 presents strong evidence that there is a significant interocean exchange of thermocline and intermediate water between the South Atlantic and Indian oceans. Eastward flowing water at 10°W composed of South Atlantic Central (thermocline) Water is too enriched with chlorofluoromethanes 11 and 12 and oxygen to be the sole source of similar θ-S water within the northward flowing Benguela Current. About two thirds of the Benguela Current thermocline transport is drawn from the Indian Ocean; the rest is South Atlantic water that has folded into the Benguela Current in association with the Agulhas eddy-shedding process. South Atlantic Central water passes in the Indian Ocean by a route to the south of the Agulhas Return Current. The South Atlantic water loops back to the Atlantic within the Indian Ocean, perhaps mostly within the Agulhas recirculation cell of the southwest Indian Ocean. Linkage of Atlantic and Indian Ocean water diminishes with increasing depth; it extends through the lower thermocline into the Antarctic Intermediate Water (AAIW) (about 50% is derived from the Indian Ocean) but not into the deep water. While much of the interocean exchange remains on an approximate horizontal “isopycnal” plane, as much as 10 × 106 m3 s−1 of Indian Ocean water within the 25 × 106 m3 s−1 Benguela Current, mostly derived from the lower thermocline and AAIW, may balance deeper Atlantic export of North Atlantic Deep Water (NADW). The addition of salt water from the evaporative Indian Ocean into the South Atlantic Ocean thermocline and AAIW levels may precondition the Atlantic for NADW formation. While AAIW seems to be the chief feed for NADW, the bulk of it enters the subtropical South Atlantic, spiked with Indian Ocean salt, within the Benguela Current rather than along the western boundary of the South Atlantic.

Geochemical studies of the Weddell sea

The origin of Antarctic Bottom Water is discussed in terms of the distributions of a number of geochemical tracers in the major water masses of the Weddell Sea. Oxygen, phosphate, nitrate and total inorgabic carbon are shown to be negligibly altered by consumption or production during sub-surface circulation and mixing. All the conservative properties of Weddell Sea Bottom Water and Antarctic Bottom Water are explained as simple mixtures of Winter Water, Warm Deep Water, and Western Shelf Water. Silica is markedly non-conservative, showing enrichments up to ≈35 μM kg−1 which are due mainly to interactions with the bottom. The deuterium and oxygen-18 stable isotope data show that the high salinity of Western Shelf Water is principally the result of freezing rather than evaporation. The isotopic composition of Western Shelf Water also requires a significant admixture of melt-water from the base of the Filchner Ice Shelf, and mass-balance calculations linking the rate of shelf ice melting to the formation of bottom water give a production rate of about 5 × 106 m3 s−1 for Weddell Sea Bottom Water with potentiatial −0.9°C, or about 8 × 106 m3 s−1 in terms of classical Antarctic Bottom Water with a potential temperature of −0.4°C. Concentrations of the radioisotopes carbon-14 and tritium are exceptionally low in the Weddell Sea despite the fact that the CO2 atmospheric exchange rate is comparable to the global average. The low values are seen to be the result of a short surface residence time, a large sub-surface mixing component, and exchange inhibition by sea ice especially during the winter. Unlike the average world ocean, where molecular exchange is about three times more important than precipitation in transporting atmospheric tritium to surface waters, about four times more tritium is added to the Weddell Sea by precipitation than by molecular exchange. The flux of new Weddell Sea Bottom Water based on the tritium data is estimated very roughly at about 3 × 106 m3 s−1, or about 4.5 × 106 m3 s−1 expressed in terms of classical Antarctic Bottom Water.

Global oceanic emissions of nitrous oxide

The global N2O flux from the ocean to the atmosphere is calculated based on more than 60,000 expedition measurements of the N2O anomaly in surface water. The expedition data are extrapolated globally and coupled to daily air-sea gas transfer coefficients modeled at 2.8°×2.8° resolution to estimate a global ocean source of about 4 (1.2–6.8) Tg N yr−1. The wide range of uncertainty in the source estimate arises mainly from uncertainties in the air-sea gas transfer coefficients and in the global extrapolation of the summertime-biased surface N2O data set. The strongest source is predicted from the 40–60°S latitude band. Strong emissions also are predicted from the northern Pacific Ocean, the equatorial upwelling zone, and coastal upwelling zones occurring predominantly in the tropical northern hemisphere. High apparent oxygen utilization (AOU) at 100 m below the mixed layer is found to be correlated positively both to N2O production at depth and to the surface N2O anomaly. On the basis of these correlations, the expedition data are partitioned into two subsets associated with high and low AOU at depth. The zonally averaged monthly means in each subset are extrapolated to produce two latitude-by-month matrices in which monthly surface N2O is expressed as the deviation from the annual mean. Both matrices contain large uncertainties. The low-AOU matrix, which mainly includes surface N2O data from the North Atlantic and the subtropical gyres, suggests many regions with positive summer deviations and negative winter deviations, consistent with a seasonal cycle predominantly driven by seasonal heating and cooling of the surface ocean. The high-AOU subset, which includes the regions most important to the global N2O ocean source, suggests some regions with positive winter deviations and negative summer deviations, consistent with a seasonal cycle predominantly driven by wintertime mixing of surface water with N2O-rich deep water. Coupled seasonal changes in gas transfer coefficients and surface N2O in these important source regions could strongly influence the global ocean source.