Moore, Robert M.

Permanent URI for this collectionhttps://hdl.handle.net/10222/22167

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Open Access
Composite global emissions of reactive chlorine from anthropogenic and natural sources: Reactive Chlorine Emissions Inventory
(1999-04) Keene, WC; Khalil, MAK; Erickson, DJ; McCulloch, A.; Graedel, TE; Lobert, JM; Aucott, ML; Gong, SL; Harper, DB; Kleiman, G.; Midgley, P.; Moore, RM; Seuzaret, C.; Sturges, WT; Benkovitz, CM; Koropalov, V.; Barrie, LA; Li, YF
Emission inventories for major reactive tropospheric Cl species (particulate Cl, HCl, ClNO2, CH3Cl, CHCl3, CH3CCl3, C2Cl4, C2HCl3, CH2Cl2 and CHClF2) were integrated across source types (terrestrial biogenic and oceanic emissions, sea-salt production and dechlorination, biomass burning, industrial emissions, fossil-fuel combustion, and incineration). Composite emissions were compared with known sinks to assess budget closure; relative contributions of natural and anthropogenic sources were differentiated. Model calculations suggest that conventional acid-displacement reactions involving S-(IV)+O-3, S-(IV)+ H2O2, and H2SO4 and HNO3 scavenging account for minor fractions of sea-salt dechlorination globally. Other important chemical pathways involving sea-salt aerosol apparently produce most volatile chlorine in the troposphere. The combined emissions of CH3Cl from known sources account for about half of the modeled sink, suggesting fluxes from known sources were underestimated, the OH sink was overestimated, or significant unidentified sources exist. Anthropogenic activities (primarily biomass burning) contribute about half the net CH3Cl emitted from known sources. Anthropogenic emissions account for only about 10% of the modeled CHCl3 sink. Although poorly constrained, significant fractions of tropospheric CH2Cl2 (25%), C2HCl3 (10%), and C2Cl4 (5%) are emitted from the surface ocean; the combined contributions of C2Cl4 and C2HCl3 from all natural sources may be substantially higher than the estimated oceanic flux.
Open Access
Methyl-Chloride (Ch3cl) Production in Phytoplankton Cultures
(1995-01) TAIT, VK; MOORE, RM
Unialgal nonaxenic cultures of seven species of phytoplankton, including both warm- and cold-water organisms, were examined under halocarbon-clean conditions for the production of CH3Cl. Incubations of all species showed CH3Cl increases significantly greater than in the control medium. The magnitude of increase varied with the phytoplankton species present and in some cases also with growth stage. Longer time series showed that CH3Cl continued to increase after the death of all the phytoplankton cells. Although direct production as a by-product of phytoplankton metabolism cannot be ruled out earlier in the time series, indirect chemical and (or) biotic reaction of algal-associated organic matter is required to explain this continued increase. Characterization of the role of bacteria in both pre- and postsenescent stage CH3Cl production will require comparable experiments carried out under axenic conditions.
Open Access
A seasonal study of methyl bromide concentrations in the North Atlantic (35 degrees-60 degrees N)
(2006-04) Tokarczyk, R.; Moore, RM
Methyl bromide concentrations in and over the North Atlantic were examined during spring, summer, and fall 2003. The results demonstrate that seasonality plays a great role in controlling methyl bromide fluxes from and into the ocean in this area. The North Atlantic acted as a sink of the atmospheric gas during the spring, a source during the summer, and a weak sink during the fall. The annual air-sea flux of methyl bromide from the North Atlantic area between 30 degrees N and 60 degrees N (approximately 15.4x10(6) km(2)) was estimated to be in the range of -0.3 to -0.6 Gg y(-1), with the methyl bromide flux varying between -4.0x10(6)+/- 1x10(6) g d(-1), 1.6x10(6)+/- 0.6x10(6) g d(-1), and -0.6x10(6)+/- 0.4x10(6) g d(-1) in spring, summer, and fall, respectively. Methyl bromide production necessary to balance air-sea exchange with oceanic losses was greater in the southern part than in the northern part of the studied area; no oceanic production was necessary to balance methyl bromide loss from the Arctic waters around 60 degrees N. While the regional contribution to the methyl bromide global oceanic flux is small, it is also complex and dynamic. Our data suggest that in this part of the ocean the flux is not so much dependent on sea surface temperature as it is on other, still unknown environmental variables.
Open Access
Effect of the nonlinearity of the carbonate system on partial pressure of carbon dioxide in the oceans
(1995-04) Trela, P.; Sathyendranath, S.; Moore, R. M.; Kelley, DE
Partial pressure of CO sub(2) is a nonlinear function of several seawater properties. Due to the nonlinearity in this relationship, the partial pressure of a uniform ocean would be different from that of a nonuniform ocean with the same bulk seawater properties. Assuming uniformity of seawater properties at some temporal and spatial scales in carbon models leads to systematic errors in partial pressure of CO sub(2). In this paper we evaluate the magnitude of these errors. We partition the Geochemical Ocean Sections Study and Transient Tracers in the Oceans data according to the horizontal structure of several box models from the literature. Our results suggest that assumption of uniformity at large scales leads to underestimation of global surface ocean partial pressure of CO sub(2) by at least 3-12 mu atm. Nonlinear effects also introduce systematic errors in the buffer factor estimated from bulk seawater properties. We find the standard deviation of partial pressure of CO sub(2) to be an indicator of the magnitude of the nonlinear effects. We discuss the implications of these errors for some conclusions drawn from carbon models. Biogeochemical processes, such as mixing, gas exchange, or biological activity, influence the distribution of the seawater properties. A shift in spatial or temporal patterns of these processes can modify the nonuniformity of the seawater properties and thus alter the partial pressure of the surface waters, even if the mean intensities of the processes remain constant.
Open Access
Carbon disulfide in the North Atlantic and Pacific Oceans
(American Geophysical Union, Washington, DC, 1999-03) Xie, Huixiang; Moore, Robert M.
No abstract available.
Open Access
Methyl iodide in the NW Atlantic: Spatial and seasonal variation
(2009-07) Wang, Lu; Moore, Robert M.; Cullen, John J.
While the global ocean is an important source of atmospheric methyl iodide (CH(3)I), the major producers of CH(3)I within the ocean remain unclear. During a seasonal study in the NW Atlantic, the relationship between CH(3)I and some characteristic phytoplankton pigments was examined in order to identify possible phytoplankton producers of CH(3)I. Although no characteristic pigments exhibited a strong positive correlation with CH(3)I, in the surface mixed layer, there was a weak correlation (R = 0.35, n = 70, p = 0.003) between the concentrations of CH(3)I and zeaxanthin, a pigment characteristic of cyanobacteria in the open ocean. In this study, a moderate correlation was observed between the surface mixed layer CH(3)I concentration and depth-averaged daily radiant exposure (R = 0.61, n = 15, p = 0.02), which indicates a positive influence of solar radiation on CH(3)I production. However, the results from this study do not conclusively show whether the influence was exerted through photochemistry or other pathways. A positive correlation between the CH(3)I concentration and sea surface temperature was also observed (R = 0.61, n = 79, p
Open Access
Production of chlorinated hydrocarbons and methyl iodide by the red microalga Porphyridium purpureum
(1999-05) Scarratt, MG; Moore, RM
Two experiments were performed using axenic batch cultures of the red microalga Porphyridium purpureum. The cultures were grown in sealed 5-liter glass vessels under a high-purity artificial atmosphere and analyzed for the production of several halocarbons, including chloroform (CHCl(3)), methylene chloride (CH(2)Cl(2)), methyl iodide (CH(3)I), trichloroethylene (C(2)HCl(3)), and tetrachloroethylene (C(2)CL(4)). Two cultures and a control were used in each experiment. The first experiment followed the system for 17 d at low Light intensity (20 mu mol quanta m(-2) s(-1)), while the second was comprised of 7 d at low light followed by 24 h at high light intensity (800 mu mol quanta m(-2) s(-1)). In both experiments, only chloroform and methyl iodide were produced in measurable quantities. This is the first report of chloroform production in a microalgal species. The chlorophyll a (Chl a)-normalized production rate of chloroform in the various cultures ranged between 1.3 x 10(-7) and 7.8 x 10(-7) mol (g Chl a)(-1) d(-1) (15-93 mu g [g Chl a](-1) d(-1)). Chloroform production peaked during the logarithmic growth phase. Methyl iodide production ranged between 2.0 x 10(-7) and 1.2 x 10(-6) mol (g Chl a)(-1) d(-1) (28-170 mu g [g Chl a](-1) d(-1)). Exposure of the cultures to high irradiance (800 mu mol quanta m(-2) s(-1)) did not stimulate the production of any of the compounds. In contrast to an earlier published account involving this species of algae, the production of tri- and tetrachloroethylene was not detected in any of the cultures under either low or high irradiance.
Open Access
A new measurement of CO sub(2) eddy flux in the nearshore atmospheric surface layer
(1991) Smith, S. D.; Anderson, R. J.; Jones, E. P.; Desjardins, R. L.; Moore, R. M.; Hertzman, O.; Johnson, B. D.
Fluxes of CO sub(2) in the atmospheric surface layer have been measured at a shoreline site by the eddy correlation method using a new CO sub(2) sensor with greater sensitivity than the ones used in earlier studies. In this experiment, preliminary to more extensive measurements at an offshore site, 13 upward and downward fluxes were observed to respond to differences in pCO sub(2) between water and air. As in an earlier study, a negative correlation of CO sub(2) flux was found with hourly change in wind speed.
Open Access
Dissolved organic phosphorus concentrations in the northeast subarctic Pacific Ocean
(1992) Ridal, J. J.; Moore, R. M.
Shipboard determinations of dissolved organic P (DOP) concentrations were made for NE subarctic Pacific Ocean samples with three different oxidation-hydrolysis methods: UV irradiation, acid persulfate digestion, and a rigorous method that combines the UV and persulfate treatments (combination method). The UV technique was 71 plus or minus 9% and the persulfate technique 83 plus or minus 9% efficient relative to the combination method for these coastal and open-ocean surface samples. Combination method results indicate that levels of DOP in the mixed layer of the NE Pacific during August and September ranged from 0.17 to 0.38 mu m. These values are comparable to those found for the NW Atlantic in a previous study with similar methodology. A significant inverse correlation (r super(2) = 0.76) was found between DOP, measured by the combination method, and apparent oxygen utilization. Analysis of a small number of samples by crossflow ultrafiltration showed that 75-85% of DOP in surface seawater was comprised of 10,000 NMW) fractions, which formed 33-100% of the total DOP in these waters.
Open Access
An isotopic labeling method for determining production of volatile organohalogens by marine microalgae
(2000-12) Murphy, Cormac D.; Moore, Robert M.; White, Robert L.
An isotopic method has been developed to establish the biological production of volatile organohalogens. The marine microalgae Porphyridium purpureum and Dunaliella tertiolecta were grown in seawater medium containing NaH13CO3, and volatile organohalogens were extracted and analyzed by gas chromatography-mass spectrometry (GC-MS). Isotopically labeled methyl halides were formed in each microalgal culture, and the 13CHCl3 found in the P. purpureum culture confirmed the production of chloroform reported by Scarratt and Moore (Limnol. Oceanogr. 1999. 44: 703-707). No incorporation of 13C into dichloromethane was observed, even though slightly increased CH2Cl2 concentrations were detected in both algal cultures at the end of the incubation period.
Open Access
Aerobic hydrogen production and dinitrogen fixation in the marine cyanobacterium Trichodesmium erythraeum IMS101
(2008-11) Punshon, Stephen; Moore, Robert M.
Rates of hydrogen production and acetylene reduction were measured in aerobic cultures of the marine cyanobacterium Trichodesmium erythraeum IMS101 grown in a supplemented seawater medium low in combined inorganic nitrogen. Both hydrogen production and acetylene reduction conformed to a circadian pattern with maximum activity in the afternoon. Normalized hydrogen production rates ranged from 0.06 to 0.71 nmol H-2 mu g chlorophyll a (Chl a)(-1) h(-1), while nitrogen fixation rates, calculated using an assumed ratio of 4 mol acetylene to 1 mol dinitrogen, ranged from 0.12 to 4.71 nmol N-2 Chl a(-1) h(-1). Yields of hydrogen from nitrogen fixation were in the range 0.15-0.48 mol H-2 evolved per mol N2 reduced. A comparatively low net rate of H2 uptake was observed in one culture during the dark period (-0.01 nmol H-2 mu g Chl a(-1) h(-1)). These measurements suggest that T. erythraeum is potentially a net source of hydrogen to the low-latitude surface ocean.
Open Access
Measurements of methyl chloride in the Northwest Atlantic
(American Geophysical Union, 1994-04) Tait, V. K.; Moore, R. M.; Tokarczyk, R.
Methyl chloride was measured directly in seawater using a purge and trap system and gas chromatography with electron capture detection. The results indicate that surface waters of the northwest Atlantic are a source of methyl chloride to the atmosphere during late spring/early summer. The average surface concentration was 271 pM ( sigma = 68 pM), supersaturated with respect to an assumed tropospheric boundary layer mixing ratio of 0.7 ppbv. Elevated concentrations were observed throughout the region in waters above the seasonal thermocline. Near-surface maxima of differing thickness and intensity were also seen within this upper layer. Broad maxima within the 200-800m depth range were associated with water masses more recently subducted from the surface than the surrounding main thermocline waters. Coastal inputs of methyl chloride appear not to be an important source in the area of study. Although there is some indication of elevated concentrations associated with higher phytoplankton activity in shelf edge regions, the picture concerning phytoplankton production of methyl chloride is still unclear. Further work is required to look at direct and indirect mechanisms by which phytoplankton may influence the distribution of methyl chloride in the oceans. The global ocean-to-atmosphere flux estimated from this data set, 3.3-4.8 x 10 super(10) mol CH sub(3)Cl/yr (1.7-2.4 x 10 super(12) g CH sub(3)Cl/yr) suggests that the oceans may contribute a smaller flux of methyl chloride to the atmosphere than previously thought.
Open Access
Trichloroethylene and tetrachlorethylene in Atlantic waters
(American Geophysical Union, Washington, DC, 2001-11) Moore, Robert M.
No abstract available.
Open Access
Photochemical Production of Methyl-Iodide in Seawater
(1994-08) MOORE, RM; ZAFIRIOU, OC
It is generally accepted that methyl iodide is a major contributor to the flux of iodine from the ocean to the atmosphere, but its sources in the ocean are largely unknown, an exception being production by certain species of coastal macrophytic algae. Preliminary results reported here indicate production of methyl iodide in filtered seawater that has been irradiated with either sunlight or an artificial light source having a spectral output closely approximating to sunlight at sea level. The production was enhanced when the water samples were deoxygenated and by the addition of iodide to this water. The results appear to be consistent with a mechanism involving reaction between photochemically produced methyl radicals and iodine atoms. It is estimated that the process is capable of making a significant contribution to global iodine fluxes.
Open Access
Bromoperoxidase and iodoperoxidase enzymes and production of halogenated methanes in marine diatom cultures
(1996-09) Moore, RM; Webb, M.; Tokarczyk, R.; Wever, R.
Halogenated methanes produced in the oceans are important as carriers of chlorine, bromine, and iodine into the atmosphere. There they play roles in the regulation of ozone in the stratosphere and perhaps in the Arctic troposphere at polar sunrise. While the mechanisms for the production of some polyhalogenated compounds by marine macrophytes have previously been substantially elucidated, the same has not been true in the case of marine phytoplankton. We describe laboratory experiments on the production of various brominated and iodinated compounds in cultures of marine diatoms, obtained from the Provasoli-Guillard Center for Culture of Marine Phytoplankton collections (Bigelow Laboratory for Ocean Sciences, Maim, USA; CCMP). Species examined included Nitzschia sp. (CCMP 580), Nitzschia arctica, Porosira glacialis, and two Navicula sp. (CCMP 545 and 546). A suite of brominated compounds, notably bromoform and dibromomethane, is produced by the Nitzschia and Porosira species. Nitzschia sp.(CCMP 580) was grown In sufficient quantities to allow the identification of a bromoperoxidase enzyme, which is assumed to be responsible not only for the CHBr3 and CH2Br2 production but also for CH2I2 which was measured in those cultures. Chloroiodomethane was produced, either directly by the algae or by a photochemical reaction of CH2I2. One Navicula species (CCMP 545), found to produce CH2I2 and CH2ClI, was shown to possess an iodoperoxidase. Bromoform and dibromomethane were not detected in cultures of this species. Other compounds produced in certain of these non axenic cultures included methyl and ethyl iodide, and bromoiodomethane.
Open Access
Ocean-atmosphere exchange of methyl bromide: NW Atlantic and Pacific Ocean studies
(1998-07) Groszko, W.; Moore, RM
Measurements of methyl bromide partial pressure and concentration in surface water and air samples in the NW Atlantic Ocean in July 1995 and the Pacific Ocean in October 1995 are presented, Mean atmospheric mixing ratios were found to be 11.4 +/- 0.7 parts per trillion by volume (pptv) for the northern hemisphere and 10.0 +/- 0.5 pptv for the southern hemisphere. Cold, high-latitude water in the Labrador Sea and warm water in the central Pacific were undersaturated in methyl bromide, and some supersaturated waters were found in the Gulf Stream in the Atlantic and around 35 degrees S in the South Pacific. By a simple extrapolation, the global ocean is estimated to be a net sink of 10 (3 to 13) Gg of methyl bromide per year from the atmosphere, with the range including a factor of 2 uncertainty in the piston velocity.
Open Access
Methyl iodide distribution in the ocean and fluxes to the atmosphere
(1999-05) Moore, RM; Groszko, W.
Methyl iodide concentrations have been measured in air samples, surface, and subsurface waters of the NW Atlantic, NE Atlantic, and Pacific Oceans. They are shown to be substantially oversaturated in all surface waters. Our best estimate of methyl iodide flux from the ocean to the atmosphere is 0.9 - 2.5 x 10(9) mol yr(-1), but further substantial and unquantifiable uncertainities exist because of the limited spatial and temporal data on which this flux estimate is based. Pronounced subsurface maxima in methyl iodide concentrations seen in the Pacific Ocean and the Sargasso Sea are thought to result from production and accumulation of the gas in the relatively poorly ventilated waters beneath the surface mixed layer. Our calculations suggest that latitudinal variations in methyl iodide concentrations in the Pacific Ocean are partly controlled by temperature-dependent chemical loss.
Open Access
Geochemical Profiles in the Central Arctic Ocean - their Relation to Freezing and Shallow Circulation
(1983) MOORE, RM; LOWINGS, MG; TAN, FC
No abstract available.
Open Access
A relationship between heat transfer to sea ice and temperature-salinity properties of Arctic Ocean waters
(1988) Moore, R. M.; Wallace, DWR
It is demonstrated that the characteristic temperature-salinity relationship shown by thermocline waters of the Arctic Ocean can be reproduced using a simple model based on transfer of heat directly from these waters to sea ice. From this we deduce that there is direct sensible heat flux from waters of Atlantic origin to the ice cover, such interaction could play a major role in determining the physical properties of Arctic water masses.
Open Access
Dichloromethane in North Atlantic waters
(2004-09) Moore, RM
[1] Dichloromethane is an atmospheric trace gas that has a tropospheric lifetime on the order of 5 months and has major anthropogenic sources. Evidence has been presented for an oceanic source. This paper reports measurements of dichloromethane in waters of the North Atlantic and Labrador Sea that are interpreted as showing that the compound has a primarily atmospheric source and appears to persist for years to decades in the intermediate and deep ocean. These characteristics have the potential to yield apparent supersaturation of the gas in surface ocean waters which may be incorrectly interpreted as an oceanic source.

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