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  • 2000-2004  (43)
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  • 1
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    Partial pressure and air–sea flux of CO2 in the Northeast Atlantic during September 1995 (2001)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 48 (14-15). pp. 3179-3189.
    Details
    Publication Date: 2020-08-05
    Description: Previous work has shown that during early summer, the partial pressure of CO2 (pCO(2)) in surface waters north of about 45 degreesN in the Atlantic exhibits widespread undersaturation. In many areas. this follows after a "spring bloom" of phytoplankton, at which time, nutrient concentrations and pCO(2) decrease sharply from their winter surface values. As part of OMEX I, the late summer distribution of surface water pCO(2) was surveyed in the northeastern Atlantic on cruises of R/V Poseidon and R/V Belgica in 1995. The pattern of the surface distribution of the sea-air pCO(2) difference (Delta pCO(2)) measured on these ship surveys was generally iri accord with that observed in this area in early to mid-summer of 1981. The greatest CO2 undersaturation (-95 mu atm) during our surveys was observed near the west coast of Iceland, with Delta pCO(2) increasing to about -60 mu atm away from the coast. In shelf waters south of Ireland, the pCO(2) was relatively higher than in surface waters of the open ocean adjacent to the Celtic Shelf margin, but the Celtic Shelf waters were still undersaturated relative to the atmospheric CO2 concentration. Because of the variation of wind speed, the synoptic distribution of air-sea CO2 flux, derived from the transfer velocity and Delta pCO(2), does not resemble the distribution of Delta pCO(2) itself. The sharp increase in wind speed at about 53 degreesN, 20 degreesW during the R/V Poseidon survey produces an order of magnitude rise in the estimated air-sea flux of CO2, to a level of about 10-14 mol m(-2) a(-1). The overall synoptic picture appears to be one of moving centers of higher air-sea fluxes that occur where storms pass over regions of surface water pCO(2) undersaturation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(01)00036-4
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Methane cycling in the Weddell Sea determined via stable isotope ratios and CFC-11 (2004)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 18 (2). GB2012.
    Details
    Publication Date: 2018-03-16
    Description: The physical, chemical/biological processes that control the methane dynamics in the Weddell Sea are revealed by the distributions of methane (CH4), its stable carbon isotope ratio, δ13C-CH4, and the conservative transient tracer, chlorofluorocarbon-11 (CFC-11, CCl3F). In general, a nearly linear correlation between CH4 and CFC-11 concentrations was observed. Air-sea exchange is the major source of methane to this region, and the distribution of methane is controlled mainly by mixing between surface water and methane-poor Warm Deep Water. A significant influence of methane oxidation over the predominant two end-member mixing was only found in the Weddell Sea Bottom Water (WSBW) of the deep central Weddell Basin, where the turnover time of methane appears to be about 20 years. Mixing also controls most of the δ13C-CH4 distribution, but lighter than expected carbon isotopic ratios occur in the deep WSBW of the basin. From box model simulations, it appears that this “anomaly” is due to methane oxidation with a low kinetic isotope fractionation of about 1.004. The surface waters in the Weddell Sea and the Antarctic Circumpolar Current showed a general methane undersaturation of 6 to 25% with respect to the atmospheric mixing ratio. From this undersaturation and model-derived air-sea exchange rates, we estimate a net uptake of CH4 of roughly −0.5 μmol m−2 d−1 during austral autumn.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2003GB002151
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    The emission of methane from mud diapirs offshore Nicaragua and Costa Rica (2003)
    In:  [Talk] In: EGS-AGU-EUG Joint Assembly 2003, 06.-11.04.2003, Nice, France .
    Details
    Publication Date: 2020-05-26
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 4
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    Experimental determination of the fate of rising CO2 droplets in seawater (2002)
    American Chemistry Society
    In:  Environmental Science & Technology, 26 . pp. 5441-5446.
    Details
    Publication Date: 2017-03-07
    Description: Direct oceanic disposal of fossil fuel CO2 is being considered as a possible means to moderate the growth rate of CO2 in the atmosphere. We have measured the rise rate and dissolution rate of freely released CO2 droplets in the open ocean to provide fundamental data for carbon sequestration options. A small amount of liquid CO2 was released at 800 m, at 4.4 degrees C, and the rising droplet stream was imaged with a HDTV camera carried on a remotely operated vehicle. The initial rise rate for 0.9-cm diameter droplets was 10 cm/s at 800 m, and the dissolution rate was 3.0 micromol cm(-2) s(-1). While visual contact was maintained for 1 h and over a 400 m ascent, 90% of the mass loss occurred within 30 min over a 200 m ascent above the release point. Images of droplets crossing the liquid-gas-phase boundary showed formation of a gas head, pinching off of a liquid tail, and rapid gas bubble separation and dissolution.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1021/es025909r
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    An experiment demonstrating that marine slumping is a mechanism to transfer methane from seafloor gas-hydrate deposits into the upper ocean and atmosphere (2003)
    Springer
    In:  Geo-Marine Letters, 22 (4). pp. 198-203.
    Details
    Publication Date: 2017-05-24
    Description: The scientific community is engaged in a lively debate over whether and how venting from the gas-hydrate reservoir and the Earth’s climate is connected. The various scenarios which have been proposed are based on the following assumptions: the inventory of methane gas-hydrate deposits is locally enormous, the stability of marine gas-hydrate deposits can easily be perturbed by temperature and pressure changes, enough methane can be released from these deposits to contribute adequate volumes of this isotopically distinct greenhouse gas to alter the composition of oceanic or atmospheric methane reservoirs, and the mechanisms exist for the transfer of methane from deeper geologic reservoirs to the ocean and/or atmosphere. However, some potential transfer mechanisms have been difficult to evaluate. Here, we consider the possibility of marine slumping as a mechanism to transfer methane carbon from gas hydrates within the seafloor into the ocean and atmosphere. Our analyses and field experiments indicate that large slumps could release volumetrically significant quantities of solid gas hydrates which would float upwards in the water column. Large pieces of gas hydrate would reach the upper layers of the ocean before decomposing, and some of the methane would be directly injected into the atmosphere.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00367-002-0113-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Measurements of the fate of gas hydrates during transit through the ocean water column (2002)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 29 (22). p. 2081.
    Details
    Publication Date: 2018-02-20
    Description: We report on controlled experiments to document the fate of naturally occurring methane hydrate released from the sea floor (780 m, 4.3°C) by remotely operated vehicle (ROV) disturbance. Images of buoyant sediment-coated solids rising (∼0.24 m/s) from the debris cloud, soon revealed clear crystals of methane hydrate as surficial material sloughed off. Decomposition and visible degassing began close to the predicted phase boundary, yet pieces initially of ∼0.10 m size easily survived transit to the surface ocean. Smaller pieces dissolved or dissociated before reaching the surface ocean, yet effectively transferred gas to depths where atmospheric ventilation times are short relative to methane oxidation rates.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2002GL014727
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Gas hydrate dissociation triggering mass wasting on the Costa Rica continental margin (2004)
    In:  [Poster] In: AGU Fall Meeting 2004, 13.-17.12.2004, San Francisco, USA .
    Details
    Publication Date: 2012-09-25
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 8
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    Noble gases and radiocarbon in natural gases (2002)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 29 (10). p. 1423.
    Details
    Publication Date: 2018-03-21
    Description: In samples of pure natural gas hydrates from Hydrate Ridge, Cascadia Margin, virtually no helium and neon components are present providing evidence that the light noble gases are not incorporated into the structure of natural methane hydrates. In contrast, the hydrates contain significant amounts of argon, krypton and xenon. These gases show a distinct fractionation pattern, with the heavier ones preferentially incorporated into the gas hydrate structure. The hydrate methane is devoid of 14C indicating that there is no contribution of a recent (14C-active) organic carbon reservoir to the hydrate carbon pool. On the basis of the δ13C and δ2H signature, it appears that microbial CO2-reduction is the dominant CH4 production pathway.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2001GL014013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Dissolution rates of pure methane hydrate and carbon-dioxide hydrate in undersaturated seawater at 1000-m depth (2004)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 68 (2). pp. 285-292.
    Details
    Publication Date: 2017-09-27
    Description: To help constrain models involving the chemical stability and lifetime of gas clathrate hydrates exposed at the seafloor, dissolution rates of pure methane and carbon-dioxide hydrates were measured directly on the seafloor within the nominal pressure-temperature (P/T) range of the gas hydrate stability zone. Other natural boundary conditions included variable flow velocity and undersaturation of seawater with respect to the hydrate-forming species. Four cylindrical test specimens of pure, polycrystalline CH4 and CO2 hydrate were grown and fully compacted in the laboratory, then transferred by pressure vessel to the seafloor (1028 m depth), exposed to the deep ocean environment, and monitored for 27 hours using time-lapse and HDTV cameras. Video analysis showed diameter reductions at rates between 0.94 and 1.20 μm/s and between 9.0 and 10.6 · 10−2 μm/s for the CO2 and CH4 hydrates, respectively, corresponding to dissolution rates of 4.15 ± 0.5 mmol CO2/m2s and 0.37 ± 0.03 mmol CH4/m2s. The ratio of the dissolution rates fits a diffusive boundary layer model that incorporates relative gas solubilities appropriate to the field site, which implies that the kinetics of the dissolution of both hydrates is diffusion-controlled. The observed dissolution of several mm (CH4) or tens of mm (CO2) of hydrate from the sample surfaces per day has major implications for estimating the longevity of natural gas hydrate outcrops as well as for the possible roles of CO2 hydrates in marine carbon sequestration strategies.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.gca.2003.07.001
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Methane and pCO2 in the Kuroshio and the South China Sea during maximum summer surface temperatures (2001)
    Elsevier
    In:  Marine Chemistry, 75 . pp. 89-108.
    Details
    Publication Date: 2017-08-22
    Description: The methane concentration and pCO2 in surface waters and the overlying marine air were continuously surveyed along the pathway of the Kuroshio, from the eastern coast of Honshu to Taiwan, and then across the eastern part of the East China and South China Seas in September of 1994. Off Honshu, the CH4 content was controlled by the confluence of the relatively CH4-poor waters of the Kuroshio and the Oyashio and the CH4-rich Tsugaru Warm Current, the latter carrying water into the Pacific Ocean with a methane content more than twice the equilibrium value with the atmospheric CH4 partial pressure. Along the Kuroshio, the surface water was supersaturated in methane with respect to the atmosphere by 10–15% and appears considerably enriched relative to open Pacific surface waters at same latitudes. The northeastern part of the South China Sea, part of the deep basin of this marginal sea, showed CH4 concentrations similar to those found in open-ocean waters. In contrast, highly variable oversaturations up to 700% were observed along the northwestern coast of Borneo, most probably related to known seepage from oil and gas deposits in this area. The pCO2 of surface water was higher than the atmospheric pCO2 throughout the area surveyed. However, the ΔpCO2 of the surface waters varied from close to 0 to more than 60 μatm. The observed oversaturation in areas influenced by the Kuroshio confirm that, during a short period in late summer, the surface waters of this current between Taiwan and Japan act as a moderate source for atmospheric CO2.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0304-4203(01)00026-3
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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