Abstract:
We collected water samples from gas plumes and measured dissolved methane concentrations shipboard during a 2014 cruise to Green Canyon (GC185) and Mississippi Canyon (MC118) methane seeps to improve our understanding of bubble dissolution. Samples were collected by remotely operated vehicle in vertical profiles following bubble streams from the seafloor up to 200 m above bottom. Samples were also collected at constant depth, 100 m above bottom, in horizontal transects across a bubble plume. Water samples were analyzed shipboard for dissolved methane gas concentrations reported here. Gas phase samples were returned to shore for gas composition analysis. These samples were co-located with measurements of bubble physical properties derived from high-speed videography reported elsewhere.
Suggested Citation:
Breier, Chip. 2015. Methane Concentrations in Gas Plumes from Mississippi and Green Canyon Seeps, July 2014. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7N014GM
Data Parameters and Units:
Dissolved methane concentrations are reported in umol per liter and were measured by gas chromatography. GISRcruise: cruise number of the GISR consortium project; OETsamplename: the OET designation for this sample event; sample: the sample names designated by Breier and Seewald in their sample naming system; purpose: the purpose the sample was collected for; dive: Hercules dive number; yyyy: year of event in UTC; mon: month of event in UTC; day: day of event in UTC; starthr: start hour of event in UTC; startmin: start minute of event in UTC; stophr: stop hour of event in UTC; stopmin: stop minute of event in UTC; depth: depth of event in meters; temp: water temperature in Celsius measured by Hercules CTD, note not at the point of sample collection; ox: dissolved oxygen in umol per liter measured by Hercules, optode: note not at the point of sample collection; sal: salinity measured by Hercules CTD, note not at the point of sample collection; latd: ROV lat degrees; latmin: ROV lat minutes; NS: ROV northern or southern hemisphere; latdd: ROV latitude decimal degrees; lond: ROV longitude degrees; lonm: ROV longitude minutes; EW: ROV east or west from reference longitude; londd: ROV longitude decimal degrees; SUPR: logical 1 if suspended particulate rosette sampler sample type use for collecting samples for dissolved methane analysis, 0 otherwise; IGT : Logical 1 if Isobaric gas tight sampler was used for collecting gas samples for gas composition analysis, 0 otherwise; description: description of sampling event; type: SUPR or IGT; port: port number of sampler, SUPR has 14 ports, IGT has two sample bottles; dmeth: dissolved methane concentration in umol per liter measured by gas chromatography; GCnitrogen: percent gas composition measured by gas chromatography; GCmethane: percent gas composition measured by gas chromatography; GCco2: percent gas composition measured by gas chromatography; GCethane: percent gas composition measured by gas chromatography; GCpropane: percent gas composition measured by gas chromatography; GCisobutane: percent gas composition measured by gas chromatography; GCnbutane: percent gas composition measured by gas chromatography; GCneopentane: percent gas composition measured by gas chromatography; GCisopentane: percent gas composition measured by gas chromatography; GCnpentane: percent gas composition measured by gas chromatography; GCtotal: sum of measured gas percentages. Mississippi canyon: 28.85358, -88.48781; Green Canyon: 27.36981, -90.57096. Gas phase composition is reported in percent and was measured by gas chromatography.
Instruments:
Water samples were collected by remotely operated vehicle using two different precision sampling instruments: the SUPR sampling system for large volume samples (Breier et al. 2014) and isobaric gas tight samplers (Seewald et al. 2002). J.A. Breier, C.S. Sheik, D. Gomez-Ibanez, R.T. Sayre-McCord, R. Sanger, C. Rauch, M. Coleman, S.A. Bennett, B.R. Cron, M. Li, C.R. German, B.M. Toner, G.J. Dick, A large volume particulate and water multi-sampler with in situ preservation for microbial and biogeochemical studies, Deep Sea Research Part I: Oceanographic Research Papers, Volume 94, December 2014, Pages 195-206, ISSN 0967-0637, http://dx.doi.org/10.1016/j.dsr.2014.08.008. Jeffrey S. Seewald, Kenneth W. Doherty, Terence R. Hammar, Stephen P. Libera tore, A new gas-tight isobaric sampler for hydrothermal fluids, Deep Sea Research Part I: Oceanographic Research Papers, Volume 49, Issue 1, January 2002, Pages 189-196, ISSN 0967-0637, http://dx.doi.org/10.1016/S0967-0637(01)00046-2.
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