Oceanic Trace Gas Measurements by Membrane Inlet Mass Spectrometry (MIMS) A Sensitive, New Age Approach

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1 Oceanic Trace Gas Measurements by Membrane Inlet Mass Spectrometry (MIMS) A Sensitive, New Age Approach Philippe Tortell Dept. of Earth and Ocean Sciences & Dept. of Botany University of British Columbia Vancouver BC, Canada

2 With thanks to. University of British Columbia Nina Nemcek, Chris Payne, Anjali Nayar, Cheryl Martin Institute of Ocean Sciences; Fisheries and Oceans Canada Frank Whitney, Marie Robert, Darren Tuele, Doug Anderson University of California, Santa Cruz Ken Bruland, Geoffrey Smith, Raphe Kudela University of Delaware David Hutchins, Clinton Hare University of Charleston Giacomo DiTullio, Sarah Riseman, Peter Lee Hiden Analytical Mark Buckley, Adrian Jessop

3 Outline Motivation: Why oceanic trace gases? Instrument development and assessment Field measurements in the Subarctic Pacific Ocean / Bering Sea: Spatial distribution of CO 2, O 2, DMS, and N 2. Future directions

4 Greenhouse gases co-vary with temperature over glacial cycles Petit et al. (1997) Nature

5 Anthropogenic Perturbations of Greenhouse Gases IPCC 2001

6 Dimethylsulfide (DMS) Increases Energy Reflectance in the Atmosphere Marine microorganisms are a major Source of DMS to the atmosphere Foodweb Processes Microbial Activity Grazing Watson and Liss (1998) Trans. Roy Soc. London

7 Dimethylsulfide fluctuations over the last glacial cycle [DMS] Temperature Lerand et al. (1991) Nature 350:

8 Oceanic processes are critically important in the cycling of climatologically active trace gases Additionally, gas measurements reveal a wealth of information about how the oceans function

9 Gases as Biogeochemical Tracers CO 2 + H 2 O CH 2 O + O 2 Photosynthesis CO 2 / O 2 : Photosynthesis / Respiration N 2 : Denitrification N 2 O: Denitrification, Nitrification H 2 S: SO 4 2- oxidation CH 4 : Methanogenesis, Methane oxidation Gases as Physical Tracers sinking Respiration CFC s, / He: Ocean circulation N 2 / Ar / O 2 : Bubble injection CH 2 O + O 2 CO 2 + H 2 O

10 Gas Measurement in seawater Many highly sensitive, accurate, and precise techniques exist: Gas Chromatography (N 2, Ar, CH 4, N 2 O, DMS etc.) Infrared Absorbance (IR) / coulometry (CO 2 ), polarography (O 2 ) Isotope Ratio Mass Spectrometry (N 2, O 2, Ar, CO 2, N 2 O etc.) Some of these methods are specific for single gases, while others are costly, laborious, and not well suited to in-situ measurements at sea. Looking for a single method to easily/rapidly measure many gases simultaneously in real-time. Membrane Inlet Mass Spectrometry Developed in the late 60 s, subsequently applied to a variety of environmental problems: (volatile organics, soil /sediment gas fluxes). Oceanographic work has been largely restricted to laboratory analysis of major gases (N 2, O 2, CO 2, Ar) in coastal waters. Application to ship-board open ocean studies

11 Instrumentation I: Hiden Analytical Triple filter quadropole mass spectrometer controller detectors mass filter ion source filament RF field Generator Gas In

12 sample out Instrumentation II: Large Area Membrane Inlet System sample in Silicone membrane vacuum

13 Flow Rate Effects O 2 / Ar CO 2 / Ar 1.4 N 2 / Ar Relative Signal Argon Carbon Dioxide Oxygen Nitrogen Flow Rate (ml min -1 ) Flow Rate (ml min -1 ) Temperature effects..

14 Field Trials: Summer 2003 Trial 1: Subarctic Pacific Ocean (May / June 2003): Coastal Oceanic transect (Line P + ARGO Stations). Initial field testing Trial 2: Bering Sea (Aug. / Sept. 2003): Cross-shelf transects. Underway measurement of O 2 / CO 2 / DMS concentrations across a strong productivity gradient

15 CCGS John P. Tully

16 Instrument Calibration Repeat Calibrations over ~ 3 week period at sea Ion current m/z 44 (10-8 Torr) Ion Current m/z 62 (10-12 Torr) PCO 2 (µatm) Dimethylsulfide (nmol L -1 ) Current atmospheric CO 2 ~ 375 µatm

17 Oceanic DMS Concentrations Kettle et al GBC # of Observations DMS (nmol L -1 )

18 0 100 Mass Spec O 2 / Ar Method Validation I Oxygen Depth Profiles: Subarctic Pacific: June All stations Depth (m) Winkler O 2 (ml L -1 ) Station ARGO Mass Spec O 2 / Ar Winkler O 2 (ml L -1 )

19 Method Validation II DMS Depth Profile; Bering Sea Aug Depth (m) Mass Spec GC GC Data from Peter Lee Univ. of Charleston Dimethylsulfide (nmol L -1 )

20 0 Stn Argo4 O 2 / Ar Typical Depth Profiles Subarctic Pacific All Sations 16 Depth (m) 1000 O 2 / Ar CO CO 2 (m/z 44 Torr)

21 DMS Profiles Depth (m) greater stratification DMS (nmol L -1 ) P4 P8 Argo5 Argo σ t Density

22 Application of MIMS in denitrification studies Denitrification: The use of NO 3- as an alternative electron acceptor in respiration by heterotrophic bacteria. NO 3- NO 2- NO N 2 O N 2 Major loss term for fixed N 2 in the biosphere (only occurs under low O 2 )

23 Denitrification in Saanich Inlet Mass Spec O 2 : Ar Mass Spec N 2 : Ar Depth (m) Intense bacterial respiration depletes oxygen N 2 : Ar NO 3- deficit NO 3-16 * P Winkler O 2 (ml L -1 ) Nitrate (µm) * [Phosphate] (µm) Redfield N

24 Underway Data Collection

25 Continuous Flow-Through Operation waste line From seawater line Silicone membrane vacuum

26 Underway Measurements Queen Charlotte Strait June e-8 3.0e-8 2.5e-8 2.0e-8 1.5e Julian Day DMS (nmol L -1 ) 0 CO2 (m/z 44 Torr) PCO2 (µatm) O2 / Ar Chla (µg L -1 ) 2 20 mass spec equilibrator

27 Field Trial #2 Bering Sea Aug. Sept. 2003

28 R/V Kilo Moana University of Hawaii

29 The Bering Sea is separated from the N. Pacific by the Aleutian Island arc Bering Sea Black dots = earthquake epicenters

30 Bering Sea Bathymetry Western Gyre Shelf

31 Chlorophyll a Distribution (SeaWiFS) Spring 2003 Western Gyre Green Belt Inner Shelf

32 Western Gyre Shelf Break

33 Large CO 2 Gradients in the Bering Sea Codispoti et al Nature 296: p PCO 2 (µatm) bloom progression 150

34 Cruise Track

35 Nitrate Concentration High production N/Si/P limited Low production; Fe-limited

36 Chlorophyll Fluorescence The Green Belt

37 Nitrate (µm) 15 Bering Sea Transect PCO2 (µatm) Green Belt O2 / Ar Salinity (ppt) Dimethylsulfide (nm) Temp C Gyre Longitude (Deg. E) Shelf

38 Argon / Temperature Signal: Argon (m/z 40 Torr) Transect 2 2.0e-7 1.9e-7 1.8e-7 1.7e Temperature (C) Longitude (Deg. E)

39 Sept. 1 Transect Longitude (Deg. E) Temperature Chla flour. Dimethylsulfide (nm) O2 / Argon CO2 (µatm)

40 Sept. 1 Gas Relationship O 2 / Ar DMS (nmol L -1 ) PCO 2 (µatm) PCO 2 (µatm)

41 DMS concentrations affected by a number of ecological factors Foodweb Processes Microbial Activity Grazing Watson and Liss (1998) Trans. Roy Soc. London

42 Taxonomic Variability in DMSP Production χ = 3.4 ± 4.5 χ = 44.1 ± 41.2 χ = 24.4 ± 11.4

43 220 Gas Distributions across The Green Belt CO 2 (µatm) O 2 / Ar DMS (nm) Salinity (ppt) Temperature Julian Day

44 Thus Far MIMS is a viable alternative to other methods Lower Precision but higher through put Application to traditional gas profiling with discrete samples Use for flow-through studies New scientific insight? As of yet, just powerful confirmation of what we know already..

45 Up next. Further method development: larger area membrane for higher sensitivity; In situ gas calibration system using mass flow controllers; enhanced pumping system to minimize flow disturbance. New Scientific Insights likely to come from: Systematic underway sampling / monitoring Distribution of DMS related to phytoplankton species composition and foodweb Structure Effects of CO 2 concentrations on phytoplankton physiology. Isotope studies of trace gas cycling. 15 N labeled NH 4+ and NO 3- additions look for 15 N 2 and 15 N 2 O production 34 S labeling of DMSP to look at DMS foodweb cycling 18 O 2 and 13 CO 2 labeling to measure primary production