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Sulfide flux from cold seeps using an ISUS chemical sensor

Sulfide flux from cold seeps using an ISUS chemical sensor. Josh Plant Ken Johnson Luke Coletti Steve Fitzwater Carole Sakamoto. Motivation. Demonstrate optical measurements of HS - at depth over extended periods Chemical flux at cold seeps difficult to measure!

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Sulfide flux from cold seeps using an ISUS chemical sensor

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  1. Sulfide flux from cold seeps using an ISUS chemical sensor Josh Plant Ken Johnson Luke Coletti Steve Fitzwater Carole Sakamoto

  2. Motivation • Demonstrate optical measurements of HS- at depth over extended periods • Chemical flux at cold seeps difficult to measure! • Provide direct in situ measurements of chemical flux with enhanced temporal resolution

  3. ISUS In Situ Ultraviolet Spectrometer HS- NO3- & Br- are the primary UV absorbers in seawater! Unique UV absorption spectrum allows direct measurement Change in spectrum is due to change in ion concentrations Sample absorbance spectrum is sum of all absorbing species Deconvolution of overlapping peaks enables determination of ion concentrations

  4. HS- is a strong UV absorber between 230 – 300 nm Cold seep fluids high in HS- Spectral deconvolution uses multiple wavelengths Shift fit window to measure higher concentrations

  5. Flush Wait Recirculation Measure Measure Deployment Recirculation pH pH Recirc Pump Recirc Pump Flush Pump FlushPump ISUS HS- ISUS HS- CTD CTD Tube of 100 mm mesh HS- Sediment

  6. Cseawater H CChamber Cfluid HS- benthic flux measurements Chamber concentration proportional to difference between seawater and seep fluid Cchamber = Cfluid( 1–e-kt) K = Fluid velocity / chamber height Flux = fluid velocity * Cfluid

  7. Extravert Cliff Seeps Most active seeps found in Monterey Bay Very focused flow Support chemosynthetic communities 960 meter depth Barren Zone Clams 2m x 1m Bacterial Mat

  8. July 2006 Daily Velocity Calculations Chamber flushed daily Sampled hourly Cfluid 2 – 4 mM HS- Velocity 5 – 20 m day-1

  9. July 2006 Flux Chamber data Seep fills chamber in less than an hour! Fluid Velocity an underestimate in high flow cases Temperature and HS- correlated

  10. September 2006 Flux Chamber data Flush every 30 minutes 2 samples per cycle, Time 1 and Time 2 Chamber concentration related to tides

  11. September 2006 Velocity Calculations Strong tidal signal - highest flow at low tide! Velocity similar to July data 5 to 30 m day-1 30 to 180 Liters day-1 through 8cm diameter chamber

  12. Temperature & HS- highly correlated Relationship similar on July & Sept deployments 3 degrees above ambient Warm sulfide rich source – a warm seep!!

  13. Conclusions ISUS effective for high resolution HS- measurements Fluid flow 100x faster than previous measurements in area Enabled resolution of velocity response to tides System adaptable

  14. Acknowledgements David and Lucile Packard Foundation R / V Point Lobos crew and Ventana pilots Shannnon Boedecker & Annette Gough

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