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! Provide direct in situ measurements of chemical flux with enhanced temporal resolution

ISUS In Situ Ultraviolet Spectrometer Unique UV absorption spectrum allows direct measurement Deconvolution of overlapping peaks enables determination of ion concentrations Sample absorbance spectrum is sum of all absorbing species HS - NO 3 - & Br - are the primary UV absorbers in seawater! Change in spectrum is due to change in ion concentrations

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

Recirc Pump ISUS HS- Flush Pump pH CTD Sediment Recirc Pump ISUS HS - CTD pH Flush Pump HS - Tube of 100  m mesh Deployment Recirculation Measure Wait Recirculation Measure Flush

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

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

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

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

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

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

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

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

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