[SIO GP Seminars] FRIDAY: 3:15 PM: Bruce Luyendyk, UCSB

[Robin Matoza]

Geophysics Seminar Announcement-
Join us on Friday for this week's Geophysics Seminar.

This week, the seminar will by a joint IGPP-GSMCG seminar held at the  
usual IGPP time and location:

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Friday, November 17, 3:15 PM
   (refreshments served at 3:00 PM)
   Munk Conference Room

Bruce Luyendyk, Earth Science Dept., UCSB

Title: "Natural marine hydrocarbon seeps in the northern Santa  
Barbara Channel"

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ABSTRACT
Present day hydrocarbon seepage from reservoirs beneath the world’s  
continental margins discharge oil and natural gas into the ocean and  
atmosphere.  Marine seeps have received increasing interest in part  
because they indicate the presence of hydrocarbon deposits and  
because they are sources of regional ocean and air pollution,  
including oil slicks, dissolved oil and hydrocarbon gas in the ocean,  
floating oil and beach tar, and methane and reactive organic gases  
discharged into the atmosphere.
On the northern continental shelf of the Santa Barbara Channel,  
California the Coal Oil Point marine seep field discharges at least  
100,000 m3 of gas into the atmosphere and 100 bbl of oil into the  
ocean each day. These seepage rates were determined from a  
combination of calibrated sonar surveys and in situ gas and oil  
capture at the sea surface. At the sea surface the gas is between 60  
and 80 percent methane. Oceanographic observations at Coal Oil Point  
show that up to half the volume of methane vented at the sea floor  
dissolves in the water column during transport of hydrocarbon gas  
bubbles 20 to 70 meters to the ocean surface; the remaining half  
enters the atmosphere. The Coal Oil Point seep field emits daily at  
least 40 metric tons of methane to the atmosphere.  d13C values are  
between –40 o/oo and –45 o/oo suggesting that the methane is  
thermogenic in origin.

Gas flux from the Coal Oil Point seep field can be used to estimate  
the total contribution of marine seeps to the global atmospheric  
methane budget.  The estimates, which range between 18 and 48 Tg/yr,  
almost 10% of the world’s budget, were constructed by assuming that  
the Coal Oil Point field is one of the larger or largest marine  
sources of methane in the world. 
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