April 27th, 2003; Leg 5, Day #7
R/V Western Flyer
transited overnight to a basin in the northwest of the Gulf.
The unique topography
of the area helps create a warm, deep-water layer.
Today ROV Tiburon’s CTD sensor
measured temperatures of nearly 12
degrees Celsius at 800 meters depth. By this depth in Monterey Bay, the
water is a chilly 4 degrees C.
hydrographic properties provided Peter
Ed Peltzer a different
temperature regime in which to replicate their liquid carbon dioxide
dissolution experiments with Tiburon. The experiments use the
high-resolution video capabilities of MBARI’s ROVs and a specially
designed “bubble box” to image changes in gas samples as the ROV moves
vertically in the water column.
Past experiments using
this device on ROVs Ventana and Tiburon have yielded new
insights into the dissolution and ascent rate of greenhouse gases and gas
hydrates. These measurements are important for climate change models and
for predictions of how release of gas material in the deep ocean—for
example, by an underwater landslide that exposes a
gas hydrate field—may impact the upper ocean and atmosphere. In Monterey
Bay experiments, the cool water temperatures cause liquid carbon dioxide
droplets to form a hydrate “skin” which slows down the dissolution
rate. Brewer and Peltzer predicted that in warm water conditions, the
liquid carbon dioxide droplets would dissolve and rise more quickly.
Now the ship is heading south again to the Guaymas Basin, back to the transform fault area that we studied previously. The next two days will involve tests of the laser Raman spectrometer at a gas venting site. The ship transits have given us a chance to see new scenery, both day and night. Last night we saw an incredible display of bioluminescence in the water in front of the ship’s bow. Schools of fish of varying sizes could be discerned in vivid blue-green hue as they encountered the bioluminescent plankton in the surface waters.