August 10 - August 17, 2006
ROV Dive 4: Time-Lapse Photography and the Carbon Dioxide Bath
Today’s serene weather and calm seas have enabled the Brewer group to immediately get back to work after yesterday’s hiatus. Early this morning, we were able to deploy the cylindrical underwater elevator frame/platform to deliver our time-lapse camera to the ocean bottom. Hydrate cores will be placed in a mesh container directly in front of the camera lens and allowed to dissociate over a period of two days.
By 9:30am, we reached the sea floor with the ROV, promptly set up the mesh cage, and cored two nearby hydrate samples: one from the higher oil-concentration region and the other from a purer hydrate area of the outcrop. Next, we began our carbon dioxide replacement experiment, where we hoped to use the Raman laser to observe carbon dioxide entering the hydrate molecular cage and expelling the original methane. To do so, we collected two additional pure hydrate cores and placed them in the Pyrex viewing chamber. Subsequently, we filled the open-bottom chamber with liquid carbon dioxide, which at this depth is less dense than seawater, and the whole chamber was sealed by setting it down on a steel plate on the elevator frame. The remainder of the day was spent collecting core samples from other sites around the canyon and comparing their compositions with the Raman laser. Finally, we used a heat flow probe to measure temperature gradients in one meter of sediment above the hydrate mounds. The values we received from the sensor, however, indicated that there was minimal heat transfer.
Tomorrow, we hope to collect additional hydrate samples from both the higher oil-concentration regions and purer regions of the mounds and bring them back to the surface under pressure so that they will be preserved for laboratory study.