Helping hands for free vehicles

November 13, 2012

In the glowing light of the sunrise, all science and engineering members were awake by 6:00 a.m. to assist with preparations for deploying two free vehicles (instruments that are not tethered to the ship): the free vehicle grab respirometer (FVGR) and the benthic elevator.

Paul McGill and Rich Henthorn assess wind and wave conditions during the early-morning deployment of the FVGR. Photo: Carola Buchner.

Paul McGill and Rich Henthorn assess wind and wave conditions during the early-morning deployment of the FVGR. Photo: Carola Buchner.

Ken Smith, the chief scientist for the cruise, pioneered the use of the FVGR for deep-water respiration measurements in the early 1980s. Since then, a next-generation FVGR designed at MBARI under his guidance has been used to measure the oxygen consumption of sediment communities in the abyssal sediments of Station M.

All members of the science and engineering teams worked together to prepare the FVGR for deployment. Photo: Carola Buchner.

All members of the science and engineering teams worked together to prepare the FVGR for deployment. Photo: Carola Buchner.

The FVGR is dropped to the seafloor; once there, it lowers four, square “grabs” into the sediment. The grabs enclose a specified volume of sediments, the water overlying the sediments, and the animals and microbes living within them. Right now, and for up to five days from now, these grabs will be left in place, measuring oxygen concentrations in the overlying water to measure the amount of biological activity occurring in the sediment. Through these measurements, estimates of sediment community oxygen consumption (SCOC)—a way of measuring biological activity on the seafloor—have been tracked for over 20 years at Station M. Through long-term sampling, the Smith lab has learned that the benthos (seafloor) at Station M, and probably other regions of the deep sea, appears to consume oxygen at a higher rate than the food arriving to the seafloor would suggest is possible. However, episodic events such as intense falls of detrital aggregates, or “marine snow,” from surface waters may provide the pulses of energy needed to sustain life in the seafloor sediments.

In a few days, an acoustic signal will be sent from the ship, telling the FVGR to close its grabs (capturing the sediments inside) and float to the surface. The sediments will provide a glimpse into the communities that consumed the oxygen measured by the oxygen sensors.

The FVGR is dropped into the ocean, where it will begin its 4,000-meter (13,000-foot) descent to ultimately measure biological activity on the abyssal seafloor. Photo: Carola Buchner.

The FVGR is dropped into the ocean, where it will begin its 4,000-meter (13,000-foot) descent to ultimately measure biological activity on the abyssal seafloor. Photo: Carola Buchner.

After deploying the FVGR, an elevator was deployed that, as its name suggests, transports items from the ocean surface to the seafloor. Two sets of experiments were deployed with the elevator: chambers for respiration measurements for Henry Ruhl and in situ dyeing chambers for studying deep-sea sponges for me. These experimental chambers will wait on the elevator on the seafloor until tomorrow’s remotely operated vehicle (ROV) dive, when the ROV will deploy the instruments in situ (on the seafloor).

The elevator was deployed with two experiments on it: respiration chambers for measuring oxygen consumption, and chambers for in situ experiments using a fluorescent dye. Photo: Carola Buchner.

The elevator was deployed with two experiments on it: respiration chambers for measuring oxygen consumption, and chambers for in situ experiments using a fluorescent dye. Photo: Carola Buchner.

The final work for the day involved a video transect of the seafloor 3,900 meters (12,800 feet) below to supplement the 23-year data series, and acoustic signaling to the benthic rover, which will be recovered tomorrow morning.

—Amanda Kahn