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Deep-Sea Chemistry Logbook Day 4: Bacteria heaven on the seafloor March 17, 2012 Persistence paid off today from searching an unexplored area of the sea floor with a beautiful outcrop covered with large patches of yellow bacteria-an indication of sulfur-laden water rising up from below.
A close-up of a rocky ridge riddled with cracks and holes venting sulfur-laden warm fluids. Returning today to the valley where we had seen the big yellow mass of pulsating bacteria two days ago, several more small vents were discovered. After several hours of exploring the slopes, Peter Brewer directed the pilots to fly the remotely operated vehicle a little further afield, to a spot where an old map showed a hint of a ridge. It took a while to get there, but we came upon the best discovery of the expedition so far. A ridge of rocks and rubble was covered with yellow bacteria surrounding holes and cracks all throughout the ridge and along its base. Each of these holes was surrounded by mats of bacteria that thrive on the sulfur. The sulfur vents are an external sign of the volcanic activity below the seafloor. The valley we traversed beneath the Gulf of California is slowly spreading apart. As it does, cracks open up in the seafloor and cold seawater seeps in, reaching the hot volcanic activity below. The water comes back out of the same cracks hotter and carrying some of the chemicals present in the volcanic emissions below.
The ridge and rubble were bathed in sulfur-rich fluids, attracting bacteria that rely on chemosynthesis for energy. Unlike plants which rely on energy from the sun, chemosynthetic organisms convert chemicals, such as sulfur, to energy and do not need sunlight. To check just how hot the venting fluids were, a thermistor was inserted into several of the crevices where shimmering water was visible. While the ambient seawater was about 2.5 degrees Celsius (37 degrees Fahrenheit), the venting fluids were as much as 5.9 degrees Celsius (42.6 degrees Fahrenheit). Not very hot, but certainly enough to indicate the volcanic activity below.
A thermistor is inserted into one of the fissures to measure the temperature of the venting fluids. They were clearly warmer than surrounding seawater, but not very hot.
The team also successfully used the laser Raman spectrometer in some of the vents. The team "reached new lows" when it used a longer probe than ever before, enabling measurements of the chemical components as deep as 55 centimeters into the seafloor. The full analysis of the spectra obtained when the laser light scattered off the fluids will be carried out in the lab at a later date. While we may have hoped for bigger, hotter, denser fields of vents, the day's discoveries were certainly rewards after exploring this seafloor valley northeast of La Paz.
A special treat today was the chance to see a pod of pilot whales swimming around the ship. —Nancy Barr
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Deep-Sea Chemistry
Equipment
The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.
ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.
By bouncing a specially tuned laser beam off of almost any object or substance—solid, liquid, or gas—a laser Raman spectrometer can provide information about that object's chemical composition and molecular structure.
A push-core looks like a clear plastic tube with a rubber handle on one end. Just as its name implies, the push core is pushed down into loose sediment using the ROV's manipulator arm. As the sediment fills up the core, water exits out the top through one-way valves. When the core is pulled up again, these valves close, which (most of the time) keeps the sediment from sliding out of the core tube. When we bring these cores back to the surface, we typically look for living animals and organic material in the sediments.
The CTD measures conductivity (which helps determine salinity), temperature, and density (which helps determine depth). This particular CTD runs profiles of the water column (surface to bottom) and along the way, collects discrete water samples (at specific predetermined depths) using the rosette of niskin bottles. Each bottle can collect a water sample. The transmissometer measures the number of particles in the water and the oxygen sensors tell us how much dissolved oxygen is present. Both of these instruments go onto the CTD rosette and give us a profile of the water column.
Vibracoring is a common technique used to obtain samples from water-saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance.
MBARI's heat-flow probe is mounted on the side of the ROV Doc Ricketts inside the vertical stainless steel box. This both protects the delicate probe and provide the track so that the probe can be inserted into the sediment along a totally straight path. The probe contains five high precision platinum sensors which are used to measure the vertical temperature gradient in the sediments. This gradient along with some knowledge of the heat capacity of the sediment allows scientists to calculate the rate of heat loss from the sediments into the ocean. Crew
R/V Western Flyer
ROV Doc Ricketts
Research Team
Peter has taken part in more than 30 deep-sea cruises, and has served as chief scientist on major expeditions and on more than 90 ROV dives with MBARI ships and vehicles. His research interests include the ocean geochemistry of the greenhouse gases. He has devised novel techniques both for measurement and for extracting the oceanic signatures of global change. At MBARI his current interests include the geochemistry of gas hydrates, and the evolution of the oceanic fossil fuel CO2 signal. He has developed novel techniques for deep ocean laser Raman spectroscopy, and for testing the principles and impacts of deep ocean CO2 injection.
Ed is an ocean chemist who has been with MBARI since 1997. He has been involved in developing in situ laser Raman spectrometry instruments and lab based analytical techniques to study the composition of gases in gas hydrates and deep-sea vents. He has collaborated on the development of new instrumentation for the measurement of temperature and pH from ROVs and deep-sea observatories. As the group's project manager, Ed is also responsible for expedition planning and logistics.
Nancy manages the editing, design, and production of the MBARI annual report and participates in a variety of editorial and communication projects. She also oversees the institute website. For this expedition she will be in charge of the daily reports that will be posted to this website and will assist with other science crew tasks.
Peter has worked as a research technician for several scientists at MBARI. For the past 10 years he has supported the research efforts of Peter Brewer and his interests regarding the ocean chemistry of greenhouse gases such as methane and carbon dioxide. Peter is responsible for the design, testing, maintenance, and deployment of the oceangoing science hardware and works closely with the marine operations group to integrate new equipment and technology with MBARI's ROVs.
Martín Hernández Ayón is a chemical oceanographer. His research is focused on the inorganic carbon system, ocean acidification and biogeochemistry in the coastal regions of Baja California, the Sea of Cortez, the subtropical region where the oxygen minimum zone is located, and, more recently, the Gulf of Mexico.
Gaby is a graduate student in the coastal oceanography program at the University of Baja California in Ensenada, Mexico. She is doing her graduate studies on the dynamics of CO2 in seawater from a coastal monitoring site known as Ensenada Station.
Abbey Chrystal is a graduate student in earth and planetary sciences at the University of California, Santa Cruz. Her research focuses on reconstructing long-term records of past ocean carbonate chemistry parameters. On this cruise she will be collecting sediment push cores and bottom water samples to help calibrate the relationship between the shell chemistry of benthic foraminifera and the chemistry of the bottom water and porewater chemistry in which they grow.
Joseph Murray is a first year ocean sciences Ph.D. student in the lab of Dr. Adina Paytan at the University of California, Santa Cruz. He is interested in coastal marine chemistry and the impact of submarine groundwater discharge on marine biogeochemical cycles. His current research is focused on using oxygen and nitrogen isotopes in nitrate to study sources and cycling of nitrogen in the coastal ocean. As part of this cruise, he plans to collect samples in order to study the impact of anthropogenic fertilizer runoff from the Yaqui Valley on the marine nitrogen cycle in the Gulf of California, including assessing the role groundwater discharge plays in this process. |
