New tools and techniques for marine science

1998 Projects

Project 6

New tools and techniques for marine science

Principal Investigator: Hans Jannasch

Co-investigators: Peter Brewer, Gernot Friederich, Paul McGill, Ed Peltzer, Carole Sakamoto

Scientists are becoming increasingly aware that the ocean is a highly variable realm where many cycles are driven by sporadic and short-term events such as storms, upwelling, and phytoplankton blooms. Better knowledge of processes that affect the variability of important chemical compounds in the ocean is essential for improving scientific understanding of the interactions between the seafloor, the ocean environment, and the atmosphere. For example, in many areas of the ocean, levels of phytoplankton productivity are limited by the availability of the nutrient nitrate. In other regions where nitrate is abundant, a lack of iron or phosphate may curb productivity. Drawing carbon dioxide from the atmosphere, via surface waters, phytoplankton sustain ocean food-chains. Thus, deciphering chemical cycles associated with phytoplankton is of great importance. The origins and fates of many other chemicals in the atmosphere, throughout the water column, and at the seafloor are likewise integral to the workings of ocean ecosystems.

This project continues MBARI’s long-term efforts to advance the understanding of marine chemical processes through the development of better instruments, systems, and methods. Project tasks are geared to evolving advanced instruments for in situ, continuous, real-time measurements of ocean chemistry. The efforts fall into three main categories:

P6A Ocean biogeochemical processes—Focusing on processes affecting the oceanic distribution and cycling of greenhouse gases, notably carbon dioxide and methane, this sub-project encompasses:

Studying the deep-ocean release of carbon dioxide—The ultimate fate of carbon dioxide released to the atmosphere by the burning of fossil fuels is storage in the deep ocean, as atmospheric CO₂ is slowly taken up by the oceans. Recent concerns about mitigating possible greenhouse effects induced by human-produced CO₂ emissions have led to the suggestion that direct burial of CO₂ in the deep ocean might be a solution. Little is known about the possible consequences of such a strategy. To address these uncertainties, in February MBARI researchers will employ the ROV Tiburon and the R/V Western Flyer to release several liters of liquid carbon dioxide into containers and directly onto the seafloor. They will monitor the results to gain insights into the physical chemistry of this process and shed light on what may become a significant means of dealing with the problem of anthropogenically released CO₂.

Natural gas venting—Methane, another major form of carbon found in the ocean environment, is of scientific interest for its roles in seafloor ecology (as a bacterial substrate and a metabolic product) and as a greenhouse gas. Worldwide, methane hydrate deposits are estimated to contain 20 quadrillion cubic meters of methane gas. The gas reacts with water and converts to solid hydrate only at precise combinations of pressure and temperature. Recent MBARI research at a site off northern California has shown that these deposits are delicately poised at their stability points and perturbations (such as an El Niño warming or long-term climate change) can lead to their decomposition. In 1998 MBARI researchers will study natural seafloor venting of methane in the Santa Barbara Basin. They expect to gain a better understanding of what may happen should large areas of methane hydrates decompose.

P6B Continuing development of in-situ analyzers and samplers—The success of the in-situ nitrate OsmoAnalyzer, currently in use on moorings in Hawaii, Bermuda, and the equatorial Pacific, as well as Monterey Bay, has prompted the adaptation of this relatively low-cost, simple, long-term monitoring device to other significant chemicals. An OsmoAnalyzer for hydrogen sulfide—a compound of major interest, in part for its role in supporting life at hydrothermal vents and cold seeps—is nearly finished. Similar analyzers for iron and manganese are also under development. The MBARI chemical analyzer group expects to test prototypes of the sulfide, iron, and manganese instruments in 1998. A major redesign effort to simplify the analyzer, improve its duration, and to increase its overall reliability is currently underway. Due to the significant interest expressed by the oceanographic community, negotiations are continuing with a potential commercial partner for transferring the technology to make it generally available.

MBARI-originated OsmoSamplers, which are capable of continuously collecting fluid samples over several years, are in use at geological study sites in Monterey Bay, on the Juan de Fuca Ridge, and on the submarine volcano Loihi.

Refinements on both types of sensors are ongoing, based on the results of field use.

P6C Chemical mapping tools—Institute scientists and technicians are continuing to refine tools for improving measurements that will help pin down marine chemical processes and identify biogeochemical responses to changes in climate and ocean circulation (see Project 1). Measuring the various forms of carbon in the ocean reveals different aspects of the cycling of this all-important element. A device for determining the partial pressure of carbon dioxide—the difference between atmospheric and oceanic CO₂levels—has been used on MBARI moorings since 1993. Information from this sensor tells whether the ocean is acting as a sink for CO₂or, in areas of strong upwelling, as a CO₂source. Researchers also are using MBARI-originated shipboard systems for continuous sampling of total carbon dioxide, which indicates levels being taken up by photosynthesizing phytoplankton. Similar shipboard techniques are used to sample nitrate and silicate, another important nutrient. Upgrades are planned for the computer software that enables the sampling data to be combined with geographic information to create chemical "maps." In the coming year a dissolved organic carbon analyzer and an alkalinity titrator will be constructed to aid in the study of the ocean’s carbon system. For ROV use, a methane detector and an in-situ pH probe will be tested. These will allow continuous mapping of methane and pH—which is sensitive to CO₂ concentrations—making it possible to conduct directs searches for chemical plumes near the sea-floor.

MBARI chemists also are assembling equipment to synthesize gas hydrates in the laboratory. They will study, among other things, how hydrates "grow" and dissolve, how they react with seawater, and other factors that affect their stability. To assist these studies, existing gas chromatography equipment is undergoing modifications for measuring methane and other light hydrocarbon gases in seawater and sediment samples.

Chemical mapping, lab studies, and increasingly sophisticated measurements of key chemical compounds will contribute important information to modeling mid-latitude, coastal upwelling systems such as that of Monterey Bay.

Next: Feasibility studies

Last updated: 07 October 2004