WHOI Funding and Awards --> Cecil H. and Ida M. Green Technology Innovation Awards --> 1997 Abstracts

Abstracts of 1997 Cecil H. and Ida M. Green Technology Innovation Awards

A Probe to Measure the In-Situ Electrical Resistivity of Seafloor Sediments
Rob L. Evans, Barrie Walden and Neal Driscoll

Porosity is one of the key physical properties that describe marine sediments, and distinguishes, for example, sands from muds. Measuring and mapping spatial and temporal changes in porosity is crucial to understanding many key issues of coastal geology including, but not limited to, how beaches are eroded; where rivers deposit their loads; and how sediments evolve off-shore to form geologic strata.

Electrical resistivity is being used far more frequently as a measure of sedimentary porosity. Two kinds of shallow measurements have been made to date: High resolution measurements made on core samples collected from the seafloor; and those made on a 1 to 10-m scale using geophysical surveying methods.
There are two problems to be addressed: first, linking the lab and field scale data can be difficult; second, delicate high-porosity sedimentary structures are inevitably disturbed during recovery from the seafloor to lab.
We propose to construct a 1-m long probe that can be pushed into the seafloor obtaining a high-resolution, in-situ profile of resistivity with depth, providing immediate access to the details of surficial resistivity structures at higher resolution than field scale techniques can provide, but over a depth interval that allows the link to the geophysical scale to be made. The probe will be deployable by ROV, submersibles or even by divers operating in the near shore environment.
We will use the new probe during two ONR-funded cruises (Driscoll) as part of a seafloor observatory project, allowing us to monitor the temporal evolution of porosity, particularly with regard to sedimentary compaction and re-working. The funded observatory will provide key constraints on the nature of cross-shelf versus along-shelf hydrodynamic processes and their associated sedimentary response, the formation of sedimentary signatures (e.g., "event" strata), and preservation of the longer-term stratigraphic record. The development of the proposed in-situ resistivity probe will allow us for the first time to determine the surficial porosity structure and how the porosity structure varies with time in non-cohesive sediments. Our long term vision is to deploy a large number of resistivity probes as part of a network of seafloor tripods, with the instrument suite at the seafloor measuring both the hydrodynamic processes and the accompanying sedimentary response.

Construction of Laboratory Pulse During Probe Fluorometer for Comparison of Bio-Optical and ¹⁴C Measurement of Phytoplankton Photosynthesis in Coastal Waters
Craig D. Taylor

Over the past decade much has been gained in the understanding of the optical properties of photosynthesis. Sub-cellular physiological and biophysical events during photosynthesis can be sensed fluorometrically and quantitatively described mathematically. Response of phytoplankton to changes environmental nutrient status is readily detectable bio-optically and sufficient understanding of the photosynthetic process has been gained to provide estimates of phytoplankton production rates from fluorometric measurements of phytoplankton present in the environment. These important measurements have normally been possible only via labor intensive and expensive ¹⁴C incubation studies. Use of bio-optical approaches to the measurement of primary production and response of phytoplankton to anthropogenic inputs will be highly desirable in ecological and environmental monitoring studies. Savings by conducting required measurements in minutes rather than multiple hours to days will permit substantial increases in the temporal and spatial resolution of studies where investigators are attempting to measure or predict effects of anthropogenic change against a background of variable natural phenomena.
In spite of the information that has been gathered to introduce fluorometric approaches to the study of environmental photosynthesis, most of the effort has focused upon detecting effects of change in nutrient status on phytoplankton physiological state. Relatively few studies have focused on extensive head-to-head comparison of bio-optically derived measures of primary production rates with ¹⁴C-incubation studies over a large variety of conditions.
The primary objective of this proposal is to build and test an inexpensive laboratory Pulse During Probe (PDP) fluorometer for acquisition of data for the bio-optical estimation of phytoplankton production rates and for sensing potential changes in phytoplankton nutrient status. This instrument will form the basis for future process level studies in New Bedford Harbor/Buzzards Bay where an extensive comparison between bio-optical- and ¹⁴C-based measurements of primary production and phytoplankton physiological state in the marine coastal environment will be possible.

Development of a High Temperature Combustion Discrete Injection Total Dissolved Nitrogen Analyzer
Catherine Goyet

The development of a prototype high temperature combustion discrete injection (HTC/DI) total dissolved nitrogen (TDN) analyzer is proposed based upon recent advances in HTC/DI - DOC analytical technology. A DOC high temperature combustion furnace will be modified to optimize oxidation conditions for nitrogen, and the gas purification line prior to the chemiluminescence detector will be re-designed specifically for the throughput of nitric oxide. Once the system has been optimized for maximum sensitivity and analytical precision for all forms of nitrogen, samples of local interest (e.g., Vineyard Sound or Waquoit Bay) will be run as a demonstration of proof-of-concept. The development of this instrument will fill a gap in the sea-going arsenal available to marine chemists and biologists, and open a door to rapid at-sea measurements of TDN (and thus DON) that will be comparable to the current state-of-the-art for DOC determinations. Such measurements are essential to increasing our understanding of the role of dissolved organic matter in the global cycles of carbon and nitrogen, the functioning of the microbial loop and the importance of DON in the nitrogen budgets of coastal ponds.

Development of a New Gas-Tight Hydrothermal Fluid Sampler
Jeffrey Seewald

Dissolved gases play a critical role in numerous biogeochemical processes associated with convective circulation of seawater-derived hydrothermal fluids though the oceanic crust at oceanic spreading centers. The design and construction of a chemically inert gas-tight device for sampling hydrothermal vent fluids with the submersible Alvin and ROV Jason is proposed This sampler will allow quantitative determination of the dissolved concentrations of both volatile and non-volatile species in high temperature vent fluid samples. In addition to being gas-tight, the sampler will allow direct control of filling rate to minimize the potential for entrainment of ambient seawater while sampling diffuse vents. The availability of an easy to use gas-tight fluid sampler will greatly increase our knowledge of dissolved gas abundances in a variety of natural fluids and constrain physical and chemical processes that regulate fluid-rock/sediment interaction at or below the seafloor.

Development of an Improved Cryogenic Charcoal Trap System for Noble Gas Mass Spectrometry
Dempsey E. Lott, III

Noble gases are used as tracers of air-sea gas exchange, ice/water interactions, ground-water paleo-temperature proxies, mantle structure, and planetary evolution. Their beauty lies in their chemical inertness and their breadth of physical characteristics. The Helium Isotope Laboratory is currently equipped with an automated seawater sample-processing system for the extraction and measurement of He, Ne, and Ar at the 0.3% level. The noble gases are cryogenically trapped and sequentially released for mass spectrometric measurement. With the Green award, the principle investigator will design, construct, and test a new multi-stage cryogenic system to extend the measurement capabilities of the system to include Kr and Xe. The ability to automate the complete suite of noble gas measurements at the sub-percent level on a single sample will significantly increase the scientific capabilities of both Dr. Jenkins' and Dr Kurz's laboratories and will, in the process, create new funding opportunities.

A Surface Processes Instrument Platform
Wade R. McGillis, Donald B. Peters, Glenn McDonald, and John W. H. Dacey

The physical and biogeochemical importance of the interface between the ocean and the atmosphere is matched only by the sheer extent of the interface. When we speak of three-fourths of the Earth's surface being covered by ocean, we describe, in fact, the interface. Where the ocean meets the atmosphere is one of the most continuously dynamic regimes of the ocean, and fluxes at this surface are overwhelmingly important in determining all manner of processes within the ocean and the atmosphere. Measuring the processes at the air-water interface is crucial to understanding the fluxes of gases, heat, water vapor and momentum. The very factors that make the interface important are also what make its investigation so difficult: the interface lies between two fluid media, the processes occurring at this interface are also most dynamic exactly when their measurement is most difficult - when wind and sea state are high. We propose to design, fabricate, and deploy a wave-following surface instrument platform to allow measurements of processes at the atmosphere-ocean interface. The system will be deployable in a wide range of sea states from ships and other platforms. Our initial focus will be on gas exchange, where measurements near the surface on both sides of the interface are essential, and where expeditious sampling and analysis are vital. The platform will be designed to provide for modification for use with other sampling systems and will provide WHOI with a vehicle to expand its studies of coastal and open ocean processes.

Imaging the Mixed-Layer with Expendable Acoustic Drifters
E. A. Terray, M. Johnson, and A. J. Plueddemann


We propose to develop a new drifter for use in measuring the three-dimensional flow in the oceanic surface mixed-layer. Each drifter will measure its depth (using a pressure transducer) and temperature, and telemeter this information acoustically several times each minute, together with an identity code. Differences in arrival times of this signal to a network of receivers can then be used to determine the drifter's horizontal position. An important objective of the development is to keep the unit cost low so that the drifters can be regarded as expendable. This, coupled with the ability to distinguish individual drifters by their 'codes', will permit seeding of the mixed-layer with a relatively large number (~ 20 or so) of drifters at any one time, permitting direct observation of the large-scale vertical transport.

Using a Subsurface Buoy to Measure Ocean Wave Heights
Mark Grosenbaugh and Richard Arthur


We propose to develop and test a subsurface buoy system for measuring wave amplitudes in the open ocean along the Continental Shelf Traditional methods for measuring wave amplitudes are based on "wave following" surface buoys whose own motion is assumed to equal that of the waves. However, it has been shown that this assumption is incorrect when steep waves slam into the surface buoy such as in high sea states. Under these conditions, waves can break over the buoy and cause the wave measurements to underestimate the actual amplitudes. The large wave forces that accompany these events can also cause high tensions in the mooring line - at the point where it attaches to the surface buoy. The mooring line has been known to break at this point allowing the surface buoy to drift free. Putting the instrumentation 10 to 20 meters below the ocean surface on a subsurface buoy reduces the wave forces and increases survivability. This has been done recently with acoustic doppler current profilers but at great cost. We propose to use a differential pressure scheme that has the potential to produce, for a lower cost, measurement accuracy that is comparable to present systems.