MBARI-authored abstracts for AGU SF  Dec 11-16, 2006:

Thursday

0800h
AN: IN41B-0885
TI: The Marine Metadata Initiative: The Next 3 Years
AU: * Bermudez, L, Graybeal, J

The Marine Metadata Initiative (MMI) mission is to promote the exchange, integration and use of marine data through enhanced data publishing, discovery, documentation and accessibility. MMI started in September 2004, and it recently got funded for three more years. This presentation will walk through the different projects the MMI is working on and will present the coming challenges to build cyberinfrastructure and help the observing systems become interoperable.
UR: http://marinemetadata.org/
DE: 4599 General or miscellaneous
DE: 9820 Techniques applicable in three or more fields
SC: Earth and Space Science Informatics [IN]
MN: 2006 Fall Meeting


Wednesday

HR: 08:30h
AN: MR31A-03 INVITED
TI: Novel observations on the massive Barkley Canyon hydrates
AU: * Brewer, P G, Peltzer, E T, Kirkwood, W J, Dunk, R M, Walz, P, Hester, K , Sloan, E D

We report on the early results of an August 2006 expedition to the massive exposed hydrates found at 850m depth in Barkley Canyon, off-shore Vancouver Island. We used the ROV Tiburon to explore, image, and sample the site, and also to carry out a series of novel experimental techniques and measurements in situ. We used the DORISS II laser Raman spectrometer for direct real time in situ measurement of hydrate composition and structure. The DORISS II system was equipped with highly modified pressure compensated optical fibers, resulting in far less signal loss than in earlier versions. This resulted in identification of gases including methane, ethane, propane, and isobutane in the Structure II hydrate simply by holding the probe head in the vehicle arm, pointing, and focusing the beam with a moveable internal stage. The site revealed white, easily cored, non-fluorescent hydrate underlying much harder yellow oil stained hydrate with significant fluorescence. Raman spectra were obtained of both hydrate types. A newly built small coring system was used to obtain specimens of well defined shape, which were inserted into a mesh chamber for time lapse video imaging to determine dissolution rates. Pressurized and non-pressurized cores were also obtained for cross- calibration in the on-shore laboratory using Raman, NMR, and XRD. A first attempt at an in situ CH4-CO2 hydrate conversion experiment was made by inserting buoyant cored specimens into a glass walled chamber, introducing ~ 2 liter liquid CO2, and placing the unit on a flat plate to seal the system and prevent large scale loss of dissolved CO2 to the surrounding ocean. We collaborated with MBARI's AUV mapping team, who obtained high resolution bathymetry, side scan, and sub-sea floor acoustic images of the site.
DE: 3004 Gas and hydrate systems
DE: 3999 General or miscellaneous
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460)
DE: 4825 Geochemistry
SC: Mineral and Rock Physics [MR]
MN: 2006 Fall Meeting


Thursday

HR: 1340h
AN: MR43A-1063
TI: An autonomous multibeam, sidescan, and subbottom survey of a methane hydrate outcrop in Barkley Canyon, offshore Vancouver Island
AU: * Caress, D W, Thomas, H J, Kirkwood, W J, Brewer, P G

We have used the MBARI Mapping AUV (autonomous underwater vehicle) to conduct a multibeam bathymetry, subbottom, and sidescan survey of a massive, partially exposed hydrate deposit found in Barkley Canyon, off-shore Vancouver Island. The Mapping AUV is a torpedo-shaped, 6000 m rated vehicle designed and constructed by MBARI. The vehicle is equipped with a 200 kHz multibeam sonar, 110 kHz and 410 kHz chirp sidescan sonar, and a 2-16 kHz sweep chirp subbottom profiler. The multibeam provides a 120 degree swath with 0.94 degree by 0.94 degree beam resolution. The endurance of the AUV is eight hours at 3 knots. Navigation derives from an inertial navigation system (INS) incorporating a ring laser gyro aided by GPS at the surface and by velocity-over- ground observations from a Doppler velocity log (DVL) when within 130 m of the seafloor. A navigational precision of 0.05% of distance traveled is achieved with continuous DVL bottom lock. An acoustic modem allows surface aiding of navigation during deep descents. The Barkley Canyon hydrates outcrop is located at 850 m depth on the northwest canyon wall on a 0.5 km wide, 1 km long, plateau perched 150 m above the canyon floor. The AUV surveyed a 1.8 km by 1.6 km area encompassing the plateau, the canyon wall above, and the canyon floor below. The survey was conducted from a 50 m altitude with 150 m line spacing. The multibeam bathymetry achieves a 1-meter lateral resolution and a vertical precision of 0.3 m. The bathymetry reveals an east-west trending scarp that steps up as much as 15 m on the southern, downhill side. This scarp extends from a gully on the canyon wall obliquely across the plateau to the canyon floor. Adjacent to the canyon wall, the scarp forms an 8 m deep, 140 m long closed basin. The hydrate outcrops are located 80 m from the scarp on the downhill side. We interpret this scarp as evidence of an active reverse fault cutting the Barkley Canyon wall. Such a fault may provide a conduit for the upward migration of hydrocarbons associated with the hydrate deposit. The subbottom profiler achieved penetrations up to 0.04 second (at least 30 m) into the canyon wall and canyon axis sediments. However, no sedimentary structure was imaged across the plateau. This lack of penetration may be due to the presence of gas in the sediments. ROV-based studies of the hydrate deposit, including in-situ laser Raman spectrometer measurements and sampling, are reported by Brewer et al. in a companion abstract.
DE: 3004 Gas and hydrate systems
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3080 Submergence instruments: ROV, AUV, submersibles
SC: Mineral and Rock Physics [MR]
MN: 2006 Fall Meeting

Monday

HR: 1340h
AN: V13A-0644
TI: Caldera Formation on the Vance Seamounts
AU: * Clague, D, Paduan, J, Cousens, B, Cornejo, L, Perfit, M, Wendt, R, Stix, J, Helo, C

The Vance Seamounts are a chain of near-ridge volcanoes located just west of the southern Juan de Fuca Ridge. The six volcanoes are built on ocean crust ranging from 0.78 Ma at the southeastern end to 2.55 Ma in the northwest. Morphologic analysis indicates that the volcanoes were constructed sequentially and get younger to the southeast towards the ridge axis. Like many near-ridge volcanoes, some of the Vance Seamounts have large offset calderas that presumably formed above evacuated shallow magma chambers within the upper ocean crust. In summer 2006, we completed 6 dives using MBARI's ROV Tiburon to study the formation of these calderas. The floor of each caldera consists of flat-lying volcaniclastite, under about 25 cm of pelagic sediment. Some caldera floors have mounds of post-caldera pillow flows. The caldera walls have a lower section covered by talus and an upper section of interbedded massive flows with columnar joints (to 11 m thick) and pillow basalts. The top of each caldera wall has a unit of volcanic mudstone to sandstone ranging from 20 cm to 2 m thick. The fine matrix of many of these samples is green hydrothermal clay. The finest siltstone to mudstone samples appear to be layers of massive tan hydrothermal clays. Talus fragments, lava and volcaniclastite outcrops are universally coated and cemented by 1 to 4 cm-thick deposits of hydrothermal Mn-oxide crusts, even on the youngest of the volcanoes. Volcanic particles in the sandstones are mostly dense angular glass, but bubble-wall fragments (limu o Pele) are present and indicate formation during low-energy pyroclastic eruptions. Without the few percent limu o Pele fragments, the glass fragments would resemble those inferred to form by quench granulation. We suggest that quench granulation is actually pyroclastic fragmentation that occurs as coalesced magmatic gas bubbles disrupt the molten lava surface at the vents. Our observations confirm that the more southeasterly offset calderas truncated thick flows that ponded inside older calderas to the northwest, as proposed based solely on morphology (Clague et al., 2000). The limu o Pele fragments in the volcaniclastic deposits on the rim and floor of the calderas demonstrate that the formation of each caldera was accompanied by pyroclastic eruptions. At the same time, the abundance of hydrothermal clays and thick Mn-crusts, and the wide dispersal of the glass particles show that discharge of voluminous warm hydrothermal fluids accompanied the pyroclastic eruptions and caldera collapse. Seawater apparently migrated down along the normal faults bounding the caldera and mixed with existing high- temperature hydrothermal aquifers within each volcano, leading to discharge of large volumes of mixed warm hydrothermal fluid. The hydrothermal clays and Mn-oxides precipitated directly from this plume of fluid. This focusing of hydrothermal fluid discharge along ring faults is similar to that observed in large silicic calderas. Each caldera collapsed during a brief time period since no volcaniclastic deposits were observed in any of the sequences in the caldera walls. Only a tiny percentage of the magma stored in the magma chamber prior to collapse erupted during the pyroclastic eruptions, so the vast majority must have been intruded into the ocean crust adjacent to the volcanoes, probably along still active ridge-parallel faults.
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 8434 Magma migration and fragmentation
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2006 Fall Meeting


Wednesday

HR: 08:05h
AN: V31E-01 INVITED
TI: Vertical Motions of Oceanic Volcanoes
AU: * Clague, D A, Moore, J G

Oceanic volcanoes offer abundant evidence of changes in their elevations through time. Their large-scale motions begin with a period of rapid subsidence lasting hundreds of thousands of years caused by isostatic compensation of the added mass of the volcano on the ocean lithosphere. The response is within thousands of years and lasts as long as the active volcano keeps adding mass on the ocean floor. Downward flexure caused by volcanic loading creates troughs around the growing volcanoes that eventually fill with sediment. Seismic surveys show that the overall depression of the old ocean floor beneath Hawaiian volcanoes such as Mauna Loa is about 10 km. This gross subsidence means that the drowned shorelines only record a small part of the total subsidence the islands experienced. In Hawaii, this history is recorded by long-term tide-gauge data, the depth in drill holes of subaerial lava flows and soil horizons, former shorelines presently located below sea level. Offshore Hawaii, a series of at least 7 drowned reefs and terraces record subsidence of about 1325 m during the last half million years. Older sequences of drowned reefs and terraces define the early rapid phase of subsidence of Maui, Molokai, Lanai, Oahu, Kauai, and Niihau. Volcanic islands, such as Maui, tip down toward the next younger volcano as it begins rapid growth and subsidence. Such tipping results in drowned reefs on Haleakala as deep as 2400 m where they are tipped towards Hawaii. Flat-topped volcanoes on submarine rift zones also record this tipping towards the next younger volcano. This early rapid subsidence phase is followed by a period of slow subsidence lasting for millions of years caused by thermal contraction of the aging ocean lithosphere beneath the volcano. The well-known evolution along the Hawaiian chain from high to low volcanic island, to coral island, and to guyot is due to this process. This history of rapid and then slow subsidence is interrupted by a period of minor uplift lasting a few hundred thousand years as the island migrates over a broad flexural arch related to isostatic compensation of a nearby active volcano. The arch is located about 190±30 km away from the center of volcanic activity and is also related to the rejuvenated volcanic stage on the islands. Reefs on Oahu that are uplifted several tens of m above sea level are the primary evidence for uplift as the islands over-ride the flexural arch. At the other end of the movement spectrum, both in terms of magnitude and length of response, are the rapid uplift and subsidence that occurs as magma is accumulated within or erupted from active submarine volcanoes. These changes are measured in days to years and are of cm to m variation; they are measured using leveling surveys, tiltmeters, EDM and GPS above sea level and pressure gauges and tiltmeters below sea level. Other acoustic techniques to measure such vertical movement are under development. Elsewhere, evidence for subsidence of volcanoes is also widespread, ranging from shallow water carbonates on drowned Cretaceous guyots, to mapped shoreline features, to the presence of subaerially-erupted (degassed) lavas on now submerged volcanoes. Evidence for uplift is more limited, but includes makatea islands with uplifted coral reefs surrounding low volcanic islands. These are formed due to flexural uplift associated with isostatic loading of nearby islands or seamounts. In sum, oceanic volcanoes display a long history of subsidence, rapid at first and then slow, sometimes punctuated by brief periods of uplift due to lithospheric loading by subsequently formed nearby volcanoes.
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3075 Submarine tectonics and volcanism
DE: 8415 Intra-plate processes (1033, 3615)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2006 Fall Meeting

Tuesday

HR: 1340h
AN: V23E-0687
TI: Similarities in Chemistry of North Gorda Ridge basalts with Ultra-slow Spreading Ridge Lavas Due to Decreasing Magma Supply
* Davis, A S, Clague, D A, Paduan, J B

Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 9644 United States
AB: Chemical variability of MORB has been reported from ultra-fast to ultra-slow spreading ridges. Despite the large number of studies, high density of precisely located samples is still rare for most ridge segments. Using MBARI's ROV Tiburon and a rock corer, we collected 71 basalt glasses along the axial valley of the 65 km- long, northern Gorda Ridge segment. To explore the temporal variability at the central part of the segment, we collected an additional twenty samples over a distance of 4 km up the eastern valley wall, corresponding to a maximum age of about 150, 000 years. Lava compositions along the ridge axis show considerable major-and minor element diversity (MgO 8.4-4.4%, K2O 0.07-0.36%) for lavas erupted in close proximity. Although they form a near-continuum, the compositions can be separated into two groups, one is typical N-MORB (K2O/TiO2 < 0.09) and the other a more enriched T-MORB (K2O /TiO2 > 0.09). The chondrite-normalized REE patterns also reflect this grouping with Ce/YbN <1 and Zr/Nb >20 for N- MORB and Ce/YbN >1 and Zr/Nb <20 for T-MORB. Although the maximum compositional diversity and the highest Na8.0 is observed at the shallowest central part of the ridge segment, nearly as much diversity exists at the deepest part (>3,800 m) near the non-transform offset at the southern end. Except for two more enriched compositions, off-axis samples are LREE-depleted N-MORB with a narrow compositional range (MgO 7.7±0.3%, Zr/Nb=38-50). In comparison, basalts from the southern Cleft segment of the Juan de Fuca Ridge, which has a comparable spreading rate but different ridge morphology, all plot on the N-MORB trend with high Zr/Nb (30-40) and slight LREE depletion (Smith et al. 1994). In contrast, ultra-slow spreading ridges like Knipovich, Gakkel, and Mohns, with ridge morphologies similar to North Gorda although reaching even greater depth (>4000m), have erupted predominantly E-MORB. Their least enriched compositions overlap with the most LREE-enriched North Gorda lava although most have Zr/Nb<10 and (Ce/Yb)N >1.0 and up to 3.2 (e.g. Haase et al., 1996; Muhe et al., 1997, Hellevang and Pedersen, 2005). On a Zr/Nb versus K2O /TiO2 plot, the basalts from the ultra-slow ridges lie along a common mixing trend with the North Gorda basalts. Apparently, as the magma budget and/or partial melting decreases a more enriched component (especially in K and LREE) widely present in the oceanic mantle is incorporated to a greater degree. At North Gorda Ridge, morphology as well as chemical characteristics appears to evolve toward that of ultra-slow spreading ridges.
DE: 1021 Composition of the oceanic crust
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1065 Major and trace element geochemistry
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
DE: 8410 Geochemical modeling (1009, 3610)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2006 Fall Meeting


Thursday

HR: 09:30h
AN: IN41C-07
TI: Distributed Observatory Management
AU: * Godin, M A, Bellingham, J G

A collection of tools for collaboratively managing a coastal ocean observatory have been developed and used in a multi-institutional, interdisciplinary field experiment. The Autonomous Ocean Sampling Network program created these tools to support the Adaptive Sampling and Prediction (ASAP) field experiment that occurred in Monterey Bay in the summer of 2006. ASAP involved the day-to-day participation of a large group of researchers located across North America. The goal of these investigators was to adapt an array of observational assets to optimize data collection and analysis. Achieving the goal required continual interaction, but the long duration of the observatory made sustained co-location of researchers difficult. The ASAP team needed a remote collaboration tool, the capability to add non-standard, interdisciplinary data sets to the overall data collection, and the ability to retrieve standardized data sets from the collection. Over the course of several months and "virtual experiments," the Ocean Observatory Portal (COOP) collaboration tool was created, along with tools for centralizing, cataloging, and converting data sets into common formats, and tools for generating automated plots of the common format data. Accumulating the data in a central location and converting the data to common formats allowed any team member to manipulate any data set quickly, without having to rely heavily on the expertise of data generators to read the data. The common data collection allowed for the development of a wide range of comparison plots and allowed team members to assimilate new data sources into derived outputs such as ocean models quickly. In addition to the standardized outputs, team members were able to produce their own specialized products and link to these through the collaborative portal, which made the experimental process more interdisciplinary and interactive. COOP was used to manage the ASAP vehicle program from its start in July 2006. New summaries were posted to the COOP tool on a daily basis, and updated with announcements on schedule, system status, voting results from previous day, ocean, atmosphere, hardware, adaptive sampling and coordinated control and forecast. The collection of standardized data files was used to generate daily plots of observed and predicted currents, temperature, and salinity. Team members were able to participate from any internet-accessible location using common Internet browsers, and any team member could add to the day's summary, point out trends and discuss observations, and make an adaptation proposal. If a team member submitted a proposal, team-wide discussion and voting followed. All interactions were archived and left publicly accessible so that future experiments could be made more systematic with increased automation. The need for collaboration and data handling tools is important for future ocean observatories, which will require 24-hour per day, 7-day a week interactions over many years. As demonstrated in the ASAP experiment, the COOP tool and associated data handling tools allowed scientists to coherently and collaboratively manage an ocean observatory, without being co-located at the observatory. Lessons learned from operating these collaborative tools during the ASAP experiment provide an important foundation for creating even more capable portals.
UR: http://aosn.mbari.org/
DE: 0525 Data management
DE: 0910 Data processing
DE: 3050 Ocean observatories and experiments
DE: 3225 Numerical approximations and analysis (4260)
DE: 6344 System operation and management
SC: Earth and Space Science Informatics [IN]
MN: 2006 Fall Meeting


Wednesday

HR: 16:30h
AN: OS34C-03
TI: The Potential of Silent Tsunamis Along the Central California Margin
AU: * Greene, H G, Murai, L, Niven, E, Nishenko, S, Hanson, K, Rietman, J, Thio, H, Ichinose, G

Government and industry concerns about the impacts of tsunamis on critical infrastructures have resulted in an extensive assessment of mass movement events along the central California margin. Part of this study includes the evaluation of potential mass movements along the coastline and in the heads of submarine canyons that may have locally generated tsunamis in the past and may have the potential to generate tsunamis in the future. We report upon landslides concentrated within the Arquello-Conception and Partington canyon systems and adjacent slopes, estimate time of movement of the features, model potential tsunami inundation and runups, and speculate on future failures. Landslide deposits from trans-terrestrial failures in the Partington Canyon area are well imaged in recently collected multibeam bathymetric data sets. In this area faulting controls the head of the canyon and landslide movement has deflected the present day channel. In contrast, mass movement of the Arquello-Conception canyon system are concentrated at the canyon heads and appear to result from retrogressive erosional activity initiated by fluid flow and expulsion of gases from hydrocarbon reservoirs at depth. Examination of these two canyon systems and their adjacent areas provide insight into the mechanisms, loci and amount of submarine mass movement in the central California region and their ability to direct tsunami waves to critical coastal areas. Since most of the sites of failures are close to shore, little time is required for the waves to arrive at the shoreline and their generation may occur silently, without a seismic trigger. Therefore, locating areas where potential silent tsunamis may generate is critical to emergency preparation processes. We use the results of this work to determine where the likelihood of tsunamis deposits on land may be found.
DE: 3070 Submarine landslides
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting


Monday

HR: 17:15h
AN: OS14A-06
TI: The Extent and Recurrence of Holocene Turbidity Currents in Monterey Canyon and Fan Channel, offshore California
AU: * Johnson, J E, Paull, C K, Normark, W, Ussler, W

The Monterey Canyon and fan channel system is a large and active conduit for sediment transport on the central California margin. The proximity of the canyon head to the shoreline, coupled with longshore sand transport in Monterey Bay, allows frequent (several/year) sediment gravity flows to enter the canyon and deposit coarse gravel and sand down the canyon axis. ROV-guided observations and sampling and data from canyon monitoring activities (measurements of near-seafloor currents, turbidity, pressure, temperature, and salinity) have been collected by MBARI and USGS scientists throughout the Monterey canyon-fan channel system during the last decade (see Johnson et al., 2001; Paull et al., 2003; Xu, et al., 2004; Paull et al., 2005). Based on the known timing of these measured events in comparison with local earthquake, storm, and river discharge data, the most common triggers for the observed events are intense storm wave disturbance and/or random canyon wall failures. How frequently these events pass out of the upper canyon and extend across the fan, however, has thus far remained elusive. Recently, ROV-collected vibracore transects across the active fan channel (depth ~3.5-3.65 km) were obtained. This tool allows the cores to be precisely located and closely spaced, enabling lateral facies interpretation at an unprecedented scale. At one of the prominent bends in the active fan channel, the axial channel is characterized by laterally variable high energy deposits at least a meter thick, composed of gravel, coarse sand, and rip-up clasts. Deposits on inner bend-levees contain multiple graded sand and silt horizons (turbidite events) up to 15 cm thick, separated by hemipelagic clays. Within the inner bend levee, the most complete and well correlated event stratigraphy is preserved in a narrow, 200 m wide, region about 50 m above the channel floor. In contrast to the axial channel and inner levee, the outer bend of the fan channel is composed of erosionally exposed older strata. Radiocarbon dating and measurements of DDTr indicate the last turbidity current that passed through the fan channel occurred prior to 1945 A.D. and after 1717-1891 A.D., which is consistent with the 1906 San Andreas earthquake as a possible trigger for this event. Additional radiocarbon data indicate the average recurrence for events that pass through the fan channel is about ~230 years, much longer than the subannual upper canyon events mentioned above. Our results suggest that during the recent Holocene upper canyon events occur at a high (subannual) frequency, but are likely triggered by small events and restricted to the upper canyon. This is in contrast to our interpretation of the deposits recovered in the fan channel, which are suggestive of full canyon and fan channel flushing events that may be initiated by exceptionally large triggers like earthquakes or severe storms.
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4219 Continental shelf and slope processes (3002)
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting


Monday

HR: 09:25h
AN: OS11D-05
TI: Diatom Vertical Migration to Acquire Iron
AU: * Johnson, K S, Kolber, Z, Needoba, J, Elrod, V, Fitzwater, S, Foster, R, Klimov, D, Tanner, S

The vertical profiles of nitrate and dissolved iron (Fe) concentrations in the open ocean are characterized by sharp increases (nitracline and ferricline) beneath the euphotic zone. However, the ferricline in the Pacific Ocean is often displaced 10's to more than 100 meters below the nitracline and it is often well below the euphotic zone. The water between the nitracline and ferricline acts as a High Nitrate, Low Iron (HNLFe) condition where low Fe concentration may limit nitrate acquisition. In October 2005, we studied the potential for diatoms to vertically migrate for Fe in a highly oligotrophic region 800 km SW of Monterey Bay (34N, 129W). The nitracline was found at 115 m depth and a ferricline at 160 m depth. A deep chlorophyll maximum (0.25 μg/L) was located near 100 m. Samples were collected at four depths from the chlorophyll maximum to just below the ferricline using non-contaminating samplers deployed on eleven dives of the Remotely Operated Vehicle Tiburon. These samplers were designed to separate rising and sinking phytoplankton cells. Bulk and size-fractionated samples from the top and bottom of the samplers were analyzed with a next generation, Fast Repetition Rate Fluorometer that had sufficient sensitivity to measure variable fluorescence in samples with chlorophyll concentrations of 0.01 μg/L. Significant differences (P<0.001) in variable fluorescence (Fv/Fm), a physiological indicator of photosynthetic status, were found between rising and sinking phytoplankton in the large (>10 to 300 μm) size class at depths above the ferricline, but not below. Rising cells had higher Fv/Fm, indicating they were more iron replete. The large phytoplankton population was primarily composed of pennate diatom species. There is a near balance in concentrations of rising and sinking cells, suggesting that the difference is not simply due to export of dying cells. Our results indicate that the shade flora of large diatoms within the deep chlorophyll maximum migrate vertically through HNLFe waters to the ferricline depth where they acquire iron. Vertical migration to acquire iron would explain the large tail in deep chlorophyll concentration profiles that extends well below the nitracline and ends just below the ferricline.
DE: 4273 Physical and biogeochemical interactions
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4855 Phytoplankton
DE: 4875 Trace elements (0489)
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting


Monday

HR: 1340h
AN: OS13C-1571
TI: Functional Relationship Between Phytoplankton and Aerobic Anoxygenic Photosynthetic Bacteria: Modes of Coexistence
AU: * Kolber, Z S, Haffa, A, Klimov, D

Aerobic Anoxygenic Photosynthetic Bacteria (AAPs) are ubiquitously distributed in the upper ocean. Although they contain bacteriochlorophyll a (BChla), the main absorption bands in the near UV (370 nm) and infrared (800-850 nm) make this pigment impractical in light harvesting below the first few meters of the water column. Instead, they utilize carotenoids as major light harvesting pigments. Since these carotenoids absorb in the 430-550 nm range, phytoplankton and AAPs utilize a similar portion of the available light spectrum. As AAPs cannot utilize water as the electron donor, they transfer electrons between a range of organic/inorganic electron donors and electron acceptors, thus significantly participating in the redox cycle in the upper ocean. We have measured the vertical distribution and photosynthetic properties of both phytoplankton and AAPs in a highly oligotrophic region 800 km SW of Monterey Bay (34N, 129W), and we have consistently observed the presence of a BChla maximum about 30 to 40 meters above the chlorophyll maximum, indicating that phytoplankton and AAPs occupy different ecological niches in the water column. However, the abundance of AAPs generally displayed a maximum at dawn and a minimum at the dusk, indicating a high level of mortality. This diel cycle was observed in 5 micron and 3 micron size fractions, indicating active grazing by small protists. Incubation experiments with natural, mixed population of AAPs and phytoplankton results in an unusually high accumulation of AAPs in DCMU-treated samples, indicating that pigmented protists do contribute significantly to AAP grazing in a tightly-controlled microbial loop. On the other hand, AAP incubations in pure cultures indicate that they biomineralize sulfur, thus affecting the sulfur cycle. All of these observations indicate that the role of AAPs in the upper ocean ecology is defined by their relationship with phototrophic and heterotrophic communities, rather than by their relative contribution to the carbon and energy cycles.
DE: 4239 Limnology (0458, 1845, 4942)
DE: 4264 Ocean optics (0649)
DE: 4273 Physical and biogeochemical interactions
DE: 4294 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting

Monday

HR: 1340h
AN: V13A-0650
TI: A characterization of the megafauna on Davidson Seamount
AU: * Lundsten, L, DeVogelaere, A P, Barry, J P, Clague, D A

Seamounts offer hard substrate, complex habitat, elevated current velocities, and other features that allow for the existence of unique assemblages of organisms, often dominated by long-lived and fragile corals and sponges. Seamount faunas have high rates of endemism with biogeographic patterns analogous to land-based island faunas. Seamount organisms, particularly long-lived deep-sea corals, are particularly vulnerable to bottom trawling and other resource extraction techniques. Davidson Seamount, located 120 km southwest of Monterey, CA, USA, is an example of a relatively undisturbed and pristine seamount habitat. Volcanic in origin, Davidson Seamount was formed 12-16 million years ago atop a fossil spreading center, which produced a unique pattern of northeast trending ridges on the seamount. Remotely Operated Vehicle (ROV) dives at Davidson Seamount were conducted in 2000 and 2006 by a collaboration of scientists, resource managers and educators. Sixteen dives were annotated in detail using MBARI's Video Annotation Reference System (VARS), yielding more than 60,000 biological observations. Over 170 organisms were identified to the lowest possible taxon. The distribution of organisms in relation to the bathymetric complexity of the seamount were analyzed using ArcGIS 9.1 and NOAA's Benthic Terrain Modeler (BTM) to relate faunal distributions to slope, aspect, and bathymetric position. Video transects completed in 2006 were analyzed to quantify species' density and richness. Several new species were observed and collected, and are currently being described by taxonomists. Results of this study indicate that corals and sponges may have species-specific depth distributions with little overlap of large habitat forming phyla. Moreover, substratum type, slope, and aspect are important in determining the distribution of some coral species. This baseline survey is valuable in describing the fauna of Davidson Seamount, has been used in developing essential fish habitat zones where trawling is regulated by the National Marine Fisheries Service, and will be critical in the final determination for the potential inclusion of the seamount as part of the Monterey Bay National Marine Sanctuary.
DE: 1705 Biogeosciences
DE: 9350 North America
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2006 Fall Meeting

Friday

HR: 1340h
AN: OS53A-1088
TI: Carbon Cycle Dynamics in the Labrador Sea During the Spring to Summer Phytoplankton Bloom
AU: * Martz, T, DeGrandpre, M, Strutton, P, McGillis, W, Drennan, W

The Labrador Sea is a region of intense physical and biological activity. This area is a globally significant site of air-sea CO2 flux, deep water formation, and perhaps organic carbon export. It is therefore important to characterize these processes and the interplay between them. We report here the carbon cycle dynamics during the summer 2004 phytoplankton bloom observed from a 70-day Air-Sea Interaction Buoy (ASIS) deployment in the Labrador Sea. Physical and biogeochemical properties were measured at multiple depths in the upper 35 m by autonomous pCO2, PAR, Chl-a fluorescence, beam-c, optical backscatter, CTD, and ADCP sensors. Using the in situ pCO2, air-sea flux of CO2 and net community metabolism (NCM) are estimated. Our findings indicate that during the main phytoplankton bloom, temperature and NCM drive large opposing trends in seawater pCO2. Changes in particulate organic carbon, obtained from beam-C and optical backscatter, provide a linkage between the observed CO2 drawdown and organic carbon production. This connection may allow inference on the less-understood flux of organic carbon in this region thus providing a link between air-sea CO2 flux and carbon export. Evaluation of net community production in the context of mixed layer depth and compensation irradiance reveals a general adherence to the classic Critical Depth Hypothesis. ADCP backscatter reveals an intriguing relationship between magnitude and phase of diel pCO2 cycling in the upper 10 m, presumably driven by zooplankton migration.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1055 Organic and biogenic geochemistry
DE: 4277 Time series experiments (1872, 3270, 4475)
DE: 4504 Air/sea interactions (0312, 3339)
DE: 4855 Phytoplankton
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting

Monday

HR: 1340h
AN: V13A-0640
TI: Erratic Continental Rocks on Volcanic Seamounts off California and Oregon
AU: * Paduan, J B, Clague, D A, Davis, A S

 
The seamounts off the California continental margin, and those well offshore of California and Oregon that formed near mid-ocean ridges, are all constructed of basaltic lava flows and volcanic breccias and sandstones. However, explorations of these seamounts using dredges, and more recently, the remotely operated vehicle Tiburon, frequently recover rocks of a wide assortment of continental lithologies including gabbro, granodiorite, silicic volcanics, limestone, dolomite, and metamorphic rocks. These rocks are often rounded like river and beach cobbles, and the softer rocks are bored as by worms or bivalves. They are covered with manganese oxide crusts of thicknesses that range from a patina to several cm, approaching the thickness on the in-situ basaltic rocks. These rocks are often easier to collect than the basalts. We recognize these rocks to be erratics of continental origin. Erratics have been documented as being transported by icebergs at higher latitudes, but this mechanism is unlikely to be responsible for the erratics we have found as far south as 31.9° N. Three brief papers published by K.O. Emery from 1941 to 1954 proposed that such erratics found in many thick sections of fine-grained sedimentary sequences such as the Monterey Formation, were transported long distances by kelp holdfasts, tree roots, or in the guts of pinnipeds. We propose that these vectors also transport erratics to seamounts, where they have been accumulating since the seamounts formed millions of years ago. Those seamounts that were once islands would have intercepted even more erratics along their shorelines while they stood above sea level. We have recovered or observed such erratics on the Vance Seamounts; Gumdrop, Pioneer, Guide, Davidson, Rodriguez, San Juan, Little Joe, and San Marcos Seamounts; on the muddy bottom of Monterey Bay; and on Northeast Bank and along the Patton Escarpment at the western edge of the California Borderland. These locations are as far as 250 nautical miles from shore and extend along the entire west coast of the continental United States. Studies that fail to recognize the presence of erratics, even at temperate latitudes, may result in unrealistically complex interpretations of the regional geology
DE: 3022 Marine sediments: processes and transport
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3075 Submarine tectonics and volcanism
DE: 8415 Intra-plate processes (1033, 3615)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2006 Fall Meeting



Thursday

HR: 1340h
AN: OS43C-0682
TI: Assessing Methane Release From the Colossal St\oregga Submarine Landslide
AU: * Paull, C K, Ussler, W, Keaten, R, Holbrook, W S, Hill, T, Mienert, J, Haflidason, H, Johnson, Winters, W, Lorenson, T, Aiello, I

The St\oregga Slide, on the Norwegian margin, is the largest known Holocene-aged continental margin slope failure complex and is believed to have occurred in sediments that contained gas hydrate. Pore water sulfate gradients in long piston cores from the slide complex, that serve as a proxy for the relative amount of methane presently in the sediments, and other sedimentological data provide three constraints on the pre- and post- slide event conditions associated with the last major St\oregga Slide event: (1) Marine slope failure involving methane-gas-hydrate-bearing sediments is one mechanism proposed for releasing enormous quantities of methane to the ocean and atmosphere. Sulfate gradients suggest a considerable inventory of methane occurs in sediments adjacent to, and unaffected by, the slide events, but indicate methane is notably absent from sediments on the sole of the slide and in distal slide deposits. Either methane was lost during previous failure events or was never present in significant concentrations within the sediments that failed. (2) Seafloor pockmarks and subsurface chimney features are common on the Norwegian continental margin north of the St\oregga Slide scar. Such features are generally inferred to be associated with fluid expulsion and imply overpressures in the subsurface. Sulfate gradients in cores from within the pockmarks are less than those from outside the pockmarks, which indicates the methane flux to the seafloor is presently smaller within the pockmarks than in the adjacent undisturbed sediments. Methane-derived authigenic carbonates and Bathymodiolus shells obtained from a pockmark core at >6.3 mbsf indicate methane was previously available to support a chemosynthetic community within the pockmark. 14C measurements of planktonic foraminifera overlying and interlayered with the shell-bearing sediment indicate methane was present on the seafloor within the pockmark earlier than 14 ka 14C years BP, well before the St\oregga Slide event (7.2 ka 14C years BP) and imply overpressured fluids existed within the Norwegian continental margin during the last major advance of Pleistocene glaciation. (3) Cores from the Norwegian Basin show extremely well-sorted sediments in the uppermost 18 m that were likely deposited by the last major St\oregga slide event. These sediments appear to have entered the basin as fluidized mud. Seawater-like or higher pore water sulfate concentrations suggest pore fluids within these sediments mixed with oxygenated seawater during the slide event and the rate of sulfate reduction in these sediments has been negligible since deposition in the basin.
DE: 1051 Sedimentary geochemistry
DE: 3002 Continental shelf and slope processes (4219)
DE: 3004 Gas and hydrate systems
DE: 3022 Marine sediments: processes and transport
DE: 3070 Submarine landslides
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting


Monday

HR: 0800h
AN: OS11C-1507
TI: Visualization tools for model/data comparisons and decision making during the Monterey Bay 2006 experiment.
AU: * Pawlowski, L, Kolber, D, Godin, M, Chavez, F P

During summer 2006, almost 100 different oceanographic sensors have captured for more than one month the properties of the waters of the Californian Central Coast. Data were assimilated in quasi-real time by three hydrodynamical models to forecast the evolution of the local conditions such as currents, sea water temperature, salinity and to adapt accordingly the sampling strategy of the involved unmanned vehicles (AUV, gliders). Due to the high diversity of data and models (sources, file structures, time and spatial coverage, periodicity of sampling…), the collected informations were first converted into a standardized format which allows one to quickly find and extract the relevant variables from the main data server of the experiment. Visualization softwares were developed to provide live maps of the latest locations of instruments, surface plots and vertical transects of currents, temperature and salinity from data and models. These products were mainly used for decision making, for model intercomparison and to evaluate the quality of the data assimilation process for each model. Plots were updated several times a day and automatically posted on an internet collaborative portal. Softwares were adaptive in regards of the availability of simulations and datasets from satellite, aircraft, robotic vehicles, research vessels, moorings, drifters… Their modular structures allowed a quick implementation of new instruments during the experiment. Profiles from gliders and AUV served as references for intercomparisons between models for salinity and temperature. As simulations were not synchronized between models, the involved algorithm selected, for all gliders, relevant portions of their tracks to serve as references for model intercomparison. These portions were delimited to prioritize the comparison for each model between observations and nowcasts/hindcasts and also to evaluate the loss of forecasting capabilities with time. We provide here several examples of these graphical products for different situations we encountered during the experiment.
UR: http://aosn.mbari.org/
DE: 4255 Numerical modeling (0545, 0560)
DE: 4260 Ocean data assimilation and reanalysis (3225)
DE: 4262 Ocean observing systems
DE: 4263 Ocean predictability and prediction (3238)
DE: 4294 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting


Thursday

HR: 1340h
AN: MR43A-1067
TI: An Experimental Determination of Natural Clathrate Hydrate Dissolution Rates in the Deep Sea
AU: * Peltzer, E T, Walz, P M, Brewer, P G, Dunk, R M, Hester, K, Sloan, E D

In August of 2006 we carried out a series of geochemical experiments on the massive Structure II hydrate mounds in Barkley Canyon using MBARI's ROV Tiburon deployed from the R/V Western Flyer. One of the primary questions regarding the fate of this hydrate exposure at 850m depth is the temporal persistence of un-sedimented surfaces exposed to steady currents of seawater undersaturated with methane. Previous work on the dissolution rate of laboratory prepared methane hydrate (Rehder et al., 2004) showed diameter reduction rates of ~3 m/year. These formations appeared largely unchanged from the earlier descriptions and photographs contained in media reports released in 2002 and later (Chapman et al., 2004; Lu et al., 2005) leading us to speculate that these hydrates are far slower to dissolve. In order to quantify their dissolution rates, samples of the outcropping hydrate, both a pure white hydrate and a much harder yellow, oil-stained hydrate, were collected using an ROV operated coring device and hydraulically expelled into an open mesh container for time-lapse photography over the course of the next 48 hours. By exposing these samples of natural hydrate to the flow of ambient seawater we hoped to observe the dissolution rate consistent with the local environmental conditions. Initial analysis of the time-lapse photographs obtained using a Nikon Cool-pix camera revealed an apparent diameter reduction rate for the yellow hydrate of approximately 0.040 μm/s, corresponding to a volume loss rate of 1.3×10-6cm3/cm2/s. The observed dissolution rate of the white hydrate was significantly faster, consistent with the observed large-scale undercutting of the exposed layered structures. Assuming that the yellow hydrate has a density of 0.93 g/cm3 and an average hydration number near 6, this yields a guest gas loss rate of about 9.4×10-9 mol/cm2/s. This is approximately one-fourth the rate that was observed for the dissolution of synthetic Structure I methane hydrates under similar conditions in Monterey Bay. Thus the lifetime of the exposed surfaces must be short unless there is some form of active expulsion of fresh hydrates taking place. Chapman et al. (2004). Eos, Trans. Amer. Geophys. Union. 85: 361, 365. Lu et al. (2005). J. Geophys. Res. 110: B10204, doi:10.1029/2005JB003900. Rehder et al. (2004). Geochim. et Cosmochim. Acta 68: 285-292.
DE: 3004 Gas and hydrate systems
DE: 3999 General or miscellaneous
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460)
DE: 4825 Geochemistry
DE: 4854 Physical chemistry
SC: Mineral and Rock Physics [MR]
MN: 2006 Fall Meeting


Tuesday

HR: 1340h
AN: V23B-0615
TI: Mapping AUV Survey of Axial Seamount
AU: * Thomas, H, Caress, D, Conlin, D, Clague, D, Paduan, J, Butterfield, D, Chadwick, W, Tucker, P

In late August and early September 2006, the MBARI Mapping Autonomous Underwater Vehicle (AUV) was deployed for 5 missions on Axial Seamount during a NOAA NeMO cruise on the R/V Thompson. The objective of the survey was to determine the geologic history of the summit of Axial Seamount using high resolution multibeam, sidescan, and sub-bottom profiler data. The Mapping AUV is a torpedo-shaped, 6000 m rated vehicle designed and constructed by MBARI. The vehicle is equipped with a 200 kHz multibeam sonar, 110 kHz and 410 kHz chirp sidescan sonar, and a 2-16 kHz sweep chirp sub-bottom profiler. The multibeam provides a 120-degree swath with 0.94 degree by 0.94 degree beam resolution. The endurance of the AUV is eight hours at 3 knots. Navigation derives from an inertial navigation system (INS) incorporating a ring laser gyro aided by GPS at the surface and by velocity-over- ground observations from a Doppler velocity log (DVL) when within 130 m of the seafloor. A navigational precision of 0.05 percent of distance traveled is achieved with continuous DVL bottom lock. An acoustic modem allows surface aiding of navigation during deep descents. The AUV ran two types of missions: those on the rim of the caldera were run at 90 m altitude with a line spacing of 250 m and those on the caldera floor were run at 50 m altitude with a line spacing of 150 or 175 m. The surveys covered most of 1998 lava flow on the south rim of the caldera and northern part of the south rift zone, the southern region of the caldera floor where hydrothermal vents are common, the northeast rim of the caldera where volcaniclastic deposits related to caldera collapse drape the surface, the north rift zone, and the northern portion of the caldera floor. The low-altitude maps have a resolution of 1 m, so large individual lava pillars and hydrothermal chimneys can be seen, fissures stand out clearly, and the regions of collapsed lobate flows and lava channels are prominent. Many of the flows, including the 1998 flow, have drained lava ponds and channel systems that closely resemble on-land flow channels. Three ROV ROPOS dives explored the channel margins of lobate flows and their abundant pillars and located new sulfide chimneys based on the new maps. The northeast rim of the caldera is cut by numerous fissures, some of which served as eruptive vents for post-caldera flows that are on top of volcaniclastic deposits. The CHIRP sub-bottom profiler did not resolve the roughly 2-m thick deposits observed and sampled with a vibracorer during a recent ROV Tiburon dive. The north rift zone is a constructional ridge that is cut by numerous fissures within 1.6 km of the caldera. Northeast trending fissures are located about 1-1.5 km east of the north rift zone. A lobate flow along the base of the northeastern caldera wall has 9 collapse pits, 10-50 m across and 7-13 m deep, aligned like skylights along a tube system on subaerial flows. Nearby to the northwest, there is a flat lava pond with a bathtub ring of lava around it that is 3 m shallower than the pond surface. The 900 m wide flat surface and the rim are both tilted with the side closest to the center of the caldera about 1.5 m shallower than the northeastern corner of the pond. Fifteen round 5 m tall, 10-40 m diameter mounds of unknown origin are scattered on the flow surface. The AUV generates high-resolution maps for geologic analysis not possible using previously existing mapping systems. Such maps will facilitate the next generation of detailed geologic studies of the seafloor.
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3080 Submergence instruments: ROV, AUV, submersibles
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2006 Fall Meeting


Tuesday

HR: 11:20h
AN: B22A-05
TI: Rates of Anaerobic Oxidation of Methane and Authigenic Carbonate Mineralization in Methane-Rich Deep-Sea Sediments Inferred from Models and Field Data
AU: * Ussler, W, Paull, C K

Porewater chemical data obtained from a giant gravity core (10.5-m long) collected in methane-rich sediments from 647 m water depth in the northern Gulf of Mexico defines sub-bottom gradients in unprecedented detail. This core penetrated the sulfate-methane interface (SMI) at ~3 meters below the seafloor (mbsf). Dissolved inorganic carbon (DIC) concentrations reach a maximum (13.5 mM) and pore water δ13C DIC (-63.2‰ PDB) and δ13C methane (-89.5‰ PDB) are most negative at the SMI. Below the SMI porewater sulfate is nearly depleted, methane concentrations rise sharply with simultaneous formation of a bubble-textured sediment, and fine-grained methane-derived authigenic carbonate nodules and cements are common. The sharp peaks in the DIC concentration and isotope values centered at the SMI indicate that DIC is being produced by anaerobic oxidation of methane (AOM) within a narrow zone centered around the SMI. The detailed sulfate and DIC concentration profiles, and DIC δ13C values have enabled geochemical models to be constructed that explore the rate of DIC formation from AOM. Model results closely match the measured DIC concentration and δ13C isotope profiles and indicate that the microbiological conversion of methane carbon to DIC is rapid in geologic terms and that AOM is occurring at the present position of the SMI. Isotope values for authigenic carbonate found immediately below the present- day SMI (δ13C = -60.2±0.7‰ PDB at 4.4 mbsf) are consistent with derivation of the carbonate carbon from methane via AOM at the former location of a SMI. These observations and model results suggest that AOM and precipitation of methane-derived carbonate occur on time-scales of centuries. The metabolic rates inferred from modeling field data compare favorably with available rate data obtained from laboratory microbial incubations and radiolabeled tracer experiments.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1051 Sedimentary geochemistry
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, SC: Biogeochemistry [B]
MN: 2006 Fall Meeting


Wednesday

HR: 1340h
AN: OS33A-1683
TI: Error Analysis and Sampling Design for Ocean Flux Estimation
AU: * Zhang, Y, Bellingham, J G, Davis, R E, Chavez, F

In this paper we present error analysis and sampling design for estimating flux of heat or other quantities (e.g., nitrate, oxygen) in the ocean using mobile or stationary platforms. Flux estimation requires sampling the current velocity and the flux variable (e.g., temperature for heat flux) along a boundary. When we run autonomous underwater vehicles (AUVs) on a boundary to take spatial samples, the ocean field evolves over time. This non-synoptic sampling leads to an estimation error of the flux. We formulate the estimation error as a function of the spatio-temporal variability of the studied ocean field, the cross-section area of the boundary, the number of deployed vehicles, and the vehicle speed. Based on the error metric, we design AUV sampling strategies for flux estimation. We also compare the flux estimation performance of using AUVs with that of using traditional mooring arrays. As an example, we study heat flux estimation using statistics from Monterey Bay and for various sampling configurations. The sampling requirement is determined by how fast the product of temperature and normal current velocity varies in time and space. We estimate the temporal and spatial scales of temperature and current velocity by measurements from moorings, bottom-mounted stations, ships, and AUVs. It is found that current velocity varies much faster than temperature in both temporal and spatial domains, hence the variability of their product is quite high. The consequence of this variability on heat flux estimation is presented.
DE: 4262 Ocean observing systems
SC: Ocean Sciences [OS]
MN: 2006 Fall Meeting