Ocean Sciences General Contributions III
Presiding: M McNutt, Monterey Bay Aquarium Research Institute; B Mullenbach, Texas A&M University; R Hetland, Texas A&M University
OS52A-01 10:30h
Multidimensional Laser Scanning System for Underwater Mapping of Small Structures and Bottom Topography
A multidimensional laser scanning imaging system is under development to investigate new concepts in underwater imaging. The system is a modification of the 3D Laser Imaging & Tracking Electro-optical System (3D LITES; HBOI, patent &35; 5,418,608) that was developed for 3D mapping applications in biological oceanography. The new 3D-FLITES ("F" stands for added Fluorescence capability) captures both spatial and spectral data and offers extended operation capabilities. The system can capture the range to each pixel in the sensor's field of view, the relative reflectance of each pixel (similar to "conventional" images) and five channels of fluorescence emission in the scene, captured sequentially. Multidimensional data sets can be instrumental in bottom topography mapping and object identification. The 3D FLITES has the unique capability to operate in user-selectable line or raster scanning modes if mounted on a moving platform. In raster mode two perpendicular mirrors are driven, allowing the operator to capture single frames (capturing either reflectance or fluorescence data) or a stream of images in fast rate (16 frames per second). With this operational flexibility the operator can combine a "fly over" scanning mode with "look ahead", "look sideways" and "zoom" modes. The current system is limited in range and resolution; nevertheless it can serve as a test-bed to evaluate operational parameters, data acquisition and signal processing protocols that could lead to a smaller, more efficient system in the future.
OS52A-02 10:45h
Modification of ocean-estuary salt fluxes by density-driven advection of a headland eddy
Scalar exchange between San Francisco Bay and the coastal ocean is examined using shipboard observations made across the Golden Gate Channel. Ocean-estuary exchange is often described as a combination of two independent types of mechanisms: density-driven exchange such as gravitational circulation and tidal asymmetries such as tidal trapping. In this study we found that exchange is also governed by an interaction between these mechanisms. Tidally trapped eddies created in shallow shoals are mixed into the main channel earlier in the tidal cycle during the rainy season because the eddies are pushed seaward by gravitational circulation. This interaction increases the tidally averaged dispersive salt flux into the bay. The study consists of experiments during each of three 'seasons': winter/spring runoff (March 2002), summer upwelling (July 2003), and fall relaxation (October 2002). Within each experiment, transects across the channel were repeated approximately every 12 minutes for 25 hours during both spring tide and the following neap tide. Velocity was measured from a boat-mounted ADCP. Scalar concentrations were measured from a tow-yoed SeaSciences Acrobat. Salinity exchange over each spring-neap cycle is quantified with harmonic analysis. Harmonic results are decomposed into flux mechanisms using temporal and spatial correlations. The temporal correlation of cross-sectional averaged salinity and velocity (tidal pumping flux) is the largest part of the dispersive flux of salinity into the bay. From the tidal pumping portion of the dispersive flux, it is shown that there is less exchange than was found in earlier studies. Furthermore, tidal pumping flux scales strongly with flow due to density-driven movement of tidally trapped eddies and density-driven increases in ebb-flood frictional phasing. Complex bathymetry makes salinity exchange scale differently with flow than would be expected from simple tidal pumping and gravitational circulation models.
http://www.ce.berkeley.edu/research/fluids
OS52A-03 11:00h
A methodology for the turbulent kinetic energy model to determining skin sea surface temperature in climate study
We presented an Effective Thickness Parameterization (ETP) and showed how it can be used in a Turbulence Kinetic Energy (TKE) type ocean model to determine Skin Sea Surface Temperature (SST) and to account for the warm-layer effect as well as the surface-cooling effect. Estimating the thickness of the conductive sublayer is according to Sauders (1967) and the proportionality constant in the Sauders formulation is according to Artale et al. (2002). Our simulation shows that determination of temperatures at the skin layer and at an uppermost layer with 1-mm thickness is found sufficient to reproduce the cool-skin effect. A vertical resolution of 1-2 m is needed to keep track of the absorption of solar radiation in the top few meters and to reproduce the warm-layer effect. Data from research vessel Vickers taken during the TOGA COARE program are used for a case study, in which the observed cool-skin effect and the warm-layer effect are reproduced using the above discretizations. Our results show that a cool skin constantly increases atmospheric heat input to the ocean by ~ 8 W m-2, and that a warm layer decreases it by ~ 1 W m-2.
OS52A-04 11:15h
Variability of Spectral Flux of Energy in Inertia-Gravity Waves
Analysis of moored current meter measurements at high sampling rates (15 to 30 min) is carried out in order to identify possible mechanisms responsible for the observed rate, Q, of direct spectral flux of wave energy through the equilibrium range of weakly-nonlinear baroclinic inertia-gravity wave (IGW) spectrum. The values of Q can be estimated by fitting a theoretical spectrum of IGW (containing Q among its key parameters) to observed spectra of horizontal velocity fluctuations. Having thus found Q(t) for short time intervals (such as 20 days), it is natural to compare its evolution with time histories of various external factors that may be responsible for energy flux variations on larger timescales - seasonal to interannual. Among such factors we tested wind energy, the kinetic energy of vortical oceanic large-scale motions, and the Richardson, Rossby, and Froud numbers. The latter two numbers have been suggested in some theoretical studies as controlling the loss of energy by vortical motions to the internal IGW mode. Although interactions between the slow vortical motions and the fast gravity waves have been always thought as rather insignificant, our data appear to indicate that they do occur and are in fact not negligible.
OS52A-05 11:30h
Monthly Radiocarbon Variability during the 1760s in the Eastern Tropical Pacific
Monthly samples from a Galapagos coral that lived from AD 1760-1771 were analyzed for Δ14C. High Δ14C values were found for coral that grew from January to March, when upwelling is weak or absent at the Galapagos. Low Δ14C values were obtained mid-year during strong upwelling. The seasonal variability of Δ14C ranged from 10-28 ‰; this is greater than the seasonal variability at other tropical or subtropical locations owing to intense seasonal upwelling in the eastern equatorial Pacific. The Δ14C data suggest that three El Nino events occurred during this period. Δ14C values were high (average -64‰) during the upwelling seasons of 1762-64 relative to the other years (average -74‰), which resemble a short-lived climatic shift similar to that identified for 1976 by Guilderson and Schrag [1998]. The monthly Δ14C record revealed most of its variance at the 5-yr period, similar to ENSO periodicity during the 20th century, though the record is too short for these results to be conclusive. These data will be discussed in the context of a longer annual record of Δ14C being reconstructed from the same coral sequence.
OS52A-06 11:45h
Ocean Biogeochemistry and Phytoplankton Ecology in a Global Simulation
A coupled Biogeochemistry/Ecosystem/Circulation (BEC) model is used to examine ocean biogeochemistry and phytoplankton ecology at the global scale. Phytoplankton groups represented in the model include diatoms, diazotrophs, coccolithophores and picoplankton. The groups experience differential grazing pressure and compete for light and the potentially growth-limiting nutrients iron, nitrate, ammonium, phosphate, and silicate. The model includes several key aspects of the global nitrogen cycle including nitrogen fixation (by the diazotrophs), water column denitrification under low oxygen conditions, and atmospheric nitrogen deposition to the oceans. We examine how these nitrogen fluxes influence ecosystem structure and also how light and nutrient availability restrict phytoplankton growth rates over seasonal timescales. Atmospheric deposition of mineral dust also inputs dissolved iron to the ocean model. These iron additions modify phytoplankton community composition, and rates of production and export in the iron-limited High Nitrate, Low Chlorophyll regions, and indirectly modify ecosystem dynamics by altering rates of nitrogen fixation in nitrogen-depleted, tropical and subtropical regions. We will examine the links between dust/iron deposition and nitrogen cycling in the oceans.