OS21A-18 0830h
Driving Mechanism of Band Structure of Mean Current Over the Continental Shelf
A two-layer numerical model is used to investigate the continental shelf circulation forced by western boundary currents along shelf edges. Emphasis is placed on an effect by frontal eddies (or frontal waves), which are reproduced in the model with the shelf edge along which a western boundary current is imposed. After long-term integration, the model reaches the equilibrium state in which alternating bands of long-term mean currents are found over the continental shelf. The generation of the band structure is consistent with the observational results obtained by acoustic Doppler current profilers on the shelf of the East China Sea. The western boundary current is accompanied by frontal waves, so vertical momentum transfer occurs due to the diffusive stretching. Topographic Rossby waves are excited on the shelf slope due to the vertical momentum transfer. Thereafter, energy of the waves proceeds to flow toward the lower-frequency limit by resonant interactions. The along-shelf wavenumber also vanishes to satisfy the dispersion relation of the topographic Rossby wave. Consequently, the alternating bands of mean current are found over the continental shelf.
OS21A-19 0830h
Chemical Composition Of Marine Aerosol Particles In the Northeast Asian Marginal Sea
Input flux of lithogenic aerosol into the Northeast Asia Marginal Sea was high in the spring and winter seasons but low in the summer season. Especially, input of lithogenic aerosol over the East China Sea was very weak in the summer. Also, the input amounts of lithogenic aerosol gradually decreased in order of the Bohai Sea, the Yellow Sea and the East China Sea. Elements like Al, K, Ca, Ba, Sc, Cr, V, Mn, Co, Se, Rb, Sr, Y, Zr, Nb, Sn, Th, U and rare-earth group in aerosol particles mostly have their origin in the lithogenic materials. Sodium of aerosol in the North Eastern Asia is mostly derived from marine salts. But, in the spring season, about 50 % of Na in the aerosol collected the Bohai and Yellow Seas is originated in lithogenic source. Elements like Mg, K and Ca incoming into the Yellow and Bohai Seas are mostly lithogenic source. However, those of the East China Sea in summer time have their origin in marine salts. Trace metals like Ni, Cu, Zn As, Mo, Cd and Pb in marine aerosols inflow into the study area through anthropogenic processes such as burning of fossil fuel. Most of nitrate and ammonia in aerosol collected in the study area are originated from the burning of fossil fuel. Their input strength was the maximum in the winter and spring and the minimum in the summer season. Most of sulfates in the aerosol come from the industrial region located in Chinese east coast. It is inferred based on S/Ca ratios that aerosol originated in the desert of Chinese continental are transferred into the East China Sea passed by the Bohai and Yellow Seas. It is estimated that oceanic input of aerosol is the maximum in the Yellow Sea and is the minimum in the East China Sea. While the wet depositions of aerosol were not so much in the Bohai Sea where precipitation is lower, those in the Yellow Sea are relatively abundant because of the high rainfall.
OS21A-20 0830h
Island Mass Effect In Marquesas Islands: The 2000 Anomaly
Chlorophyll a in the Marquesas islands (218E-222E / 8S-11S) from the period of 1997-2002 have been analyzed and shows that it is affected by a clear seasonal signal and also by the 1997-1998 El Nino event. Values of [Chla] varies from 0,07 mg.m-3 to above 0,25 mg.m-3 with the lowest value during El Nino. During the 1998 La Nina event, [Chla] values were about 0,25 mg.m-3. This values were expected to be the highest but higher [Chla] were found in 1999 and 2000. In order to explain these high [Chla], we investigate the island mass effect using sea surface height anomaly, ocean color, wind, precipitations and sea surface temperature (SST) data. Good correlation is found between [Chla] and SST. As previously reported, the island mass effect in the Marquesas island is a combination of turbulent mixing and advection from the South Equatorial Current (SEC) flowing through and around the islands, and iron-enriched waters originating from land drainage and hydrothermal flux through old volcanic formations. Analysis of the available data confirms the existence of a turbulent mixing with presence of cyclonic and anticyclonic eddies around seamounts and islands. Strong magnitude of SEC is associated with high [Chla]. High precipitations (at the origin of land drainage) are not in phase with high [Chla]. However, the previous hypotheses are not valid to explain the high 2000 [Chla].
OS21A-21 0830h
Paleontology aids coastal engineering: examples from the Indian Ocean and the Caribbean of enhanced understanding of coastal dynamics
Carbonate sediments are born, not made. They exist in dynamic equilibrium between production and destruction. Many models of sediment movement on shorelines are derived from clastic examples, and fit carbonate coastlines only with difficulty. We have combined field surveys of benthic biota, estimates of sediment production from skeletal growth and bioerosion, and sediment destruction by comminution and dissolution with dynamic models of sediment movement in the littoral zone, achieving improved understanding of coastal processes of erosion and deposition. Mauritius is fringed by shallow lagoons, often with luxuriant stands of Acropora. The offshore region is exhumed Pleistocene-all the sediment on the beaches comes from the lagoons. From surveys of coral cover, and estimates of sediment production from reef, sand and hardground areas, we produced dynamic models that faithfully hindcast shoreline dynamics for decades, and allowed identification of regions especially vulnerable to erosion. The rate and degree of shoreline recovery after cyclone events could be understood only after incorporation of sediment production rates. On the south coast of Barbados, one of the main issues in stabilising and rehabilitation the coastline is the balance between sediment from longshore drift and local sources. By identifying localised areas of characteristic sediment-producers (e.g., the foraminiferan Homotrema rubrum, the green alga Halimeda), we were able to determine the balance between proximal and distal sediment sources. The resulting model hindcasts the coastline through all the major hurricanes of the past 30 years.
OS21A-22 0830h
A Numerical Study of a Kyucho and a Bottom Intrusion in the Bungo Channel, Japan
The generation and propagation mechanisms of a Kyucho and a bottom intrusion in the Bungo Channel, Japan, have been studied numerically using the three-dimensional primitive equations with hydrostatic balance. The model is a regional model south of Japan, which includes the east coast of Kyushu, the south coast of Shikoku, the Bungo Channel and the Seto Inland Sea. The horizontal grid spacing is 2 km around the region from the Bungo Channel to the sea off the east coast of Kyushu, and is 5 km around the marginal seas. A linear stratification is assumed for the background density based on the observation during the summer in the Bungo Channel. The model Kuroshio is driven by the inflow at the opening of the Tokara Strait and the compensated outflow on the western side of the Izu Ridge. Based on the previous observational description, the experiments are designed to generate a Kuroshio small meander off the east coast of Kyushu by varying the maximum inlet speed. During the increasing phase of the inlet speed, a small meander is actually generated. On the downstream side of the developing small meander, a relatively warm Kuroshio water is engulfed and a warm filament is formed. This warm filament is advected by the Kuroshio and encounters the southwest coast of Shikoku. Then the warm water is intruded along the east coast of the Bungo Channel as a first-mode baroclinic Kelvin wave, which is a manifestation of a Kyucho. As the propagation of the small meander proceeds, the cold eddy associated with the small meander approaches the southern mouth of the Bungo Channel. Then the cold water is uplifted and is eventually intruded into the Bungo Channel along the bottom layer due to the upwelling on the sloping continental shelf. This is a manifestation of a bottom intrusion, and is supposed to propagate as a density current with exhibiting a bottom-intensified structure. From the above numerical result, it is concluded that the occurrences of a Kyucho and a bottom intrusion are the successive events associated with the propagation of a small meander generated off the east coast of Kyushu. This is quite a contrast with the previous observational description, in which the generation mechanism of a Kyucho and a bottom intrusion was concluded to be independent.
OS21A-23 0830h
Determining Freshwater Sr Isotopic Contribution to Paleosalinity in the Pliocene San Joaquin Basin, California
The Late Neogene San Joaquin Basin was filled by an inland sea with a surface area of $\sim$1725 km$^{2}$ and an average depth of $\sim$125 m. It connected to the Northeast Pacific Ocean at its northwest margin through the $\sim$30 km long and <50 m deep Priest Valley Strait. The basin was bounded to east by the southern Sierra Nevada, to the south and west by the San Emigdio and central Coast Ranges, and deltaic deposits to the north. Five major rivers deposited coarse clastics derived from southern Sierra Nevada granitic rocks in deltas along the mountain front on the eastern basin margin. The Priest Valley Strait silled the basin thus limiting mixing of freshwater influx with marine waters and causing the San Joaquin sea to be generally brackish throughout the Pliocene with limited periods of normal marine conditions coincident with highest eustatic levels. Bryant et al. (1995) reported paleosalinity <5$\permil$ in the San Joaquin sea from analysis of $^{87}$Sr/$^{86}$Sr data of Loomis (1992) using the seawater Sr curve of Hodell et al. (1990) and freshwater Sr isotopic composition of a modern Sierra Nevada river from Ingram and Sloan (1992) as analogous of late Neogene conditions. The taxa analyzed for $^{87}$Sr/$^{86}$Sr and Sr concentration by Loomis (1992) are all low-salinity tolerant estuarine species. However, in reproducing the work of Bryant et al. (1995) using the improved seawater Sr curve of Farrell et al. (1995) I found the paleosalinity calculated from the Loomis (1992) data averaged 2.7$\permil$ which would have been below the minimum salinity tolerances of the taxa from which the isotopic data were measured. With the seawater endpoint a know quantity, the mixing curve is sensitive to freshwater Sr concentration and that Sr concentrations reported from modern Sierra Nevada streamwaters are too low to have affected the San Joaquin sea isotopic composition. While the Sr isotopic composition for Neogene seawater is well known (see Farrell et al., 1995), the Sr isotopic composition and concentration of Neogene southern Sierra Nevada river water has been problematical and best estimated from modern rivers. Riverine Sr isotopic composition reflects the $^{87}$Sr/$^{86}$Sr of rocks eroded in the catchment basin (Ingram and Sloan, 1992). Dowling et al. (2003, Table 4)showed subsurface weathering of silicate minerals and subaqueous groundwater discharge contributes 20 times the Sr concentration to the Bay of Bengal as that from the Ganges-Brahmaputra river system. While there are ample measurements of Sr concentration from southern Sierra Nevada streamwaters there are few $^{87}$Sr/$^{86}$Sr measurements. With this background, I compiled published rock analyses of 101 samples from the southern Sierra Nevada and calculated the average $^{87}$Sr/$^{86}$Sr and Sr concentration for each of the five watersheds. Published streamwater Sr concentrations for each watershed were compiled and the relative contribution of each watershed to the total freshwater influx to the basin was calculated from 50-yr flow data to yield average Sr concentration per watershed. From these data, and the 20-times ratio of the Sr concentration in groundwater versus river water entering the Bay of Bengal, I calculated a weighted average estimate Sr isotopic composition for freshwater influx to the San Joaquin sea to be $^{87}$Sr/$^{86}$Sr of 0.70762 and Sr concentration of 0.24 ppm. Recalculating the Pliocene mixing curve with these values yielded average paleosalinity from the Loomis (1992) data of 6.0$\permil$ which would have been within the range tolerated by Pliocene estuarine taxa in the San Joaquin Basin.
OS21A-24 0830h
High-Resolution Pore Water Oxygen Profiles of Organic-Rich Coastal Sediments and Estimation of Organic Carbon Oxidation Rates
We used an oxygen microelectrode coupled with a micromanipulator, which drives the electrode at a 50-micrometer interval, to get high-resolution profiles of pore water oxygen concentration in box-cored sediment samples collected from 7 stations in the southern coastal sea of Korea. Oxygen penetration was limited to the uppermost a few millimeters of sediments. By applying a one-dimensional diffusion-reaction model to the oxygen profiles close to sediment/water interface, we estimated oxygen consumption rates to be 11 to 28 mmol O2 m-2 day-1. These rates showed a positive correlation with organic carbon contents in the sediments. Benthic organic carbon oxidation rates (OCOR) were subsequently calculated by using a modified Redfield ratio (O2/Corg=170/117) to be in the range of 90 to 228 mg C m-2 day-1. We presume that our OCOR could be greater than average because most of our coring stations were close to point sources of organic pollutants. Our results imply that it is necessary to get high-resolution measurements of redox-sensitive species in pore waters in order to get the better understanding of early diagenesis of coastal sediments.
OS21A-25 0830h
The effect of Tsushima Warm Current on the thermohaline circulation of the East/Japan Sea
Watanabe et al. (2003) show that the temperature of the deep water in the northern part of East/Japan Sea (EJS) oscillates with 20 year cycle as the North Pacific Index, although the intermediate to deep circulation of EJS is independent of that in the North Pacific. This suggests that the interdecadal scale variation in the EJS is caused by external factors such as the atmospheric conditions and the Tsushima warm current (TWC). Using a four-box model based on Stommel (1961) with an inflow and outflow system, we have investigated the roles of the external forcing in the interdecadal scale variation of the EJS thermohaline circulation. The model shows that the effect of TWC is manifested more strongly in the northern boxes where watermass formation occurs than the southern boxes, although the southern surface box is connected to TWC directly. The effect of the surface boundary conditions can be observed in all surface boxes, however. The model also shows TWC could have strong effect on the deep water mass formation rate.
OS21A-26 0830h
Modeling Wave-Current Induced Sediment Transport In A Tidal Flat
Deep Bay (Hong Kong) has a relatively shallow flow depth and consists of up to 30% of intertidal silt flats. Wave actions play an important role in the fate and transport of sediment in the shallow bay. A 3-dimensional split-operator finite element model has been applied to simulate the wave-current induced transport of cohesive sediment in Deep Bay. The wave climate is calculated by the conservation of wave action equation and the eikonal equation that take into account of wave refraction-diffraction and time varying non-uniform currents. The wind action has also been incorporated in the wave climate calculation. A tidal flow model is synchronously coupled with the wave model through a wave-current bottom boundary layer model and vertical eddy viscosity coefficients. A drying-wetting procedure is added to increase the numerical precision on the tidal flat calculation. The model was calibrated and verified against a set of 16-hour field measurements including water elevations, flow velocities, suspended sediment concentration, wind conditions, and swell properties collected in 1986 during a spring tidal period and a neap tidal period. The computed results are in the good agreement with the field measurements. The calibrated/validated model was then applied to simulate the sediment transport process in Deep Bay with the current coastline configuration and bathymetry setup. The wind factor is found to be important in modifying the wave propagation pattern in the bay region. It is also found that the suspended sediment concentration increases by 20 times if wave actions are in comparable magnitude with the current flow. The suspended sediment concentration is relatively higher at the month of the bay and may result in the formation of underwater bars at the bay entrance. The residual sediment flux in the bay is small suggesting that sediment deposition process is significant inside the bay. The computed results are useful for shore and environmental protection and coastal project management in the bay.
OS21A-27 0830h
Mature nature of back-arc basin magmatism in the actively spreading southern Mariana Trough
During the cruise of KAIREI, JAMSTEC, (KR03-13), from the November to December, 2003, submarine volcanic rocks were dredged from six sites on the active spreading ridges and two from the off-ridge seamounts at the southern Mariana Trough between 12.5 to13.5 deg. N. The chemical composition of those rocks, analyzed by XRF, are compared with those of previously studied rocks taken from the adjacent submarine arc volcanoes in this region for characterizing the heat source and geologic settings of the magmatism. The rocks from the spreading ridges are basaltic to andesitic composition, while the andesitic to dacitic composition for the rocks from two off-ridge seamounts, at one of which the active black smoker venting was newly found in October, 2003. Most of the major element concentrations linearly correlate to SiO2 content, suggesting that the chemical composition of the rocks from the spreading ridge and off-ridge seamounts were changed through differentiation of the magma(s) originated from the same or similar source(s). The higher silica and magnesium content and lower Mg\# in the studied rocks than those from the adjacent arc volcanoes are probably due to the lower temperature of source magmas. However, potassium depletion and phosphorous enrichment compared with those concentrations of arc volcanic rocks reflect the back-arc basin type nature of the source magmas of studied rocks. Back-arc basin type magmatism is more obvious in the trace element chemistry, i.e, the studied rocks show rather closer chemical composition to those of normal-MORB than those of the arc rocks. The back arc basin type nature of the magmatism is more obvious in the southern segment of the ridges south from 13deg.08min.N than in the northern segment. The topographic feature of ridge crest of southern segment, which is shallower than the northern segment, without axial valley is similar to the high speed spreading center such as East Pacific Rise. Combining with the chemical characteristics of the volcanic rocks and topographic features, the lower temperature back-arc basin type magmas would be actively producing in the shallow wedge mantle than the adjacent arc magmas in the studied area.
OS21A-28 0830h
Constraining the History of Circum-Antarctic Circulation With Paleo-Bathymetry Maps for the Southern Ocean
On a geological timescale first-order changes in paleo-climate, paleo-oceanography and marine sedimentation are controlled by plate tectonics through the distribution of land masses and ocean basins, the opening and closing of oceanic gateways, and changes in topography both on land and at sea. The breakup of Gondwanaland and subsequent isolation of Antarctica have lead to changing climatic conditions over time, in particular the cooling of the Southern Ocean region and growth of the Antarctic ice-sheet. Our objective is to produce a set of enhanced paleo-bathymetry maps based on plate reconstruction models for the Southern Ocean to help constrain the dynamic relationship between plate tectonics, ocean basin development, ocean circulation and climate change. We are now using the paleo-age grids to create a series of paleoceanic basement-depth grids, based on a thermal boundary layer depth-age model. We plan on generating enhanced paleo-bathymetry (topography) grids by combining geophysical models for oceanic crustal depth and geological data (water depth and other proxies) for continental margins; including key stratigraphic and fossil data from DSDP/ODP sites on stretched continental crust in the Drake Passage region and the Tasmanian gateway. In particular, we aim to investigate the effect of the opening and closing of oceanic gateways and changing ocean topography through time. It is known that the Antarctic Circumpolar Current (ACC) is strongly dependent on deep bottom topography, particularly the mid-ocean ridge system. However, no systematic modelling of the evolution of oceanic circulation with changing land and ocean floor topography has ever been carried out. It is hoped this work would offer a more realistic/resolved starting input for ocean basin configuration (paleo-geographic model) and topography (paleo-bathymetry model). It would be a valuable tool to assess boundary conditions for oceanographic circulation models and next generation CCM's; in particular it would help assess deep-water circulation and related climate change further back in geological time.
OS21A-29 0830h
Status of Real-time Operational Ocean Forecasting Model Developments at NCEP/NOAA
The Environmental Modeling Center/NOAA has been actively involved in developing a capability to produce real time ocean forecasts on an operational basis. The forecast system provides nowcasts and forecasts of the three dimensional state of the oceans on a daily basis and would consist of a suite of models that would address global scale, basin scale, and regional scale forecasting needs. In the initial stages of development, the ocean forecast system would be forced by mass, momentum, and heat fluxes from NCEP's operational numerical weather prediction models. Subsequently, coupled ocean-atmosphere model development issues would be addressed. Producing operational ocean forecasts started (in collaboration with NOS and Princeton university) with the use of Princeton Ocean Model covering a large area off the East Coast of U.S. The model domain extends from approximately 26.50 to 48.00N latitudes and from the coast out to 50.00W longitude. The horizontal resolution in the ocean model changes from 10 km near the coast to about 20 km offshore and the model has 19 sigma levels in the vertical. The domain has open boundaries at its southern and eastern extremes and is bounded by the coast line at its western extreme. Prescription of open-ocean boundary conditions and river inflow conditions on its coastal boundary is based on monthly climatologies. The ocean model is forced by surface fluxes derived from NCEP's operational mesoscale meteorological model (Eta model). Three semi-diurnal and three diurnal tidal components are also included in the model. Assimilation of SST data from in-situ and satellite sensors as well the sea surface height anomalies from satellite altimeters is included in the forecast system. The system (East Coast Regional Ocean Forecast System) produces a nowcast and a 48?hour forecast once every day and has become fully operational at NCEP in March 2002. Graphic products and grid point numerical fields are made available to the users over the internet at http://polar.ncep.noaa.gov. Efforts to generate such oceanographic nowcast/forecast information to cover all the coastal areas of the U.S. (the entire east Coast including the Gulf of Mexico and the Inter-American Seas, West Coast, Gulf of Alaska, and the Hawaii Region) and to provide a capability to run coupled ocean?atmosphere prediction models are now under progress using the Hybrid Coordinate Ocean Model (HYCOM) system as the basis. This system consists of a global model with a horizontal resolution (currently) of 1/3 degree and a separate basin scale model for the Atlantic Basin extending from 75 degrees north to 25 degrees south. High resolution domains for the West Coast of U.S., Gulf of Alaska, and the Hawaii Region will be nested within the global HYCOM domain. The basin scale and regional scale versions of HYCOM models will have 26 vertical levels and will be forced by fluxes from operational global atmospheric forecast model. All the HYCOM system models will include a full suite of ocean data assimilation procedures. The initial efforts of the HYCOM based system are focused on the Atlantic Basin domain using a curvilinear horizontal grid with a variable grid resolution which permits accurate predictions for coastal areas of the entire East Coast of U.S. including Gulf of Mexico and Inter-American Seas and supports development of improved coupled ocean-atmosphere models for tropical hurricane prediction. Preliminary results from the Atlantic Basin model and details on the future plans will be presented.
http://polar.ncep.noaa.gov
OS21A-30 0830h
SOUTHBERG: Preliminary results of the operation of 4 seismic stations on Iceberg C-16, Ross Sea, Antarctica
During the Austral Summer 2003-04, we operated a PASSCAL array of 4 short-period seismometers on Iceberg C-16, which was detached from the Ross Ice shelf in 2000 and is presently "parked" North of Ross Island. A broadband STS-2 instrument was also run at the central station. The up times range from 40 to 70 days, with 33 days of continuous, simultaneous recording at all 4 stations. The principal signals detected are of three kinds: (i) short, sharp, events featuring a white spectrum, and which probably represent simple episodes of cracking taking place in the ice; (ii) long episodes of relatively broad-band noise, of variable amplitude, lasting hundreds to thousands of seconds, occasionally superimposed over somewhat preferential frequencies; and (iii) resonant signals characterized by extremely narrow spectral lines (with overtones), similar to those recorded in Polynesia in 2000 from drifting icebergs and by seismic stations operating in the Ross Island region since 1998 [Talandier et al., 2002; Ruiz, 2003], with the frequency of all overtones fluctuating proportionately. One such signal, occurring on 15 January 2004, and targeted for preliminary analysis, appears to correlate with an episode of collision with and friction against B-15A, as documented from GPS data obtained on the latter. This interpretation is supported by enhanced amplitudes at the station closest to the contact with B-15A, and a phase advance for the development of the signal at that station. The signal was also recorded with similar characteristics by the land-based Erebus seismic monitoring network on nearby Ross Island. The iceberg stations also recorded teleseismic events, but feature a very high noise level below 0.04 Hz.
OS21A-31 0830h
Measuring complicated ice flow using differential SAR interferometry on Antarctic inland ice sheet
SAR interferometry proves to be the most effective method to measure the glacier velocity. However till now, most of the D-INSAR ice flow research activities are in Arctic and Antarctic costal ice shelf, where the ice flow concentrate between ridges and the pattern of fringe is simple and transparent. Grove Mountain is a newly-found meteorites trap where more than 4,000 meteorites were found. Large area of blue ice fields and many nunataks and outcrops spread the kernel region of Grove Mountain. Ice flow in Grove Mountain is quite complicated for the presence of outcrops and subglacial peaks. According to the data availability and D-INSAR methodology, five ERS and two JERS-1 synthetic aperture radar (SAR) interferometric data from two adjacent orbits acquired in 1996 are used. For one orbit, an ERS-1/2 tandem image pair and a subsequent ERS-1 image with 35-day interval are processed using 3-pass differential INSAR to get the ice flow fringe. In the other orbit, an ERS-1/2 tandem image pair is used to generate the DEM, while a JERS-1 pair with 44 days apart were combined for 4-pass differential INSAR to get the ice flow information. The overall visibility and continuity of the fringe from the JERS-1 pair is much better than that from ERS pair for L-band SAR interferometry allows longer temporal baseline and greater displacement in glacier velocity measurements. The research gives the ice flow result in Grove Mountain.