OS53A-01
On the Squeezing of the North Brazil Current Rings Through the Lesser Antilles as Observed From Satellite Data
The North Brazil Current Rings (NBCR) penetration into the Caribbean Sea is being investigated employing a merged altimeter-derived sea height anomaly (TOPEX/Poseidon, Jason-1 and ERS-1,2), the ocean surface color data (SeaWiFS) and Global Drifter Program information. Four strategies are being applied to process the data: (1) calculations of Okubo-Weiss parameter for NBCR identification, (2) longitude-time plots (also known as Hovmöller diagrams), (3) two-dimensional Radon transforms and (4) two-dimensional Fourier transforms. A twofold NBCR structure has been detected in the region under investigation. The results have shown that NBC rings mainly propagate into the Caribbean Sea along two principal pathways (near 12ºN and 17ºN) in the ring translation corridor. Thus, rings following the southern pathway in the fall-winter period can enter through very shallow southern straits as non-coherent structures. A different behavior is observed near the northern pathway (near 17ºN), where NBC rings are thought to have a coherent structure during their squeezing into the eastern Caribbean, i.e. conserving the principal characteristics of the incident rings. We attribute this difference in the rings' behavior to the vertical scales of the rings and to the bottom topography features in the vicinity of the Lesser Antilles.
OS53A-02
The response of the East China Sea to the Typhoon Ewiniar 2006
Response of the upper ocean to the typhoon Ewiniar 2006 in the northern East China Sea (ECS) has been investigated using observations at Ieodo Ocean Research Station (IORS) and TRMM Microwave Imager (TMI) data. Typhoon Ewiniar 2006 lasted about twelve days since it was born near the Micronesia in the Western Pacific. It moved generally northward and it was less than two days on the ECS until it made a landfall on the western region of Korea. Evidences of the interaction between the typhoon Ewiniar and the ECS have been found at the data gathered IORS, especially when the distance between the Ewiniar and IORS was shortest (less than 70 km). The water temperature drop in the upper layer was very large as much as about 9 - 10 ° C during 15 hours. The TMI sea surface temperature supports this evidence showing about 7.6 ° C drop of the water temperature during a day. Though the cooling of upper ECS seems to be happened along the entire Ewiniar track in the ECS, the temperature drop range was not as high as at the IORS. Waters around ECS shelf near to the IORS affected much more because of relatively shallow water depth with thin mixed layer as well as cold and relatively saline bottom waters underlying it. It should be noted that this strong influence of the typhoon Ewiniar on the ECS shelf plays a negative feedback to the Ewiniar intensity resulting in rapid weakening of its strength. The interaction between the Ewiniar and the waters around the IORS is larger than other ECS area could be explained by the relatively low translation speed of the typhoon Ewiniar.
OS53A-03
Larval Fish Assemblages, Environment and Circulation in a Semienclosed Sea (Gulf Of California).
Fish larvae and hydrographic data collected in the Gulf of California in December 2002 are used to describe the larval fish assemblages and to explore their relationships with environmental variables. The Bray-Curtis dissimilarity index defined three larval fish assemblages, whose goeographical distribution coincided with three areas defined by Principal Component Analysis of the environmental variables. The affinity of most of the species with the environmental characteristics of their areas of distribution could be interpreted as an indication that spawning occurred inside those areas. However, it is not known when the spawning took place, and the fast currents in the Gulf could rapidly disperse eggs and larvae. Since transport and retention is best studied from a Lagrangian point of view, the currents from a 3D numerical model were used to track large numbers of particles released in the different larval fish assemblage areas. Particle-tracking and connectivity matrices can help in assessing larval fish retention in seas that, like the Gulf of California, have well defined circulation patterns. On time scales around 30 days, retention occurred for the North assemblage in the Upper Gulf, for the Channel- Central assemblage in the anticyclone over the Norhern Gulf and in Ballenas Channel, and for the South assemblage in the eddy over San Pedro Mártir basin and in the shallow zone off the peninsula. Therefore, the Lagrangian analysis revealed that the observed larval fish assemblages have a permanency long enough to allow the larve to remain in a favorable environment until they develop motility.
OS53A-04
Penetration of Anthropogenic Chlorofluorocarbon Gases to Thermocline and Intermediate Waters in the Northwestern Gulf of Mexico
Distributions of the dissolved chlorofluorocarbons (CFCs) were measured at several locations in the northwestern Gulf of Mexico during the Omega 06 expedition in August 2006 as time-dependent tracers for decadal-scale ocean circulation and ventilation processes. Vertical profiles of CFC-11 concentrations exhibit a maximum (~2 pmol/kg) associated with the base of salinity maximum layer (S~36.5 at ~26 σθ), and monotonically decreasing concentrations with increasing depth below this layer. A deepest hydrographic measurement (~1900 m) near an anticyclonic Loop Current Eddy shows deepest penetration of CFC-11 over 1000 m depth and below which depth the concentration was at blank level. The penetration depth of CFC-11 in this area is deeper than the oxygen minimum depth (400-500 m) and the intermediate salinity minimum depth (700-800 m). Higher concentrations of CFC-11 and dissolved oxygen near the anticyclonic eddy compared to the other areas at the same depth due to a deepening of isopycnals suggest a potential of diffusive ventilation of intermediate waters by eddy disintegration process near the southern and western shelf areas in the Gulf. Unlike CFC-11, CFC-113 and carbon tetrachloride show rapid decrease with depth toward minimum concentration levels in the upper 200 m water column indicating a presence of non- physical removal mechanism for these gases.
OS53A-05
Sediment Re-suspension in a Shallow Tidal Sea: The Upper Gulf of California.
Current velocity and concentration of suspended particulate matter (SPM) were measured near the sea bed at two stations on opposite sides of the Upper Gulf of California, during a fortnightly cycle. This shallow, macro tidal inverse estuary is very turbid due to high concentration of re-suspended sediments. During spring tides SPM concentration revealed a strong quarter-diurnal signal and "twin-peak" structure, both typical of the semi-diurnal tidal forcing. During neap tides, remarkable high concentration peaks exceeded those observed in spring tides. Values of the erosion threshold and the concentration rate of change were obtained from the time series of bed shear stress and SPM concentration. A simple expression in terms of the concentration rate or change and the normalized excess bed shear stress was used to calculate single-level, near-bed SPM concentration during the fortnightly cycle. A variable erosion threshold ( 0.05 to 0.5 Pa ) extracted from the 15-day time series allowed calculation of high concentration events under neap tide conditions. Such outstanding events are proposed to be caused by the re-suspension of bottom fluff layers under low bed shear stress, combined with near-bed horizontal advection.
OS53A-06
Metal in sediments of coastal lagoon, SE Gulf of Mexico, for Scanning Electron Microscopy
The entrance of metals product of the numerous residual, agricultural and industrial water unloadings, is registered in the sediment layers of the bottoms lagunares. The quantitative analysis of present metals by SEM, contributes accurate data on the superficial characteristics of the sediments in which it is catched the metal, assuring reliable data, obtained quickly.
OS53A-07
Interannual variability of satellite-derived productivity in the Gulf of Mexico and its association with ENSO events
The spatial and temporal variability of satellite-derived primary productivity indices and its relation to the El Niño Southern Oscillation (ENSO) in the Gulf of Mexico (GoM) were investigated during the period 1996-2007. Time series of chlorophyll a concentration (Chl-a, referred to as Chlo when derived from the standard band ratio algorithms), net primary production (NPP) and export flux of carbon (EF) were estimated using satellite-derived data from the OCTS and SeaWiFS and sea surface temperature data (SST) from the AVHRR. We also compared estimates of Chl-a using the GSM01 algorithm (ChlGSM) and discussed the influence of colored dissolved and detrital organic material (CDM). Chlo and ChlGSM were examined by the EOF method to identify areas with similar spatial and temporal variability. The first EOF derived from both sources was well correlated with the ENSO of 1997-1998, 2002 and 2004. During the 1997-1998 ENSO Chl-a was increased in the northern part (Chlo and ChlGSM increased by ~180%) but suppressed in the south-western shelf (Chlo and ChlGSM decreased by ~20%). Differences between the OC4v4 and GSM01 algorithms were higher in the northern part and were related to the influence of the CDM on Chl-a estimates. Nevertheless, the effects of the ENSO were not masked by the CDM influence as the signal was recognized on both of the Chl-a estimates. Enhanced NPP and EF were found in the south-western GoM as a response to mesoscale eddies. The overall results suggest a very large response of primary productivity and SST indices in the GoM to the ENSO forcing.
OS53A-08
Low Frequency Waves Through the Gulf of California: Observations and Models
Long time series of sea surface temperature and surface height along the Mexican Pacific coast show that propagating coastal Kelvin waves, some cases propagate to the interior of the Gulf of California, while in some other cases they completely skip the gulf and the waves propagate through the gulf mouth to the western side of the peninsula de Baja California and to the north. Using satellite observations to identified events and a combination of numerical (ROMS) and analytical model, we investigate this phenomena focusing on discerning the set of conditions (mainly intensity and frequency of the waves) that determine which of these two main outcomes develops. Preliminary results are presented.
OS53A-09
Seasonal Sea Level Variations in the Gulf of Mexico
Surface height anomaly data and numerical model results are analyzed to identify the low-frequency variability of the sea level in the Gulf of Mexico. East-west and north-south oscillations with annual period are identified, which are associated with the low-frequency wind variability.
OS53A-10
Regionalization of the Gulf of Mexico Based on the Annual Cycle of Chlorophyll-a Concentration
Monthly mean SeaWiFS chlorophyll-a concentration data for the period 1997-2005 are analyzed in order to identify regions with similar behavior in the Gulf of Mexico basin. Based on Principal Component, EOFs, and scatterplot analyses, 12 regions are identified with different chlorophyll-a concentration variability on the annual scale. The physical processes that may be associated in each region are discussed.
OS53A-11
Visualization of Coastal Attached Waves in the Gulf of Mexico
Different visualization techniques were implemented in order to visualize coastal trapped waved in the Gulf of Mexico. Model sea surface height anomalies data were filtered in order to enhance the high frequency variability associated with coastal waves and filter low frequency anomalies, mainly associated with the Loop Current and eddies. OpenGL interactive visualizations allow the user to zoom in any region of interest, stop, run or even run back the animation and look from different angles.
OS53A-12
The circulation around Chinchorro Bank
Chinchorro Bank is the only atoll-like reef in the Caribbean Sea, centered at 87° 21' W, 18° 35' N. It has an oval shape and approximately 44 km length and 20 km width. A channel separating its western rim from the Yucatan Peninsula has a width of 30 km and a sill depth of 700 m. The channel has a mean northward current of 30 cm/s implying a mean transport on the order of 7 Sv. Ten months (5/2006-2/2007) of direct measurements at three locations around the Bank, just outside the reef rim at 20 m depth, combined with previous current information from nearby deep-water current moorings, are used to investigate the circulation in the region. The recent dataset includes measurements of the current profile, subsurface pressure, bottom water temperature and surface waves, along with geostrophic current estimates calculated from pressure sensors on both sides of the channel. Although the flow at the three locations have significant westward mean currents, revealing the influence of the large-scale prevailing flow in the Bank's surroundings, only the southern location is highly correlated with the along-channel geostrophic flow. The coastal boundary layer seems to be decoupled from the along-channel main flow at the western (i.e. the lateral boundary of the channel) and the northern reef flanks. Altimetry and drifter observations show southern flow events within the channel that are caused by the passage of cyclonic eddies through the region. These eddies, of radius larger than the channel's width and with their western edge against the Yucatan Peninsula, sometimes remain in the Bank's vicinity for several days before drifting northward. Although winds and wave-induced flow play secondary roles in the long-term circulation patterns, their influence increases during intense winter meteorological events, locally known as "Nortes".
OS53A-13
Larval Fish Assemblages and Geostrophic Circulation in Bahía de La Paz and the Surrounding Southwestern Region of the Gulf of California.
Using hydrographic data and zooplankton samples from four oceanographic cruises during May, July and October 2001 and February 2002, we analyze the relationship between larval fish assemblages and geostrophic flows in Bahía de La Paz and the neighbouring Southwest Gulf of California. The analysis of fish larvae distribution linked to geostrophic circulation is an innovative interdisciplinary approach for the understanding of fish larvae ecology. The Bray-Curtis Dissimilarity Index defined two types of larval fish assemblages with seasonal variations: 1) The Coastal assemblage which was dominated by epipelagic coastal species like Sardinops caeruleus, Ophistonema spp. and 2). The Oceanic assemblages: Oceanic and Transitional-Oceanic assemblages, both dominated by mesopelagic species like Vinciguerria lucetia, Diogenichthys laternatus, Benthosema panamense but with different relative larval abundance and frequency of occurrence. The seasonal variations of the assemblages inside Bahía de La Paz appear to be related to the water exchanges between the bay and the Gulf of California. During July and October the geostrophic flow through the North Mouth is strong and as consequence, the Transitional-Oceanic assemblage cover practically the whole bay, while during February and May, when the geostrophic transport through the North Mouth is weak, the Coastal assemblage spreads over the whole bay. Results show that the spatial distribution of larval fish assemblages during the sampled periods is linked with the patterns of geostrophic circulation. This suggests that large amounts of fish larvae are transported by geostrophic flow, rather than by the total currents (Ekman plus geostrophic). The cyclonic geostrophic pattern of circulation during the warm period was also detected with direct observations of velocities from June to October of 2004.
OS53A-14
Sea Surface Temperature Anomalies in the Gulf of California
A twenty year set of sea surface temperature measurements, taken by Pathfinder V5 satellite between January 1985 and December 2004, reveals that, in average, the lower levels of temperature are concentrated between the 28°N and 30°N. This is the region where the large islands and umbrals, in the middle gulf, are located. It has been shown that this is an important factor in the oceanography of the region. The Regional Ocean Modeling System (ROMS) has been used to identify the relevant factors involved in the characteristic and latitudinaly anomalous cooling of the region. We are particulary interested on the relevance of tides through tidal mixig and pumping. Heat balances have been calculated using ROMS run with and without tidal forcing to isolate the different mechanisms and components of the heat balance equation. Preliminary results are presented.
OS53A-15
The Death of Two Eddies, Against the Shelf
A set of five moorings deployed in front of the coast of Tamaulipas, western Gulf of Mexico, provided fourteen months (from August 2004 to November 2005) of surface to bottom observations of currents and temperature that document the processes associated with the collision and dissipation of two warm mesoscale eddies with the continental slope. Two Loop Current eddies (Titanic and Ulysses) were identified reaching the study area during the observation period. On September 2004, the two southernmost 2000-m moorings show that temperature and salinity increases throughout the entire water column, related to eddy Titanic; similarily; on April 2005, eddy Ulysses caused a strong increase of temperature in the 3500-m mooring. The velocity field suggests three different régimes: a coastal region, the continental slope currents, and the abyssal circulation. Over the slope, three different layers can be identified: a surface layer (above 500 m depth), influenced by eddies and transients, a deep layer (under de 1900 m) with a persistent southerly current and a transition layer (from 500 to 1900 m) that separates them. The variance ellipses at ~ 700 m at the 3500-m mooring have no a predominant orientation of the mayor axis. At the northernmost 2000-m mooring, the axis of maximum variation is oriented with the bathymetry, but at the southernmost 2000-m mooring it is perpendicular to the coast. The spectral characteristics of the measurements are also discussed.