OS51D-01 INVITED
Topographic Rossby Waves in the Gulf of Mexico
Topographic Rossby waves (TRWs) have been investigated using arrays of current meter moorings and RAFOS drifters in three major regions of the deep Gulf of Mexico basin. They are the central northern Gulf, where the Sigsbee escarpment plays an important role in insulating the slope from energetic deep waves, around the northern and western sides of the Loop Current (LC) in the eastern basin, and over in the western Gulf, where fluctuations are much less energetic than further east. Ray tracing indicates that the western boundary of an extended LC is a likely generation region for TRWs. Further, the steep Sigsbee escarment tend to trap short (~ 10 day) period TRWs in the vicinity of 90W, and rectify longer period waves into a westward mean flow, manifested as a bottom trapped jet along the escarpment, in general agreement with recent theoretical models. Similar mechanisms appear to be important along the steep Mexican slope in the western Gulf. Lagrangian drifters deeper than 1500 m show generally rectilinear tracks that are compatible with propagating TRWs. There has been little evidence in these tracks of the existence of deep lower-layer eddies that are connected to, and translate with upper-layer LC anticyclones in some model simulations of the western basin of the Gulf. An overview of TRWs in the Gulf of Mexico basin, based primarily on extensive recent observations in the last 5 years, will discuss their characteristics, propagation, along with speculations on their generation and decay.
OS51D-02 INVITED
Surface velocity patterns in the Gulf of California from satellite-tracked drifters
A surface drifter program in the Gulf of California was started in June 2004, with monthly releases from ferries during one year and additional group releases from oceanographic cruises (still underway). A very strong (up to 80 cm/s) inflowing surface current on the mainland side of the Gulf was observed in June 2004 and July 2005, which can carry drifters from the entrance to the Upper Gulf in three weeks. The coastal current lasts a few weeks at most, but transports a large amount of heat into the Gulf, and is probably responsible for the observed progression of the surface isotherms during (climatological) June-July toward the head. Direct observations (CTD+LADCP) show that the coastal current is geostrophic and reaches to ~400 m depth. In July the coastal current disappears and eddies (both cyclonic and anticyclonic) become more evident. By August, these eddies are the dominant circulation feature, with surface currents ~25-50 cm/s, rotation period ~3-5 days and reaching to depths up to 1000 m. The eddy regime lasts until November, then a general surface outflow sets in and lasts until the next spring.
OS51D-03
Multidecadal Oscillations in the Northern Caribbean Salinity Gradient: Connections Between Surface Temperature, Wind Stress, Salinity and Ekman Transport
Coral skeletal oxygen isotopic variations are primarily controlled by temperature and the oxygen isotopic composition of the surface seawater. In most cases, this is controlled by regional changes in evaporation and precipitation, but may also be caused by advection of water masses with distinct isotopic composition. We present δ18O data from a coral growing off shore from southwestern Puerto Rico, representing surface temperature and seawater δ18O changes between 1751 and 2004 C. E. The data document multidecadal salinity variability in the Northern Caribbean that correlates with northern hemisphere sea surface temperature anomalies. The most recent shift in this multidecadal pattern occurs around 1970, and modern instrumental records are used with coral Δ14C from the same core to demonstrate what may have happened during previous shifts in the coral δ18O record. We hypothesize that the salinity changes around southwestern Puerto Rico are due to the advection of low salinity water from the southern Caribbean and/or Equatorial Atlantic regions in response to changes in mean wind stress curl and the resultant northward Ekman transport.
OS51D-04
IAS Mesoscale Surface Circulation Observed Through Satellite Altimetry and its Influence in a Small Scale, Coastal Domain, Studied with a ROMS Model of the Cariaco Basin.
The Intra-Americas Sea (IAS) surface circulation is characterized by large scale currents. The Caribbean current,
which originates in the Lesser Antilles, travels westwards through the Caribbean Sea and eastern Mexico and
passes through the Gulf of Mexico to finally form the Gulf Stream. This complex system of currents is also
characterized by a high mesoscale variability, such as eddies and meanders. The objectives of this work are
twofold: first, the multi-scale surface circulation of the IAS is described using satellite altimetry. The topographic
influence of the different basins forming the IAS, the characteristic time and spatial scales, and the time variability
of the surface circulation will be addressed. The second objective is to analyze the influence of this large scale
circulation on a small scale coastal domain with a ROMS-based model of the Cariaco basin (Venezuela). Cariaco
is a deep (1400 m), semi-enclosed basin connected to the open ocean by two shallow channels (Tortuga and
Centinela Channels). Its connection with the open sea, and therefore the ventilation of the basin, occurs in the
surface layers. The Cariaco ROMS model will be used to study the exchanges of mass, heat and salt through the
channels. A 1/60 degree ROMS model nested in the global 1/12 degree HYCOM model from the Naval Research
Laboratory will be used for this study. In addition, a series of observations (satellite altimetry and in situ
temperature, salinity and velocity data), will be used to assess the influence of the Caribbean circulation on the
basin.
http:ocgmod2.marine.usf.edu
OS51D-05
On the Origin of Mesoscale Variability in the Caribbean Sea
The circulation in the Caribbean Sea is investigated using a two-way nested high resolution configuration of the Océan Parallélisé (OPA) primitive equation model that includes the North Atlantic (1/3 degree) and Intra- Americas Sea (1/15 degree resolution). Consistent with altimetry data, the simulations show a westward growth of baroclinic eddies with maxima of variability in the Colombia Basin. The mesoscale presents a westward shift from periods of 50 days near the Lesser Antilles to periods of 100 days in the Cayman Basin associated with the growth and merging of eddies. Energy diagnostics suggest that baroclinic instability is the dominant mechanism controlling the variability in the Venezuela/Colombia Basins whereas in the Cayman Basin, barotropic instability is more important. The broad scale flow of the southern branch of the Subtropical Gyre divides into two branches within the Caribbean. The southern branch merges with the return flow from the meridional overturning circulation conforming the main Caribbean Current close to the continental coast, with the northern branch flowing close to the southern boundary of the Greater Antilles. This flow separation is associated with enhanced potential vorticity gradients which explains why the flow is more prone to instability. Seasonal variations in eddy kinetic energy are also analyzed.
OS51D-06
Fine Resolution Termohaline Structure Of The Yuctatan Coastal Sea
In the Yucatan peninsula there are a variety processes that drastically affect the thermohaline structure of the coastal seas. Some of these include hyperhaline lagoons that export salt to the ocean, upwelling events that propagate to the coast, persistent submarine groundwater discharges, and very high evaporation rates caused by the intense solar radiation. On July 2006 a fine resolution oceanographic campaign was performed on the Yucatan coast to study the detailed structure of thermohaline processes and currents from the shore to the 10 m isobath. A total of sixty nine transects that cover the entire northern stretch of the Yucatan coast were made. The transects extend seven kilometers in the offshore direction and have an alongshore spacing of 5 km. The temperature and salinity characteristics of the water column were monitored with a SEABIRD SBE 19 CTD performing profiles every 500 m along each transect. Ocean currents were measures along the same transect using a 1.5 MHz Acoustic Doppler Profiler (Sontek). The results clearly show the effects of coastal lagoons on the adjoining sea, with net salt export associated with hyperhaline lagoons (e.g. Ria Lagartos) or more estuarine influence of lagoons such as Celestun, where groundwater discharges play the role of rivers on the estuary. An assessment of this influence on the coastal ocean will be presented. It is well known the meteor impact at the end of the Cretacic era at Chicxulub, Yucatan, generated a crater with multiple rings which is evident from horizontal gravity gradients of the Yucatan mainland, and that associated with the outer ring there is a high concentration of cenotes (sinkholes) (Pope et al. 1991; Hildebrand, et al. 1995). It has also been shown that groundwater flows along this cenote ring towards the ocean, and the zones where the ring intersects the coast (Celestun and Dzilam Bravo) have impressive geologic features known as ‘submarine water springs' where freshwater springs as a fountain in the ocean. Additional (higher resolution) field campaigns have been performed in the vicinity of such features. Results will be presented where the effect of such intense submarine groundwater discharges (SGD) on the coastal ocean of the Yucatan is evident. The salinity in the surrounding areas of the SGD sites can vary from 10 to 26 psu, this is a substantial effect when considering that the background coastal salinity ranges between 35 to 36 psu. The salinity signal also shows that SGD events in some regions of the Yucatan coast can alter the ambient salinity dramatically and be momentarily more important than those SGD associated with the cenote ring. Pope K.O. et al. 1991. Nature. Mexican site for K/T impact crater? V-351, 105. Hildebrand, A.R. et al. 1995. Nature. Size and structure of the Chicxulub crater revealed by horizontal gravity gradients and cenotes. V-376. p. 415-417.
OS51D-07
Thermal and salinity signals across the San Lorenzo Sill in the Gulf of California. Are gulfies and IPW cascading down slope already in historical data?
Midscale high salinity structures known as "gulfies" are identified in the central regions of the Gulf of California using all available hydrographic historical data. Cluster of temperature and salinity data are arrayed in a 400 km line from Guaymas basin (26 N,112 W) to the upper limit of Angel de la Guardia Island with the propose of provide evidences of the outflow and inflows in the close proximity to San Lorenzo-San Esteban sill. Based on discrete data analysis three layers of fluid are identified over the sill, two layers in opposite directions and one deep layer of cold inflow (mouth to head), particularly active during winter. The first layer, near surface is a high salinity warm outflow across the sill, from head to mouth, within a depth of 150 m forming eddy like pulses with a form and structure that may be related to "gulfies". The second layer across the sill is in opposite direction (mouth to head). Temperature and salinity data shows that this layer is formed by Subsurface Subtropical Water of Pacific Ocean origin. The third layer cross the sill near bottom (450m), this layer is a cold temperature and low salinity inflow of Pacific Intermediate Water PIW available in the Guaymas Basin apparently with more predominance during winter time. Signal analysis shows that high salinity water outflow progressing over the sill with a velocity of 4 km day-1, apparently with a larger transport during winter. The PIW inflow progress over the sill with a velocity of 0.6 kmday- 1, cascading immediately down the slope one it had crossed the sill. The amount of heat integrated above 500 m reveals that the lowest overall temperature is in the region close to the sill; while the warmer overall temperature is in the west region of the gulf along Ballenas-Salsipuedes channel.
OS51D-08
Thermosteric effect of the seasonal sea level variation component in the adjacent seas to Korean peninsula
The analysis of seasonal sea level variation in surrounding seas to Korean peninsula revealed that there exist some systematic pattern for the Sa amplitude varying from 20 to 10cm, depending upon the regions such as the Yellow Sea, South Sea and East/Japan Sea (EJS). Results from the analysis of coastal tidal data are presented as well as the analysis result from the satellite altimetry data of Topex/Poseidon, which shows that Sa amplitude from the adjusted sea level are about 7 or so in the Yellow Sea, while its magnitude in the East/Japan Sea is about 3cm. The physical factors, such as atmospheric force and thermosteric force, to influence the seasonal variation of sea level are examined in order to understand the mechanism of spatially systematic variation of the seasonal sea level variation component Sa. The spatial distribution of Sa amplitude by inverse barometric effect varies 10cm to 8cm from the Yellow Sea, through South Sea, to the EJS, respectively. This inverse barometric force alone does not explain the amplitude variation over the surrounding seas to Korean peninsula. Interesting point to note is that additional major contribution is from the origin of sea level change by the thermosteric effect. Naturally we focus upon the contribution of thermosteric sea level to the observed Sa variability in the Yellow and East/Japan Seas. In the Yellow Sea the Sa amplitudes by the thermosteric effect are about 5 to 7cm from 10 to 20 year data analysis, and the phase of peak amplitude occurs in August by seasonal solar radiation, similarly to the phase lag of early July by inverse barometric effect. Meanwhile, the amplitude contribution by the thermosteric sea level in the EJS is 3 to 4cm, and Sa peak lags by about 50˘©¨ˇthan in the Yellow Sea, due to possibly different physical phenomenon from the Yellow Sea in summer season. It is known that the cold water mass from the northern EJS flows toward the southern and southwestern direction, which may drive a different TSL contribution from the Yellow Sea where solar radiation is the main forcing to water column. Summation of two component with representative phase lag explains reasonably better the observed Sa results in the Yellow and East/Japan Seas than inverse barometric effect. Therefore, it is likely that the main driving force to the spatial amplitude variability of the Sa component is the differently lagged contribution from the shallow Yellow Sea and deep EJS where North Korea Cold water and/or EJS Intermediate Water keeps flowing southwestward, toward the Korean coasts of the EJS. Analysis result of the Sa amplitude from Topex/Poseidon data also shows such a pattern in the surrounding seas to Korean peninsula. Acknowledgement: This work was partially supported by research program (PG45100 and PE97604).