OS52A-01 INVITED
CANEK: 10 Years of Observations and Modeling of the Circulation in the Caribbean Sea and the Gulf of Mexico
The studies of the Gulf of Mexico and the Caribbean Sea within the CANEK Program initiated in December 1996 and continue until now. More than 12 oceanographic cruises, the deployment of year-long shallow and deep moorings at several locations within the GM and the Mexican Caribbean and numerical modeling efforts, have permitted to investigate important aspects of the circulation in the region. Among the most important findings of the Program: 1) That the transport through the Yucatan Channel (YC) during (8/1999-7/2001) was 24 Sv, representing a deficit with respect to the transport of the Gulf Stream within 18 degree water characteristic of the Subtropical Atlantic and less than the "expected" 28 Sv. 2) Deep counterflows (from the Gulf of Mexico into the Caribbean Sea) were found on both sides of Yucatan Channel; The deep flow there is intimately related with the extension and penetration of the Loop Current into the Gulf of Mexico. 3) The flow variability in the Mexican Caribbean, including the Yucatan Current, is dominated by the presence of meso-scale eddies of both signs. The vorticity anomalies that flow through the channel directly influence the retraction of the Loop Current and the detachment of anticyclonic eddies, that latter propagate westward, dominating a large part of the observed variability in the Gulf. 4) The circulation on fringing reef lagoons along the Mexican Caribbean is mostly dominated by surface waves breaking over the reef and spilling water inward. These flows are modulated by sea level changes related to the position and intensity of the Yucatan Current. An analysis of these observations in conjunction with satellite altimetry and SST and numerical model simulations, demonstrate the indirect connection between the different basins in the Caribbean Sea, that is modulated by the instability of the prevailing currents in the region
OS52A-02 INVITED
Impact of the Atlantic Warm Pool on Climate and Hurricanes: An Overview of Recent Understanding
The Atlantic Warm Pool (AWP) with a large body of warm water is comprised of the Intra-Americas Sea (i.e., the Gulf of Mexico and the Caribbean Sea) and the western tropical North Atlantic. Located to its northeastern side is the North Atlantic Subtropical High (NASH) that produces the tropical easterly trade winds. The easterly trade winds carry moisture from the tropical North Atlantic into the Caribbean Sea where the flow intensifies forming the Caribbean Low-Level Jet (CLLJ). The CLLJ then splits into two branches: One turning northward and connecting with the Great Plains Low-Level Jet (GPLLJ), and the other one continuing westward across Central America into the eastern North Pacific. The easterly CLLJ and its moisture transport are maximized in the summer and winter, whereas they are minimized in the fall and spring. This semi-annual feature results from the semi-annual variation of sea level pressure in the Caribbean region owing to the westward extension and eastward retreat of the NASH. The summertime strong easterly CLLJ is associated with a maximum of sea level pressure, a relative minimum of rainfall (the mid-summer drought), and a minimum of tropical cyclogenesis in July in the Caribbean Sea. The NCAR community atmospheric model ensemble runs show that climate response to the AWP heating extends beyond the AWP region to the eastern North Pacific and North America, owing to the westward propagation of Rossby wave response. The effect of the AWP is to weaken the summertime NASH, especially at its southwestern edge. The AWP also strengthens the summertime continental low over the North American monsoon region. In response to these pressure changes, the easterly CLLJ and its moisture transport are weakened, but its semi-annual feature does not change. The AWP-induced change of atmospheric circulation changes the moisture convergence that results in increased rainfall in the AWP region and the eastern North Pacific. The model runs also show that the effect of the AWP is to weaken the southerly GPLLJ and its northward moisture transport and thus to decrease rainfall in the United States east of the Rocky Mountains. Finally, the AWP largely reduces the tropospheric vertical wind shear in the main development region that favors hurricane formation and development during August-October.
OS52A-03
Deep overflow of Atlantic waters to the Caribbean Sea through Windward Passage
From October 2003 to February 2005 a field experiment was conducted in the Windward Passage to determine the mean flow structure in the passage and its variability on time scales from tidal to seasonal. The study included measurements of the deep inflow of North Atlantic Deep Water over the ~1670 m sill in Windward Passage. These are the first direct measurements of this deep inflow, which represents one of only two pathways by which deep waters of the Caribbean and Gulf can be ventilated from the Atlantic (the other being the Anegada/Jungfern passage south of Puerto Rico). Current meters located at the sill recorded a persistent inflow with typical speeds of 20-40 cm/s, and only occasional interruptions. Four shipboard surveys of the passage provide an additional view of the deep overflow and its penetration into the abyssal Caribbean. Preliminary estimates of the mean deep inflow suggest a value near 0.4 Sv, which is about twice the corresponding value for the Anegada/Junfern inflow and indicates that Windward Passage in fact may be the dominant deep water source for the Caribbean. The source of the deep inflow through Windward passage is derived from a branch of the Deep Western Boundary Current (DWBC) that splits off the main path of the DWBC outside the Bahamas and filters through deep passages in the central Bahamas, a new discovery made in this program. Repeated sections made across the deep passages in the southern Bahamas show that nearly all of the upper DWBC (associated with waters formed in the Labrador Sea), is diverted through these passages to form a strong deep jet of 5-7 Sv flowing southeastward along the coasts of Cuba and Hispaniola, inside the Bahamas island arc. A small portion of this flow spills through Windward Passage before this deep jet rejoins the main path of the DWBC off Puerto Rico.
OS52A-04
Two Overflows in the Northern Gulf of California
Two overflows in the Northern Gulf of California are marked by strong average slopes of 15 and 5%. The long term (~ a year) average current at both sills is bottom intensified with average speeds of about 30 and 15 cm/s, respectively. At both sills there are strong tidal currents, but the low-frequency currents are quite persistent with very few flow reversals. Near-bottom stratification upstream (with respect to the overflows) of both sills is relatively strong, but downstream of the sills the near-bottom water is very well mixed and the bottom density is essentially the same as the one found at the sills, despite the almost two-fold (~ 600 m) and more than three-fold (~ 1500 m) increase in depth at the downstream basins. The homogenization of a thick bottom layer downstream, albeit close to the sills, is indicative of very strong mixing. These hydrographic patterns were observed during three different seasons. These results indicate that the deep water in Ballenas Channel is renewed by these overflows which enter at sill depths of ≤ 400 m and which are capable of reaching the deepest part of the basin at ~ 1500 m.
OS52A-05
The Colombia Current: An Eastern Tropical Pacific Coastal Current, Early Oceanographic Characteristics
Newly gathered hydrographic data from the Colombia Pacific Ocean is combined with remote sensing data to reassess the properties of the costal current named Colombian Current by Wooster (1959). The Colombian Pacific Ocean is located between 84°-76°W and 1°30'-5°N (oceanic zone), 1°30'- 7°N (coastal zone): This area is well-known also like Panama Bight. New hydrographic data were occupied along the Colombian Pacific coast during March of 2006, making 41 stations with measurements of CTD until a maximum depth of 1200 m, depending on the depth of the marine bottom. On the other hand, sea surface temperatures (SST) were obtained from the MODIS-AQUA satellite and sea surface wind speed and wind direction stem from QuickScat, both averaged for March 2006. Hydrographic grid layers necessary to obtain dynamic topography variable were made with objective mapping calculating is not total dynamic height, but the dynamic height between consecutive levels or "thickness". The purpose of this methodology is that in very coastal campaigns it can have a substantial number of stations that do not arrive at the reference level. Finally geostrophic velocity was computed for the Colombian Current area at several layers. The coast was characterized by low salinities due to river runoff in the North zone. The sea surface temperature during the month of March of 2006 was especially low in the oceanic zone, reaching temperatures between 19°C and 24°C.The dynamic topography indicated the presence of a surface coastal current flowing towards the north and a crosscurrent to 400 m of depth never before described. The wind corresponded to the pattern of the wind jet of Panama. During March the ITCZ moves south, drawing the Panama jet across the Isthmus and over the Pacific. Upwelling curl associated with the left (southeast) flank of this jet generates a cyclonic eddy in the Panama Bight and SST cooling in its center. In the Panama Bight, the curl dipole produces a cyclonic circulation with northward flow along the Colombian coast. Cool SST along the coast of Colombia might be a response to the upwelling curl, especially considering that the mean poleward winds favor coastal downwelling.
OS52A-06
Connectivity in the Northern Gulf of California From Particle Tracking in a Three-Dimensional Numerical Model
The northern Gulf of California, Mexico, is one of the most productive and diverse marine ecosystems in the world. It currently harbors three marine protected areas, including two biosphere reserves. Despite its significance as a conservation site and its importance for Mexico's fisheries, proper knowledge of population connectivity and larvae dispersal from spawning sites is largely lacking. Our study focuses on connectivity in the northern gulf resulting from advection by currents and turbulent diffusion during summer, the main spawning period of various key commercial species. We calculated connectivity matrices in the northern Gulf from currents produced by the output of a three-dimensional baroclinic numerical model and a random walk process to simulate turbulent motions. We released 2000 hypothetical passive particles in each of 21 areas along the coast (between 0-60 m deep) during the summer and followed their trajectories for periods of 2, 4, 6, and 8 weeks. For the case of full time transport, the effects of tidal currents are minimal in the overall dispersal of passive particles on the time scales studied. However, this can be substantially altered if the particles are allowed to avoid being transported for periods of time. We found that regional hydrodynamics explain a cyclonic downstream connectivity along the coast, from the mainland to the Baja California coast. Our results provide the basis for a full connectivity study where larvae behavior and settlement habitat will be included
OS52A-07
Lagrangean description of the gulf of California: numerical model
Results of a new implementation of a circulation model (ROMS) for the Gulf of California are presented. The general circulation characteristics for the Gulf are described based on these results. Emphasis is placed on understanding the similarities and differences with previous model. It is shown that the seasonal circulation is dominated by a series of shallow gyres with an alternating sense of circulation and spatial scales as the wide of the gulf. We discuss the formation and evolution of these gyres in relation to theirs forcing agents (i.e. winds, boundary forcing through the mouth and geometry) and generating processes (i.e. instabilities) and dissipation. The implication of the gyres on the redistribution of characteristics is analyzed. A Lagrangean description of the gulf is presented.
OS52A-08
Volume Transport and Variability at Windward Passage
The Gulf Stream system is fed via Atlantic inflow through the passages of the Bahamas and the Caribbean. In contrast to the large amount of research focusing on the downstream components of this system (Florida Current, Gulf Stream, Gulf Stream extension), far fewer measurements of Atlantic inflow into the Caribbean Sea through the Caribbean passages have been made. Of all of the major Caribbean passages, the volume transport and variability through Windward Passage is probably the least well understood, even though it is recognized as an important inflow channel. Between October 2003 and February 2005, a moored current meter array was deployed across the shallowest part of Windward Passage, and four hydrographic and lowered-ADCP surveys were conducted in the region. Stations were located along sections at Windward Passage and passages upstream, including passages between Cuba and Great Inagua, and Haiti and Great Inagua, and selected passages through the southern Bahamas and Turks and Caicos. Sections were also occupied downstream of Windward Passage across the axis of the Cayman Basin. The transport entering Windward Passage is highly variable, including reversals to net outflow. Transports measured during the cruises ranged from -0.3 Sv (outflow) to 9.4 Sv (inflow), with an average inflow of 3.8 Sv. Corresponding transports derived from the current meter array range from approximately -5 to 15 Sv, with an average inflow of 3.6 Sv. On average there is net inflow in the surface and thermocline layers (above ~600 m), net outflow in the intermediate layer (~700-1200 m), and a deep inflow just above the bottom. Data gathered from lowered and hull-mounted instrumentation during these surveys have helped to resolve the vertical and horizontal structure of the flow through the passage and will be used in conjunction with the hydrographic data to quantify the volumes of the different water masses flowing through the passage and their regional pathways.