Texas Louisiana Research Articles

Circulation over the continental shelf in the northern Gulf of Mexico

More than 750 surface drifters were deployed over the northern continental shelf in the Gulf of Mexico (gulf) from 1993 through 1998. Drifters were mostly air-deployed on a schedule giving continuous data over much of the Texas–Louisiana and west Florida shelves for an entire year. The drifter data are analyzed to give descriptive, statistical, and dynamical views of the northern gulf circulation on synoptic to seasonal scales. Circulation on both the Texas–Louisiana and west Florida shelves is characterized by coherent along-shore and across-shore modes which explain more than 50% of the variance. A pronounced seasonal cycle exists on the Texas–Louisiana shelf, but not the west Florida shelf. Both shelves display synoptic signals due to local wind forcing. Strong connectivity between the shelves occurs during isolated period of strong winds associated with the passage of tropical storms. Eddies impinging upon the shelf are responsible for moving drifters cross-shore. Offshore flows generally occur prior to reversals in the along-shore direction. Regions with near zero mean velocities but large total energy exist. Drifters leave these areas and move thorough much of the Gulf and into the Atlantic within 90 days despite negligible annual mean Eulerian velocities.

Caddo Archives and Economies

This article is a discussion of archival research on contact through historic period (ca. A.D. 1519 to 18th century) Caddo groups in eastern Texas and west central Louisiana. First, I describe general objectives for current and long-term research on the Caddo Indians, followed by the central issues the article will address. A brief summary of protohistoric and historic events, actors, and sources will be followed by methodological considerations, as well as a discussion of Caddo economies, concluding with some reflections on Caddo archives and economies. This article explores the complex and interrelated economies of Native American and European populations during the colonization process in early Spanish Texas.

Bossier Tribes, Caddo in North Louisiana's Pineywoods

Clarence Webb (1948) christened Bossier more than a half century ago. Its namesake was the northwestern Louisiana parish where several Bossier sites were located, but it could just as easily been named after Webster, Claiborne, Harrison, Columbia, or other political subdivisions in northwestern Louisiana, southwestern Arkansas, or eastern Texas where its distinctive pottery was found. This is Caddo country, linguistically and ethnically. Bossier is the issue of Caddoan cultural tradition, a culmination of agents, practices, and histories that transpired in the Red River valley and adjoining Pineywoods hills between ca. A.D. 1300 and 1500. Bossier is best known for its pottery. Pottery hoists the load for this examination, but other factors such as presence or absence of mounds and relative geographic location help me contextualize Bossier pottery and contemplate Bossier materiality as the product of human minds and hands. I organize pottery data, new and old, by a simple arithmetic measure, an average index of similarity. I don't see how more robust statistical comparisons could do any better when data come from potsherds picked up from bare spots on the ground but not from underneath the pine straw. Powerful statistics don't create powerful data. They don't create data at all.

Seasonal circulation fields in the northern Gulf of Mexico calculated by assimilating current meter, shipboard ADCP, and drifter data simultaneously with the shallow water equations

Velocity measurements from current meter moorings, shipboard acoustic Doppler current profilers (ADCPs), and satellite-tracked drifters are used to estimate the seasonally averaged barotropic circulation throughout the continental shelf in the northern Gulf of Mexico in two regions: the Northeast Gulf of Mexico (NEGOM) shelf and the Louisiana–Texas (LATEX) shelf. A variational assimilation approach (weighted least squares) is used to combine the data simultaneously with a system of dynamical equations (time-independent shallow water equations), where the weights are based on the expected errors in the dynamical equations and measurements. Smoothing and boundary constraints are also included in this system to impose a spatial decorrelation scale and to restrict the component of flow that is perpendicular to the coastline, respectively. Seasonal solutions are therefore best fits to the weighted measurements, dynamics, and constraints, and thus do not fit any component exactly. Analysis of the solution deviations to the dynamical equations reveal where and during which seasons the dynamics and data are in disagreement. The largest deviations from the proposed dynamics occur at the head of the DeSoto Canyon on the NEGOM shelf and at the southwest corner of the LATEX shelf. Therefore, in these areas, there are processes occurring that are not described by the simplified barotropic dynamics. At the head of the DeSoto Canyon, the large source of error is believed to be due to deep-ocean water penetrating across the shelfbreak, whereas the process that occurs at the southwest corner of the LATEX shelf is proposed to be a result of a convergence zone caused by loop current eddies. Error analysis reveals that current meter data are more capable of constraining the solution than the other two data types due to its ability to more accurately observe barotropic currents. Separate experiments are conducted using the shipboard ADCP and drifter data sets individually to determine the relative observation capability. These experiments reveal that both data types provide reasonable estimations of seasonal flow fields. Results on the LATEX shelf suggest that shipboard ADCP data is more capable of observing the seasonal barotropic flow than drifter data. Whereas, on the NEGOM shelf results imply that drifter data are more capable. This result, however, may be skewed due to the shipboard ADCP and drifter data sets being collected during different years.

Comparative Sensitivity of the VecTest Antigen-Capture Assay, Reverse Transcriptase-PCR, and Cell Culture for Detection of West Nile Virus in Dead Birds

The sensitivity of the VecTest antigen-capture and RT-PCR assays were compared to brain tissue culture in Vero cells for the detection of WNV in a sample of dead birds collected in East Texas and southern Louisiana during the summer of 2003. Cell culture was used as the gold standard, because it yielded the most positives. Direct culture of brain tissue and the WNV antigen-capture assay, done on oropharyngeal swabs, gave statistically comparable results (46% and 40% positive, respectively). In contrast, RT-PCR done on brain homogenates was significantly less sensitive than direct tissue culture (33% compared to 46%, respectively). Results indicated that RT-PCR may not be consistently the most sensitive assay for detection of WNV in dead bird brain tissue and that the VecTest antigen-capture assay has a number of advantages over the other two detection techniques for routine surveillance activities.

Abundance, genetic diversity and conservation of Louisiana black bears (Ursus americanus luteolus) as detected through noninvasive sampling

Although the Louisiana black bear (Ursus americanus luteolus) is currently listed as threatened under the Endangered Species Act, there have been no attempts to estimate range-wide abundance. This subspecies was thought to occupy a near contiguous range across southern Mississippi, Louisiana and east Texas but is now restricted to three isolated areas in Louisiana. In 1964, Louisiana initiated a restocking program in which black bears from Minnesota were introduced into two of these areas. It is not clear how the additions affected population structure or if substantial breeding occurred between native and introduced bears. Using baited sites to snare hair samples, and microsatellite DNA analysis to distinguish individuals, we estimated abundance of two geographically isolated bear populations in south central Louisiana: Inland and Coastal. Additionally, we examined genetic variation both within and between the two populations. Mark recapture analysis of the distribution of individual captures during two primary sampling periods resulted in population estimates of 77 ± 9 for Coastal and 41 ± 6 for Inland. Genetic analysis revealed significant population differentiation (FST = 0.206) between the two populations. The apparently smaller Inland population exhibited more diversity than the Coastal, which suggests that the genetic structure of the Inland population has been influenced by the reintroduction. Both of these populations are isolated and face considerable demographic and genetic threats, thus conservation measures to protect both are warranted. However, the Coastal population is more representative of Louisiana black bears prior to reintroduction and special consideration should be given to insure its integrity.

Seasonal circulation on the western shelf of the Gulf of Mexico using a high‐resolution numerical model

The seasonal circulation on the western shelf of the Gulf of Mexico is studied using a high‐resolution numerical simulation, historical hydrographic data, sea level data, and satellite images. Three regions are distinguished, the Tamaulipas‐Veracruz (TAVE) shelf, the Louisiana‐Texas (LATEX) shelf, and the western Campeche Bank. On the TAVE shelf there is a swift reversal of the along‐shelf current, downcoast from September to March and upcoast from May to August when there is upwelling due to offshore Ekman transport. Circulation on the western Campeche Bank is upcoast throughout the year. The LATEX shelf has a cyclonic circulation, except during summer months when the flow is eastward. During spring‐summer the upcoast current on the TAVE shelf reaches the southern Texas shelf where it encounters a downcoast coastal current favoring offshore transports. In the fall‐winter, the downcoast current reaches the southern Bay of Campeche where it meets an opposing along‐shelf current, generating seasonal offshore transports. During fall and winter, cool low‐salinity water from the Mississippi and Atchafalaya Rivers is advected westward along the LATEX shelf onto the TAVE shelf, developing along‐shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break. The main forcing over the western shelf of the gulf is the along‐coast wind stress component. The existence of the cross‐shelf transports in the confluence regions is supported by chlorophyll a data. Up to 80% of the seasonal sea level variability is explained by the along shelf currents and the low‐frequency variability of the atmospheric sea level pressure.

Variations in shoreface progradation and ravinement along the Texas coast, Gulf of Mexico

Shoreface architecture, evolution (mid‐Holocene to present) and depths of transgressive ravinement were examined from Sabine Pass, at the Texas–Louisiana border, to South Padre Island, near the Texas–Mexico border, using 30 shoreface transects. Shoreface transects extend out to 16‐m water depth, each created from an echo‐sounding profile and, on average, seven sediment cores. The shoreface is composed of three broad sedimentological facies: the upper shoreface, composed almost entirely of sand; the proximal lower shoreface, composed of sand with thickly to medium‐bedded (50–10 cm) mud; and the distal lower shoreface, composed dominantly of mud with medium‐ to thinly bedded (20–3 cm) sand. Shoreface architecture and evolution is extremely variable along the Texas coast. Shoreface gradients increase from 2·25 m km–1 in east Texas to 3·50 m km–1 in south Texas. Shoreface sands coarsen towards south Texas. East and south Texas shoreface deposits are thin and retrograding whereas central Texas shoreface deposits are thicker and prograding. Central Texas is characterized by stacked shoreface successions, whereas in east Texas, lower shoreface sands are preserved only in offshore banks. Preservation of shoreface deposits is low in south Texas. Although eustatic fluctuations and accommodation space have a strong impact on overall mid‐Holocene to present shoreface evolution and preservation potential, along‐strike variations in sediment supply and wave energy are the main factors controlling shoreface architecture. The transgressive ravinement surface varies from –6 to –15 m along the Texas coast.

Cloud-to-Ground Lightning in the United States: NLDN Results in the First Decade, 1989–98

The physical and geographical characteristics of over 216 million cloud-to-ground lightning flashes recorded during the first decade (1989–98) of operation of the National Lightning Detection Network (NLDN) covering the entire continental United States are presented. These characteristics include the total cloud-to-ground flash density, the positive flash density, the percentage of positive flashes, the first stroke negative and positive peak currents, and the multiplicity for negative and positive flashes. All analyses were done with a spatial resolution of 0.2° corresponding to an approximate resolution of 20 km. Flash densities were not corrected for detection efficiency; the measured values are presented. The maximum measured flash density is found to exceed 9 flashes km−2 across Florida in the Tampa–Orlando–Cape Canaveral corridor, near Fort Myers, and between Lake Okeechobee and the Atlantic Ocean. The mean monthly flash count peaks in July at approximately 5.5 million flashes. Positive flash density maxima, greater than 0.4 flashes km−2 occur in southern Florida; Houston, Texas; and along the Texas–Louisiana border. A broad region of relatively high positive density also occurs throughout the Midwest. The mean monthly positive flash count peaks in June and July at approximately 240 000 flashes in each month. The annual mean percentage of lightning that lowered positive charge was highest in the upper Midwest, exceeding 10% or 20% throughout most of the region. High percentages are also characteristic along the West Coast. The annual percentage of positive lightning has increased from 3% in 1989 to approximately 9% in 1998. The authors believe the increase is the result of improved sensor detection capability in the past decade. The mean monthly percentage of positive lightning flashes ranged from 4% in August to 17% in December for the decade. The annual median negative peak current ranged from 30 kA in 1989, decreasing steadily to about 20 kA in 1998. The annual median positive peak current ranged from 55 kA in 1989 decreasing to about 22 kA in 1998. The annual median peak negative and positive currents have approximately the same value since 1995, the first year after the NLDN upgrade. The monthly median first stroke peak currents for the decade peak in the winter and reach a minimum in May (positive current) and July (negative current). The mean monthly negative multiplicity for the decade ranges from 2.1 in February to 2.5 from June to October. The mean monthly positive multiplicity is approximately 1.2 throughout the year. The diurnal variation of the maximum flash rate over land was examined and found to peak during 1200–2000 local time (LT) with an exception for the upper Midwest, which peaked during 2000–0400 LT. Over water surrounding the continental United States, the lightning flash rate peaks primarily in the morning hours from 0400 to 1200 LT.

A two-dimensional response to a tropical storm on the Gulf of Mexico shelf

Surface current data from drifting buoys and remotely sensed wind data recorded over the continental shelf in the northeastern Gulf of Mexico during the passage of tropical storm Josephine in October 1996 are examined. Drifter data show the existence of a strong surface jet (velocities reaching 1 m s −1) that moves up the west Florida shelf and westward along the Louisiana–Texas shelf, and lasts for nearly 1 week. The coastal jet occurs during an intense synoptic scale wind event where wind speeds reach 15 m s −1. A simple force balance and statistical analysis are performed to assess the role of strong wind forcing. The primary balance shows an Ekman-type current. The role of local acceleration is greatest when winds are directed along bathymetry. A simple two-dimensional strongly forced shelf response model developed from the linear steady-state momentum equations also indicates larger along-shore currents due to both Ekman-type forcing by cross-shore winds and a cross-shore pressure gradient arising from conservation of mass. Model parameters fit empirically are within 15% of theoretical values. The simple model explains 30% and 46% of the variance in the observed along-shore and cross-shore surface currents, respectively.

Long‐term changes in concentrations and flux of nitrogen in the Mississippi River Basin, USA

AbstractCurrent and historical data show that nitrogen concentrations and flux in the Mississippi River Basin have increased significantly during the past 100 years. Most of the increase observed in the lower Mississippi River has occurred since the early 1970s and is due almost entirely to an increase in nitrate. The current (1980–99) average annual nitrogen (N) flux from the Mississippi Basin to the Gulf of Mexico is about 1 555 500 t year−1, of which about 62% is nitrate‐N. The remaining 38% is organic nitrogen and a small amount of ammonium. The current (1980–99) average nitrate flux to the Gulf is almost three times larger than it was during 1955–70. This increased supply of nitrogen to the Gulf is believed to be partly responsible for the increasing size of a large hypoxic zone that develops along the Louisiana–Texas shelf each summer. This zone of oxygen‐depleted water has doubled in areal extent since it was first measured in 1985. The increase in annual nitrate flux to the Gulf can be largely explained by three factors: increased fertilizer use, annual variability in precipitation and increased streamflow, and the year‐to‐year variability in the amount of nitrogen available in the soil‐ground water system for leaching to streams. The predominant source areas for the nitrogen transported to the Gulf of Mexico are basins draining southern Minnesota, Iowa, Illinois, Indiana, and Ohio. Basins in this region yield 1801 to 3050 kg N km−2 year−1 to streams, several times the N yield of basins outside this region. Published in 2001 by John Wiley & Sons, Ltd.

Distribution and controlling mechanisms of primary production on the Louisiana–Texas continental shelf

The northwest (NW) Gulf of Mexico is marked by strong seasonal patterns in regional and mesoscale circulation and variable effects of riverine/estuarine discharge, which influence distributions of nutrients, phytoplankton biomass and primary production. During a series of five cruises in the NW Gulf of Mexico in 1993 and 1994, an extensive data set was collected including nutrients, phytoplankton biomass (chlorophyll a), and photosynthesis–irradiance ( P– E) parameters. Primary production was estimated using P– E parameters in conjunction with profiles of biomass and irradiance. Relatively high biomass and primary production were observed in inner shelf waters during spring conditions of high river discharge. This was attributed to the retention of biomass and nutrients on the shelf by the combination of high river outflow and a westward flow along the inner shelf with consequent onshore Ekman component. During summer, when surface currents shifted towards the north and east, values of nutrients, biomass and primary production were relatively high east of Galveston Bay and decreased outward from the coast. This pattern was apparently a consequence of nutrient inputs from riverine, upwelling and benthic sources. Nutrients, biomass and productivity in the western portion of the study area in summer were generally lower as a result of the upcoast flow of oligotrophic offshore water. Inter-annual variability was observed between November 1993 and 1994 with higher biomass and productivity occurring in November 1993. This was partially attributed to higher river discharge prior to November 1993, retention of biomass and nutrients by the downcoast flow along the inner shelf, and possibly, injection of nutrients onto the shelf at the shelf break. Our findings demonstrate that the interaction of circulation and availability of light and nutrients are largely responsible for variations in primary production. Nitrogen appeared to be the primary limiting nutrient, however, a potential for phosphate limitation was also observed particularly during periods of higher river discharge. Light availability was a critical variable during the fall and winter months, when higher primary production was restricted to shallow waters where vertical mixing was constrained by bottom topography. In deep waters, counteractive changes in nutrient and light availability apparently resulted in minor temporal variation between seasons. The annual carbon production in the Louisiana–Texas (LATEX) continental shelf region was estimated to be 159 g C m −2 year −1, which is within the range of prior estimates for this region. Given that the area of the study region was approximately 140,000 km 2, this would be equivalent to an areal carbon production of about 22.2 million metric tons.

Delineation of Essential Habitat for Juvenile Red Snapper in the Northwestern Gulf of Mexico

Seasonal habitat suitability index models were developed for juvenile red snapper Lutjanus campechanus in the western Gulf of Mexico. Habitat factors considered in the analysis included water temperature, salinity, and dissolved oxygen at the bottom; depth and density of offshore petroleum platforms; and low-relief bottom structures. High-value habitat for juvenile red snapper is characterized by depths between 18 and 64 m, water temperatures of 24–26°C, salinities around 35%, and dissolved oxygen levels of at least 5 mg/L. Density of low-relief structures was not a significant habitat element, and an inverse association was found between juvenile red snapper abundance and the density of offshore platforms. Results of the model analysis suggest that the step-like expansion of the hypoxic area (dissolved oxygen ≤ 2 mg/L) offshore of the mouth of the Mississippi River and west to the Louisiana–Texas border, which first occurred in 1993, has reduced habitat carrying capacity for juvenile red snapper in this region by up to 25%, averaging 19%. This environmental change may limit the level to which overfished Gulf red snapper stocks can be rebuilt to historical levels.

Caddoan Ceremonial Sites of the Caddoan Cultural Area of Arkansas, Louisiana, Oklahoma, and Texas: Draft Caddo National Landmark Nomination

Since 1997, we have been working on the development of a National Historic Landmark (NHL) cover nomination for Caddoan ceremonial sites - earthen mounds in the Caddoan cultural area of southwestern Arkansas, northwestern Louisiana, eastern Oklahoma, and northeastern Texas. Such a nomination establishes the historic context within which all similar cultural properties can be evaluated for significance according to the NHL criteria, as it establishes the research and other criteria by which a cultural property may be identified as a significant archeological resource.

Factors Influencing Model Skill for Hindcasting Shallow Water Currents during Hurricane Andrew

Abstract Hurricane Andrew made landfall in the Gulf of Mexico after crossing directly over several moored current meter arrays deployed on the Louisiana–Texas shelf. The resulting three-dimensional current, temperature, and salinity time series are used in a quantitative analysis of the factors affecting the hindcast skill of ocean circulation models. This paper describes parameters for quantifying a model’s skill at matching both maximum currents and time series at specific locations and depths. It then briefly discusses the following factors with respect to currents hindcast with the Princeton Ocean Model: 1) model domain size; 2) horizontal resolution, including the bathymetry and coastline; 3) vertical resolution (i.e., number of model levels); 4) the surface drag formulation;5) the bottom drag coefficient; 6) turbulent mixing parameters and sources of turbulence; and 7) the initial temperature field. Model performance is found to be most dependent on parameters within the turbulent energy closure sch...

The Potential Applications of Optical Dating to the Sandy Uplands of East Texas and Northwest Louisiana

The fine, sandy soils of East Texas and Northwest Louisiana have been the source of archaeological debate for some time. This discourse concerns the mode of burial of cultural material in the easily eroded soils and the mechanics of recent (Holocene) landform evolution. Because these deposits are typically well-drained, organic matter does not preserve well, thus hindering the dating of the geomorphic events that figure prominently in their development and the prehistoric occupations which lie buried throughout uplands of this region. A relatively new dating technique, optical dating, has much to offer this region and the archaeological community as it measures the period of time that has elapsed since sand grains were last exposed to sunlight. Hence, it directly dates the time of sediment transportation and deposition. This method is therefore applicable to a number of archaeological and geomorphic processes which may not be dated by traditional methods, owing to the lack of organic matter suitable for radiocarbon dating. In geomorphic contexts, optical dating may be preferred over radiocarbon as it directly dates the time of sedimentation rather than the age of organic matter in features such as buried soils that may be significantly different from the geomorphic event which fossilized the soil.

Factors Associated with Consumer Preferences for Convenience Meat

An ordered-probit model was used to examine the preferences of Louisiana and southeast Texas residents for convenience meat. The results suggested that male, younger or unmarried respondents, and Catholics had higher probabilities of agreeing that they preferred convenience meat than their corresponding counterparts. However, unmarried male Caucasians had the highest probability of strongly agreeing or somewhat agreeing that they preferred to buy convenience meat. The results also suggested that price was an important determinant in shaping these preferences.

Influences of river discharge on biological production in the inner shelf: A coupled biological and physical model of the Louisiana-Texas Shelf

A coupled biological and physical model was applied to study the influence of river discharge on biological variability on the Louisiana-Texas (LATEX) continental shelf. The physical part included a primitive-equation turbulent closure model, and the biological part was a simple phytoplankton (P), zooplankton (Z), and nutrient (N) model. The model was forced by freshwater discharge from the river and ran prognostically under initial conditions of springtime water stratification and a steady-state solution of the P-Z-N model with no horizontal dependence. A nutrient source was included at the mouth of the river. The model predicted a well-defined density frontal zone on the inner shelf. The biological field showed a region of high phytoplankton biomass in the whole water column near the coast and a moderately high biomass patch in the upper 10 m at the outer edge of the frontal zone. A high concentration dome of nutrients was found near the bottom within the frontal zone. New production of nutrients was high throughout the whole water column near the coast and in the upper 10 m at the outer edge of the density front, but lower in the frontal zone. The model results were in reasonable agreement with observational data taken from a May 1993 interdisciplinary survey on the LATEX shelf. Cross-shelf distribution of biological production varied significantly with direction of wind stress but not with the diurnal tide. The model results suggested that the bottom-rich nutrient distribution within the frontal zone was caused by the interaction of physical and biological processes. Physical processes caused the formation of an area of high nutrient concentration in the weak current region within the frontal zone. Subsequent biological processes limited the increase of nutrients in the upper euphotic zone and hence led to the bottom-rich nutrient pattern.

Cyperus entrerianus: A Little Known Aggressive Sedge in the Southeastern United States

Four of the world's worst weeds are in the genus Cyperus. These are smallflower umbrella sedge (C. difformis L.), yellow nutsedge (C. esculentus L.), riceflatsedge (C. iria L.), and the world's worst weed, purple nutsedge (C. rotundus L.) (7). Fourteen additional Cyperus species are listed in the Composite List of Weeds1. Cyperus is in the sedge family (Cyperaceae) which consists of about 600 species found mostly in tropical to warm-temperate regions around the world (9). Cyperus entrerianus Böckeler is an aggressive, robust, fast growing, tenacious pest that produces large numbers of seeds (4). Apparently, it was introduced into the southeastern United States from temperate South America or Mexico (2). Presently, it is found in the southeastern United States from southeastern Texas to southern Georgia (4). The senior author has observed severe infestations of this weed in ditches, pastures, and fallow fields in southwestern Louisiana and southeastern Texas. Our objectives are to alert weed scientists, agronomists, and others concerned to the potential of this species and to discuss its biology, distribution, ecology, and taxonomy.

Eddy‐ and wind‐forced shelf circulation

Cochrane and Kelly (1986) proposed a cyclonic gyre as the large‐scale mean circulation on the Louisiana‐Texas (LATEX) shelf, produced by a convergence of coastal currents in the west and a divergence in the east. While currents near the coast are presumably wind and buoyancy driven, the origin of the eastward flow on the outer shelf and shelf break, which forms the seaward limb of the gyre, as well as the near shore convergence and divergence, are not well understood. A numerical model is used to show that the western convergence and shelf break current are driven by collision and stalling of westward propagating Loop Current eddies in the northwest Gulf of Mexico and the divergence in the east is caused by shoreward intrusion in the Mississippi Canyon. The western convergence and shelf break current are modulated by the wind curl, strongest in summer and weakest in winter. On the shelf, westward transport is comparable to that observed (∼0.15 Sv, 1 Sv = 106 m3 s−1) only when the westward wind stress is significant (>0.3 dyn cm−1). A peak transport of 0.21 to 0.25 Sv occurs in autumn, of which 0.1 Sv is due to wind, 0.07 Sv is due to river buoyancy, and 0.04 to 0.08 Sv is due to eddies. Without the mean westward wind, buoyant waters from the Mississippi do not spread onto the LATEX shelf.