Winter Cold Fronts Research Articles

The use of NOAA AVHRR satellite data for mapping sediment variability in the marine and coastal environment

Sediment-rich effluent from the Atchafalaya River (USA) flows into the clear waters of the Gulf of Mexico along the Louisiana Coast. The sediment, which serves as a material for shoreline progradation, is transported by near shore currents to various portions of the coastal zone. Satellite data from the National Oceanographic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR), 1.1km resolution, atmospherically corrected channel 1 and 2, are used to map the suspended sediment transport in the Atchafalaya Bay region of the Louisiana coastal zone. The turbid water equation was solved with the Newton method of non-linear curve fitting using the suspended sediment concentration obtained from the field sample analysis and the satellite-derived Reflectance values for Rw. The values of the constants Fs and Gs are 0.66 and 32.86, respectively, with R2 = 0.8895 and the root mean square error for reflectance is 0.0089. Results based on four satellite images show that the suspended sediment plume transported along the shore, to the west is 10km wide on the average when southeast winds dominate. However, the suspended sediment transported to the deep sea in response to the passage of winter cold fronts could reach as far out to the sea as 70km when the northeast winds dominate. The area near Big Constance Lake, which has a persistently higher concentration of suspended sediment around the year, is a suspected non-depositional area. The southwest winds cause a circulation in the bay and thus periods of higher depositional rates. Journal of Building and Land Development Vol. 13 (2) 2006: pp. 65-73

Estimation of Detection Probability in Manatee Aerial Surveys at a Winter Aggregation Site

Abstract: Estimating components of detection probability is crucial to improving the design of aerial surveys for wildlife populations, and this is especially true for species of marine mammals that are threatened or endangered. To evaluate the probability that Florida manatees (Trichechus manatus latirostris) will be detected by observers during aerial surveys, we conducted 6 series of survey flights, during mornings and afternoons on 14‐16 consecutive days over the Tampa Electric Company's (TECO) Big Bend power plant discharge canal in Tampa Bay, Florida, USA (winter 2000 through 2003). Our objective was to understand how our ability to detect manatees at a winter aggregation site affects aerial survey counts, so that we may improve techniques for estimating manatee population size. We estimated the probability that manatees would be present at the warm‐water discharge of the plant during winter cold fronts and estimated the overall detection probability of manatees present at the plant and the 2 components that make up the probability of detection (the probability of being available and the probability of being detected given they are available). We used telemetry tags and marker flags (n = 15) to facilitate capture‐recapture analyses. The probability that marked manatees would be at the plant varied from 48% to 68% across flight series and was inversely related to the ambient water temperature. Based on sightings of marked animals, estimates of the overall probability of detecting a manatee ranged from 45% to 69% across flight series (x̄ = 58%, n = 6). The probability that a manatee would be available to an observer ranged from 73% to 94% across flight series (x̄ = 83%) but was constant among years (83%, 81%, and 78%; x̄ = 81%). The probability that an available manatee would be detected by an aerial observer was variable across flight series (55‐95%) and years (73%, 86%, and 66%, x̄ = 73%). Independent estimates of the probability that a manatee would be available to the observer on one pass were obtained from time‐depth data loggers and ranged from 5% to 33% (x̄ = 19%, SE = 3.7%), and the probability that a manatee would be available during ≥1 of 10 passes ranged from 41% to 98% (x̄ = 88%, 95% confidence bounds 0.71‐0.95). We adjusted survey counts using measures of detectability. Although corrected counts presented here are site‐specific, adjusting counts based on detection probability will greatly improve reliability of population estimates from all aerial surveys. Special sampling to estimate components of detection probability should be built into all aerial surveys to ensure that reliable and unbiased information on species abundance is used to evaluate wildlife populations.

Coastal mudflat accretion under energetic conditions, Louisiana chenier-plain coast, USA

Mudflat accretion on the chenier-plain coast of Louisiana, northern Gulf of Mexico, is anomalous in an area that otherwise experiences widespread land loss due to rapid relative sea level rise. Accretion is shown to be related to energetic events (winter cold fronts and occasional tropical-depression storms) using a 17-year record of meteorological conditions and aerial surveys. The results indicate substantial differences between the behavior of sand- and mud-dominated coastal systems under energetic conditions. Comparison of the Louisiana chenier plain to other mud-rich coasts indicates that certain conditions are necessary for mudflat accretion to occur during energetic atmospheric activity. These include an abundant supply of fine-grained fluvial sediment and resuspension events that maintain an unconsolidated sea floor, dominant onshore wind direction during energetic conditions, particularly when onshore winds coincide with high fluvial sediment input to the coastal ocean, and a low tidal range.

Nitrogen and phosphorus transport between Fourleague Bay, LA, and the Gulf of Mexico: the role of winter cold fronts and Atchafalaya River discharge

Nutrient fluxes were measured between Fourleague Bay, a shallow Louisiana estuary, and the Gulf of Mexico every 3 h between February 1 and April 30, 1994 to determine how high velocity winds associated with cold fronts and peak Atchafalaya River discharge influenced transport. Net water fluxes were ebb-dominated throughout the study because of wind forcing and high volumes of water entering the northern Bay from the Atchafalaya River. Flushing time of the Bay averaged <8 days; however, more rapid flushing occurred in response to northerly winds with approximately 56% of the volume of the Bay exported to the Gulf in 1 day during the strongest flushing event. Higher nitrate+nitrite (NO 2+NO 3), total nitrogen (TN), and total phosphorus (TP) concentrations were indicative of Atchafalaya River input and fluxes were greater when influenced by high velocity northerly winds associated with frontal passage. Net exports of NO 2+NO 3, TN, and TP were 43.5, 98.5, and 13.6 g s −1, respectively, for the 89-day study. An average of 10.6 g s −1 of ammonium (NH 4) was exported to the Gulf over the study; however, concentrations were lower when associated with riverine influence and wind-driven exports suggesting the importance of biological processes. Phosphate (PO 4) fluxes were nearly balanced over the study with fairly stable concentrations indicating a well-buffered system. The results indicate that the high energy subsidy provided by natural pulsing events such as atmospheric cold fronts and seasonal river discharge are efficient mechanisms of nutrient delivery to adjacent wetlands and nearshore coastal ecosystems and are important in maintaining coastal sustainability.

Cold Front Acceleration over Lake Michigan

Abstract High-resolution Eta Model simulations of a strong but relatively dry late winter surface cold front that occurred during the STORM-FEST project depicted a pronounced acceleration of the front during the afternoon hours over the southern end of Lake Michigan. In this note, the impact of the lake on the front is examined. Reduced lower atmosphere turbulence due to both thermal stabilization and diminished surface roughness acting on postfrontal northerly winds increased frontogenesis strongly over the lake. The enhanced frontal circulation increased the front speed so that a noticeable frontal bulge occurred over the southern end of Lake Michigan. Some observational evidence is available to support the simulated frontal acceleration.

Taphonomic and Paleoenvironmental Evidence of Holocene Shell-Bed Genesis and History on the Northeastern Gulf of Mexico Shelf

Subsurface shell beds that are common on the eastern Alabama/western Florida Panhandle shelf provide paleoenvironmental and taphonomic data that demonstrate a dynamic depositional history with reactivation and amalgamation to the base of the Holocene marine transgressive package. In most of the ten shell beds we examined, shallow-marine mollusks, large soritid foraminifera, and cupularid bryozoans are common. Bioclasts occur in all preservation states, but a majority are pristine or only slightly altered. Normal grading, and concave-up, stacked, and random fabrics are common. In three of these shell beds, a relict estuarine component characterized by poorly-preserved Chione cancellata can be detected. Three other shell beds contain 1 of 2 estuarine molluscan assemblages. One assemblage is characteristic of fine-grained and the other of coarser-grained substrates. In all estuarine shell beds, bioclast preservation ranges from excellent to mixed, and bioclasts have random fabrics and locally are normally graded. Most molluscan remains are indigenous and assemblages range from within-habitat time-averaged to environmentally condensed. Shell beds are thick (up to about 75 cm) and overlie bay or shoreface ravinement surfaces, indicating that shell beds first accumulated as coarse transgressive deposits, and are composite concentrations modified by multiple events. Shell beds, however, are amalgamated. Only fabrics reflecting the final modifying events are preserved, and evidence of previous accumulation processes are obliterated. For marine shell beds especially, these final agents were, and possibly continue to be, highenergy events such as storms (winter cold fronts, hurricanes) or currents associated with Loop Current eddies. Episodically high sedimentation rates associated with these events may have acted as a buffer, preventing a long history of reworking and exposure (thus reducing shell alteration) typical of transgressive lags. Our results indicate that: 1) within-habitat time-averaged and environmentally condensed assemblages can be distinguished by combining taphonomic and environmental data, even when the ranges of environmentally disparate species overlap, 2) transgressive-lag deposits can be composed of well-preserved bioclasts, and 3) transgressive lags can be reworked and amalgamated but still be recognizable on the basis of their stratigraphic context.

A remarkable winter cold front hailstorm, 22 February 1995

A remarkable winter cold front hailstorm, 22 February 1995

The Eastern Chenier Plain: An Update on Downdrift Coastal Progradation Associated with the Building of a New Holocene Delta Lobe in the Mississippi Delta Complex: ABSTRACT

The Eastern Chenier Plain: An Update on Downdrift Coastal Progradation Associated with the Building of a New Holocene Delta Lobe in the Mississippi Delta Complex: ABSTRACT

Theoretical and measured aeolian sand transport on a barrier island, Louisiana, USA

ABSTRACTOver the past 100 years, the Isles Dernieres, a low lying barrier island chain along the coast of central Louisiana, Usa, has undergone more than 1 km of northward beach face retreat with the loss of 70% of its surface area. The erosion results from a long term relative sea level rise coupled with day to day wind and wave action that ultimately favours erosion over deposition. At a site in the central Isles Dernieres, 8 days of wind and beach profile measurements during the passage of one winter cold front documented aeolian erosion and deposition patterns under both onshore and offshore winds. For offshore winds, the theoretical erosion rate, based on wind shear velocity, closely matched the measured erosion rate; for onshore winds, the theoretical rate matched the measured rate only after being corrected by a factor that accounted for beach face morphology.In late February 1989, a strong cold front moved into coastal Louisiana. That cold front stalled over the Gulf of Mexico, resulting in 4 days of strong northerly winds at a study site on the Isles Dernieres. During those 4 days, the wind moved sand from the backshore to the upper beach face. When the cold front finally moved out of the area, the wind shifted to the south and decreased in strength. The onshore wind then restored some of the upper beach face sand to the backshore while increased wave activity moved the rest into the nearshore.The theoretical estimate of 1·28 m3 m−1 for the rate of sand transport by the northerly wind compares well with the measured backshore erosion rate of 1·26 m3 m−1, which was determined by comparing beach profiles from the start and end of the period of northerly winds. The theoretical estimate of 0·04 m3 m−1 for the rate of sand transport by the southerly wind, however, is notably less than the measured rate of 0·45 m3 m−1. The large discrepancy between the two rates can be explained by a difference in the shear velocity of the wind between the beach face, where the erosion occurred, and the backshore, where the wind stress was measured. Using an empirical relationship for the wind shear drag coefficient as a function of coastal environment, the theoretical estimate for the rate of sand transport by the southerly wind becomes 0·44 m3 m−1

Epibenthic gastropods of the middle Florida keys: the role of habitat and environmental stress on assemblage composition

A survey of epibenthic prosobranch gastropods was undertaken in both seagrass and hard substratum (coral or old reef rock) habitats on opposite sides of the Florida Keys (Florida Bay and Hawk Channel) to compare faunal differences attributable to differences in the above two habitats and environments. Additionally, two data sets (26 continuous months) of daytime dissolved oxygen, surface salinity and water temperature from Florida Bay (Long Key) and Hawk Channel (Key Largo) environments were compared to determine differences that might constitute environmental stresses likely to affect the fauna. The above data were collected to determine if several hypotheses concerning effects of stress on organisms, assemblage, community and faunal composition were consistent with data on assemblage structure. These hypotheses were that: (1) stress should reduce the average size of organisms; (2) shorten food chains; (3) reduce predation intensity; (4) reduce species richness and diversity; and (5) increase the relative abundance of predator-susceptible ancestral species (i.e. Archaegastropoda). Water quality data suggest that the two most likely forms of stress in deeper (>1 m) areas of Florida Bay adjacent to the Keys are cold water temperatures associated with winter cold fronts and low predawn oxygen associated with warm summer temperatures, high salinity, and periodic algal and seagrass drift buildups. Seagrass sites had high population densities and low diversity due to the dominance of Astraea americana Gmelin (American star shell) in Florida Bay and Modulus modulus L. in Hawk Channel seagrass habitats. Florida Bay sites had high species richness on a small spatial scale, but Hawk Channel sites had more species and greater encounter rates of new species on a larger scale. Predawn oxygen measurements taken during July in four habitats were positively correlated with prosobranch species richness and diversity. Faunal data, analysed on a population density basis, fit the above hypotheses of body size, trophic level, and evolutionary age of the species. Attempts to measure predation on an experimental prosobranch ( A. americana) were unsuccessful but a tethering experiment with a sea urchin ( Echinometra lucunter L.) indicated higher predation in the less stressful Hawk Channel than Florida Bay hard substratum sites. Stress appears to reduce the abundance of higher trophic levels (both prosobranch and finfish predators) resulting in the dominance of ancestral forms not adapted to predation but tolerant of environmental stress. Eutrophication or increased oxygen demands in Florida Bay could result in further species richness and diversity declines.

Carbonate-periplatform sedimentation by density flows: A mechanism for rapid off-bank and vertical transport of shallow-water fines

Existing theories of off-bank sediment transport cannot account for rapid rates of sedimentation observed in Bahama bank and Florida shelf periplatform environments. Analysis of the physical processes operating during winter cold fronts suggests that accelerated off-bank transport of shallow-water mud may be achieved by sinking off-bank flows of sediment-charged hyperpycnal (super-dense) platform waters.

Slope-Current fluctuations northeast of Taiwan winter 1990

During the winter of 1990, two current-meter moorings were deployed in the outer shelf region across a canyon northeast of Taiwan. The data indicate that a steady flow exists in the southward, along-slope direction, opposite to the nearby northward-flowing Kuroshio current. Tides run transverse to the mean flow. Fluctuations in subtidal current mostly occur on the south side of the canyon, concentrated in the synoptic (2–4 days) band and oriented in the cross-slope direction. From the nearby winds and coastal sea-level observations, it is clear that the rotating-wind field associated with the passage of winter cold front is responsible for generating the observed energetic fluctuations. The northeasterly monsoon wind is very effective in piling up water against the northern coast of Taiwan and establishing an out-flowing geostrophic current. Trailing wind behind the high-pressure system has exactly the opposite effect. The investigation suggests that due to the winter-weather pattern, the area northeast of Taiwan is an important region for water exchange between the East China Sea and the Kuroshio.

Geologic evidence of net onshore sand transport throughout the Holocene marine transgression, southwest Florida

The Holocene sediment sequence within the Ten Thousand Islands area of southwest Florida consists of more than 3 m of marine shelly quartz sand which overlies a thin layer (<1 m) of paralic and freshwater sediment. Although this transgressive sequence is similar to that produced during the erosional shoreface retreat of sandy, storm dominated shorelines, sedimentologic and stratigraphic features suggest the southwest Florida shoreline retreated landward primarily by submergence. The shelly quartz sand was derived from an offshore source subsequent to the initial stages of marine transgression. The specific mechanism responsible for onshore sand transport can only be speculated at the present time as climatic and wave data are essentially nonexistent for this remote area. However, net onshore sand transport implies that low steepness waves have mobilized a larger volume of sediment than waves of high steepness. Low steepness waves are generated under prevailing wave conditions and by the swell of distant tropical cyclones. High steepness waves are associated with winter cold fronts or the direct landfall of a tropical cyclone. Because wave heights average only 10 cm along this low energy coastline it is entirely possible that the swell of distant tropical cyclones is the principle mechanism by which sand is transported onshore and incorporated into the Holocene sediment sequence of the Ten Thousand Islands area.

Decapod and stomatopod assemblages on a system of seagrass-covered mud banks in Florida Bay

The latticework of seagrass-covered mud banks in Florida Bay, Florida Keys, USA, divides the bay into distinct subenvironments and supports a robust seagrass community subject to pronounced physical stress. Throw-trap sampling of decapods and stomatopods during 1984 and 1985 (December–April, May–August and September–November of each year) showed that bank sides exposed to turbulence had low abundance but similar species richness to that of bank tops and sheltered sides. The fauna was more Gulf-Carolinean than Antillean. The crustacean communities of the different subenvironments, however, were distinct, with both Antillean and temperate assemblages represented and with one isolated area markedly depauperate. The two subenvironments adjacent to the Atlantic Ocean and Gulf of Mexico had the greatest densities. Multiple-regression techniques suggested that vegetational habitat characteristics played a secondary role compared to various physical factors. We hypothesize that (1) restricted circulation (compounded by winter cold-fronts or other seasonal causes of density minima), (2) juxtaposed faunal provinces, and (3) the wider salinity range of the isolated regions of the bay were primarily responsible for the strikingly different communities of the various subenvironments.

Distribution and Textural Character of Surficial Sediments, Isles Dernieres to Ship Shoal Region, Louisiana: ABSTRACT

ABSTRACT Since 1986, the U. S. Geological Survey and the Louisiana Geological Survey have undertaken field studies of the physical processes responsible for the widespread and extremely rapid coastal erosion of Louisiana's barriers along the Mississippi River delta plain coast. The study area encompasses the coastal and inner shelf region from Raccoon Point to Sandy Point and includes a data base of 40 ft (12 m) long vibracores, surface grab samples, sidescan sonar, high-resolution seismic reflection profiles, and precision hydrographic profiles. This paper presents results from detailed grab sample surveys in the coastal-shelf sector that includes the Isles Dernieres barrier island chain seaward almost 19 mi (30 km), to include Ship Shoal. The surface and near surface sediments of the region reflect fluvial, deltaic and nearshore marine origins with evidence of winnowing and reworking by waves and currents associated with frequent tropical storms and winter cold fronts. Beach sediments on the four islands are remarkably uniform in grain size (fine quartz sand), except for often abundant beach rock and carbonate shell debris, and are generally moderately to very well-sorted. The shoreface and inner shelf are mantled with muddy sands and sandy muds, whereas Ship Shoal is almost wholly fine quartz sand, similar in many sedimentologic respects to the Isles Dernieres. These findings are consistent with the model of coastal evolution presented by Penland et al (1988) in which Ship Shoal was described as the prototypical example of a drowned coastal barrier undergoing submarine reworking and migrating landward in pace with the rapid rates of eustatic sea-level rise and basin subsidence.

Distribution and abundance of the West Indian manatee Trichechus manatus around selected Florida power plants following winter cold fronts: 1984–1985

Ten one-day aerial surveys were conducted in winter, 1984–1985, to assess manatee distribution and abundance around five Florida Power & Light Company (FPL) plants: Cape Canaveral (PCC), Riviera (PRV), Port Everglades (PPE), Lauderdale (PFL) and Fort Myers (PFM). A total of 3804 manatees was observed, with a maximum of 636 animals for a single survey. Individual surveys for 1984–1985 produced higher combined counts for all plants than in previous years. Maximum counts for PRV, PPE and PFM were the highest recorded for those particular plants. The maximum count for PCC in 1984–1985 was lower than counts from most previous years, and the maximum from PFL was intermediate, relative to maxima from previous years. The counts along the east coast of Florida probably reflected a southward redistribution of manatees as well as very cold January weather after warm December conditions. The high count at PFM probably resulted from cold January weather and surface resting behaviour by the manatees which made them more visible than usual. Calves represented 10·3% of the animals observed near the FPL plants and in Hobe Sound. PFM had a higher percentage of calves than did other plants.

Hard-coral distribution and cold-water disturbances in South Florida: variation with depth and location

Line transects were used to sample the structure and diversity of the hermatypic coral community (Scleractinia) on four shallow shelf-edge reefs in South Florida (25° 22′N to 25° 29′N). Low diversities, cover and abundance indicated that this area was a suboptimum habitat for reef-building corals. The lack of acroporids on the shallow fore-reef, the increase in total coral cover with depth and the greater abundance of Montastrea annularis in the deepest zones suggests that cooling of surface water during severe winter cold fronts is a major environmental control on the distribution of hermatypic corals with depth. Such disturbances, occurring more frequently than hurricanes, may preclude the hard-coral community from attaining higher levels of cover and abundance. The shallow zones on the reefs nearest to tidal passes, through which cooled by water enters the reef tract, had the least developed community. In the deeper reef-zones, species richness and abundance increased from north to south over a distance of 13 km.

Comparison of Two Holocene Tidal Flats--Andros Island, Bahamas, and Caicos, British West Indies: ABSTRACT

Minor climatic and physiographic differences have caused dramatic differences in sedimentation between the tidal flats of Andros, northwestern Bahamas, and Caicos in the southeastern Bahama chain. Both tidal flats are leeward of large islands and adjacent to broad, shallow platforms that provide carbonate mud to the flats. Each flat forms a sediment wedge 4 m (13 ft) thick (Andros flats are 200 × 30 km, 125 × 19 mi; Caicos, 60 × 10 km, 37 × 6 mi), and each contains an outer channeled flat and an inner algal marsh. Both flats have cementation and protodolomite forming on channel-margin levees and the inner algal marsh. Differences in rainfall, wind regime and orientation promote important sedimentological differences. Andros receives nearly twice as much rainfall as Caicos; gypsum forms in cemented crusts in Caicos, but not on Andros. Andros receives brief strong pulses of northwest wind following passage of 40 to 60 winter cold fronts per year. The northwest exposure of the margin of the Andros flat thus is flooded several times each year by sediment-laden waters. This flooding focuses on the shore and channel margins, building broad, strongly laminated levees. Caicos flats, in contrast, face south, and neither winter cold fronts nor summer trade winds blow onshore. Levees are poorly developed. Caicos is dominated by brisk easterly trade winds, causing persistent turbidity in nearshore waters. This is dispersed through tidal channels, largely filling interdistributary ponds to a level at which organic-rich intertidal algal mats can flourish. Lower energy conditions on Andros provide insufficient sediment to fill ponds. End_of_Article - Last_Page 537------------

Carbon production and export from Biscayne Bay, Florida. I. Temporal patterns in primary production, seston and zooplankton

Five stations along a transect from the western shore of Biscayne Bay, Florida to the Florida Current were sampled monthly for one year. The variability and amount of seston particulate organic carbon, adenosine triphosphate, chlorophyll a, primary production and zooplankton decreased along the seaward transect. The greater inshore biomass and variability of seston were the result of the allochthonous input of detritus and inorganic nutrients via terrestrial runoff. Annual primary production in this subtropical coastal lagoon ranged from 13 to 46 g C m −2 yr −1. Chlorophyll a in the bay ranged from 1 to 3 mg chlorophyll a m −2. In contrast, chlorophyll a in the surface centimetre of the sediment ranged from 50 to 300 mg chlorophyll a m −2. In this clear, shallow (2 to 3 m), oligotrophic lagoon, over 90% of total primary production is by submerged macrophytes and benthic algae. The high zooplankton biomass in the bay is most likely sustained by macrophyte detritus and the resuspension of benthic diatoms by the high winds associated with summer squalls and winter cold fronts.

Impact of winter cold fronts upon shallow-water reef communities off west-central Florida : Bullock, L. H. and G. B. Smith, 1979. Fla Scient., 42(3): 169–172

Impact of winter cold fronts upon shallow-water reef communities off west-central Florida : Bullock, L. H. and G. B. Smith, 1979. Fla Scient., 42(3): 169–172