Northeast Coast Of South America Research Articles

143 years since the migration of the cattle egret Bubulcus ibis (Linnaeus, 1758) from Africa to the Andes

The cattle heron is native of the tropical and subtropical areas of Africa and Asia, from where it arrived on the northeast coast of SouthAmerica in 1877 and extended its distribution range to Central America and North America. It has undergone dynamic demographictransformations that have led to the colonization of vast areas, through a process of world expansion that has turned it into a cosmopolitanbird. Various factors such as its large size, long-distance flight capacity, its omnivore condition, its opportunistic nature, its remarkableability to adapt to new environments; as well as deforestation and the establishment of grasslands for cattle on a large scale, havecontributed to the expansion of its distribution range. In the present work a historical review of the colonization of the cattle heron iscarried out since its arrival to America. Here we would see how geographic and environmental factors have contributed to the distributionof its populations in different ecosystems ranging from the marine coasts up to 4,400 meters high in the Andes of South America. Aswell, this work highlights the importance of meteorological and genetical tools that provide information about the routes that the specieshas followed in conquering new areas.

The Amazonian Low-Level Jet and Its Connection to Convective Cloud Propagation and Evolution

AbstractWe describe the existence of an Amazonian low-level jet (ALLJ) that can affect the propagation and life cycle of convective systems from the northeast coast of South America into central Amazonia. Horizontal winds from reanalysis were analyzed during March–April–May (MAM) of the two years (2014–15) of the GoAmazon2014/5 field campaign. Convective system tracking was performed using GOES-13 infrared imagery and classified into days with high and weak convective activity. The MAM average winds show a nocturnal enhancement of low-level winds starting near the coast in the early evening and reaching 1600 km inland by late morning. Mean 3-hourly wind speeds maximize at 9–10 m s−1 near 900 hPa, but individual days can have nighttime low-level winds exceeding 12 m s−1. Based on objective low-level wind criteria, the ALLJ is present 10%–40% of the time over the Amazon during MAM depending on the location and time of day. The evolution of the ALLJ across the Amazon impacts the frequency of occurrence of cloud clusters and the intensity of the moisture flux. In addition, the ALLJ is associated with the enhancement of northeasterly flow in the midtroposphere during active convective days, when vertical momentum transport may be occurring in the organized cloud clusters. During the weakly active convective period, the ALLJ is weaker near the coast but stronger across the central Amazon and appears to be linked more directly with the South American low-level jet.

Hippocampal neurogenesis and volume in migrating and wintering semipalmated sandpipers (Calidris pusilla)

Long distance migratory birds find their way by sensing and integrating information from a large number of cues in their environment. These cues are essential to navigate over thousands of kilometers and reach the same breeding, stopover, and wintering sites every year. The semipalmated sandpiper (Calidris pusilla) is a long-distance migrant that breeds in the arctic tundra of Canada and Alaska and winters on the northeast coast of South America. Its fall migration includes a 5,300-kilometer nonstop flight over the Atlantic Ocean. The avian hippocampus has been proposed to play a central role in the integration of multisensory spatial information for navigation. Hippocampal neurogenesis may contribute to hippocampal function and a variety of factors including cognitive activity, exercise, enrichment, diet and stress influence neurogenesis in the hippocampus. We quantified hippocampal neurogenesis and volume in adult migrating and wintering semipalmated sandpipers using stereological counts of doublecortin (DCX) immunolabeled immature neurons. We found that birds captured in the coastal region of Bragança, Brazil during the wintering period had more DCX positive neurons and larger volume in the hippocampus than individuals captured in the Bay of Fundy, Canada during fall migration. We also estimate the number of NeuN immunolabeled cells in migrating and wintering birds and found no significant differences between them. These findings suggest that, at this time window, neurogenesis just replaced neurons that might be lost during the transatlantic flight. Our findings also show that in active fall migrating birds, a lower level of adult hippocampal neurogenesis is associated with a smaller hippocampal formation. High levels of adult hippocampal neurogenesis and a larger hippocampal formation found in wintering birds may be late occurring effects of long distance migratory flight or the result of conditions the birds experienced while wintering.

Role of Land Surface Processes in South American Monsoon Development

Abstract This study explores the role of vegetation biophysical processes (VBPs) in the structure and evolution of the South American monsoon system (SAMS) with an emphasis on the precipitation field. The approach is based on comparing ensemble simulations by the National Centers for Environmental Prediction general circulation model (GCM) in which the land surface parameterization in one ensemble includes an explicit representation of vegetation processes in the calculation of surface fluxes while the other does not [GCM/Simplified Simple Biosphere Model (SSiB) and GCM/Soil, respectively], but with similar monthly mean surface albedo and initial soil moisture. The ensembles consist of five pairs of 1-yr integrations differing in the initial conditions for the atmosphere. The results show that, during the austral summer, consideration of explicit vegetation processes does not alter the monthly mean precipitation at the planetary scale. However, at continental scales, GCM/SSiB produces a more successful simulation of SAMS than GCM/Soil. The improvement is particularly clear in reference to the seasonal southward displacement of precipitation during the onset of the SAMS and its northward merging with the intertropical convergence zone during the monsoon mature stage, as well as better monthly mean austral summer precipitation over the South American continent. The changes in surface water and energy balances and circulation in October (monsoon onset) and December (the start of the monsoon mature stage) were analyzed for a better understanding of the results and mechanisms involved. It was found that the major difference between the simulations is in the partitioning of latent heat and sensible heat fluxes (i.e., different Bowen ratio), which produced different latitudinal and longitudinal thermal gradients at the surface. A stronger sensible heat flux gradient between continent and ocean in the GCM/SSiB simulation helped generate an enhanced ventilation effect, which lowered moist static energy (MSE) over the northeast coast of South America leading to stronger counterclockwise turning of the low-level wind from the Atlantic Ocean toward the continent during the premonsoon and early monsoon stages, modifying moisture flux convergence (MFC). It was further identified that the seasonality of savanna and shrublands to the south and east of the Amazon rain forest contributed to the variability of heating gradients and influenced the SAMS onset and its northward merge with the ITCZ at the early monsoon mature stage. The comparison of the differences between precipitation, evaporation, advection of MSE, and MFC based on simulations using two different land parameterizations suggested that the VBP modulated the surface water budget, but its impact on precipitation was determined by the changes in circulation via changes in heat gradient and MSE.

DNA from primitive maize landraces and archaeological remains: implications for the domestication of maize and its expansion into South America

To study the origins of South American maize, without the complicating factors introduced by the extensive movement of genotypes during the post-Columbian period, we made a genetic analysis of primitive landraces and preserved maize remains. Fifteen alcohol dehydrogenase 2 ( Adh2) allele sequences were obtained from the landraces and 11 from the archaeological specimens. When these and six previously published Adh2 sequences were aligned, three allele groups were seen, distinguished by the structure of a dinucleotide repeat sequence. The three allele groups had distinct distributions within South America, the distributions supporting a model in which the two Central American agricultural systems—highland and lowland—generated separate expansions of maize cultivation into South America. One expansion centred on a highland culture that spread from Central America through the Panama highlands into the Andean regions on the western side of South America, and the second expansion centred on a lowland culture which spread along the lowlands of the northeast coast of South America, entering the continent through the river systems. The Adh2 biogeography was consistent with limited cultural contact across the Andes between northern Chile and Paraguay. From the diversity of the Adh2 allele sequences, we deduced that maize has undergone a rapid rate of evolution since domestication.

Lagrangian flow observations of the Amazon River discharge into the North Atlantic

Nine satellite‐tracked drifters with near‐surface drogues were launched in or near the mouth of the Amazon River on the north Brazil shelf during 1989–1991 at four different stages of river discharge. The drifters initially moved along shelf toward the northwest over the north Brazil shelf with mean speeds varying from 41 to 128 cm/s and a maximum along‐shelf velocity of 197 cm/s. Many drifters experienced strong acceleration near 2°N between the 5‐m and 20‐m isobaths, caused in part by the sharp reduction in cross‐shelf cross‐sectional area near the shore‐perpendicular Cabo Norte shoal. The drifter trajectories showed strong cross‐shelf tidal variability in the flow field near the Amazon River mouth, and the largest low‐frequency, along‐shelf variability was located over the open shelf just north of Cabo Norte. Good visual correlation between drifter along‐shelf velocity and along‐shelf wind stress supports the dynamical model of Lentz (this issue) that subtidal fluctuations in near‐surface along‐shelf currents in the Amazon River Plume are strongly wind driven. Drifters left the north Brazil shelf after about 5 to 30 days. Three drifters moved northwestward parallel to the northeast coast of South America, crossed the shelf break near 8°N, and moved into deeper North Atlantic water where they began looping in anticyclonic eddies (often called retroflection eddies or loopers) with periods of approximately 11 days as they moved northwestward to the Caribbean Sea. Four drifters initially moved along shelf toward the northwest and then offshore between 3°N and 7°N, where they followed the retroflection of the North Brazil Current. Only one drifter entered the zonal current system that characterizes the equatorial Atlantic circulation.

Mud-Flat Cycles, Incised Channels, and Relative Sea-Level Changes on a Paleocene Mud-Dominated Coast, Ellesmere Island, Arctic Canada

ABSTRACT The Upper Paleocene Cape Pillsbury Member on west-central Ellesmere Island, consisting of thick (600+ m), cyclical, calcareous mud-flat and laterally associated mixed mud-sand shelf deposits, provides an example of deposition on a mud-dominated coast. Mud-flat cycles are characterized by laminated mudstone. Cross-bedding is conspicuously rare. Normal grading of mudstone laminae suggests that deposition from suspension was significant. Storms also were common on this mud-dominated coast, as evidenced by beds of locally derived mud-chip conglomerate that commonly are intercalated with the laminated mudrocks, and by hummocky cross-stratification in the deeper shelf facies. Soft-sediment folding and microfaulting is ubiquitous in the mudrock facies. The deformation is analogous to flowsli es in muddy tidal flats now accumulating on the exposed northeast coast of South America. The flowslides are the only potential indicators of ebb-flood tidal reversals in the entire mudstone succession. Most of the mudrock cycles are incised by sand-filled channels. The channels were excavated during a drop in relative sea level (that terminated the preceding cycle). Subsequent filling of channels began when sediment flux in the channels exceeded the rate of sea-level fall. Thin coal seams capping some of the sand-filled channels may be the first indications of early transgression. The next cycle of laminated mudstone accumulated during the succeeding transgressive/progradational phase, but the distinction between these two components is not clear. The mud-flat and shelf facies were mostly progradational, accumulating during successive rises and high stands of relative sea level.

Description of a Giant Circumglobal Lamprogrammus Species (Pisces: Ophidiidae)

L AMPROGRAMMUS Alcock, 1891 (in WoodMason and Alcock, 1891) is a genus of oceanic ophidiid fishes found around the world beneath tropical and subtropical seas. Smaller examples are occasionally captured in the mesoto bathypelagic, whereas larger fish are caught most often with bottom trawls fished at bathyal depths. We have studied four distinctive, elongate, specimens, the largest nearly 2 m long. Three are from the Southern Hemisphere: one from off the coast of Chile, another from off the northwest coast of Australia, and a third from off Angola. A fourth example was caught off the northeast coast of South America. These

Properties of thermal staircases off the northeast coast of South America, spring and fall 1985

In spring and fall 1985, air expendable bathythermograph surveys of a large area off the northeast coast of South America revealed an extensive field of subthermocline thermal staircases which is probably the site of vigorous salt fingering. During both seasons the staircases were shallowest in the south (180–360 m) and deepest in the northwest (420–650 m), occurring on the average between the 8° and 13°C isotherms. Typically, each staircase consisted of 10 well‐mixed layers with average thickness of 16 m and average interlayer temperature change of 0.52°. Thicker layers seemed to be associated with larger temperature changes. No seasonal variation in these parameters was observed. The interfaces separating the layers had a modal thickness of 2 m, with interfaces in the spring tending to be thinner than in the fall. The region bounded by 10°–14°N, 52°–57°W tended to have staircases with more layers, thicker layers, and larger interlayer temperature changes. The sharp northeastern staircase field boundary occurs at the confluence of the Subtropical Underwater and the Antarctic Intermediate Water, suggesting that the staircases may be formed in this region and then extend south and west to form the rest of the field.

Improved Depth and Temperature Conversion Equations for Sippican AXBTs

In October 1985, in a region of large-scale thermohaline ”staircases” off the northeast coast of South America, five shallow and seven deep Sippican AXBTs (air deployed expendable bathythermographs) were hand deployed from the research vessel USNS Bartlett during times when CTD (conductivity, temperature, and depth) casts were being conducted. AXBT temperature and depth values calculated from several standard conversion equations were compared with the CTD values and improved conversion equations were derived. Two different elapsed fall time-to-depth conversion equations were found for the shallow and deep AXBTs, but only one frequency-to-temperature conversion equation. The depth equations, accurate to ±5 m over the range 0–700 m, were z = 1.5573t −0.000301t2 for shallow AXBTs and z = 1.6325t −0.000215t2 for deep, with z the depth in meters and t the elapsed fall time of the probe in seconds. The temperature equation, accurate to ±0.2°C between 6–28°C, was T = −38.6045 + 0.0271075F, with T the temperature in degree centigrade and F the transmitted frequency in hertz.

Characteristics of thermohaline steps off the northeast coast of South America, July 1983

XBT and CTD measurements made in the Atlantic Ocean southeast of Barbados reveal a series of large thermohaline steps lying between the salinity maximum of the Subtropical Underwater at about 100 m and the salinity minimum of the Antarctic Intermediate Water at about 800 m. Historical data indicate that the steps are a permanent feature of the area extending over some 10 6 km 2. At two multicast stations in July 1983 the average step was 19.0 dbar in thickness, and the average interface between steps was 2.1 dbar thick. Mean potential temperature, salinity and potential density changes across the interfaces were, respectively, 0.526°C, 0.084 psu, and 0.030. Internal structure was noted in some of the steps, as well as features resembling intrusions. The low value of the density ratio, approximately 1.5, supports the hypothesis that the steps are caused by intense salt finger activity. Estimates of vertical fluxes of heat and salt through the staircases are large enough to suggest that the process plays a major role in vertical exchange across the thermocline in this region and, consequently, a major role in determining the T-S properties of the equatorial thermocline and of the Caribbean Current-Gulf Stream system.

The effect of thermohaline steps on range‐dependent acoustic propagation near the northeast coast of South America using high resolution data

The effects of large thermohaline steps on acoustic transmission loss (TL) for a range‐independent sound velocity profile (SVP) near the northeast coast of South America were reported [Chin‐Bing and King, J. Acoust. Soc. Am. Suppl. 1 76, S84 (1984)] using a high resolution SVP (in depth), a discrete standard depth SVP, and a depth thinned SVP. The thermohaline step structure created adjacent regions of near isovelocity connected by a high gradient small transition region; this “step” structured SVP affected the TL even at low frequencies. The study is now extended to include recent experimental high resolution range‐dependent thermohaline data. Range‐dependent TL comparisons are made using SVPs obtained from (1) the high resolution data, (2) an oceanographic forecast model, (3) discrete standard depths, and (4) a depth thinned profile. This range‐dependent study supports the basic finding from the range‐independent study—TL structure can be adversely affected by failing to include the detailed SVP step structure. Furthermore, oceanographic forecasts models that provide SVPs need a high degree of accuracy in regions where these vertical anomalies exist.

The effect of large thermohaline steps on acoustic propagation near the northeast coast of South America

The acoustical impact on transmission loss due to a thermohaline step profile has been studied using a typical thermohaline step profile taken off the northeast coast of South America in July 1983. Superimposed on the smooth canonical temperature and salinity profiles of the ocean are vertical “fine structure” (1–100 m) perturbations which can affect the acoustic transmission. One mechanism which can cause this “fine structure” is double diffusion (multi-component diffusion) in which each component has a different molecular diffusivity. Under the proper conditions, very dramatic thermohaline steps can occur in which very well mixed regions of 5–200 m thickness are separated by sharp, several meter thick, high gradient interfaces. The impact on the sound velocity profile (SVP) is to create adjacent regions of near isovelocity connected by a high gradient small transition region. Only since the advent of continuous profiling temperature and salinity sensors have these steps been detected; discrete water samples (“bottle casts”) usually did not reveal them. It is seen that transmission loss can be significantly affected even at low frequencies (50 Hz) by failing to include the detailed step structure in the SVP. Furthermore, SVP thinning algorithms using tolerances which seem to preserve the step structure in the SVP can also give erroneous results in the transmission loss.

Near equatorial eddies in the North Atlantic

Surveys of the large scale near equatorial eddies (≃400km across) off the northeast coast of South America with expendable bathythermographs from ships of opportunity and aircraft indicate that a large eddy (6N‐11N) to the north and a southern eddy‐like feature (2N‐6N) probably are a permanent part of the circulation. Both features were observed during the periods of seasonal extremes, March and September, although during the latter period the structure of the eddies had enlarged and deepened, indicating a pronounced seasonal variability.

Oceanographic activities of the Hydrographic Office and the United States Navy During 1937 and plans for 1938

The Hydro‐graphic Office, in carrying out its mission to the maritime world, has contributed during the past year much to the science of oceanography in widely separated oceanic areas of the Earth's surface.Hydrographic surveys have been continued in the Caribbean area and along the northeast coast of South America, together with a continuance of dynamic sounding work.

Ocean Currents on the North-East Coast of South America

Ocean Currents on the North-East Coast of South America