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Hermes Mianzan - One of the best experts on this subject based on the ideXlab platform.
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young green turtles chelonia mydas exposed to plastic in a Frontal area of the sw atlantic
Marine Pollution Bulletin, 2014Co-Authors: Hermes Mianzan, Victoria Gonzalez Carman, Marcelo E Acha, Sara M Maxwell, Diego Albareda, Claudio CampagnaAbstract:Ingestion of anthropogenic debris represents an important threat to marine turtle populations. Information has been limited to inventories of debris ingested and its consequences, but why ingestion occurs and the conditions that enable it are less understood. Here we report on the occurrence of plastic ingestion in young green turtles (Chelonia mydas) inhabiting the Rio de la Plata (SW Atlantic). This Estuarine area is characterized by a Frontal system that accumulates anthropogenic debris. We explored exposure of green turtles to plastic and its ingestion via debris distribution, habitat use and digestive tract examination. Results indicated that there is considerable overlap of Frontal accumulated plastic and core foraging areas of the animals. Exposure results in ingestion, as shown by the high frequency of plastic found in the digestive tracts. The Rio de la Plata Estuarine Front is an area of conservation concern for young green turtles.
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Acoustic study of the Rio de la Plata Estuarine Front
ICES Journal of Marine Science, 2006Co-Authors: A.g. Cabreira, Adrian Madirolas, G. Alvarez Colombo, Eduardo M. Acha, Hermes MianzanAbstract:During December 1999, a transect 260 km long was carried out along the major axis of the Rio de la Plata estuary. Acoustic (120 kHz), oceanographic, and zooplankton sampling were performed to extract a continuous, quasi-synoptic acoustic view of the estuary's salt wedge. Three different zones were identified. The riverine and marine zones were characterized by vertically homogeneous water and low volume-backscattering strength (S v ). The mixohaline zone was characterized by a strong vertical salinity gradient and the highest S v values. There were no relationships between the reflection value calculated from the salinity gradient and suspended matter (sediments) and measured S v . The greatest abundance of acoustically detectable organisms was at the halocline depth, coincident with the echo recordings. The positions of the halocline and the two Fronts were determined on the basis of aggregations of the different planktonic groups. The physical presence of the salt wedge, as shown by a “biological wedge”, was well described by the acoustic technique employed.
Zhanghua Wang - One of the best experts on this subject based on the ideXlab platform.
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Inter-comparison of optically stimulated luminescence (OSL) ages between different fractions of Holocene deposits from the Yangtze delta and its environmental implications
Marine Geology, 2021Co-Authors: Xiaomei Nian, Zhanghua Wang, Weiguo Zhang, Qianli Sun, Zhongyuan ChenAbstract:Abstract In fluvial and deltaic environments, different grain-size fractions experience varying degrees of bleaching of OSL signals due to variations in hydrodynamics and depositional processes. This has led to ambiguity for selection of grain-size fraction suitable for OSL dating. Comparison of OSL results from multiple grain-size fractions is one approach to ensure the reliability of OSL ages. We determined the quartz OSL ages of four grain-size fractions from fine silt to sand, together with the single grain OSL sensitivity in a Holocene sediment core from the Yangtze delta. For samples from the lower part of the sediment succession (including tidal river, tidal trough fill, Estuarine Front, tidal sand and delta Front facies), OSL ages determined for different grain-size fractions were generally mutually consistent within the age range of ~2–9 ka, implying minor portion of incompletely bleached grains in the sediment at the time of burial. In contrast, significant partial bleaching was observed for three samples from younger delta Front facies deposited during 0.4–0.6 ka. In these three samples, fine-silt quartz OSL ages were overestimated by ~0.5–2.0 ka compared with ages of coarser fractions. Based on the investigation of quartz luminescence sensitivity, we suggest that the southward shift of the Yellow River and increasing erosion in the Yangtze River catchment have led to enhanced water turbidity, resulting in partial bleaching of the sediment and substantial overestimation of the quartz OSL ages of fine silt during 0.4–0.6 ka. Alternatively, the erosion of older deposits and their redeposition elsewhere could retain large residual OSL ages. Notably, fine-silt quartz provides reliable ages for the period of 9–2 ka, suggesting that there was a lower degree of water turbidity compared with that since 2 ka. Therefore, the degree of OSL age overestimation may provide an indication of changes in water turbidity and sedimentary environment. Overall, our findings highlight the complexity of OSL dating in delta environments, and that an understanding of sediment transport and depositional processes is critical for reliable OSL dating.
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Assessing C/N and δ13C as indicators of Holocene sea level and freshwater discharge changes in the subaqueous Yangtze delta, China:
The Holocene, 2011Co-Authors: Qing Zhan, Zhanghua Wang, Yan Xie, Jianlei XieAbstract:To examine the applicability of C/N and organic carbon stable isotope (δ13C) in studies of the Holocene sea level and freshwater discharge in the large river mouth of Yangtze, we observed the distribution of carbon, nitrogen and δ13C in a late-Quaternary core (ZK9) collected from the present subaqueous delta. We also collected published data of the two proxies for the suspended particulate matter (SPM) and surficial sediments from the lower Yangtze River to the adjacent East China Sea. The results show that the Estuarine Front is an important boundary for terrestrial and marine contribution of the organic component in the modern sedimentary environment. In the core ZK9, sediments deposited during c. 13–9 cal. ka BP are characterized by high values of TOC (0.54–1.16%), CaCO3 (0.35% on average), and C/N (>12), which reflect an inner tidal Estuarine environment dominated by C3 terrestrial organic carbon input. During c. 9–0.7 cal. ka BP, both TOC content (0.57% on average) and C/N ratio (
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Lithological and palynological evidence of late Quaternary depositional environments in the subaqueous Yangtze delta, China
Quaternary Research, 2010Co-Authors: Zhanghua Wang, Qing Zhan, Jianlei Xie, Yoshiki Saito, Yonghong DongAbstract:Abstract AMS 14C ages of post-glacial core sediments from the subaqueous Yangtze delta, along with sedimentary structures and distributions of grain size, pollen spores, and dinoflagellate cysts, show an Estuarine depositional system from 13 to 8.4 cal ka BP and a deltaic system from 5.9 cal ka BP to the present. The Estuarine system consists of intertidal to subtidal flat, Estuarine, and Estuarine-Front facies, characterized by sand–mud couplets and a high sedimentation rate. The deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate, markedly fewer coastal wetland herbaceous pollens, and more dinoflagellate cysts. We explain the extremely high sedimentation rate during 9.2–8.4 cal ka BP at the study site as a result of rapid sea-level rise, high sediment load due to the unstable monsoonal climate, and subaqueous decrease of elevation from inner to outer estuary. A depositional hiatus occurred during 8.2–5.9 cal ka BP, the transition from Estuarine to deltaic system, caused possibly by a shortage of sediment supply resulting from delta initiation in paleo-incised Yangtze valley and strong tidal or storm-related reworking in offshore areas. The subsequent development of deltaic system at the study site indicates accelerated progradation of Yangtze delta post-5.9 cal ka BP.
Yonghong Dong - One of the best experts on this subject based on the ideXlab platform.
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Lithological and palynological evidence of late Quaternary depositional environments in the subaqueous Yangtze delta, China
Quaternary Research, 2010Co-Authors: Zhanghua Wang, Qing Zhan, Jianlei Xie, Yoshiki Saito, Yonghong DongAbstract:Abstract AMS 14C ages of post-glacial core sediments from the subaqueous Yangtze delta, along with sedimentary structures and distributions of grain size, pollen spores, and dinoflagellate cysts, show an Estuarine depositional system from 13 to 8.4 cal ka BP and a deltaic system from 5.9 cal ka BP to the present. The Estuarine system consists of intertidal to subtidal flat, Estuarine, and Estuarine-Front facies, characterized by sand–mud couplets and a high sedimentation rate. The deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate, markedly fewer coastal wetland herbaceous pollens, and more dinoflagellate cysts. We explain the extremely high sedimentation rate during 9.2–8.4 cal ka BP at the study site as a result of rapid sea-level rise, high sediment load due to the unstable monsoonal climate, and subaqueous decrease of elevation from inner to outer estuary. A depositional hiatus occurred during 8.2–5.9 cal ka BP, the transition from Estuarine to deltaic system, caused possibly by a shortage of sediment supply resulting from delta initiation in paleo-incised Yangtze valley and strong tidal or storm-related reworking in offshore areas. The subsequent development of deltaic system at the study site indicates accelerated progradation of Yangtze delta post-5.9 cal ka BP.
W. Rockwell Geyer - One of the best experts on this subject based on the ideXlab platform.
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Hydraulic control of a highly stratified Estuarine Front
Journal of Physical Oceanography, 2005Co-Authors: Daniel G. Macdonald, W. Rockwell GeyerAbstract:Abstract Observations at the mouth of the Fraser River (British Columbia, Canada) indicate an abrupt Frontal transition between unstratified river outflow and a highly stratified river plume with differences in salinity greater than 25 psu across a few meters in the vertical direction and several hundred meters in the horizontal direction. The Front roughly follows a natural break in the bathymetry, crossing the channel at an angle of approximately 45°, and is essentially stationary for a period of approximately 3.5 h centered on the low tide following the larger of two daily ebbs. The location of the Front is coincident with observations of significantly supercritical internal Froude numbers at the Front, based on velocities in the along-flow direction. This observation contradicts the one-dimensional theory, which indicates that the Froude number should be 1. However, because the Front is oriented obliquely to the outflow, a coordinate system can be selected that is normal to the Front and for which a c...
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Turbulent energy production and entrainment at a highly stratified Estuarine Front
Journal of Geophysical Research, 2004Co-Authors: Daniel G. Macdonald, W. Rockwell GeyerAbstract:[1] Rates of turbulent kinetic energy (TKE) production and buoyancy flux in the region immediately seaward (� 1 km) of a highly stratified Estuarine Front at the mouth of the Fraser River (British Columbia, Canada) are calculated using a control volume approach. The calculations are based on field data obtained from shipboard instrumentation, specifically velocity data from a ship mounted acoustic Doppler current profiler (ADCP), and salinity data from a towed conductivity-temperature-depth (CTD) unit. The results allow for the calculation of vertical velocities in the water column, and the total vertical transport of salt and momentum. The vertical turbulent transport quantities (u 0 w 0 , S 0 w 0 ) can then be estimated as the difference between the total transport and the advective transport. Estimated production is on the order of 10 � 3 m 2 s � 3 , yielding a value of e(nN 2 ) � 1 on the order of 10 4 . This rate of TKE production is at the upper limit of reported values for ocean and coastal environments. Flux Richardson numbers in this highly energetic system generally range from 0.15 to 0.2, with most mixing occurring at gradient Richardson numbers slightly less than 1 = 4 . These values compare favorably with other values in the literature that are associated with turbulence observations from regimes characterized by scales several orders of magnitude smaller than are present in the Fraser River. INDEX TERMS: 4546 Oceanography: Physical: Nearshore processes; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; 4235 Oceanography: General: Estuarine processes;
Eduardo M. Acha - One of the best experts on this subject based on the ideXlab platform.
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Distribution of whitemouth croaker (Micropogonias furnieri, Desmarest 1823) larvae in the Rio de la Plata Estuarine Front
Estuarine Coastal and Shelf Science, 2009Co-Authors: Mara Silvia Braverman, Eduardo M. Acha, Domingo A. Gagliardini, Martín RivarossaAbstract:Abstract Whitemouth croaker ( Micropogonias furnieri ) larvae obtained and hydrographic data collected in the Rio de la Plata estuary (35°S–56°W) between 1987 and 2000 were used to explore the early life stages spatial and temporal distribution patterns and their relation to oceanographic features. The spatial distribution, restricted to a band in the inner part of the estuary, coincided with the bottom salinity Front and the maximum turbidity zone (MTZ, turbidity Front). Larvae were present during the warmest months (October through May) within a range of 14–24.5 °C temperature and 0.9–33 salinity. A vertically stratified sampling performed in the region where the largest abundance was found (December 2005 and March 2006) was used to test the hypothesis that larvae retention occurs in the bottom salinity Front. The vertically stratified sampling showed larvae throughout the water column with high predominance in the river–estuary transition zone. A positive correlation between abundance and the bottom salinity horizontal gradient was found. The size analysis showed that the largest individuals (>10 mm SL), probably undergoing the settlement process, inhabited near the bottom and that the smallest ( Results support the Estuarine retention hypothesis of previous studies on whitemouth croaker gravid females, eggs distribution and outcomes from a numerical simulation model. Retention in the salinity Front/MTZ would allow larvae to benefit from food accumulation in the region, the high turbidity level provide shelter against predators and retention in the estuary secure closeness to the main nursery ground.
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Acoustic study of the Rio de la Plata Estuarine Front
ICES Journal of Marine Science, 2006Co-Authors: A.g. Cabreira, Adrian Madirolas, G. Alvarez Colombo, Eduardo M. Acha, Hermes MianzanAbstract:During December 1999, a transect 260 km long was carried out along the major axis of the Rio de la Plata estuary. Acoustic (120 kHz), oceanographic, and zooplankton sampling were performed to extract a continuous, quasi-synoptic acoustic view of the estuary's salt wedge. Three different zones were identified. The riverine and marine zones were characterized by vertically homogeneous water and low volume-backscattering strength (S v ). The mixohaline zone was characterized by a strong vertical salinity gradient and the highest S v values. There were no relationships between the reflection value calculated from the salinity gradient and suspended matter (sediments) and measured S v . The greatest abundance of acoustically detectable organisms was at the halocline depth, coincident with the echo recordings. The positions of the halocline and the two Fronts were determined on the basis of aggregations of the different planktonic groups. The physical presence of the salt wedge, as shown by a “biological wedge”, was well described by the acoustic technique employed.