Relative sea level history, which is the result of the combined effects of land subsidence, sedim... more Relative sea level history, which is the result of the combined effects of land subsidence, sediment supply and absolute sea level history may be reconstructed from preserved sediment thicknesses. However, variations in the preserved sediment thicknesses between different sedimentary environments strongly limit the accuracy of this type of geological approach, particularly in fluvial channelized systems, such as delta plains. To address this, we apply three different and independent stratigraphic approaches to the case of the Ganges-Brahmaputra-Meghna Delta (GBMD). Our approach has been made possible by a broad dataset of geological archives we have collected, which includes more than 400 hand-drilled stratigraphic wells, 198 radiocarbon ages, and river seismic reflection data (255 km of high-resolution multichannel seismic images). The seaward gradient of accommodation and the limit of the subsiding delta plain are estimated, assuming that the delta is near or at the base-level, which is considered to be the relative sea-level. First, a statistical analysis of the variability of preserved sediment thicknesses is used to derive the average pattern of accommodation from the Holocene isopach. Secondly, the preserved sediment thicknesses are analyzed by geomorphotectonic domains to estimate an average pattern of accommodation. Thirdly, the burial history of the seismically imaged last glacial incision of the Brahmaputra River is reconstructed. Results suggest that the variability of preserved sediment thicknesses can be up to 35% in a delta plain between river channel and flood plain deposits for the same relative sea-level history. Taking this variability into consideration, the Holocene relative sea-level history of the GBMD and the most likely pattern of subsidence are determined. Results provide evidence of moderate Holocene subsidence over the delta, gently increasing seaward from <0.2 mm/yr landward of the Hinge Zone, which can be considered as the northern limit of the subsiding delta plain, to 2 ± 0.7 mm/yr in the middle fluvial delta to 4 ± 1.4 mm/yr in the lower tidal delta. This enables us to construct the first millennial-scale map of subsidence pattern on the GBMD in which uncertainties on subsidence rates are provided. This map may aid in evaluating the negative impact that human modification may have on subsidence and relative sea level in the GBMD, and thereby help to determine better sustainable coastal management practices for the GBMD and other large delta plains.
Quantitative interrogation of grain sizes in sedimentary systems has the potential to improve pre... more Quantitative interrogation of grain sizes in sedimentary systems has the potential to improve predictions of stratigraphic architecture, facies distributions, and downstream reservoir characteristics. To quantify these relationships, downstream fining data are coupled with rates of mass extraction, with input grain-size distribution, accommodation, and sediment input from multiple transport pathways providing primary controls on resulting sediment dispersal patterns. We spatially apportioned mass distribution along three sediment delivery pathways with distinct accommodation characteristics within the Ganges-Brahmaputra-Meghna Delta to calculate chi (í µí¼), the total fraction of supplied sediment flux lost to deposition at any given point. Low rates of downstream fining and sand-rich channel facies characterize a bypass-dominant pathway along the western margin of Sylhet basin, whereas two splay deposits that prograde into the underfilled basin interior exhibit higher rates of fining and preservation of mud-rich facies. Both splay deposits show a shift from sand-dominated to mixed sand and mud facies and increased mud preservation (above 30%) at a í µí¼ value of ∼0.8. No comparable increase in mud preservation occurs along the bypass-dominated pathway, suggesting that this course operated in an inherently different extraction mode due to limited mid-Holocene accommodation. A similarity solution model effectively reproduces most of the spatial patterns of mass extraction observed in Sylhet basin, except in one location receiving lateral sediment input from a distributary channel. These field and modeling results indicate that grain-size data and sediment volume measurements can be used to not only reconstruct paleodynamics of transport networks and resulting stratigraphy but also lead to predictive insights on subsurface heterogeneity, and thus improved reservoir and aquifer characterization.
The contribution of subsidence to relative sea level rise in the Ganges-Brahmaputra delta (GBD) i... more The contribution of subsidence to relative sea level rise in the Ganges-Brahmaputra delta (GBD) is largely unknown and may considerably enhance exposure of the Bengal Basin populations to sea level rise and storm surges. This paper focuses on estimating the present-day subsidence induced by Holocene sediment in the Bengal Basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr. Using a viscoelastic Earth model and sediment deposition history based on in situ measurements, results suggest that massive sediment influx initiated in the early Holocene under a strengthened South Asian monsoon may have contributed significantly to the present-day subsidence of the GBD. We estimate that the Holocene loading generates up to 1.6 mm/yr of the present-day subsidence along the GBD coast, depending on the rheological model of the Earth. This rate is close to the twentieth century global mean sea level rise (1.1-1.7 mm/yr). Thus, past climate change, by way of enhanced sedimentation, is impacting vulnerability of the GBD populations. Plain Language Summary This paper estimates the land subsidence induced by sediments deposited in the Bengal Basin and by the sea level rise over the past 18,000 years. The results of numerical modeling demonstrate that the coast of the Ganges-Brahmaputra delta subsides at a rate of about 1-1.6 mm/yr depending on the lithospheric thickness and the Earth mantle viscosity. This is comparable to the rate of global mean sea level rise during the twentieth century. Thus, the intense sedimentation generated by climate changes in the past contributes significantly to the present-day subsidence of the Bengal coast.
Since the 1960s, ~5000 km2 of tidal deltaplain in southwest Bangladesh has been embanked and conv... more Since the 1960s, ~5000 km2 of tidal deltaplain in southwest Bangladesh has been embanked and converted to densely inhabited, agricultural islands (i.e., polders). This landscape is juxtaposed to the adjacent Sundarbans, a pristine mangrove forest, both well connected by a dense network of tidal channels that effectively convey water and sediment throughout the region. The extensive embanking in poldered areas, however, has greatly reduced the tidal prism (i.e., volume of water) transported through local channels. We reveal that >600 km of these major waterways have infilled in recent decades, converting to land through enhanced sedimentation and the direct blocking of waterways by embankments and sluice gates. Nearly all of the observed closures (~98%) have occurred along the embanked polder systems, with no comparable changes occurring in channels of the Sundarbans (<2% change). We attribute most of the channel infilling to the local reduction of tidal prism in poldered areas...
Simple pebble tools, ephemeral cultural features, and the remains of maritime and terrestrial foo... more Simple pebble tools, ephemeral cultural features, and the remains of maritime and terrestrial foods are present in undisturbed Late Pleistocene and Early Holocene deposits underneath a large human-made mound at Huaca Prieta and nearby sites on the Pacific coast of northern Peru. Radiocarbon ages indicate an intermittent human presence dated between ~15,000 and 8000 calendar years ago before the mound was built. The absence of fishhooks, harpoons, and bifacial stone tools suggests that technologies of gathering, trapping, clubbing, and exchange were used primarily to procure food resources along the shoreline and in estuarine wetlands and distant mountains. The stone artifacts are minimally worked unifacial stone tools characteristic of several areas of South America. Remains of avocado, bean, and possibly cultivated squash and chile pepper are also present, suggesting human transport and consumption. Our new findings emphasize an early coastal lifeway of diverse food procurement str...
The sediment budget of Jamaica Bay (New York, USA) has been determined using the natural particle... more The sediment budget of Jamaica Bay (New York, USA) has been determined using the natural particle-reactive radionuclides 234Th and 210Pb. Inventories of excess thorium-234 (234Thxs , half-life = 24.1 d) were measured in bottom sediments of the Bay during four cruises from September 2004 to July 2006. The mean bay-wide inventory for the four sampling periods ranged from 3.5 to 5.0 dpm cm–2 , four to six times that expected from 234 Th production in the overlying water column. The presence of dissolved 234 Th and a high specific activity of 234Thxs on particles at the bay inlet (~30 dpm g-1) indicated that both dissolved and particulate 234Th could be imported into the bay from the ocean. Based on these observations , a mass balance of 234Th yields an annual input of ~39 ± 14 x 10^10 g sediment into the bay. Mass accumulation rates determined from profiles of excess 210 Pb (half-life = 22.3 y) in sediment cores require annual sediment import of 7.4 ± 4.5 x 10^10 g. Both radionuclides indicate that there is considerable marine-derived sediment import to Jamaica Bay, consistent with earlier work using 210Pb. Such sediment input may be important in sustaining longer-term accretion rates of salt marshes in the bay.
High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal... more High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal deltaplain of southwest Bangladesh. To identify the sources of dissolved salts and As, groundwater samples from the regional shallow Holocene aquifer were collected from tubewells during the dry (May) and wet (October) seasons in 2012-2013. Thirteen drill cores were logged and 27 radiocarbon ages measured on wood fragments to characterize subsurface stratigraphy. Drill cuttings, exposures in pits and regional studies reveal a >5 m thick surface mud cap overlying a ~30 m thick upper unit of interbedded mud and fine sand layers, and a coarser lower unit up to 60 m thick dominated by clean sands, all with significant horizontal variation in bed continuity and thickness. This thick lower unit accreted at rates of ~2 cm/year through the early Holocene, with local subsidence or compaction rates of 1-3 mm/year. Most tubewells are screened at depths of 15-52 m in sediments deposited 8000-900...
International journal of environmental health research, Jan 8, 2016
National drinking water assessments for Bangladesh do not reflect local variability, or temporal ... more National drinking water assessments for Bangladesh do not reflect local variability, or temporal differences. This paper reports on the findings of an interdisciplinary investigation of drinking water insecurity in a rural coastal south-western Bangladesh. Drinking water quality is assessed by comparison of locally measured concentrations to national levels and water quality criteria; resident's access to potable water and their perceptions are based on local social surveys. Residents in the study area use groundwater far less than the national average; salinity and local rainwater scarcity necessitates the use of multiple water sources throughout the year. Groundwater concentrations of arsenic and specific conductivity (SpC) were greater than surface water (pond) concentrations; there was no statistically significant seasonal difference in mean concentrations in groundwater, but there was for ponds, with arsenic higher in the dry season. Average arsenic concentrations in local ...
The lithologic composition and grain size distribution of sediments are primary determinants of t... more The lithologic composition and grain size distribution of sediments are primary determinants of their inherent reflectance properties. However, moisture content is also known to have a strong influence on reflectances of soils and sediments. If the effects of sediment composition, grain size and moisture content could be distinguished spectrally, it might be possible to map these properties at synoptic scales using hyperspectral, or perhaps even broadband, remote sensing. Mapping the spatiotemporal distribution of sediment composition and moisture content could provide unique constraints on both the processes by which the sediments are deposited as well as the constraints they may impose on subsequent water flow and sediment transport. The Ganges–Brahmaputra delta (GBD) is formed by the convergence of these two great rivers and is superlative in both size and geologic activity. Sediment redistribution and channel migration associated with the annual floods disrupt the lives of hundreds of thousands of people living on the GBD but is also critical for maintaining the delta area fertile and above sea level. The 30+ year archive of Landsat imagery could provide a basis for spatiotemporal analysis of these fluvial dynamics if sediment properties could be inferred or measured from reflectance spectra. However, before confronting the challenge of broadband detection we must understand the spectral properties of the sediments under more controlled laboratory conditions. Bidirectional reflectance spectroscopy of 109 sediment samples from the GBD yields a spectral mixing space that appears to be structured by variations in moisture content, grain size and possibly lithology. Although the individual Empirical Orthogonal Functions of the Principal Components do not correspond to unique absorption features, clustering within the mixing space is clearly influenced by moisture content and grain size. Laboratory spectra of sediment reflectance measured under varying moisture content yield distinct trajectories through the spectral mixing space for different grain size distributions of sieved sediments. These variations in moisture content account for > 98% of spectral variance observed in these samples. Drying trajectories of coarse, fine and mixed sediments are distinct and suggest that moisture and grain size might be spectrally distinguishable. These results are consistent with Angstrom's hypothesis of moisture-driven spectral absorption but more controlled experiments are necessary to test the hypothesis rigorously.
Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded... more Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded new evidence of late Pleistocene cultural deposits that shed insights into the early human occupation of the Pacific coast of South America. Radiocarbon dates place this occupation between ~ 14,200 and 13,300 cal yr BP. The cultural evidence shares certain basic technological and subsistence traits, including maritime resources and simple flake tools, with previously discovered late Pleistocene sites along the Pacific coast of Peru and Chile. The results help to expand our knowledge of early maritime societies and human adaption to changing coastal environments.
In November 2007 the eye of a major tropical storm, Cyclone Sidr, tracked over the offshore canyo... more In November 2007 the eye of a major tropical storm, Cyclone Sidr, tracked over the offshore canyon associated with the Ganges-Brahmaputra river delta. Known as the Swatch of No Ground (SoNG), this large canyon incises within 30 km of the deltaic coast and is accreting rapidly (10 to >50 cm/yr) with fluvially derived sediments. Historically numerous tropical storms have affected the northern Bay of Bengal each year, but more recently cyclogenesis has been weak and Sidr is the first major cyclone to impact the Bengal shelf since 1991. As part of an ongoing study, our research team had just completed a high-resolution sub- bottom sonar (chirp) survey of the SoNG canyon head six months prior to Cyclone Sidr. Following the storm, we organized a second sub-bottom survey to assess the storm's impact on canyon morphology and sedimentation patterns. A comparison of our pre- and post-storm surveys reveal dramatic mass failures around the canyon wall, but also vast areas that were large...
Relative sea level history, which is the result of the combined effects of land subsidence, sedim... more Relative sea level history, which is the result of the combined effects of land subsidence, sediment supply and absolute sea level history may be reconstructed from preserved sediment thicknesses. However, variations in the preserved sediment thicknesses between different sedimentary environments strongly limit the accuracy of this type of geological approach, particularly in fluvial channelized systems, such as delta plains. To address this, we apply three different and independent stratigraphic approaches to the case of the Ganges-Brahmaputra-Meghna Delta (GBMD). Our approach has been made possible by a broad dataset of geological archives we have collected, which includes more than 400 hand-drilled stratigraphic wells, 198 radiocarbon ages, and river seismic reflection data (255 km of high-resolution multichannel seismic images). The seaward gradient of accommodation and the limit of the subsiding delta plain are estimated, assuming that the delta is near or at the base-level, which is considered to be the relative sea-level. First, a statistical analysis of the variability of preserved sediment thicknesses is used to derive the average pattern of accommodation from the Holocene isopach. Secondly, the preserved sediment thicknesses are analyzed by geomorphotectonic domains to estimate an average pattern of accommodation. Thirdly, the burial history of the seismically imaged last glacial incision of the Brahmaputra River is reconstructed. Results suggest that the variability of preserved sediment thicknesses can be up to 35% in a delta plain between river channel and flood plain deposits for the same relative sea-level history. Taking this variability into consideration, the Holocene relative sea-level history of the GBMD and the most likely pattern of subsidence are determined. Results provide evidence of moderate Holocene subsidence over the delta, gently increasing seaward from &lt;0.2 mm/yr landward of the Hinge Zone, which can be considered as the northern limit of the subsiding delta plain, to 2 ± 0.7 mm/yr in the middle fluvial delta to 4 ± 1.4 mm/yr in the lower tidal delta. This enables us to construct the first millennial-scale map of subsidence pattern on the GBMD in which uncertainties on subsidence rates are provided. This map may aid in evaluating the negative impact that human modification may have on subsidence and relative sea level in the GBMD, and thereby help to determine better sustainable coastal management practices for the GBMD and other large delta plains.
Quantitative interrogation of grain sizes in sedimentary systems has the potential to improve pre... more Quantitative interrogation of grain sizes in sedimentary systems has the potential to improve predictions of stratigraphic architecture, facies distributions, and downstream reservoir characteristics. To quantify these relationships, downstream fining data are coupled with rates of mass extraction, with input grain-size distribution, accommodation, and sediment input from multiple transport pathways providing primary controls on resulting sediment dispersal patterns. We spatially apportioned mass distribution along three sediment delivery pathways with distinct accommodation characteristics within the Ganges-Brahmaputra-Meghna Delta to calculate chi (í µí¼), the total fraction of supplied sediment flux lost to deposition at any given point. Low rates of downstream fining and sand-rich channel facies characterize a bypass-dominant pathway along the western margin of Sylhet basin, whereas two splay deposits that prograde into the underfilled basin interior exhibit higher rates of fining and preservation of mud-rich facies. Both splay deposits show a shift from sand-dominated to mixed sand and mud facies and increased mud preservation (above 30%) at a í µí¼ value of ∼0.8. No comparable increase in mud preservation occurs along the bypass-dominated pathway, suggesting that this course operated in an inherently different extraction mode due to limited mid-Holocene accommodation. A similarity solution model effectively reproduces most of the spatial patterns of mass extraction observed in Sylhet basin, except in one location receiving lateral sediment input from a distributary channel. These field and modeling results indicate that grain-size data and sediment volume measurements can be used to not only reconstruct paleodynamics of transport networks and resulting stratigraphy but also lead to predictive insights on subsurface heterogeneity, and thus improved reservoir and aquifer characterization.
The contribution of subsidence to relative sea level rise in the Ganges-Brahmaputra delta (GBD) i... more The contribution of subsidence to relative sea level rise in the Ganges-Brahmaputra delta (GBD) is largely unknown and may considerably enhance exposure of the Bengal Basin populations to sea level rise and storm surges. This paper focuses on estimating the present-day subsidence induced by Holocene sediment in the Bengal Basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr. Using a viscoelastic Earth model and sediment deposition history based on in situ measurements, results suggest that massive sediment influx initiated in the early Holocene under a strengthened South Asian monsoon may have contributed significantly to the present-day subsidence of the GBD. We estimate that the Holocene loading generates up to 1.6 mm/yr of the present-day subsidence along the GBD coast, depending on the rheological model of the Earth. This rate is close to the twentieth century global mean sea level rise (1.1-1.7 mm/yr). Thus, past climate change, by way of enhanced sedimentation, is impacting vulnerability of the GBD populations. Plain Language Summary This paper estimates the land subsidence induced by sediments deposited in the Bengal Basin and by the sea level rise over the past 18,000 years. The results of numerical modeling demonstrate that the coast of the Ganges-Brahmaputra delta subsides at a rate of about 1-1.6 mm/yr depending on the lithospheric thickness and the Earth mantle viscosity. This is comparable to the rate of global mean sea level rise during the twentieth century. Thus, the intense sedimentation generated by climate changes in the past contributes significantly to the present-day subsidence of the Bengal coast.
Since the 1960s, ~5000 km2 of tidal deltaplain in southwest Bangladesh has been embanked and conv... more Since the 1960s, ~5000 km2 of tidal deltaplain in southwest Bangladesh has been embanked and converted to densely inhabited, agricultural islands (i.e., polders). This landscape is juxtaposed to the adjacent Sundarbans, a pristine mangrove forest, both well connected by a dense network of tidal channels that effectively convey water and sediment throughout the region. The extensive embanking in poldered areas, however, has greatly reduced the tidal prism (i.e., volume of water) transported through local channels. We reveal that >600 km of these major waterways have infilled in recent decades, converting to land through enhanced sedimentation and the direct blocking of waterways by embankments and sluice gates. Nearly all of the observed closures (~98%) have occurred along the embanked polder systems, with no comparable changes occurring in channels of the Sundarbans (<2% change). We attribute most of the channel infilling to the local reduction of tidal prism in poldered areas...
Simple pebble tools, ephemeral cultural features, and the remains of maritime and terrestrial foo... more Simple pebble tools, ephemeral cultural features, and the remains of maritime and terrestrial foods are present in undisturbed Late Pleistocene and Early Holocene deposits underneath a large human-made mound at Huaca Prieta and nearby sites on the Pacific coast of northern Peru. Radiocarbon ages indicate an intermittent human presence dated between ~15,000 and 8000 calendar years ago before the mound was built. The absence of fishhooks, harpoons, and bifacial stone tools suggests that technologies of gathering, trapping, clubbing, and exchange were used primarily to procure food resources along the shoreline and in estuarine wetlands and distant mountains. The stone artifacts are minimally worked unifacial stone tools characteristic of several areas of South America. Remains of avocado, bean, and possibly cultivated squash and chile pepper are also present, suggesting human transport and consumption. Our new findings emphasize an early coastal lifeway of diverse food procurement str...
The sediment budget of Jamaica Bay (New York, USA) has been determined using the natural particle... more The sediment budget of Jamaica Bay (New York, USA) has been determined using the natural particle-reactive radionuclides 234Th and 210Pb. Inventories of excess thorium-234 (234Thxs , half-life = 24.1 d) were measured in bottom sediments of the Bay during four cruises from September 2004 to July 2006. The mean bay-wide inventory for the four sampling periods ranged from 3.5 to 5.0 dpm cm–2 , four to six times that expected from 234 Th production in the overlying water column. The presence of dissolved 234 Th and a high specific activity of 234Thxs on particles at the bay inlet (~30 dpm g-1) indicated that both dissolved and particulate 234Th could be imported into the bay from the ocean. Based on these observations , a mass balance of 234Th yields an annual input of ~39 ± 14 x 10^10 g sediment into the bay. Mass accumulation rates determined from profiles of excess 210 Pb (half-life = 22.3 y) in sediment cores require annual sediment import of 7.4 ± 4.5 x 10^10 g. Both radionuclides indicate that there is considerable marine-derived sediment import to Jamaica Bay, consistent with earlier work using 210Pb. Such sediment input may be important in sustaining longer-term accretion rates of salt marshes in the bay.
High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal... more High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal deltaplain of southwest Bangladesh. To identify the sources of dissolved salts and As, groundwater samples from the regional shallow Holocene aquifer were collected from tubewells during the dry (May) and wet (October) seasons in 2012-2013. Thirteen drill cores were logged and 27 radiocarbon ages measured on wood fragments to characterize subsurface stratigraphy. Drill cuttings, exposures in pits and regional studies reveal a >5 m thick surface mud cap overlying a ~30 m thick upper unit of interbedded mud and fine sand layers, and a coarser lower unit up to 60 m thick dominated by clean sands, all with significant horizontal variation in bed continuity and thickness. This thick lower unit accreted at rates of ~2 cm/year through the early Holocene, with local subsidence or compaction rates of 1-3 mm/year. Most tubewells are screened at depths of 15-52 m in sediments deposited 8000-900...
International journal of environmental health research, Jan 8, 2016
National drinking water assessments for Bangladesh do not reflect local variability, or temporal ... more National drinking water assessments for Bangladesh do not reflect local variability, or temporal differences. This paper reports on the findings of an interdisciplinary investigation of drinking water insecurity in a rural coastal south-western Bangladesh. Drinking water quality is assessed by comparison of locally measured concentrations to national levels and water quality criteria; resident's access to potable water and their perceptions are based on local social surveys. Residents in the study area use groundwater far less than the national average; salinity and local rainwater scarcity necessitates the use of multiple water sources throughout the year. Groundwater concentrations of arsenic and specific conductivity (SpC) were greater than surface water (pond) concentrations; there was no statistically significant seasonal difference in mean concentrations in groundwater, but there was for ponds, with arsenic higher in the dry season. Average arsenic concentrations in local ...
The lithologic composition and grain size distribution of sediments are primary determinants of t... more The lithologic composition and grain size distribution of sediments are primary determinants of their inherent reflectance properties. However, moisture content is also known to have a strong influence on reflectances of soils and sediments. If the effects of sediment composition, grain size and moisture content could be distinguished spectrally, it might be possible to map these properties at synoptic scales using hyperspectral, or perhaps even broadband, remote sensing. Mapping the spatiotemporal distribution of sediment composition and moisture content could provide unique constraints on both the processes by which the sediments are deposited as well as the constraints they may impose on subsequent water flow and sediment transport. The Ganges–Brahmaputra delta (GBD) is formed by the convergence of these two great rivers and is superlative in both size and geologic activity. Sediment redistribution and channel migration associated with the annual floods disrupt the lives of hundreds of thousands of people living on the GBD but is also critical for maintaining the delta area fertile and above sea level. The 30+ year archive of Landsat imagery could provide a basis for spatiotemporal analysis of these fluvial dynamics if sediment properties could be inferred or measured from reflectance spectra. However, before confronting the challenge of broadband detection we must understand the spectral properties of the sediments under more controlled laboratory conditions. Bidirectional reflectance spectroscopy of 109 sediment samples from the GBD yields a spectral mixing space that appears to be structured by variations in moisture content, grain size and possibly lithology. Although the individual Empirical Orthogonal Functions of the Principal Components do not correspond to unique absorption features, clustering within the mixing space is clearly influenced by moisture content and grain size. Laboratory spectra of sediment reflectance measured under varying moisture content yield distinct trajectories through the spectral mixing space for different grain size distributions of sieved sediments. These variations in moisture content account for > 98% of spectral variance observed in these samples. Drying trajectories of coarse, fine and mixed sediments are distinct and suggest that moisture and grain size might be spectrally distinguishable. These results are consistent with Angstrom's hypothesis of moisture-driven spectral absorption but more controlled experiments are necessary to test the hypothesis rigorously.
Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded... more Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded new evidence of late Pleistocene cultural deposits that shed insights into the early human occupation of the Pacific coast of South America. Radiocarbon dates place this occupation between ~ 14,200 and 13,300 cal yr BP. The cultural evidence shares certain basic technological and subsistence traits, including maritime resources and simple flake tools, with previously discovered late Pleistocene sites along the Pacific coast of Peru and Chile. The results help to expand our knowledge of early maritime societies and human adaption to changing coastal environments.
In November 2007 the eye of a major tropical storm, Cyclone Sidr, tracked over the offshore canyo... more In November 2007 the eye of a major tropical storm, Cyclone Sidr, tracked over the offshore canyon associated with the Ganges-Brahmaputra river delta. Known as the Swatch of No Ground (SoNG), this large canyon incises within 30 km of the deltaic coast and is accreting rapidly (10 to >50 cm/yr) with fluvially derived sediments. Historically numerous tropical storms have affected the northern Bay of Bengal each year, but more recently cyclogenesis has been weak and Sidr is the first major cyclone to impact the Bengal shelf since 1991. As part of an ongoing study, our research team had just completed a high-resolution sub- bottom sonar (chirp) survey of the SoNG canyon head six months prior to Cyclone Sidr. Following the storm, we organized a second sub-bottom survey to assess the storm's impact on canyon morphology and sedimentation patterns. A comparison of our pre- and post-storm surveys reveal dramatic mass failures around the canyon wall, but also vast areas that were large...
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