Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the per... more Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10–14.5 cal ka bp). Independent evaluations of the Cariaco Basin calendar and 14C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to 14C age agreement with terrestrial 14C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin 14C reservoir age remained stable throughout the Younger Dryas and late Allerød climatic events and that the varve and 14C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of 14C change not seen in the coral records. 14C plateaus can be identified at 9.6, 11.4, and 11.7 14C ka bp...
Deep-sea corals are a promising new archive of paleoclimate. Coupled radiocarbon and U-series dat... more Deep-sea corals are a promising new archive of paleoclimate. Coupled radiocarbon and U-series dates allow 14C to be used as a tracer of ocean circulation rate in the same manner as it is used in the modern ocean. Diagenetic alteration of coral skeletons on the seafloor requires a thorough cleaning of contaminating phases of carbon. In addition, 10% of the coral must be chemically leached prior to dissolution to remove adsorbed modern CO2. A survey of modern samples from the full δ14C gradient in the deep ocean demonstrates that the coralline CaCO3 records the radiocarbon value of the dissolved inorganic carbon.
We have measured radiocarbon in prebomb known-age shells and coral from the Indian Ocean and sout... more We have measured radiocarbon in prebomb known-age shells and coral from the Indian Ocean and southeast Asia to determine marine reservoir age corrections. Western Indian Ocean results show a strong14C depletion due to upwelling in the Arabian Sea, and indicate that this signal is advected over a wide area to the east and south. In contrast, the surface waters of the South China Sea contain relatively high levels of14C, due in part to the input of well-equilibrated water masses from the western Pacific. The easternmost regions of the Indian Ocean are also strongly influenced by the flowthrough of Pacific waters north of Australia.
Publisher Summary This chapter focuses on the methods that can determine chemical or structural f... more Publisher Summary This chapter focuses on the methods that can determine chemical or structural features of biological agent particles that are signatures of particular methods of growth and post-growth processing (often referred to as “weaponization”). The detection of these signatures in a sample of a bio-weapon (BW) agent can aid the attribution by indicating: (1) the level of sophistication of the producer, (2) the access to particular types of agent weaponization information, (3) the likelihood that the material could be or has been produced at a significant scale, (4) and by providing essential sample matching data for ascertaining a putative relationship with other samples obtained in other venues. An example of the use of biologicals in forensic science is DNA, amplied by the Polymerase Chain Reaction (PCR) technique, legally admissible in courtas evidence. DNA evidence is successfully used in the court to convict or clear people of crimes because each person's DNA is unique. High-resolution techniques are being applied to investigations; such as Environmental scanning electron microscopy (ESEM) is used for taking high-resolution images under hydrated conditions; this avoids any artifacts associated with the critical point drying process that is required under normal Scanning Electron Microscopy (SEM) operations. ESEM is also equipped with Energy Dispersive X-ray (EDX) microanalysis and Backscatter capabilities. SEM is a standard “workhorse” technique for characterizing particulate samples, found in many laboratories worldwide. It provides excellent imaging of the surfaces of agent particles and other material in a sample, and is used for identifying likely agent particles for analysis by other instruments. When combined with EDX, the elemental composition of the material in the imaged region can be determined. These techniques continue to signature libraries of correlations between analyses and growth and processing conditions of growth, it will be necessary to develop an information system which combines types of data to determine unique signatures.
The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use o... more The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial–interstadial oscillations. Owens Lake records of total organic carbon, magnetic susceptibility, and chemical composition of the carbonate-free, clay-size fraction indicate that Tioga glaciation began ∼24,500 and ended by ∼13,60014C yr B.P. Many of the components of glacial rock flour (e.g., TiO2, MnO, BaO) found in Owens Lake sediments achieved maximum values during the Tioga glaciation when valley glaciers reached their greatest extent. Total organic carbon and SiO2(amorphous) concentrations reached minimum values during Tioga glaciation, resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of Owens Lake. At least 20 stadial–interstadial oscillations occurred in the Sierra Nevada between 52,600 and 14,00014C yr B.P. Total organic carbon data from a Pyra...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
The presence of elevated 14C contamination in a laboratory preparing samples for natural radiocar... more The presence of elevated 14C contamination in a laboratory preparing samples for natural radiocarbon analysis is detrimental to the laboratory workspace as well as the research being conducted. Elevated 14C contamination occurs via many different pathways, but procedures can be adopted to prevent and remove this type of contamination. In this paper we present our current practices for preventing contamination,
Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the per... more Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10–14.5 cal ka bp). Independent evaluations of the Cariaco Basin calendar and 14C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to 14C age agreement with terrestrial 14C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin 14C reservoir age remained stable throughout the Younger Dryas and late Allerød climatic events and that the varve and 14C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of 14C change not seen in the coral records. 14C plateaus can be identified at 9.6, 11.4, and 11.7 14C ka bp...
Deep-sea corals are a promising new archive of paleoclimate. Coupled radiocarbon and U-series dat... more Deep-sea corals are a promising new archive of paleoclimate. Coupled radiocarbon and U-series dates allow 14C to be used as a tracer of ocean circulation rate in the same manner as it is used in the modern ocean. Diagenetic alteration of coral skeletons on the seafloor requires a thorough cleaning of contaminating phases of carbon. In addition, 10% of the coral must be chemically leached prior to dissolution to remove adsorbed modern CO2. A survey of modern samples from the full δ14C gradient in the deep ocean demonstrates that the coralline CaCO3 records the radiocarbon value of the dissolved inorganic carbon.
We have measured radiocarbon in prebomb known-age shells and coral from the Indian Ocean and sout... more We have measured radiocarbon in prebomb known-age shells and coral from the Indian Ocean and southeast Asia to determine marine reservoir age corrections. Western Indian Ocean results show a strong14C depletion due to upwelling in the Arabian Sea, and indicate that this signal is advected over a wide area to the east and south. In contrast, the surface waters of the South China Sea contain relatively high levels of14C, due in part to the input of well-equilibrated water masses from the western Pacific. The easternmost regions of the Indian Ocean are also strongly influenced by the flowthrough of Pacific waters north of Australia.
Publisher Summary This chapter focuses on the methods that can determine chemical or structural f... more Publisher Summary This chapter focuses on the methods that can determine chemical or structural features of biological agent particles that are signatures of particular methods of growth and post-growth processing (often referred to as “weaponization”). The detection of these signatures in a sample of a bio-weapon (BW) agent can aid the attribution by indicating: (1) the level of sophistication of the producer, (2) the access to particular types of agent weaponization information, (3) the likelihood that the material could be or has been produced at a significant scale, (4) and by providing essential sample matching data for ascertaining a putative relationship with other samples obtained in other venues. An example of the use of biologicals in forensic science is DNA, amplied by the Polymerase Chain Reaction (PCR) technique, legally admissible in courtas evidence. DNA evidence is successfully used in the court to convict or clear people of crimes because each person's DNA is unique. High-resolution techniques are being applied to investigations; such as Environmental scanning electron microscopy (ESEM) is used for taking high-resolution images under hydrated conditions; this avoids any artifacts associated with the critical point drying process that is required under normal Scanning Electron Microscopy (SEM) operations. ESEM is also equipped with Energy Dispersive X-ray (EDX) microanalysis and Backscatter capabilities. SEM is a standard “workhorse” technique for characterizing particulate samples, found in many laboratories worldwide. It provides excellent imaging of the surfaces of agent particles and other material in a sample, and is used for identifying likely agent particles for analysis by other instruments. When combined with EDX, the elemental composition of the material in the imaged region can be determined. These techniques continue to signature libraries of correlations between analyses and growth and processing conditions of growth, it will be necessary to develop an information system which combines types of data to determine unique signatures.
The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use o... more The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial–interstadial oscillations. Owens Lake records of total organic carbon, magnetic susceptibility, and chemical composition of the carbonate-free, clay-size fraction indicate that Tioga glaciation began ∼24,500 and ended by ∼13,60014C yr B.P. Many of the components of glacial rock flour (e.g., TiO2, MnO, BaO) found in Owens Lake sediments achieved maximum values during the Tioga glaciation when valley glaciers reached their greatest extent. Total organic carbon and SiO2(amorphous) concentrations reached minimum values during Tioga glaciation, resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of Owens Lake. At least 20 stadial–interstadial oscillations occurred in the Sierra Nevada between 52,600 and 14,00014C yr B.P. Total organic carbon data from a Pyra...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
The presence of elevated 14C contamination in a laboratory preparing samples for natural radiocar... more The presence of elevated 14C contamination in a laboratory preparing samples for natural radiocarbon analysis is detrimental to the laboratory workspace as well as the research being conducted. Elevated 14C contamination occurs via many different pathways, but procedures can be adopted to prevent and remove this type of contamination. In this paper we present our current practices for preventing contamination,
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Papers by Michaele Kashgarian