Mark L Roberts
Biographic Data
| ID | 5597498 |
|---|---|
| NAME | Mark L Roberts |
| GIVEN NAMES | Mark L |
| FAMILY NAME | Roberts |
| SIGNATURE | ROBERTS M L |
| VERIFIED | No |
| TOTAL WORKS | 11 |
| TOTAL CITATIONS | 32 |
| AUTHOR COUNT | 11 |
| EDITOR COUNT | 0 |
| FIRST PUBLICATION YEAR | 2010 |
| LATEST PUBLICATION YEAR | 2024 |
| H-INDEX | 3 |
Improving Ionplus Micadas Performance With Recessed Graphite
Cathodes with recessed sample surfaces have several benefits in cesium sputter ion sources, including higher output, more efficient use of sample material, and improved focusing of the extracted ion beam. However, the Ionplus MICADAS uses cathodes with a graphite surface that is essentially flush with the sample holder. To evaluate the performance of recessed graphite with the MICADAS and determine the optimal surface depth, we tested four differ…
Radiocarbon in Dissolved Organic Carbon by Uv Oxidation
This note describes improvements of UV oxidation method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). The procedural blank is reduced to 2.6 ± 0.6 μg C, with Fm of 0.42 ± 0.10 and δ 13 C of –28.43 ± 1.19‰. The throughput is improved from one sample per day to two samples per day
Implications of Single-Step Graphitization for Reconstructing Late Holocene Relative Sea-Level Using Radiocarbon-Dated Organic Coastal Sediment
Late Holocene relative sea-level reconstructions are commonly generated using proxies preserved in salt-marsh and mangrove sediment. These depositional environments provide abundant material for radiocarbon dating in the form of identifiable macrofossils (salt marshes) and bulk organic sediment (mangroves). We explore if single-step graphitization of these samples in preparation for radiocarbon dating can increase the number and temporal resoluti…
Radiocarbon in Dissolved Organic Carbon by Uv Oxidation
This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ 13 C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring …
Ultra-Small Graphitization Reactors for Ultra-Microscale 14 C Analysis at the National Ocean Sciences Accelerator Mass Spectrometry (Nosams) Facility
In response to the increasing demand for 14 C analysis of samples containing less than 25 μg C, ultra-small graphitization reactors with an internal volume of ∼0.8 mL were developed at NOSAMS. For samples containing 6 to 25 μg C, these reactors convert CO 2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. G…
Improved Precision of Radiocarbon Measurements for CH 4 and CO 2 Using GC and Continuous-Flow AMS Achieved by Summation of Repeated Injections
Compound specific radiocarbon measurements can be made instantaneously using a gas chromatograph (GC) combustion system coupled to a 14 C AMS system fitted with a gas ion source. Samples below 10 μg C can be analyzed but the precision is reduced to 5–10% because of lower source efficiency. We modified our GC for CH 4 and CO 2 analysis and injected samples multiple times to sum data and increase precision. We attained a maximum precision of 0.6% f…
A High-Throughput, Low-Cost Method for Analysis of Carbonate Samples for 14 C
The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution has developed an automated system for high-throughput, low-cost analysis of radiocarbon in carbonate samples (e.g. corals, carbonaceous sediments, speleothems, etc.). The method bypasses graphitization and pretreatment, and reduces costs to about 1/5th the price of a graphite-based 14 C carbonate analysis, with a throughput of 6…
Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation
Radiocarbon analysis is an important tool in quantifying soil organic matter (SOM) dynamics within the terrestrial carbon cycle. However, there is increasing appreciation that representing SOM as a single, homogeneous pool with a single, mean 14 C concentration is inadequate. We investigate whether the differing patterns in CO 2 release during ramped-temperature oxidation reflect organic matter of different ages, and hypothesize that thermally la…
Fire History of a Giant African Baobab Evinced by Radiocarbon Dating
The article reports the first radiocarbon dating of a live African baobab ( Adansonia digitata L.), by investigating wood samples collected from 2 inner cavities of the very large 2-stemmed Platland tree of South Africa. Some 16 segments extracted from determined positions of the samples, which correspond to a depth of up to 15–20 cm in the wood, were processed and analyzed by accelerator mass spectrometry (AMS). Calibrated ages of segments are n…
A Continuous-Flow Gas Chromatography 14 C Accelerator Mass Spectrometry System
Gas-accepting ion sources for radiocarbon accelerator mass spectrometry (AMS) have permitted the direct analysis of CO 2 gas, eliminating the need to graphitize samples. As a result, a variety of analytical instruments can be interfaced to an AMS system, processing time is decreased, and smaller samples can be analyzed (albeit with lower precision). We have coupled a gas chromatograph to a compact 14 C AMS system fitted with a microwave ion sourc…
Age and Growth Rate Dynamics of an Old African Baobab Determined by Radiocarbon Dating
In 2008, a large African baobab ( Adansonia digitata L.) from Makulu Makete, South Africa, split vertically into 2 sections, revealing a large enclosed cavity. Several wood samples collected from the cavity were processed and radiocarbon dated by accelerator mass spectrometry (AMS) for determining the age and growth rate dynamics of the tree. The 14 C date of the oldest sample was found to be of 1016 ± 22 BP, which corresponds to a calibrated age…
Ultra-Small Graphitization Reactors for Ultra-Microscale 14 C Analysis at the National Ocean Sciences Accelerator Mass Spectrometry (Nosams) Facility
In response to the increasing demand for 14 C analysis of samples containing less than 25 μg C, ultra-small graphitization reactors with an internal volume of ∼0.8 mL were developed at NOSAMS. For samples containing 6 to 25 μg C, these reactors convert CO 2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. G…
Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation
Radiocarbon analysis is an important tool in quantifying soil organic matter (SOM) dynamics within the terrestrial carbon cycle. However, there is increasing appreciation that representing SOM as a single, homogeneous pool with a single, mean 14 C concentration is inadequate. We investigate whether the differing patterns in CO 2 release during ramped-temperature oxidation reflect organic matter of different ages, and hypothesize that thermally la…
Age and Growth Rate Dynamics of an Old African Baobab Determined by Radiocarbon Dating
In 2008, a large African baobab ( Adansonia digitata L.) from Makulu Makete, South Africa, split vertically into 2 sections, revealing a large enclosed cavity. Several wood samples collected from the cavity were processed and radiocarbon dated by accelerator mass spectrometry (AMS) for determining the age and growth rate dynamics of the tree. The 14 C date of the oldest sample was found to be of 1016 ± 22 BP, which corresponds to a calibrated age…
Radiocarbon in Dissolved Organic Carbon by Uv Oxidation
This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ 13 C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring …
Fire History of a Giant African Baobab Evinced by Radiocarbon Dating
The article reports the first radiocarbon dating of a live African baobab ( Adansonia digitata L.), by investigating wood samples collected from 2 inner cavities of the very large 2-stemmed Platland tree of South Africa. Some 16 segments extracted from determined positions of the samples, which correspond to a depth of up to 15–20 cm in the wood, were processed and analyzed by accelerator mass spectrometry (AMS). Calibrated ages of segments are n…
Improved Precision of Radiocarbon Measurements for CH 4 and CO 2 Using GC and Continuous-Flow AMS Achieved by Summation of Repeated Injections
Compound specific radiocarbon measurements can be made instantaneously using a gas chromatograph (GC) combustion system coupled to a 14 C AMS system fitted with a gas ion source. Samples below 10 μg C can be analyzed but the precision is reduced to 5–10% because of lower source efficiency. We modified our GC for CH 4 and CO 2 analysis and injected samples multiple times to sum data and increase precision. We attained a maximum precision of 0.6% f…
A High-Throughput, Low-Cost Method for Analysis of Carbonate Samples for 14 C
The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution has developed an automated system for high-throughput, low-cost analysis of radiocarbon in carbonate samples (e.g. corals, carbonaceous sediments, speleothems, etc.). The method bypasses graphitization and pretreatment, and reduces costs to about 1/5th the price of a graphite-based 14 C carbonate analysis, with a throughput of 6…
A Continuous-Flow Gas Chromatography 14 C Accelerator Mass Spectrometry System
Gas-accepting ion sources for radiocarbon accelerator mass spectrometry (AMS) have permitted the direct analysis of CO 2 gas, eliminating the need to graphitize samples. As a result, a variety of analytical instruments can be interfaced to an AMS system, processing time is decreased, and smaller samples can be analyzed (albeit with lower precision). We have coupled a gas chromatograph to a compact 14 C AMS system fitted with a microwave ion sourc…
Fire History of a Giant African Baobab Evinced by Radiocarbon Dating
The article reports the first radiocarbon dating of a live African baobab ( Adansonia digitata L.), by investigating wood samples collected from 2 inner cavities of the very large 2-stemmed Platland tree of South Africa. Some 16 segments extracted from determined positions of the samples, which correspond to a depth of up to 15–20 cm in the wood, were processed and analyzed by accelerator mass spectrometry (AMS). Calibrated ages of segments are n…
A Continuous-Flow Gas Chromatography 14 C Accelerator Mass Spectrometry System
Gas-accepting ion sources for radiocarbon accelerator mass spectrometry (AMS) have permitted the direct analysis of CO 2 gas, eliminating the need to graphitize samples. As a result, a variety of analytical instruments can be interfaced to an AMS system, processing time is decreased, and smaller samples can be analyzed (albeit with lower precision). We have coupled a gas chromatograph to a compact 14 C AMS system fitted with a microwave ion sourc…
Age and Growth Rate Dynamics of an Old African Baobab Determined by Radiocarbon Dating
In 2008, a large African baobab ( Adansonia digitata L.) from Makulu Makete, South Africa, split vertically into 2 sections, revealing a large enclosed cavity. Several wood samples collected from the cavity were processed and radiocarbon dated by accelerator mass spectrometry (AMS) for determining the age and growth rate dynamics of the tree. The 14 C date of the oldest sample was found to be of 1016 ± 22 BP, which corresponds to a calibrated age…
Improved Precision of Radiocarbon Measurements for CH 4 and CO 2 Using GC and Continuous-Flow AMS Achieved by Summation of Repeated Injections
Compound specific radiocarbon measurements can be made instantaneously using a gas chromatograph (GC) combustion system coupled to a 14 C AMS system fitted with a gas ion source. Samples below 10 μg C can be analyzed but the precision is reduced to 5–10% because of lower source efficiency. We modified our GC for CH 4 and CO 2 analysis and injected samples multiple times to sum data and increase precision. We attained a maximum precision of 0.6% f…
A High-Throughput, Low-Cost Method for Analysis of Carbonate Samples for 14 C
The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution has developed an automated system for high-throughput, low-cost analysis of radiocarbon in carbonate samples (e.g. corals, carbonaceous sediments, speleothems, etc.). The method bypasses graphitization and pretreatment, and reduces costs to about 1/5th the price of a graphite-based 14 C carbonate analysis, with a throughput of 6…
Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation
Radiocarbon analysis is an important tool in quantifying soil organic matter (SOM) dynamics within the terrestrial carbon cycle. However, there is increasing appreciation that representing SOM as a single, homogeneous pool with a single, mean 14 C concentration is inadequate. We investigate whether the differing patterns in CO 2 release during ramped-temperature oxidation reflect organic matter of different ages, and hypothesize that thermally la…
Ultra-Small Graphitization Reactors for Ultra-Microscale 14 C Analysis at the National Ocean Sciences Accelerator Mass Spectrometry (Nosams) Facility
In response to the increasing demand for 14 C analysis of samples containing less than 25 μg C, ultra-small graphitization reactors with an internal volume of ∼0.8 mL were developed at NOSAMS. For samples containing 6 to 25 μg C, these reactors convert CO 2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. G…
Radiocarbon in Dissolved Organic Carbon by Uv Oxidation
This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ 13 C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring …
Radiocarbon in Dissolved Organic Carbon by Uv Oxidation
This note describes improvements of UV oxidation method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). The procedural blank is reduced to 2.6 ± 0.6 μg C, with Fm of 0.42 ± 0.10 and δ 13 C of –28.43 ± 1.19‰. The throughput is improved from one sample per day to two samples per day
Implications of Single-Step Graphitization for Reconstructing Late Holocene Relative Sea-Level Using Radiocarbon-Dated Organic Coastal Sediment
Late Holocene relative sea-level reconstructions are commonly generated using proxies preserved in salt-marsh and mangrove sediment. These depositional environments provide abundant material for radiocarbon dating in the form of identifiable macrofossils (salt marshes) and bulk organic sediment (mangroves). We explore if single-step graphitization of these samples in preparation for radiocarbon dating can increase the number and temporal resoluti…
Improving Ionplus Micadas Performance With Recessed Graphite
Cathodes with recessed sample surfaces have several benefits in cesium sputter ion sources, including higher output, more efficient use of sample material, and improved focusing of the extracted ion beam. However, the Ionplus MICADAS uses cathodes with a graphite surface that is essentially flush with the sample holder. To evaluate the performance of recessed graphite with the MICADAS and determine the optimal surface depth, we tested four differ…
Geology (9 works) · Accelerator mass spectrometry (8 works) · Chemistry (8 works) · Radiocarbon dating (8 works) · Paleontology (7 works) · Chromatography (6 works) · Materials Science (6 works) · Carbon fibers (5 works) · Isotope Analysis in Ecology (5 works) · Mass spectrometry (5 works)