Darrell S Kaufman
Dados Biográficos
| ID | 4129463 |
|---|---|
| NOME | Darrell S Kaufman |
| PRENOMES | Darrell S |
| SOBRENOME | Kaufman |
| ASSINATURA | KAUFMAN D S |
| AFILIAÇÕES | Northern Arizona University |
| ORCID | 0000-0002-7572-1414 |
| VERIFICADO | Sim |
| TOTAL DE OBRAS | 33 |
| TOTAL DE CITAÇÕES | 8 |
| TOTAL COMO AUTOR | 33 |
| TOTAL COMO EDITOR | 0 |
| PRIMEIRO ANO DE PUBLICAÇÃO | 1991 |
| ANO MAIS RECENTE DE PUBLICAÇÃO | 2025 |
| ÍNDICE H | 2 |
The size of the Greenland Ice Sheet during Marine Isotope Stage 3
Ice-sheet volume during Marine Isotope Stage (MIS) 3 (57–29 ka) is controversial. Several recent studies have proposed that the Greenland Ice Sheet was smaller during MIS 3 than it is today based on radiocarbon ages of molluscan bivalve shells reworked into sedimentary deposits adjacent to the present ice margin. Such a result contrasts with available records of MIS 3 climate, ice volume, and sea level. We revisited a site previously interpreted …
Radiocarbon dating of lake sediment using low-temperature combustion
The bulk organic-matter content of near-surface sediment is widely used for radiocarbon ( 14 C) dating, despite often containing organic carbon (OC) older than the depositional age. Low-temperature combustion can mitigate the influence of old OC, producing ages closer to the depositional age. We developed a simple method to determine the 14 C age of the low-temperature ( 14 C and % OC in two aliquots: one heated at 250°C and one unheated. The low…
Comparing Micadas Gas Source, Direct Carbonate, and Standard Graphite 14 C Determinations of Biogenic Carbonate
Northern Arizona University, Flagstaff, Arizona, USA, recently installed a MIni CArbon DAting System (MICADAS) with a gas interface system (GIS) for determining the 14 C content of CO 2 gas released by the acid dissolution of biogenic carbonates. We compare 48 paired graphite, GIS, and direct carbonate 14 C determinations of individual mollusk shells and echinoid tests. GIS sample sizes ranged between 0.5 and 1.5 mg and span 0.1 to 45.1 ka BP (n …
Reconstructing postglacial hydrologic and environmental change in the eastern Kenai Peninsula lowlands using proxy data and mass balance modeling
Despite extensive paleoenvironmental research on the postglacial history of the Kenai Peninsula, Alaska, uncertainties remain regarding the region's deglaciation, vegetation development, and past hydroclimate. To elucidate this complex environmental history, we present new proxy datasets from Hidden and Kelly lakes, located in the eastern Kenai lowlands at the foot of the Kenai Mountains, including sedimentological properties (magnetic susceptibi…
Late-Glacial and Holocene Lake-Level Fluctuations on the Kenai Lowland, Reconstructed from Satellite-Fen Peat Deposits and Ice-Shoved Ramparts, Kenai Peninsula, Alaska
Recent decades of warmer climate have brought drying wetlands and falling lake levels to southern Alaska. These recent changes can be placed into a longer-term context of postglacial lake-level fluctuations that include low stands that were as much as 7 m lower than present at eight lakes on the Kenai Lowland. Closed-basin lakes on the Kenai Lowland are typically ringed with old shorelines, usually as wave-cut scarps, cut several meters above mod…
Comparing Direct Carbonate and Standard Graphite 14 C Determinations of Biogenic Carbonates
The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14 C) dating of submilligram samples of biogenic carbonate without graphitization is becoming widely used in a variety of studies. We compare the results of 153 paired direct carbonate and standard graphite 14 C determinations on single specimens of an assortment of biogenic carbonates. A reduced major axis regression shows a strong relationship between direct carbo…
A 16,000-yr-long sedimentary sequence from Lakes Peters and Schrader (Neruokpuk Lakes), northeastern Brooks Range, Alaska
Sediments that accumulate in high-latitude lakes serve as valuable environmental archives of changing conditions in a region currently undergoing rapid change. A previously unexplored sedimentary sequence reaching back 16,000 years from Lakes Peters and Schrader (Neruokpuk Lakes) in the northeastern Brooks Range (69°N), Alaska, shows distinct changes in accumulation rates and biophysical properties including bulk density (BD), organic matter (OM)…
Aminochronology and time averaging of Quaternary land snail assemblages from colluvial deposits in the Madeira Archipelago, Portugal
Understanding the properties of time averaging (age mixing) in a stratigraphic layer is essential for properly interpreting the paleofauna preserved in the geologic record. This work assesses the age and quantifies the scale and structure of time averaging of land snail-rich colluvial sediments from the Madeira Archipelago (Portugal) by dating individual shells using amino acid racemization calibrated with graphite-target and carbonate-target acc…
Quaternary marine terrace chronology, North Canterbury, New Zealand, using amino acid racemization and infrared-stimulated luminescence
Extensive marine terraces along the North Canterbury coast of the South Island of New Zealand record uplift in this tectonically active area. Although the terraces have been studied previously, applications of Quaternary geochronological techniques to the region have been limited. We use infrared-stimulated luminescence (IRSL), amino acid racemization (AAR), and radiocarbon to determine ages of terraces at three locations—Glenafric, Motunau Beach…
Holocene glacier fluctuations inferred from lacustrine sediment, Emerald Lake, Kenai Peninsula, Alaska
Physical and biological characteristics of lacustrine sediment from Emerald Lake were used to reconstruct the Holocene glacier history of Grewingk Glacier, southern Alaska. Emerald Lake is an ice-marginal threshold lake, receiving glaciofluvial sediment when Grewingk Glacier overtops the topographic divide that separates it from the lake. Sub-bottom acoustical profiles were used to locate core sites to maximize both the length and resolution of t…
Holocene biogeography of Tsuga mertensiana and other conifers in the Kenai Mountains and Prince William Sound, south-central Alaska
Several important North American coastal conifers – having immigrated during the Holocene from the southeast – reach their northern and upper elevation limits in south-central Alaska. However, our understanding of the specific timing of migration has been incomplete. Here, we use two new pollen profiles from a coastal and a high-elevation site in the Eastern Kenai Peninsula–Prince William Sound region, along with other published pollen records, t…
Holocene summer temperature reconstruction from sedimentary chlorophyll content, with treatment of age uncertainties, Kurupa Lake, Arctic Alaska
Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert d…
A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight, Brazilian shelf
To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São…
Holocene storminess inferred from sediments of two lakes on Adak Island, Alaska
The abundance of sedimentary organic material from two lakes was used to infer past Holocene storminess on Adak Island where frequent storms generate abundant rainfall and extensive cloud cover. Andrew and Heart Lakes are located 10 km apart; their contrasting physical characteristics cause the sedimentary organic matter to respond differently to storms. Their records were synchronized using correlated tephra beds. Sedimentation rates increased b…
Late glacial and Holocene environmental changes inferred from sediments in Lake Myklevatnet, Nordfjord, western Norway
Continental-scale temperature variability during the past two millennia
The impact of Little Ice Age cooling on mountain hemlock (Tsuga mertensiana) distribution in southcentral, Alaska
Long-term river discharge and multidecadal climate variability inferred from varved sediments, southwest Alaska
Sedimentological analyses of 289 years (AD 1718–2006) of varved sediment from Shadow Bay, southwest Alaska, were used to investigate hydroclimate variability during and prior to the instrumental period. Varve thicknesses relate most strongly to total annual discharge (r 2 = 0.75, n = 43, p 2 = 0.63, n = 43, p 2 = 0.61, n = 43, p 2 = 0.004, n = 287, p = 0.33). Relations between varve thickness and annual climate variables (temperature, precipitati…
Recent Warming Reverses Long-Term Arctic Cooling
Climate Reversal The climate and environment of the Arctic have changed drastically over the short course of modern observation. Kaufman et al. (p. 1236 ) synthesized 2000 years of proxy data from lakes above 60° N latitude with complementary ice core and tree ring records, to create a paleoclimate reconstruction for the Arctic with a 10-year resolution. A gradual cooling trend at the start of the record had reversed by the beginning of the 20th …
Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska
Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14 C ages on macrofossils. Tephras layers are typically fine, gray ash, 1–5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contain…
Numerical dating of a Late Quaternary spit-shoreline complex at the northern end of Silver Lake playa, Mojave Desert, California
Oxygen isotope composition of annually banded modern and mid-Holocene travertine and evidence of paleomonsoon floods, Grand Canyon, Arizona, USA
Holocene and modern travertine formed in spring-fed Havasu Creek of the Grand Canyon, Arizona, was studied to determine the factors governing its oxygen-isotope composition. Analysis of substrate-grown travertine indicates that calculated calcite-formation temperatures compare favorably with measured water temperatures, and include silt-rich laminae deposited by monsoon-driven floods. Ancient spring-pool travertine is dated by U-series at 7380 ± …
Holocene glacier fluctuations, Waskey Lake, northeastern Ahklun Mountains, southwestern Alaska
Lake sediments from Waskey Lake, Ahklun Mountains, southwestern Alaska were studied to decipher the history of upvalley glacier fluctuations during the Holocene. Several indicators of glacier activity were measured including: magnetic susceptibility, organic-matter content, grain-size distribution, bulk-sediment mineralogy and diatom assemblages. Seven radiocarbon ages on macrofossils, along with cross-checks by tephrochronology, provide the chro…
Late Quaternary Spring-Fed Deposits of the Grand Canyon and Their Implication for Deep Lava-Dammed Lakes
One of the most intriguing episodes in the Quaternary evolution of the Grand Canyon of the Colorado River, Arizona, was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge. Stratigraphic evidence for these deep lava-dammed lakes is expectedly sparse. Possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake. At two of the sit…
The Last Interglacial to Glacial Transition, Togiak Bay, Southwestern Alaska
An 18-m-high coastal bluff at Togiak Bay (northwestern Bristol Bay, southwestern Alaska) exposes marine, lacustrine, fluvial, glacial, volcanic, and organic deposits that record the ∼50,000-year-long transition from the peak of the last interglaciation to the early Wisconsin glaciation. The base of the section is dominated by stratified sand and silt extending up to 4.3 m above sea level; marine diatoms are present, and pollen assemblages are cha…
Holocene summer temperature reconstruction from sedimentary chlorophyll content, with treatment of age uncertainties, Kurupa Lake, Arctic Alaska
Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert d…
Holocene glacier fluctuations, Waskey Lake, northeastern Ahklun Mountains, southwestern Alaska
Lake sediments from Waskey Lake, Ahklun Mountains, southwestern Alaska were studied to decipher the history of upvalley glacier fluctuations during the Holocene. Several indicators of glacier activity were measured including: magnetic susceptibility, organic-matter content, grain-size distribution, bulk-sediment mineralogy and diatom assemblages. Seven radiocarbon ages on macrofossils, along with cross-checks by tephrochronology, provide the chro…
Comparing Direct Carbonate and Standard Graphite 14 C Determinations of Biogenic Carbonates
The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14 C) dating of submilligram samples of biogenic carbonate without graphitization is becoming widely used in a variety of studies. We compare the results of 153 paired direct carbonate and standard graphite 14 C determinations on single specimens of an assortment of biogenic carbonates. A reduced major axis regression shows a strong relationship between direct carbo…
Late glacial and Holocene environmental changes inferred from sediments in Lake Myklevatnet, Nordfjord, western Norway
Middle Pleistocene age of the Nome River glaciation, northwestern Alaska
During the middle Pleistocene Nome River glaciation of northwestern Alaska, glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals. The age of the Nome River glaciation is constrained by laser-fusion 40 Ar/ 39 Ar analyses of basaltic lava that overlies Nome River drift at Minnie Creek, central Seward Peninsula, that average 470,000 ± 190,000 yr (±1σ). Milligram-size subsamples of the lava were d…
The Last Glaciation in Central Magellan Strait, Southernmost Chile
Glacial landforms and drift stratigraphy in central Magellan Strait, southernmost Chile, document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern Andes. The lobes developed comparatively low-gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small-scale changes in the mass balance. Such low profiles and rapid calving in…
Age of Pre-late-Wisconsin Glacial-Estuarine Sedimentation, Bristol Bay, Alaska
Pleistocene glacial-estuarine sediment deposited in an intertidal environment of northeastern Bristol Bay, southwestern Alaska, was dated using a variety of approaches, including infrared stimulated and thermoluminescence (IRSL and TL) techniques. Analysis of modern and 14 C-dated Holocene tide-flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation, thereby lending confidence to ages obtained from similar …
Chevron Ridges and Runup Deposits in the Bahamas from Storms Late in Oxygen-Isotope Substage 5e
Landward-pointing V-shaped sand ridges several kilometers long are common along the windward margin of the Bahama Islands. Their axes share a northeast–southwest trend. Internally, the ridges contain low-angle oolitic beds with few erosional truncations. Commonly interbedded are tabular, fenestrae-rich beds such as those formed by the sheet flow of water over dry sand. Defined here as “chevron ridges,” these landforms appear to have originated in…
Reinterpretation of the Burmester Core, Bonneville Basin, Utah
Initial interpretation of the sediments from the Burmester core (Eardley et al. (1973). Geological Society of America Bulletin 84, 211–216) indicated that 17 deep-lake cycles, separated by shallow-lake and soil-forming intervals, occurred in the Bonneville basin during the Brunhes Chron (the last 780 × 10 3 yr). Our re-examination of the core, along with new sedimentological, geochronological, and paleontological data, indicate that only four dee…
Late Pleistocene Glaciation of the Southwestern Ahklun Mountains, Alaska
Glacial deposits in the southwestern Ahklun Mountains, southwestern Alaska, record two major glacier advances during the late Pleistocene. The Arolik Lake and Klak Creek glaciations took place during the early and late Wisconsin, respectively. During the Arolik Lake glaciation, outlet glaciers emanated from an ice cap centered over the central portion of the Ahklun Mountains and expanded beyond the present coast. During the Klak Creek glaciation,…
Whole-Rock Aminostratigraphy and Quaternary Sea-Level History of the Bahamas
The surficial geology of the tectonically stable Bahamian archipelago preserves one of the most complete records of middle to late Quaternary sea-level-highstand cycles in the world. However, with the exception of deposits from marine isotope substage (MIS) 5e, fossil corals for radiometric dating of this rich stratigraphic sequence are rare. This study utilizes the previously published, independent lithostratigraphic framework as a testing groun…
The Last Interglacial to Glacial Transition, Togiak Bay, Southwestern Alaska
An 18-m-high coastal bluff at Togiak Bay (northwestern Bristol Bay, southwestern Alaska) exposes marine, lacustrine, fluvial, glacial, volcanic, and organic deposits that record the ∼50,000-year-long transition from the peak of the last interglaciation to the early Wisconsin glaciation. The base of the section is dominated by stratified sand and silt extending up to 4.3 m above sea level; marine diatoms are present, and pollen assemblages are cha…
Age of the Cutler Dam Alloformation (Late Pleistocene), Bonneville Basin, Utah
Luminescence geochronology, especially infrared stimulated luminescence analyses on marsh mud, shows that a relatively deep lake reached its peak (∼1340 m above sea level) in the Bonneville basin 59,000±5000 yr ago. The age is consistent with nonfinite 14 C ages and with amino acid geochronology on ostracodes. The Cutler Dam Alloformation was deposited during this lake cycle, which, like the subsequent Bonneville lake cycle, appears to have reach…
Late Quaternary Spring-Fed Deposits of the Grand Canyon and Their Implication for Deep Lava-Dammed Lakes
One of the most intriguing episodes in the Quaternary evolution of the Grand Canyon of the Colorado River, Arizona, was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge. Stratigraphic evidence for these deep lava-dammed lakes is expectedly sparse. Possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake. At two of the sit…
Holocene glacier fluctuations, Waskey Lake, northeastern Ahklun Mountains, southwestern Alaska
Lake sediments from Waskey Lake, Ahklun Mountains, southwestern Alaska were studied to decipher the history of upvalley glacier fluctuations during the Holocene. Several indicators of glacier activity were measured including: magnetic susceptibility, organic-matter content, grain-size distribution, bulk-sediment mineralogy and diatom assemblages. Seven radiocarbon ages on macrofossils, along with cross-checks by tephrochronology, provide the chro…
Oxygen isotope composition of annually banded modern and mid-Holocene travertine and evidence of paleomonsoon floods, Grand Canyon, Arizona, USA
Holocene and modern travertine formed in spring-fed Havasu Creek of the Grand Canyon, Arizona, was studied to determine the factors governing its oxygen-isotope composition. Analysis of substrate-grown travertine indicates that calculated calcite-formation temperatures compare favorably with measured water temperatures, and include silt-rich laminae deposited by monsoon-driven floods. Ancient spring-pool travertine is dated by U-series at 7380 ± …
Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska
Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14 C ages on macrofossils. Tephras layers are typically fine, gray ash, 1–5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contain…
Numerical dating of a Late Quaternary spit-shoreline complex at the northern end of Silver Lake playa, Mojave Desert, California
Recent Warming Reverses Long-Term Arctic Cooling
Climate Reversal The climate and environment of the Arctic have changed drastically over the short course of modern observation. Kaufman et al. (p. 1236 ) synthesized 2000 years of proxy data from lakes above 60° N latitude with complementary ice core and tree ring records, to create a paleoclimate reconstruction for the Arctic with a 10-year resolution. A gradual cooling trend at the start of the record had reversed by the beginning of the 20th …
Long-term river discharge and multidecadal climate variability inferred from varved sediments, southwest Alaska
Sedimentological analyses of 289 years (AD 1718–2006) of varved sediment from Shadow Bay, southwest Alaska, were used to investigate hydroclimate variability during and prior to the instrumental period. Varve thicknesses relate most strongly to total annual discharge (r 2 = 0.75, n = 43, p 2 = 0.63, n = 43, p 2 = 0.61, n = 43, p 2 = 0.004, n = 287, p = 0.33). Relations between varve thickness and annual climate variables (temperature, precipitati…
Continental-scale temperature variability during the past two millennia
The impact of Little Ice Age cooling on mountain hemlock (Tsuga mertensiana) distribution in southcentral, Alaska
A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight, Brazilian shelf
To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São…
Holocene storminess inferred from sediments of two lakes on Adak Island, Alaska
The abundance of sedimentary organic material from two lakes was used to infer past Holocene storminess on Adak Island where frequent storms generate abundant rainfall and extensive cloud cover. Andrew and Heart Lakes are located 10 km apart; their contrasting physical characteristics cause the sedimentary organic matter to respond differently to storms. Their records were synchronized using correlated tephra beds. Sedimentation rates increased b…
Late glacial and Holocene environmental changes inferred from sediments in Lake Myklevatnet, Nordfjord, western Norway
Holocene summer temperature reconstruction from sedimentary chlorophyll content, with treatment of age uncertainties, Kurupa Lake, Arctic Alaska
Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert d…
Holocene glacier fluctuations inferred from lacustrine sediment, Emerald Lake, Kenai Peninsula, Alaska
Physical and biological characteristics of lacustrine sediment from Emerald Lake were used to reconstruct the Holocene glacier history of Grewingk Glacier, southern Alaska. Emerald Lake is an ice-marginal threshold lake, receiving glaciofluvial sediment when Grewingk Glacier overtops the topographic divide that separates it from the lake. Sub-bottom acoustical profiles were used to locate core sites to maximize both the length and resolution of t…
Holocene biogeography of Tsuga mertensiana and other conifers in the Kenai Mountains and Prince William Sound, south-central Alaska
Several important North American coastal conifers – having immigrated during the Holocene from the southeast – reach their northern and upper elevation limits in south-central Alaska. However, our understanding of the specific timing of migration has been incomplete. Here, we use two new pollen profiles from a coastal and a high-elevation site in the Eastern Kenai Peninsula–Prince William Sound region, along with other published pollen records, t…
Quaternary marine terrace chronology, North Canterbury, New Zealand, using amino acid racemization and infrared-stimulated luminescence
Extensive marine terraces along the North Canterbury coast of the South Island of New Zealand record uplift in this tectonically active area. Although the terraces have been studied previously, applications of Quaternary geochronological techniques to the region have been limited. We use infrared-stimulated luminescence (IRSL), amino acid racemization (AAR), and radiocarbon to determine ages of terraces at three locations—Glenafric, Motunau Beach…
Geology and Paleoclimatology Research (31 obras) · Geology (23 obras) · Paleontology (18 obras) · Oceanography (17 obras) · Physical geography (16 obras) · Geomorphology (14 obras) · Holocene (13 obras) · Geography (12 obras) · Glacial period (12 obras) · Isotope Analysis in Ecology (12 obras)