bluuebunny/crossref_metadata_2025 huggingface dataset:
Subdivision of Late Pleistocene Moraines in the Cordillera Blanca, Peru, Based on Rock-Weathering Features, Soils, and Radiocarbon Dates
Authors: Rodbell Donald T.
Published: September 2002

The progressive development of unusual rock-weathering features and soils and minimum-limiting radiocarbon dates provide a basis for subdividing four groups of late Pleistocene moraines on the west side of the Cordillera Blanca, northern Peru (9°20′1°000′S, 77°10′-77°30′W). Boulders on the youngest late Pleistocene moraines have 10 to 14-cm-tall weathering posts; soils on these moraines yield mean profile development index (PDI) values of 0.05 ± 0.04 (±1σ). These moraines date between ca. 13,500 and 9700 ± 500 yr B.P., older than previously postulated. The next older moraines have boulders with weathering-post heights between 20 and 25 cm and soils with PDI values of 0.08 ± 0.07, and were deposited prior to 13,280 ± 190 yr B.P., probably during the last glacial maximum (marine isotope stage 2). Moraines from an older glaciation have boulders with weathering posts between 39 and 50 cm high, soils that yield PDI values of 0.21 ± 0.07, and are older than 19,700 ± 340 yr B.P. Boulders on moraines from a still older glaciation have lost ca. 50% of their above-ground volume, and have weathering posts between 62 and 70 cm high. PDI values for soils on these moraines are 0.32 ± 0.06. Linear and logarithmic models of weathering-post and soil development with time are used to estimate minimum and maximum ages for the two oldest moraine groups. Linear models suggest that the second oldest moraines are between ca. 20,500 and 46,500 yr B.P., and that the oldest moraines are between ca. 29,000 and 72,000 yr B.P. In contrast, logarithmic models suggest ages of greater than ca. 75,500 yr B.P. and greater than ca. 500,000 yr B.P., respectively.
Asynchronous Droughts in California Streamflow as Reconstructed from Tree Rings
Authors: Earle Christopher J.
Published: September 2002

Streamflow since 1560 A.D. for four rivers within the Sacramento River Basin, California, has been reconstructed dendroclimatically. Both the highest and the lowest reconstructed streamflows occurred during the historical period, with high flows from 1854 to 1916 and low flows from 1917 to 1950. Prolonged (decade-scale) excursions from the mean have been the norm throughout the reconstructed period. The periods of high and low streamflow in the Sacramento Basin are generally synchronous with wet and dry periods reconstructed by dendroclimatic studies in the western United States. The record indicates a number of asynchronous droughts or wet years. The strongest contrasts are developed between northern (western Washington and Oregon or the Columbia Basin) and southern (the Sacramento Basin or central California) climate regions. These asynchronous events may be due to variation in the latitude of the subtropical high and in the latitudinal position of winter storms coming off the Pacific. No association was found with El Niño-Southern Oscillation events.
Toba Ash on the Indian Subcontinent and Its Implications for Correlation of Late Pleistocene Alluvium
Authors: Acharyya Subhrangsu Kanta , Basu Prabir Kumar
Published: September 2002

The Toba ash occurs extensively in the Indian subcontinent and marks a ca. 74,000-yr-old event. In the Bay of Bengal and Indian Ocean it is about 10 cm thick, whereas in several alluvial basins, it is usually 1-3 m thick. The latter occurs in a partly reworked state but as nearly chemically pure first-cycle sediments, The ash has a broad northwesterly dispersal pattern. Samples of ash from the Indian subcontinent compare closely with the youngest (74,000 yr B.P.) Toba Tuff and the deep-sea Toba ash in bulk chemical composition, REE signature, and bubble-wall shard morphology. However, a more proximally located and thicker (2-5 m) ash-bed, from the alluvial basins in the gneissic area and close to east coast, has a lower magnitude negative Eu anomaly, possibly because of minor contamination by feldspathic silt. Quaternary sediments in the central Narmada and middle Son basins contain rich late and middle Pleistocene mammalian and cultural records. Based on the presence of the ash layer marker and stratigraphic relations, late Pleistocene sediments within the subcontinent can be correlated with those from central India and the deep sea.
Quaternary Glaciations in the Río Mendoza Valley, Argentine Andes
Authors: Espizua Lydia E.
Published: September 2002

In the Río Mendoza valley, five Pleistocene drifts and one Holocene drift are distinguished by multiple relative-age criteria, including surface-rock weathering, development of rock varnish, moraine morphology, soil-profile development, and stratigraphic relationships. Several absolute ages suggest a preliminary chronology. During the oldest (Uspallata) glaciation, a system of valley glaciers flowed 110 km from the Andean drainage divide and 80 km from Cerro Aconcagua to terminate at 1850 m. Drift of this ice advance is older than a widespread tephra dated by fission-track at 360,000 ± 36,000 yr. During the Punta de Vacas advance, ice terminated at 2350 m, while during the subsequent Penitentes advance, the glacier system ended at 2500 m. A travertine layer overlying Penitentes Drift has U-series age of 24,200 ± 2000 yr B.P. The distribution of Horcones Drift, which is inferred to represent the last glacial maximum, delimits an independent ice stream that flowed 22 km down Horcones valley to 2750 m. A later readvance (Almacenes) reached 3250 m. Confluencia Drift is considered to be Neoglacial in age and extends downvalley to 3300 m. The moraine sequence is compared with those studied by Caviedes (1972) along Río Aconcagua on the Chilean flank of the Andes.
Climate-Volcanism Feedback and the Toba Eruption of ∼74,000 Years Ago
Authors: Rampino Michael R. , Self Stephen
Published: September 2002

A general feedback between volcanism and climate at times of transition in the Quaternary climate record is suggested, exemplified by events accompanying the Toba eruption (∼74,000 yr ago), the largest known late Quaternary explosive volcanic eruption. The Toba paroxysm occurred during the δ18O stage 5a-4 transition, a period of rapid ice growth and falling global sea level, which may have been a factor in creating stresses that triggered the volcanic event. Toba is estimated to have produced between 1015 and 1016 g of fine ash and sulfur gases lofted in co-ignimbrite ash clouds to heights of at least 32 ± 5 km, which may have led to dense stratospheric dust and sulfuric acid aerosol clouds. These conditions could have created a brief, dramatic cooling or "volcanic winter," followed by estimated annual Northern Hemisphere surface-temperature decreases of ∼3° to 5°C caused by the longer-lived aerosols. Summer temperature decreases of ⩾10°C at high northern latitudes, adjacent to regions already covered by snow and ice, might have increased snow cover and sea-ice extent, accelerating the global cooling already in progress. Evidence for such climate-volcanic feedback, following Milankovitch periodicities, is found at several climatic transitions.
Evidence for Regional Stream Aggradation in the Central Oregon Coast Range during the Pleistocene-Holocene Transition
Authors: Personius Stephen F. , Kelsey Harvey M. , Grabau Paul C.
Published: September 2002

Low, nearly continuous terraces of similar age are present along streams in drainage basins that range in size from Drift Creek (190 km2) to the Umpqua River (11,800 km2) in the Oregon Coast Range. Radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000-11,000 14C yr B.P. Beveled bedrock surfaces (straths) that underlie the fluvial sediments are 1-8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied. Where exposed, the bedrock straths are overlain by 2-11 m of fluvial sediment that consists of a bottom-stratum (channel) facies of sandy pebble-cobble gravel and a top-stratum (overbank) facies of sandy silt or silt. Eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in Coast Range drainage basins during the Pleistocene-Holocene transition. The cause of such widespread aggradation is unknown but may be related to climate-induced changes in the frequency of evacuation of colluvium from hollows, which are common in all drainage basins in the region.
Paleoclimatic Significance of the Stable Isotopic Composition and Petrology of a Late Pleistocene Stalagmite from Botswana
Authors: Holmgren Karin , Karlén Wibjörn , Shaw Paul A.
Published: September 2002

High-resolution δ18O and δ13C analyses of a stalagmite from Lobatse II Cave reveal late Pleistocene environmental changes in Botswana. Large shifts in δ18O and δ13C are observed between two main periods of deposition. The first period, between 51,000 and 43,000 yr B.P., was warm and humid and may have been associated with some C3 vegetation. The second period, between 27,000 and 21,000 yr B.P., had temperatures approximately 2°C lower, and vegetation dominated by drought-adapted C4 plants. The intervening period, between 43,000 and 27,000 yr B.P., bounded by two major hiatuses in stalagmite growth, produced discontinuous speleothem formation, probably under dry conditions. New 230 Th/234U mass spectrometry age determinations for the stalagmite generally agree with previously measured 230 Th/234U ages.
Dynamical Processes on Desert Pavements and the Healing of Surficial Disturbances
Authors: Haff Peter K. , Werner B.T.
Published: September 2002

Mature desert pavements are traditionally regarded as hallmarks of stability, but their stability is dynamic, not static. In a study aimed at documenting this dynamic stability and its role in healing surface disturbances, experiments were performed over a 5-yr period on small cleared patches, or plats, on pavement surfaces in Panamint Valley, California. These experiments show that stones from plat edges begin to resurface the clearing at rates of about 1% per year on 40-cm-square plats and 10% per year on 10-cm-square plats. Stones contributing to the regenerated pavement have smaller average diameters than stones on the surrounding pavement. Cavities 5–10 cm deep, formed in mature pavement by removal of embedded boulders, fill by ravel and slope failure. After five years, cavity depth has been reduced by as much as 60%. Forty-year-old boulder cavities are nearly completely refilled and have been repaved by smaller than average pavement stones. Gaps caused by removal of small stones (2–3 cm) have completely healed in 5 yr. Displacement of surface stones by small animals is a major component of the healing process.
The Alpine “Iceman” and Holocene Climatic Change
Authors: Baroni Carlo , Orombelli Giuseppe
Published: September 2002

The finding of a prehistoric mummified corpse at the upper edge of the accumulation area of an alpine glacier, together with its unique set of artifacts, provided new information on glacier dimensions during the little-known phases of major glacier shrinkage that characterized the warmest parts of the Holocene. The sudden burial of the corpse in a permanent snow cover occurred 5300–5050 cal yr B.P., indicating a significant climatic change that induced glacier expansion at the beginning of Neoglaciation. New geomorphologic data and two AMS 14C ages from buried soils suggest that the present glacier size, following over 100 yr of shrinkage, is comparable to that immediately preceding Neoglaciation. Therefore, we can deduce that the current global climatic warming may have interrupted the environmental conditions prevailing in the Alps during Neoglacial time, restoring characteristics similar to those prevailing during the climatic optimum that were never achieved during the second half of the Holocene.
A 350014C yr High-Resolution Record of Water-Level Changes in Lake Titicaca, Bolivia/Peru
Authors: Abbott Mark B. , Binford Michael W. , Brenner Mark , Kelts Kerry R.
Published: September 2002

Sediment cores collected from the southern basin of Lake Titicaca (Bolivia/Peru) on a transect from 4.6 m above overflow level to 15.1 m below overflow level are used to identify a new century-scale chronology of Holocene lake-level variations. The results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century-scale lake-level changes. Detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores. A chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water-level fluctuations. Two methods were used to estimate the14C reservoir age. Both indicate that it has remained nearly constant at ∼25014C yr during the late Holocene. Core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level, implying negative moisture balance for the northern Andean altiplano over the last 3500 cal yr. Between 3500 and 3350 cal yr B.P., a transition from massive, inorganic-clay facies to laminated organic-matter-rich silts in each of the four cores signals a water-level rise after a prolonged mid-Holocene dry phase. Evidence of other significant low lake levels occurs 2900–2800, 2400–2200, 2000–1700, and 900–500 cal yr B.P. Several of the low lake levels coincided with cultural changes in the region, including the collapse of the Tiwanaku civilization.
Temperature and Salinity Effects on Alkenone Ratios Measured in Surface Sediments from the Indian Ocean
Authors: Sonzogni Corinne , Bard Edouard , Rostek Frauke , Dollfus Denis , Rosell-Melé Antoni , Eglinton Geoffrey
Published: September 2002

We compare alkenone unsaturation ratios measured on recent sediments from the Indian Ocean (20°N–45°S) with modern sea oceanographic parameters. For each of the core sites we estimated average seasonal cycles of sea surface temperature (SST) and salinity, which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery. The unsaturation index (U37K′) ranges from 0.2 to 1 and correlates with water temperature but not with salinity. TheU37K′versus SST relationship for Indian Ocean sediments (U37K′= 0.033 SST + 0.05) is similar to what has been observed for core tops from the Pacific and Atlantic oceans and the Black Sea. A global compilation for core tops givesU37K′= 0.031 T + 0.084 (R= 0.98), which is close to a previously reported calibration based on particulate organic matter from the water column. For temperatures between 24° and 29°C, however, the slope seems to decrease to about 0.02U37K′unit/°C. For Indian Ocean core tops, the ratios of total C37alkenones/total C38alkenones and the slope of theU37K′-SST relationship are similar to those previously observed for cultures ofEmiliania huxleyibut different from those previously published forGephyrocapsa oceanica.EitherE. huxleyiis a major producer of alkenones in the Indian Ocean or strains ofG. oceanicaliving in the northern Indian Ocean behave differently from the one cultured. In contrast with coccolithophorid assemblages, the ratios of C37alkenones to total C38alkenones lack clear geographic pattern in the Indian Ocean.
Archaeological Evidence for Village Abandonment Associated with Late Holocene Earthquakes at the Northern Cascadia Subduction Zone
Authors: Hutchinson Ian , McMillan Alan D.
Published: September 2002

Geologic evidence suggests that great (magnitude 8 or larger) earthquakes, or series of such earthquakes, occurred six times in the past 3000 yr at the northern Cascadia subduction zone. The archaeological record, and native oral traditions, demonstrate that native villages along the adjacent coasts of southern British Columbia and Washington State were occasionally abandoned in the late Holocene as a result of these earthquakes and associated tsunamis. We infer the temporal pattern of village occupation and abandonment from midden stratigraphy and from an activity index based on the probability distributions of radiocarbon ages at 30 archaeological sites in three regions of northern Cascadia. Deposits of probable tsunami origin are interbedded with, or bound, cultural strata at several sites. Earthquakes probably predate hiatuses in occupation, or periods of low inferred human activity, at many sites. The strongest correlation between earthquake incidence and site abandonment occurs in the Nootka Sound region. Effects of tsunamis vary with village location, coastal morphology, and late Holocene sea-level history.
Termination of the Last Glaciation in the Iberian Peninsula Inferred from the Pollen Sequence of Quintanar de la Sierra
Authors: Peñalba M. Cristina , Arnold Maurice , Guiot Joël , Duplessy Jean-Claude , de Beaulieu Jacques-Louis
Published: September 2002

A 4.5-m-thick late-glacial pollen sequence, supported by 17 AMS 14C dates, has been investigated at the Quintanar de la Sierra marshland (Iberian cordillera, north-central Spain). Pollen zones were defined that correspond to successive phases in vegetation history during the end of the Late Würm, late-glacial interstade, and Younger Dryas periods. A transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data. A first expansion ofJuniperus and Hippophae, about 13,500 14C yr B.P., indicates the beginning of the late-glacial interstade which is characterized by a Juniperus–Betula–Pinus succession that suggests higher temperatures and moisture than during full-glacial time. The Younger Dryas interval is recorded by a 120-cm-thick sediment unit that is dominated by herbaceous pollen. Transfer function estimates suggest that the climate during this period was cold, with low precipitation during most of the year, although not in summer. The Holocene arboreal recolonization in the area started about 10,000 14C yr B.P., with a renewed Juniperus–Betula–Pinus succession related to a strong increase in annual temperature and precipitation. The start of this process was synchronous with mean sea-surface temperature changes, as recorded from the nearby SU 81-18 marine core. The strong affinity with other European late-glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial–interglacial transition was similar in both northwestern and southwestern Europe.
Late Holocene Sea Temperatures along the Central California Coast
Authors: Jones Terry L. , Kennett Douglas J.
Published: September 2002

Mussel shells from central California coastal archaeological sites record changes in sea surface temperatures in the past 2000 years. Water temperatures, inferred from oxygen isotopes in the shells, were about 1°C cooler than present and stable between 2000 and 700 yr ago. Between about 700 and 500 yr ago, seasonal variation was greater than present, with extremes above and below historic levels. Water temperatures were 2–3°C cooler than today 500–300 yr ago. The interval of variable sea temperatures 700–500 yr ago partially coincided with an interval of drought throughout central California. A coincident disruption in human settlement along the coast suggests movements of people related to declining water sources. Quantities of fish bone in central coast middens dating to this same period are high relative to other periods, and the remains of northern anchovies, a species sensitive to changing oceanographic conditions, are also abundant. The continued use of local fisheries suggests that changes in settlement and diet were influenced more by drought than by a decrease in marine productivity, as fish provided a staple during an interval of low terrestrial productivity.
Fluctuations of Outlet and Valley Glaciers in the Southern Andes (Argentina) during the Past 13,000 Years
Authors: Wenzens Gerd
Published: September 2002

In the southern Argentine Andes, ten advances of valley glaciers were used to reconstruct the late-glacial and Holocene glacier history. The accumulation areas of these glaciers lie in the Precordillera and are thus independent of fluctuations of the South Patagonian Icefield. Like the Viedma outlet glacier, the valley glaciers advanced three times during late-glacial time (14,000–10,000 yr B.P.). The youngest advance correlates with the Younger Dryas Stade, based on two minimum AMS14C dates of 9588 and 9482 yr B.P. The second oldest advance occurred before 11,800 yr B.P. During the first half of the Holocene, (ca. 10,000–5000 yr B.P.), advances culminated about 8500, 8000–7500, and 5800–5500 yr B.P. During the second half of the Holocene, advances occurred between ca. 4500 and 4200 yr B.P., as well as between 3600 and 3300 yr B.P. In the Rı́o Cóndor valley three subsequent advances have been identified.
Pollen Analysis of a Late-Glacial and Holocene Sediment Core from Mono Lake, Mono County, California
Authors: Davis Owen K.
Published: September 2002

Pollen analysis of a 752-cm core from Mono Lake, Mono County, California indicates generally high lake levels 11,600–7000 14C yr B.P., moderate lake levels until ca. 4000 14C yr B.P., and fluctuating levels to the present. Drying events, with lake levels near or below the historic minimum are dated ca. 8800, 4000, 2400, and 1100 14C yr B.P. Chronologic control is provided by six radiocarbon dates and six volcanic ashes. The rate of upland vegetation change is greatest 11,000, 4000, and 1130 14C yr B.P. Juniperus and Sequoaidendron pollen declines 11,000 yr B.P., marking the transition from late-glacial juniper woodland to Holocene steppe. High values (5–20%) of Sequoaidendron pollen are unique to this study and may indicate the presence of these trees east of the Sierra crest. The pollen-based reconstructions of climate are generally cooler and wetter than today, with relatively dry but cool climate during the early Holocene. The contrast between higher lake levels and more arid vegetation during the early Holocene can be explained by insolation-driven seasonality. Greater summer insolation produced summer drought, but lower winter insolation led to greater snowpack, greater spring runoff, and higher lake levels. Increased Artemisia and other Compositae pollen percentages mark the establishment of modern vegetation ca. 2000 14C yr B.P. During the late Holocene, the pollen-based reconstructions of climate generally match the Mono Lake fluctuations proposed by Stine (1990), but fewer fluctuations are recorded.
Late Pleistocene Glaciation of the Southwestern Ahklun Mountains, Alaska
Authors: Briner Jason P. , Kaufman Darrell S.
Published: September 2002

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, ice-cap outlet glaciers terminated ∼60 km upvalley from Arolik Lake moraines. The area also supported numerous alpine glaciers that expanded from small massifs. During both episodes of glaciation, these alpine glaciers apparently reached their maximum positions sometime after the retreat of the ice-cap outlet glaciers. Equilibrium-line altitudes for reconstructed alpine glaciers of the Klak Creek glaciation average ∼390 ± 100 m elevation in the western Ahklun Mountains, which is at most 500 m, and possibly only 200 m, below the estimated modern equilibrium-line altitude. The maximum late Pleistocene advance in the southwestern Ahklun Mountains occurred during the early Wisconsin, similar to advances elsewhere in western Alaska, but in contrast to the isotopic signal in the deep-sea record of global ice volume. The restricted extent of Klak Creek glaciers might reflect the increased distance to the Bering Sea resulting from eustatic sea-level regression and decreased evaporation resulting from lower sea-surface temperatures and increased sea-ice extent.
The Full-Glacial Forests of Central and Southeastern Europe
Authors: Willis Katherine J. , Rudner Edina , Sümegi Pal
Published: September 2002

The presence of trees in central and southern Europe during the last full-glaciation has long been a matter of debate. A low but persistent presence of fossil tree pollen in central and southern European full-glacial paleoecological sequences has been interpreted either as representing long-distance pollen transport from southerly refuges or as representing in situ refugial populations. Here we present macroscopic charcoal results from 31 sequences located throughout Hungary that provide unequivocal evidence for the presence of at least seven different tree types between approximately 32,500 and 16,500 14C yr B.P. This evidence is presented in conjunction with molluscan and pollen analyses to indicate that during the last full-glaciation, trees grew as far north as Hungary, probably in microenvironmentally favorable sites. These areas provided an important cold-stage refugium for the European flora and fauna.
Long-Term Temperature Trends and Tree Growth in the Taymir Region of Northern Siberia
Authors: Jacoby Gordon C. , Lovelius Nikolai V. , Shumilov Oleg I. , Raspopov Oleg M. , Karbainov Juri M. , Frank David C.
Published: September 2002

The northernmost conifers in the world are located well above the Arctic Circle in the Taymir region of northern Siberia and have been recording the thermal environment for centuries to millennia. The trees respond to temperatures beyond the narrow season of actual cambial cell division by means of root growth, photosynthesis, lignification of cell walls, and other biochemical processes. Data from annual tree-ring widths are used to reconstruct May–September mean temperatures for the past four centuries. These warm-season temperatures correlate with annual temperatures and indicate unusual warming in the 20th century. However, there is a loss of thermal response in ring widths since about 1970. Previously the warmer temperatures induced wider rings. Most major warming and cooling trends are in agreement with other high-latitude temperature reconstructions based on tree-ring analyses with some regional differences in timing of cooling in the late 18th century and of warming in the late 19th century.
Quaternary Glaciers and Climate on Cerro Chirripó, Costa Rica
Authors: Orvis Kenneth H. , Horn Sally P.
Published: September 2002

Glacial lake sediments and glacial geomorphology in Valle de las Morrenas, a glacial trough on the north face of Cerro Chirripó, Costa Rica, provide evidence on high-altitude Pleistocene conditions in Central America. The most recent glacier in the valley (Chirripó stage I) receded very rapidly near the end of the Younger Dryas chronozone. Radiocarbon dates on basal organic sediments from lakes beneath upper, middle, and lower limits of that glacier fall close together, and two-sigma calibrated ages overlap for the period 9700–9600 cal yr B.P. Earliest datable transition sediments from the central lake date to 12,360–11,230 cal yr B.P. Larger, older moraines, and associated trimlines, allowed reconstruction of three paleoglaciers (Chirripó stages II, III, and IV). Computer analysis of hypsometry using published tropical-glacier vertical mass balance profiles yields ELAs of 3506–3523, 3515–3537, and 3418–3509 m, respectively; Chirripó II ELA-estimate positions applied to Chirripó I yield an ELA of 3538–3546 m. We infer minimal temperature depressions of 7.4–8.0°C for the Chirripó I–IV stages. Modeling the behavior of modern tropical glaciers yields basinwide net accumulation estimates of 440–620, 550–830, and 960–1760 mm yr−1 for the Chirripó II, III, and IV stages.
Early Holocene Marine Flooding of the Black Sea
Authors: Uchupi Elazar , Ross David A.
Published: September 2002

Echo-sounding data recorded in the Black Sea in 1969 imaged a chain of hills 5- to 150-m high at a depth of 2000–2200 m that resemble hills on the lower continental rise. Like those hills, the features in the western Black Sea may have been created by bottom currents. The easterly flowing currents inferred to have formed the hills may be related to a catastrophic flood of the Black Sea from the Sea of Marmara 7150 yr ago.
A >130,000-Year-Long Pollen Record from Pittsburg Basin, Illinois
Authors: Teed Rebecca
Published: September 2002

Pittsburg Basin, in south-central Illinois, contains a sediment record extending from the present back to the end of the late Illinoian glaciation, when central Illinois was covered with Picea/Pinus forest. During the last interglaciation, a temperate deciduous forest more diverse than Holocene Quercus/Carya forest replaced the Illinoian late-glacial boreal forest. Prairie pollen types and the charcoal/pollen ratio, indicating fire frequency, temporarily increased. Then forest, with high Juniperus percentages, became dominant once more, as the charcoal/pollen ratio dropped. After the last interglaciation, the charcoal/pollen ratio increased again and prairie and wetland surrounded Pittsburg Basin through the entire Wisconsinan glacial age. The area was still prairie in late Wisconsinan time, but with some Picea and Pinus. During the Holocene, the region has been a mixture of prairie and Quercus/Carya forest. During the last interglaciation, Pittsburg Basin was surrounded by vegetation different from that surrounding it during the present interglaciation. Rather than indicating substantial differences in climate between analogous phases of different glacial/interglacial cycles, this variation may be due to changes in fire frequency, which could be caused by small changes in climate, human activity, or differences in soil.
Stratigraphic and Microfossil Evidence for Late Holocene Tsunamis at Swantown Marsh, Whidbey Island, Washington
Authors: Williams Harry , Hutchinson Ian
Published: September 2002

Four muddy sand sheets occur within a tidal marsh peat at Swantown on the west coast of Whidbey Island, Washington. The two largest sand sheets pinch out about 100 m inland and became thinner and finer-grained landward. All four sand sheets contain marine microfossils and have internal stratification. They record repeated inundation of the marsh over a short time period by distinct pulses of sediment-laden ocean water, consistent with deposition by a tsunami wave train. The layers have been radiocarbon-dated to 1160–1350, 1400–1700, 1810–2060, and 1830–2120 cal yr B.P. The overlap in age between the two youngest layers and inferred great earthquake events at the Cascadia plate boundary, some 250 km to the west, suggests they were emplaced by tsunamis from this source area. The two older layers do not correlate with plate-boundary events. They may be products of tsunamis caused by earthquakes on local faults in the Strait of Juan de Fuca or by submarine landslides in this area.
Climate Variability in East-Central California during the Past 1000 Years Reflected by High-Resolution Geochemical and Isotopic Records from Owens Lake Sediments
Authors: Li Hong-Chun , Bischoff James L. , Ku Teh-Lung , Lund Steven P. , Stott Lowell D.
Published: September 2002

Core OL-97A, retrieved from the depocenter of Owens Lake, represents a depositional history spanning the past 1000 yr. Among the 17 elements analyzed in the acid-leachable fractions of 315 salt-free samples (at ∼3 yr/sample), Mg and Li, which come chiefly from authigenic Mg-hydroxy-silicates, were found to have concentration variations reflecting lake salinity and climatic changes during the past. A total of 231 isotopic measurements on carbonates from the same samples in the upper 181 cm show that δ18O and δ13C values range from −5.66 to 0.12‰ (PDB) and 1.38 to 4.28‰ (PDB), respectively. The rate of change with time in δ18O records the rate of change in lake's volume due to climate fluctuations, whereas variations in δ13C reflect mainly variations in biological productivity, nutrient supply, and dissolved carbonate in the lake. Results indicate an effectively dry climate between A.D. 950 and 1220, corresponding to the Medieval Climatic Anomaly (a warm period in northern Europe), during which Owens Lake approached playa conditions. Wet climates prevailed during A.D. 1220–1480, producing relatively large and deep lakes. Beginning about A.D. 1550, the regional climate turned colder but had frequently oscillating precipitation. Six wet/dry cycles with ∼50-yr duration occurred between A.D. 1480 and 1760, during the later half of which Owens Lake became a playa. Since ∼A.D. 1880, the lake level has steadily dropped from its historic high stand under strong impact of human activity.
Alpine Evidence for Atmospheric Circulation Patterns in Europe during the Last Glacial Maximum
Authors: Florineth Duri , Schlüchter Christian
Published: September 2002

The configuration of Alpine accumulation areas during the last glacial maximum (LGM) has been reconstructed using glacial–geological mapping. The results indicate that the LGM ice surface consisted of at least three major ice domes, all located south of the principal weather divide of the Alps. This implies that the buildup of the main Alpine ice cover during oxygen isotope stage (OIS) 2 was related to precipitation by dominant southerly atmospheric circulation, in contrast to today's prevalent westerly airflow. Such a reorganization of the atmospheric circulation is consistent with a southward displacement of the Oceanic Polar Front in the North Atlantic and of the associated storm track to the south of the Alps. These results, combined with additional paleoclimate records from western and southern Europe, allow an interpretation of the asynchronous evolution of the different European ice caps during the last glaciation. δ18O stages (OIS) 4 and 3 were characterized by location of the Polar Front north of 46°N (Gulf of Biscay). This affected prevailing westerly circulation and thus, ice buildup in western Scandinavia, the Pyrénées, Vosges, and northern Alps. At the LGM, however, the Polar Front lay at ∼44°N, causing dominating southerly circulation and reduced precipitation in central and northern Europe.
Holocene Climate Variability in Antarctica Based on 11 Ice-Core Isotopic Records
Authors: Masson Valérie , Vimeux Françoise , Jouzel Jean , Morgan Vin , Delmotte Marc , Ciais Philippe , Hammer Claus , Johnsen Sigfus , Lipenkov Vladimir Ya. , Mosley-Thompson E. , Petit Jean-Robert , Steig Eric J. , Stievenard Michel , Vaikmae Rein
Published: September 2002

A comparison is made of the Holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east Antarctica (Vostok, Dome B, Plateau Remote, Komsomolskaia, Dome C, Taylor Dome, Dominion Range, D47, KM105, and Law Dome) and west Antarctica (Byrd), with temporal resolution from 20 to 50 yr. The long-term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations. All the records confirm the widespread Antarctic early Holocene optimum between 11,500 and 9000 yr; in the Ross Sea sector, a secondary optimum is identified between 7000 and 5000 yr, whereas all eastern Antarctic sites show a late optimum between 6000 and 3000 yr. Superimposed on the long time trend, all the records exhibit 9 aperiodic millennial-scale oscillations. Climatic optima show a reduced pacing between warm events (typically 800 yr), whereas cooler periods are associated with less-frequent warm events (pacing >1200 yr).
Holocene Coastal Environments near Pompeii before the A.D. 79 Eruption of Mount Vesuvius, Italy
Authors: Pescatore Tullio , Senatore Maria Rosaria , Capretto Giovanna , Lerro Gaia
Published: September 2002

Studies of some 70 bore holes around ancient Pompeii, on the southwestern slope of the Somma-Vesuvius volcano, allow the reconstruction of Holocene environments earlier than the A.D. 79 eruption. This eruption produced about 10 km3 of pyroclastic material that buried the Roman cities of Pompeii, Herculaneum, and Stabiae and promoted a shoreline progradation of 1 km. The Sarno coastal plain, in a post-Miocene sedimentary basin, has been affected by Somma-Vesuvius volcanic activity since the late Pleistocene. At the Holocene transgressive maximum, the sea reached an area east of ancient Pompeii and formed a beach ridge (Messigno, 5600 and 4500 14C yr B.P.) more than 2 km inland from the present shore. Progradation of the plain due to high volcanic supply during the following highstand resulted in a new beach ridge (Bottaro-Pioppaino, 3600 14C yr B.P.) 0.5 km seaward of the Messigno ridge. Ancient Pompeii was built as the shoreline continued to prograde toward its present position. Deposits of the A.D. 79 eruption blanketed the natural levees of the Sarno River, marshes near the city and on the Sarno's floodplain, the morphological highs of Messigno and Bottaro-Pioppaino beach ridges, and the seashore. That shore was probably 1 km landward of the present one.
Paleohydrological Records from Peat Profiles and Speleothems in Sutherland, Northwest Scotland
Authors: Charman Dan J. , Caseldine Chris , Baker Andy , Gearey Ben , Hatton Jackie , Proctor Chris
Published: September 2002

Paleohydrological changes during the late Holocene are inferred from humification, testate amoebae, and pollen evidence from three blanket peat profiles in northwest Scotland. Replicate peat humification records from the Traligill basin share the same patterns of change for a 600-yr period of overlap between 1800 and 2400 cal yr B.P. The shared patterns, inferred from samples with a resolution of 5–13 yr, represent basinwide hydrological changes. In a nearby, but hydrologically separate, area with caves beneath peat, the luminescence emission wavelength measured in two speleothem samples correlated with the humification record in the overlying peat. This correlation implies that speleothem luminescence emission wavelength depends primarily on decay rates in the soils from which drip waters are derived, as long as there is no major change in soil or vegetation. The peat and speleothem records from the cave site further correlate with the peat records from the Traligill basin. Taken together, the records thus represent a regional climatic signal. Peaks in surface wetness replicated in two or more records occur at ca. 2300, 2090, 2030, 1820, 1600, and 1440 cal yr B.P. Further peaks occur at 800, 570, and 115 cal yr B.P. in the humification and stalagmite records that extend to the present day. Correlative changes have been observed, not only in other peat records from Scotland but also in ice accumulation at GISP2. These further correlations imply that precipitation regimes in Scotland and Greenland were in phase during the late Holocene.
δ13C of Loess Organic Matter as a Potential Proxy for Paleoprecipitation
Authors: Hatté Christine , Antoine Pierre , Fontugne Michel , Lang Andreas , Rousseau Denis-Didier , Zöller Ludwig
Published: September 2002

Paleoprecipitation reconstructions on the basis of pollen are well known, but they do not provide high temporal resolution for glacial periods. High-resolution paleoprecipitation reconstructions for the last glaciation based on the isotopic record organic matter in loess from Nussloch (Rhine Valley, Germany) are consistent with paleoprecipitation inferred from peat in the same area using an independant method. Thus, δ13C of loess organic matter can be used as a proxy for paleoprecipitation.
Early Human Occupation at Devil's Lair, Southwestern Australia 50,000 Years Ago
Authors: Turney Chris S. M. , Bird Michael I. , Fifield L. Keith , Roberts Richard G. , Smith Mike , Dortch Charles E. , Grün Rainer , Lawson Ewan , Ayliffe Linda K. , Miller Gifford H. , Dortch Joe , Cresswell Richard G.
Published: September 2002

New dating confirms that people occupied the Australian continent before the earliest time inferred from conventional radiocarbon analysis. Many of the new ages were obtained by accelerator mass spectrometry14C dating after an acid–base–acid pretreatment with bulk combustion (ABA-BC) or after a newly developed acid–base–wet oxidation pretreatment with stepped combustion (ABOX-SC). The samples (charcoal) came from the earliest occupation levels of the Devil's Lair site in southwestern Western Australia. Initial occupation of this site was previously dated 35,00014C yr B.P. Whereas the ABA-BC ages are indistinguishable from background beyond 42,00014C yr B.P., the ABOX-SC ages are in stratigraphic order to ∼55,00014C yr B.P. The ABOX-SC chronology suggests that people were in the area by 48,000 cal yr B.P. Optically stimulated luminescence (OSL), electron spin resonance (ESR) ages, U-series dating of flowstones, and14C dating of emu eggshell carbonate are in agreement with the ABOX-SC14C chronology. These results, based on four independent techniques, reinforce arguments for early colonization of the Australian continent.
Composition and Flux of Holocene Sediments on the Eastern Laptev Sea Shelf, Arctic Siberia
Authors: Bauch Henning A. , Kassens Heidemarie , Naidina Olga D. , Kunz-Pirrung Martina , Thiede Jörn
Published: September 2002

A 467-cm-long core from the inner shelf of the eastern Laptev Sea provides a depositional history since 9400 cal yr. B.P. The history involves temporal changes in the fluvial runoff as well as postglacial sea-level rise and southward retreat of the coastline. Although the core contains marine fossils back to 8900 cal yr B.P., abundant plant debris in a sandy facies low in the core shows that a river influenced the study site until ∼8100 cal yr B.P. As sea level rose and the distance to the coast increased, this riverine influence diminished gradually and the sediment type changed, by 7400 cal yr B.P., from sandy silt to clayey silt. Although total sediment input decreased in a step-like fashion from 7600 to 4000 cal yr B.P., this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components. While this maximum probably resulted from middle Holocene climate warming, the low input of sand to the site after 7400 cal yr B.P. probably resulted from further southward retreat of the coastline and river mouth. Since about 4000 cal yr B.P., total sediment flux has remained rather constant in this part of the Laptev Sea shelf due to a gradual stabilization of the depositional regime after completion of the Holocene sea-level rise.
Holocene History of the Bering Sea Bowhead Whale (Balaena Mysticetus) in Its Beaufort Sea Summer Grounds off Southwestern Victoria Island, Western Canadian Arctic
Authors: Dyke Arthur S. , Savelle James M.
Published: September 2002

The fossil remains of 43 bowhead whales were mapped on the raised beaches of western Wollaston Peninsula, Victoria Island, Canadian Arctic, near the historic summer range limit of the Bering Sea stock in the Beaufort Sea. The elevations and radiocarbon ages of the remains demonstrate that the bowhead ranged commonly into the region following the submergence of Bering Strait at ca. 10,000 14C yr B.P. until ca. 8500 14C yr B.P. During the same interval, bowheads ranged widely from the Beaufort Sea to Baffin Bay. Subsequently, no whales reached Wollaston Peninsula until ca. 1500 14C yr B.P. Late Holocene populations evidently were small, or occupations were brief, in comparison to those of the early Holocene. Although the late Holocene recurrence may relate to the expansion of pioneering Thule whalers eastward from Alaska, there are few Thule sites and limited evidence of Thule whaling in the area surveyed to support this suggestion.
Chronology of Inland Eolian Dunes on the Coastal Plain of Georgia, USA
Authors: Ivester Andrew H. , Leigh David S. , Godfrey-Smith D. I.
Published: September 2002

Most inland eolian dunes associated with rivers on the Georgia Coastal Plain probably date to glacial periods. Direct dating of the dune sand by optically stimulated luminescence dating, combined with limiting ages from radiocarbon dating, shows that dunes formed during isotope stage 2, stage 3, the transition between stages 4 and 5, and isotope stage 6 or earlier. Most of the dates indicate dune activity between 30,000 and 15,000 years ago. Holocene activity included limited and local reworking of the crests of some thick dunes along streams that flow from the Piedmont.
A Late Glacial–Holocene Tephrochronology for Glacial Lakes in Southern Ecuador
Authors: Rodbell Donald T. , Bagnato Stefan , Nebolini Jeffrey C. , Seltzer Geoffrey O. , Abbott Mark B.
Published: September 2002

Despite the presence of numerous active volcanoes in the northern half of Ecuador, few, if any, distal tephras have been previously recognized in the southern one third of the country. In this article, we document the presence of thin (0.1–1.0-cm-thick) distal tephras comprising glass and/or phenocrysts of hornblende and feldspar in sediment cores from five glacial lakes and one bog in Las Cajas National Park (2°40′–3°00′S, 79°00′–79°25′W). The lake cores contain from 5 to 7 tephras, and each has a diagnostic major element geochemistry as determined from electron microprobe analysis of ∼710 glass shards and ∼440 phenocrysts of feldspar and hornblende. The loss of sodium with exposure to the electron microbeam causes a 10±7 wt.% (±1σ) reduction in Na content, which we empirically determined and corrected for before correlating tephras among the sediment cores. We use a similarity coefficient to correlate among the sediment cores; pair-wise comparison of all tephras generally yields an unambiguous correlation among the cores. Six tephras can be traced among all or most of the cores, and several tephras are present in only one or two of the cores. Twenty-six accelerator mass spectrometry 14C dates on macrofossils preserved in the sediment cores provide the basis for establishing a regional tephrochronology. The widespread tephras were deposited ∼9900, 8800, 7300, 5300, 2500, and 2200 cal yr B.P. The oldest tephras were deposited ∼15,500 and 15,100 cal yr B.P., but these are not found in all cores. Two of the tephras appear correlative with volcaniclastic strata on the flanks of Volcán Cotopaxi and one tephra may correlate with strata on the flanks of Volcán Ninahuilca; both volcanoes are in central Ecuador. The absence of tephras in sediment cores correlative with the numerous eruptions of active volcanoes of the past two millennia implies that the earlier eruptions, which did deposit tephras in the lakes, must have been either especially voluminous, or southerly winds must have prevailed at the time of the eruption, or both.