bluuebunny/crossref_metadata_2025 huggingface dataset:
Pacific Pleistocene Paleoclimatic Stratigraphies: A Comparative Analysis of Results
Authors: Valencia Mark J.
Published: December 2004

Global atmospheric and oceanic circulation effects of expansion of continental ice sheets initiated upwelling in the western equatorial Pacific and simultaneously intensified upwelling in the eastern equatorial Pacific; contraction of the ice sheets reversed the process. Published Pleistocene paleoclimatic stratigraphies correlated across the entire equatorial Pacific exhibit eight such cycles in the Brünhes epoch. The extrapolated chronostratigraphies for the equatorial Pacific compare favorably with published paleoclimatic schemes for the southeastern, eastern, and northern Pacific Ocean. The Southern Ocean record exhibits fewer, and possibly also consistently older, climatic variations. A time progression or lack of synchrony of marine Pleistocene climatic events is not inconsistent with modified “Milankovitch” hypotheses, such as that involving Antarctic ice-sheet instability.
Horizontal Quaternary Shorelines of the Mediterranean
Authors: Hey R.W.
Published: December 2004

The high-level Quaternary shorelines of the Mediterranean are now in a fragmentary condition, but on some parts of the coast it has been possible to reconstruct one or more over a distance of many kilometers. A few of these reconstructed segments of shoreline are tilted or otherwise deformed, but the great majority appear to be virtually horizontal. The horizontal segments show no clear preference for any particular level or levels, from which it is concluded that all have been vertically displaced by earth movements.
Identification and Significance of a Late Pleistocene Tephra in Canterbury District, South Island, New Zealand
Authors: Kohn B. P.
Published: December 2004

A rhyolitic ash 4 to 8 cm thick is well preserved within a thick loess unit in a coastal section 2 km long near Teviotdale, Canterbury district, South Island, New Zealand. The ash (informally named Tiromoana ash) contains fresh glass shards which give a fission-track age of 20,300 ± 7100 yr B.P. The only possible source for such a tephra with this age range is from Taupo Volcanic Zone (TVZ), North Island, some 550 km north of Teviotdale. Within the time span ca. 15,000 to 42,000 yr B.P. five widespread and voluminous rhyolitic tephras (viz. Rerewhakaaitu Ash, Rotoehu Ash, Kawakawa Tephra, Omataroa Tephra, and Mangaone Tephra) were erupted from TVZ. On the basis of the fission-track age, ferromagnesian mineralogy, and electron-microprobe analyses of glass shards and titanomagnetites from Tiromoana ash and the five possible correlatives listed above, Tiromoana ash is correlated with Kawakawa Tephra (dated by 14C at ca. 20,000 yr B.P.). This is the only known occurrence to date of Kawakawa Tephra in the South Island. Its preservation is attributed to special site conditions (low precipitation and minimal sheet erosion) leeward of a prominent terrace. The identification of the ash at Teviotdale as Kawakawa Tephra supports recently revised age assignments for the upper loess sheet in Canterbury. Moreover, it implies that loess enclosing Kawakawa Tephra in nonglaciated districts of southern North Island and Taupo Volcanic Zone is a correlative.
Time Series and Postglacial Forest Ecology
Authors: Green David G.
Published: December 2004

Forest ecology suffers from a lack of long-term community records. Preserved pollen data are richer in such information than is generally realized. By applying suitable statistical techniques to pollen records, one can learn much about competition, succession, and population dynamics in past tree communities. In this study, preserved pollen records from Everitt Lake, Nova Scotia, are analyzed as time series. Time domain studies reveal the post-fire responses of individual tree taxa. Correlograms yield models of past forest succession patterns. The models explain some effects of changing fire frequency, thus suggesting mechanisms by which fire, competition, and climate combine to produce long-term forest composition changes. Frequency domain studies suggest relationships between disturbance cycles, stand composition, and forest mosaics. Fire frequencies are seen to be highest where fire-dependent species abound and most regular where tree stands have uniform, not mixed, composition.
The Selection of Sites for Paleovegetational Studies
Authors: Jacobson G. L. , Bradshaw R. H. W.
Published: December 2004

The judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation. We present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local, extralocal, and regional pollen sampled by lake basins of different size. The distinctive sampling properties of lakes, peats, and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites. Combinations of site types in a single study most fully exploit the information contained in sediments.
Fire and Other Disturbances of the Forests in Mount Rainier National Park
Authors: Hemstrom Miles A. , Franklin Jerry F.
Published: December 2004

The recent history of catastrophic disturbances in forests was reconstructed at Mount Rainier National Park. Basic data were ages of trees based on ring counts of early seral conifer species and maps of age-class boundaries from field work and aerial photographs. Maps illustrate age classes of the forests and show disturbances from fires, snow avalanches, and lahars (volcanic mudflows). Fires are by far the most important major disturbers, followed by snow avalanches and lahars. Fires over 250 ha in size are called fire events. Burns over 1000 ha, which may have been one fire or a series of fires within a short time, are called fire episodes. Important fire events or episodes occurred in the years 1230, 1303, 1403, 1503, 1628, 1688, 1703, 1803, 1825, 1856, 1858, 1872, 1886, 1894, 1930, and 1934 A.D. The largest fire episode was in 1230; it affected approximately 47% of the forests in the park. The majority of the forests are over 350 yr old, and several stands are over 1000 yr old. Stands 350 yr and 100 to 200 yr in age are the most extensive age classes in the park. Three fire frequency indices are compared. None describe fire frequency at Mount Rainier well. Natural fire rotation was estimated at about 434 yr. All but two episodes of major fires since 1300 A.D. correspond well with major droughts reconstructed for locations east of the Cascade Range crest. Impacts of humans on the disturbance regime may have increased the frequency of fire in the 1850–1900 period, followed by a decrease in frequency after 1900. Fuel build-up as a result of fire suppression should have no significant impact on fire frequency, since fires are relatively infrequent and fuels accumulate naturally.
Paleoceanography of Surface Waters in the Gulf of Mexico during the Late Quaternary
Authors: Brunner Charlotte A.
Published: December 2004

Late Quaternary paleotemperatures and paleosalinities of surface waters of the Gulf of Mexico were estimated using a multivariate statistical analysis of census data of planktonic foraminifera. Two climatic extremes were selected for detailed basinwide study, the climatic optimum 125,000 yr ago and the glacial maximum 18,000 yr ago. In addition, patterns of climatic change were examined in seven piston cores from 127,000 yr ago to the present day. During the climatic optimum 125,000 yr ago temperature distributions in surface waters were similar to those of the present. The 22°C winter isotherm trended northeastward across the central basin and paleotemperatures decreased northward. Summer distributions were nearly homogeneous and ranged between 28° and 29°C. Winter salinities were 1‰ fresher than present values in the northmost Gulf and 0.4‰ fresher in the central basin. Summer salinities were similar during both times. In contrast, during the last glacial maximum temperatures were 1° to 2°C cooler in winter and 1°C cooler in summer, and isotherms formed a circular pattern in the Gulf during both seasons. Salinity was 0.3‰ fresher in winter than at present but 0.6‰ saltier in summer. Conditions deteriorated from the climatic optimum to the glacial maximum. In the Mexico Basin, winter temperatures were 2°C cooler from 75,000 to 45,000 yr ago (Y6 to Y3 Subzones), summer temperatures reached a minimum (3°C cooler) 32,000 yr ago (Y2–Y3 boundary), and seasonality reached minimal values (5°C) from 45,000 to 15,000 yr ago. All three parameters became similar in value to those in the Straits of Florida from 45,000 to 15,000 yr ago, suggesting that the exchange of surface waters was enhanced at this time between the two regions. Summer salinities remained similar to present conditions in the Mexico Basin, whereas, winter salinities increased 2‰ by 32,000 yr ago and then fell 0.5‰ until the glacial maximum ended. The Westerlies may have migrated southward over the Mexico Basin in winter from 32,000 to 15,000 yr ago.
Late Quaternary Faunal Change in Coastal Arabian Sea Sediments
Authors: Borole D. V. , Rao K. Kameswara , Krishnamurthy R. V. , Somayajulu B. L. K.
Published: December 2004

Carbonate content and faunal composition of two gravity cores from the coastal Arabian sea provide evidence of a major environmental change in surface ocean waters about 13,000 yr B.P. Radiocarbon dating indicates that deposition rates ranged from 1.8 to 9.8 cm/103 yr, with a major change in rate occurring in one core at about 7500 yr B.P.
Terrace Stratigraphy in the Tunica Hills of Louisiana
Authors: Alford John J. , Kolb Charles R. , Holmes Joseph C.
Published: December 2004

The age and number of important fossil-producing late Pleistocene terraces in the Tunica Hills have recently become quite controversial. One hypothesis holds that only a single loess-mantled Farmdalian terrace flanks the streams in this area. The other maintains that there are two terraces. The youngest is considered essentially Holocene in age while the older is Sangamon in age. Radiometric and stratigraphic evidence collected for this study indicates that there are two terraces. The youngest is late Woodfordian to Holocene in age while the other is Farmdalian.
Coastal Morphology and Late Quaternary History, Cayman Islands, West Indies
Authors: Woodroffe C. D. , Stoddart D. R. , Harmon R. S. , Spencer T.
Published: December 2004

Instrumental surveys of coastal profiles in the Cayman Islands, western Caribbean, reveal the presence of a horizontal erosional bench at +1.9 m on Grand Cayman and a deep horizontal notch at +6.4 m on Cayman Brac, but no raised erosional features on Little Cayman. Each island is surrounded by a horizontal constructional raised reef, usually below +2 m, here dated by U-series methods as 124,000 ± 8000 yr old, and hence broadly contemporary with other western Atlantic raised reefs of similar elevations. The different raised erosional features indicate independent vertical tectonic movement of the three islands, predating the formation of the raised reef. The accordance and horizontality of the raised reef indicates stability of the islands since the last interglacial times. An erosional notch at present sea level has formed since the sea reached its present level less than 2100 B.P., and algal benches on exposed coasts are also in equilibrium with present conditions.
Speleothems, Travertines, and Paleoclimates
Authors: Hennig G. J. , Grün R. , Brunnacker K.
Published: December 2004

Age data for about 660 speleothems and about 140 spring-deposited travertines were collected, including many unpublished results. These data were plotted as histograms and also as error-weighted frequency curves on a 350,000-yr scale. These plots clearly show periods of increased speleothem/travertine growth as well as times of cessation. The periods of most frequent speleothem growth were between approximately 130,000 and 90,000 yr ago and since about 15,000 yr ago. Such periods before 150,000 yr ago, however, cannot be yet recognized because of a lack of sufficient data and the associated uncertainties of dates in this age range. A comparison with the oxygen-isotope record of deep-sea core V28–:238 shows a clear relationship, indicating that terrestrial calcite formation is controlled by paleoclimatic fluctuations. The evident climatic stimulation of Quaternary calcite formation is readily explained geochemically and is substantiated by the obvious difference in speleothem/travertine growth as a function of geographic position.
Holocene Flooding and Species Diversity in Southwestern Amazonia
Authors: Campbell Kenneth E. , Frailey David
Published: December 2004

A thick blanket of Holocene alluvium lies over southwestern lowland Amazonia, and may possibly occur throughout much of the Amazon Basin. These deposits resulted from massive, seasonal flooding from about 11,000 to about 5000 yr B.P. that was followed by two cycles of erosion and deposition. Interpretations based on these geologic data suggest that southwestern lowland Amazonia is ecologically an “island” in a state of supersaturated disequilibrium as a result of colonization from Pleistocene refugia on its perimeter, and that habitats of highest diversity may be the most recent in origin. Conservation efforts and studies of Amazonian biogeography, soils, and paleoethnography should be reevaluated in light of the geologic data.
Packrat Middens from Canyon de Chelly, Northeastern Arizona: Paleoecological and Archaeological Implications
Authors: Betancourt Julio L. , Davis Owen K.
Published: December 2004

In western North America, pollen data from highland lakes are often used to reconstruct vegetation on the adjacent lowlands. Plant macrofossils and pollen from packrat middens now provide a means to evaluate such reconstructions. On the basis of pollen diagrams from the Chuska Mountains, H. E. Wright, Jr., A. M. Bent, B. S. Hansen, and L. J. Maher, Jr., ((1973), Geological Society of America Bulletin, 84 , 1155–1180) arrived at conservative estimates for late Pleistocene depression of highland conifers. In their interpretation, a proposed slight depression of 500 m for lower tree line precluded expansion of Pinus ponderosa into elevations now in desertscrub. Instead, it was suggested that pinyon pine and Artemisia occupied the lowland plateaus. Packrat midden records on either side of the Chuskas fail to verify this model. Early Holocene middens from Chaco Canyon, New Mexico, and a terminal Pleistocene midden from Canyon de Chelly, Arizona, show that blue spruce, limber pine, Douglas fir, dwarf juniper, and Rocky Mountain juniper expanded at least down to 1770 m elevation Neither Colorado pinyon nor ponderosa pine was found as macrofossils in the middens. Artemisia pollen percentages are high in the terminal Pleistocene midden, as they are in the Chuska Mountain pollen sequence, suggesting regional dominance by sagebrush steppe. Of 38 taxa identified, only 3 are shared by middens dated 11,900 and 3120 yr B.P. from Canyon de Chelly, indicating a nearly complete turnover in the flora between the late Pleistocene and late Holocene. Although corn was previously thought to have been introduced to the Colorado plateaus after 2200 yr B.P., the midden dated 3120 yr B.P. contains pollen of corn and other indicators of incipient agriculture.
Sponge Gemmules from Lake Sediments in the Puget Lowland, Washington
Authors: Turner Judith
Published: December 2004

Gemmules of five species of freshwater sponge found in deposits at Cedar Mountain bog in the southeastern Puget Lowland were used to infer that during the late-glacial period the water was calcareous, was not deficient in SiO2, was aerobic, and had a pH in the range 6.6–8.5. This is consistent with plant fossil data. In view of their paleoenvironmental potential it is worth looking for gemmules when extracting other fossils from lake sediments.
Two-Step Deglaciation: 14C-Dated High-Resolution δ18O Records from the Tropical Atlantic Ocean
Authors: Berger W. H. , Killingley J. S. , Metzler C. V. , Vincent E.
Published: December 2004

Eight box cores from the tropical Atlantic were studied in detail with regard to foraminiferal oxygen isotopes, radiocarbon, and Globorotalia menardii abundance. A standard Atlantic oxygen-isotope signal was reconstructed for the last 20,000 yr. It is quite similar to the west-equatorial Pacific signal published previously. Deglaciation is seen to occur in two steps which are separated by a pause. Onset of deglaciation is after 15,000 yr B.P. The pause is centered between 11,000 and 12,000 yr B.P., but may be correlative with the Younger Dryas (10,500 yr B.P.) if allowance is made for a scale shift due to mixing processes on the sea floor. Step 2 is centered near 10,000 yr B.P. and is followed by a brief excursion toward light oxygen values. This excursion (the M event) may correlate with the Gulf of Mexico meltwater spike.
Pollen and Radiolarian Records from Deep-Sea Core RC14-103: Climatic Reconstructions of Northeast Japan and Northwest Pacific for the Last 90,000 Years
Authors: Heusser Linda E. , Morley Joseph J.
Published: December 2004

Using modern pollen and radiolarian distributions in sediments from the northwest Pacific and seas adjacent to Japan to interpret floral and faunal changes in core RC14-103 (44°02′N, 152°56′E), we recognize two major responses of the biota of eastern Hokkaido and the northwest Pacific to climatic changes since the last interglaciation. Relatively stable glacial environments (∼80,000–20,000 yr B.P.) were basically cold and wet (<4°C and ∼1000 mm mean annual temperature and precipitation, respectively) with boreal conijers and tundra/park-tundra on Hokkaido, and cool (<16°C) summer and cold (<1.0°C) winter surface temperatures offshore. Contrasting nonglacial environments (∼10,000–4000 yr B.P.) were warm and humid (>8°C and >1200 mm mean annual temperature and precipitation, respectively), supporting climax broadleaf deciduous forest with Quercus and Ulmus/Zelkova, with surface waters in the northwest Pacific characterized by warm (>1.5°C) winter and cold (10.4°–14.3°C) summer temperatures. Climatic evidence from RC14-103 shows a high degree of local and regional variation within the context of global climatic change. Correlative ocean and land records provide the detailed input necessary to assess local/regional responses to variations in other key elements (i.e., solar radiation, monsoonal variations) of the northeast Asian climate system.
Relative Dating of Quaternary Deposits Based on P-Wave Velocities in Weathered Granitic Clasts
Authors: Crook Richard
Published: December 2004

A new quantitative, reproducible method for determining relative ages of unconsolidated Quaternary deposits containing granitic clasts has been developed and tested. The technique makes use of a microseismic timer to determine the compressional wave velocity (clast-sound velocity) in each clast of a group chosen from a single deposit. From these data a group mean velocity is determined that is proportional to the age of the deposit: the youngest deposits having the highest velocities. The clast-sound velocity method was used to study Quaternary deposits in the San Gabriel Valley and San Gabriel Mountains, California, using a previously proposed four-part age classification for the deposits. The clast-sound velocity group means for the four age groups were found to be statistically separable at better than 99% confidence. A velocity/age correlation curve was determined for these deposits using two radiocarbon dates and one paleomagnetic determination. This curve suggests that the clast-sound velocity method may be used to determine ages of deposits up to one million years old when calibrated with sufficient radiometric dates and may also be used as a tool for correlating undated deposits.
The Pleistocene Hominid Site of Ternifine, Algeria: New Results on the Environment, Age, and Human Industries
Authors: Geraads Denis , Hublin Jean-Jacques , Jaeger Jean-Jacques , Tong Haiyan , Sen Sevket , Toubeau Philippe
Published: December 2004

A new multidisciplinary research program, started in 1981, provided new data on the stratigraphy, fauna, and human industries, as well as the first results on paleomagnetism and sedimentology, for the Ternifine site in Algeria, which yielded the earliest hominid remains known in North Africa. The fossils were deposited in a swamp or lake surrounded by a very open, dry environment. The lake was fed by artesian springs that raised the underlying Miocene sands. Although nothing suggests a camp or butchery site, we discovered the first undisputable bone artifact in this site, the earliest known in this part of Africa. According to paleontological data, 700,000 yr B.P. is a likely age for the Ternifine deposits, which is consistent with the paleomagnetic results.
Man and Climate in the Maya Lowlands
Authors: Leyden Barbara W.
Published: December 2004

A 15-m sedimentary core from Lake Salpeten provides the first complete Holocene sequence for the lowlying Peten District, Guatemala. Today, Lake Salpeten is a brackish, calcium sulfate lake near saturation surrounded by tropical semievergreen forest. The basal pollen record depicts sparse juniper scrub surrounding a lake basin that held ephermal pools and halophytic marshes. The lake rapidly deepened to > 27 m in the early Holocene and may have been meromictic, because nearly 2 m of gypsum “mush” was deposited. Mesic forests were quickly established and persisted until the Maya entered the district 3000 yr ago and caused extensive deforestation. Any climatic information contained in the pollen record of the Maya period is thus masked, but a regional pollen sequence linked to the archaeological record is substantiated because environmental disturbance was pervasive. Local intensification of occupation and population growth are seen as an increased deposition of pollen of agricultural weeds and colluviation into the lake, while the Classic Maya collapse is marked by a temporary decline in Compositae pollen. Effects of perturbations induced by the Maya persist in the pollen and limnetic record 400 yr after the Spanish conquest.
Influence of Late Quaternary Climatic Changes on Geomorphic and Pedogenic Processes on a Desert Piedmont, Eastern Mojave Desert, California
Authors: Wells Stephen G. , McFadden Leslie D. , Dohrenwend John C.
Published: December 2004

Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Dorn, 1984) on the adjacent Soda Mountains piedmont provide age constraints for alluvial and eolian deposits. These deposits are associated with climatically controlled stands of Lake Mojave during the past 15,000 yr. Six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces, as well as on soil-geomorphic data. All but one of these stratigraphic units were deposited in response to time-transgressive climatic changes beginning approximately 10,000 yr ago. Increased eolian flux rates occurred in response to the lowering of Lake Mojave and a consequent increase in fine-sediment availability. Increased rates of deposition of eolian fines and associated salts influenced pedogenesis, stone-pavement development, and runoff-infiltration relations by (1) enhancing mechanical weathering of fan surfaces and hillslopes and (2) forming clay- and silt-rich surface horizons which decrease infiltration. Changes in alluvial-fan source areas from hillslopes to piedmonts during the Holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less-permeable soils. Inferred increased in early to middle Holocene monsoonal activity resulted in high-magnitude paleo-sheetflood events on older fan pavements; this runoff triggered piedmont dissection which, in turn, caused increased sediment availability along channel walls. Thus, runoff-infiltration changes during the late Quaternary have occurred in response to eolian deposition of fines, pedogenesis, increased sheetflood activity in the Holocene, and vegetational changes which are related to many complicated linkages among climatic change, lake fluctuations, and eolian, hillslope, and alluvial-fan processes.
Pleistocene Climatic Changes and Landscape Evolution in the Kashmir Basin, India: Paleopedologic and Chronostratigraphic Studies
Authors: Bronger Arnt , Pant Rajendra K. , Singhvi Ashok K.
Published: December 2004

The Kashmir Basin is filled with Pliocene-Pleistocene fluvio-lacustrine sediments. On the flank of the Pir Panjal these sediments, called “Lower Karewas”, are covered with loess deposits up to 25 m thick that contain numerous middle and late Pleistocene paleosols, mostly polygenetic pedocomplexes, which were classified by micromorphological studies. Thermoluminescence dates provide a chronostratigraphy of the late Pleistocene loess-paleosol sequences. On the Himalayan flank, the “Upper Karewas” are covered only with late Pleistocene loess-paleosol sequences. Their base is the last interglacial soil, developed ca. 110,000 ± 10,000 yr B.P. This soil is genetically comparable to the modern soil and, therefore, is thought to have developed under a deciduous forest in a “xeric” soil moisture regime. The loesses of last glacial age on both flanks of the basin contain three humus-rich Ah, mostly Aht, horizons, indicating three warm and mostly humid climatic episodes between ca. 80,000 and 50,000 yr B.P. The middle Pleistocene loesses contain at least four Bwt, or thick Bt, horizons developed during four interglacial periods, having climates similar to the present. Large parts of the Karewa Lake must have lasted until the end of the penultimate glacial age.
Summer Temperature Patterns over Europe: A Reconstruction from 1750 A.D. Based on Maximum Latewood Density Indices of Conifers
Authors: Briffa Keith R. , Jones Philip D. , Schweingruber Fritz H.
Published: December 2004

Temperature variations over Europe are reconstructed for a 6-month “summer” season from April to September for the period 1750–1850 using a network of maximum latewood density chronologies of coniferous trees. Around 44% of the variance of the whole temperature grid was explained in calibration. Independent verification indicates that over the reconstruction period the explained variance averaged over the whole grid should lie in the range 30 to 35%. The reconstructions are better in the north of the region (about 50% explained temperature variance based on comparison with independent climate data) than in the south (below 20%). The temperature recontructions indicate cooler summers over Europe from 1812 to 1816 and during the 1830s. The summers of the 1820s were the warmest reconstructed. Decadal variations occur on a regional scale but no similar periods of anomalously cooler or warmer summers occurred between 1750 and 1810 throughout Europe.
Stratigraphic Charcoal Analysis on Petrographic Thin Sections: Application to Fire History in Northwestern Minnesota
Authors: Clark James S.
Published: December 2004

Results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern Minnesota to determine if charcoal data accurately reflect fire regimes. Pollen and opaque-spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr. A good correspondence was found between fossil-charcoal and fire-scar data. Individual fires could be identified as specific peaks in the charcoal curves, and times of reduced fire frequency were reflected in the charcoal data. Charcoal was absent during the fire-suppression era from 1920 A.D. to the present. Distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment. Fire was less frequent during the 19th century, and charcoal was substantially less abundant. Fire was frequent from 1760 to 1815, and charcoal was abundant continuously. Fire scars and fossil charcoal indicate that fires did not occur during 1730–1750 and 1670–1700. Several fires occurred from 1640 to 1670 and 1700 to 1730. Charcoal counted from pollen preparations in the area generally do not show this changing fire regime. Simulated “sampling” of the thin-section data in a fashion comparable to pollen-slide methods suggests that sampling alone is not sufficient to account for differences between the two methods. Integrating annual charcoal values in this fashion still produced much higher resolution than the pollen-slide method, and the postfire suppression decline of charcoal characteristic of my method (but not of pollen slides) is still evident. Consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments.
Modeling the Growth and Decay of the Antarctic Peninsula Ice Sheet
Authors: Payne A. J. , Sugden D. E. , Clapperton C. M.
Published: December 2004

A model of the growth and decay of the Antarctic Peninsula Ice Sheet during the last glacial/interglacial cycle is used to identify the main controls on ice sheet behavior. Using as input glaciological assumptions derived by W. F. Budd and I. N. Smith (1982, Annals of Glaciology 3, 42–49), bedrock topography, isostatic compensation, and mass balance relationships, the model is driven by sea-level change over the last 40,000 yr in association with assumed changes in the rate of melting beneath ice shelves. An ice sheet dome over 3.5 km thick grows on the offshore shelf and straits west of the Antarctic Peninsula and reaches a maximum at 18,000 yr B.P. Collapse begins at 14,000 yr B.P. but becomes rapid and continuous after 10,000 yr B.P. The present stable ice cover is achieved at 6500 yr B.P. Ice growth and decay are characterized by thresholds which separate periods of steady state from periods of rapid transition; the thresholds usually relate to topography. Tests show that ice sheet behavior is most sensitive to sea-level change, basal marine melting, and accumulation and is less sensitive to isostasy, spatial variation in accumulation, calving rates, and ice flow parameterization. Tests of the model against field evidence show good agreement in places, as well as discrepancies which require further work.
A Comparison of Deep Antarctic Ice Cores and Their Implications for Climate Between 65,000 and 15,000 Years Ago
Authors: Jouzel J. , Raisbeck G. , Benoist J.P. , Yiou F. , Lorius C. , Raynaud D. , Petit J.R. , Barkov N.I. , Korotkevitch Y.S. , Kotlyakov V.M.
Published: December 2004

Three ice cores drilled in the central part of the Antarctic continent extend back to the last glacial period: one from West Antarctica (Byrd) and two from East Antarctica (Vostok and Dome C). This period is also partly covered by a few cores from the coastal areas. In these cores, climatic information is mostly derived from the isotopic profiles (δD or δ18O) from which surface temperature and, more indirectly, precipitation rate can be estimated. The main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period (from ca. 65,000–15,000 yr B.P.). The time scales have been examined in detail and a new 40,000 yr chronology for the Dome C core adopted. Special emphasis is placed on the link between the concentration of 10Be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers. Elevation changes of the ice sheet, derived from gas content and isotopic data, bear directly on interpretations of past temperature and precipitation rate changes.
Late Wisconsin and Early Holocene Glacial History, Inner Ross Embayment, Antarctica
Authors: Denton George H. , Bockheim James G. , Wilson Scott C. , Stuiver Minze
Published: December 2004

Lateral drift sheets of outlet glaciers that pass through the Transantarctic Mountains constrain past changes of the huge Ross ice drainage system of the Antarctic Ice Sheet. Drift stratigraphy suggests correlation of Reedy III (Reedy Glacier), Beardmore (Beardmore Glacier), Britannia (Hatherton/Darwin Glaciers), Ross Sea (McMurdo Sound), and “younger” (Terra Nova Bay) drifts; radiocarbon dates place the outer limits of Ross Sea drift in late Wisconsin time at 24,000–13,000 yr B.P. Outlet-glacier profiles from these drifts constrain late Wisconsin ice-sheet surface elevations. Within these constraints, we give two extreme late Wisconsin reconstructions of the Ross ice drainage system. Both show little elevation change of the polar plateau coincident with extensive ice-shelf grounding along the inner Ross Embayment. However, in the central Ross Embayment one reconstruction shows floating shelf ice, whereas the other shows a grounded ice sheet. Massive late Wisconsin/Holocene recession of grounded ice from the western Ross Embayment, which was underway at 13,040 yr B.P. and completed by 6600-6020 yr B.P., was accompanied by little change in plateau ice levels inland of the Transantarctic Mountains. Sea level and basal melting probably controlled the extent of grounded ice in the Ross Embayment. The interplay between the precipitation (low late Wisconsin and high Holocene values) and the influence of grounding on outlet glaciers (late Wisconsin thickening and late Wisconsin/Holocene thinning, with effects dying out inland) probably controlled minor elevation changes of the polar plateau.
Lacustrine Sedimentation in a Semiarid Alpine Setting: An Example from Ladakh, Northwestern Himalaya
Authors: Fort Monique , Burbank Douglas W. , Freytet Pierre
Published: December 2004

The Lamayuru lacustrine strata in Ladakh typify many of the carbonate-rich Pleistocene alpine lakes found in the semiarid environment of the northern Himalaya. Created by a 200-m-thick landslide, the lake was in existence by at least 35,000 yr ago, and may have persisted until 500–1000 yr ago. Represented in the center by thin turbidites and laminated muds, the lacustrine sedimentation along the lake margins and low-relief deltas characteristically displays a marked contrast between (1) clastic lenses representing rapid, sporadic, matrix-poor debris flows and periglacial inputs from the alpine slopes and (2) abundant, diverse, shallow-water, biologically dominated carbonate strata, among which organism-rich, chalky beds and oncolithic and encrusted stem-rich strata predominate. Resemblances of the Lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the Greater Himalayan crest suggest that the alpine, semi-arid environment would favor diversified, spacially restricted carbonate sedimentation punctuated by occasional clastic influxes. Such a depositional regime contrasts strongly with that found immediately south of the Himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes.
Dating of Late Pleistocene Interglacial and Interstadial Periods in the United Kingdom from Speleothem Growth Frequency
Authors: Gordon David , Smart Peter L. , Ford D.C. , Andrews J.N. , Atkinson T.C. , Rowe P.J. , Christopher N.S.J.
Published: December 2004

The growth of speleothems is indicative of interglacial and interstadial conditions in the United Kingdom, since their growth is dependent on two factors. First, the occurrence of significant diffuse groundwater recharge and, second, the biogenic production of carbon dioxide in the soil, both are dependent on temperature and water availability. The growth frequency of speleothems is examined using a cumulative distributed error frequency method applied to 341 uncontaminated uranium-series age determinations. The curves derived are shown to be statistically stable, and the ages of the peaks are interpreted as the best estimates of the ages of interglacial and interstadial periods. Ten such periods are recognized during the interval 220,000 to 20,000 yr B.P., considerably more than are currently recognized in the UK pollen- and coleoptera-based Quaternary stratigraphy. Correlations between the speleothem growth frequency peaks and last interglacial (Ipswichian) sites can be made, but correlations with last glacial (Devensian) interstadial sites are limited because of the paucity of dates. The speleothem growth frequency record provides a well-dated terrestrial chronology for the past 140,000 yr B.P., which directly reflects regional palaeoclimatic conditions in Britain, and should prove very useful in unravelling the complex stratigraphy of the Devensian and Ipswichian stages.
Evidence for Wisconsinan Glaciations in the Verrill Canyon Area, Scotian Slope
Authors: Mosher David C. , Piper David J. W. , Vilks Gustavs V. , Aksu A. E. , Fader Gordon B.
Published: December 2004

A composite thickness of about 25 m of sediment has been cored from the Verrill Canyon on the Scotian Slope. It is interpreted that the majority of this sequence was deposited in a glaciomarine environment during oxygen isotopic stage 2 and the top of stage 3. These sediments, as seen in high-resolution seismic reflection profiles, are well stratified, become thicker upslope, are laterally variable in thickness, and pass upslope into possible outer shelf tills. Three wedge-shaped units of incoherent reflections interfinger with the parallel reflections and terminate in water depths greater than 700 m. These wedge-shaped units are interpreted as slumped diamict and outwash deposits. The age of the uppermost wedge-shaped unit is 26,000–21,000 yr based on extrapolation of radiocarbon dates. This unit documents a late Wisconsinan glacier readvance on the outer Scotian Shelf. The underlying wedge-shaped unit, estimated to be 70,000 yrs old, extends further west along the continental slope, and may represent a more extensive early Wisconsinan ice advance. A third wedge-shaped unit, inferred to have formed during isotopic stage 6, is possibly a remnant of the first glaciation in the study area.
Clay-Mineral Assemblages from Late Quaternary Deposits on Vancouver Island, Southwestern British Columbia, Canada
Authors: Blaise Bertrand
Published: December 2004

On Vancouver Island, the Dashwood Drift, Cowichan Head Formation, Quadra Sand, and Vashon Drift were deposited during late Pleistocene glacial and interstadial periods and show large variations in clay-mineral contents partly related to changing climatic conditions. Glacial deposits are characterized by iron-rich chlorite, illite (both well crystallized), and smectite with a morphology reflecting rapid derivation from volcanic rocks. The clay mineralogy of nonglacial deposits is more complex, and is marked by the presence of vermiculite, kaolinite, halloysite, and irregular mixed-layer minerals. Nonglacial clay minerals are poorly preserved and show a higher state of alteration due to pedogenesis. Large variations in nonglacial deposits compared to glacial deposits are also due to secondary factors such as selective sorting, soil and rock source variations, differences in sedimentary environment, and diagenesis. These secondary factors do not seem to obliterate significantly the climatic imprint on the clay minerals. These studies also permit the recognition of glacially reworked sediments, the determination of relationships between two units in the same section, and the establishment of the conditions of clay-mineral formation.
Tree-Ring Evidence for Climatically Effective Volcanic Eruptions
Authors: Scuderi Louis A.
Published: December 2004

Ringwidth variations from temperature-sensitive upper timberline sites in the Sierra Nevada show a marked correspondence to the decadal pattern of volcanic sulfate aerosols recorded in a Greenland ice-core acidity profile and a significant negative growth response to individual explosive volcanic events. The appearance of single events in the mid-latitude tree-ring record, in connection with ice-core evidence from the arctic and historical records from the Mediterranean, indicates that the majority of these events represent climatically effective volcanic eruptions, producing temperature decreases on the order of 1°C for up to 2 yr after the initial eruption. Clusters of climatically effective volcanic events may serve as a trigger to glaciation and are consistently associated with lowered ringwidths and late-Holocene glacier advance in the Sierra Nevada. The tree-ring record strongly suggests forcing of solar radiation receipt and temperatures by increased volcanic aerosols, especially during the Recess Peak advances and Matthes (Little Ice Age) advances from 1400 to 1850 A.D. Intervals with an absence of significant volcanic aerosol production or historically documented eruptive activity correspond to intervals of significantly increased indexed ringwidth values, minimal numbers of severe annual negative ringwidth anomalies, and an absence of glacial deposits in the southern Sierra Nevada.
Palynology of Oxygen Isotope Stage 6 and Substage 5e from the Cover Beds of a Marine Terrace, Taranaki, New Zealand
Authors: Bussell M. Royd
Published: December 2004

Cover beds on uplifted Quaternary marine terraces in the Taranaki-Wanganui area of New Zealand include organic deposits which yield abundant pollen. In the west at Ohawe, marine shore platform deposits are overlain by laterally extensive lignites and laharic breccia, interbedded with alluvium and capped by tephra-rich loess. Following a time of presumably interglacial marine deposition on the platform, a long period of glacial climate is suggested by pollen floras dominated by grass and shrubland taxa. Trees were sparse, but the abundance of podocarps, Nothofagus, and tree ferns increased during at least one interval, suggesting minor climatic amelioration. Near the top of the section, a major change in regional vegetation is recorded by a dominance of pollen derived from podocarp-hardwood forest taxa, including Ascarina, interpreted as indicating a fully interglacial climate. The marine platform, previously assigned to oxygen isotope substage 5e, is now placed in stage 7. The overlying deposits were deposited during glacial stage 6, while interglacial substage 5e is recorded by sediment and pollen assemblages near the top of the section.
Holocene Glacier Variations of Blåisen, Hardangerjøkulen, Central Southern Norway
Authors: Neshe Atle , Dahl Svein Olaf
Published: December 2004

A 1-m-deep gully section 460 m beyond the maximum Little Ice Age marginal moraines of Blåisen, Hardangerjøkulen, central southern Norway, revealed alternations of minerogenic and organic sediments. The geographical/geological settings of the dated section provides a unique on/off signal of Holocene glacier fluctuations of Blåisen. Lithostratigraphy, sediment characteristics, and radiocarbon dates from the study section indicate one period of glacier (re)advance between the late Preboreal deglaciation of the inland ice sheet and 8660 ± 100 yr B.P. A grey sand layer 56–57 cm below the surface is interpreted to be of fluvial/colluvial origin and is radiocarbon dated to about 7700 yr B.P. At 48 cm below the surface, a bluish-grey sand/silt layer is radiocarbon dated to 7590 ± 12 yr B.P. (6560–6240 B.C.) and interpreted to be glaciofluvial origin. A minor glacier oscillation postdates 1130 ± 70 yr B.P. (810–990 A.D.). The Medieval/Little Ice Age glacier advance of Blåisen beyond its modern extent occurred after 1040 ± 60 yr B.P. (960–1030 A.D.). Calculations of the modern and Little Ice Age equilibrium-line altitudes (ELAs) on Hardangerjøkulen suggest an ELA depression of ca. 130 m during the Little Ice Age maximum.
Late Quaternary Evolution of a Fjord Environment in Preservation Inlet, New Zealand
Authors: Pickrill Richard A. , Fenner Julianne M. , McGlone Mathew S.
Published: December 2004

High-resolution seismic profiles, as well as sedimentological and micropaleontological analyses of three cores, are used to reconstruct the environmental and sedimentological evolution of Preservation Inlet, the southernmost New Zealand fjord. Toward the end of the last glaciation, a series of deep oligotrophic lakes, impounded by shallow sills, occupied Preservation Inlet. Glaciers filled the headwater valleys and the vegetation consisted of a sparse cover of grass, scrub, and shrubs. The principal rivers discharged into the head of these lakes forming large sandy deltas, while finely laminated clays were deposited in the distal basins. As the climate started warming ca. 18,000 yr B.P., the snowline rose and glaciers retreated. Developing forests were dominated by Metrosideros and Cyathea fringed by coastal shrubland. In the now more productive lakes, a rich freshwater fauna developed, sedimentation rates increased, and organic mud accumulated. Under rapidly rising sea level, between 9500 and ca. 8000 yr B.P., the sills enclosing the lakes were successively overtopped. Marine water intruded into the fjord basins and flooded the deltas at the head of the lakes. By 6500 yr B.P. sea level had stabilized and the fjord assumed its present condition. Shrubs decreased in abundance and forests dominated by Weinmannia and Dacrydium cupressinum then developed. A forest dominated by Nothofagus fusca spread between 2000 and 1500 yr B.P., indicating a cooler climate. In Preservation Inlet and other New Zealand fjords, eustatic sea-level rise has been greater than isostatic rebound or tectonic uplift. Coastal inundation has resulted in a transgressional sequence from a limnic to marine environment. This contrasts with fjord coasts of the northern hemisphere where isostatic rebound has produced coastal emergence, or coastal emergence followed by submergence.
A multiple process solution to the logical problem of language acquisition
Authors: MACWHINNEY BRIAN
Published: December 2004

Many researchers believe that there is a logical problem at the centre of language acquisition theory. According to this analysis, the input to the learner is too inconsistent and incomplete to determine the acquisition of grammar. Moreover, when corrective feedback is provided, children tend to ignore it. As a result, language learning must rely on additional constraints from universal grammar. To solve this logical problem, theorists have proposed a series of constraints and parameterizations on the form of universal grammar. Plausible alternatives to these constraints include: conservatism, item-based learning, indirect negative evidence, competition, cue construction, and monitoring. Careful analysis of child language corpora has cast doubt on claims regarding the absence of positive exemplars. Using demonstrably available positive data, simple learning procedures can be formulated for each of the syntactic structures that have traditionally motivated invocation of the logical problem. Within the perspective of emergentist theory (MacWhinney, 2001), the operation of a set of mutually supportive processes is viewed as providing multiple buffering for developmental outcomes. However, the fact that some syntactic structures are more difficult to learn than others can be used to highlight areas of intense grammatical competition and processing load.
Overgeneralizations, competition, and recovery: solving the logical problem with positive evidence
Authors: LI PING
Published: December 2004

It would seem to be incomplete for any introduction to language acquisition to leave the ‘logical problem of language acquisition’ untouched – in fact, it would seem to be logical to just start the introduction with the logical problem. MacWhinney lays out a proposal here that attempts to dismantle the logical structure of the logical problem: there is no logical problem, if we consider carefully (a) the actual input that children receive from parents, and (b) the mechanisms that children use to handle possible pitfalls in extracting grammar from the input.