Eolian Records In The North American Midcontinent

Full Glacial and Late Glacial Times Loess During the LGM, loess was deposited over much of the North American midcontinent, particularly in the central United States (Fig. 7). Little loess was deposited in Canada during the last glacial period because the FIGURE 7 Map showing the distribution of mostly late Pleistocene loess and mostly Holocene eolian sand in the midcontinent region of North America and inferred paleowinds during the last glacial maximum (LGM). Loess distribution data...

Introduction

Vegetation is one of the most important terrestrial proxies for evaluating climate change. In this chapter, we document vegetation changes during the Holocene in the Americas and discuss the climate signal that vegetation changes imply. The primary data are pollen and macrofossils from lake and peatland sediments. Pollen is a particularly valuable climate proxy because it typically forms a continuous time series and registers the timing and rates of climate change. Macrofossils do not occur as...

Info

AThe numbers correspond to site locations in Fig. 1 (sites 1-37) and Fig. 2 (sites 38-46). aThe numbers correspond to site locations in Fig. 1 (sites 1-37) and Fig. 2 (sites 38-46). er Lake at ca. 4700 B.P., probably by geomorphic means (diversion of the Walker River), yielded a late Holocene record of moisture variation, reconstructed primarily from diatom and ostracode data (Bradbury, 1987 Bradbury et al., 1989). The data indicate low lake levels and high salinity between 2400 and 2000 B.P.,...

Global Modes Of Ssta Variability

After removal of the interannual global ENSO mode (Fig. 2) from the K98 SSTA data, we computed the ordinary (not complex) EOFs of the non-ENSO residuals for the DJF season during the period 1871-1991. The first three leading modes explain 6.1, 5.4, and 3.6 of the residual unfiltered variance after removal of trends. The total 15.1 is comparable to the 13.4 explained by the global ENSO mode for the same season. As frequently occurs when the geographic scale of a data set is much larger than the...

Geomorphic Records Of Paleoclimate

One of the major features that defines the Quaternary period is the appearance of continental ice sheets in the Northern Hemisphere. The earlier assumption was that by documenting global synchroneity of continental ice sheet and mountain glacier movements, one could prove the existence of a single large-scale, global climate forcing. Although historical records document that even on a regional scale glaciers do not respond similarly to climate change, this has been generally ignored on longer...

Abrupt Climate Change and Pre Columbian Cultural Collapse

HODELL, JASON H. CURTIS, MICHAEL F. ROSENMEIER, MICHAEL W. BINFORD, AND MARK B. ABBOTT Holocene climate changes in the circum-Caribbean and Andean Altiplano are inferred by using paleolim-nological methods. Paleoenvironmental data provide a climatic context in which the Maya (Yucat n Peninsula) and Tiwanaku (Bolivian-Peruvian Altiplano) cultures arose, persisted, and collapsed prior to European contact, ca. A.D. 1500. In the circum-Caribbean, the arid late Pleistocene...

Atlantic Ocean

FIGURE 7 The Younger Dryas chron (interval 3) for the Americas deduced from paleovegetation reconstructions, showing the hypothetical southern limit of the influence of cold Arctic air during the Southern Hemisphere summer months. Full circles indicate records where no change is detected. B0lling-Aller0d interval) penetration of polar air masses (Latrubesse and Ramonell, 1994 Bradbury, 1997 Bradbury et al., 2000 Lezine and Denefle, 1997), as presented by the mobile polar high concept of Leroux...

Npp

ANumbers in parentheses give percent confidence level estimates, which are based on correlations with 1000 synthetic time series having first-order autoregressive characteristics of the tree-ring indicators. Lag 0 or lag +1 correlations significant above the 90 level in both calibration periods are in bold. Sensitivity of indicator to local conditions as described by Villalba et al. (2000) CAT, coastal Alaskan temperature NPT, northern Patagonian temperature SWP, southwest U.S. Palmer Drought...

Laguna Carilaufquen Grande

The closed basins of Lagunas Cari-Laufquen Grande and Chica (Fig. 1C) lie in a tectonic depression surrounded by basalt plateaus or mesetas of the Mesozoic to Tertiary age (Coira, 1979). In contrast to Lake Mascardi, this region was not affected by the last glaciation of the Andes. Laguna Cari-Laufquen Grande is located at an elevation of 800 m and is an ephemeral, brackish water body with an average depth of 3.0 m during the rainy season. Mean annual precipitation is ca. 200 mm, falling...

Conclusions

Viewed from this very general, low-resolution perspective, full glacial-early Holocene lake records along the PEP 1 transect (Fig. 22) document only six major interacting climate scenarios (Fig. 23) 1. Unglaciated Arctic lake systems witness progressive warming related to deglaciation by a reduction in the thickness and seasonal extent of ice cover and a concomitant increase in productivity. Additional records could certainly show other climate lake interactions related to changing moisture...

Atmospheric Associations

Superposed on these SST patterns, and interacting with them, are the atmospheric counterparts (and consequences) of the CT and GR SST variations. Regression coefficients relating 500-mbar height anomalies (deviations of the heights of 500 mbar pressure surfaces in the atmosphere from their long-term seasonal averages) to the CT and GR series are shown in Figs. 4a and 4c. Note that regression coefficients are related to correlation coefficients by where p is a regression coefficient, r is the...

Clear Pond Lake Tulane

FIGURE 10 Representative pollen diagrams from the Southeast Clear Pond (Watts et al., 1996) and Lake Tulane (Grimm et al., 1993). FIGURE 10 Representative pollen diagrams from the Southeast Clear Pond (Watts et al., 1996) and Lake Tulane (Grimm et al., 1993). nie (Watts, 1975), and Buck Lake (Watts et al., 1996) in the Florida peninsula are deep lakes with excellent Holocene records. At Buck Lake, which is now over 17 m deep and was dry until after 10,000 B.P., a shallow-water assemblage occurs...

Secular Trends And The Global Enso Mode

One reason for considering secular trends and the global ENSO mode first is that they will be removed from the data prior to analysis of decadal-multidecadal variability. It is also appropriate to discuss them together because of current speculation that global warming may affect ENSO variability (Trenberth and Hoar, 1996). More generally, the characteristics of ENSO, or even its existence (or lack of it) during prehistoric periods, may be dependent on the background climate (Sun, 2000). We...

Synopsis Of Site Records

Zagoskin Lake Norton Sound, Alaska (63.40N, 162.08oW 15 m) Zagoskin Lake occupies a small, circular maar crater (500 m diameter) without significant fluvial input from the surrounding low, peat-mantled, volcanic surface (Ager, 1982). Overall, the geochemical record (e.g., Al) of Zagoskin Lake indicates a complacent lacustrine record with major sediment input from eolian sources (Fig. 2). However, biogenic silica and organic matter that relate to the productivity of the lake system...

F

FIGURE 7 Trajectory of the cold air mass over South America during the intense cold episodes of July 1994. (A) 7 July, (B) 8 July, (C) 9 July, and (D) 10 July. Arrows indicate different pressure levels in the atmosphere. (Adapted from Sanchez and Silva Dias, 1996.) ed with freezes caused by overnight radiative cooling in Florida. They move into the Gulf of M xico or Atlantic Ocean, becoming part of the warm Atlantic subtropical high. The third set of anticyclone paths (Fig. 8C) is associated...

Resumen

Los registros paleoambientales del norte al sur de Am rica desde el ltimo M ximo Glacial muestran cambios ambientales que son similares en el momento y direcci n, a pesar de la diferente extensi n de la cobertura de hielo y la opuesta variaci n estacional de la insolaci n entre los dos hemisferios. El mecanismo particular que conecta las variaciones entre las dos regiones no se comprende a n bien. Nuestro conocimiento de los par metros de control del cambio clim tico global y regional durante...

Chalmers Clapperton And Geoffrey Seltzer

Alpine glaciers respond sensitively to climate change, and records of glacial advance and retreat can be used to assess patterns of climate change in widely disparate areas. Along the Pole-Equator-Pole Americas (PEP 1) transect, maximum glaciation during Marine Isotope Stage 2 (MIS 2) was reached ca. 24,000-20,000 14C B.P. in regions receiving precipitation sufficient to produce an increase in glacial mass balance as global temperatures cooled. Exceptions to this scenario were glaciers that...

Vegetation

Midlatitudes of Western North America The predominance of conifers in western North American forests arose in the middle and late Tertiary period as a result of long-term global cooling, tecton-ism, and changes in atmospheric composition and weathering rates (Barron, 1985 Raymo et al., 1988 Ruddiman and Kutzbach, 1989, 1991). In western North America, summer-dry conditions were intensified with regional tectonism and rain shadow develop ment in the late Tertiary period (Barnosky,...

Pollen Records And Past Neotropical Savanna Environments

Table 1 and Fig. 4 show the relevant pollen sites available for this study and their site characteristics, such as location, 14C age range, number of radiocarbon dates, and references. Today, a few sites are within contact zones or within the forested areas of transition zones. The 32 pollen records listed are located between 7 N and 21 S, extending over a distance of more than 4000 km. 18.3.1.1. Llanos Orientates of Colombia Six radiocarbon-dated pollen records from six lake cores are...

North America

In Alaska, studies of last glaciation advances have been made in the Brooks Range, the Alaska Range, the Alaska Peninsula, and Kodiak Island (Porter et al., 1983 Hamilton and Thorson, 1983 Mann and Peteet, 1994). Radiocarbon dating of organic material associated with glacial and glaciofluvial deposits supports a time-distance diagram presented by Porter et al. (1983, Fig. 4.7) showing two glacial maxima in the Brooks Range during MIS 2, at ca. 24,000-22,000 14C B.P. and 19,500-17,000 14C B.P....

Vera Markgraf And Geoffrey O Seltzer

Instrumental and High-Resolution Records of Recent Climate Change 435 23.3. Climate Change and Human Societies 436 23.4. Geomorphic Records of Paleoclimate 436 23.5. Vegetation and Lake Records 437 23.6. Interhemispheric Climate Linkages 438 Acknowledgments 440 Numbers in parentheses indicate the pages on which the authors' contribution begin. Mark B. Abbott (87) Department of Geosciences, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts 01003-5520 F. S....

Polar Outbreaks And Their Significance In The Climate Of The Americas

South American Polar Outbreaks Synoptic-scale incursions of midlatitude air moving into tropical and subtropical latitudes east of the Andes (leeward side) are observed all year long in two preferred regions the first is located close to the mountains between 20 and 30 S, and the second region is located in southern Brazil, extending into the adjacent Atlantic. In summer (December-February), cold air from higher southern latitudes moves into tropical latitudes behind a cold front and...

Central America And The Circumcaribbean Region

Circum Caribbean

A relatively limited number of paleolimnological records exist for M xico, Central America, and the cir-cum-Caribbean region, between 30 and 8 N latitude. Records for Central America south of M xico are predominantly palynological studies (e.g., Horn, 1993 Islebe et al., 1996 Islebe and Hooghiemstra, 1997) and will not be considered in this chapter (see Grimm et al., 2000). The locations of sites reviewed in this section are shown in Fig. 5. The highest density of Holocene lacustrine records...

The Late Pleistocene Hunters

IN CENTRAL CHILE (11,400-9700 14C B.P.) At the current state of knowledge, the earliest well-dated and widely accepted sites of human occupation in southern South America are Monte Verde MV-II (12,50014C B.P. see Fig. 1) and Piedra Museo (12,890 90 14C B.P.) (Meltzer et al., 1997 Miotti and Cattaneo, 1997). In central Chile, the earliest unambiguous evi- FIGURE 1 Map showing the locations of the archaeological sites in Chile cited in the text. FIGURE 1 Map showing the locations of the...

Late Pleistocene Aridity Regimes In Both Hemispheres And Their Effects On Human Occupation

Faunal remains from late Pleistocene lakes in the lowlands of southern South America show a dominance of mastodons with evidence of human predation dated between 11,000 and 10,000 14C B.P. (Montane, 1968 Varela, 1976 Nunez et al., 1994a,b), resembling the classical kill-butcher sites in North America (Bryan et al., 1978 Saunders, 1980 Graham et al., 1981). On the other hand, the southeastern and southwestern portions of Ontario (Canada) have the highest frequency of mastodons (Mammuthus...

Summary And Conclusions

Although the sample of reasonably well-researched cases where pre-Columbian Middle American societies were affected by explosive volcanism is small, at least some patterns are presented here in a preliminary fashion. The trends or patterns are presented as five factors, each of which is explored for the range of variation seen in the data and is examined for the ways in which it affects the resilience or vulnerability of societies. These factors are demography, experience, adaptation, economy,...

South America

As the Andes extend for more than 7000 km between latitudes 100N and 550S, they cross most of the zonal climate belts between equatorial and cool temperate regions of an entire hemisphere. Because mountain glaciers and ice caps formed throughout this mountain transect during the last glacial cycle (Clapperton, 1983, 1993a,b), chronologies of morainic deposits obtained in key parts of the Andes provide an opportunity to examine the interhemispheric synchrony of glacier advances and, thus,...

South American Lowlands

For South America, records are discussed from the lowlands and the Andes (Fig. 14). 19.4.1. Llanos Orientales (Colombia) Six lake records from the Llanos Orientales (Wijmstra and van der Hammen, 1966 Behling and Hooghiemstra, 1998, 1999, 2000) indicate that the early Holocene land scape was extensive grass savanna with few woody taxa and small areas of gallery forest along and between the rivers. Annual precipitation must have been lower and the annual dry season longer than they are today. In...

Southern Hemisphere

Few detailed Holocene records exist at present for the Southern Hemisphere (Fig. 8). For the northern Altiplano of Bolivia and Peru, dating of paleolake shorelines (Servant and Fontes, 1978 Servant et al., 1995) and sedimentological and ostracode data from cores in the small basin of Lake Titicaca indicate high lake stands during late glacial times and a subsequent decline (Wirrmann and DeOliveira Almeida, 1987 Wirrmann and Mourguiart, 1995), although the timing of the regression is not very...

In The Americas And Their Impact On Regional Agriculture

This section documents how extreme meteorological events such as polar outbreaks can affect human activities. Statistics on coffee and orange production are used as qualitative indicators of long-term climate variability in the region, as related to interhemispheric indicators of polar outbreaks in present-day climates. 3.4.1. Chronology and Impacts of Polar Outbreaks in Coffee-Growing Regions of South America Since the Late Eighteenth Century Coffee was introduced to Brazil from French Guiana...

Signature Of Saharan Dust In Western Atlantic Island Soils

Barbados O Florida Keys Bahamas Age of reef terrace or eolianite (ka) FIGURE 22 Records of dust flux from Saharan Africa to the Americas over glacial-interglacial cycles of the past 500,000 years. Top Oxygen isotope record of foraminifera in deep-sea sediments at site 663A in the Atlantic Ocean showing glacial-interglacial cycles. Middle Accumulation rates of terrigenous sediments at site 663A, interpreted to be a measure of Saharan dust flux to the Atlantic Ocean. Arrows show correspondence...

J F M A M J J Asondj F M A M

FIGURE 5 The correlation function, calculated over the interval 1861-1988, showing the relationships between Santiago de Chile total monthly precipitation and tree-ring width variations at El Asiento in central Chile. Positive correlation indicates that above-average tree growth is associated with above-average values of precipitation. Correlation coefficients greater than 0.18 and 0.24 are significant at the 95 and 99 confidence level, respectively. lected in 1974 by LaMarche (1975). For...

Conclusions For Southern South America

Paleontological, archaeological, and paleoclimato-logical records for south-central and northern Chile suggest a strong relation between late Pleistocene and Holocene changing climates, changing environments, and changing human occupational and cultural patterns. In central Chile, the Paleo-Indian hunters specialized in exploiting Pleistocene megafauna, particularly in places around lakes ecological refuges where natural resources were locally concentrated in an environment under generally...