Introduction

The climate of the Western Hemisphere is defined by global wind systems set in motion by temperature contrasts between the poles and the equator. These elements of atmospheric dynamics deliver the moisture and, in part, the temperature regimes and wind stresses that determine the limnology of lakes. This chapter explores the relation between climate and lakes along a transect (the Pole-Equator-Pole: Americas [PEP 1] transect) extending from Alaska to southern Patagonia, and it extrapolates past climate states from their sediment records. The probable causes of limnoclimatic changes relative to altered glacial global wind systems remain speculative, but a coherent synthesis demands that all elements of the puzzle fit into a picture that is at least as focused as individual lake chronologies allow.

Limnological histories as revealed by paleontologi-cal and sedimentological proxies from lake sediment sequences form complex and detailed, often site-specific, records of limnoclimatic change at potentially high resolution. As such, they do not provide unequivocal evidence for deciphering interhemispheric changes in global climate dynamics. A considerable danger exists of over- or misinterpreting a lake record in terms of climate, particularly global climate (e.g., as forced by insolation), when, in fact, only local circumstances have caused proxy variations. The only suitable approach to answering large-scale questions from such fine-scale records is to look for spatial and temporal consistencies among site records that demand overarching explanations related to climate dynamics at regional to hemispheric scales. This is the approach we attempt to use. It will become evident that the number of suitable sites is still too few to develop particularly coherent interhemispheric linkages of past-climate changes in required detail. Nevertheless, the outlines of the major full and late glacial climatic interactions can be seen from intersite comparisons. It is hoped that such comparisons will stimulate further research into the question of past-climate interactions.

There are basically three ways in which insolation and the atmosphere—generally through the distribution, temporal residence, and interaction of air masses—significantly affect lakes: (1) by governing the amount and seasonality of moisture sources, including loss of moisture through evaporation and lags in moisture delivery as a result of snow accumulation and sub sequent melting; (2) by controlling the annual and seasonal variations in temperature as determined by distribution, interaction, and residence times of air masses; and (3) by directing the amount and seasonality of wind stress as related to temperature gradients and the residence or passage of air masses. Interpretation of paleolimnological records should seek such generalized causal (?) climate-based relations if lake records are to contribute significantly to the understanding of climate change.

Lakes respond to climate changes affecting water balance (precipitation and evaporation related to winds and temperature) by rising and falling and (or) by becoming fresher or more saline. These changes can be complicated by the interplay between surface- and groundwater sources of differing chemistry and volumes and by loss of lake water to the groundwater system. Variable lags between snowmelt and runoff also have important consequences to lake biology. Temperature obviously affects the amount and seasonality of ice cover in temperate lakes and, therefore, influences stratification, nutrient dynamics, and the life histories of many organisms. Wind, apart from its role in enhancing evaporation, determines the length and strength (depth) of circulation in combination with temperature effects on water density. Wind and runoff characteristics thereby play critical roles in determining the oxygen content and nutrient dynamics of lakes and also can indirectly impact the light regime of lakes by turbidity. Cloud and snow cover can directly vary the amount of light a lake receives.

Although these climate-lake interactions have certainly operated to form the lake records summarized below, rarely has their impact on the record been understood at more than a superficial level. Their effects vary from lake to lake, depending on lake size, depth, morphometry, degree of protection, and surrounding geological terrain. Climatic, biological, and limnologi-cal monitoring are prerequisites to full paleoclimatic interpretation of lake records. Unfortunately, paleoclimate studies without a paleolimnological focus— pollen records, for example—rarely provide even minimal descriptive information about the limnological character of the investigated site. Without such information, dutifully recorded abundances of aquatic microfossils (Pediastrum, Botryococcus, Isoetes, Myriophyl-lum, etc.) become difficult or impossible to properly interpret in either paleolimnological or paleoclimatic terms.

The records summarized in Section 16.2 represent a selection of sites between Alaska and southern Patagonia that lie near the western margin of North and South America (Fig. 1). Site selection aims at highlighting climate changes related to or buffered by the Pacific

FIGURE 1 Locations of sites with paleolimnological records spanning full and (or) late glacial through early Holocene environments. Letter designations indicate lake or site name: Z, Zagoskin Lake; K, Klamath Lake; La, Lake Lahontan; O, Owens Lake; E, Lake Estancia; Ba, Cuenca de Babicora; P, Lago de Pátzcuaro; Q, Laguna Quexil; Y, La Yeguada; Li, Laguna Los Lirios; V, Lago de Valencia; F, Laguna de Fúquene; S, Laguna Surucucho; J, Lago de Junín; T, Lago Titicaca; U, Salar de Uyuni; Le, Laguna Lejía; Be, Salinas del Bebedero; CL, Laguna Cari Laufquen; Ca, Lago Cardiel.

FIGURE 1 Locations of sites with paleolimnological records spanning full and (or) late glacial through early Holocene environments. Letter designations indicate lake or site name: Z, Zagoskin Lake; K, Klamath Lake; La, Lake Lahontan; O, Owens Lake; E, Lake Estancia; Ba, Cuenca de Babicora; P, Lago de Pátzcuaro; Q, Laguna Quexil; Y, La Yeguada; Li, Laguna Los Lirios; V, Lago de Valencia; F, Laguna de Fúquene; S, Laguna Surucucho; J, Lago de Junín; T, Lago Titicaca; U, Salar de Uyuni; Le, Laguna Lejía; Be, Salinas del Bebedero; CL, Laguna Cari Laufquen; Ca, Lago Cardiel.

Ocean in an attempt to simplify, if possible, climate-lake relations along the PEP 1 transect. Although the summary is not exhaustive, most major records have been included. Their spotty distribution may guide future research to key areas for more complete coverage. Many records lack sufficient chronological control to build a particularly strong case for climate-mediated limnologic change at high resolutions. Nevertheless, most records document distinct limnological modes associated with full glacial, late glacial, and early Holocene environments. These variable and sometimes detailed records, based on assorted paleolimnological evidence, have been interpreted generally in terms of presumed climate controls on lake character. The age control on all figured lake records is in thousands of radiocarbon years before present.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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