Sources Of Paleoclimatic Information

Many natural systems are dependent on climate where evidence of such systems in the past still exists, it may be possible to derive paleoclimatic information from them. By definition, such proxy records of climate all contain a climatic signal, but that signal may be relatively weak, embedded in a great deal of extraneous noise arising from the effects of other (non-climatic) influences. The proxy material has acted as a filter, transforming climatic conditions at a point in time, or over a...

Coral Records Of Past Climate

The term coral is generally applied to members of the order Scleractinia, which have hard calcareous skeletons supporting softer tissues (Wood, 1983 Veron, 1993). For paleoclimatic studies, the important subgroup is the reef-building, massive corals in which the coral polyp lives symbiotically with unicellular algae (zoo-xanthellae) these are known as hermatypic corals (as opposed to ahermatypic, which contain no algal symbionts and are not reef-builders). The algae produce carbohydrates by...

Dry Fallout

Ice melting and Erosion Lacustrine Sediments FIGURE 3.21 Schematic diagram of the 2l0Pb global cycle, illustrating the source, transport, deposition, and post-depositional, redistribution processes (from Preiss et al., 1996). amount of ionizing radiation that the sample has been exposed to over time, from surrounding sediments. The decay of radioisotopes in the surrounding matrix produces free electrons in the mineral grains, which become trapped at defects in the crystal lattice the longer the...

High Temperature

Reduced net tomata closure during day Less production of cell parts and substances Possible changes in- production of s, growth regulators Less food translocated and., stored throughout the tree Increased - consumption of foods LESS POTENTIAL FOR RAPID CAMBIAL GROWTH (to A) FIGURE 10.5 A schematic diagram showing how low precipitation and high temperature before the growing season may lead to a narrow tree ring in arid-site trees (Fritts, 1971). lated with a number of different climatic factors...

Faunal Assemblage Paleoclimatology

FIGURE 6.19 Venn diagram illustrating conditions that are ideal (top) and nonideal (bottom) for calibrating a transfer function. In an ideal situation, the calibration data set C encompasses the range of all biological and environmental conditions that exist in the down-core data set D. In a non-ideal situation the calibration data set C does not reflect all the biological and environmental conditions that are represented within the down-core data set D and a no-analog condition results (shaded...

Within The Column

Current vectors, temperature, and salinity FIGURE 12.2 Schematic diagram illustrating how the atmosphere and ocean are divided into columns in a typical coupled general circulation model experiment. Ocean and atmospheric grid sizes are commonly different. Computations take place simultaneously for all grid boxes at all specified levels (McGuffie and Henderson-Sellers, 1997). are too small to be represented by even a 2 x 2 grid spacing. In such cases, the process is represented in a simplified...

I

FIGURE 5.27 Schematic diagram to illustrate the potential problems caused by flow boudinage on the interpretation of two adjacent ice cores due to the pinching out of layers. period certainly represent some sort of large-scale climatic process, but the differences between GRIP and GISP2 cores at greater depth point to possible disturbances in one or both of the cores. One way to resolve the problem is to look for evidence of inclined or disturbed layering in the core stratigraphy at depth...

Upton Warren Interstadial Beetles

FIGURE 8.6 Changes in majo'r vegetation zones in rocky areas of central-south Nevada over the past 22,000 yr, as recorded by macrofossils in the middens of packrats. Dashed lines indicate the approximate elevation of ecotones.The pygmy conifer pinon-juniper woodland desert scrub transition varied from wet to dry sites, as indicated by the broad ecotone Spaulding, 1990 . Insects are the most abundant class of animals on Earth and representatives of the group can be found in virtually every type...

Lakelevel Fluctuations

Throughout the arid and semiarid part of the world, there is commonly no runoff surface water discharge to the oceans. Instead, surface drainage may be essentially nonexistent in areic regions or it may terminate in interior land-locked basins where water loss is almost entirely due to evaporation endoreic regions . In these basins of inland drainage Fig. 7.18 , changes in the hydrological balance as a result of climatic fluctuations may have dramatic effects on water storage. During times of...

Dating Methods Involving Chemical Changes

Hiatella Arctica

Two general categories of dating methods are based on chemical changes within the samples being studied since they were emplaced. The first involves amino-acid analysis of organic samples, generally used to assess the age of associated inorganic deposits. The method may also be used to estimate paleotemperatures from organic samples of known age. The second category encompasses a number of methods that assess the amount of weathering that an inorganic sample has experienced. They are primarily...

Quantitative Paleoclimatic Reconstructions Based On Pollen Analysis

Pollen Transfer Function

Paleoclimatic reconstruction from fossil pollen spectra is based on the notion that, as vegetation distribution is largely determined by climate, it should be possible to use that distribution as represented in the fossil pollen spectra to reconstruct past climate. Large databases of surface pollen samples generally from the surface sediments of lakes are now available for many parts of the world see Appendix B and these have enabled pollen assemblages to be calibrated directly in terms of...

Cpdb

14c Suess Effect

A change in 814C of only l o i.e., a change in 813C of 0.5 o corresponds to an age difference of -8 yr. Consequently, if two contemporaneous samples differed in 813C by 25 o, they would appear to have an age difference of -400 years Olsson and Osadebe, 1974 . To avoid such confusion, it has been recommended that the 13C value of all samples be normalized to -25 o, the average value for wood. By adopting this reference value, comparability of dates is possible. This is particularly important in...

Former Vegetation Distribution From Punt Macrofossils

Ferrel Cell

It is not uncommon for plant macrofossils to be found far beyond the range of the particular species today. Where climatic controls on present-day plant distributions are known, their former distribution may be interpreted paleoclimatically, from dated macrofossils. Fluctuations of three major biogeographical boundaries have been studied in considerable detail using macrofossils the arctic treeline the alpine treeline and the lower or dryness treeline of semiarid and arid regions. In each case,...

Antarctic Bottom Water

Core V28 238 Image

Globorotalia tumida Globorotalia menardii ' Globigerinoides ruber Sphaeroidinella dehiscens' Pulleniatina obliguiloculata Globorotalia tumida Globorotalia menardii ' Globigerinoides ruber Sphaeroidinella dehiscens' Pulleniatina obliguiloculata 5000 FIGURE 6.34 Changes In percentage abundance of several diagnostic planktonic foraminifera in equatorial Atlantic core tops with increasing water depths due to differential dissolution.The more corrosive Antarctica Bottom Water dissolves poorly...

Climate And Climatic Variation

FIGURE 2.16 Variations of eccentricity, obliquity, precession, and the combination of all three factors ETP over the last 800,000 years with their principal periodic characteristics indicated by the power spectrum to the right of each time series upper diagram . Below is the time series of July solar radiation at 10, 65, and 80 N expressed as departures from A.D. 1950 values . Note that the radiation signal at high latitudes is dominated by the 41,000 year obliquity cycle whereas at lower...

Paleotemperature Records From Alkenones

Alkenone Glacial Cycles

Certain marine phytoplankton of the class Prymnesiophyceae, most notably the coccolithophorid Emilyania huxleyi, respond to changes in water temperature by altering the molecular composition of their cell membranes. Specifically, as water temperature decreases, they increase the production of unsaturated alkenones ketones . Cells contain a mixture of long-chain alkenones with 37, 38, or 39 carbon atoms n-C37 to n-C39 , which are either di- or tri-unsaturated designated for example, as C37.2 and...

Yearly Pollen Influx

Paleoclimatology Maps

8 years represented by 1 cm thickness 50 000 grains deposited on a cm2 surface each year 25 years represented by 1 cm thickness 800 grains deposited on a cm2 surface each year FIGURE 9.8 Examples of pollen influx pollen flux density calculations from measurements of pollen concentration and the rate of accumulation of the sediment matrix Davis, 1963 . 1993b R. S. Webb et al., 1993 . Consequently, pollen flux density studies have taken a back seat to pollen percentages in most modern...

Ocean Circulation Changes And Climate Over The Last Glacialinterglacial Cycle

Analysis of 813C and Cd Ca in benthic foraminifera and 8lsO in planktic forams reflecting temperature and or salinity changes in surface waters have enabled circulation changes to be reconstructed over the last glacial-interglacial cycle in some detail longer-term changes in 813C are examined by Raymo et al. 1990 . These studies indicate that significant changes in the thermohaline circulation of the oceans have occurred. Although production and circulation of NADW was similar to today in the...

Dissolution Of Deepsea Carbonates

Aragonite Compensation Depth

Throughout the deep ocean basins of the world, a major factor affecting preservation of carbonate tests is the rate of dissolution at depth. The oceans are predominantly undersaturated with respect to calcium carbonate at all depths below the upper mixed layer the zone above the thermocline Olausson, 1965, 1967 . After death of the organisms, deposition of the test on the ocean floor leads to dissolution in the undersaturated water Adelsack and Berger, 1977 . Pteropod tests composed of calcium...

Marine Sediments and Corals

6.2 Paleoclimatic Information from Biological Material in Ocean Cores 193 6.3 Oxygen Isotope Studies of Calcareous Marine Fauna 198 6.3.1 Oxygen Isotopic Composition of the Oceans 199 6.3.2 Oxygen Isotope Stratigraphy 206 6.3.4 Sea-level Changes and hlsO 215 6.4 Relative Abundance Studies 216 6.5 Paleotemperature Records from Alkenones 233 6.6 Dissolution of Deep-sea Carbonates 236 6.7 Paleoclimatic Information from Inorganic Material in Ocean Cores 242 6.8 Coral Records of Past Climate 247...

Snowlines And Glaciation Thresholds

In regions of permanent snow accumulation, it is possible to identify an altitudinal zone separating the lower region of seasonal snow accumulation from the upper region of permanent snow. The term zone is used because from year to year the actual boundary or snowline will vary in elevation, depending on the particular FIGURE 7.9 Paleotemperature reconstruction for Europe based on periglacial features right column compared to other long proxy data records Maarleveld, 1976 . FIGURE 7.9...

Stable Isotope Analysis

1h218o 1h2h16o Hdo

The study of stable isotopes primarily deuterium and 180 is a major focus of paleodimatic research. Most work has been on stable isotope variations in ice and firn, and in the tests of marine fauna recovered from ocean cores. However, increasing attention is being placed on other natural isotope recorders, such as speleothems FIGURE 5.1 Location of principal ice-coring sites in the Canadian Arctic and Greenland, and in Antarctica. FIGURE 5.1 Location of principal ice-coring sites in the...

Timescales Of Climatic Variation

Climate varies on all timescales and space scales, from interannual climatic variability to very long-period variations related to the evolution of the atmosphere and changes in the lithosphere. Examples of known climatic fluctuations are shown in Fig. 2.14. In this diagram, each row represents an expansion, by a factor of ten, of each interval on the row above it. Thus, one can envisage short-term high-frequency variations nested within long-term lower-frequency variations Webb, 1991 ....

Loess Deposition And Paleoclimate

Magnetic Susceptibility Austria Loess

Loess is a deposit of wind-blown silt that blankets large areas of the continents. It is characteristically creamy-brown in color and calcareous, consisting predominantly of quartz feldspars and micas Pye, 1984, 1987 . Geographically, loess is extensive in the North American Great Plains, south-central Europe, Ukraine, central Asia, China, and Argentina Fig. 7.1 . In North America, loess deposits are related to formerly extensive outwash deposits from the Laurentide ice sheet and to the...

Lake Windermere Interstadial

Chelford Interstadial

FIGURE 8.7 Reconstructed July paleotemperatures based on insect remains in areas of the southern and central British Isles since the last Ipswichian interglacial. Annual temperature ranges are also shown Coope, l977b .The period before 50,000 yr B.R dashed line is very uncertain and there may have been a more gradual, monotonic decline in temperature from 120,000 yr B.R to 60,000 yr B.P. any climatic amelioration Coope, 1975b . Evidently the Coleoptera were sufficiently mobile that they could...

Thermohaline Circulation Of The Oceans

Thermohaline Circulation

Circulation of water at the ocean surface is largely a response to the overlying atmospheric circulation which exerts drag at the surface. However, circulation of deeper waters in the oceans of the world is a consequence of density variations, which result from differences in temperature and salinity brought about by sensible and latent heat fluxes, precipitation, and runoff at the ocean surface this is termed the thermohaline circulation. In areas where surface waters become relatively dense,...

Speleothems

World Karst Distribution

Speleothems are mineral formations occurring in limestone caves, most commonly as stalagmites and stalactites, or slab-like deposits known as flowstones. They are composed primarily of calcium carbonate, precipitated from ground water that has percolated through the adjacent carbonate host rock. Certain trace elements may also be present often giving the deposit a characteristic color one of these, uranium, can be used to determine the age of a speleothem, as discussed in what follows....

Radiocarbon Years Bp

Desert Regions The United States

FIGURE 8.1 A reconstruction of Holocene treeline fluctuations in southwestern Keewatin, Northwest Territories, Canada.Treeline position is based on radiocarbon-dated tree macrofossils in situ north of the present treeline, and on dates on buried forest and tundra soils north and south of the modern treeline Sorenson and Knox, 1974 . more extensive boreal forest zone show an additional warming of 1 C in summer and 4 C in spring. This was the result of higher net radiation due to lower albedo...

The Climate System

Although it is common to consider climate as simply a function of the atmospheric circulation over a period of time, to do so overlooks the complexity of factors that determine the climate of a particular region. Climate is the end-product of a multitude of interactions between several different subsystems the atmosphere, oceans, biosphere, land surface, and cryosphere which collectively make up the climate system. Each subsystem is coupled in some way to the others Fig. 2.3 such that Changes...

Info

Specmap Stack Mis

FIGURE 6.14 Schematic diagram illustrating the relationship between orbital forcing and the signal that is eventually preserved in the sedimentary record. then to examine the coherency spectrum of the tuned record with the spectrum of orbital forcing at frequencies other than those used in the tuning procedure. In the tuned records obtained by Imbrie et al., 1984 , coherency was not only very high in the tuning bands but also in the -100 ka eccentricity band, which was not used in tuning at...

How Rapidly Does Vegetation Respond To Changes In Climate

Paleoclimatology Maps

An important question that arises in studies of high resolution e.g., varved sediments is What is the lag response of vegetation to climate change Can the pollen record provide information on short period, large amplitude changes in climate, or to put the question more generally What are the frequency response characteristics FIGURE 9.3 Generalized vegetation map of eastern North America and isopoll maps of selected taxa and groups of taxa at 500 yr B.P. Contours shown are 5 and 10 for forbs,...

Paleomagnetism

Paleomagnetism Magnetic Dip

Variations in the Earth's magnetic field, as recorded by magnetic particles in rocks and sediments, may be used as a means of stratigraphie correlation. Major reversals of the Earth's magnetic field are now well known and have been independently dated in many localities throughout the world. Consequently, the record of these reversals in sediments can be used as time markers or chronostratigraphic horizons. In effect, the reversal is used to date the material by correlation with reversals dated...

Paleoclimatic Reconstruction From Long Quaternary Pollen Records

Pollen Diagram Grande Pile

There are now numerous palynological records that span the late Quaternary and, in some cases, extend back continuously into the Pliocene. Dating is, of course, problematic beyond the range of radiocarbon dating 40,000 yr in most cases and often the records are simply assumed to extend back to the last interglacial, and beyond, based on the character of the pollen record itself. In some cases, correlation with marine oxygen isotope stratigraphy, either directly in marine sedimentary records or...

Isotope Dendroclimatology

Meteoric Water Latitude

Many studies have demonstrated empirically that variations in the isotopic content of tree rings 813C, 8lsO, and 82H are in some way related to climate.33 Early studies used whole wood samples but some studies now suggest that latewood may need to be isolated from earlywood to get a clear signal of climatic conditions in the growth year Switsur et al., 1995 Robertson et al., 1995 . In mid- and high latitudes, there is a positive relationship sensu lato between the oxygen and hydrogen isotopic...

Fundamentals Of Dendroclimatology

Resin Duct Wood

A cross section of most temperate forest trees will show an alternation of lighter and darker bands, each of which is usually continuous around the tree circumference. These are seasonal growth increments produced by meristematic tissues in the tree's cambium. When viewed in detail Fig. 10.1 it is clear that they are made up of sequences of large, thin-walled cells earlywood and more densely packed, thick-walled cells latewood . Collectively, each couplet of earlywood and latewood comprises an...

A I Calculation of Radiocarbon Age and Standardization Procedure

Tropical Deserts

Although it is not necessary for a user of radiocarbon dates to know, in detail, how the actual value is arrived at, some understanding of the procedure is enlightening, particularly when considering adjustments for 14C fractionation effects see Section 3.2.1.4c . The whole subject is a complex sequence of calibrations, adjustments, and corrections. The following brief explanation is offered for the adventurous. In order to make dates from different laboratories comparable, a standard material...

Paleoclimatic Information From Biological Material In Ocean Cores

Calcareous Foram Test

Paleoclimatic inferences from biogenic material in ocean sediments derive from assemblages of dead organisms thanatocoenoses , which make up the bulk of all but the deepest of deep-sea sediments biogenic ooze . However, thanatocoenoses are generally not directly representative of the biocoenoses assemblages of living organisms in the overlying water column. For example, selective dissolution of thin-walled specimens at depth see Section 6.6 , differential removal of easily transported species...

Radioisotopic Methods

Spontaneous radioactive decay by the loss of nuclear particles a or 3 particles and, as a result, they may transmute into a new element.5 For example, 14C decays to 14N, and 40K decays to 40Ar and 40Ca. Furthermore, the decay rate is invariant so that a given quantity of the radioactive isotope will decay to its daughter product in a known interval of time this is the basis of radioisotopic dating methods. Providing that the radioisotope clock is started close to the stratigraphically relevant...

Biological Dating Methods

Rhizocarpon Geographicum Growth Curve

Biological dating methods generally use the size of an individual species of plant as an index of the age of the substrate on which it is growing. They may be used to provide minimum age estimates only, as there is inevitably a delay between the time a substrate is exposed and the time it is colonized by plants, particularly if the surface is unstable e.g., in an ice-cored moraine . Fortunately this delay may be short and not significant, particularly if the objective is simply establishing a...

Paleoclimatic Reconstruction From Ice Cores

Normalised Precipitation

Ice cores have revolutionized our understanding of Quaternary paleoclimatology by providing high resolution records of many different parameters, recorded simultaneously at each location. Here, we highlight the main results from the northern and southern hemispheres and show how these records are related to each other, and to changes in forcing. 5.4.1 Ice-core Records from Antarctica A number of long ice-core records are available from Antarctica but the crown jewel of Antarctic ice cores is...

Dating Ice Cores

Cause Younger Dryas

One of the most important problems in any ice-core study is determining the age-depth relationship. Many different approaches have been used and it is now clear that very accurate timescales can generally be developed for at least the last 10,00012,000 yr if accumulation rates are high enough. Prior to that, there is increasing uncertainty about the age of ice, but new approaches are constantly improving age estimates, allowing comparisons with other proxy records to be made with more...

Periglacial Features

Hydrolaccolith Karte

The use of fossil periglacial phenomena as an index of former climatic conditions is limited by two basic problems. First, dating periglacial features directly is often difficult, if not impossible generally they are dated by reference to the deposits within which they are found, thereby obtaining only a maximum age for the features. Secondly, although regions of modern periglacial activity can be circumscribed by particular isotherms, the occurrence of similar activity in the past can only...