Reid A. Bryson

Late- and postglacial climatic change in the northern Midwest, USA: Quantitative estimates derived from fossil pollen spectra by multivariate statistical analysis

Abstract Canonical correlation analysis provides a means of reconstructing quantitative time series of past climatic variables during the last 15,000 years from fossil pollen spectra collected at three sites in the northern Midwest. This multivariate statistical technique was applied to a spatial array of modern pollen and climatic data in order to derive a set of mathematical transfer functions. These transform the fossil pollen spectra directly into quantitative estimates of past climatic values. The basic sequence of climatic events that is reconstructed is in general agreement with previous studies of postglacial climates in the Midwest, but quantitative estimates for certain of the variables, e.g., temperature and precipitation, are given for the first time. Fossil pollen from three cores collected from lakes in Wisconsin and Minnesota allow a preliminary reconstruction of past east-west and north-south gradients of the climatic variables. Because changes in the circulation patterns in midlatitudes are the principal mechanism causing fluctuations in temperature and precipitation, past records of the atmospheric circulation are reconstructed along with records of temperature and rainfall. The time series derived show that the most pronounced climatic change indicated in Wisconsin and Minnesota occurred at the end of the Pleistocene (the beginning of the Holocene). This change is particularly evident in the climatic variables related to temperature, which rose ca. 3.3°C. A decrease in snowfall also occurred. During the Holocene, the most marked change appears in the results from Kirchner Marsh, where the amount of dry western air began to increase and the precipitation to decrease about 9500 B.P. A reversal of these changes occurred about 5000 B.P. In contrast, relatively little change occurred among the reconstructed values from Wisconsin; a marked east-west precipitation gradient, therefore, developed in this region of the Midwest from 9500 to 5000 B.P.

Holocene variations of monsoon rainfall in Rajasthan

Two reconstructed histories of the monsoon rainfall in Rajasthan show that the monsoon was weak or absent in latest glacial time. With the advent of Holocene climatic patterns, fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history. The two reconstructions, separated by only 150 km, have some features in common and some striking differences. Both show maximum monsoon amounts in the early Holocene, with a roughly two-thirds decrease to the present. Both show salinization in sub-Boreal time. Both show long intervals of near complete desiccation in the last four millennia. The shorter term variations, however, are not closely parallel. These shorter term variations may be explained in terms of the behavior of the present day interannual variability.

Synoptic Climatology of the Arizona Summer Precipitation Singularity

Using the percent of climatological stations reporting rain as a measure of the raininess of a particular day in Arizona, a large increase in rainfall within a few days is found to occur about July...

Dating climatic episodes of the Holocene

Abstract Monitoring evidence indicates that the Holocene embraced a sequence of rather discrete climatic episodes. The transitions between these environmental episodes apparently were abrupt and globally synchronous. This paper reports on statistical analyses of radiocarbon dates associated with environmental change and cultural change. Over 800 14C dates associated with pollen maxima and minima, sea level maxima and minima, and top and bottom surfaces of peat beds were simultaneously analyzed to identify times of globally synchronous environmental discontinuities. Some 3700 14C dates associated with 155 cultural continua of the world were collectively analyzed to identify worldwide synchroneities in appearance and termination of the cultures. Significant globally synchronous discontinuities were identified in each independent analysis. The dates of environmental and cultural discontinuities are rather similar, particularly during the recent half of the Holocene. The fact that the cultural discontinuities mostly follow rather closely those of the paleobotanical record suggests that there has been a distinct climatic impact on the cultural history of man.

Volcanic Activity and Climatic Changes

Radiocarbon dates of volcanic activity suggest variations that appear to be related to climatic changes. Historical eruption records also show variations on the scale of years to centuries. These records can be combined with simple climatic models to estimate the impact of various volcanic activity levels. From this analysis it appears that climatic prediction in the range of 2 years to many decades requires broad-scale volcanic activity prediction. Statistical analysis of the volcanic record suggests that some predictability is possible.

possibilities of major climatic modification and their implications: Northwest India, a case for study

On the basis of field observations and theoretical studies it is believed that the dense pall of local dust over northwestern India and West Pakistan is a significant factor in the development of s...

Radiocarbon and Soil Evidence of Former Forest in the Southern Canadian Tundra.

Radiocarbon dating of charcoal on podzols along a transect reaching 280 kilometers north of the present tree line from Ennadai Lake indicates that former forests were burnt about 3500 years ago and again about 900 years ago. These forests probably were associated with periods of relatively mild climate.

Paleosols and the forest border in Keewatin, N.W.T.

Abstract The morphology of paleosols and radiocarbon-dated charcoal from buried surface horizons of soils provide evidence to suggest that between periods of northward forest encroachment tundra climate has dominated areas at least 50 km south of the present forest/tundra border in southwest Keewatin. The present forest/tundra border climate is nearly as severe as any climate that has prevailed in the area since deglaciation.

Northern Hemisphere Airstream Regions

Abstract Near-surface airstream source regions of the Northern Hemisphere have been identified using 16-year mean resultant winds from 3° latitude by 3° longitude grids. Tracing the airstreams back to their divergent centers reveals 19 different sources during various seasons of the year. Five of these sources(air originating over the North and South Pacific and Atlantic Oceans and air over Turkey) are resident in the Northern Hemisphere 12 months of the year. Another three (central Asian, Arctic and central East Asian air) exist for at least 11 months per year. The remaining 11 source regions are present from 1–9 months per year and their area of influence is much less than that of the 5 year-long sources. In the mean, there are several favored locations for frontal zones, e.g., a north–south band in Mexico (dividing Atlantic from Pacific air), a north–south band in northern South America, and two northeast–southwest trending bands over the cast coasts of Asia and North America, representing the mean lea...

Late quaternary volcanic modulation of Milankovitch climate forcing

SummaryA preliminary global volcanicity index time series was developed from the total available record of radiocarbon dated eruptions. This was combined with a previously developed simple model of Pleistocene glaciation based on the integral of the seasonal contrast of hemispheric irradiance. The combined integral gave a modeled glacial volume time-series which matched both the general variation of glacial volume in the last forty thousand years and the short-term events as well. Particularly well-modeled were the Alleröd-Younger Dryas-Two Creeks complex of Late Glacial events and the Cochrane stillstand.From this time-series was derived an ice albedo series which was combined with the calculated irradiance to drive a hemispheric heat budget model to obtain time series of monthly hemispheric surface temperatures. The climatic episodes depicted by these time series match the known field data quite well. Indeed the modeling of the “Little Ice Age” and other features suggest that most of the century-to-millennia events are driven by variations in volcanicity.ZusammenfassungVon der Gesamtheit der erhältlichen Aufzeichnungen radiokarbon-datierter Ausbrüche wurde eine vorläufige globale Vulkanitätsindex-Zeitreihe erstellt. Diese wurde mit einem früher entwickelten, einfachen Modell der Pleistozänvereisung, das auf dem Integral des jahreszeitlichen Kontrasts der hemisphärischen Einstrahlung basiert, kombiniert. Das so kombinierte Integral ergab ein Modell der Zeitreihe des Eisvolumens, das sowohl den allgemeinen Schwankungen (des Eisvolumens) in den letzten 40 000 Jahren als auch kurzfristigen Ereignissen Rechnung trug. Besonders gut wiedergegeben waren der Allerod-Younger-Dryas-Two-Creeks-Komplex der jüngeren Eiszeit und der Cochrane-Stillstand.Von diesen Zeitreihen wurde eine Eisalbedo-Zeitreihe abgeleitet, die in Kombination mit der errechneten Einstrahlung die Aufstellung eines hemisphärischen Wärmebilanzmodells erlaubte und somit Zeitreihen des Monatsmittels hemisphärischer Oberflächentemperatur. Die klimatischen Episoden, die in diesen Zeitserien dargestellt sind, passen recht gut zu den bereits bekannten Felddaten. Tatsächlich läßt die Modellierung der „Kleinen Eiszeit“ und anderer Erscheinungen vermuten, daß die meisten Ereignisse im Zeitraum von Jahrhunderten bis Jahrtausenden durch Schwankungen der Vulkanität gesteuert werden.