Lysanna Anderson

Modern pollen/climate calibration for southern South America

Abstract Using the response surface technique a modern pollen/climate calibration is presented for the mid-latitudes in southern South America between latitudes 39°S and 44°S, extending from the west coast in Chile across the Andes into the Patagonian steppe region. The climate parameters identified that relate to the present-day pollen distribution of the nine most important pollen types ( Nothofagus dombeyi -type, Nothofagus obliqua -type, Podocarpus , Weinmannia , Caldcluvia / Eucryphia -type, Cupressaceae, Myrtaceae, Misodendrum and steppe-types) are summer precipitation, summer and winter temperatures. Using the modern pollen/climate data set, three fossil pollen records (Mallin Aguado and Lago Moreno, east of the Andes, and Caunahue, west of the Andes) are interpreted in terms of these three seasonal climate parameters. Despite intervals of no-analog fossil pollen assemblages, the reconstruction shows similar climate trends on both sides of the Andes during the last 21 000 cal. yr BP (17 000 yr BP), with summer precipitation as low or markedly lower than today prior to 17 000 cal. yr BP (14 500 yr BP), as high or higher than today between 15 000 and 12 500 cal. yr BP (12 500 and 10 500 yr BP), and again lower than today between 12 500 and 8000 cal. yr BP (10 500 and 7200 yr BP). Summer and winter temperatures were low (or high) when summer precipitation was high (or low).

Fire history of Patagonia: clima te versus human cause

Human societys concern about future environmental changes in response to both natural forcings, such as climate, and ever increasing human impact can only be addressed if the interaction between the natural and man-made forcings are fully understood. One parameter that lends itself for such analysis is fire. The historical record is toa short and ambiguous to provide data adequate to discriminate between natural and man-induced changes in fire frequencies. Paleoenvironmental records, inclusive of both the historic and the prehistoric past, can provide an appropriate data set with which to address this question. These data include paleoclimate reconstructions, pollen, and charcoal records from dated sediment sections, and information on past human impact derived from historical and archaeological evidence. The Patagonian region is well suited for such a study because of its climatic diversity, its wide range of ecosystems, and the adaptation of its ecosystems to fire. Records from latitudes 36o to 55oS suggest that although prehistoric human activities may have amplified extent of fires, climate played the central role. Changes in patterns of climate variability were particularly important. Whenever variability was high, during the late glacial and the late Holocene, fires were abundant. Late glacial variability is probably related to fluctuations in the extent of Antarctic sea-ice which in turn influences the latitudinal position of the westerly stormtracks; late Holocene variability, on the other hand, is related to the influence of El Nino/Southern Oscillation

Paleoclimate, Paleoclimate history of the Arctic

Although the Arctic occupies less than 5% of the Earths surface, it includes some of the strongest positive feedbacks in the climate system. Reconstructing the climate history of the Quaternary requires a suite of climate proxies that can be placed in a secure time frame. Most Arctic proxies reflect past summer temperatures, although a subset is sensitive to winter temperatures and/or precipitation. During the Quaternary, the Arctic has experienced a greater change in temperature, vegetation, and ocean surface characteristics than has any other Northern Hemisphere latitudinal band. Arctic temperature amplification is a consequence of several strong positive feedbacks. They include the fast feedbacks of snow and ice albedo, sea-ice insulation, vegetation, and permafrost, as well as a suite of slower responding feedbacks operating on glacial–interglacial timescales tied to the growth and decay of aerially extensive, thick continental ice sheets. Large changes in Arctic temperatures impact regions outside the Arctic through their proximal influence on the planetary energy balance and circulation of the Northern Hemisphere atmosphere and ocean, and with potential global impacts through changes in sea level, the release of greenhouse gases, and impacts on the oceans meridional overturning circulation. Quantitative paleoclimate reconstructions for specific cold and warm times during the Quaternary suggest that Arctic temperature changes have been 3 to 4 times the corresponding hemispheric or globally averaged changes. This article provides a brief overview of climate changes leading up to the last ice age, then overviews the changes in Arctic climate during the Quaternary.