Pollen‐inferred palaeoclimate reconstruction in the Alps during the Lateglacial and the early Holocene: how to estimate the effect of elevation and local parameters

The modern analogue technique (MAT) was applied to six pollen sequences from the Belledonne Massif (northwestern French Alps) to estimate the effect of altitude and local parameters on pollen‐based climate reconstruction during the Lateglacial and the early Holocene. The six sites (Le Vivier (345 m a.s.l.), Les Etelles (700 m a.s.l.), La Coche (980 m a.s.l.), Montendry (1330 m a.s.l.), Le Grand Leyat (1660 m a.s.l.), La Gouille (1800 m a.s.l.)) are located in different vegetation belts (mixed deciduous woods, conifer woods, alpine pastures with maple). The main vegetation changes in the past are recorded at each site. The evolution of four climate parameters (coldest month temperature, warmest month temperature, mean annual temperature, annual precipitation) was quantitatively inferred from pollen data using MAT. The curves obtained were compared to the Les Etelles site, which was the least affected by non‐local pollen transport. The results show consistent trends for the climate parameters reconstructed at the different sites. However, the reconstruction does not indicate a decrease in temperature values related to the increasing elevation. Difficulties in reconstructing the altitudinal variations of climate parameters from pollen data during the periods studied are discussed and perspectives for improvement are considered. Copyright © 2009 John Wiley & Sons, Ltd.     

Lateglacial and Holocene climate oscillations in the South-western Alps: An attempt at quantitative reconstruction

The high topographic complexity of the Alpine region is the origin of important climate differences that characterise the different areas of the Alps. These differences might have had a strong influence on vegetation and on migrations of human populations in the past. Based on an improved database containing about 3000 modern pollen samples, the standard “Modern Analogue Technique” has been applied to five pollen sequences from the subalpine belt of the South-western Italian Alps (Laghi dell’Orgials, 2240 m, Lago delle Fate, 2130 m, Torbiera del Biecai, 1920 m, Rifugio Mondovì, 1760 m, Pian Marchisio, 1624 m) to provide quantitative climate estimates for the Lateglacial and Holocene periods. Consistent climate trends are reconstructed for the different sequences. Sites recorded in detail the climate variations when they were located at the limit of two ecotones. Sites above the tree line recorded lower temperature values and less important variations. Climate was cold and dry during the Oldest and Younger Dryas and close to present-day values during the Bølling/Allerød interstadial. At the beginning of the Holocene, climate changed to warmer and moister conditions; a high number of climate fluctuations are recorded at several sites. A climate optimum is recorded in the Atlantic period, which caused a development of fir above its present-day altitudinal distribution. Climatic differences recorded at the various sites are discussed taking into account the limits of the method.     

The problem of the Eulerian oscillations: A weakness of numerical versus analytical methods

The application of computer technology has permitted more and more problems of dynamical astronomy to be solved more easily, quickly, and accurately. In this area, numerical integration is often very efficient, and sometimes essential. There is often, however, a temptation to choose numerical integration simply because it is the easiest way to attack the problem. Sometimes this works to the detriment of a satisfactory understanding of the physics of the problem under study. It is particularly the case for the free, or Eulerian, oscillations. The forces that create such a motion are not of gravitational origin and are not even conservative. The theory can only specify the frequencies of oscillation, not their amplitudes nor phases. The case is complicated when the free oscillations interact with gravitationally-forced oscillations, a situation that is almost inevitable, since nothing is isolated in the Universe. The first author has particularly studied this problem in the case of the rotation of the Moon, and published the first credible determinations of the lunar free libration. In this kind of problem, the observations have to be used and care must to be taken to create no spurious free librations in the results by using numerical integrations to describe the other related motions. A differential correction of the starting conditions to fit the observations does not necessarily give any valid information on the real free oscillation contained in the data. An analytical model is necessary, if the goal of the research is to understand the origins and characteristics of an Eulerian oscillation in such a system.