Simultaneous determination of stable carbon, oxygen, and hydrogen isotopes in cellulose.

A technological development is described through which the stable carbon-, oxygen-, and nonexchangeable hydrogen-isotopic ratios (δ(13)C, δ(18)O, δ(2)H) are determined on a single carbohydrate (cellulose) sample with precision equivalent to conventional techniques (δ(13)C 0.15‰, δ(18)O 0.30‰, δ(2)H 3.0‰). This triple-isotope approach offers significant new research opportunities, most notably in physiology and medicine, isotope biogeochemistry, forensic science, and palaeoclimatology, when isotopic analysis of a common sample is desirable or when sample material is limited.

Climate change as the dominant control on glacial-interglacial variations in C3 and C4 plant abundance.

Although C4 plant expansions have been recognized in the late Miocene, identification of the underlying causes is complicated by the uncertainties associated with estimates of ancient precipitation, temperature, and partial pressure of atmospheric carbon dioxide (PCO2). Here we report the carbon isotopic compositions of leaf wax n-alkanes in lake sediment cores from two sites in Mesoamerica that have experienced contrasting moisture variations since the last glacial maximum. Opposite isotopic trends obtained from these two sites indicate that regional climate exerts a strong control on the relative abundance of C3 and C4 plants and that in the absence of favorable moisture and temperature conditions, low PCO2 alone is insufficient to drive an expansion of C4 plants.

A 14,000-year oxygen isotope record from diatom silica in two alpine lakes on Mt. Kenya.

Oxygen isotopes are sensitive tracers of climate change in tropical regions. Abrupt shifts of up to 18 per mil in the oxygen isotope ratio of diatom silica have been found in a 14,000-year record from two alpine lakes on Mt. Kenya. Interpretation of tropical-montane isotope records is controversial, especially concerning the relative roles of precipitation and temperature. Here, we argue that Holocene variations in delta(18)O are better explained by lake moisture balance than by temperature-induced fractionation. Episodes of heavy convective precipitation dated approximately 11,100 to 8600, 6700 to 5600, 2900 to 1900, and <1300 years before the present were linked to enhanced soil erosion, neoglacial ice advances, and forest expansion on Mt. Kenya.

On the arid margin: the relationship between climate, humans and the environment. A review of evidence from the highlands of central Mexico.

There has long been speculation as to the relationship between climate, humans and the environment. Until recently, however, it has proved difficult to establish the degree to which these factors are interlinked. Here we draw on evidence that has recently emerged from a series of investigations in central México to evaluate the long-term human impact on the environment and to establish the impact that late Holocene changes in the climate have had on the indigenous populations that lived on the arid frontier of Mesoamerica. Data from these studies indicate that: 1) the indigenous peoples of central México had a significant and often detrimental impact on the landscape, causing widespread land degradation; 2) The onset of anthropogenic accelerated erosion coincided with the introduction of sedentary agriculture in this region; 3) Fluctuations in the climate of central México over the last 4,000 years have had a significant impact on the subsistence strategies of the population which extended its territory into the northern arid lands during wetter periods, but rapidly abandoned these areas when the climate became drier.