A long marine history of carbon cycle modulation by orbital-climatic changes

Pacing of the marine carbon cycle by orbital forcing during the Pliocene and Pleistocene Ice Ages [past 2.5 million years (Myr)] is well known. As older deep-sea sediment records are being studied at greater temporal resolution, it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late Mesozoic and Tertiary, despite the absence of large continental ice sheets over much of this time. Variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing, and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change. For the past 35 Myr, much of the variance in carbonate content carries the “polar” signal of obliquity [41,000 years (41 kyr)] forcing. Over the past 125 Myr, there is evidence from marine sediments of the continued role of precessional (≈21 kyr) climatic cycles. Repeat patterns of sedimentation at about 100, 400, and 2,400 kyr, the modulation periods of precession, persistently enter into marine carbon cycle records as well. These patterns suggest a nonlinear response of climate and/or the sedimentation of organic carbon and carbonates to precessional orbital perturbations. Nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects. Nonlinearities in the carbon cycle may have transformed orbital-climatic cycles into long-wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean.

Two terrestrial records of rapid climatic change during the glacial–Holocene transition (14,000– 9,000 calendar years B.P.) from Europe

Two independent multidisciplinary studies of climatic change during the glacial–Holocene transition (ca. 14,000–9,000 calendar yr B.P.) from Norway and Switzerland have assessed organism responses to the rapid climatic changes and made quantitative temperature reconstructions with modern calibration data sets (transfer functions). Chronology at Kråkenes, western Norway, was derived from calibration of a high-resolution series of 14C dates. Chronologies at Gerzensee and Leysin, Switzerland, were derived by comparison of δ18O in lake carbonates with the δ18O record from the Greenland Ice Core Project. Both studies demonstrate the sensitivity of terrestrial and aquatic organisms to rapid temperature changes and their value for quantitative reconstruction of the magnitudes and rates of the climatic changes. The rates in these two terrestrial records are comparable to those in Greenland ice cores, but the actual temperatures inferred apply to the terrestrial environments of the two regions.

Malaria’s Eve: Evidence of a recent population bottleneck throughout the world populations of Plasmodium falciparum

We have analyzed DNA sequences from world-wide geographic strains of Plasmodium falciparum and found a complete absence of synonymous DNA polymorphism at 10 gene loci. We hypothesize that all extant world populations of the parasite have recently derived (within several thousand years) from a single ancestral strain. The upper limit of the 95% confidence interval for the time when this most recent common ancestor lived is between 24,500 and 57,500 years ago (depending on different estimates of the nucleotide substitution rate); the actual time is likely to be much more recent. The recent origin of the P. falciparum populations could have resulted from either a demographic sweep (P. falciparum has only recently spread throughout the world from a small geographically confined population) or a selective sweep (one strain favored by natural selection has recently replaced all others). The selective sweep hypothesis requires that populations of P. falciparum be effectively clonal, despite the obligate sexual stage of the parasite life cycle. A demographic sweep that started several thousand years ago is consistent with worldwide climatic changes ensuing the last glaciation, increased anthropophilia of the mosquito vectors, and the spread of agriculture. P. falciparum may have rapidly spread from its African tropical origins to the tropical and subtropical regions of the world only within the last 6,000 years. The recent origin of the world-wide P. falciparum populations may account for its virulence, as the most malignant of human malarial parasites.