The tropics are the main source of the atmosphere's sensible and latent heat, and water vapour, and are therefore important for reconstructions of past climate. But long, accurately dated records of southern tropical palaeoclimate, which would allow the establishment of climatic connections to distant regions, have not been available. Here we present a 210,000-year (210-kyr) record of wet periods in tropical northeastern Brazil--a region that is currently semi-arid. The record is obtained from speleothems and travertine deposits that are accurately dated using the U/Th method. We find wet periods that are synchronous with periods of weak East Asian summer monsoons, cold periods in Greenland, Heinrich events in the North Atlantic and periods of decreased river runoff to the Cariaco basin. We infer that the wet periods may be explained with a southward displacement of the Intertropical Convergence Zone. This widespread synchroneity of climate anomalies suggests a relatively rapid global reorganization of the ocean-atmosphere system. We conclude that the wet periods probably affected rainforest distribution, as plant fossils show that forest expansion occurred during these intermittent wet intervals, and opened a forest corridor between the Amazonian and Atlantic rainforests.

Eight fluorescent dyes (amino G acid, photine CU, fluorescein, lissamine FF, pyranine, rhodamine B, rhodamine WT, and sulpho rhodamine B) were compared in laboratory and field experiments to assess their utility in quantitative tracing work. The properties considered included sensitivity and minimum detectability, the effect of water chemistry on dye fluorescence, photochemical and biological decay rates, adsorption losses on equipment and sediments, toxicity to man and aquatic organisms, and cost. The orange fluorescent dyes are more useful than the blue and green because of the lower background fluorescence at the orange wave band, which permits higher sensitivities to be obtained. Pyranine fluorescence is strongly affected by pH over the range encountered in natural waters, which precludes its simple use in quantitative work. Amino G acid, photine CU, pyranine, and fluorescein all have high photochemical decay rates. Pyranine, lissamine FF, and amino G acid are the dyes most resistant to adsorption, but rhodamine WT, fluorescein, and sulpho rhodamine B also have moderately high resistance. Rhodamine B is readily adorbed by most materials. Rhodamine WT (orange), lissamine FF (green), and amino G acid (blue) are the three tracer dyes recommended; they may be used simultaneously to trace three injection sites with the filter combinations suggested. 1972]. Of the commonly used fluorescent dyes, fluorescein (Colour Index (CI)45350 [Society of Dyers and Colourists, 1971]) has been used since the end of the nineteenth cent•ury [Dole, 1906]. It is visibly detectable in low concentrations but has very poor stability under sunlight. Thus in the early 1960's, when workers in the United States and Japan were assessing fluorescent dyes for quantitative tracing work in surface waters, they adopted the equally fluorescent dye rhodamine B (CI 45170 [Pritchard and Carpenter, 1960]). However, it became apparent that rhodamine B was readily adsorbed onto sediments, and subsequently, sulpho rhodamine B (CI 45100) was introduced. Although this dye was resistant to adsorption, it was comparatively expensive and was later replaced by the cheaper Copyright ¸ 1976 by the American Geophysical Union. Paper number 6W0149. dye rhodamine WT, which was developed specifically for tracing work (U.S. patent 3, 367, 946). Reynolds [1966] used the green dye pyranine (CI 59040) for tracing percolation water because it was very resistant to adsorption. Recently, a group of' blue fluorescent dyes, known as optical brighteners because of their use in whitening paper, textiles, and other off-white products, have been applied to water tracing [Glover, 1972].There has been a little previous work on the suitability of rhodamine WT for water tracing, but considerably more data are available for fluorescein, sulpho rhodamine B, and rhodamine B. However, much of this information cannot be directly compared between one study and another because of differences in experimental techniques. Furthermore, little work has been presented on the use of pyranine, the...

A long record of atmospheric 14 C concentration, from 45 to 11 thousand years ago (ka), was obtained from a stalagmite with thermal-ionization mass-spectrometric 230 Th and accelerator mass-spectrometric 14 C measurements. This record reveals highly elevated Δ 14 C between 45 and 33 ka, portions of which may correlate with peaks in cosmogenic 36 Cl and 10 Be isotopes observed in polar ice cores. Superimposed on this broad peak of Δ 14 C are several rapid excursions, the largest of which occurs between 44.3 and 43.3 ka. Between 26 and 11 ka, atmospheric Δ 14 C decreased from ∼700 to ∼100 per mil, modulated by numerous minor excursions. Carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle.

2004. Quaternary ecological and geomorphic changes associated with rainfall events in presently semi-arid northeastern Brazil.ABSTRACT: Several geomorphic features and palaeobiotic remains in now semi-arid northeastern Brazil indicate major palaeoenvironmental changes during past periods of increased rainfall. 230 Th mass spectrometric ages of speleothems and travertines have allowed the determination of the timing and duration of wetter than present conditions. The data demonstrate that wet events have occurred throughout much of the Pleistocene, present dry conditions having been established at the end of the Younger Dryas. A markedly different fauna comprising megafaunal elements not adapted to the present low arboreal scrubland caatinga vegetation existed in the area. Palaeobotanical remains embedded in travertine indicate forested vegetation at these wetter intervals, suggesting that the caatinga was then replaced or mixed with a semi-deciduous forest. Due to the abundance of travertine sites containing fossil botanical remains in northeastern Brazil, it is believed that forest expansion occurred over large areas of the now semi-arid zone, showing that the long hypothesised forested links between biodiversity-rich Amazon and Atlantic rainforests may indeed have existed during these moister phases.

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