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Abstract: Lake Estancia''s transition from a Big Dry episode during the first half of the Mystery Interval to a Big Wet episode during the second half has equivalents in records from across the planet. At the time of this transition, Chinese monsoons experienced pronounced weakening, closed-basin lakes in both the Great Basin of the western United States and in the southern Altiplano of South America underwent a major expansion, mountain glaciers in Southern Hemisphere middle latitudes had retreated, and the rates of increase of CO2 and of δ18O in Antarctic ice underwent a decrease. Finally, the precipitous drop in dust rain over Antarctica and the Southern Ocean terminated as did a similar drop in the 13C to 12C ratio in atmospheric CO2. These changes are consistent with a southward shift of the thermal equator. The cause of such a shift is thought to be an expansion of sea ice caused by a shutdown in deep water production in the northern Atlantic. This creates a dilemma because a similar southward shift is an expected consequence of the Heinrich event #1 which initiated the Mystery Interval. [Copyright &y& Elsevier]

Abstract We measured U/Ca ratios, 4He concentrations, 234U/238U, and 238U/235U in a subset of well-preserved aragonitic scleractinian fossil corals previously described by Gothmann et al. (2015). Comparisons of measured fossil coral He/U ages with the stratigraphic age demonstrate that well-preserved coral aragonite retains most or all of its radiogenic He for 10's of millions of years. Such samples must be largely or entirely free of alteration, including neomorphism. Measurements of 234U/238U and 238U/235U further help to characterize the fidelity with which the original U concentration has been preserved. Analyses of fossil coral U/Ca show that the seawater U/Ca ratio rose by a factor of 4–5 between the Early Cenozoic and today. Possible explanations for the observed increase include (1) the stabilization of U in seawater due to an increase in seawater [CO 3 2−], and a resulting increase in UO 2 -CO 3 complexation as originally suggested by Broecker (1971); (2) a decrease in the rate of low-temperature hydrothermal alteration from Early Cenozoic to present, leading to a diminished U sink and higher seawater [U]; or (3) a decrease in uranium removal in reducing sediments, again leading to higher seawater [U]. [ABSTRACT FROM AUTHOR]