Le Geotop - Dr. Prosenjit Ghosh : Reversal of rainfall seasonality... (4-5-2017)

Dr. Prosenjit Ghosh : Reversal of rainfall seasonality... (4-5-2017)

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Dr. Prosenjit Ghosh (Centre for Earth Sciences, Indian Institute of Science)

Reversal of rainfall seasonality during the northward drift of India During Late Cretaceous warm world

Jeudi 4 mai 2017 à 13h30/ Thursday, May 4, 2017, 1:30pm

Local PK-7605, 201 ave. Président-Kennedy, UQAM

Résumé / Abstract :

The Cretaceous greenhouse climate is thought to have been accompanied by major changes in Earth’s hydrological cycle, but detailed hydroclimate reconstructions for this anomalously warm period are rare.  Here I will show that the δ18O of calcitic shells of Villorita cyprinoides (Black Clam) from the modern day Cochin estuary, southern India, together with CO2 clumped isotope ratios (Δ47), record changes in water temperature (SST) and  δ18O reflecting the seasonal pattern of the Indian summer monsoon.  Analysis of Δ47 in the Early Maastrichtian well preserved fossil mollusc, Phygraea vesicularis, from the Kallankuruchi Formation in southern India shows that local SSTs were 3-5°C warmer during the Cretaceous at ~30°S latitude.  However, SST and water δ18O were correlated directly, indicating maximum storm activity and rainfall in winter, similar to the climate at ~30°S today.  Our findings suggest that mid-latitude atmospheric circulation patterns may not have been altered significantly by Cretaceous global warming. However, the seasonal temperature and precipitation recorded in our observation was bimodal – much different from Today.