Peter Molnar

1. A big controversy in geodynamics concerns how mantle lithosphere, the cold top part of the mantle below the crust, can be removed, as seems to have happened beneath many mountain belts and high plateaus. Presumably this occurs by some form of convective instability, for cold mantle lithosphere is thought to be denser than the hotter material beneath it. Changes in the styles of crustal deformation across much of Asia changed beginning near 10-15 millions years ago, as if a common process underlay all of these changes. We seek tests of the hypothesis that surface of the Tibetan Plateau rose and by doing so, it applied increased pressure to the surroundings, much as occurs when the level in a water tower rises. One current objective is to determine if Tibet’s surface did indeed rise at that time; we hope to exploit tools of organic biogeochemistry to determine past surface temperatures, which we will use to infer past elevations. We also examine seismological constraints on the deep structure to determine whether there is evidence that blobs of mantle lithosphere have dripped from remaining thinned lithosphere.

2. Regarding ice ages, we are pursuing the hypothesis that the emergence of islands in Indonesia altered Canadian climate enough to permit ice sheets to grow there. The line of logic includes many steps: (1) islands attract rainfall; (2) enhanced rainfall leads to a warmer upper troposphere; (3) which strengthens atmospheric circulation, like the Walker Circulation; (4) islands have emerged in Indonesia over the past 5 Myr; (5) the Walker Circulation may have strengthened since that time, and transformed eastern tropical Pacific sea-surface temperatures from El Niño-like and warm, to the cooler, more La Niña-like as now; (6) during El Niño events, Canada is warm enough to melt last winter's snow, but during La Niña such melting occurs less readily. So, more islands in Indonesia may have have gradually cooled Canada, and thus enabled winter snow to survive cooler summers than before. Toward this end, we are pursuing an understanding of how islands attract rainfall.  

This work has led too to a digression: an understanding of what enabled large mammals suddenly, 2-3 million years ago, to pass from North (or South) America through the Isthmus of Panama and then into South (or North) America. The isthmus seems to have been emergent since 15-20 million years ago. The hypothesis we pursue is that recurring ice ages and continental ice sheets on Canada cooled and aridified the jungles of Panama to make them more like savannas, though which the mammals passed. 

3.  Most models that include global warming call for increased Indian monsoon rainfall, but over the past 30 years, as the globe has warmed, Indian monsoon rainfall has decreased.  Although much work has been done with the goal of predicting monsoon rainfall amounts, Balaji Rajagopalan and I have focused on early and late seasons, when farmers plant and harvest crops. We have been pursuing known influences, like the El Niño-Southern Oscillation and heating over Tibet, with some success. We plan to introduce additional possible influences, such as sea surface temperatures in the Indian Ocean, as well as refine how we treat other boundary conditions.