Christina Ravelo

Out of the tropics: the Pacific, Great Basin lakes, and late Pleistocene water cycle in the western United States

Changing Rains The water cycle of the western United States has varied dramatically across the glacial cycles of the Pleistocene, possibly because of changes in the tracks of the storms that deliver moisture to the region. Lyle et al. (p. 1629) present evidence from a collection of Great Basin lakes which show that water levels rose over the last 20,000 years because of moisture transported from the tropical Pacific, not from a southward diversion of the westerly storm track. Furthermore, the timing of the lake level highs in the Great Basin shows a progression from south to north that does not coincide with the northward progression of wet intervals. Precipitation source regions for western North America changed substantially over the last deglaciation. The water cycle in the western United States changed dramatically over glacial cycles. In the past 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation has been hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.

Determining Priorities for a New International Ocean Drilling Program: Integrated Ocean Drilling Program New Ventures in Exploring Scientific Targets (INVEST); Bremen, Germany, 23–25 September 2009

A multidisciplinary, international community meeting was held in Germany to define the research goals of the new Integrated Ocean Drilling Program (IODP) New Ventures in Exploring Scientific Targets (INVEST) program. The meeting, attended by 584 participants from 21 countries and more than 200 institutions and agencies, featured 12 keynote lectures and 50 working groups. Participants defined five innovative research directions that are central to the study of the Earth system and that require ocean drilling. First, climate change impacts can be studied through ocean drilling. The study of long-term climate change impacts on the environment is only possible through examination of the geologic record. Meeting attendees agreed that future ocean drilling is essential to the study of cryosphere dynamics and sea level change. Drilled ocean sediments will provide critical high-fidelity records of marine and terrestrial ecosystem responses and feedbacks to climate change. Ocean drilling is vital to studies of long-term changes in the hydrologic cycle as they relate to greenhouse gas and other forcings and to studies of the processes that account for abrupt climate changes and climate extremes.