Links between Late Cenozoic Paleoclimates and Human History
Gerald H. Haug, Geological Institute, ETH Zürich, Switzeralnd
Larry C. Peterson, RSMAS Miami, USA
Gergana Yancheva, Jens Mingram, GFZ Potsdam
Daniel M. Sigman, Princeton University, USA
Ralf Tiedemann, AWI Bremerhaven, Germany
A unifying theme in paleoclimate research is well summarized by a piece of advice that I once heard the late Sir Nicolas Shackleton give to an audience of paleoceanographers: "Whatever you do, do it in high resolution." The underlying message, I believe, is that much 'noise' in geologic records is actually composed of meaningful environmental signals. A central goal is to use new approaches and techniques that do justice to the complexity of geologic records, in order to allow previously hidden signals to emerge.
On the millennial to subdecdal timescale, climate archives with an appropriate memory are anoxic marine basins and lakes. In the anoxic Cariaco Basin off northern Venezuela, millimeter to micrometer-scale geochemical data in the laminated sediments of the Cariaco Basin have been interpreted to reflect variations in the hydrological cycle and the mean annual position of the Intertropical Convergence Zone (ITCZ) over tropical South America during the past millennia. These data with decadal to (sub)annual resolution show that the Terminal Collapse of the Classic Maya civilization occurred during an extended dry period from 700 to 900 AD. Data of comparable quality and resolution have been extracted from sediments of lake Huguang Maar in coastal southeast China. The record indicates a stronger winter monsoon prior to the Bølling-Allerød warming, during the Younger Dryas, and during the middle and late Holocene, when cave stalagmite oxygen isotope data indicate a weaker summer monsoon. A remarkable similarity in the records of ITCZ migration in east Asia and the Americas from 700 to 900 AD raises the possibility that the coincident declines of the Tang Dynasty in China and the Classic Maya in Central America were catalyzed by the same ITCZ migrations. Comparison of our records with the Chinese dynastic history suggests that drought played a role in the terminations of Dynasties during the past 4000 years.
On the Cenozoic timescale, the Ocean Drilling Program (ODP) has provided key archives for detailed paleoclimate reconstructions. The Pliocene warm interval, from 4.6 to 2.73 Ma, is the most recent time in Earth's history when the world was 2-3 degree C warmer than the Holocene, the last 10 thousand years during which human population has flourished. We report that a major climate-related change in high-latitude ocean productivity, which occurred 2.7 million of years ago and has persisted to today, had a surprisingly rapid onset. Anthropogenic warming that returns temperatures to those of the warm Pliocene should be expected to return the high North Pacific diatom flux of that time, with unknown consequences for regional climate, fisheries, and ocean/atmosphere carbon flux. And the data reported here indicate no reason that this could not happen within the 21st century.