Southward Shift of the Pacific ITCZ During the Holocene. Issue 12 (15th December 2018)

• Record Type: Journal Article
• Authors: Sachs, J. P.; Blois, J. L.; McGee, T.; Wolhowe, M.; Haberle, S.; Clark, G.; Atahan, P.
• Is Part Of: Paleoceanography and paleoclimatology. Volume 33:Issue 12(2018)
• Page Start: 1383
• Page End: 1395
• Publication Date: 2018-12-15
• Subjects: Palau -- hydrogen isotopes -- lipid biomarkers -- Holocene -- ITCZ -- hydroclimate; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2018PA003469
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: The Holocene (0–11.7 ka BP) appears warm and stable in ice core and global temperature reconstructions as well as in transient climate simulations. This seeming quiescence of Earth's climate belies large secular changes in seasonal and zonal mean radiation receipts resulting from variations in orbital precession and obliquity. Here we show that the tropical Pacific, a key mediator of global climate, underwent a profound climatic shift during the Holocene. Hydrogen isotope ratios of the algal lipid dinosterol, isolated from marine lake sediments in Palau, increased by 50‰ between 7.7 and 4.5 ka BP, indicating a reduction in precipitation. This implied drying coincided with increased rainfall to the southwest of Palau in Borneo, weakened northern hemisphere monsoons, strengthened southern hemisphere monsoons, and an equatorward shift of terrestrial photosynthesis. A southward shift of the Intertropical Convergence Zone, forced by insolation, is the most likely cause of these climatic and biospheric changes. Plain Language Summary: Rainfall is one of the more difficult climate parameters to reconstruct and, unfortunately, is also poorly represented in mathematical models of climate. The central importance of rainfall to human societies, however, makes it critical that climate models do a better job forecasting precipitation changes. They can be improved by comparing their outputs to past climate states when things like greenhouse gases or solar radiation receipts differed. Toward that end, this study presents a new reconstruction of tropical rainfall spanning the last 10, 000 years, the period since the last ice age ended, from a saltwater lake in Palau in the western tropical North Pacific Ocean. It is based on the ratio of heavy and light hydrogen in a lipid from single‐celled algae preserved in sediment. A large increase of heavy hydrogen 7, 700–4, 500 years ago indicates a significant reduction in rainfall. During this same time monsoon systems of Asia and Africa weakened. The likely cause for these changes was a southward shift of the tropical rain bands in response to changes in Earth's orbital geometry. Climate models now have a new constraint on the tropical precipitation response to changes in solar radiation, which can be used to improve forecasts of future rainfall. Key Points: Hydrogen isotope ratios of microalgal lipids in marine lakes of Palau reflect rainfall changes A 50 per mil increase in the hydrogen isotope ratio of dinosterol between 7.7 and 4.5 ka BP indicates drying of Palau A southward shift of the Intertropical Convergence Zone was the likely cause, supported by increased rainfall south of Palau in Borneo