title: Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y.
abstract: The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18-24 cal ka B.P.) monsoon with similar δ(18)O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9-11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka.
authors.affiliation: Department of Geoscience, University of Nevada, Las Vegas, NV 89154, USA. matthew.lachniet@unlv.edu
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Lachniet
authors.forename: Yemane
authors.initials: Y
authors.lastname: Asmerom
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Bernal
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Polyak
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Vazquez-Selem
mesh_terms: D001267:Atlantic Ocean; D002119:Calcium Carbonate / Q000737:chemistry*; D002250:Carbon Radioisotopes / Q000032:analysis; D059552:Caves / Q000737:chemistry*; D002980:Climate; D049690:History, Ancient; D006813:Humidity; D008800:Mexico; D010103:Oxygen Isotopes / Q000032:analysis; D011891:Rain; D013696:Temperature; D014872:Water Movements
chemical_list: D002250:Carbon Radioisotopes; D010103:Oxygen Isotopes; D002119:Calcium Carbonate
keywords: Sierra Madre del Sur; cave; paleoclimatology; plant domestication; stalagmite