ABRUPT DISRUPTIONS OF MONSOON CONVECTION IN CENTRAL AMERICA OVER THE LAST GLACIAL PERIOD RECORDED IN SPELEOTHEM RECORDS FROM GUATEMALA

Understanding natural variability of monsoon rainfall is crucial to predict future monsoon changes. As such, paleoclimate records from the tropics and subtropics provide unequivocal information of past monsoon changes against which climate model results can be tested. Proxy records from monsoon domains like East Asian and South American Summer Monsoon indicate a unified, global-scale monsoonal response to precession cycles of insolation on orbital-to-millennial timescales, defined as the Global Paleo-Monsoon. However, other monsoon locations do not show an obvious local orbital-insolation forcing, highlighting the strong regional features of each monsoon domain. In Central America, for instance, integrated marine and terrestrial hydroclimate proxies exhibit markedly diverse records, hampering a determination of how internal ocean-atmosphere dynamics and forcing mechanisms operate on paleoclimate timescales. Here, we present a new speleothem oxygen-isotope (δ¹⁸O) record from Guatemala and discuss potential mechanisms controlling the Central America Monsoon (CAM) strength over the last ~130 thousand years. Our preliminary data are partially correlated to autumn orbital insolation 15°N, and largely decoupled from the orbital summer curve. Abrupt positive δ¹⁸O excursions of ca. 3-4 permil (‰) are observed during MIS 5b, 5a-4 transition, as well as during MIS 3 and 2, and are interpreted as weak monsoon intervals (WMIs) when convection was less intense. These intervals are synchronous with periods of autumn insolation minima, lower greenhouse gases (i.e., CO₂, CH₄) concentrations, but variable ice volume. Furthermore, some WMIs are synchronous to some North Atlantic cold events (i.e., Heinrich events and Greenland stadials). We argue that orbital-to-millennial monsoon convection in Central America is controlled by coupled external (insolation) and internal (abrupt North Atlantic cold events and changes in boundary conditions) forcing, and respond to stability threshold conditions that can cause abrupt monsoon disruptions in both warm and cold climate states.