Hydroclimate of subtropical Mexico since the last glacial maximum and evaluation of some Pacific and Atlantic forcings

Abstract : The northern Mexico forms parts of subtropical North America and receives most of its annual rainfall during the summer and autumn months. An early summer precipitation peak is associated with the North American Monsoon (NAM) and Tropical cyclones (TC) originating in the Pacific and Atlantic Oceans contribute moisture during the late summer and autumn. We reconstruct paleoclimate of the western and eastern parts of subtropical Mexico since the Last Glacial Maximum (LGM) from chemical composition of sediments deposited in the Santiaguillo Basin and El Potosi Basin located at c.25°N latitude. Both the millennial-scale proxy based paleohydrological records show contrasting dynamics. The latest LGM was characterized by humid conditions in Santiaguillo and arid conditions in El Potosi. During the deglaciation, Santiaguillo received less runoff and El Potosi received more runoff compared to the LGM. The wetter climate of Santiaguillo during the latest LGM was probably related to formation of TC in the eastern North Pacific with restricted rainfall swaths. Formation of TC with expanded rainfall swaths brought more precipitation to a region located at higher latitude and reduced the amounts of runoff into Santiaguillo. NAM was either absent or weaker during both these intervals. During the early Holocene, enhanced NAM as well as TC with expanded rainfall swaths brought more summer and autumn precipitations. We evaluated the paleohydrology of El Potosi with respect to sea surface temperature of the Gulf of Mexico and size of the Atlantic warm pool. The shift from drier LGM to wetter deglaciation occurred as Gulf of Mexico became warmer and more moisture from the Atlantic Ocean was transported into the region. The Atlantic warm pool was either absent or formed intermittently during the latest LGM and deglaciation. Over the Holocene, the Gulf of Mexico remained warmer and AWP gradually expanded in size. This might have modified the cyclone tracks and shifted the wet regime to higher latitudes