Initiation of a stable convective hydroclimatic regime in Central America circa 9000 years BP

Abstract

Many Holocene hydroclimate records show rainfall changes that vary with local orbital insolation. However, some tropical regions display rainfall evolution that differs from gradual precessional pacing, suggesting that direct rainfall forcing effects were predominantly driven by sea-surface temperature thresholds or inter-ocean temperature gradients. Here we present a 12,000 yr continuous U/Th-dated precipitation record from a Guatemalan speleothem showing that Central American rainfall increased within a 2000 yr period from a persistently dry state to an active convective regime at 9000 yr BP and has remained strong thereafter. Our data suggest that the Holocene evolution of Central American rainfall was driven by exceeding a temperature threshold in the nearby tropical oceans. The sensitivity of this region to slow changes in radiative forcing is thus strongly mediated by internal dynamics acting on much faster time scales.

Persistent Link Between Caribbean Precipitation and Atlantic Ocean Circulation During the Last Glacial Revealed by a Speleothem Record From Puerto Rico

“…This structure is also visible in the δ 13 C and Mg/Ca values (Figure 4), indicating significant changes in regional precipitation amount and convective activity. In agreement with previous hydroclimate reconstructions from the tropical Atlantic realm (Arienzo et al, 2017; Lachniet et al, 2009; Winter et al, 2020) and SST reconstructions from the Caribbean and the Florida Strait (Parker et al, 2015; Them Il et al, 2015), lower (higher) speleothem δ 18 O values during interstadial (stadial) phases are associated with wetter and warmer (drier and cooler) conditions and greater (less) convective rainfall intensity (Figure 6).…”

“…In addition, the modern isotopic amount effect also reflects the seasonally varying moisture sources and rainfall types, that is, convective activity (Govender et al, 2013; Scholl et al, 2009). During drier glacial periods, convective activity may have been weaker (Winter et al, 2020) and moisture recycling more dominant, which would both shift the weighted annual mean of the δ 18 O values of the drip water towards higher values. This would imply that the amount effect was less evident as it is today as suggested by the modern relationship.…”

Investigating Mexican paleoclimate with precisely dated speleothems

“…which is a safe assumption based on monitoring data and an abundance of speleothems that use this interpretation (Lases-Hernandez et al, 2019; Medina-Elizalde, Winter et al, 2020). However, northern Mexico is closer to Texas than it is to the Peninsula, and ẟ 18 Oprecip in Texas is impacted by shifting moisture sources (Wong et al, 2015a).…”

“…show the relationship between Atlantic SST and precipitation in Mesoamerica; for example, there were significantly more hurricanes in the GoM during a positive AMV than a negative phase (Méndez & Magaña, 2010;Poore et al, 2009). A negative AMV (cooler SST) is connected to wetter conditions in northern Mexico and drier conditions in the Yucatán and Central America (Méndez & Magaña, 2010;Winter et al, 2020) due to increased moisture transport into Mexico with strengthened CLLJ. The NAO mode describes changes in sea level pressure, where a positive NAO refers to an increased pressure gradient between the Icelandic Low and the North Atlantic Subtropical High (NASH) (Hurrell & Deser, 2010).…”

“…North Atlantic SSTs lead to increased precipitation in northern Mexico and decreased precipitation in the Yucatán Peninsula and southern Mexico (Bhattacharya et al, 2015Bhattacharya & Chiang, 2014;Rodriguez-Vera et al, 2019;Winter et al, 2015Winter et al, , 2020. The mechanism behind the negative correlation is variability in the CLLJ, where warmer SSTs can decrease the strength of the CLLJ, reducing moisture transport into Mexico ).…”