Common Era time-transgressive forcing of Caribbean water balance

Tropical North Atlantic sea surface temperatures and low-latitude rainfall covary, but prehistoric subtropical rainfall records are often misaligned. Here, a submarine groundwater discharge record from the northern Bahamas archives regional water balance in the northeastern Atlantic Warm Pool. We compare the reconstruction to the tropical North Atlantic seasonal temperature gradient, which can help inform how northeastern Caribbean rainy seasons are influenced by the Atlantic Warm Pool. A positive water balance in the northern Bahamas aligned with a ~0.9 °C seasonal temperature gradient from 0 to 950 CE, with both covarying on multi-decadal timescales. Aridity began at ~950 CE when a ~2.2 °C seasonal temperature gradient increase likely shortened the wet season. From 1450 to 1850 CE, frequent hurricanes offset aridity in the northeastern Caribbean by elevating rainfall. This record archives time-transgressive changes in hydroclimate forcing, and suggests that projected changes to rainfall seasonality must be considered when assessing tropical water security risk. The balance between precipitation and evaporation in the Caribbean region during the Common Era can be estimated through analyses of sedimentary foraminiferal assemblages that record submarine groundwater discharge.