Obert, J. C.

The seasonality of hydroclimate during past periods of warmer than modern global temperatures is a critical component for understanding future climate change scenarios. Although partially analogous to these scenarios, the last interglacial (LIG, Marine Isotope Stage 5e, ~127-117 ka) is a popular test-bed. We present coral δ18O monthly resolved records from multiple Bonaire (southern Caribbean) fossil corals (Diploria strigosa) that date to between 130 and 118 ka. These records represent up to 37 years and cover a total of 105 years, offering insights into the seasonality and characteristics of LIG tropical Atlantic hydroclimate. Our coral δ18O records and available coral Sr/Ca- sea surface temperature (SST) records reveal new insights into the variable relationship between the seasonality of tropical Atlantic seawater δ18O (δ18Oseawater) and SST. Coral δ18O seasonality is found to co-vary with SST and insolation seasonality throughout the LIG, culminating in significantly higher than modern values at 124 and 126 ka. At 124 ka, we reconstruct a two month lead of the coral δ18O vs. the Sr/Ca-SST annual cycle and increased δ18Oseawater seasonality. A fully-coupled climate model simulates a concomitant increase of southern Caribbean Sea summer precipitation and depletion of summer δ18Oseawater. LIG regional hydroclimate differed from today's semiarid climate with a minor rainy season during winter. Cumulatively our coral δ18O, δ18Oseawater and model findings indicate a mid-LIG northward expansion of the South American Intertropical Convergence Zone into the southern Caribbean Sea, highlighting the importance of regional aspects within model and proxy reconstructions of LIG hydroclimate seasonality.