Last Interglacial Hydroclimate Seasonality Reconstructed From Tropical Atlantic Corals

The seasonality of hydroclimate during past periods of warmer than modern global temperatures is a critical component for understanding future climate change scenarios. Although only partially analogous to these scenarios, the last interglacial (LIG, Marine Isotope Stage 5e, similar to 127-117 ka) is a popular test bed. We present coral delta O-18 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 delta O-18 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 delta O-18 (delta O-18(seawater)) and SST. Coral delta O-18 seasonality is found to covary 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 2 month lead of the coral delta O-18 versus the Sr/Ca-SST annual cycle and increased delta O-18(seawater) seasonality. A fully coupled climate model simulates a concomitant increase of southern Caribbean Sea summer precipitation and depletion of summer delta O-18(seawater). LIG hydroclimate at Bonaire differed from today's semiarid climate with a minor rainy season during winter. Cumulatively, our coral delta O-18, delta O-18(seawater), 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.