Hydroclimate Dipole Drives Multi-Centennial Variability in the Western Tropical North Atlantic Margin During the Middle and Late Holocene
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AbstractMeridional shifts of the North Atlantic Subtropical High (NASH) western edge create a dipole that drives hydroclimate variability in the southeastern United States and Caribbean region. Southwest displacements suppress rainfall in the southern Caribbean. Northwest displacements drive southeast United States and northern Caribbean drying. Projections for the 21st century suggest a more meridionally displaced NASH, which jeopardizes Caribbean island communities dependent on rainfed aquifers. While recent work indicates that Atlantic and Pacific Oceanatmosphere variability influenced the NASH during the instrumental period, little is known about NASH behavior and subsequent hydroclimate responses over longer timescales. To address this limitation, we developed a 6000years long rainfall record through the analysis of calcite raft deposits archived within sediments from a coastal sinkhole in the northeast Bahamas (Abaco Island). Increased (decreased) calcite raft deposition provides evidence for increased (decreased) rainfall driven by NASH variability. We use simulations from the Community Earth System Model to support this interpretation. These simulations improve our understanding of NASH behavior on timescales congruous with the reconstruction and suggest an important role for the state of the Pacific Ocean. Furthermore, model simulations and a compilation of regional hydroclimate reconstructions reveal that the NASHdriven dipole dominates northern and southern Caribbean rainfall on centennial timescales. These results bring Holocene Caribbean hydroclimate variability into sharper focus while providing important context for present and future changes to regional climate. Additionally, this study highlights the need for improved future predictions of the state of the Pacific Ocean to best inform water scarcity mitigation strategies for atrisk Caribbean communities.
