Atlantic ITCZ variability during the Holocene based on high-resolution speleothem isotope records from northern Venezuela

Abstract

Few high-resolution paleoclimate proxy records exist in the region located under the direct influence of the Intertropical Convergence Zone (ITCZ) in South America and most of them were retrieved from the Cariaco Basin off the coast of Venezuela. Here we present new ẟ18O and ẟ13C records of Venezuelan speleothems collected in caves adjacent to Cariaco, covering the mid- and late-Holocene. We document previously undetected secular-to multidecadal-scale climate variability in the core region of the ITCZ, which is compared to other high-resolution records from the North Atlantic, Caribbean and tropical South America. Over the mid-Holocene our record exhibits broad swings between periods of reduced (8.3–8.0, 6.5–5.0, 4.1–3.6 ka BP) and increased (8.5, 8.0–6.5, 4.9–4.2 ka BP) rainfall. In particular, between 5.5 and 5.0 ka BP, increases in polar and subpolar North Atlantic ice rafted debris and a reduction in North Atlantic Deep Water (NADW) formation might have contributed to the southward displacement of the North Atlantic Subtropical High (NASH) and the ITCZ, which led to severe dry conditions in north central Venezuela and an enhancement of the South American Monsoon System (SAMS). During the late-Holocene, contrary to data from Cariaco reported in previous studies, our results point to drier conditions during the Medieval Climate Anomaly (MCA, 900–1100 CE), which were further amplified during positive Atlantic Multidecadal Oscillation (AMO) phases. Wet conditions, however, prevailed during the first part of the Little Ice Age (LIA, 1400–1500 CE). No speleothem deposition occurred during the main LIA period, which might be related to drier conditions in response to a southward displacement of the ITCZ that led to major moisture convergence over the SASM domain. Our new records from Venezuela provide a reliable proxy for ITCZ behavior over the Atlantic – South America domain and document past dynamics in relation to other climate systems (NASH and SAMS), while providing new evidence of ITCZ – North Atlantic teleconnections during the Holocene.