Multiscale Atlantic Forcing of ITCZ Shifts and Hydroclimatic Variability in Northeastern Brazil over the Last Millennium

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Abstract
This study investigates the non-stationary evolution of Atlantic multidecadal variability and its influence on hydroclimate in Northeastern Brazil (NEB) over the last millennium. By integrating high-resolution paleoclimate proxies (speleothems and marine sediments) with isotope-enabled climate simulations from the GISS-E2-R model, we move beyond confirming the well-established AMV-ITCZ link and instead document how the tropical Atlantic-South American climate system responded to a superposition of drivers across distinct climatic intervals. During the Medieval Climate Anomaly (950-1300 CE), variability was characterized by a persistent 64-year cycle associated with a positive phase of Atlantic Multidecadal Variability (AMV) and a northward displacement of the Intertropical Convergence Zone (ITCZ), intensifying aridity over NEB. The transition period (1301-1499 CE) was characterized by a more irregular 8-year cycle, likely reflecting enhanced climatic instability driven by interactions among ENSO dynamics, volcanic forcing, and internal Atlantic variability. During the Little Ice Age (1500-1849 CE), a 32-year cycle emerged, associated with a negative AMV phase, a southward ITCZ shift, and wetter conditions over NEB. Our findings demonstrate that NEB hydroclimate reflects a non-stationary superposition of internal variability (AMV, ENSO) and external forcings (volcanism, solar variability), rather than a single dominant driver. This multi-scale framework provides a long-term perspective for understanding present-day climate variability and improving future drought risk projections in the region. Graphical Abstract The This graphical summary illustrates how Atlantic Multidecadal Variability (AMV), Pacific forcing, and external drivers influenced the position of the Intertropical Convergence Zone (ITCZ) and rainfall patterns in Northeastern Brazil (NEB) over the last millennium. During the Medieval Climate Anomaly (MCA, 950–1300 CE), a positive AMV phase contributed to a northward ITCZ shift and drier conditions. The transition period ( 1300–1500 CE) was marked by an 8-year mode reflecting interactions among ENSO, volcanic forcing, and Atlantic variability. During the Little Ice Age (LIA, 1500–1849 CE), a negative AMV phase favored a southward ITCZ migration and wetter conditions. These fluctuations reflect a superposition of internal variability and external forcings, rather than a single dominant driver, providing a long-term perspective for improving future climate adaptation in NEB.
Funding Information
  • Ministério da Ciência, Tecnologia e Inovação

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