Interhemispheric antiphasing of neotropical precipitation during the past millennium

Abstract

Significance Understanding Intertropical Convergence Zone (ITCZ) responses to external forcing is critical for predicting climate change in a warming world. We analyzed paleoclimate records of precipitation change in the neotropics and climate model simulations that span the preindustrial last millennium to assess ITCZ behavior on multicentury timescales. Our results demonstrate that the ITCZ shifted southward during the Little Ice Age in the Atlantic basin in response to relative cooling of the Northern Hemisphere driven by volcanic forcing. This finding contrasts with studies suggesting that changes in ITCZ width and/or strength, rather than a change in mean position, occurred during the Little Ice Age. This reinforces the idea that ITCZ responses to external forcing are region specific.

Incoherency in Central American Hydroclimate Proxy Records Spanning the Last Millennium

“…It is difficult to reconcile the distinct differences in hydroclimate proxy records from CAM by invoking changes in ITCZ dynamics alone. A southward shift in the ITCZ during the LIA (Haug et al., 2001; Hodell et al., 2005; Steinman et al., 2022) would have produced persistent regional droughts in the CAM region during boreal summer if changes in the mean zonal position of the ITCZ were the only factor controlling hydroclimate. Our analysis does not support this inference, indicating that other ocean‐atmosphere processes as well as local climate controls related to complex topography (e.g., Baldwin et al., 2021) must be stronger contributors than ITCZ dynamics to the complex hydroclimate changes observed in the CAM proxy records.…”

“…A substantial body of evidence points to a change in ITCZ dynamics during the last millennium. This is especially true during the Little Ice Age (LIA; ∼1300 to 1850 CE), when the ITCZ is hypothesized to have shifted to a more southerly mean position (Haug et al., 2001; Hodell et al., 2005; Steinman et al., 2022). Such an occurrence, were it to be conclusively identified in the paleo‐proxy data, would provide insight on CAM hydroclimate responses to a potential future southward shift in the ITCZ, which some models project should occur as temperatures increase globally (Christensen et al., 2007; Mamalakis et al., 2021).…”

“…For example, proxy records from the northern Yucatán Peninsula (Hodell et al., 2005) and northern South America (Haug et al., 2001) indicate regional droughts at this time, suggesting a potential southward displacement of the rain belt, while proxy records from Belize (Asmerom et al., 2020), the highland regions of Guatemala (Stansell et al., 2020; Winter et al., 2020), central (Lozano‐García et al., 2007) and northeastern Mexico (Wright et al., 2022), and El Salvador (Wojewódka‐Przybył et al., 2022) do not support this pattern. This implies that ITCZ dynamics alone cannot explain the complex variability in CAM hydroclimate deduced from proxy records (Steinman et al., 2022). These contrasting results suggest that spatial heterogeneity in precipitation variability could be a persistent feature of CAM climate on decadal and longer timescales.…”

Decline in seasonal predictability potentially destabilized Classic Maya societies

“…The ITCZ sensitively tracks changes in the interhemispheric temperature gradient. At multi-decadal time scales, changes in the ITCZ's mean position, its meridional range and its strength are all possible but remain debated for the Common Era, as argued by Asmerom et al using the YOK-G record 28,73,74 . Most rainfall reconstructions from the Maya lowlands suggest considerable ITCZ-induced regional drying during the LIA 52 .…”

“…In fact, recent studies favour scenarios of regionally heterogeneous ITCZ responses and challenge prevailing latitudinal shift hypotheses. A compilation of regionally disparate records suggests that it is crucial to take into account additional modes of ITCZ dynamics, including expansion/contraction and region-specific weakening/intensification 74 . In particular, correlations between additional records from the Neotropics and the YOK-G δ 13 C record studied here indicate that the ITCZ's control on the study region was considerably less dominant before 1400 CE than it is today due to ITCZ expansion/contraction 28 .…”