Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw

Abstract

The presence of a low- to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital and glacial-interglacial timescales, but its existence over the most recent past remains unclear. Here we investigate, based on climate proxy reconstructions from both hemispheres, the inter-hemispherical phasing of the Intertropical Convergence Zone (ITCZ) and the low- to mid-latitude teleconnections in the Northern Hemisphere over the past 2000 years. A clear feature is a persistent southward shift of the ITCZ during the Little Ice Age until the beginning of the 19th Century. Strong covariation between our new composite ITCZ-stack and North Atlantic Oscillation (NAO) records reveals a tight coupling between these two synoptic weather and climate phenomena over decadal-to-centennial timescales. This relationship becomes most apparent when comparing two precisely dated, high-resolution paleorainfall records from Belize and Scotland, indicating that the low- to mid-latitude teleconnection was also active over annual-decadal timescales. It is likely a combination of external forcing, i.e., solar and volcanic, and internal feedbacks, that drives the synchronous ITCZ and NAO shifts via energy flux perturbations in the tropics.

Local and Remote Forcing of Denitrification in the Northeast Pacific for the Last 2,000 Years

“…One explanation could be enhanced poleward transport of ETNP waters to Southern California. However, an equatorward ITCZ displacement would have led to similar equatorward migration of the NPH and AL (Christoforou & Hameed, ; Lechleitner et al, ), suppressing coastal upwelling in Southern California while enhancing upwelling in the Gulf of California (Barron & Bukry, ; Pérez‐Cruz, ). Reduced the sea surface height at the southern boundary of CCS would decrease poleward CUC flow, producing a δ 15 N result opposite to the one observed (Connolly et al, ; Taylor et al, ).…”

Speleothem Paleoclimatology for the Caribbean, Central America, and North America

“…This, in turn, is indicative of a more dominant influence of ENSO activity in speleothems from mid and western Central America, as proposed for many of these records [6,8,9,130] A negative correlation is observed between δ 18 Ospel of CHIL-1, the southernmost record from the Isthmus of Panama, and both YOKI (Belize) and JX-6 (Mexico). A number of precipitation-based records suggest that the seasonal extremes of the ITCZ rainbelt respond to local summer insolation, and consequently the rainbelt seasonal range undergoes latitudinal migrations [10,[132][133][134][135][136]. Other evidence suggests that the ITCZ rainbelt contracted/expanded around its mean position [120,[137][138][139].…”

“…According to this argument, asymmetric extratropical forcings like ice sheets or freshwater hosing produce meridional shifts in the zonal mean rainbelt, but orbital variations produce expansion/contractions in terms of the global zonal mean [120]. However, the driving regional mechanisms still remain elusive since the dynamic response of the rainbelt variation is regionally variable, depending on surface type (land or ocean) and surrounding continental configuration [10,120].…”

“…Speleothem records from this region have revealed critical climate teleconnections between the polar regions, the tropics, and the mid-latitudes at decadal to orbital timescales [3][4][5][6]. These records have provided evidence for the effects of climate variability on ancient civilizations [7-9], and contributed toward open questions and key debates regarding Earth's climate system [3,10]. Here, we discuss the spatial and temporal coverage of North and Central American and Caribbean speleothem records included in SISAL_v1 and the predominant controls on δ 18 O spel variability in each region.…”

Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

“…Most regional studies associate this increase in rainfall with a northward shift of the SHW (Tyson and Preston-Whyte, 2000;Chase and Meadows, 2007). A global study using high-resolution records (Lechleitner et al, 2017) also documents a southward shift of the ITCZ during the LIA interval; however, no data from the southern hemispheric midlatitudes are included and we suggest that the effects of this shifts are limited to locations north of our study site. In the uppermost Gouritz catchment (Seweweekspoort site) a major SHW-sourced rainfall regime has been documented .…”