Understanding how El Niño-Southern Oscillation (ENSO) responds to natural variability is of key importance for future climate projections under a warming climate. However, there is no clear consensus on what drives ENSO’s variability on centennial timescales. Here, we find that the epikarst in southeastern Alaska is effective at filtering ENSO and solar irradiance signals from the Aleutian Low regional climate, which are subsequently recorded in the speleothem proxy data. By applying a correlation test, we find that ENSO was significantly influenced by solar irradiance over the past ~3,500 years. This relationship dissolved after ~1970 CE, with ENSO now being dominated by anthropogenic forcing. This implies a new ENSO mean state that will need to be incorporated into future climate projections.

Marine Isotope Stage (MIS) 5c, between ~106,000 and ~93,000 years ago, represents an important warm period on Earth in which the current anthropogenic warming can be contextualized. Although viewed as a pronounced interstadial, its climate expression is regionally disparate, with different regions on Earth showing evidence of either cooler conditions than modern-day or warmer conditions than modern-day. It is therefore important to expand temperature reconstructions to different regions on Earth to gain a better picture of climate dynamics during MIS 5c. In Alaska, there are no quantitative temperature reconstructions for MIS 5c, vastly limiting our knowledge of temperature changes in this climatically sensitive high-latitude region. Here, we fill-in this gap by providing the first quantitative temperatures from MIS 5c in Alaska using hydrogen isotopes from fluid inclusions in precisely dated speleothems. We find that regional temperatures during MIS 5c were within error of modern-day (2021 CE) temperatures, likely representing the most recent time period that regional temperatures were as high as modern-day.

The high sensitivity of tropical hydro-climate to the mean position of the intertropical convergence zone (ITCZ) at different time scales is well known. However, recent research suggests a more complex behaviour of the northern hemispheric tropical rain belts in the western tropical Atlantic. Here we present a precisely dated speleothem multi-proxy record from a well-monitored cave from Puerto Rico, covering the period between 46.2 and 15.4 ka BP in unprecedented resolution. This allows the investigation of multi-decadal to millennial-scale climate variability. The proxy records document a pronounced response of regional rainfall to abrupt centennial to millennial-scale climatic excursions in the North Atlantic across the Last Glacial (i.e., Heinrich Stadials and Dansgaard/Oeschger events). In particular, we observe a strong agreement between the speleothem proxy data and the strength of the Atlantic meridional overturning circulation, supporting a persistent link of regional precipitation to oceanic forcing. Spectral analysis suggests that multi-decadal to centennial variability persisted in the regional hydro-climate not only during stadial and interstadial conditions, but also during the Last Glacial Maximum, supporting the hypothesis that the Atlantic low-latitude regions respond to internal modes of climate variability on these time scales regardless of the global climate state. The compilation with other paleo-precipitation records enables the reconstruction of past changes in position, strength and extent of the ITCZ in the western tropical Atlantic in response to millennial and orbital global climate change.