Tropical Pacific climate variability and Atlantic–Pacific teleconnections under Holocene and Last Interglacial forcings

The tropics are a pivotal amplifier of global climate variability and change, largely through interannual phenomena such as the El Niño-Southern Oscillation (ENSO) and other tropical basin interactions, which underscores the importance of accurately modeling their behavior under changing climate forcings. Here, we investigate how mean state, seasonality, and interannual variability of the tropical Pacific respond to altered boundary conditions in past warm climates. We also examine how these changes affect teleconnections with the tropical Atlantic, specifically the Caribbean Sea.

Motivated by past warm climate time-windows covered by monthly-resolved proxy records of sea-surface temperature (SST) and hydrology derived from fossil corals, we use the fully coupled water and carbon isotope-enabled Community Earth System Model (iCESM) to perform time-slice simulations for three key climate intervals: Pre-Industrial (PI), Mid-Holocene (6 ka), and Last Interglacial (124 ka) at a nominal horizontal resolution of 1° in the atmosphere, land, ocean and sea-ice components. Mid-Holocene coral records from the Line Islands (central tropical Pacific) and Bonaire (southern Caribbean), as well as Last Interglacial coral records from Bonaire, are used for model–data comparisons.

In response to the changes in orbital and greenhouse-gas boundary conditions, both 6 ka and 124 ka simulations show distinct climate anomalies. The tropical eastern Pacific exhibits La Niña-like conditions in SST with a cooling by 0.4°C and 0.5°C during boreal winter for 6 ka and 124 ka, respectively, which is also evident from an increased zonal sea-level pressure gradient as compared to PI. Contrasting anomalies north and south of the equator over the tropical Pacific result in a statistically significant increase of the meridional SST asymmetry by 0.3°C for 6 ka and 0.6°C for 124 ka as compared to PI. These point to a reorganization of the tropical Pacific mean state. Concurrently, both of our simulations reveal a significant reduction in the interannual variability of SST in the Central Pacific and a significant increase in the Eastern Pacific, with 124 ka showing larger amplitudes of the anomalies by up to 20% relative to PI. Taken together, these patterns indicate a response of the tropical Pacific to warmer boundary conditions, altering large-scale atmospheric circulation and affecting teleconnections into neighboring basins.

Moreover, previous research points to relationships between Pacific SST interannual variability and southern Caribbean SST seasonality under modern climate conditions. Both our 6 ka and 124 ka simulations show increased SST seasonality in the southern Caribbean, which is consistent with evidence from coral records. In an ongoing analysis combining our simulations and available coral records from the Atlantic and Pacific, we further explore the characteristics of potential connections between seasonality and variability during past warm intervals in order to get deeper insights into Atlantic–Pacific climate dynamics and teleconnections under warm climates.