A modified seasonal cycle during MIS31 superinterglacial favors stronger ENSO variability

It has long recognized that the amplitude of the seasonal cycle can substantially modify climate features in distinct timescales. This study evaluates the impact of enhanced seasonality characteristic of the Marine Isotope Stage 31 (MIS31) on the El Niño-Southern Oscillation (ENSO). Based upon coupled climate simulations driven by present day (CTR) and MIS31 boundary conditions, we demonstrated that the CTR simulation shows signicant concentration of power in the 3–7 year band and on the multidecadal time scale between 15–30 years. However, the MIS31 simulation shows drastically modified temporal variability of the ENSO, with stronger power spectrum at interannual time scales but absence of the decadal periodicity. Increased meridional gradient of SST and wind stress in the Northern Hemisphere subtropics, in concert with weaker seasonal cycle of the windstress in the MIS31 simulation, revealed to be the primary candidates responsible for changes in the equatorial variability. The oceanic response to the MIS31 ENSO extends to the extratropics, and fits nicely with SST anomalies delivered by paleoreconstructions. The implementation of the MIS31 conditions results in distinct global monsoon system and its link to the ENSO in respect to current conditions. In particular, the Indian monsoon intensified but no correlation with ENSO is found in the MIS31 climate, diverging from conditions delivered by our current climate in which this monsoon is significatly correlated with the NINO34 index. This indicates that monsoonal precipitation for this interglacial is more closely connected to hemispherical features than to the tropical-extratropical climate interaction.