ALBERT

Description: Marine Isotope Stage 31 (MIS31, between 1085 and 1055 ka) was characterized by higher extratropical air temperatures and a substantial recession of polar glaciers compared to today. Paleoreconstructions and model simulations have increased the understanding of the MIS31 interval, but questions remain regarding the role of the Atlantic and Pacific oceans in modifying the climate associated with the variations in Earth's orbital parameters. Multi-century coupled climate simulations, with the astronomical configuration of the MIS31 and modified West Antarctic Ice Sheet (WAIS) topography, show an increase in the thermohaline flux and northward oceanic heat transport (OHT) in the Pacific Ocean. These oceanic changes are driven by anomalous atmospheric circulation and increased surface salinity in concert with a stronger meridional overturning circulation (MOC). The intensified northward OHT is responsible for up to 85 % of the global OHT anomalies and contributes to the overall reduction in sea ice in the Northern Hemisphere (NH) due to Earth's astronomical configuration. The relative contributions of the Atlantic Ocean to global OHT and MOC anomalies are minor compared to those of the Pacific. However, sea ice changes are remarkable, highlighted by decreased (increased) cover in the Ross (Weddell) Sea but widespread reductions in sea ice across the NH.

Description: Marine Isotope Stage 31 (MIS31, between 1085 ka and 1055 ka) was characterized by higher extratropical air temperatures and a substantial recession of polar glaciers compared to today. Paleoreconstructions and modeling efforts have increased the understanding of MIS31 interval, but questions remain regarding the role of the Atlantic and Pacific Oceans in modifying climate anomalies associated with the variations in Earth’s orbital parameters. Based on multi-century coupled climate simulations, it is shown that under the astronomical configuration of the MIS31 and forced by modified West Antarctic Ice Sheet (WAIS) topography, there exists a substantial increase in the thermohaline flux and its associated northward oceanic heat transport (OHT) in both the Atlantic and Pacific Oceans. In the Atlantic, these changes are driven by enhanced oceanic heat loss to the atmosphere and increased water density. In the Pacific, anomalous wind-driven circulation in concert with stronger meridional overturning circulation results in greater northward OHT that contributes up to 85 % of the global OHT anomalies, adding to an overall reduction in sea ice in the Northern Hemisphere (NH) due to Earth’s astronomical configuration at the time. Sea-ice changes in the Southern Hemisphere (SH) are highlighted by decreased (increased) cover in Ross (Weddell) Sea.

Description: 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.

Description: It has long been recognized that the amplitude of the seasonal cycle can substantially modify climate features in distinct timescales. This study evaluates the impact of the 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 demonstrate that the CTR simulation shows a significant concentration of power in the 3–7-year band and on the multidecadal timescale between 15 and 30 years. However, the MIS31 simulation shows drastically modified temporal variability of the ENSO, with stronger power spectrum at interannual timescales but the absence of decadal periodicity. Increased meridional gradient of sea surface temperature (SST) and wind stress in the Northern Hemisphere subtropics are 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 a 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 significantly correlated with the NIÑO34 index. This indicates that monsoonal precipitation for this interglacial is more closely connected to hemispherical features than to the tropical–extratropical climate interaction.