Abstract
Abstract. 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.
Highlights
The Marine Isotope Stage 31 (MIS31; early Pleistocene 1085–1055 ka) is a key paleoclimate period to simulate and analyze the global environmental response to a significantly modified climate forcing (Lisiecki and Raymo, 2005; Yin and Berger, 2012)
Though previous studies have claimed that the equatorial Pacific interannual variability is primary forced by equatorial wind stress (Nonaka et al, 2002; Timmermann and Jin, 2002), and the decadal variability is strongly connected to the off-equatorial wind stress, our results show that the atmospheric flow between 0 and 20◦ N can induce decadal variability (Fig. S3)
This investigation centered on a comparison between present-day conditions (CTR) and those characteristics of a super-interglacial epoch, the Marine Isotope Stage 31 (MIS31)
Summary
The Marine Isotope Stage 31 (MIS31; early Pleistocene 1085–1055 ka) is a key paleoclimate period to simulate and analyze the global environmental response to a significantly modified climate forcing (Lisiecki and Raymo, 2005; Yin and Berger, 2012) This interval was characterized by boreal summer temperatures that were several degrees greater than modern climate (up to 6 ◦C), with a substantial recession of the Northern Hemisphere (NH) sea ice (Melles et al, 2012; Justino et al, 2017). The far-reaching effect of equatorial dynamics on climate has been found by Karami et al (2015) They argued that lower summer sea surface temperatures (SSTs) in the central tropical Pacific during MIS13 contribute to the strengthening of the northern Pacific subtropical high, increasing the transport of moisture into the East Asia summer monsoon (EASM). Verifying the potential effect of atmospheric CO2 on the stability of the West Antarctic Ice Sheet (WAIS) will be a key climate factor in decades to come (Nicolas et al, 2017)
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