The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Abstract

Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ∼6000 years before present). The main forcing that contributed to this intensification is related to changes in the Earth's orbital parameters. Nonetheless, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modeling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.

Response of the Low‐Level Jet to Precession and Its Implications for Proxies of the Indian Monsoon

“…Precipitation over northeastern Africa and the western equatorial Indian Ocean increase on account of higher summer insolation in P min compared to P max (Figure S4 in Supporting Information ). The convective heating over these two regions drives a Matsuno‐Gill‐like response of the lower tropospheric winds (Jalihal, Bosmans, et al., 2019; Pausata et al., 2021). The ensuing Kelvin wave produces an anomalous easterly that leads to narrowing of the LLJ and also causes its maxima to shift northward (Jalihal, Bosmans, et al., 2019; Pausata et al., 2021).…”

“…The convective heating over these two regions drives a Matsuno‐Gill‐like response of the lower tropospheric winds (Jalihal, Bosmans, et al., 2019; Pausata et al., 2021). The ensuing Kelvin wave produces an anomalous easterly that leads to narrowing of the LLJ and also causes its maxima to shift northward (Jalihal, Bosmans, et al., 2019; Pausata et al., 2021). In the current study, we find a similar dependence at the interannual timescales as well in P min .…”

“…Thus, suggesting that the orbital scale variability of the LLJ consists of fluctuations in the strength, meridional location, and width, whereas, its interannual fluctuations are primarily due to changes in its strength (Figure S6 in Supporting Information S1). The variations in the strength, magnitude, and location of the LLJ on precession timescales are due to the additional influence of convective heating over northeastern Africa and the western equatorial Indian Ocean (Jalihal, Bosmans, et al, 2019;Pausata et al, 2021;Figure S4 in Supporting Information S1).…”

Sahara’s surface transformation forced an abrupt hydroclimate decline and Neolithic culture transition in northern China

“…However, proxy archives from the MH point to widespread global vegetation changes, including expanded forest cover in Eurasia and greener conditions in southern and eastern Asia. 42 Therefore, it is plausible that these broader vegetation changes in Europe and Asia could have further influenced the increased rainfall and the northern migration of EASM.…”