Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago

Abstract

Variations in the amount of solar radiation reaching the Earth are thought to influence climate, but the extent of this influence on timescales of millennia to decades is unclear. A number of climate records show correlations between solar cycles and climate, but the absolute changes in solar intensity over the range of decades to millennia are small and the influence of solar flux on climate is not well established. The formation of stalagmites in northern Oman has recorded past northward shifts of the intertropical convergence zone, whose northward migration stops near the southern shoreline of Arabia in the present climate. Here we present a high-resolution record of oxygen isotope variations, for the period from 9.6 to 6.1 kyr before present, in a Th-U-dated stalagmite from Oman. The delta18O record from the stalagmite, which serves as a proxy for variations in the tropical circulation and monsoon rainfall, allows us to make a direct comparison of the delta18O record with the Delta14C record from tree rings, which largely reflects changes in solar activity. The excellent correlation between the two records suggests that one of the primary controls on centennial- to decadal-scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation.

Holocene Variability in the Indian Ocean Monsoon: A Stalagmite- Based, High-Resolution Oxygen Isotope Record from Southern Oman

“…The Q5 δ 18 O record is consistent with the scenario depicted in Figure 1b, showing postulated northward displacement of the ITCZ around 7 kyr BP. Such a shift of the ITCZ into the Arabian Peninsula, as inferred from lake sediments (McClure, 1976) and stalagmites Neff et al, 2001), would lift the height of the temperature inversion, leading to stronger convective cloud development and higher monsoonal rainfall over southern Oman. Moreover, the fine structure in the Q5 δ 18 O record suggests that characteristic variations also occur at much higher frequencies, affording the opportunity to gain insight into monsoon circulation dynamics and variability under a range of boundary conditions, and at time-scales relevant to humans.…”

“…When stalagmites are deposited in isotopic equilibrium (i.e., no evaporation), calcite δ 18 O values reflect either changes in the isotopic composition of precipitation or changes in mean annual air temperature within the cave. Previous work on stalagmites from northern and southern Oman have demonstrated that changes in calcite δ 18 O over time primarily reflect changes in the amount of precipitation Neff et al, 2001). More negative δ 18 O values indicate greater monsoon precipitation, because δ 18 O of monsoon-type precipitation is commonly correlated inversely to the amount of precipitation (the socalled "amount effect" , see Dansgaard, 1964).…”

Atmospheric circulation processes contributing to a multidecadal variation in reconstructed and modeled Indian monsoon precipitation

“…Positive anomaly in solar irradiance corresponds to heavy monsoon rainfall. However, as also indicated in Neff et al [2001], Burns et al [2002], and Kodera [2004], a direct effect of changing solar irradiance on the monsoon is unlikely, and the irradiance anomaly has to go through the lower boundary of the atmosphere, e.g., via the surface, including sea surface temperature anomalies, to influence the monsoon.…”

“…Among the studies that examined multidecadal variations in Indian monsoon, some have investigated and suggested the multidecadal variation in the solar irradiance as a possible cause [e.g., Mehta and Lau, 1997;Neff et al, 2001;Agnihotri et al, 2002;Burns et al, 2002;Fleitmann et al, 2003;Kodera, 2004;Bhattacharyya and Narasimha, 2005;Berkelhammer et al, 2010]. Many of these studies show that the solar irradiance and monsoon intensity variations have been comparable in phase at decadal-centennial timescales.…”

Solar forced transient evolution of Pacific upper water thermal structure during the Holocene in an earth system model of intermediate complexity

“…Since the Holocene is featured by significant millennial-centennial fluctuations of solar activities [6], there are a growing number of paleoclimatic studies pointing toward a stronger solar forcing on past climate [7][8][9][10][11]. The enhanced response of the Western Pacific Warm Pool (WPWP) is first recorded in surface temperature anomalies between the Medieval and the Little Ice Age [12].…”