A solar (irradiance) trigger for millennial‐scale abrupt changes in the southwest monsoon?

Abstract

[1] Marine sedimentary records of the last glacial from tropical monsoon latitudes indicate climate fluctuations comparable to rapid changes in d 18O recorded in Greenland. Synchronizing two high-resolution sedimentary records from the Oman and Pakistan margins, we resolve millennial-scale reversals in sea surface temperature (SST) gradient (DSST) across the Arabian Sea which directly correspond with the majority of DansgaardOeschger (D-O) events for the last 65 kyr. The relative amplitude of individual monsoon and D-O events appears comparable, suggesting coupled and at least hemispheric forcing. To explore this quasi-cyclic forcing, we compare alkenone-based geologic data with modern satellite-derived DSST estimates between sites. Interstadial conditions fall within the range of monsoons during the Holocene, but stadial conditions have no analogs. Following published associations between Eurasian Winter Snow Cover (EWSC) and monsoon rainfall, and El Niño/Southern Oscillation (ENSO) events and anomalous EWSC, we find a good correlation between the Southern Oscillation Index (SOI) and Arabian Sea DSST throughout the modern data set. An apparent 11-year cyclicity in the SOI reveals an association between the monsoon, SOI, and solar output variability. The SOI primarily tracks solar total irradiance, but the SOI monsoon linkage becomes nonlinear during excursions of the SOI associated with El Niño Events. Strong El Niños coincide precisely with minimum solar irradiance during the solar cycle, which we attribute to threshold behavior in tropical Pacific SSTs and associated trade wind strength. We propose that both short-term (interannual-decadal) and long-term (centennial-millennial) changes in solar output are consistent with records of ENSO variability, monsoon intensity, and D-O event timing.

Tropical climate variability from the last glacial maximum to the present

“…These results add to a growing body of evidence of alkenone and foraminiferal abundance derived SST estimates implying 83 that SSTs in the Arabian Sea were 2 -4°C cooler than present at the LGM (Emeis et al, 1995;Bard et al, 1997;Rostek et al, 1997;Sonzogni et al, 1998;Cayre and Bard, 1999;Higginson et al, 2004;Naidu and Malmgren, 2005).…”

“…Since then, a number of investigations employing the use of alkenones (Emeis et al, 1995;Bard et al, 1997;Rostek et al, 1997;Sonzogni et al, 1998;Higginson et al, 2004) and foraminiferal abundances (Cayre and Bard, 1999;Naidu and Malmgren, 2005) have suggested that LGM SSTs were in fact on the order of 3°C cooler than present. With the exception of Sonzogni et al (1998), these studies have utilized a time series approach, thus giving a temporal, rather than spatial, history of SST.…”

“…Curry et al, 1992). The second record is an alkenone SST reconstruction published by Higginson et al (2004). Like Mg/Ca, alkenones provide a quantitative estimate of SST.…”

“…The Higginson et al (2004) record is from 723B. We consider all of these records on the timescales on which they were originally published.…”

“…In recent years, a number of time series records have been published that utilize quantitative proxies for SST, such as alkenones and artificial neural networks (Emeis et al, 1995;Doose-Rolinski et al, 2001;Higginson et al, 2004;Naidu and Malmgren, 2005). These quantitative SST records often disagree with the SSTs implied by the percent G. bulloides records.…”