New Arabian Sea records help decipher orbital timing of Indo-Asian monsoon

article i nfo core (MD04-2861) covering the last 310 ka, and retrieved in the northern Arabian Sea near the Makran margin, an area influenced by summer and winter Indian monsoon. The grain size proxy deals with the regional continental climate through fluvial and eolian processes. It cannot be linked to changes in nutrient content of AMOC and present the same phase relationship (timing) than the other SM proxies. This demonstrates that the productivitysignals(Bromine)inthenorthernArabianSea aremainlycontrolledbySMdynamics andnotAMOC modulated nutrients at orbital scale changes. Wethus build a multi-proxy record of SM variability (i.e. SMstack) using statistical tools (principal component analysis) further compiled on an age model constructed independently from orbital tuning. We find that strong SM lag by 9±1 ka the NH summer insolation maximum (minimumofprecession,June21perihelionandobliquitymaximum)intheprecessionband,andby6±1.3 kain the Obliquity band. These results are consistent with previous studies based on marine and terrestrial records in bothIndianandAsianregions,exceptAsianspeleothems.Ourstudysupportsthehypothesisthatinternalclimate forcing (decreased ice volume together with the increase of latent heat export from the southern Indian Ocean) set the timing of strong Indo-Asian summer monsoons within both the precession and obliquity cycle. The external forcing (direct sensible heating) initiate monsoonal circulation. Strong Indian winter monsoon (WM) occurs between ice maxima and northern hemisphere sensible heat minima, indicating that both act to strengthen WM circulation. The summer and winter monsoons are in antiphase in the precession band suggesting that the two systems are dynamically linked.