Anomalous widespread arid events in Asia over the past 550,000 years

Abstract

Records of element ratios obtained from the Maldives Inner Sea sediments provide a detailed view on how the Indian Monsoon System has varied at high-resolution time scales. Here, we present new records from IODP Site U1471 based on a refined chronology through the past 550,000 years. The record's high resolution and a proper approach to set the chronology allowed us to reconstruct changes in the Indian Monsoon System on a scale of anomalies and to verify their relationships with established records from the East Asian Monsoon System. On the basis of Fe/sum and Fe/Si records, it can be demonstrated that the Asia continental aridity tracks sea-level changes, while the intensity of winter monsoon winds responds to changes in Northern hemisphere summer insolation. Furthermore, the anomalies of continental aridity and intensity of winter monsoon winds at millennial-scale events exhibits power in the precession band, nearly in anti-phase with Northern hemisphere summer insolation. These observations indicate that the insolation drove the anomalies in the Indian Summer Monsoon. The good correspondence between our record and the East Asian monsoon anomaly records suggests the occurrence of anomalous widespread arid events in Asia.

Evidence of magnetite reduction and primary magnetization destruction during early diagenesis in sediments from Maldives Inner Sea

“…The detrital sediments in the Inner Sea of the Maldives are mainly of aeolian origin from the deserts of the Indian-Asian landmass. Their variation over time is related to the expansion and retraction of the arid zones with a ~100 kyr cyclicity and to the intensity of the Indian winter monsoon winds with a ~20 kyr cyclicity (Kunkelova et al, 2018;Carrasqueira et al, 2023). Therefore, as it was related to the Fe/sum record, the variation in magnetic parameters related to material provenance should show this cyclicity.…”

“…This lithogenic fraction has previously been associated with aeolian dust transported from the deserts of the Indian-Asian landmass by dry north-easterly winds during the winter monsoon (Bunzel et al, 2017;Kunkelova et al, 2018). Their contribution to the Inner Sea of the Maldives has been linked to the extension of arid zones on the Indian-Asian landmass, which evolves in response to the ~100 kyr cyclicity in global ice volume (Bunzel et al, 2017;Kunkelova et al, 2018;Carrasqueira et al, 2023). Located in the deepest part of the Inner Sea, where the seafloor is essentially flat, IODP Site U1471 (4°45.98'N and 73°08.11E; Figure 1) is at a water depth of 419.3 meters, near the outflow of the southern branch of the Kardiva Channel into the Inner Sea.…”

“…In our record, a secondary peak in remanence values was found at 0.56 mbsf (Figure 4; sample 3). According to the most recently published chronology for record U1471 (Carrasqueira et al, 2023), this sample is 13.1 Ka old (just before the start of the Holocene). In the sedimentary records of the Inner Sea of the Maldives, the Holocene was characterized by increased mud deposition, leading to a decrease in porosity (Paul et al, 2012;Lindhorst et al, 2019).…”

“…If authigenic greigite is currently crossing the SD stable grain size barrier in this depth interval, the modern geomagnetic field is currently being recorded in the sediment at these depths. According to the recently published chronology for Site U1471 (Carrasqueira et al, 2023), at 2.8 and 3.3 mbsf the record has ages of 102 and 103 Ka, respectively, so there is a possibility that the magnetostratigraphy-based chronology for Site U1471 has an error of almost The IRM@1T data reach a plateau from 4 to 6 mbsf (Figure 6; arrow 3). These results are directly related to a higher concentration of hard minerals, as indicated by the low S ratio values (Figure 6).…”

“…The almost complete dissolution of magnetite in the upper 2 mbsf and the subsequent growth of greigite from an SP size to an SD size with a measurable signal, as found at 3.06 mbsf, indicates that at some point between these two events Fe 2+ was available to be transported by diffusion and/or advection of the interstitial water and recrystallize in a different stratum. This process may have compromised the reliability of the Fe record, which is currently used to address changing arid conditions in the Indian-Asian landmass (e.g., Kunkelova et al, 2018;Carrasqueira et al, 2023;).…”