Suchergebnisse

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 records from International Ocean Discovery Program (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 exhibit power in the precession band, nearly in antiphase 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.

Planktonic foraminifer oxygen isotopes through MIS 12 were analysed from Ocean Drilling Program Site 977 in the Alboran Sea. After the correction of the sea surface temperature (SST) effect on the δ18O composition of foraminiferal calcite, the resulting seawater δ18O (δ18Ow) was used to reconstruct variations in the δ18Ow of the Atlantic inflow into the Mediterranean. A synchronous record from the KC01B core, in the Ionian Sea, was used to evaluate changes in the oxygen isotope gradient within the Mediterranean due to hydrological variations during MIS 12. Instead of the glacial δ18Ow enrichment expected for the Mediterranean, lower values than today have been observed both in the Alboran and the Ionian seas, especially between 455 ka and the end of MIS 12 (424 ka). These negative oxygen isotope anomalies must have been caused by a flux of freshwater to the Mediterranean during MIS 12. Although the largest fraction of the freshwater anomalies entered the Mediterranean through the Atlantic inflow, especially during Heinrich stadials, the Mediterranean δ18Ow gradient allowed us to identify other sources of freshwater to the eastern basin. One of these sources was probably the meltwater generated at the southern margin of the Fennoscandian ice-sheet that entered via the Caspian and Black seas. However, the proximity of core KC01B to the Adriatic Sea points to meltwater delivered from the Alpine ice-sheet and transported through the Po river into the Mediterranean as the main cause of the Ionian Sea 18O depletions. ; This work was funded by the FPU contract of the Ministry of Education and Professional Formation FPU2015/03283 awarded to Lucia A. Azibeiro and project RTI 2018-099489-B-100 of the Ministry of Science, innovation and Universities of the Spain government granted to the Grupo de Geociencias Oceánicas (GGO) of the University of Salamanca. The Spanish Ministry of Science and Innovation, Severo Ochoa Project CEX2018-000794-S is likewise acknowledged. We are very grateful to IODP for providing the samples used in this study and appreciate the work of Jose Ignacio Martin Cruz in the picking of planktonic foraminifers for isotope analyses and Marta Casado, Yolanda Gonzalez-Quinteiro, Bibiano Hortelano, Walter Hale and Inma Fernandez for laboratory assistance. We thank the scientific data provided by Samuel Toucanne. The authors thank Philip Hughes and other anonymous reviewer for their constructive comments and suggestions. ; Peer reviewed