Details

Autor(en) / Beteiligte

• Gebregiorgisa, D
• Hathornea, E C
• Sijinkumarb, A V
• Nathc, BNagender
• Nuernberga, D
• Franka, M

Titel

South Asian summer monsoon variability during the last similar to 54 kyrs inferred from surface water salinity and river runoff proxies

Ist Teil von

• Quaternary science reviews, 2016-04, Vol.138, p.6-15

Erscheinungsjahr

2016

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and delta super(18)O analyses and to estimate seawater delta super(18)O ( delta super(18)O sub(sw)). The difference between surface and thermocline temperatures ( Delta T) and delta super(18)O sub(sw) ( Delta delta super(18)O sub(sw)) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our Delta delta super(18)O sub(sw) time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the delta super(18)O sub(sw) and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at similar to 18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum delta super(18)O sub(sw) values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation, which is consistent with model simulations.