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This thesis investigates the paleoclimate of the Indus River Basin and surrounding areas of northwest (NW) South Asia over the last 12,000 years, covering a critical period of human history. The region’s climate is characterized by two overlapping rainfall systems: the Indian Summer Monsoon (ISM) and the Indian Winter Monsoon (IWM). A shift in these monsoon systems has been documented throughout South Asia at 4.2 ka BP, with potential effects on the development and decline of the Indus Civilization (c. 5- 3.6 ka BP). This thesis examines the connection between climate and cultural shifts by providing new records from three climate archives spanning 1500 km from the Arabian Sea to the Thar Desert and Himalayan Mountains. The chapters feature δ18O and δ13C of three foraminifer species in marine core 63KA over 8.8-7.6 ka BP and 5.4-3.0 ka BP, gypsum from three Holocene Thar Desert playa lakes, and sub-annually resolved trace element and stable isotope data from DHAR-1 speleothem covering 4.2-2.5 ka BP. The major findings from this thesis contribute to a more comprehensive understanding of climate change in NW South Asia throughout the Holocene. The three Thar Desert playa lakes began accumulating gypsum c. 11 ka BP, aligning with a post- glacial strengthening ISM. Prismatic gypsum crystals and uniformly high δ18O of gypsum hydration water from early-mid Holocene deposits suggest relatively deep lake levels during this phase. Similarly, the δ18O of marine core 63KA foraminifer species dwelling in surface and thermocline layers demonstrate a stronger ISM over 8.8-7.6 ka BP and a strengthening IWM from 8.8-8.6 ka BP. By 4.8 ka BP, the ISM started weakening, but IWM strength peaks from 4.5-4.3 ka BP. A wet period c. 5-4.4 ka BP is also apparent from high δ18O of gypsum hydration water at Karsandi playa. The late Holocene droughts after 4.2 ka BP are well-documented by the precise (age error ± 18 years) DHAR-1 reconstruction, which tracks ISM strength via δ18O and winter aridity using δ13C, Sr2+ U2+, and Ba2+. Weakened ISM and IWM both contributed to the 230-year drought period with three distinct arid phases (4.2-4.17 ka BP, 4.14-4.08 ka BP, and 4.06-3.97 ka BP). Core 63KA shows minimum Indus River discharge and weakened IWM over the same interval, whereas Lunkaransar playa shows a protracted lake level decline, and aeolian sand replaces gypsum deposition at Karsandi by 3.2 ka BP. Shallow playa systems briefly recover at Lunkaransar and Khajuwala during the late Holocene, but Khajuwala eventually desiccates permanently. |