Enhanced weathering input from South Asia to the Indian Ocean since the late Eocene

nhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau(HTP)has been considered as the major cause of pCO_(2) decline and Cenozoic cooling.However,this hypothesis remains to be validated,largely due to the lack of a reliable reconstruction of the HTP weathering flux.Here,we present a 37-million-year record of the difference in the seawater radiogenic neodymium isotopic composition(△ε_(Nd))of Ocean Drilling Program(ODP)sites and Fe-Mn crusts between the northern and central Indian Ocean,which indicates the contribution of regional weathering input from the South Asian continent to the Indian Ocean.The results show a long-term increase in △ε_(Nd) and thus provide the first critical evidence of enhanced South Asian weathering input since the late Eocene.The evolution coincided well with major pulses of surface uplift in the HTP and global climatic transitions.Our foraminiferal eNd record suggests that tectonic uplift and silicate weathering in South Asia,especially in the Himalayas,might have played a significant role in the late Cenozoic cooling.

Evolution of Asian drying since 30 Ma revealed by clay minerals record in the West Pacific and its tectonic-climatic forcing

As the second largest dust source on the globe,the tectonic and climatic evolution of continental Asia has an important impact on regional and global climate change.The West Pacific is the main sediment sink for eolian dust transported eastward from the Asian interior.Clay minerals,as the major fine-grained weathering products of continental rocks,can be readily transported by wind or currents over long distances and thus have been widely used in the reconstruction of paleoclimate and weathering history.However,the overall evolutionary tendency and response mechanism of clay mineral records over large spatial and long timescales across Asia remain unclear.Here,two continuous and high-resolution clay mineral records since 30 Ma were reconstructed from sediments at Deep Sea Drilling Program(DSDP)Sites 292 and 296 in the Philippine Sea.Clay minerals and Sr-Nd isotope compositions were used to constrain provenance and reconstruct the drying history of the dust source region since the Oligocene.The results show that the clay-sized detrital sediments in the Philippine Sea are a mixture of Asian eolian dust and volcanic materials from the West Pacific arcs.Based on the clay mineral compositions and eolian flux,we reveal that the Asian interior has been continuously drying since the late Oligocene and that stepwise enhanced aridification occurred at approximately 20,14,7,and 3 Ma.Compared with other regions of the world,the relative contents of illite and chlorite increased more dramatically in Asia during the late Cenozoic,and the inconsistency became more obvious at approximately 20 Ma.Since 3 Ma,illite and chlorite have increased consistently across the globe.Combined with the Asian tectonic and climatic history,we suggest that the increase in illite and chlorite from Asia between 20 and 3 Ma was mainly in response to the uplift of the Himalayan-Tibetan Plateau,whereas after 3 Ma,it was primarily controlled by global cooling driven by the expansion of the Arctic ice sheet.

Milankovitch theory and monsoon

The widely accepted“Milankovitch theory”explains insolation-induced waxing and waning of the ice sheets and their effect on the global climate on orbital timescales.In the past half century,however,the theory has often come under scrutiny,especially regarding its“100-ka problem.”Another drawback,but the one that has received less attention,is the“monsoon problem,”which pertains to the exclusion of monsoon dynamics in classic Milankovitch theory even though the monsoon prevails over the vast low-latitude(
30N to
30S)region that covers half of the Earth’s surface and receives the bulk of solar radiation.In this review,we discuss the major issues with the current form of Milankovitch theory and the progress made at the research forefront.