Erosion, Chemical Weathering and the Uplift of the New Guinea Highlands

Chemical weathering in Southeast Asia is increasingly recognised as being a core control over global climate, particularly the cooling of Earth during the Cenozoic. This is particularly true during the Neogene when chemical weathering fluxes from the Himalayas decreased through time, meaning that silicate weathering in that region was not the primary control over falling CO₂ levels in the atmosphere. Instead, chemical weathering of sediments eroded from the arc and ophiolite terrains in Southeast Asia may be critical. Recent study of marine sedimentary deposits offshore Eastern New Guinea now show that there is a trend towards more intense chemical weathering in that region over the last 20 million years and especially since 6 Ma. Collision between New Guinea and Australia primarily commenced around 15 Ma when erosion from uplifting arc terrains made the sources especially reactive. Since that time uplift has created a large island with increasing erosion from continental Australian sources, reducing the reactivity. We estimate that sediments eroded from New Guinea maybe approximately 2 to 3 times as effective at consuming of CO₂ as their equivalents in South Asia. Over shorter, orbital timescales there is more erosion from accreted Australian crust during interglacial times when the stronger rainfall was able to penetrate deep into the New Guinea Highlands than during glacial times when erosion was more focused on mafic rocks along the coast. Chemical weathering intensity follows global climatic cycles with generally less weathering during interglacial warm periods, likely related to faster transport driven by high fluvial discharge.