Chemical Weathering of Mafic Sources in Neogene New Guinea as a Control on Global Climate

Silicate weathering is recognized as being critical in removing greenhouse CO₂ gas from the atmosphere, which offsets the CO₂ supplied by mantle degassing during magmatism. In doing so chemical weathering keeps the Earth’s climate in a relative steady state condition. However, where the most important CO₂ sink is remains enigmatic. In this work, we analysed deep-sea clastic sediments recovered by International Ocean Discovery Program Site U1485 from the northern coast of Papua New Guinea to understand the evolution of weathering in New Guinea in the last 0.3 Ma. Major element compositions indicate increased chemical weathering. This is consistent with increasing proportions of kaolinite, indicative of enhanced tropical weathering. Sr and Nd isotopes, together with key trace elements indicate increasing erosion from magmatic arc and ophiolite sources. Isotope mixing calculations indicate that most of the sediment is derived from the colliding magmatic arc. Comparison of sediment with onshore bedrock compositions implies that the source terrains have been especially reactive and efficient at removing CO₂ from the atmosphere, especially compared to Himalayan bedrocks. Weathering in eastern New Guinea now accounts for ~16% of global CO₂ consumption. We argue that this island has played an important role in driving global cooling.