Yifan Du

"Chemical weathering of silicate rocks as an important process in regulating atmospheric CO2 over geological timescales and control the global climate."

PhD project title:

Chemical Weathering Response of New Guinea to Orbital Scale Climate Variability.

 

Project description:

 Chemical weathering of silicate rocks is recognized as an important process in regulating atmospheric CO2 over geological timescales and thus control the global climate. Historically, the uplift of the Himalaya and Tibetan Plateau have been invoked as being the primary driver of Cenozoic cooling, but recent weathering budgets now suggest that this is unlikely. Instead, weathering in tropical zones, especially Indonesia and the Maritime Continent have been highlighted as potentially influential. New Guinea in particular stands out as a driver of CO2 sequestration because of its great size, >2500 km long, and rapid uplift following collision between the Indonesian arc and Australia starting at ~12 Ma. Moreover, the high ranges of New Guinea comprise mafic arc and ophiolitic rocks that are especially susceptible to chemical weathering. Recent analyses of a long-term sediment record from the Gulf of Papua support the role of New Guinea as a climate driver by showing increasing intensity of chemical weathering since the Mid Miocene, consistent with its emergence as an island and despite the cooling of the planet since that time, a process that might be expected to have slowed chemical weathering rates. In this project I will explore the role of New Guinea in modulating climate on shorter, orbital timescales, ~300 k.y.

It has already been proposed that exposure of wide continental shelves across the Maritime Continent/Sunda land might function as an amplifier of global climate change. Exposure of marine sediments to chemical weathering during sea level low stands increases the total amount of chemical weathering and further reduces CO2 concentrations in the atmosphere. Conversely, sea level rise curtails this process and fosters the development of coastal wetlands that provide greenhouse gas methane to the atmosphere, strengthening the global warming. Although analyses have been done on the Sunda and South China shelves no similar data has been provided from New Guinea. I will analyze 240 samples from International Ocean Discovery Program (IODP) Site U1485 offshore northern New Guinea extending to ~300 ka and providing a relatively high-resolution record of how New Guinea has responded to the last two glacial cycles. I will use major element data, especially Na, K, Mg, Ca and Al to estimate the changing intensity of chemical weathering and to calculate the rate of CO2 consumption using well established methods.

When coupled with later seismic work this will provide a volume estimate of how much CO2 is sequestered as a result of New Guinea weathering. I specifically target the following hypotheses. 

• Colder and drier conditions during glacial maxima result in slower chemical weathering and deposition of less weathered material (proxied by K/Al and the Chemical Index of Alteration).
• Stronger erosion in the New Guinea Highlands during glaciation increase sediment flux to the ocean and cause an increase in total chemical weathering (Ti/Ca, Fe/Ca proxies).