Environmental tipping points during supercontinent breakup

GSTDTAP

项目编号	NE/R004978/1
	Environmental tipping points during supercontinent breakup
	Thomas Michael Gernon
主持机构	University of Southampton
项目开始年	2018
	2018-07-02
项目结束日期	2020-07-01
资助机构	UK-NERC
项目类别	Research Grant
项目经费	40364(GBP)
国家	英国
语种	英语
英文摘要	Throughout Earth history, supercontinents (united continental landmasses) assemble and break up in a repeating cycle of plate tectonics. It has been suggested that this 'supercontinent cycle' drives the chemistry of the ocean-atmosphere system, and in turn influences Earth's climate. However, this association is largely qualitative and the detailed mechanisms, feedbacks and chemical fluxes leading up to turning points in Earth history remain to be quantified. Understanding how these processes are interrelated requires integration of geochemical, climate and tectonic modelling tools and expertise. We propose to integrate our existing volcanic weathering models (NE/K00543X/1) with dynamic plate models developed by world-leading groups at Sydney and Adelaide, to quantify the geochemical footprint of supercontinent breakup. Specifically, we will consider the breakup of Rodinia ~750 million years ago (Ma) and Gondwana at ~180 Ma. Both events were heralded by an apparently similar chain of events, including intensified volcanism and weathering, but resulted in fundamentally different climatic responses. Rodinia breakup culminated in a 'Snowball Earth' glaciation lasting tens of millions of years, whereas Gondwana breakup gave rise to the Cretaceous greenhouse world. We hypothesise that the climatic outcome of supercontinent breakup is governed to a first order by the arrangement of the resulting continents, or plate topology. Supercontinent breakup spells chaos for the Earth system. Large Igneous Provinces release vast amounts of CO2 and aerosols, trapping heat inside the atmosphere making the planet warmer. Breakup also brings intensified chemical weathering, that is, rainwater reacting with rocks to flush dissolved elements via rivers into the oceans. This occurs because tearing up a landmass produces more seaways, resulting in closer proximity to the oceans for a higher proportion of the continental landmass. Our work has shown that forming new mid-ocean-ridges, an integral part of breakup, leads to intense weathering of fresh volcanic rocks. When rivers and volcanoes flush elements such as calcium into seawater, these combine with CO2 to form CaCO3, ultimately reducing atmospheric CO2 levels and potentially causing a net cooling effect. Continents near the equator are more prone to chemical weathering than those near the poles, so plate topology is a powerful driver of climate. As illustrated by this example, slight changes in certain processes or states could tip the Earth into a long-lived greenhouse, or an icehouse phase, depending on a combination of background geological conditions (i.e. a 'butterfly effect'). Our current NERC-funded research demonstrates a major role for volcanic ash dispersal and ridge volcanism in affecting the Earth's carbon cycle and marine biological pump. Coupled with volcanic outgassing, these feedbacks might be sufficiently powerful to destabilise the climate system and tip the response in either direction. Our models will use a Monte Carlo approach to resolve system complexity, and account for uncertainties in geological conditions and fluxes. As continental 'unzipping' strongly influences chemical fluxes from the continents and ocean crust, combining our simulations with dynamic plate motion models will significantly reduce uncertainties in weathering flux estimates. Bayesian models will allow us to deconvolve links between rates of volcano-tectonic processes and geochemical proxies of environmental change. Together with interrogation of Earth system models, this will allow us to better understand climate forcings, and thereby develop a framework for understanding 'tipping points' during supercontinent breakup. Although Snowball Earth and the Cretaceous world are often regarded as polar opposites, chemical weathering during these periods likely stimulated, respectively, the rise of complex life and radiation of planktonic organisms, which play a crucial role in regulating ocean chemistry.
来源学科分类	Natural Environment Research
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/87172
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Thomas Michael Gernon.Environmental tipping points during supercontinent breakup.2018.