Links between deep Earth processes and hyperthermal and extreme cooling events
Climate patterns on Earth fluctuate between greenhouse and icehouse states over multimillion-year timescales,interspersed with hyperthermal and extreme cooling periods that last hundreds of thousands to millions of years.Generally,the Precambrian epoch was characterized by a greenhouse climate,whereas the Phanerozoic eon oscillated between three greenhouse and three icehouse phases.The greenhouse phases were Cambrian-late Ordovician,late Silurian-late Devonian,and late Permian-early Cenozoic;the icehouse phases were the late Ordovician-late Silurian,late Devonian-late Permian,and late Cenozoic periods.During the transitions from Permian to Triassic,the mid-Cretaceous,and the Paleogene to the Neogene,intense warming expanded temperate climates to the poles,marking typical hyperthermal events.During the Neoproterozoic Sturtian and Marinoan glaciations,Earth's surface was almost entirely sheathed in ice,a phenomenon known as a"snowball Earth".In contrast,during the peaks of the Hirnantian glaciation,the Late Paleozoic Ice Age,and the Late Cenozoic Ice Age,ice coverage expanded to mid-and low-latitudes,representing typical extreme cooling events.Shifts in the Earth's climate are largely influenced by changes in atmospheric carbon dioxide(CO2)levels,which are determined by the balance between carbon sources and sinks in the ocean-atmosphere system.The primary source of atmospheric CO2 is carbon reservoirs beneath the Earth's surface,which are released into the atmosphere primarily through magmatic processes,including large igneous provinces,continental arcs,and continental rifts.Conversely,these magmatic activities can also cool the Earth's surface in three ways:(1)By injecting sulfate aerosols,formed from sulfur dioxide(SO2),into the stratosphere,triggering a"volcanic winter";(2)through the absorption of atmospheric CO2 during the chemical weathering of fresh igneous rock;and(3)by enhancing marine primary productivity through the release of phosphorus and iron into the ocean,which facilitates carbon sequestration.Plate tectonics play a significant role in increasing global weatherability,by promoting continental accretion and bringing continents into warm and humid tropical regions.Continental arcs can serve as both carbon sources and sinks during the early and late stages of arc development,cycling over approximately 50 million years.Specifically,tropical arc-continent collisions are potent in absorbing CO2 through intensive chemical weathering,playing a pivotal role in climate cooling.Generally,extensive continental arcs,in conjunction with a minimum extent of tropical arc-continent collision correspond to greenhouse conditions(e.g.,the Cambrian-late Ordovician,late Silurian-late Devonian,and late Permian-early Cenozoic).Conversely,a reduction in continental arc activity,coupled with the peak extent of tropical arc-continent collision,corresponds to icehouse conditions(e.g.,the late Ordovician-late Silurian,late Devonian-late Permian,and late Cenozoic).Hyperthermal events are typically attributed to the rapid accumulation of atmospheric CO2 from the large-scale eruptions and the emplacement of vast mafic igneous provinces.For example,the hyperthermal events at the Permian-Triassic and Paleogene-Eocene boundaries coincided with the Siberian Traps and the North Atlantic igneous province,respectively.Extreme cooling events,on the other hand,are associated with two processes:(1)Increased chemical weathering of mafic large igneous provinces in tropical regions(e.g.,the Sturtian Snowball Earth);and(2)the"volcanic winter"resulting from the explosive eruption of silicic large igneous provinces and frequent felsic volcanism(e.g.,the Late Paleozoic Ice Age Maximum).While large-scale magmatic activities can account for most hyperthermal and extreme cooling events,the feedbacks between volcanic activity and Earth's surface processes,as well as the initiation and maintenance mechanisms for these events remain unclear.As such,future research should prioritize high-precision dating of large-scale magmatic activities and hyperthermal and extreme cooling events,along with integrated simulations of deep Earth processes and climate change.
deep Earth processgreenhouse climateicehouse climatehyperthermal eventextreme cooling event
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