Effects of the plate tectonic super cycle on climate Describe and explain the links between plate tectonics and climate. Be able to use contrast with its effects on evolution. The supercycle in Australia Australia has three main Archean cratons (2.5-4.5 bya) These were the first blocks of the Australian continent. They may have joined together around 2.3 bya as part of a new supercontinent. Several younger cratons were added to the continent over the next 2 billion years, pushing into the existing cratons as the supercycle continued. The Supercycle in Australia Around 500 mya, Australia’s east coast was part of a subduction zone. This created a volcanic island arc, seen in ancient volcanic mountains in NSW Central West. In the next 100 Million years, the subduction zone moved east to become a continent-ocean collision zone, seen in the fold mountain chain of the Great dividing range. This coincided with the formation of the Pangean supercontinent with Australia as part of the great southern land mass of Gondwana. The Supercycle and sea-level change fall • As supercontinents are formed, continental plates are compressd, decreasing the total surface area. • Mountain formation (orogeny) and mantle uplift squeeze and raise the continental plates even further. • This effect results in an increase i n surface ocean water, but a decrease in sea level by up to 400 metres. • During the fragmenting stages of the Supercycle, continental plates are stretched, elongated as they rift and diverge. • Total continental area increases and total ocean surface decreases, resulting in the sea levels increasing during these stages. The Supercycle and sea-level change fall Influences on Climate – Volcanic activity. Volcanoes Ash and SO2 can cause global cooling (latitude of volcano can influence the degree). Decreased CO2 link to extinction events. Volcanic eruptions can influence the weather when their dust clouds obscure the Sun. Also, sulfuric acid droplets (aerosols) can reflect the Sun's radiation. Cooling the planet. The best known volcanic eruptions with the greatest effect on climate that have occurred in recent history are Laki fissure eruption on Iceland in 1783, Tambora, Indonesia, in 1815 (explosive eruption) Krakatoa in 1883 (explosive eruption) On large continents, masses of snow and ice are able to accumulate and spread. This accumulated snow and ice can reflect up to 85% of the heat/light hitting the Earth in this region. It’s called the Albedo effect. When ice sheets form over a continent at the poles, circulation of oceanic water increases Warm salty water flows to the poles. Ø It loses heat Ø The now cold dense water sinks and flows back to equatorial regions Ø Oceanic currents dissolve nutrients and gases and mixes them throughout the oceans This is a disruption to the thermohaline currents (GOC) that impact the worlds climate Icehouse State Changes to ocean current flow shift the motion of trade winds, cold nutritious-rich ocean waters and the Walker circulation (linked to El Nino and La Nina) The formation of a supercycle often leads to a long-lived period of glaciation Such conditions occur when the elevated supercontinent moves over the North or South Pole and a giant ice sheet forms on top of it. When glaciation occurs sea levels drop Continents are exposed to weathering and erosion One weathering process involves minerals reacting with carbonic acid. This takes CO2 out of the atmosphere. Erosion supplies higher levels of nutrients to the oceans Higher nutrients levels increase organism abundance which in turn take more carbon dioxide from the atmosphere Greenhouse Conditions CONTINENTS SPREADING APART • These arise when seafloor and subduction are most active during the dispersal of continental fragments that follows breakup of the supercontinent. • At this time in the cycle enough Co2 is being released into the atmosphere via volcanic activity that a great deal of greenhouse warming occurs and the climate heats. * MOR = Mid Ocean Ridge As supercontinents break up • Sea levels rise = Continents are flooded, so nutrient levels drop • Increased volcanic activity along MOR release CO2 (flood basalts) • Increased subduction melts limestone sediments returning CO2 to the atmosphere • Increased CO2 increase global temperatures Your Turn • Read pages 33-42 of spotlight textbook. • Complete activity 2.4 on page 39 • Then complete activity 2.5 on page 41 (use google charts for question 3). • Share your answers with Mrs Parker.
