Scientists say: Climate has an effect on Plate Tectonics!
Guest post by Max Heikenfeld
“Well, you must have mixed things up here, beginners mistake in the fist week..” That might have been what some of you have thought while reading the title. It is of course true that geological processes are one of the main drivers of the evolution of the climate systems. A few of you might be familiar with the names Pinatubo, Tambora and El Chichón: the names of volcanoes that featured strong eruptions with a direct impact on the climate for the following years. These effects were mainly caused by the transport of large amounts of particles into the stratosphere blocking a small amount of the incoming solar radiation back into space before it could reach the Earth’s Surface, thus leading to a substantial cooling of the Earth for the following months and years. The so called Year Without a Summer of 1816 after the eruption of Tambora in Indonesia is the most drastic of these events in recent centuries.
On a larger time-scale, plate tectonics have a strong influence on the climate system, for example by blocking or opening large oceans straits such as the Drake passage between South America and Antarctica or the southern ocean between Australia and the Antarctic landmass. Both directly influenced the Antarctic Circumpolar current, the strongest ocean circulation, thus causing a complete change in the patterns of the global ocean circulations.
These two effects are both fascinating and very important for our understanding of the climate system, but probably things that you already knew before.
So let’s get back to the title! During this week’s lecture session on the “Dynamic Earth” dealing with feedback mechanisms, Prof. Bruce Levell introduced us to the feedback of climate to the geologic processes in the subsurface. The erosion rate at the surface is strongly dependent on temperature and precipitation, the two most important variables in the description of past and present climates. More rain obviously leads to more dissolution of rock material and faster transport into the oceans, with higher temperatures favouring the associated chemical reactions. Stronger erosion in turn leads to a thinning of the crust. This leads to changes in the forces between different tectonic plates where they overlay each other in subduction zones. This can finally lead to the mentioned effect on geologic processes in the subsurface, since a lighter parcel of continental crust can “slide“ along another piece of the crust much easier when it is lighter due to the removal of material at its top in the described erosion processes. The geologic processes involved in the movement of the plates are of course much more complicated, but scientists have shown that the simple analogy holds for different geological settings on Earth.
The overall effect of this feedback on the climate is definitely smaller that the reverse process described above, but one is definitely not wrong in stating a direct effect of the Climate System on the processes in the Earth’s interior as I did in the title.
Lamb, S. & Davis, P., 2003, Cenozoic climate change as a possible cause for the rise of the Andes, Nature 425, 792-797.
Max Heikenfeld is a research student in the 2014 cohort.