New model mechanistically links Earth’s interior processes with surficial ones

It is well known that climate and CO₂ are linked.  Generally, CO₂-induced changes in climate have occurred over geological timescales of tens to hundreds of thousands of years allowing feedback mechanisms to take effect.  However, some changes have happened rapidly, with CO₂ remaining long enough in the atmosphere to cause global warming.  Major, rapid sources of this greenhouse gas are Large Igneous Provinces (LIPs) that typically formed from massive outpourings of basalt and caused ocean acidification, oceanic anoxic events and environmental stress leading to mass extinctions. Past Large igneous province (LIP) emplacement is commonly associated with mantle plume upwelling but the role of mantle plumes in controlling the onset and timing of LIP magmatism, and therefore environmental change, is poorly understood.

In this study, past and present scientists from Oxford Earth Sciences (including faculty members Hugh Jenkyns, Tamsin Mather and Conall Mac Niocaill) examined the sedimentary signature of the Toarcian oceanic anoxic event (T-OAE; ~183 Ma), which is plausibly linked to formation of the Karoo-Ferrar LIP, presently exposed in southern Africa and Antarctica. They combined global plate reconstruction models, which show changes in continental plate velocities, with Lower Toarcian sedimentary mercury (Hg) concentrations from a cored borehole in Wales known for its high-resolution ammonite biostratigraphy.  Since gaseous mercury is given off by volcanoes, its enrichment in the cored borehole at the time of the T-OAE is the ‘smoking gun’ that ties these disparate magmatic, sedimentary and environmental phenomena together, linking the occurrence of major volcanic activity, in what is nowadays known as southern Africa, Antarctica and Australia to some of the most severe climatic and environmental changes ever.

Core from Wales containing the Toarcian mercury anomaly laid out at the British Geological Survey. Photo by S.P. Hesselbo.

Crucially, the new data demonstrates that the timing and duration of Karoo-Ferrar LIP emplacement was governed by the slowing down of the Pangaean plate motion, associated with a reversal in plate-movement direction. This new model, which they believe is applicable to other LIPS in the geological record, mechanistically links Earth’s interior processes with surficial ones and shows it to be an important process in controlling past climate.

You can read the full paper here.