A GEOCLIM simulation of climatic and biogeochemical consequences of Pangea breakup

Abstract

[1] Large fluctuations in continental configuration occur throughout the Mesozoic. While it has long been recognized that paleogeography may potentially influence atmospheric CO 2 via the continental silicate weathering feedback, no numerical simulations have been done, because of the lack of a spatially resolved climate-carbon model. GEOCLIM, a coupled numerical model of the climate and global biogeochemical cycles, is used to investigate the consequences of the Pangea breakup. The climate module of the GEOCLIM model is the FOAM atmospheric general circulation model, allowing the calculation of the consumption of atmospheric CO 2 through continental silicate weathering with a spatial resolution of 7.5°long  4.5°lat. Seven time slices have been simulated. We show that the breakup of the Pangea supercontinent triggers an increase in continental runoff, resulting in enhanced atmospheric CO 2 consumption through silicate weathering. As a result, atmospheric CO 2 falls from values above 3000 ppmv during the Triassic down to rather low levels during the Cretaceous (around 400 ppmv), resulting in a decrease in global mean annual continental temperatures from about 20°C to 10°C. Silicate weathering feedback and paleogeography both act to force the Earth system toward a dry and hot world reaching its optimum over the last 260 Myr during the Middle-Late Triassic. In the super continent case, given the persistent aridity, the model generates high CO 2 values to produce very warm continental temperatures. Conversely, in the fragmented case, the runoff becomes the most important contributor to the silicate weathering rate, hence producing a CO 2 drawdown and a fall in continental temperatures. Finally, another unexpected outcome is the pronounced fluctuation in carbonate accumulation simulated by the model in response to the Pangea breakup. These fluctuations are driven by changes in continental carbonate weathering flux. Accounting for the fluctuations in area available for carbonate platforms, the simulated G 3

Evaluating the effects of terrestrial ecosystems, climate and carbon dioxide on weathering over geological time: a global-scale process-based approach

“…This is a useful first-order approach but cannot capture spatially explicit effects or the effect of changing continental configurations on temperature and runoff [18][19][20][21], nor the location of highly reactive volcanic rocks with respect to regional or local climate and vegetation. Therefore, we now extend the modelling approach of Taylor et al [10] into two dimensions (latitude by longitude) to investigate the effects of regional and seasonal variations in the activity of vegetation and mycorrhizal fungi as well as climate on continental weathering processes over geological time.…”

Did high Neo-Tethys subduction rates contribute to early Cenozoic warming?

“…In contrast, available records suggest its strong shoaling at that time (Pälike et al 2012;Slotnick et al, 2014), which according to Komar et al (2013) hardly conforms to the intense weathering deduced form carbon cycle models. However, previous GEOCLIM modeling showed that a constant silicate weathering flux does not mean a fixed pCO 2 (and thus a fixed CCD), due to the major role played by continental configuration on pCO 2 values (Donnadieu et al, 2006). The second observation is based on δ 7 Li chemistry of Paleocene and Eocene marine sediments, compiled by Misra and Froelich (2012).…”

“…The model uses an ocean geometry divided into two polar oceans (including a photic zone and a deep ocean reservoir), a low-to mid-latitude ocean (including a photic zone, a thermocline and a deep ocean reservoir), two epicontinental seas (both with a photic zone and a deep epicontinental reservoir) and the atmosphere. A full description of GEOCLIM and its components COMBINE and FOAM can be found in Goddéris and Joachimski (2004) and Donnadieu et al (2006).…”

“…Due to the non-consensus about the Earth degassing rate for the last 200 Ma, the degassing flux was assumed constant and fixed at a modern value of 6.8 × 10 18 molCO 2 Ma −1 , which is required in the model to balance the global consumption through the weathering of silicate lithologies (Donnadieu et al, 2006). Each terrestrial grid was prescribed a similar lithology, in which basalt weathering reaches a 30 % contribution of the total silicate weathering flux taken at present day (Dessert et al, 2003) (similar to UNI configuration of Lefebvre et al, 2013).…”

Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics

“…In particular, the Mesozoic amalgamation and subsequent dismemberment of the Pangean supercontinent has played a vital role in the paleogeographic, paleobiological, tectonic and climatic evolution of the planet as it resulted in the opening and closure of oceanic gateways that regulated and impacted climate patterns and the paleogeography of the planet (Cocks and Torsvik, 2002;Scotese et al, 1999;Torsvik and Van der Voo, 2002;Golonka et al, 2006;Seton et al, 2012). Creating interactive digital models of paleogeography enables the estimation of land and ocean distributions that can be linked to paleoclimate simulations as demonstrated by Gyllenhaal et al (1991), Ross et al (1992), Donnadieu et al (2006) and others. A variety of global and regional paleogeographic models have been constructed, but their differences and uncertainties are difficult to assess.…”