Evolution and driving mechanisms of water circulation during the late Paleozoic to early Mesozoic

Abstract

<p indent="0mm">Water circulation plays a crucial role in the Earth’s systems, linking the atmosphere, hydrosphere, lithosphere, and biosphere. During the Paleozoic-Mesozoic transition, climatic and environmental conditions turned into crises, caused by a sudden and serious global warming, accompanied by the largest known extinction event of all time. Several studies have been conducted to discover the causes of this notable climate change. Nevertheless, the evolution of water circulation processes during the Paleozoic-Mesozoic transition is still unclear. Several lithologic indicators present in paleoclimate records have been described over the last few decades. Based on these data, we defined climate zones and calculated their area values using Thiessen polygons and Geographic Information System technology to visualize climate evolution during the Paleozoic-Mesozoic transition. Results of a few of the climate simulations showed changes in precipitation and the amplitudes of the inter-tropical convergence zone (ITCZ) seasonal migration. The results showed several changes in water circulation during the late Paleozoic to early Mesozoic. (1) The climate zones reconstructed by sedimentary and paleontological records showed a remarkable arid expansion. The distribution area of evaporites began to expand in the Middle to Late Permian and reached a peak in the Early Triassic, returned to Middle-Late Permian levels in the Middle Triassic, and thereafter continued to narrow during the Late Triassic to Early Jurassic. (2) Global precipitation was higher during the Late Carboniferous and Early Jurassic and lower in the Middle to Late Permian and Early Triassic. Such a “V” shape represents considerable swing. (3) The assembly of Pangea might have led to “giant land surface winds” in Pangaea and “trans-equatorial winds” in the Tethys region, resulting in a global “megamonsoon”. (4) Seasonal movements of the ITCZ were located at lower latitudes from the Silurian to Carboniferous and from the Jurassic to the present, while reaching higher latitudes with large seasonal oscillations during the Permian-Triassic. Depending on the timing of events, these major changes in water circulation coincided with the assembly of Pangaea, the Variscan or Hercynian orogeny, the end of the late Paleozoic ice age, major carbon emissions, and global warming. These factors are closely related to the changes in atmospheric and water circulation during the Paleozoic-Mesozoic transition. The assembly of Pangea redistributed water storage and altered atmospheric circulation and the “megamonsoon”, while the elevation reduction of mountains traversing middle Pangea weakened the resistance of north and south winds. These factors promoted the evolution of a “megamonsoon” with strong seasonal swings of the ITCZ, which led to the expansion of arid zones and reduced precipitation during the Middle and Late Permian. Meanwhile, large carbon emissions and dramatic global warming altered the energy transition within global systems, which influenced atmospheric circulation. In addition, transformations of global plant clades affected the carbon budget and altered water circulation. In summary, strong fluctuations in water circulation were present during the Paleozoic-Mesozoic transition, especially as observed through climate zones, precipitation and runoff, the “monsoon”, and ITCZ. These crucial processes reflect the interaction between the lithosphere, atmosphere, hydrosphere, and biosphere. However, we have limited knowledge of the complete process of water circulation because geological records and climate simulations are extremely imprecise for the Paleozoic-Mesozoic transition. Future research could focus on other water circulation processes, such as the evolution of underground water, reserves, and fluxes of lakes, rather than only precipitation and “monsoons”. Moreover, the upgrade and extension of big data platforms and a larger number of climate simulations should be considered in future studies.