PERMIAN OCEAN ACIDIFICATION ALONG NW PANGEA

A transition from carbonate to silica dominated shallow shelf ecosystems occurs from Upper Carboniferous to Upper Permian of the Sverdrup Basin (Arctic Canada). In the latest Carboniferous chert expansion started in distal deep-water slope environments, when prolific warm-water photozoan carbonate factories developed on the adjacent shallow shelves. The introduction of cooler water in response to paleoceanographic changes along NW Pangea caused a shift to heterozoan factories during the Sakmarian–Artinskian. By Kungurian time, heterozoan carbonate factories narrowed substantially while hyalosponge factories had expanded well into the mid shelves. A brief return to widespread heterozoan carbonate sedimentation occurred during the Wordian, followed by further encroachment of shallow shelves by biosiliceous factories during the Capitanian and Wuchiapingian. Both carbonate and biosiliceous factories were under considerable stress prior to the Late Permian Extinction event. This reflects the Sverdrup Basin becoming progressively more acidic in response to build up of atmospheric CO2 throughout the Permian, leading to a gradual shoaling of the lysocline and the calcite compensation depth. It is proposed that ocean acidification initiated in response to amalgamation of the Pangea supercontinent which inhibited the silicate weathering-response through development of thick protective soil blankets. A latest Permian rapid and global temperature increase associated with Siberian Trap volcanism caused a rapid return to carbonate saturation even at lower pH.