Enhanced marine biological pump as a trigger for the onset of the late Paleozoic ice age.

The mid-Tournaisian carbon isotope excursion (TICE) represents the largest positive carbon isotope excursion in the late Paleozoic, coinciding with the onset of the late Paleozoic ice age (LPIA). Here, to investigate changes in the marine biological pump during the TICE, we measured barium isotopes (δBa) in two marine limestone sections in the Antler foreland basin (USA). We found the largest positive δBa shifts recorded in geological history, indicating increased marine export productivity in the Antler foreland basin, followed by the productivity-driven expansion of anoxia. The nearly identical stratigraphic trends, along with different absolute values in δBa between the two sites, suggest spatial differences in marine biological pump intensity during the Early Mississippian. Earth system model simulations indicate that a global increase of 30% in marine export productivity is needed to explain observed changes. Our findings support the idea that an enhanced marine biological pump contributed to elevated organic carbon burial and the transition from a greenhouse climate to the LPIA.