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. 2025 Jul 4;11(27):eadv2756.
doi: 10.1126/sciadv.adv2756. Epub 2025 Jul 2.

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

Feifei Zhang  1 , Alexandre Pohl  2 , Maya Elrick  3 , Guang-Yi Wei  1 , Keyi Cheng  4 , Peter Crockford  5 , Mojtaba Fakhraee  6 , Yi-Bo Lin  1 , Na Li  1 , Xiang-Dong Wang  1 , Shu-Zhong Shen  1
Affiliations

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

Feifei Zhang et al. Sci Adv. .

Abstract

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 (δ138Ba) in two marine limestone sections in the Antler foreland basin (USA). We found the largest positive δ138Ba 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 δ138Ba 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.

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Figures

Fig. 1.
Fig. 1.. The geological localities of our two study sections.
(A) Early Mississippian paleogeography of North America, modified from Scotese and Wright (69) (https://creativecommons.org/licenses/by/4.0/). The red stars indicate the locations of the study areas in the present-day. (B and C) General paleogeographic reconstruction of the Antler foreland basin during the Early Mississippian (6, 8) showing the localities of SP (B) and PR (C).
Fig. 2.
Fig. 2.. The results for δ13Ccarb, δ138Ba, δ238U, and [Ba] for the PR and SP sections.
δ238U data are from Cheng et al. (8). The geochemical profiles of δ13Ccarb (A), δ138Ba (B), Ba content (C), δ238U (D) for the PR section, and δ13Ccarb (E), δ138Ba (F), Ba content (G) for the SP section. For each study site (PR and SP), all isotope data were generated from the same suite of samples. The two gray markers for the PR section represent samples with low δ18O values (−8.56 and −8.40‰). L. Dev., Late Devonian; M. Miss., mid-Mississippian. S. crenulata, Siphonodella crenulata; G. typicus, Gnathus typicus; S. sandbergi, Siphonodella sandbergi; S. isosticha, Siphonodella isosticha.
Fig. 3.
Fig. 3.. Seafloor anoxia and primary productivity in the Earth system model cGENIE.
(A) The extent of seafloor anoxia as a function of pCO2 and PO4 inventory. Each cell represents a single simulation. Numbers and colors represent the extent of anoxia (defined as the percentage of the global benthic surface characterized by seafloor [O2] ≤ 0 μmol kg−1). Red arrows and labels represent our preferred scenario discussed in the text, selected to capture the changes in ocean temperatures, benthic anoxia, and primary productivity. (B) As per (A) for the POC export production simulated globally. (C) As per (B) for POC export at PR. (C) As per (B) for SP. Note the different color scales used in each panel.
Fig. 4.
Fig. 4.. Ocean [O2] in the Earth system model cGENIE.
(A and B) Ocean [O2] at PR as a function of pCO2 and PO4 inventory at 120 m (A) and 350 m (B) below sea level. Red arrows and labels represent scenarios discussed in the text. (C) Ocean [O2] at SP as a function of pCO2 and PO4 inventory at 120 m below sea level. Sea level changes happening at SP are expected to be the same as at PR but could not be represented here because the bathymetry at SP is too shallow in our paleogeographical reconstruction for 360 Ma interpolated at the cGENIE model resolution. However, we note that sea level rise would, if anything, further lower ocean [O2]; the simulation of the extent of anoxia at SP is therefore not affected by this bathymetric feature, and anoxia at SP stands out as a robust model result that is poorly dependent on the model bathymetry. Note the different color scales used in each panel.
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