Oceanic Anoxic Event 2 (OAE2) was a major environmental crisis that took place about 94 million years ago in the mid‐Cretaceous greenhouse world, when global ocean oxygen levels dropped sharply. This loss of oxygen led to disruptions in marine ecosystems, widespread organic carbon burial and changes in the carbon cycle. Scientists believe OAE2 was triggered by a surge in ocean nutrients—possibly from underwater volcanic activity associated with large igneous province (LIP) formation in oceans or increased rock weathering on land—which fueled massive algal blooms. However, the exact cause (submarine LIP volcanism vs. continental weathering) has been controversial. To resolve this, researchers from School of Earth Sciences and Engineering, Nanjing University studied iron isotopes of rocks from the Gongzha section, southern Tibet, China that preserves a well‐dated, high‐resolution OAE2 record. Iron is a key nutrient, and its isotopes can reveal whether it came from submarine LIP volcanism or land sources, as well as how much was used by marine life. The results show that iron isotope shifts match patterns of volcanic iron input and increased biological uptake (Fig. 1). Similar trends appear in other OAE2 records worldwide (Fig. 2), suggesting a global volcanic trigger. Hence, LIP‐related underwater eruptions—not weathering—was likely the major source of increased nutrients that sparked OAE2.

Fig.1 Iron isotope and Fe/Al data of the Gongzha section, southern Tibet along with other proxy data

Fig. 2 Similar patterns of iron isotope variations in the initial stage of OAE2 in Eastern Tethys (a), North Atlantic (b, c) and Western Tethys (d).

Source:

Li, B. C., Li, Y. X.*, Li, Y.Q., Li, W.Q., 2025. Iron isotope evidence for heightened primary productivity triggered by hydrothermally sourced nutrients during Oceanic Anoxic Event 2. Geophysical Research Letters. 52, e2024GL114116. https://doi.org/10.1029/2024GL114116