Metal deposits reveal how ice ages reshaped oxygen levels across Earth's oceans
Earth's oceans repeatedly lost oxygen and produced metal deposits during the planet's deepest ice ages. An international team of researchers analyzed manganese and other chemical signatures preserved in more than 27,000 ancient seafloor samples collected from six continents.
An international research team delved into a 2-billion-year-old geological record, unearthing fresh insights into the interplay between ice ages and ocean oxygen levels. By analyzing manganese concentrations in over 27,000 marine sediment samples from six continents, the scientists discovered a striking latitudinal gradient—higher manganese levels in polar regions compared to tropical areas during major glaciations.
This pattern remains consistent across Earth's history, from the Huronian Ice Age to the Late Paleozoic Ice Age, challenging the notion that deoxygenation solely stems from warm climate periods.
The study, published in Nature Communications, emphasizes the importance of examining manganese gradients in relation to latitude. During glaciation events, the ocean's upper layers in tropical regions exhibited lower oxygen levels, allowing manganese to dissolve and accumulate in sediments. In contrast, polar waters maintained comparatively higher oxygen levels, inhibiting manganese dissolution.
This latitudinal pattern becomes even more pronounced when compared to non-glacial periods, where manganese concentrations were nearly flat.
The researchers utilized data from the Deep-Time Marine Sedimentary Element Database, a vast collection of geological samples from North America, South America, Europe, Asia, Africa, and Oceania. To bolster their findings, they compared manganese concentrations with other chemical tracers, such as molybdenum and uranium, which exhibit opposite responses to changing oxygen levels.
The simulations conducted using the cGENIE Earth system model corroborated the sedimentary record, indicating that during the Proterozoic Snowball Earth episodes, oxygen-poor upper oceans in the tropics prevailed.
The findings suggest that during major ice ages, ocean deoxygenation occurred simultaneously with cooling and warming periods. As atmospheric oxygen levels gradually increased, the manganese gradients weakened but remained detectable during major ice ages, mirroring the ongoing rise of oxygen in Earth's atmosphere. However, the study also highlights the need for further research into the complex interactions between global wind and ocean circulation changes under different climate states and their impact on ocean oxygen levels and habitability.
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