Toxic waters extended across 5% of global ocean 93.9 mn years ago

Washington: A new study has suggested that oxygen-free and hydrogen sulfide-rich waters extended across roughly five percent of the global ocean 93.9 million years ago.

The research team led by University of California, Riverside biogeochemists reported that it was far more than the modern ocean`s 0.1 percent but less than previous estimates for this event. The research suggests that previous estimates of oxygen-free and hydrogen sulfide-rich conditions, or "euxinia," were too high. Nevertheless, the limited and localized euxinia were still sufficiently widespread to have dramatic effect on the entire ocean`s chemistry and thus biological activity. Team member Jeremy D. Owens, a former UC Riverside graduate student, who is now a postdoctoral scientist at the Woods Hole Oceanographic Institution, said that these conditions must have impacted nutrient availability in the ocean and ultimately the spatial and temporal distribution of marine life. He said that under low-oxygen environments, many biologically important metals and other nutrients are removed from seawater and deposited in the sediments on the seafloor, making them less available for life to flourish. Owens said that their work shows that even though only a small portion of the ocean contained toxic and metal-scavenging hydrogen sulfide, it was sufficiently large so that changes to the ocean`s chemistry and biology were likely profound. He asserted that what this says is that only portions of the ocean need to contain sulfide to greatly impact biota. For their analysis, the researchers collected seafloor mud samples, now rock, from multiple localities in England and Italy. They then performed chemical extraction on the samples to analyze the sulfur isotope compositions in order to estimate the chemistry of the global ocean. The study has been published in the Proceedings of the National Academy of Sciences.