The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

During the Pleistocene epoch, diatom mat blooming occurred in the global ocean for serval times, particularly during several glacial periods (MIS 14, 12, 6, 4, 2). One intriguing phenomenon related to these blooming is the deposition of Ethmodiscus rex diatom mats in tropical-subtropical oligotrophic marine zones. However, the causal mechanism of this occurrence, known as the " Ethmodiscus rex problem " remains under debate and it is crucial to understand this mechanism. This study investigates the diatom mat core GT01, which was enriched in E. rex and retrieved from the Mariana Trench’s Challenger Deep in the Western equatorial Pacific Ocean. We aim to determine the geological age of the diatom blooming event through AMS ¹⁴C dating and to explore the nitrogen source of the diatom bloom using δ¹³C, δ¹⁵Norg, and other proxies, and conduct a semi quantitative assessment of the sea surface productivity status during that period.

By comparing the nitrogen isotope signals and considering the isotopic fractionation effects of diatom biology and remineralization, it is suggested that the main source of nitrogen nutrients for E. rex diatom bursts is subsurface nitrate rather than the "new nitrogen". This viewpoint aligns with the findings of previous biological studies on Ethmodiscus species. Based on the nitrogen nutrient source, there is a further hypothesis that E. rex diatoms may also uptake nutrients such as phosphate concurrently with subsurface nitrate. The carbon isotope signal indicates a significant increase in marine primary productivity during the flourishing of E. rex diatoms. The extensive remineralization of organic matter during deposition, along with the substantial production of respired carbon, may have contributed to the reduction of atmospheric CO₂ concentration during glacial periods.

As primary producer in the ocean, diatoms are crucial in coupling nitrogen and carbon cycles in marine ecosystems. Investigating the nutrient sources and productivity of diatom mats is vital for gaining insights into the oceanic carbon and nitrogen cycles. These findings enhance our understanding of global biogeochemical cycles and their broader implications for past marine productivity and climate regulation.
 

mat-forming diatom; algae blooming; marine productivity; oceanic respired carbon pool; carbon isotope maxima events