Smith Lecture: Nutrient Cycling in Low-oxygen Marine Environments: Engineering Solutions, Invasive Species, Microbes, and Beyond
Oxygen-depleted regions of the ocean are expanding as a result of human activities. Use of fertilizers, sewage discharge into the coastal ocean, and climate change all contribute to this phenomenon, which has grave implications for marine ecosystems and causes shifts in nutrient dynamics. During this talk, I explore how such redox transitions affect nutrient cycling through the use of comprehensive geochemical data sets and mathematical models. Initially focussing on phosphorus (and iron) cycling, I examine the geochemical implications of hypoxia both in coastal regions and deep basins of the Baltic Sea – the world's largest anthropogenic "dead zone". Engineering solutions have been proposed for countering declining oxygen conditions in the Baltic Sea and, therefore, I consider the implications of one such remediation strategy. Next, I examine the impact of invasive macrofauna on benthic nutrient cycling, which are afforded the opportunity to become established when the native are displaced by hypoxia. Finally, I turn my attention to the role of microbial communities that mediate much of low-temperature geochemistry. I propose a novel gene-centric modelling approach for resolving cryptic geochemical cycles and apply this to elucidate nitrogen cycling in the Arabian Sea oxygen minimum zone.