Award: OCE-1559087

This project aims to advance our current state of knowledge regarding the mechanisms of P burial in marine sediments. The formation of calcium phosphate minerals in marine settings has long puzzled oceanographers. One of the major mechanisms proposed involves the precipitation of apatite minerals from an exogenous polyphosphate intermediate. However, the reaction pathways and geochemical conditions that lead to apatite precipitation via exogenous polyphosphate intermediates in marine systems remain unknown. The overall goal of this proposed research is to determine the mechanisms of exogenous polyphosphate mediated apatite precipitation in the marine environment using controlled laboratory and mesocosm experiments. Our research has achieved the following results: (1) An improved understanding of the ex situ hydrolysis of polyphosphate mediated by a variety of phosphatase enzymes under controlled laboratory conditions and simulated sea water condition, which provides insights into the kinetics and mechanisms of polyphosphate degradation mediated by extracellular enzymes, as well as the precipitation of calcium phosphate mineral(s) in the presence of both enzymatic activities and calcium. (2) A new research direction on the hydrolysis and degradation of polyphosphate in the presence of common mineral phases and metal cations, which provides insights into the kinetics and mechanisms of abiotic polyphosphate degradation under sedimentary conditions. (3) Insights into the transformation of polyphosphate into inorganic phosphate during the thermal treatment of solid biomass from sewage sludges, which was an extension of the project scope toward understanding phosphorus cycling in the context of human activities. Knowledge generated from this studies will transform our understanding of apatite formation in marine sediments, lead to predictive insight into which environments may (or may not) be particularly conducive to apatite precipitation through identified mechanisms. By examining routes of long-term P sequestration, our results have fundamental importance to understanding the factors regulating marine primary productivity, and related C sequestration over long timescales, and thus an understanding of the mechanisms that also drive global climate. Furthermore, this work will provide new insights into the cycling of marine polyphosphate, a historically under recognized form of phosphorus that has gained recent interest in oceanography. In addition to oceanography community, this research also has broad impacts on other disciplines. For example, phosphorus is a critical resource used in agricultural food production. However, majority of the phosphate mined for agricultural use is lost, primarily via runoff into coastal and inland waters. In addition to dwindling global P reserves and consequent threats on global food security, this unsustainable process also leads to the pollution of natural waters, eutrophication, and harmful algal blooms. Our results may have implications for strategies that may be developed to recycle phosphorus that is released to coastal and inland waters, thus closing the agricultural P cycle, limiting nutrient pollution in natural waters and enhancing future food security. Our work integrates research with education across multiple levels, both in the academy and public. Our research team consists of two junior female faculty, postdocs, PhD students, and undergraduate students with diverse scientific and cultural backgrounds. As such, our project provides the basis for a new generation of scientists with the ability to communicate effectively across traditional scientific and cultural lines, which is an important trait of a diverse globally-engaged STEM workforce. Engaging students in STEM research increases learning and retention, and motivates them to pursue careers in science and engineering. Our project combines student and postdoc training with undergraduate education and research, as well as K-12 and community outreach. Last Modified: 05/19/2019 Submitted by: Yuanzhi Tang