Award: OCE-1357242

Intellectual Merit: Understanding the natural carbon cycle is important for society. This importance is due to the role of carbon dioxide in climate change and the many ecological roles that dissolved organic carbon (DOC) plays in natural waters. One of the roles of DOC is to provide sustenance to the bacteria at the base of foodweb in many natural waters. Another is to deliver carbon from the land, through rivers, to the sea. Today we know that rivers deliver a lot of DOC to the ocean, yet when we look in the ocean we do not readily find this land derived carbon. Why this river DOC disappears so quickly has puzzled scientists for decades. Our project provided insight into how this river DOC is being processed when it reaches the ocean. Specifically, we wanted to understand how DOC quality – in this case its ease of accessibility as food for microbes – and microbial communities co-varied in coastal waters, and whether adding a little bit of highly accessible DOC led to an increase in the use of apparently inaccessible DOC by microbes. This latter effect is called priming. Priming has been proposed as a reason why river DOC, which seems to be hard for bacteria to degrade, disappears quickly when it reaches the ocean when new, easily accessible carbon is added by marine life. Much of our project focused on determining if priming actually happens in coastal waters and what mechanisms coastal marine bacteria use to breakdown this material. Trying to identify priming is challenging. Correspondingly, our work involved a mixture of fieldwork, laboratory experiments and advanced molecular analytical techniques. These studies were conducted across the three lead institutions in the project: University Tennessee Knoxville led by Dr. Alison Buchan and Dr. Drew Steen; Florida State University by Dr. Robert Spencer, and; Skidaway Institute of Oceanography, University of Georgia by Dr. Aron Stubbins. Additional sample analysis was conducted in the laboratory of Dr. Thorsten Dittmar at Oldenburg University in Germany. During the project we discovered new linkages between bacteria and riverine DOC that have advanced our understanding of how bacteria process river DOC in the coastal ocean. We also developed new analytical techniques that will advance scientists ability to measure small changes in ocean carbon and should improve their ability to better quantify the conversion of DOC to carbon dioxide in ocean waters, which is one of the most important carbon fluxes on the Earth. Our priming experiments gave varying answers dependent upon the methods used to look for priming and the timeframes of the experiments, leaving priming as an enigmatic phenomenon in need of further investigation. Broader Impacts: The project directly supported the interdisciplinary and multi-institutional training of graduate students at each of the universities involved and several undergraduate students, including Research Experiences for Undergraduates (REU) students from the University of Tennessee Knoxville and Savannah State University. Funding from this project also supported the continued development an outreach program at a primarily minority high school in Newark NJ. Finally, the scientific advances made have or continue to be presented to the public and scientific communities through outreach activities, scientific meetings, and scientific publications. Last Modified: 12/21/2018 Submitted by: Alison Buchan