Award: OCE-1061934

NSF-OCE project #1061934 was a collaborative effort in which three complementary labs work towards furthering our understanding of the nature and extent of the microbial communities that live in the seafloor aquifer. Recent studies have shown that cracks and fissures in the seafloor host a seemingly abundant community of microbes. The fluids in these cracks constitute the "subsurface aquifer", which is the largest aquifer on Earth. While it may be odd to think of an aquifer beneath an ocean, it is a distinct feature through which seawater circulates and emerges with some degree of chemical alteration. During this project, we postulated that the microbes that live in this aquifer may play a role in changing the chemical composition of these fluids. In particular, we wondered if these microbes are living off of organic matter that is entrained with the seawater as it enters the aquifer, or whether they are "making a living", so to speak, via some other means. We also wondered whether these microbes change the chemical composition of the seawater in a way that benefits the microbes, alga, and animals that live in the upper ocean. We especially wanted to know if the subsurface microbes are helping to release metals and other trace elements into the aquifer water. These in turn may have a profound influence on the health of organisms living in the overlying water. To that end, the goals of my research in this effort was to A) determine the composition of the microbial community, their metabolic rates, and B) the changes -if any- in the geochemistry of the surrounding fluids. In brief, we found that these microbes are likely changing the abundance of trace elements in marked and biologically-relevant ways, even if they are not altering the concentrations of the major components of seawater. Also, we found that this microbial community may be engaged in primary production despite living in the absence of sunlight. Primary production is the process of converting carbon dioxide to sugars, which plants do by harnessing energy from the sun. Some microbes can do this using chemical energy, without dependence on sunlight, and those living in the North Pond aquifer have that potential as well. Finally, our data show that the microbes living in the North Pond aquifer are comparable in density to the overlying water column, which suggests that they are not any more energy-limited (or replete for that matter) than the microbes in the deep ocean water. In sum, these subsurface microbes are reasonably abundant, quite active, possibly engaged in primary production, and playing a role in altering the composition of the fluids that pass through the aquifer. Two postdocs, one masters student, and several high school students from a local high school were involved in this research. Ulrike Jaekel was the first postdoctoral fellow on this project, and she benefited from this effort by learning new techniques in the Girguis lab. She is currently a lead scientist as a major oil company. Beate Kraft was the second postdoctoral fellow on this project, and she benefited by learning new techniques as well as developing hew approaches to study these kinds of samples. She is leaving my lab in 2016 to a research scientist position, and will be taking these technologies with her. Jenny Delaney is a Masters student who worked on this project, is now staying on as a lab manager here at Harvard. Finally, through our high school internship program with the Cambridge-Rindge and Latin School (a public high school that is renowned for the socio-economic diversity of its student body), several high school students participated in this research, and have since pursued undergraduate degrees in the sciences and engineering. This outcomes of this effort were the cornerstone of our educational and public outreach efforts in the last three years. These data, and their significance to our understanding of the oceans, were presented to the public through a ser...