Publication Summaries

Here I am posting short summaries for my published manuscripts, written for folks who are not scientists (or are not in the same scientific field). My hope is to increase public outreach and education. Please feel free to contact me with any questions. This idea was inspired by Jeff Clements. I am working backward through my (admittedly small) collection of manuscripts, and will have summaries of all of them up soon!

Regional patterns in ammonia-oxidizing communities throughout Chukchi Sea waters from the Bering Strait to the Beaufort Sea

Julian Damashek, Kade P. Pettie, Zach W. Brown, Matt M. Mills, Kevin R. Arrigo, and Chris A. Francis. Published in Aquatic Microbial Ecology, 2017.

The Chukchi Sea along the western coast of Alaska is a shallow and dynamic region of the Arctic Ocean. Productivity here is rampant in the summer, and rates of nitrogen (N) cycling processes are very high – because Chukchi Sea water flows into the central basin of the Arctic Ocean (and then into the northern Atlantic Ocean), N cycling in the Chukchi has big impacts on nutrient cycling throughout the region. We investigated ammonia-oxidizing microbes (ammonia-oxidizing archaea, called “AOA” or Thaumarchaeota; and ammonia-oxidizing bacteria, called “AOB”) throughout the coastal Chukchi Sea and the deeper adjacent Beaufort shelf. Ammonia oxidizers live by oxidizing ammonia to nitrite, an important step in the marine N cycle. To determine the abundance and activity of ammonia oxidizers, we used quantitative polymerase chain reaction (qPCR) assays to determine the number of their genes and RNA transcripts present in the water, with separate assays (i.e., separate quantifications) for AOA, AOB, and two specific AOA clades called “Water Column A” and “Water Column B,” which are thought to be adapted to shallow and deep ocean waters, respectively. Based on previous coastal ocean studies, we anticipated finding high AOA abundance and low AOB abundance in both regions, and far more Water Column A archaea in the Chukchi Sea and Water Column B archaea over the Beaufort shelf. In deeper, nutrient-poor Beaufort shelf waters, we indeed saw far more AOA genes (mostly Water Column B) than AOB genes. Surprisingly, throughout the shallow and nutrient-rich coastal Chukchi Sea, we found a relatively high number of AOB genes (comparable to AOA genes) and WCB genes. Ascribing mechanistic causes for these patterns is challenging, but we hypothesized: (1) AOB thrive in Chukchi Sea waters when they get “trapped” by currents at the bottom of the water column, where ammonium builds up over time due to decomposition of organic matter; and (2) WCB were transported into the Chukchi Sea from the north by physical processes (upwelling) that transport deep water from the Beaufort Sea into shallower regions. Surprisingly, transcript abundances of WCA and WCB suggested both clades were active throughout the Chukchi Sea: even when transported out of what we think is their “happy zone,” WCB may still be active – though we don’t know how this translates into growth or biogeochemical impacts. In all, we found distinct ammonia-oxidizing communities between these two Arctic regions, and our data suggest local physical processes (currents, upwelling, etc.) have substantial impacts on microbial populations.


(Photo by Zach Brown)