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 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. This sea is a very productive part of the ocean in summer – lots of phytoplankton growth and associated animal activity (birds, fish, etc.). Rates of nitrogen (N) cycling processes are very high, and due to how the water moves around the Arctic, N cycling in the Chukchi has impacts on nutrient distributions throughout much of the Arctic Sea. However, little is known about many of the important N-cycling microbes, including ammonia oxidizers.

We investigated 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. Measuring the number of their genes and RNA transcripts present in the water is the method we employed to look at the abundance and activity of these microbes – i.e., how many of them live in these waters, and how metabolically active are they.

Based on previous coastal ocean studies, we anticipated finding high AOA abundance and low AOB abundance in both regions, but this was not what we found. In deeper Beaufort shelf waters (off the northern coast of Alaska, closer to the central Arctic Sea), we indeed saw far more AOA genes than AOB genes, as expected. But throughout the shallow and nutrient-rich coastal Chukchi Sea, we found a relatively high number of AOB genes (comparable to AOA genes), and found high abundances of a specific archaeal clade that is typically abundant only in deep ocean waters. 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 phytoplankton; and (2) “deep-ocean” microbes were transported into the Chukchi Sea from the north by currents (upwelling, in this case) that transport deep water from the Beaufort Sea into shallower regions. Surprisingly, transcript abundances of different archaeal clades were similar, suggested both types were active: even when transported out of what we think is their “happy zone,” the deep-ocean archaea 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, decomposition  of organic material) have substantial impacts on microbial populations. There is a lot we still don’t know about thees ammonia oxidizers in the Chukchi Sea, but this study helped fill out the picture of their population structure and activity across a large section of this part of the ocean.

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(Photo by Zach Brown)

 

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