USAP-DC

The project addressed fundamental questions regarding the role of nitrification (the conversion of ammonium to nitrate by a two-step process involving two different guilds of microorganisms: ammonia- and nitrite-oxidizers) in the Antarctic marine ecosystem. Specifically, the project evaluated the contribution of carbon fixation supported by energy derived from the oxidation of nitrogen compounds (chemoautotrophy) to the overall supply of organic carbon to the food web of the Southern Ocean. Additionally, the project aimed to determine the significance of the contribution of other sources of reduced nitrogen, specifically organic nitrogen and urea, to nitrification because these contributions may not be assessed by standard protocols.

We quantified the oxidation rates of 15N supplied as ammonium, urea and nitrite, which allowed us to estimate the contribution of urea-derived N and complete nitrification (ammonia to nitrate, N-3 to N+5) to chemoautotrophy in Antarctic coastal waters. We compared these estimates to direct measurements of the incorporation of dissolved inorganic 14C into organic matter in the dark for an independent estimate of chemoautotrophy. We made measurements on samples taken from the major water masses: surface water (~10 m), winter water (35-174 m), circumpolar deep water (175-1000 m) and slope water (>1000 m); on a cruise surveying the continental shelf and slope west of the Antarctic Peninsula in the austral summer of 2018 (LMG18-01). Samples were also taken to measure the concentrations of nitrite, ammonia, urea and polyamines; for qPCR analysis of the abundance of relevant marker genes; and for studies of processes related to the core questions of the study. The project relied on collaboration with the Palmer LTER for ancillary data (bacterioplankton abundance and production, chlorophyll, physical and additional chemical variables). The synergistic activities of this project along with the LTER activities provides a unique opportunity to assess chemoautotrophy in context of the overall ecosystem's dynamics, including both primary and secondary production processes.

This project resulted in the training of a postdoctoral researcher and provide undergraduate students opportunities to gain hand-on experience with research on microbial geochemistry. This project contributed substantially to understanding an important aspect of nitrogen cycling and bacterioplankton production in the study area. Both PIs participate fully in the education and outreach efforts of the Palmer LTER, including making highlights of the findings available for posting to the LTER project web site, posting material to web sites at their respective departments, and incorporating material from the study in lectures and seminars presented at their respective institutions.

Person	Role
Hollibaugh, James T.	Investigator and contact
Popp, Brian	Co-Investigator

Antarctic Organisms and Ecosystems	Award # 1643466
Antarctic Organisms and Ecosystems	Award # 1643345

USAP-1643466_1

Deployment	Type
LMG1801	ship expedition

DMP_OPP163466.pdf

Repository	Title (link)	Format(s)	Status
R2R	Expedition data of LMG1801	Not Provided	exists
BCO-DMO	"Collaborative research: Chemoautotrophy in Antarctic bacterioplankton communities supported by the oxidation of urea-derived nitrogen"	Not Provided	exist

1. Doherty, S. C., Maas, A. E., Steinberg, D. K., Popp, B. N., & Close, H. G. (2021). Distinguishing zooplankton fecal pellets as a component of the biological pump using compound‐specific isotope analysis of amino acids. Limnology and Oceanography, 66(7), 2827–2841. (doi:10.1002/lno.11793)