Cycling of Nitrogen in Marine Dissolved Organic Matter Revealed by Radiocarbon Analysis of Individual Amino Acids

Dissolved organic nitrogen (DON) is one of the largest active pools of reduced N in the ocean, playing an important role in marine ecosystems. However, DON-specific ages and cycling rates remain largely unknown. Radiocarbon (¹⁴C) content indicates age since synthesis, representing a powerful tool for tracing the formation and cycling of organic molecules. However, the lack of ¹⁴C approaches specific to N-containing biomolecules has meant that direct estimates of DON cycling and age are essentially nonexistent.   Here we report a new method for the ¹⁴C analysis of individual amino acids (AAs),  the largest DON component which can be characterized at the molecular level. We show that by coupling multidimensional high-performance liquid chromatography (HPLC) with ultra-sensitive accelerator mass spectrometry (AMS), ¹⁴C analyses of individual AAs, including both their L- and D-enantiomers, can be achieved from ocean DON isolates.   We use this method to report the first L- and D- AA ¹⁴C ages  in both semi-labile high molecular weight (HMW) DON and refractory low molecular weight (LMW) DON, from the central CA margin. Specifically, we will use relative ¹⁴C ages of D-AA as direct tracers for persistence of bacterially synthesized DON components, comparing these with ¹⁴C ages of both L-AA as well as the total DOM fractions from which they derive, toward the ultimate goal of understanding the relative ages of DOC vs. DON pools, and the importance of bacterial sources in influencing DON persistence and cycling.

Presentation Preference: Oral

Primary Presenter: Yuchen Sun, University of California, Santa Cruz (sonyuushin@gmail.com)

Authors:

Yuchen Sun, Univerisity of California, Santa Cruz  (sonyuushin@gmail.com)

Taylor Broek, Stanford Univerisity  (tbroek@gmail.com)

Brett Walker, Unverisity of California, Irvine  (brettw1@uci.edu)

Matthew McCarthy, Univerisity of California, Santa Cruz  (mdmccar@ucsc.edu)