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Improved ultraviolet photo‐oxidation system yields estimates for deep‐sea dissolved organic nitrogen and phosphorus
Author(s) -
Foreman Rhea K.,
Björkman Karin M.,
Carlson Craig A.,
Opalk Keri,
Karl David M.
Publication year - 2019
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.1002/lom3.10312
Subject(s) - environmental chemistry , persulfate , chemistry , dissolved organic carbon , organic matter , phosphorus , nitrogen , ocean gyre , environmental science , oceanography , subtropics , geology , ecology , organic chemistry , biology , catalysis
Photolysis of dissolved organic matter using high‐intensity, ultraviolet (UV) light has been utilized since the 1960s as a method for the oxidation and subsequent quantification of dissolved organic nitrogen and phosphorus (DON and DOP) in both freshwater and marine water. However, conventional UV systems yielded variable and sometimes unreliable results; consequently, the method fell out of favor throughout much of the oceanographic community. Researchers turned to other oxidation methods such as persulfate oxidation or high‐temperature combustion, even though they have difficulty when DON and DOP are <10% of the total dissolved N and P (for example, in the deep sea and in surface waters at high latitudes). Here, we revive the UV oxidation method using modernized light‐generating equipment and high‐precision colorimetric analysis of the oxidation products, resulting in the most well‐constrained full ocean depth profiles of DON and DOP that are available to date. At Station ALOHA, in the North Pacific Subtropical Gyre, in the depth range of 900–4800 m, we find that DON is 2.2 ± 0.2 μ mol L −1 ( n = 49), DOP is 0.049 ± 0.004 μ mol L −1 ( n = 19), and the DOC : DON : DOP molar stochiometric relationship is 759 : 45 : 1. Preliminary estimates for the global ocean inventories of refractory DON and DOP are placed at 43.6 Pg N and 2.14 Pg P.