Nitrogen isotopic analysis of carbonate-bound organic matter in modern and fossil fish otoliths. (1st March 2018)

• Record Type: Journal Article
• Authors: Lueders-Dumont, Jessica A.; Wang, Xingchen T.; Jensen, Olaf P.; Sigman, Daniel M.; Ward, Bess B.
• Is Part Of: Geochimica et cosmochimica acta. Volume 224(2018)
• Page Start: 200
• Page End: 222
• Publication Date: 2018-03-01
• Subjects: Fish otolith -- Biogenic aragonite -- Nitrogen isotopes -- Atlantic cod; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2018.01.001
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The nitrogen isotopic composition (δ 15 N) of otolith-bound organic matter (OM) is a potential source of information on dietary history of bony fishes. In contrast to the δ 15 N of white muscle tissue, the most commonly used tissue for ecological studies, the δ 15 N of otolith-bound OM (δ 15 Noto ) provides a record of whole life history. More importantly, δ 15 Noto can be measured in contexts where tissue is not available, for example, in otolith archives and sedimentary deposits. The utility and robustness of otolith δ 15 N analysis was heretofore limited by the low N content of otoliths, which precluded the routine measurement of individual otoliths as well as the thorough cleaning of otolith material prior to analysis. Here, we introduce a new method based on oxidation to nitrate followed by bacterial conversion to N2 O. The method requires 200-fold less N compared to traditional combustion approaches, allowing for thorough pre-cleaning and replicated analysis of individual otoliths of nearly any size. Long term precision of δ 15 Noto is 0.3‰. Using an internal standard of Atlantic cod ( Gadus morhua ) otoliths, we examine the parameters of the oxidative cleaning step with regard to oxidant (potassium persulfate and sodium hypochlorite), temperature, and time. We also report initial results that verify the usefulness of δ 15 Noto for ecological studies. For three salmonid species, left and right otoliths from the same fish are indistinguishable. We find that the δ 15 Noto of pink salmon ( Oncorhynchus gorbuscha ) is related to the size of the fish for this species. We find that intra-cohort δ 15 Noto standard deviation for wild pink salmon, farmed brown trout ( Salmo trutta ), and farmed rainbow trout ( Oncorhynchus mykiss ) are all 0.4‰ or less, suggesting that δ 15 Noto will be valuable for population-level studies. Lastly, our protocol yields reproducible data for both δ 15 Noto and otolith N content in 17th century Atlantic cod otoliths. We find that 17th century cod are approximately 2 ‰ higher than modern cod, arguably consistent with either the larger size of the otoliths (and thus inferred for the fish) or with changes in baseline (primary producer) δ 15 N in the modern coastal ocean compared to the past. All told, the results of this study bode well for the utility of otolith-bound δ 15 N for investigating the environment and ecology of modern and past fish.