@article{516,
  author = {X.T. Wang and D.M. Sigman and A.L. Cohen and D.J. Sinclair and R.M. Sherrell and M.A. Weigand and D.V. Erler and H. Ren},
  title = {Isotopic composition of skeleton-bound organic nitrogen in reef-building symbiotic corals: A new method and proxy evaluation at Bermuda},
  abstract = {The skeleton-bound organic nitrogen in reef-building symbiotic corals may be a high-resolution archive of ocean nitrogen cycle dynamics and a tool for understanding coral biogeochemistry and physiological processes. However, the existing methods for measuring the isotopic composition of coral skeleton-bound organic nitrogen (hereafter, CS-δ15N) either require too much skeleton material or have low precision, limiting the applications of this relatively new proxy. In addition, the controlling factors on CS-δ15N remain poorly understood: the δ15N of source nitrogen and the internal nitrogen cycle of the coral/zooxanthellae symbiosis may both be important. Here, we describe a new ("persulfate/denitrifier"-based) method for measuring CS-δ15N, requiring only 5mg of skeleton material and yielding a long-term precision better than 0.2{\textperthousand} (1σ). Using this new method, we investigate CS-δ15N at Bermuda. Ten modern Diploria labyrinthiformis coral cores/colonies from 4 sampling sites were measured for CS-δ15N. Nitrogen concentrations (nitrate+nitrite, ammonium, and dissolved organic nitrogen) and δ15N of plankton were also measured at these coral sites. Among the 4 sampling sites, CS-δ15N shows an increase with proximity to the island, from  3.8{\textperthousand} to  6.8{\textperthousand} vs. atmospheric N2, with the northern offshore site having a CS-δ15N 1-2{\textperthousand} higher than the δ15N of thermocline nitrate in the surrounding Sargasso Sea. Two annually resolved CS-δ15N time series suggest that the offshore-inshore CS-δ15N gradient has persisted since at least the 1970s. Plankton δ15N among these 4 sites also has an inshore increase, but of only  1{\textperthousand}. Coral physiological change must explain the remaining ( 2{\textperthousand}) inshore increase in CS-δ15N, and previous work points to the coral/zooxanthellae N cycle as a control on host tissue (and thus carbonate skeletal) δ15N. The CS-δ15N gradient is hypothesized to result mainly from varying efficiency in the internal nitrogen recycling of the coral/zooxanthellae symbiosis. It is proposed that, in more productive inshore waters, greater food uptake by the coral causes a greater fraction of its low-δ15N regenerated ammonium to be excreted rather than assimilated by zooxanthellae, raising the δ15N of the inshore corals. If so, coral tissue- and CS-δ15N may prove of use to reconstruct and monitor the state of the coral/zooxanthellae symbiosis over space and time. {\textcopyright} 2014 Elsevier Ltd.},
  year = {2015},
  journal = {Geochimica et Cosmochimica Acta},
  volume = {148},
  pages = {179-190},
  publisher = {Elsevier Ltd},
  url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84918589651\&doi=10.1016\%2fj.gca.2014.09.017\&partnerID=40\&md5=a3de6b6462db52ceee05454e100283b5},
  doi = {10.1016/j.gca.2014.09.017},
  note = {ps_limited_html},
}