(Air) and refers to reproducibility of the entire extraction and measurement
process (R. Anderson, pers. comm., 1998).Interstitial waters were collected from ODP cores using standard ODP methods with a hydraulic sediment press (Manheim, 1966) and collected in air-tight syringes (Manheim and Sayles, 1974). Ammonium concentration values were measured using the colorimetric method of Solorzano (1969) and the procedure outlined in Gieskes et al. (1991) (see Paull, Matsumoto, Wallace et al., 1996). Nitrate and nitrite were not measured but are assumed to be at near-zero concentration within pore waters. Filtered pore-water aliquots were stored immediately after squeezing in flame-sealed, air-tight ampoules for onshore measurement of nitrogen isotopes.
Ammonium extraction and
nitrogen isotopic measurements of pore-water ammonium were made by Coastal
Science Labs (Austin, Texas), using a modified procedure of Velinsky et al.
(1989) (R. Anderson, pers. comm., 1998). Ammonium was extracted from pore waters
by distillation into an HCl acid trap. Care was taken to ensure that the acid
trap did not become saturated, to avoid increased alkalinity, loss of NH3,
and isotopic fractionation. Ammonia was then captured onto an artificial zeolite
molecular sieve. The zeolite (with absorbed ammonia) was loaded into
borosilicate tubes with CuO and Cu, which were then evacuated, sealed, and
heated to 590șC. The resultant N2 is directed into a VG SIRA II
model mass spectrometer. Measurement precision is at least ±0.5
(Air) and refers to reproducibility of the entire extraction and measurement
process (R. Anderson, pers. comm., 1998).
Isotopic measurements of
nitrogen contained within sedimentary organic matter are reported in Olsen
(1997) and Paull et al. (Chap.
7, this volume). These measurements were performed
using a GC-CIRMS at the University of North Carolina, Chapel Hill. Measurement
uncertainty for the entire procedure is ±0.3
(H. Mendlovitz, pers. comm., 1998).
