(Table 1) Stable nitrogen isotopes of ammonium in interstitial waters from ODP Site 164-997

• Main Authors: Borowski, Walter S, Paull, Charles K
• Format: Dataset
• Language: English
• Published: PANGAEA 2000
• Subjects: 164-997A; 164-997B; DEPTH; sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Event label; Joides Resolution; Leg164; Mass spectrometer VG SIRA; Nicaraguan Rise; North Atlantic Ocean; Ocean Drilling Program; ODP; Sample code/label; δ15N; ammonium; Sira; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.804017; https://doi.org/10.1594/PANGAEA.804017

Ammonium (NH4+) concentration profiles in piston-core sediments of the Carolina Rise and Blake Ridge generally have linear concentration profiles within the sulfate reduction zone (Borowski, 1998). Deep Sea Drilling Project (DSDP) Site 533, located on the Blake Ridge, also displayed a linear ammonium concentration profile through the sulfate reduction zone and the profile linearity continues into the upper methanogenic zone to a depth of ~200 meters below seafloor (mbsf), where the first methane gas hydrates probably occur (Jenden and Gieskes, 1983, doi:10.2973/dsdp.proc.76.114.1983; Kvenvolden and Barnard, 1983, doi:10.2973/dsdp.proc.76.106.1983). Sediments from the Ocean Drilling Program (ODP) Leg 164 deep holes (Sites 994, 995, and 997) also exhibit linear ammonium profiles above the top of the gas hydrate zone (~200 mbsf) (Paull, Matsumoto, Wallace, et al., 1996, doi:10.2973/odp.proc.ir.164.1996). We hypothesized that a possible cause of linear ammonium profiles was diffusion of ammonium from a concentrated ammonium source at depth. We further reasoned that if this ammonium were produced by microbial fermentation reactions at depth, that a comparison of the nitrogen isotopic composition of sedimentary organic nitrogen and the nitrogen with pore-water ammonium would test this hypothesis. Convergence with depth of d15N values of the nitrogen source (sedimentary organic matter) and the nitrogen product (dissolved NH4+) would strongly suggest that ammonium was produced within a particular depth zone by microbial fermentation reactions. Here, we report d15N values of pore-water ammonium from selected interstitial water (IW) samples from Site 997, sampled during ODP Leg 164.