Influence of Anoxia on Nutrient Regeneration During Organic Matter Decomposition in the Orca Basin, Gulf of Mexico
Abstract
Controls on N and P regeneration during organic matter (OM) decomposition, particularly the effects of oxygenation, remain a topic of debate. It has alternately been argued that: there is no preferential regeneration of either N or P relative to C under normal marine (i.e., oxic) conditions; N is preferentially released under oscillating redox conditions; and P is preferentially released under anoxic conditions. Upon release, remineralized nutrients can be retained in sediments or can diffuse from sediments, making them available for biological utilization and thereby increasing primary productivity and the potential delivery of OM to the sediments. To address these questions, four sediment cores were taken from the Orca Basin under different depositional regimes, oxic, oscillating, transitional, and anoxic. The Orca Basin is a small, hypersaline, anoxic/sulfidic basin on the northwest slope of the Gulf of Mexico, located 290 km south of the Mississippi delta, thus the only factors that differ between the various cores are redox state and salinity. Cores were analyzed for total organic carbon (TOC), total nitrogen (TN), organic nitrogen (TON), organic C and N isotopes, as well as a phosphorus speciation including organic, oxide-associated, authigenic, and detrital forms of P. Results indicate impacts of the oxygen regime on OM remineralization. C/N ratios indicate no preferential release of N from OM during decay. However, the N released remains sequestered in the sediments as inorganic N, and is not released to bottom waters as effectively under oscillating redox conditions. P is released preferentially from sediments relative to both C and N under anoxic conditions compared to oxic conditions. These results agree with previous studies of sedimentary systems of equivalent or older age, but studies of water column and sediment trap OM remineralization show no preferential release of P under anoxic conditions. Presumably, the timescale of study is important for the observation of preferential release of P during anoxic remineralization. It appears that decades to centuries are required for observable differences in the remineralization of C, N, and P during diagenesis.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMPP34A..02W
- Keywords:
-
- 0404 Anoxic and hypoxic environments (4802;
- 4834);
- 1051 Sedimentary geochemistry;
- 1055 Organic and biogenic geochemistry;
- 4802 Anoxic environments (0404;
- 1803;
- 4834;
- 4902);
- 4850 Marine organic chemistry (0470;
- 1050)