(Appendix) Carbon and nitrogen isotope ratios of ODP Site 160-964
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2010
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| _version_ | 1867169052318760960 |
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| author | Higgins, Meytal B Robinson, Rebecca S Carter, Susan J Pearson, Ann |
| author_facet | Higgins, Meytal B Robinson, Rebecca S Carter, Susan J Pearson, Ann |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | Nitrogen isotopes of chlorins, degradation products of chlorophyll, reflect the isotopic composition of nutrient N utilized by marine phytoplankton communities. Here we show that in sediments of the eastern Mediterranean Pleistocene and Holocene, values of d15N for chlorins and total nitrogen vary in concert, with a consistent offset of ~5 per mil reflecting the fractionation imparted during chlorophyll biosynthesis. Samples from the Integrated Ocean Drilling Program Sites 964 and 969 were analyzed at a sampling resolution of ~4-10 cm, clustered around sapropel events 2, 3, 4 and 5 (~100-170 ka). In low organic content sediments, chlorin values of ~0 per mil coincident with total nitrogen values of ~+ 5 per mil indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment. In sapropel horizons, the chlorin and total nitrogen values are 5 per mil more negative (~-5 per mil and ~ 0 per mil, respectively), resembling previously-reported, modern-day water-column particulates (~0 per mil). We suggest that nutrient conditions in the Eastern Mediterranean correspond to three scenarios and that the similarity between sapropel and modern-day bulk d15N is coincidental. Organic-poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of Atlantic-sourced nitrate. Sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine P fluxes to surface waters. Present-day conditions are dominated by anthropogenic N sources. These scenarios agree with a model of sapropel formation in which stratification caused by increased fresh-water inputs led to N fixation due to P:N nutrient imbalance. Enhanced production combined with stratification promoted and maintained anoxic deep waters, consequently increasing organic matter preservation. Such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_786705 |
| institution | PANGAEA |
| language | en |
| publishDate | 2010 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | (Appendix) Carbon and nitrogen isotope ratios of ODP Site 160-964 Higgins, Meytal B Robinson, Rebecca S Carter, Susan J Pearson, Ann 160-964; Carbon, organic, total; Carbon, organic, total, standard deviation; Comment; COMPCORE; Composite Core; DEPTH, sediment/rock; Eastern Basin; Joides Resolution; Leg160; Nitrogen, total; Nitrogen, total, standard deviation; Ocean Drilling Program; ODP; Sample comment; Δδ15N; Δδ15N, standard deviation; δ13C, organic carbon; δ13C, standard deviation; δ15N; δ15N, standard deviation Nitrogen isotopes of chlorins, degradation products of chlorophyll, reflect the isotopic composition of nutrient N utilized by marine phytoplankton communities. Here we show that in sediments of the eastern Mediterranean Pleistocene and Holocene, values of d15N for chlorins and total nitrogen vary in concert, with a consistent offset of ~5 per mil reflecting the fractionation imparted during chlorophyll biosynthesis. Samples from the Integrated Ocean Drilling Program Sites 964 and 969 were analyzed at a sampling resolution of ~4-10 cm, clustered around sapropel events 2, 3, 4 and 5 (~100-170 ka). In low organic content sediments, chlorin values of ~0 per mil coincident with total nitrogen values of ~+ 5 per mil indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment. In sapropel horizons, the chlorin and total nitrogen values are 5 per mil more negative (~-5 per mil and ~ 0 per mil, respectively), resembling previously-reported, modern-day water-column particulates (~0 per mil). We suggest that nutrient conditions in the Eastern Mediterranean correspond to three scenarios and that the similarity between sapropel and modern-day bulk d15N is coincidental. Organic-poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of Atlantic-sourced nitrate. Sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine P fluxes to surface waters. Present-day conditions are dominated by anthropogenic N sources. These scenarios agree with a model of sapropel formation in which stratification caused by increased fresh-water inputs led to N fixation due to P:N nutrient imbalance. Enhanced production combined with stratification promoted and maintained anoxic deep waters, consequently increasing organic matter preservation. Such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans. |
| title | (Appendix) Carbon and nitrogen isotope ratios of ODP Site 160-964 |
| topic | 160-964; Carbon, organic, total; Carbon, organic, total, standard deviation; Comment; COMPCORE; Composite Core; DEPTH, sediment/rock; Eastern Basin; Joides Resolution; Leg160; Nitrogen, total; Nitrogen, total, standard deviation; Ocean Drilling Program; ODP; Sample comment; Δδ15N; Δδ15N, standard deviation; δ13C, organic carbon; δ13C, standard deviation; δ15N; δ15N, standard deviation |
| url | https://doi.org/10.1594/PANGAEA.786705 |