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| Format: | Dataset Open Access |
| Language: | en |
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PANGAEA
2009
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| Online Access: | https://doi.org/10.1594/PANGAEA.726198 |
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| _version_ | 1867171763333365760 |
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| author | Meyers, Philip A Bernasconi, Stefano M |
| author_facet | Meyers, Philip A Bernasconi, Stefano M |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic d13C values systematically increase from -26 per mil to -21 per mil and d15N values systematically decrease from ~4 per mil to <0 per mil as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_726198 |
| institution | PANGAEA |
| language | en |
| publishDate | 2009 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | Carbon contents and isotopic compositions from the ODP Hole 161-974C near the center of the Tyrrhenian Basin (Table 1) Meyers, Philip A Bernasconi, Stefano M 161-974C; Accumulation rate, calcium carbonate; Accumulation rate, total organic carbon; AGE; Calcium carbonate; Calculated; Calculated as atomic ratio; Carbon, organic, total; Carbon/Nitrogen ratio; Carbon organic/inorganic ratio; Density, dry bulk; Depth, composite; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Element analyser CHN, Carlo Erba; Element analyser CHNS-O, Carlo Erba EA1108; Intercore correlation; Joides Resolution; Leg161; Ocean Drilling Program; ODP; Sample code/label; Sedimentation rate; Tirreno Sea; δ13C, organic carbon; δ15N The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic d13C values systematically increase from -26 per mil to -21 per mil and d15N values systematically decrease from ~4 per mil to <0 per mil as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation. |
| title | Carbon contents and isotopic compositions from the ODP Hole 161-974C near the center of the Tyrrhenian Basin (Table 1) |
| topic | 161-974C; Accumulation rate, calcium carbonate; Accumulation rate, total organic carbon; AGE; Calcium carbonate; Calculated; Calculated as atomic ratio; Carbon, organic, total; Carbon/Nitrogen ratio; Carbon organic/inorganic ratio; Density, dry bulk; Depth, composite; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Element analyser CHN, Carlo Erba; Element analyser CHNS-O, Carlo Erba EA1108; Intercore correlation; Joides Resolution; Leg161; Ocean Drilling Program; ODP; Sample code/label; Sedimentation rate; Tirreno Sea; δ13C, organic carbon; δ15N |
| url | https://doi.org/10.1594/PANGAEA.726198 |