Carbon contents and isotopic compositions from the ODP Hole 161-974C near the center of the Tyrrhenian Basin (Table 1)

DOI

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.

Supplement to: Meyers, Philip A; Bernasconi, Stefano M (2005): Carbon and nitrogen isotope excursions in mid-Pleistocene sapropels from the Tyrrhenian Basin: Evidence for climate-induced increases in microbial primary production. Marine Geology, 220(1-4), 41-58

Identifier
DOI https://doi.org/10.1594/PANGAEA.726198
Related Identifier https://doi.org/10.1016/j.margeo.2005.07.003
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.726198
Provenance
Creator Meyers, Philip A ORCID logo; Bernasconi, Stefano M ORCID logo
Publisher PANGAEA
Publication Year 2009
Rights Creative Commons Attribution 3.0 Unported; https://creativecommons.org/licenses/by/3.0/
OpenAccess true
Representation
Language English
Resource Type Supplementary Dataset; Dataset
Format text/tab-separated-values
Size 1566 data points
Discipline Earth System Research
Spatial Coverage (12.142 LON, 40.356 LAT); Tirreno Sea
Temporal Coverage Begin 1995-05-08T23:45:00Z
Temporal Coverage End 1995-05-10T21:00:00Z