A systematic study of highly branched isoprenoids (HBI) was carried out in
suspended particulate material (SPM) and Washington coastal sediments to determine
their origin and fate. SPM collected at 10 m depth was filtered through Nitex
membranes. C₂₅ HBI were found only in the 1.2-40 μm range over the shelf. The
particle size fractionation of SPM shows different enrichment for HEH, a common
hydrocarbon in phytoplankton, and the sum of C₂₅ HBI in the finer fractions suggesting
these hydrocarbons do not share a common source. The distribution of C₂₅ and C₃₀ HBI
correlates with the chlorophyll maxima suggesting an upper-water microbial source
associated with phytoplankton biomass.
It has been hypothesized that sulfur addition into specific biomarkers occurs
during the early stages of diagenesis. Incorporation of the HBI into a refractory
geomacromolecule via a sulfur linkage or formation of HBI-thiophenes are not evident
in the sedimentary lipids. HBI show a rapid decrease in concentration with depth in both
midshelf and slope sediments suggesting that biodegradation is the major pathway for
their disappearance in Washington coastal sediments.
Sediment cores from a midshelf and slope locations show the existence of
suboxic/anaerobic conditions within the first 5 cm in the sediments. Elemental sulfur
distribution in the midshelf appears to be controlled by bioturbation. On the slope, its
profile indicates a quasi steady state regime.
Phytane and phytenes (∑Phy) are the major products of Raney nickel
desulfurization in both midshelf and slope sediments. Spinach and a strain of Emiliana
huxleyi treated with Raney nickel showed strikingly similar patterns to the
desulfurization products of sedimentary lipids. The amount of ∑Phy in the slope
decreases abruptly by a factor of 6 in the top 2 cm and gradually increases with depth.
These results are interpreted as phytyl coming from two sources: (1) chlorophyll-a and
(2) S-bound to geomacromolecules. Partial released of phytyl moieties from chlorophyll-a
warrants a reevaluation of Raney nickel as a selective desulfurizing agent before its
application for paleoenvironmental reconstruction.
Reducing micro-environments appear to exist within the bioturbated zone in shelf
sediments. However, there is no clear evidence for phytyl moieties S-linked to
macromolecules within the mixed layer. Results obtained during this study indicate that
sulfur incorporation to biomarkers, although present, does not represent a significant
mechanism for the preservation of organic carbon in normal marine sediments. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29575 |
| Date | 23 September 1993 |
| Creators | Pinto Alvarez, Luis A. |
| Contributors | Prahl, Fredrick G. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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