A case of post-depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the Madeira Abyssal Plain

Prahl, Fredrick G.; Lange, Gert J. de; Scholten, S.; Cowie, Gregory L.

doi:10.1016/s0146-6380(97)00078-8

Cited by 118 publications

(103 citation statements)

References 30 publications

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“…The homogeneity of the unoxidized samples is also illustrated by the identical δ 13 C values of the TOC in both unoxidized samples. The oxidized samples are 0.65‰ to 2.2‰ lighter than the oxidized samples, which is consistent with data by McArthur et al (1992) and Prahl et al (1997) for the MAP a-, e-, and f-turbidites. Turbidite 18x shows a relatively small decrease of 0.65‰, whereas turbidite 23x is 2.2‰ lighter.…”

Section: Resultssupporting

confidence: 89%

“…It was concluded that the OM was degraded largely nonselectively upon oxic degradation, although oxic degradation was far more extensive than degradation with sulfate alone. Prahl et al (1997), on the other hand, concluded that TOC degradation is to some extent compound selective, because some marine phytoplankton biomarkers and plantwax n-fatty acids were lost from the oxidized samples to an extent at least as great as that for TOC, and higher plantwax-derived n-alkanes were enriched relative to TOC. They also reported that the OM was composed of marine and terrestrial components.…”

Section: Introductionmentioning

confidence: 99%

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Changes in kerogen composition across an oxidation front in Madeira Abyssal Plain turbidites as revealed by pyrolysis GC-MS

Damsté¹,

Hoefs²,

Leeuw³

et al. 1998

Proceedings of the Ocean Drilling Program, 157 Scientific Results

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Isolated kerogens from Madeira Abyssal Plain turbidite samples were qualitatively and semiquantitatively studied by means of analytical pyrolysis for the effect of oxygen exposure on organic matter preservation. The initial organic matter in the turbidite is very homogeneous and relatively high and offers an ideal case for the study of oxygen effects on organic matter preservation without the usual complications of varying sources or sedimentation rates and bioturbation. From all four studied turbidites, one sample from the oxidized part of the turbidite was compared with two samples from the unoxidized part. The aliphatic character of the kerogens after postdepositional oxidation has increased significantly, as revealed by the abundance of the n-alkanes and n-alk-1-enes in the oxidized turbidite. At the same time, the contribution of the isoprenoid alkanes and alkenes and the alkylthiophenes to the pyrolysate has decreased significantly. The relative abundances of alkylbenzenes, alkylnaphthalenes, alkylphenols, alkylindenes, and alkan-2-ones in the pyrolysates have remained relatively constant upon oxidation. The alkylbenzene, alkylphenol, alkylnaphthalene, n-alkane, and n-alk-1-ene, isoprenoid alkane, and alkene internal distributions are substantially altered in the oxidized samples. This study shows that postdepositional oxidation of sedimentary organic matter by oxygen is far more severe than by sulfate alone. Furthermore, it is clear that oxidation of the organic matter is, to a significant degree, selective.

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Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Changes in kerogen composition across an oxidation front in Madeira Abyssal Plain turbidites as revealed by pyrolysis GC-MS

Damsté¹,

Hoefs²,

Leeuw³

et al. 1998

Proceedings of the Ocean Drilling Program, 157 Scientific Results

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“…The strong increase of both IPL-derived and CL-GDGT abundance with TOC is in agreement with the behavior of other biomarkers, as revealed previously in studies addressing oxic degradation of biomarkers (e.g. Prahl et al, 1997;Hoefs et al, 2002;Sinninghe Damsté et al, 2002a) and suggests that preservation of IPL GDGTs is also strongly dependent on oxygen exposure times.…”

Section: Sedimentary Production and Preservation Of Gdgtssupporting

confidence: 89%

Intact polar and core glycerol dibiphytanyl glycerol tetraether lipids in the Arabian Sea oxygen minimum zone. Part II: Selective preservation and degradation in sediments and consequences for the TEX86

Lengger

Hopmans

Reichart

et al. 2012

Geochimica et Cosmochimica Acta

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The TEX 86 is a proxy based on a ratio of pelagic archaeal glycerol dibiphytanyl glycerol tetraether lipids (GDGTs), and used for estimating past sea water temperatures. Concerns exist that in situ production of GDGTs lipids by sedimentary Archaea may affect its validity. In this study, we investigated the influence of benthic GDGT production on the TEX 86 by analyzing the concentrations and distributions of GDGTs present as intact polar lipids (IPLs) and as core lipids (CLs) in three sediment cores deposited under contrasting redox conditions across a depth range from 900 to 3000 m below sea level in and below the Arabian Sea oxygen minimum zone (OMZ). Direct analysis of IPLs with crenarchaeol as CL via HPLC/ESI-MS 2 revealed that surface sediments in the OMZ were relatively depleted in the phospholipid hexose, phosphohexose (HPH)-crenarchaeol compared to suspended particulate matter from the water column, suggesting preferential and rapid degradation of this IPL. In sediment cores recovered from deeper, more oxic environments, concentrations of HPH-crenarchaeol peaked at the surface, probably due to in situ production by ammonia-oxidizing Archaea, followed by a rapid decrease with increasing depth. No surface maximum was observed in the sediment core from within the OMZ. In contrast, the glycolipids, monohexose-crenarchaeol and dihexose-crenarchaeol, did not change in concentration with depth in the sediment, indicating that they were relatively well preserved and likely mostly derived from fossil pelagic GDGTs. These results suggest that phospholipids are more sensitive to degradation, while glycolipids might be preserved over longer time scales, in line with previous incubation and modeling studies. Furthermore, in situ produced IPL-GDGTs did not accumulate as IPLs, and did not influence the CL-TEX 86 . This suggests that in-situ produced GDGT lipids were more susceptible to degradation than fossil CL and IPL and did not accumulate as CL. In agreement, no significant changes of TEX 86 with sediment depth in the core lipids were observed. However, consistent differences between IPL-derived TEX 86 and CL-TEX 86 were found. These could be explained by a different composition of CL-GDGT of the glyco-and phospholipids, in combination with dissimilar degradation rates of phospholipids vs. glycolipids. We also observed consistent differences in both IPL-derived and CL-TEX 86 between the different cores, equivalent to 3°C when converted to temperature, despite the proximity of the core locations. These differences may potentially be due to a larger addition of GDGTs produced in deeper, colder waters to the (sub)surface-derived GDGTs for the deeper core sites.

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“…Sampling location was the MAP in the eastern North Atlantic at 31° 26.8'N 024° 48.8'W in the proximity of well-studied turbidite deposits (De Lange, 1992;Cowie et al, 1995;Prahl et al, 1997;Cowie et al, 1998;Hoefs et al, 2002;Huguet et al, 2008;Huguet et al, 2009). The f-turbidite is a > 140 kyr old, ca.…”

Section: Samplingmentioning

confidence: 99%

“…These mixed and organic-rich sediments are oxidized by an oxidation front that moves slowly downward after deposition, referred to as the process of diagenetic burn-down (De Lange, 1992). This process of oxidation causes a decrease in lipid concentrations that can reach up to two orders of magnitude (Cowie et al, 1995;Prahl et al, 1997;Cowie et al, 1998;Hoefs et al, 2002). The substantial decrease in the concentration of all GDGTs across similar oxidation fronts of the MAP as reported by Huguet et al (2008) occurred in combination with preferential degradation of iGDGT over brGDGT molecules.…”

Section: Introductionmentioning

confidence: 99%

Differential degradation of intact polar and core glycerol dialkyl glycerol tetraether lipids upon post-depositional oxidation

Lengger

Kraaij

Tjallingii

et al. 2013

Organic Geochemistry

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Archaeal and bacterial glycerol dialkyl glycerol tetraether lipids (GDGTs) are used in various proxies, such as TEX 86 and the BIT index. In living cells, GDGTs contain polar head groups (intact polar lipids -IPLs). IPL GDGTs have also been detected in ancient marine sediments and it is unclear whether or not they are fossil entities or are part of living cells. In order to determine the extent of degradation of IPL GDGTs over geological timescales, we analyzed turbidite deposits, which had been partly reoxidized for several kyr after deposition on the Madeira Abyssal Plain. Analysis of core lipid (CL) and IPL-derived GDGTs showed a reduction in concentration by two orders of magnitude upon post-depositional oxidation, while IPL GDGTs with a mono-or dihexose head group decreased by 2-3 orders of magnitude. The BIT index for CL-and IPL-derived GDGTs increased substantially upon oxidation from 0.1 to up to 0.5. Together with changing MBT/ CBT values, this indicates preferential preservation of soil-derived branched GDGTs over marine isoprenoid GDGTs, combined with in situ production of branched GDGTs in the sediment. The TEX 86 value for IPL-derived GDGTs decreased by 0.07 upon oxidation, while that of CL GDGTs showed no significant change. Isolation of IPLs revealed that the TEX 86 value of monohexose GDGTs was 0.55, while the TEX 86 value for dihexose GDGTs was substantially higher, 0.70. Thus, the decrease in TEX 86 for IPL-derived GDGTs was in agreement with the dominance of monohexose GDGTs in the oxidized turbidite, probably caused by a combination of in situ production as well as selective preservation of terrestrial isoprenoid GDGTs. Due to the low amount of IPL GDGTs vs. CL GDGTs, the impact of IPL degradation on CL-based TEX 86 paleotemperature estimates is negligible.

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A case of post-depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the Madeira Abyssal Plain

Cited by 118 publications

References 30 publications

Changes in kerogen composition across an oxidation front in Madeira Abyssal Plain turbidites as revealed by pyrolysis GC-MS

Changes in kerogen composition across an oxidation front in Madeira Abyssal Plain turbidites as revealed by pyrolysis GC-MS

Intact polar and core glycerol dibiphytanyl glycerol tetraether lipids in the Arabian Sea oxygen minimum zone. Part II: Selective preservation and degradation in sediments and consequences for the TEX86

Differential degradation of intact polar and core glycerol dialkyl glycerol tetraether lipids upon post-depositional oxidation

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