Evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions: implication for paleotemperature reconstruction

Gong, Changrui; Hollander, David J.

doi:10.1016/s0016-7037(98)00283-x

Cited by 120 publications

(77 citation statements)

References 37 publications

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“…Some of the apparent temperature offsets of up to 2.5 C therefore depended on the quality of the age models. Nevertheless, Gong and Hollander (1999) presented evidence over the last two centuries of deposition for an average U k 0 37 offset equal to 0.9 C at the oxic site. Another way to study the possibility of diagenetic alteration of the U k 0 37 index is to look for gradients in the index with preservation of initially homogeneous material.…”

Section: Effects Of Water Column Recycling and Sediment Diagenesis Onmentioning

confidence: 92%

“…In all instances where a change was reported, degradation resulted in a preferential loss of the C 37:3 alkenone, thereby producing a warm bias. Gong and Hollander (1999) compared U k 0 37 sediment data acquired down-core at two sites in the Santa Monica Basin that differed in bottom water oxygenation. They attributed a positive U k 0 37 offset at the oxic site to indicated preferential degradation of the C 37:3 ketone.…”

Section: Effects Of Water Column Recycling and Sediment Diagenesis Onmentioning

confidence: 99%

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Alkenone Paleotemperature Determinations

Herbert

2014

Treatise on Geochemistry

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Section: Effects Of Water Column Recycling and Sediment Diagenesis Onmentioning

confidence: 92%

Section: Effects Of Water Column Recycling and Sediment Diagenesis Onmentioning

confidence: 99%

Alkenone Paleotemperature Determinations

Herbert

2014

Treatise on Geochemistry

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“…During development of the alkenone paleothermometer, diagenesis (in both the water column and sediments) was discounted as altering U K9 37 (Prahl et al 1989;Teece et al 1998). However, it is now well established that alkenones are indeed sensitive to degradation during transport through the water column (as measured by decreasing POM fluxes) or in sediments (decreasing sediment concentrations) (Gong and Hollander 1999;Wakeham et al 2002;Kim et al 2009); only about 1/3 of the alkenones exported out of the euphotic zone in the EqPac survive transport to depth (i.e., 105-m flux of C 37:2 was about three times the 3459-m flux). Furthermore, laboratory experiments with degrading E. huxleyi cells (Rontani et al 2006(Rontani et al , 2008Prahl et al 2010) and field measurements of marine POM (Rontani et al 2009;Rontani and Wakeham 2008) show that C 37:3 is more susceptible to degradation by both aerobic bacteria and autoxidation than C 37:2 , thus altering U K9 37 values and producing a false ''warming'' beyond that expected from seasonal temperature and production/export effects.…”

Section: -Cismentioning

confidence: 99%

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Rontani

Zabeti

Wakeham

2011

Limnology & Oceanography

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The behavior of organic matter (OM) in suspended and sinking particles in the equatorial Pacific Ocean was monitored by measuring lipid degradation products that are specific for biodegradation, photooxidation, and autoxidation. Photodegradation and autoxidation were significant for lipids associated with both suspended and sinking particles. Abiotically degraded terrestrial material strongly contributed to suspended particles and to sinking material in the deep ocean, probably as the result of incorporation of terrestrial particles into sinking aggregates. Analyses of degradation products of 24-methylcholesta-5,22-dien-3b-ol, 24-ethylcholest-5-en-3b-ol, and cholest-5-en-3b-ol gave diagnostic information concerning the differential behavior of phytoplanktonic, terrestrial, and zooplanktonic OM, respectively. Planktonic lipids were more susceptible to biodegradation than terrestrial lipids and biodegradation was more intense in sinking particulate organic matter (POM) than suspended POM, which we attribute to efficient transfer of singlet oxygen from suspended and senescent phytoplankton cells to associated bacteria and subsequent inhibition of heterotrophic degradation. There is a direct link between the photooxidation state of lipids of senescent phytoplankton cells in suspended particles and the apparent resistance of lipids toward biotic degradation. Terrigenous vascular plant OM, which is strongly autoxidized on land or in the atmosphere as it is transported to the remote ocean, is only weakly biodegraded during sedimentation in this open ocean setting. A significant increase in alkenone-based U K9 37 values (+0.07 equivalent to an inferred temperature change of +2uC) was observed in sinking particles with depth and the detection of epoxyalkenones further confirming the potential detrimental effect of aerobic bacterial degradation processes on the U K9 37 paleotemperature proxy.

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“…Degradation of alkenones through water and sediment columns presumably affects the alkenone unsaturation index (Freeman and Wakeham, 1992;Hoefs et al, 1998;Gong et al, 1999). If this effect is relatively large, it introduces error into paleotemperature estimations that are based on the alkenone unsaturation index.…”

Section: Introductionmentioning

confidence: 99%

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Yamamoto

Shimamoto²,

Fukuhara³

et al. 2007

Deep Sea Research Part I: Oceanographic Research Papers

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Abstract:Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index U K' 37 . Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the 1 water-sediment interface on U K' 37 . Alkenone sinking flux and U K' 37 -based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the U K' 37 -based temperatures were lower than the contemporary SSTs, suggesting alkenone production in a well-developed thermocline (shallower than 30m). During low alkenone flux periods, the U K' 37 -based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C 37:2 and C 38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux,suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The U K' 37 -based temperature usually increased with increasing depth. The preservation efficiency of alkenones was ~2.7-5.2% at the water-sediment interface. Despite the significant degradation of the alkenones, there was little difference in U K' 37 levels between sinking particles and the surface sediment.

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Evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions: implication for paleotemperature reconstruction

Cited by 120 publications

References 37 publications

Alkenone Paleotemperature Determinations

Alkenone Paleotemperature Determinations

Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

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