A Novel Approach Using Time‐Depth Distortions to Assess Multicentennial Variability in Deep‐Sea Oxygen Deficiency in the Eastern Mediterranean Sea During Sapropel S5

Dirksen, Jan Pieter; Hennekam, Rick; Geerken, Esmee; Reichart, Gert‐Jan

doi:10.1029/2018pa003458

Cited by 10 publications

(9 citation statements)

References 73 publications

(107 reference statements)

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“…The regime described in Fig. 6 can show a sudden termination of the sapropel, which is similar to that seen in records of sapropel S5 (Dirksen et al, 2019). In the model, such a sudden termination can only be achieved by forming deep water in open Mediterranean, by reverse the freshwater budget of the entire Mediterranean.…”

Section: Comparison With Geological Data and Other Modelssupporting

confidence: 83%

“…In the same core, the timing of the midpoint of S3 and S4 compared to insolation is the same, while that of S1 and S5 are different. S5 is much longer than all of the previous sapropels, does not have any burn down at at least one location (Dirksen et al, 2019), has an interruption in other locations (Rohling et al, 2006), and again shows generally different characteristics in different cores (Dirksen et al, 2019;Grant et al, 2016;Rohling et al, 2006). S6 again looks very different.…”

Section: Comparison With Geological Data and Other Modelsmentioning

confidence: 87%

“…Our model allows for such behaviour. Even when considering intra-sapropel variability, thereby surpassing a binary approach, the sapropel record is clearly not sinusoidal (see for example Grant et al, 2016;Dirksen et al, 2019).…”

Section: Describing Nonlinear Relationships and Transient Responsementioning

confidence: 99%

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The mechanism of sapropel formation in the Mediterranean Sea: Insight from long duration box-model experiments

Dirksen¹,

Meijer²

2019

Preprint

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Abstract. Periodic bottom water oxygen deficiency in the Mediterranean Sea has led to the deposition of organic rich sediments during geological history, so called sapropels. Although a mechanism linking the formation of these deposits to orbital variability has been derived from the geological record, physics-based proof is limited to snapshot and short time-slice experiments with (Oceanic) General Circulation Models. Specifically, previous modelling studies have investigated atmospheric and oceanographic equilibrium states during orbital extremes (minimum and maximum precession). In contrast, we use a conceptual box model that allows us to focus on the transient response of the Mediterranean Sea to orbital forcing and investigate the physical processes causing sapropel formation. The model is constrained by present day measurement data, while proxy data offers constraints on the timing of sapropels. The results demonstrate that it is possible to describe the first order aspects of sapropel formation in a conceptual box model. A systematic model analysis approach provides new insights on features observed in the geological record, such as timing of sapropels, intra-sapropel intensity variations and interruptions. Moreover, given a scenario constrained by geological data, the model allows us to study the transient response of variables and processes that cannot be observed in the geological record. The results suggest that atmospheric temperature variability plays a key role in sapropel formation, and that the timing of the midpoint of a sapropel can shift significantly with a minor change in forcing due to nonlinearities in the system.

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Section: Comparison With Geological Data and Other Modelssupporting

confidence: 83%

Section: Comparison With Geological Data and Other Modelsmentioning

confidence: 87%

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The mechanism of sapropel formation in the Mediterranean Sea: Insight from long duration box-model experiments

Dirksen¹,

Meijer²

2019

Preprint

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“…The clearly defined increase in monsoon intensity from~128.5 ka (Figure 9c), corroborated by rapid increases in terrigenous supply in the Nile outflow region (Dirksen et al, 2019), is some 200 years before the start of S5 deposition at~128.3 ka (Grant et al, 2016). This indicates a very rapid development of basin conditions to enable sapropel preservation following increased freshwater influx to Mediterranean surface waters.…”

Section: Sapropel Onsetmentioning

confidence: 71%

Quantification of African Monsoon Runoff During Last Interglacial Sapropel S5

Amies

Rohling

Grant

et al. 2019

Paleoceanog and Paleoclimatol

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Organic‐rich sapropel layers punctuate the eastern Mediterranean sedimentary sequence, recording deep‐sea anoxic events. The timing of sapropel deposition coincides with precession minima, which are associated with the northward migration of the monsoon rain belt over North Africa. The resultant increase in monsoon precipitation over the Sahara caused an increase in low‐δ18O freshwater runoff into eastern Mediterranean surface waters, which is reflected by negative δ18O anomalies in the records of planktic foraminiferal calcite. However, despite extensive research on sapropels, the magnitude of monsoon intensification and freshwater runoff, along with its influence on δ18O, remains elusive. Here, we present a quantification of African monsoon freshwater runoff into the eastern Mediterranean for the period of deposition of last interglacial sapropel S5 (~128.3–121.5 ka). Our method uses a box model of the Mediterranean Sea, which represents different water masses, and has been calibrated using δ18O from planktic foraminiferal species of different depth and seasonal habitats. The model was constrained with existing records of sea level and sea surface temperature then inverted to deconvolve the δ18O signal of the surface‐dwelling foraminiferal species Globigerinoides ruber (w) and calculate the freshwater runoff volume. Our calculated African monsoon runoff suggests large increases in freshwater discharge to the eastern Mediterranean (up to ~8.8 times the modern pre‐Aswan Nile discharge). Rapid onset of S5 deposition following the estimated increase in runoff strongly suggests a preconditioning of the eastern Mediterranean for sapropel deposition. Our study also provides insight into the stratification and warming of eastern Mediterranean surface waters during the S5 interval.

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“…This sample set included sediments from above, within, and below the sapropel horizon S65 (Grant et al, 2017), which was characterised by dark-coloured sediment. ODP Leg 160 shipboard biostratigraphic studies (Emeis and Party, 1996) and subsequent astrochronologies were used to tune the age model (Grant et al, 2017) that indicated the sediment for this core is of Pliocene age, 2.67 Ma. Sediment was freeze-dried and prepared for lipid extraction and TOC measurements.…”

Section: High-resolution Pliocene Sapropel (Levantine Basin)mentioning

confidence: 99%

Biomarker evidence for the occurrence of anaerobic ammonium oxidation in the eastern Mediterranean Sea during Quaternary and Pliocene sapropel formation

et al. 2019

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Abstract. The eastern Mediterranean Sea sedimentary record is characterised by intervals of organic-rich sapropel sediments, indicating periods of severe anoxia triggered by astronomical forcing. It has been hypothesised that nitrogen fixation was crucial in injecting the Mediterranean Sea with bioavailable nitrogen (N) during sapropel events. However, the evolution of the N biogeochemical cycle of sapropels is poorly understood. For example, the role of the complementary removal reactions like anaerobic ammonium oxidation (anammox) has not been investigated because the traditional lipid biomarkers for anammox, ladderane fatty acids, are not stable over long periods in the sedimentary record. Using an alternative lipid biomarker for anammox, bacteriohopanetetrol stereoisomer (BHT isomer), we present here for the first time N removal throughout the progression, e.g. formation, propagation, and termination, of basin-wide anoxic events. BHT isomer and ladderanes were analysed in sapropel records taken from three eastern Mediterranean sediment cores, spanning S1 to Pliocene sapropels. Ladderanes were rapidly degraded in sediments, as recently as the S5 sapropel. BHT isomer, however, was present in all sapropel sediments, as far back as the Pliocene, and clearly showed the response of anammox bacteria to marine water column redox shifts in high-resolution records. Two different N removal scenarios were observed in Mediterranean sapropels. During S5, anammox experienced Black Sea-type water column conditions, with the peak of BHT isomer coinciding with the core of the sapropel. Under the alternative scenario observed in the Pliocene sapropel, the anammox biomarker peaked at onset and termination of said sapropel, which may indicate sulfide inhibition of anammox during the core of sapropel deposition. This study shows the use of BHT isomer as a biomarker for anammox in the marine sediment record and highlights its potential in reconstructing anammox during past anoxic events that are too old for ladderanes to be applied, e.g. the history of oxygen minimum zone expansion and oceanic anoxic events.

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A Novel Approach Using Time‐Depth Distortions to Assess Multicentennial Variability in Deep‐Sea Oxygen Deficiency in the Eastern Mediterranean Sea During Sapropel S5

Cited by 10 publications

References 73 publications

The mechanism of sapropel formation in the Mediterranean Sea: Insight from long duration box-model experiments

The mechanism of sapropel formation in the Mediterranean Sea: Insight from long duration box-model experiments

Quantification of African Monsoon Runoff During Last Interglacial Sapropel S5

Biomarker evidence for the occurrence of anaerobic ammonium oxidation in the eastern Mediterranean Sea during Quaternary and Pliocene sapropel formation

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