Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel

Diagenetic control of nitrogen isotope ratios in Holocene sapropels and recent sediments from the Eastern Mediterranean Sea

“…When comparing reconstructed TOC accumulation rates in the S1 sapropel with TOC fluxes in the sediment traps, we found that the modern flux rates would indeed suffice to produce a sapropel under appropriate preservation conditions: sediment traps recorded a TOC-flux of 207 to 294 mg m −2 y −1 in the deeper traps (at ∼2600 m), and 1300 mg m −2 y −1 in the shallow trap (1500 m). On the other hand, the TOC accumulation rate for the S1 sapropel of core #569 (1300 m) is roughly 450 mg m −2 y −1 , which agrees with accumulation rates calculated for a larger set of S1 by de Lange et al (2008). Not only is the accumulation rate similar, but also TOC content of sinking material is in the range known from the S1 sapropel (see Tables 3 and 4) that can reach up to 4% in the Levantine Sea (Moodley et al, 2005).…”

“…This matches experimental evidence of changes in δ 15 N in algal material exposed to oxic degradation (Lehmann et al, 2002). The sapropel deposited during anoxic conditions at the seafloor or in the water column below 1800 m water depth (de Lange et al, 2008), when decay was inhibited, retained the δ 15 N of primary production. The protosapropel that developed under suboxic conditions or that reflects a shortened residence time under oxic conditions (due to the onset of bottom-water anoxia) is slightly degraded and slightly enriched in δ 15 N over the sapropel base level.…”

“…As in surface sediments and S1, the differences between the sapropels must be due to differences in organic matter preservation that may have been caused by variable degrees of sediment/water column oxygenation during deposition: the depth of the oxycline and hence the oxygen exposure time of the sinking material have been variable for each sapropel interval as indicated by biomarker records. For the S5 sapropel (which has best preservation and lowest δ 15 N), molecular fossils of anaerobic, photolithotrophic green sulphur bacteria (Chlorobiacieae) evidence a relatively shallow oxic/anoxic interface at 150 to 300 m water depth (Rohling et al, 2006), whereas during S1 sapropel deposition the interface has been at ∼1800 m (de Lange et al, 2008). An unresolved question in this context arises from our sediment trap studies (see Sect.…”

“…Möbius (juergen.moebius@zmaw.de) Mediterranean sapropel formation is attributed to a stratified water column and anoxic deep water conditions that developed as a consequence of enhanced fresh water inputs (Ryan, 1972;Rossignol-Strick et al, 1982;Rohling, 1994;Emeis et al, 2000). The youngest sapropel -termed S1 -formed between 9800 and 5700 years ago (de Lange et al, 2008) at water depths below 400 m (Anastasakis and Stanley, 1986) with inferred deep-water anoxia everywhere below 1800 m water depth (de Lange et al, 2008). The sedimentary total organic carbon (TOC) concentration reaches more than 30% in some Pliocene sapropels (Emeis et al, 1996) and is approximately 2% in S1 (Murat and Got, 2000).…”

Low slip rates and multimillennial return times for Mw 7 earthquake faults in southern Calabria (Italy)

“…To find out alternative age constraints, we compared our findings with the results of Polonia et al [2013Polonia et al [ , 2015 from three boreholes drilled in the Calabrian offshore. These authors hypothesize that several seismically induced turbidite beds interrupt both the sapropel S1 deposition (10.8-6.1 ka) [De Lange et al, 2008] and the Holocene pelagic sedimentation in the distal CA. According to this hypothesis, we observe a net overlap among the ages of our paleoearthquakes and those measured or modeled for some turbidites ( Figure 5).…”