Sapropel Layers Research Articles

Geochemical and micropaleontological characterisation of a Mediterranean sapropel S5: A case study from core BAN89GC09 (south of Crete)

Several geochemical and micropaleontological proxies were studied in a well developed sapropel S5 from a core collected south of Crete to investigate the causes and the mechanisms of its deposition, to reconstruct the paleoenvironmental and paleoceanographical conditions at time of its formation and to detect the roles played by productivity and anoxia. The geochemical proxies are also used to unravel the sediment provenance and therefore to help tracing water circulation patterns and freshwater sources. The multiproxy approach reveals that the sapropel layer has high internal variability and five different depositional phases can be identified, four within the visible sapropel layer. An increase in temperature and the development of a Deep Chlorophyll Maximum characterise the onset of the sapropel (phase 1), with enhanced productivity being favoured by local riverine input, not clearly ascribable to Nile river freshwater discharge, and by the shoaling of the pycnocline/nutricline. Surface water stratification and productivity develop, together with strong seafloor dysoxia/anoxia. Phase 2 is characterised by lower stratification, slightly lower temperature and/or higher seasonal contrast, and still high productivity. Phase 3 records high productivity, high temperature and high stratification, probably more sustained by the Nile input. A sudden partial re-oxygenation takes place at the end of this phase, changing the main features of the sapropel. In the fourth phase, productivity starts to decrease, water stratification seems to be partially broken down and sediment oxygenation increases. A transitional phase (phase 5) occurs between the end of the visible sapropel and the normal pelagic post-sapropel sedimentation, where productivity is still high and oxygenation improves compared to the visible sapropel layer. The massive occurrence of Polysphaeridium zoharyi, cyst of a red tide forming dinoflagellate, also characterises this phase. The geochemical proxies indicate that pre-sapropel and post-sapropel sediments are quite different from each other, and the provenance shifts from a more mixed to a more markedly southern origin of sediments.

Carbon and nitrogen isotope excursions in mid-Pleistocene sapropels from the Tyrrhenian Basin: Evidence for climate-induced increases in microbial primary production

The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic δ 13C values systematically increase from − 26‰ to − 21‰ and δ 15N values systematically decrease from ∼4‰ to < 0‰ as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation.

Trans-Mediterranean comparison of geochemical paleoproductivity proxies in a mid-Pleistocene interrupted sapropel

Sapropel layers in the sediment record of the Mediterranean Sea reflect periods of climate-induced elevated marine production associated with precessional minima. Some of these layers feature interruptions that represent centennial-to-millennial returns to the predominantly low-productivity conditions of this sea. We have measured multiple geochemical paleoproductivity proxies in the interrupted sapropel layer that corresponds to insolation cycle 90 (955 ka) at 1-cm intervals in a four-site transect from the Balearic Basin to the Levantine Basin to assess similarities and differences in its expression at the four locations. The interrupted sapropels are similarly divided by an organic-carbon-poor interval into an upper layer in which organic carbon concentrations reach 2–7 wt.% and a lower layer in which they peak between 1 and 3 wt.%. The interruption was essentially synchronous in the Balearic Basin, the Tyrrhenian Basin, and the Ionian Basin, but it was delayed and shorter in the Levantine Basin. Lighter nitrogen isotope compositions consistently accompany higher organic carbon accumulation rates in the sapropel layers, which implies a shift from coccolith-dominated organic matter production towards a mode of primary production in which cyanobacteria were important during times of sapropel deposition. Organic carbon isotopic compositions become heavier as organic carbon accumulation increases at three of the locations, which is consistent with elevated productivity. However, they become lighter at the Levantine Basin site, which suggests greater delivery of isotopically light fluvial waters to this part of the Mediterranean Sea. The local paleoclimate conditions conducive to sapropel formation evidently were not completely uniform across the Mediterranean region but their occurrences were synchronous. Moreover, the co-existence of an essentially same-age interruption of the sapropels at the four locations shows that climate could change rapidly and concordantly across the region at much less than precessional intervals.

Possible paleo-exchange of water masses between the Mediterranean Sea, Marmara Sea and Black Sea

In this article a way for possible paleo-exchange of water masses between the Aegean, the Marmara and the Black Sea is submitted. A key aspect according to the interpretation on hand of the possible paleo-exchange of water masses is the depth of the Bosphorus sill for the period 20000 - 7000 cal. yr. BP. Determining an established constant depth for the Bosphorus sill for the period of 20000 - 7000 cal. yr. BP is an incorrect approach to the interpretation of the paleo-climatic and paleo-geological events in the Black Sea region. Due to this reason two models of the Bosphorus sill - deep sill and shallow sill models have been accepted. The deep sill model is valid for the first two stages of the period 20 000 - 14 500 cal. yr. BP. The shallow sill model is valid for the period ~12500-7000 cal. yr. BP. For the last stage of possible paleo-exchange of water masses between Aegean, Marmara and Black Seas (7500-7000 cal. yr. BP) as a result of continuing increase in the global sea level, saline ocean water catastrophically entered the Black Sea. The new moment of possible paleo-exchange of water masses between Aegean, Marmara and Black Seas is that once started the freshwater Black Sea outflow to the Marmara Sea in 14000 cal. yr. BP did not stop until about 12500 cal. yr. BP but continued to about 9500 cal. yr. BP. That contradicts the theory of Ryan et. al., (1997), Aksu et al. (2002). A new explanation for the formation of the lower sapropel layer in the Marmara Sea has been offered.

The environment of Venice area in the past two million years

A ca. 950 m thick succession that was continuously cored in 1971 in Venice has been revisited, in order to reconstruct the environmental history of the Venice area since about 2.15 Ma. Magnetic polarity stratigraphy, integrated with refined calcareous nannofossil biostratigraphy, provides a firm chronostratigraphic framing of the succession. In order to improve the chronological resolution, we derived astrochronological refinements in the lower Pleistocene sapropel-bearing interval by a comparison with other time-correlative sections in the Mediterranean. The pollen record is used as a proxy of climatic changes and as an indirect tool in the chronological reconstruction in the upper part of the succession. The following history has been inferred: (1) in the late Gelasian (late Pliocene), the depositional area was a strongly subsiding shelf which shoaled to near sea level; (2) following a hiatus of a minimum duration of 0.2 Myr, encompassing most of the Olduvai Subchron, the shelf rapidly drowned to bathyal depths over the early Pleistocene (biozones MNN 19a to 19e: from 1.947 Ma to 0.96 Ma). This interval was characterized by starved sedimentation (less than 10 cm/kyr), represented by hemipelagic muds interbedded with sapropel layers; (3) during most of biozone MNN19f ( Pseudoemiliania lacunosa Zone, 0.96–0.42 Ma) a thick package of turbidites was laid down as a result of massive terrigenous input from the eastern Southern Alps; (4) later, in the middle part of Chron 1n (Brunhes), deltaic sedimentation, primarily related to the progradation of the paleo-Po system, led to the progressive infill of the basin. This progradational episode was a major building phase, and ended with the first appearance of continental sediments, tentatively correlated with marine oxygen isotope substage 8.4; (5) the upper part of the succession shows a cyclic organization, with an upward increasing amount of marginal-marine and subaerial deposits. In this interval the Venice area was below sea level during glacioeustatic highstands but became emergent during subsequent major glacioeustatic lowstands. Pollen data support an overall good correspondence of continental sediment packages of sequences with glacial conditions and of maximum flooding intervals with interglacial conditions.

Influence of Northern Hemisphere climate and global sea level rise on the restricted Red Sea marine environment during termination I

We present high‐resolution paleoceanographic records of surface and deep water conditions within the northern Red Sea covering the last glacial maximum and termination I using alkenone paleothermometry, stable oxygen isotopes, and sediment compositional data. Paleoceanographic records in the restricted desert‐surrounded northern Red Sea are strongly affected by the stepwise sea level rise and appear to record and amplify well‐known millennial‐scale climate events from the North Atlantic realm. During the last glacial maximum (LGM), sea surface temperatures were about 4°C cooler than the late Holocene. Pronounced coolings associated with Heinrich event 1 (∼2°C below the LGM level) and the Younger Dryas imply strong atmospheric teleconnections to the North Atlantic. Owing to the restricted exchange with the Indian Ocean, Red Sea salinity is particularly sensitive to changes in global sea level. Paleosalinities exceeded 50 psu during the LGM. A pronounced freshening of the surface waters is associated with the meltwater peaks MWP1a and MWP1b owing to an increased surface‐near inflow of “normal” saline water from the Indian Ocean. Vertical δ18O gradients are also increased during these phases, indicating stronger surface water stratification. The combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers, which were deposited under almost anoxic condition in a stagnant water body.

Geochemical evidence for paleoclimatic variations during deposition of two Late Pliocene sapropels from the Vrica section, Calabria

The near-shore paleosetting of the Vrica Pliocene–Pleistocene boundary section provides an expanded sedimentary sequence that is ideal for investigating small-scale variations in sapropel deposition. We analyzed a suite of geochemical parameters in samples from a freshly drilled core that includes sapropelic layers c (1.851 Ma) and d (1.829 Ma) to characterize their depositional variation. Both sapropelic layers differ from background sediment by having higher total organic carbon (TOC) contents, lower δ 15N values, and higher contents of redox-sensitive and chalcophile elements. Layer c consists of a lower sub-layer in which TOC content is less than that of the upper sub-layer. Layer d exists as three sub-layers that are separated by low-TOC sediment. The lowermost sub-layer is weakly expressed and lacks chalcophile element enrichment. The other two sub-layers are strongly developed and illustrate that sapropel-forming conditions can be quickly established and interrupted. The two interruptions within layer d indicate a decrease in continental runoff, verifying the importance of humid conditions over continental borderlands and freshening of Mediterranean surface waters in forming sapropels. Although organic matter production was elevated during deposition of layers c and d, barium contents of sapropels and background sediment are similar, which shows that this paleoproductivity proxy is not suitable for shallow settings like Vrica. Our results confirm that considerable paleoclimatic variation can occur during deposition of an individual sapropel layer and in closely spaced sapropel events.

Grain size evidence for variations in delivery of terrigenous sediments to a Middle Pleistocene interrupted sapropel from ODP Site 969, Mediterranean Ridge

Grain size distributions of the <63-μm terrigenous fraction of closely spaced sediment samples were measured across an interrupted sapropel sequence at ODP Site 969 on the Mediterranean Ridge to explore possible climate-related changes in delivery of wind-borne particles. Size distribution patterns are generally typical of hemipelagic sediment with a subordinate amount of eolian material. However, the eolian fraction increases in the sapropel layers, which contrasts with findings from elsewhere in the Mediterranean but is consistent with other work at this location.

Pliocene sequence stratigraphy, climatic trends and sapropel formation in the Northern Apennines (Italy)

The Pliocene stratigraphy of the Romagna Northern Apennines foredeep has been reconstructed through mapping and measuring the different lithostratigraphic units. The physically correlated sedimentary bodies have been chronologically calibrated through biostratigraphic analyses. Analysis of facies and fossil content allowed reconstructing the main depositional systems and their evolution. The co-occurrence of shallow- to deep-water environments and carbonate to siliciclastic systems allowed understanding fully the role of eustasy and climate vs. continuous tectonic deformation controlling the accommodation and basin morphology. Following a limited sea-level lowering at 4.2 Ma, associated with the first signal of cooling in the Early Pliocene, a fast growing subtropical type carbonate platform developed, in response to warm and oligotrophic surface waters. Furthermore, a significant drop in sea-level at 3.75 Ma points to an important Pliocene continental glaciation in the Northern Hemisphere. During the subsequent transgression, warm and possibly humid climate favoured the deposition of the first Pliocene sapropel around 3.3 Ma. The growth of a second generation of carbonate platform between 3.3 and 3.042 Ma suggests a renewed warm period and limited runoff. At the top of this highstand, thick sapropels developed, which can easily be correlated across the Mediterranean. The platform abruptly drowned, was overwhelmed by bio-erosion and was covered by iron–phosphate crusts; whereas in the adjacent basins numerous sapropel layers occurred, rich of biosiliceous forms, documenting the shift from C carb to C org deposition. Strong oscillations of climate, due to precessionally controlled seasonality, and increased precipitation and runoff are considered as the main causes of the increase of surface water fertility. After the 2.87 Ma sea-level drop, again very significant, the sapropel rapidly disappears, in conjunction to the development of the lowstand wedge. After this cold period, which ended around 2.6 Ma, carbonate platforms never recovered due to the enduring cooler surface waters and the onset of an active drainage on the Apenninic range. This study documents the role of the eustatic variations on the Pliocene deposition of the actively deforming Northern Apennines foredeep. The abrupt lithostratigraphic changes appear also controlled by palaeoproductivity variations associated with climate and runoff.

Ongoing modification of Mediterranean Pleistocene sapropels mediated by prokaryotes.

Late Pleistocene organic-rich sediments (sapropels) from the eastern Mediterranean Sea harbor unknown, metabolically active chemoorganotrophic prokaryotes. As compared to the carbon-lean intermediate layers, sapropels exhibit elevated cell numbers, increased activities of hydrolytic exoenzymes, and increased anaerobic glucose degradation rates, suggesting that microbial carbon substrates originate from sapropel layers up to 217,000 years old. 16S ribosomal RNA gene analyses revealed that as-yet-uncultured green nonsulfur bacteria constitute up to 70% of the total microbial biomass. Crenarchaeota constitute a smaller fraction (on average, 16%). A slow but significant turnover of glucose could be detected. Apparently, sapropels are still altered by the metabolic activity of green nonsulfur bacteria and crenarchaeota.

Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence

Multi-proxy data and radiocarbon dates from several key cores from the Black Sea and Marmara Sea document a complex paleoceanographic history for the last ∼30 000 yr. The Marmara Sea was isolated from both the Black Sea and the Aegean Sea during glacial periods when global sea-level lowering subaerially exposed the shallow sills at the Straits of Bosphorus and Dardanelles (i.e. lake stage), and reconnected through both straits during interglacial periods, when rise of global sea level breached the shallow sills (i.e. gateway stage). Micropaleontological data show that during the ‘lake stage’ the surface-water masses in both the Marmara Sea and Black Sea became notably brackish; however, during the ‘gateway stages’ there was a low-salinity surface layer and normal marine water mass beneath. Two sapropel layers are identified in the Marmara Sea cores: sapropels M2 and M1 were deposited between ∼29.5 and 23.5 ka, and ∼10.5 and 6.0 ka, respectively. Micropaleontological and stable isotopic data show that the surface-water salinities were reduced considerably during the deposition of both sapropel layers M2 and M1, and calculation using planktonic foraminiferal transfer functions shows that sea-surface temperatures were notably lower during these intervals. The presence of fauna and flora with Black Sea affinities and the absence of Mediterranean fauna and flora in sapropels M1 and M2 strongly suggest that communication existed with the Black Sea during these times. A benthic foraminiferal oxygen index shows that the onset of suboxic conditions in the Marmara Sea rapidly followed the establishment of fully marine conditions at ∼11–10.5 ka, and are attributed to Black Sea outflow into the Marmara Sea since 10.5 ka. These suboxic conditions have persisted to the present. The data discussed in this paper are completely at odds with the ‘Flood Hypothesis’ of Ryan et al. (1997), and Ryan and Pitman (1999).

Palynology of sapropelic layers from the Marmara Sea

Palynological records of the sediments from the deep basins of the Marmara Sea revealed four palynological zones indicating the changing climatic conditions during Late Glacial to Holocene. The lower two zones were defined by the high abundance of Artemisia and Chenopodiaceae that suggest the climate of the source area was cold and arid. However, the establishment of Mediterranean warm and wet climate and corresponding regression of continental aridity were shown by the decreasing Chenopodiaceae and increasing pollen grains of humid-type vegetation in Zone C. The highest total pollen with the dominance of Quercus identifies the deglaciation and coincides with the formation of sapropelic layers in the Marmara Sea. The warmer and humid condition of deglaciation was indicated with diversified moisture-demanding deciduous and coniferous pollen grains in Zone B. These pollen assemblages and their distribution pattern indicate that the source area was warm and wet, during the deposition of sapropelic layers in the Marmara Sea, and also reflect signals of Black Sea origin.

Organic geochemistry and origin of Late Glacial–Holocene sapropelic layers and associated sediments in Marmara Sea

Organic geochemistry of two sapropel/sapropelic sediment units dated 10.6–6.4 and 3.8–3.2 kyr BP and associated sediments in two gravity cores from the Marmara Sea were studied to characterize the organic matter and discuss its paleoceanographic implications. Vertical trends of C/N ratio, δ 13C and hydrogen indices show that the flooding of the Marmara Sea by the Mediterranean waters at 12 kyr BP and onset of deposition of the lower sapropelic layer at 10.6 yr BP are characterized with a high input of terrestrial organic matter. This terrestrial input decreased and marine organic matter contribution increased in time towards the top of the upper sapropelic layer at 3.2 kyr BP. The lower sapropelic layer is broadly the same age and has a similar distribution of organic-matter type as the S 1 sapropel of the Aegean Sea, suggesting their depositions may have been controlled by the same events. Both the lower Marmara sapropelic layer and the Aegean S 1 sapropel were probably deposited during a time of high influx of organic-rich river waters from the Black Sea. This influx of Black Sea water could have induced water stratification in the Marmara Sea and Aegean Sea and lead to the deposition of the sapropels.

Factors controlling metal distributions in the surface sediments of the Erdek Bay, Sea of Marmara, Turkey

A geochemical study of the Erdek Bay sediments in the Sea of Marmara, Turkey, was carried out to investigate the heavy metal distributions and sources. The bay has an average depth of 34 m and a two-layer water column stratification, with a pycnocline at 20 m. The distribution of “total” metal (Fe, Mn, Pb, Cu, Ni, Cr, Zn and Hg) concentrations, together with sequential selective extraction analyses, shows that the relatively high metal concentrations are mainly due to land-based natural inputs from the erosion products of mineralized zones and mafic–ultramafic rocks delivered to the bay by two rivers from the south. However, some Pb, Zn and Cu occur in the Fe–Mn-oxyhydroxide and organic fractions, suggesting, in part, some anthropogenic inputs in addition to the predominantly natural inputs. The vertical distribution of metal/Al ratios in a gravity core in the bay shows no significant change with depth, except for an early diagenetic enrichment at 0.7–1.6 m below sea floor (mbsf) above a 4750–3500-year-old sapropelic layer. This distribution is a further indication of the insignificant antropogenic metal pollution in the bay.

Nd isotopic compositions of Eastern Mediterranean sediments: tracers of the Nile influence during sapropel S1 formation?

Abstract Nd isotopic composition of Eastern Mediterranean sediments are used to investigate the influence of Nile flux variations during the formation of the youngest sapropel S1. Four box cores located on an east–west transect (around 35°N) at increasing distance from the Nile source were studied. ϵ Nd(0) signatures were measured in the lithogenic (alumino-silicate residue) fraction and the authigenic/biogenic (carbonates, organic matter and Fe, Mn oxyhydroxides) fraction of the sediment after 1 M HCl leaching. The ϵ Nd(0) profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sediments. These profiles follow the Gaussian-shaped Ba/Al profile shape which defines S1. The ϵ Nd(0) variations can be related to changes in the proportions of two continental sources of particulate material: Nile particles and Saharan aerosols. A simple mixing model reveals that the contribution of Nile particulates to the sediments increases relative to Saharan aerosols during sapropel formation, indicating a higher Nile discharge and a decrease in eolian input at that time. For the cores located closest to the Nile fan, the ϵ Nd(0) signatures of the leachable fraction are always higher in the sapropel layer (−5 to −4) than in the adjacent sediments (∼−6). The sapropel layer ϵ Nd(0) values increase with decreasing distance to the Nile towards values close to the Nile particulates. All the results obtained on the leachable fraction point towards a massive input of Nile freshwater during S1 deposition.

Oxygen consumption in the Eastern Mediterranean

Rates of oxygen consumption are determined by fitting simulated oxygen concentrations to observations from a medium-resolution survey of the Eastern Mediterranean in 1987 (METEOR cruise M5/6). The simulations are obtained with a previously described two-dimensional kinematic model of the sea, which is newly calibrated using concurrent hydrographic and tracer data, and with oxygen consumption as a function of depth being parameterized following previous work. The consumption rate is obtained as R(z)=22 (z/100) −2 +0.31 μmol/(kg yr) for z <1000 m , and R =0.53 μmol/(kg yr) for z ⩾1000 m . For the waters below about 700 m depth, the uncertainty in R is approximately ±35%. Significant error contributions arise from the oxygen concentration of the waters newly supplied to the deep waters, and from possible deviations from a steady state in circulation and in oxygen cycling. The upper ocean rates are rather more uncertain, but they are compatible with rates from the literature. The deduced deep-water oxygen consumption rate is considerably higher than the rates found in previous deep-ocean work. Such rather high rates, which possibly are related to the comparatively high temperatures of the deep waters, have repercussions in various contexts, e.g. in the assessment of environmental conditions in the past that led to the formation of sapropel layers. The updated circulation model yields a deep-water renewal rate for the Eastern Mediterranean only moderately different from a previous value. The rate actually replenishing the deep regime amounts to 5.1×10 5 m 3/s (±20%), of which 2.8×10 5 m 3/s (±30%) are recirculated deep water. Convective renewal of the deep regime (>1200 m depth) by the combined addition of surface and intermediate waters requires 150 years (±30%).

Palaeoproductivity and post-depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the Eastern Mediterranean S1 sapropel

Abstract In the reconstruction of bioproductivity in surface waters the extent to which a proxy has been diagenetically altered is often a matter of debate. Here we investigate how organic- and calcareous-walled dinoflagellate cysts can be used for separately estimating bioproductivity and oxygen related diagenesis. This is achieved by studying the cyst content of the most recent Eastern Mediterranean sapropel S1, that is thought to have been deposited under conditions of increased primary production in surface waters and possible anoxia in the bottom waters. Based on chemical evidence, it has been shown that the visible sapropelic layer represents only the residual lower part of what was initially a much thicker sapropel, as a result of post-depositional decay of organic matter related to oxygen penetration into the sediments. The effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected, lower part of the initial sapropel and the ‘oxidised’ upper part. Comparing the unaffected sapropelic sediments with pre- and post-sapropelic material gives insight into the relationship between fossil cysts assemblages and palaeoproductivity. Impagidinium aculeatum, Impagidinium patulum, Operculodinium israelianum, Polysphaeridium zoharyi and probably Impagidinium spp., Impagidinium paradoxum and Nematosphaeropsis labyrinthus are very resistant against aerobic decay and their accumulation rates appear to be primarily related to productivity in surface waters. Protoperidinium and Echinidinium species, on the other hand, are shown to be very sensitive and can be used to recognise oxygen-related decay. The calcareous-walled dinoflagellate cysts seem to be unaffected by oxic organic matter decay in Mediterranean sediments.

Geochemical characteristics of late Quaternary sediments from the southern Aegean Sea (Eastern Mediterranean)

Ten cores from the southern Aegean Sea have been logged for their lithological composition and seventy-three sub-samples were analysed for the determination of major and trace elements concentrations. Four lithological units were identified, namely, mud, volcanic, turbidite and sapropel. On the basis of the “Z-2” Minoan ash layer radiocarbon age sedimentation rates for the southern Aegean Sea were estimated at 3.26 to 4.15 cm kyr -1. Simple correlation analysis revealed three groups of elements associated with: (1) biogenic carbonates; (2) terrigenous alumino-silicates and (3) sapropelic layers. R-mode factor analysis applied on the carbonate-free corrected data-set defined four significant factors: (1) the “detrital alumino-silicate factor” represented by Si, Al, Na, K, Rb, Zr, Pb and inversely related to Ca, Mg, and Sr; (2) a “hydrothermal factor” loaded with Cr, Ni, Co, Cu, Fe; (3) the “volcanic ash factor” with high loadings for Ti, Al, Fe, Na and (4) a “sapropel factor” represented by Ba, Mo, and Zn. High factor scores for the “hydrothermal factor” were observed in sediment samples proximal to Nisyros Isl., suggesting a potential hydrothermal influence. Red-brown oxides and crusts dredged from this area support further this possibility. The use of factor analysis enabled for a better understanding of the chemical elements associations that remained obscured by correlation analysis.

Timing and hydrological conditions of Sapropel events in the Eastern Mediterranean, as evident from speleothems, Soreq cave, Israel

This paper explores the connection between the timing of sapropel events in the Eastern Mediterranean Sea and the time of low δ 18O events in speleothems of the Soreq cave (Israel). A new well-dated δ 18O and δ 13C profile of the Soreq cave speleothems for the last 140 kyr reveals five prominent low δ 18O events dated at: 124 to 119 kyr, with the main peak at 122 kyr (event #V); 108 to 100 kyr with peaks at 107 and 102 kyr (event #IV); 85 to 79 kyr with peak at 80 kyr (event #III); 55 to 52 kyr with a peak at 54 kyr (event #II) and 8.5 to 7 kyr with peaks at 8.5 and 7 kyr (event #I). These events are characteristic of period of enhanced rainfall in the Eastern Mediterranean area, particularly so for events #V and #I, where the marked decrease in δ 18O and the correspondingly marked increase in δ 13C indicate very wet conditions. The chronology of the low δ 18O events #V, IV, III and #I match the ages estimated for the formation of sapropels S5, S4, S3 and S1 which are also associated with high hydrological activity. Thus, it is suggested that the low δ 18O events in the Soreq cave speleothems constrain the maximum duration of the sapropel formation. Pollen data from the sapropel layers and the isotopic pattern of the speleothems indicate that sapropels S5 and S1 were deposited during very wet periods when there were major decrease in the sea surface salinity, coupled with frost-free winters and drought-free summers. Sapropels S4 and S3 were formed during periods of increased precipitation, but ones in which the general climate was Mediterranean semi-arid.

Diverse methane concentrations in anoxic brines and underlying sediments, eastern Mediterranean Sea

Elevated methane (CH 4) concentrations (128–2692×10 3 nM) occur in the hypersaline anoxic brine pools of Bannock and Urania Basins, eastern Mediterranean Sea, compared to low concentrations (17–80×10 3 nM) in the sediments below the anoxic brines. The CH 4 enrichment in the brines might be due to the long residence time of the brine in the Basin. An attempt is made to determine the sources for the enriched dissolved CH 4 by considering the influence of hydrothermal activity, the occurrence of sapropel layers (biogenic) and dissolution of gas hydrates. Furthermore, it is suggested that the enriched CH 4 in Bannock and Urania Basins is diffused and mixed with the overlying waters by local upward transport mechanisms that selectively move CH 4 upward in these Basins.