Sapropel Layers Research Articles

Origins of authigenic gypsums and carbonate minerals in sediments at a cold seep site in the Sea of Marmara

In the Western High of the Sea of Marmara, where pervasive gas hydrate and hydrocarbon gas seepage occurs, late Pleistocene-Holocene sediments are composed of a lower lacustrine and an upper marine unit. The sedimentary evolution, gypsum formation and carbonate anomaly, under the complex sedimentary environment at cold seep sites on the Western High, have not been systematically well explained. The transition from the lacustrine to marine unit occurs at around 7.5 m below the sea floor (mbsf), with a sulfidization front present in the lacustrine sediments just below it, and the marine unit includes a sapropel layer between 5.20 and 7.20 mbsf. The sedimentary sequence is characterized by authigenic minerals including pyrite, carbonates, and gypsum in the upper 0.50 mbsf, corresponding to the present-day sulfate-methane transition zone (SMTZ) near the seafloor. Mineralogical, chemical and isotopic compositions (13C, 18O, 34S, 26Mg) of the sediments in the core studied show their close relationship with intensive sulfate-driven anaerobic oxidation of methane (AOM) and other hydrocarbons. The dissolution of carbonate, related to the gas and oil migration, and organic matter enrichment might be the main cause of carbonate deficiency in the sapropel unit. Heavy carbon isotopic composition (δ13CCarb = 6.98‰) of carbonate at 4.30 mbsf implies that the carbon might be the residual by-product of subsurface biodegradation of seeping petroleum. The formation of secondary gypsum and partial dissolution of carbonate in the Sea of Marmara is commonly considered of being associated with the aerobic oxidation of pyrite. However, the euhedral authigenic gypsum studied might be with different origins, possibly including anaerobic oxidation of Fe-sulfides, carbonate deficiency in the sapropel unit and AOM. Gypsums below SMTZ are with the size of hundreds of microns. Linear pits and grooves are developed on these gypsum surfaces, probably due to corrosion by the methane-rich fluid of latest hydrocarbon seepage. Platy hexagonal gypsum in SMTZ, without any corrosion on crystal surface, might be associated with the changing flux of the acidic composition (e.g. CO2) in the seepage. Depleted-26Mg by about 1‰ in the SMTZ might be caused by the upward seepage of hydrocarbons. Magnesium isotope of authigenic carbonate could be a valid proxy for the recognition of SMTZ in a hydrate geo-system.

The Cretan Basin (South Aegean Sea, NE Mediterranean) in the Early Pliocene: a paleoceanographic reconstruction

The Aegean Sea (NE Mediterranean) represents a key area for climatic and oceanographic future projections, therefore it is crucial to define its environmental evolution during the Pliocene paleoclimatic analogue. The DSDP Site 378, located in the South Aegean Cretan Basin, provides an exceptional opportunity to investigate in detail the paleoceanographic conditions of the Early Pliocene and to examine the basin's paleoenvironmental evolution, through the study of calcareous nannofossil accumulation rates and hydroclimate proxies. The sequence has been dated in between ∼5.2–3.9 Ma, with the age of the first Zanclean marine sediments overlying the Messinian Primary Lower Gypsum demonstrating that the Cretan Basin was partially desiccated for at least ∼400 kyrs, as a result of being a shallow epicontinental area in the Late Miocene. A relatively sudden change to deep marine environment took place in the Early Pliocene linked to the accelerated rate of trench extension in the Cretan Basin. The multi-proxy study revealed intervals reflecting warm surface waters and low-oxygen conditions on the seafloor, associated with the orbitally driven presence of Early Pliocene rhythmic sapropelic layers. Between ∼5.2 and 4.6 Ma, the sapropelic layers were characterized by elevated abundance of Reticulofenestra spp. and Florisphaera profunda, depicting increased productivity throughout the photic zone. Both enhanced riverine inputs and weak presence of Levantine Intermediate Water (LIW) characterized this time interval. The alterations in the calcareous nannofossil patterns with increased Helicosphaera spp. and Umbilicosphaera jafari abundances, implying freshening and enhanced mid-photic productivity after ∼4.6 Ma, suggest strengthening of LIW intrusion combined with the full restoration of North-South Aegean marine gateways that led to the establishment of a hydrographic system similar to the modern Aegean Sea.

Sensitivity of the thermohaline circulation during the Messinian: Toward constraining the dynamics of Mediterranean deoxygenation

During the Messinian, the sensitivity of the Mediterranean Basin to ecosystem perturbation was enhanced in response to the progressive restriction of water exchange with the Atlantic Ocean. The widespread deposition of organic-rich layers (i.e. sapropel) during the Messinian testifies the perturbation of the carbon and oxygen cycles; indeed, these sediments were deposited under conditions of oxygen starvation, presumably in response to a periodic deterioration of the thermohaline circulation strength. Disentangling the causes, the effect and magnitude of the thermohaline circulation weakening during the geological past is crucial for better constraining present and near-future deoxygenation dynamics in the Mediterranean region under the current climate warming. For this purpose, we investigate a Messinian sapropel-bearing succession cropping out at Monte dei Corvi (Ancona, central Italy) with mineralogical, petrographic, micropaleontological and stable Carbon and Oxygen isotopic analyses. We show that sapropel layers were deposited in response to an increase of the sea surface buoyancy, which hampered the thermohaline circulation and thus the oxygenation of bottom water, in turn affecting the bioturbating organisms. Within the lithological cycle, the recovery of an efficient thermohaline circulation is recorded by thin packstone layers underlying the marly limestone/marlstone, which record intense bottom currents. The marly limestone/marlstone accumulated during periods of intense primary productivity and organic carbon export to the sea bottom, which promoted bottom hypoxia but not organic matter preservation. We infer that these lithological changes resulted from variations in the Adriatic Deep Water formation system, controlled by precession-driven climatic and oceanographic changes.By integrating previously published Sea Surface Temperature (SST) with new isotopic and mineralogical data, we show that variations in Sea Surface Salinity (SSS) were the leading factor controlling sapropel deposition, minimizing the role of primary productivity. The SSTs characterizing the sapropel deposits are close to the range of those projected in the Eastern Mediterranean at the end of this century under climate warming. In this scenario, future warming will be coupled with SSS increase, which will counteract the density loss provided by temperature, making the bottom deoxygenation in the Eastern Mediterranean abysses unlikely. However, additional forcing, such as winter heat waves and eutrophication, could contribute to negatively affecting the Mediterranean oxygen balance and should be considered in model-based projections.

Role of climate variability on deep-water dynamics and deoxygenation during sapropel deposition: New insights from a palaeoceanographic empirical approach

Modern marine settings are experiencing rapid deoxygenation mainly forced by global warming and anthropogenic eutrophication. Therefore, studies that assess the role of climate variability in large spatiotemporal deoxygenations during past climate changes are needed to better comprehend the consequences of the current global warming and ocean deoxygenation. In this respect, deep marine sediments associated to past oxic-to-anoxic transitions are useful palaeoarchives for understanding the interplay between climate variability, deep-water dynamics and large-scale deoxygenation. Moreover, they can offer long-term perspectives to modern marine settings that are suffering oxygen depletion due to climate change and anthropogenic pressure. In particular, sapropel layers from the Middle Pleistocene to the Holocene are excellent palaeoarchives of past large-scale deoxygenation events, since (i) they occurred during a similar Mediterranean hydrogeographic configuration to the present, (ii) have a robust chronological control, and (iii) previous studies have reconstructed the climate conditions that ruled during their deposition. In this work, we have applied empirical palaeoceanographic conceptual models to five sapropels (S1, S5, S6, S7 and S8) in three Eastern Mediterranean (EM) settings. The models suggest that the hydrographic regimes of all studied sapropels can be considered as analogues to those observed in certain modern marine restricted settings. The results obtained support the idea that climate and the degree of surface-water freshening are the primary factors that influence deep-water dynamics in marine restricted settings, that in turn control the frequency and intensity of bottom-water deoxygenation and the stability and depth of the chemocline. The deepest EM sites are the most vulnerable locations to develop bottom-water restriction and deoxygenation. Local hydrogeographic factors play an essential role in the extent and frequency of bottom-water deoxygenation. Particulate shuttling was very intense during sapropel deposition and water-mass exchange between EM and Western Mediterranean controlled the intensity of the basin reservoir effect and Mo budget in EM.

Middle-Late Pleistocene Eastern Mediterranean nutricline depth and coccolith preservation linked to Monsoon activity and Atlantic Meridional Overturning Circulation

The eastern Mediterranean Sea lies under the influence of high- and low-latitude climatic systems. The northern part of the basin is affected by Atlantic depressions and continental and polar air masses that promote intermediate and deep-water formation. The southern part is influenced by subtropical conditions and monsoon activity. Monsoon intensification results in enhanced freshwater discharge from the Nile River and other (now dry) systems along the North African margin. This freshwater influx into the Mediterranean Sea reduces surface water buoyancy loss. Disentangling the influences of these diverse climatic forcings is hindered by inherent proxy data limitations and by interactions between the climatic forcings. Here we use a wealth of published and new paleoclimate records across Termination II to understand the impacts of the higher latitude and subtropical/monsoon climate influences on coccolithophore ecology and holococcolith preservation in Aegean Sea sediment core LC21. We then use these findings to interpret coccolith assemblage variations at Ocean Drilling Program Site 967 (located nearby LC21, at the Eratosthenes Seamount) during multiple glacial-interglacial cycles across the Middle Pleistocene (marine isotopic stages 14–9). The LC21 analysis suggests that holococcolith preservation was enhanced during Heinrich Stadial 11 (∼133 ka) and cold spell C26 (∼119 ka). These two events have been previously linked to cold conditions in the North Atlantic and Atlantic Meridional Overturning Circulation weakening. We propose that associated atmospheric perturbations over the Mediterranean Sea promoted deep-water formation, and thus holococcolith preservation. Similarly, in the Middle Pleistocene (MIS 14-9) of Site 967, we observe temporal coincidence between ten episodes of enhanced holococcolith preservation and episodes of Atlantic Meridional Overturning Circulation slowdown. In Site 967, we also identified repeated fluctuations in placoliths and in Florisphaera profunda, which indicate nutricline depth variations. The development of a deep chlorophyll maximum is associated with the North Africa and wet phases, as recently observed using elemental proxy records at Site 967, during the deposition of sapropel layers. A further deep chlorophyll maximum development is identified during MISs 12 and 10, as a result of pycnocline and nutricline shoaling within the lower part of the photic zone due to glacial sea-level lowering and water mass transport reduction at both the Gibraltar and Sicily Straits. Finally, enhanced holococcolith preservation during cold/dry events is clearly correlated to weakened monsoon activity in both Africa and Asia.

Improved Planktonic, Benthic Foraminiferal and Nannofossil Biostratigraphy Aids the Interpretation of the Evolution at Hole U1468A: IODP Expedition 359, the Maldives

Extended shallow carbonate platform, pelagic, and drift deposits were drilled during International Ocean Discovery Program (IODP) Expedition 359 in the Inner Sea of the Maldives. These sediments yield rich and well-diversified benthic, planktonic foraminiferal and nannofossil assemblages spanning from the early Oligocene to the Recent. We present here the shore-based revised integrated biostratigraphy of these microfossil groups at IODP Hole 359-U1468A together with the paleobathymetric reconstruction. Our data suggests the presence of a late Oligocene carbonate platform, marked by the shallowest water depths of the entire sequence of around 80 m. This carbonate platform sequence occurred from around 29 Ma, the extrapolated minimum age estimate, at least up to 27.5 Ma and possibly up to 25.4 Ma. Up the sequence, similar carbonate production conditions occurred until 22.5 Ma across the Oligocene–Miocene transition, equated at 23.04 Ma, with increased water depths >120 m. Notably, in the time interval approximately from 24 to 21.5 Ma, orbitally induced sapropel layers indicate a change of open to restricted circulation. However, at around 22.5 Ma, pelagic deposition at a distal slope occurred with sedimentation rates of 3 cm/years. This initially occurred in water depths of >350 m but gradually reached deposition in water depths of >500 m, which persisted from 21.12 Ma until approximately the extrapolated age of 12.8 Ma. Sedimentation rates gradually increased to 10.5 cm/1000 years at around 450 m below sea floor, marking the initiation of the drift sequence as identified in seismic lines with an age estimate of 12.8 Ma. The initiation of the drift sequence is also marked by a drastic decrease in the preservation of benthic and planktonic foraminifera from good to very poor at around 12.8 Ma. The drift sequence essentially continued to the present day but was interrupted by two events: the deposition of distinct shallow water benthic shoals and a large hiatus. From 12.8 Ma, a shallowing upward bathymetry is suggested by the occurrence of shallow benthic foraminiferal assemblages that close to around 11.93 Ma reached a maximum water depth of 80 m. This shoal then prograded into the basin and persisted at least until 9.89 Ma. Basin conditions with water depths exceeding 500 m were re-established in the upper part of the sedimentary succession after a hiatus spanning approximately from 9.83 Ma to 2.39 Ma, implying that renewed open ocean conditions occurred in the Pliocene–Pleistocene part of the sedimentary record.

Climate controls on tufa deposition over the last 5000 years: A case study from Northwest Africa

The occurrence and rate of tufa deposition are controlled by a large number of external and internal factors, including climate which often represents the main allocyclic factor. In this study, the first of its kind in the Middle Atlas (Northern Morocco), we test the dependency between climate factor and Holocene tufa deposits in basin-like settings that involve enlarged barrage and extensive dammed area using sedimentologic and stratigraphic analyses complemented with a paleoclimate multi-proxy approach and radiocarbon dating. The sedimentologic and stratigraphic analyses revealed a remarkable change in the vertical stacking pattern within the main barrage-cascade: higher (lower) Aggradation/Progradation ratio between ca. 4 and ca. 2.7 cal kyr B.P. (between ca. 2.7 and ca. 0.35 cal kyr B.P.), which would have conditioned a transgressive (highstand) interval “basinward”. This shift is modulated by changes in precipitation and summer insolation, which is consistent with the petrographic analysis of the laminated microbialites (oncoids and stromatolites). The previously reported arid and cold period of the Mid-Holocene Transition (between 6 and 5 cal kyr B.P.) is recorded in the sedimentary deposits and demonstrates landscape instability. The North Atlantic high-latitude cooling events between 4.6 and 2.7 cal kyr B.P. (Bond events 2 and 3) resulted in the interruption of (bio-)calcification and the development of fen and sapropel (organic-rich facies) layers, respectively. The 4.2 ka event, might have coincided herein with a fifth-order bounding surface delineating the two depositional sequences recognized on the “basin-scale”. A multi-centennial timescale period with climate optimum conditions coinciding with enhanced calcite precipitation at the downstream-facing of the main barrage (buttress development), and centred at ca. 2 cal kyr B.P. may coincide with the Roman-Iberian Climate Optimum. A recurrent occurrence with a high frequency of sub-humid marshy conditions underscored the upper part of the highstand interval which may reflect solar imprints, as already reported in previous studies in the region. • Tufa is a promising paleoclimate archive for millennial and multicentennial variability. • Climate is the main allocyclic control on the stacking pattern at barrage-cascade settings. • Higher (lower) summer temperature enhanced (reduced) vertical accretion at the barrage sill. • Bond events 4.6 and 2.7 ka coincided with fen and sapropel development, respectively. • Tufa is likely to record solar imprints in basin-like settings.

Middle-late Holocene climate and hydrologic changes in the Gulf of Saros (NE Aegean Sea)

A multi-proxy analyses was applied on the sediment core from the Gulf of Saros (GoS) to identify and characterize climate and hydrological changes during the middle-to-late Holocene. The formation of two discrete Holocene sapropel layers in the GoS sediments was documented for the first time in the sediment core based on total organic carbon analysis. According to our paleo-proxy records, the lower Holocene sapropel was deposited under warm and humid climate conditions that gave rise to high delivery of terrestrial organic matter by numerous rivers in the northern catchment of the GoS. Biomarker and μ-XRF data were used to decipher climate variations during the middle to late Holocene. The general trends of sea-surface temperature records from the GoS and Sea of Marmara (SoM) at the beginning of late Holocene are in good agreement, underlying the influence of the Black Sea inflow. A relatively warm and wet climate together with a high sedimentation rate during the mid-Holocene Climatic Optimum resulted in high organic productivity and ensuing formation of the younger Holocene sapropel between 5.4 and 3.0 cal ka BP. Late Holocene European climate periods are evident in the Saros core records. The Roman Humid Period is represented by high variation in climate, indicating an earlier (2.5–2.3 cal ka BP) dry and a later (2.3–1.55 cal ka BP) wet periods. The abrupt return to drier condition during the Dark Ages Cold Period (1.6–1.3 cal ka BP) was followed by a wetter Medieval Climate Anomaly (1.1–0.7 cal ka BP). The paleo-proxy record of the core indicates a passage from a wetter to drier climate during the cold Little Ice Age period (730–110 cal yr BP), and highlights the influence of deforestation in the catchment of the GoS as a result of human activities during the last three centuries.

Coupling of dissolved organic carbon, sulfur and iron cycling in Black Sea sediments over the Holocene and the late Pleistocene: Insights from an empirical dynamic model

An understanding of how the coupled cycles of carbon, iron and sulfur in sediments respond to environmental change throughout Earth history requires the reconstruction of biogeochemical processes over a range of spatial and temporal scales. In this study, sediment cores from the southwestern Black Sea were analyzed to gain insight into past changes in biogeochemical processes with particular focus on the cycling of dissolved organic carbon (DOC). The sediment consists of Late Pleistocene deposits of iron oxide-rich and organic-poor lacustrine sediments, a Holocene sapropel layer deposited after the inflow of saline Mediterranean seawater about 9300 yr BP, and overlying recent marine sediments. The porewaters displayed high concentrations of DOC, acetate, dissolved iron and an extended depth interval over which sulfate and methane were both present. The historical fluctuations of the fluxes of carbon, sulfur and iron species at the seafloor that led to these present-day geochemical profiles, and which cannot be easily interpreted from the measured data alone, were hindcasted with a reaction-transport model. The model suggests that the inflow of Mediterranean seawater impacted the rain rate and reactivity of organic matter reaching the sediments, which shifted the sedimentary redox regimes throughout the Holocene that now are reflected on different lithology units. Organic matter in the sapropel layer is apparently the main source of modern-day accumulations of DOC and acetate, both of which probably sustained subsurface microbial activity throughout the post-glacial period. The ratio between DOC and dissolved inorganic carbon (DIC) flux to the bottom water decreased from ∼40% before the inflow of Mediterranean water to ∼2% at the present day. We suggest that the coexistence of methanogenesis and sulfate reduction was associated with sulfate-reducing bacteria and methanogens sharing common substrates of acetate and lactate and utilizing non-competitive substrates such as methylated compounds in the sapropel layer and in the bottom of modern marine deposits. Intense sulfur and iron cycling mainly took place in the organic-poor freshwater deposits, today characterized by high concentrations of dissolved iron and methane. In contrast to previous studies in similar environments, anaerobic oxidation of methane coupled to the reduction of ferric iron was negligible. The results have broad implications for coastal environments that are currently experiencing deoxygenation and seawater intrusion and also for understanding the role of DOC in the sedimentary carbon cycle.

Reconstruction of oceanographic and environmental conditions in the eastern Mediterranean (Kottafi Hill section, Cyprus Island) during the middle Miocene Climate Transition

The multi-proxy investigation of the deep-marine Kottafi Hill section (KHS), a part of the carbonate system of the Miocene Pakhna Formation, Cyprus, involved such proxies as calcareous nannofossil analysis, measurements of the oxygen and carbon isotope composition of the planktonic foraminifer Orbulina universa, and determination of the pollen and palynomorph contents, revealed the importance of these sedimentary sequences in the assessment of the impact of major global events during the middle Miocene on the regional scale. The KHS spans the 20.89–11.6 Ma time interval, during which eighteen OC-rich siltstone intercalated laminae have been deposited under warm and humid climate at 15.5–11.6 Ma. These layers can be possibly considered as the precursors of sapropelic layers mostly developed in the eastern Mediterranean Basin during Pliocene–Holocene. The global glacial events Mi3a–Mi5, traced by δ18O planktonic foraminifera records in the KHS, represent the stepwise cooling phase during the middle Miocene Climate Transition.

ЭВОЛЮЦИОННОЕ РАЗВИТИЕ И СОВРЕМЕННОЕ СОСТОЯНИЕ ОЗЕРА НЕРО ПО ДАННЫМ АНАЛИЗА САПРОПЕЛЯ

The paper presents the characteristics of sapropel based on the results of analysis of samples collected at 21 stations in Lake Nero. Its current state is assessed based on hydrophysical and hydrochemical parameters. A layer-by-layer (0–10, 30–40 and 60–70 cm) granulometric composition of stratigraphic cores made it possible to compare the evolutionary development of the lake corresponding to the periods 100, 300–400 and 600–800 years ago. It is found that natural hydrodynamic processes (wind-driven waves and wind-driven currents) cause erosion and mixing of the surface (0–10 cm) polluted sapropel layer with clean underlying horizons and carry pollutants absorbed on suspended particles outside the lake. The approach used made it possible to identify the ways of a shallow lake ecosystem formation and outline promising directions

Climate variability during MIS 20–18 as recorded by alkenone-SST and calcareous plankton in the Ionian Basin (central Mediterranean)

This study shows the first Mediterranean high-resolution record of alkenone-derived sea surface temperature (SST) in the marine sediments outcropping at the Ideale section (IS) (southern Italy, central Mediterranean) from late marine isotope stage (MIS) 20 - through early MIS 18. The SST pattern evidences glacial-interglacial up to submillennial-scale temperature variation, with lower values (~13 °C) in late MIS 20 and substage 19b, and higher values (up to 21 °C) in MIS 19c and in the interstadials of MIS 19a. The SST data are combined with the new calcareous plankton analysis and the available, chronologically well-constrained carbon and oxygen isotope records in the IS. The multi-proxy approach, together with the location of the IS near the Italian coasts, the lower circalittoral-upper bathyal depositional setting, and high sedimentation rate allow to document long-and short-term paleoenvironmental modifications (sea level, rainfall, inorganic/organic/fresh water input to the basin), as a response to regional and global climate changes. The combined proxies reveal the occurrence of a terminal stadial event in late MIS 20 (here Med-HTIX), and warm-cold episodes (here Med-BATIX and Med-YDTIX) during Termination IX (TIX), which recall those that occurred through the last termination (TI). During these periods and the following ghost sapropel layer (insolation cycle 74, 784 ka) in the early MIS 19, high frequency internal changes are synchronously recorded by all proxies. The substage MIS 19c is warm but quite unstable, with several episodes of paleoenvironmental changes, associated with fluctuating tropical-subtropical water inflow through the Gibraltar Strait, variations of the cyclonic regime in the Ionian basin, and the southward shift of westerly winds and winter precipitation over southern Europe and Mediterranean basin. Three high-amplitude millennial-scale oscillations in the patterns of SST and calcareous plankton key taxa during MIS 19a are interpreted as linked to changes in temperature as well as in salinity due to periodical water column stratification and mixing.The main processes involved in the climate variability include changes in oceanographic exchanges through the Gibraltar Strait during modulations of Atlantic meridional overturning circulation and/or variations in atmospheric dynamics related to the influence of westerly and polar winds acting in the paleo-Ionian basin. A strong climate teleconnection between the North Atlantic and Mediterranean is discussed, and a prominent role of atmospheric processes in the central Mediterranean is evidenced by comparing data sets at the IS with Italian and extra-Mediterranean marine and terrestrial records.

Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events

One of the outstanding issues in the study of nutrient dynamics during Oceanic Anoxic Events (OAEs) is the preservation of 15N-depleted nitrogen isotope signals, which are not observed in analogous modern environments. The favored mechanism for δ15N values below 0‰ is utilization of excess ammonium derived from underlying anoxic waters by primary producers. However, there are few modern examples available for testing this hypothesis, due to the overall well-oxygenated state of modern oceans. Here, we present sedimentary δ13Corg and δ15Nbulk data, as well as pigment biomarker ratios, from the sediments of Lake Kivu, a meromictic lake in East Africa. This system serves as a potential analogue for the development of strongly depleted δ15Nbulk in OAE black shales. We focus on intervals of organic carbon enrichment (sapropels) that are interpreted to have been the result of lake water column mixing events. Sediment δ13Corg and δ15Nbulk decrease by up to 6 and 4‰ respectively near the base of sapropel layers. These negative excursions provide evidence for the mixing of 13C-depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need, derived from the deeper anoxic basin of the lake. Support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status. Further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers.

Features of Natural Eutrophication of Shallow Lake Nero Based on Sedimentary Pigments

This study analyzes the data of spectrophotometric determination of plant pigments in the bottom sediments of Lake Nero based on bottom survey data of 2017. A low variability (Cv = 27–31%) in concentrations of chlorophyll a and pheopigments over the bottom area and vertically in the sapropel cores is established. The values of pigment concentrations in bottom sediments of the lake belong to the hypertrophic category. The hypertrophic state of the lake with respect to the pigment content (>300 μg/g of dry sediment) is maintained for the period of formation of an 80-cm sapropel layer (~800 years). Trends towards an increase in concentrations of plant pigments from the lower to upper layers of cores are revealed upon a significant relationship with concentrations of organic matter and total nitrogen, which indicates the natural eutrophication of the lake.

Paleontological Records of Holocene Environmental Changes offshore, Egypt

Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea, offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during Holocene. To achieve our goals, grain size, total organic carbon, planktic and benthic foraminifera, dinoflagellate cysts have been investigated. Few micropalaentological studies have been done in the studied area and none of them used the combined proxies of benthic foraminifera and dinoflagellate cyst. Theses combined proxies reflects more comprehensive paleoenvironmental view. Biotic and abiotic data have been analysed with multivariate technique including Redundancy Analysis (RDA). Diversity indices such as: Fisher alpha index (α) and Shannon index (H) have been applied. The foraminiferal study yields 9 planktic species and 10 benthic species. Foraminiferal assemblages have low species diversity indices especially at sapropel layer S1. Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding organic poor sediments. Sapropels occur periodically in sedimentary sequences of the last millions years, which have been the subject of extensive previous study. Redundancy Analysis (RDA) yields two groups of foraminiferal assemblages depending on the changes of total organic carbon and clay content. The dinocysts study yields 15 species, the majority of cyst types belonging to the order Gonyaulacales. The association of dinoflagellate cyst shows two depositional phases in the sediment. The sapropel layer S1, with anoxic condition and warmer temperature, is recorded at depth 28–46 cm where heterotrophic taxa dominate and the post-sapropel layer is recorded at depth 0–28 cm; where autotrophic taxa dominate.

The effects of vibration on viscoplastic dispersion medium by the example of lake sapropels

The paper is devoted to the study of the possible behavior of the sapropel layer under the influence of the vibration mechanism from the standpoint of the analysis of mathematical models of the dynamics of multiphase rheological media under the influence of vibration (amplitude, frequency). The results of the analysis showed that there are different variants of the behavior of particles entering into a multiphase system; changing the amplitude and frequency of oscillations one can produce various effects that are necessary to obtain the material.

Diagenetic transformation of organic matter in sapropel sediments of small lakes (southern West Siberia and eastern Transbaikalia)

Sapropels, biogenic lake sediments, are characterized by a reduction type of diagenesis, during which decomposition of organic compounds, modification of the pore water chemical composition and precipitation of authigenic minerals, mostly pyrite, occur. Pyrolysis data indicate that organic matter undergoes radical transformations already in the uppermost sapropel layers, and composition of the organic matter in the sediments is principally different from the composition of the organic matter of live organisms, which produce the sediments. The sapropels lose labile protein–carbohydrate compounds in the horizon of unconsolidated sediment (0–5 cm), and kerogen appears, whose macromolecular structures start to develop in the very early stages of diagenesis. Various physiological groups of microorganisms provide diagenetic transformations of the organic matter, where heterotrophic, ammonifying and sulfate-reducing bacteria play key role. Their effect is well-seen from the pore water transformation: a decrease in concentrations of SO42− and consequent increase of reduced Fe and S as pyrite in the solid phase of the sediment. Comparative analysis shows that, unlike in lakes of the Baikal area, sapropels in southern West Siberia are affected by more active sulfate reduction, which can depend on both the composition of the organic matter and the SO42− concentration in the pore waters.

Divergent Mediterranean seawater circulation during Holocene sapropel formation – Reconstructed using Nd isotopes in fish debris and foraminifera

The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition (εNd) as paleo-seawater tracer. Our εNd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional εNd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed εNd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation.

Trace metal analysis of sediment cores using a novel X-ray fluorescence core scanning method

The trace-metal composition of sediments provides important information on (past) environmental conditions, such as bottom water oxygenation, marine productivity, sediment provenance, and pollution. Whereas major and minor elements are often routinely analyzed using X-Ray Fluorescence (XRF) core scanning, analysis of trace metals with the same method is not yet established as a routine procedure. Here, we used a recently developed state-of-the-art XRF detector with a core scanner (Avaatech) to examine the optimal settings for analyzing a suite of trace metals (V, Cr, Ni, Cu, Zn, Mo, and U). Settings were optimized for fast analyses of sediment cores by extensive testing of primary energy settings, filters, and exposure times on two eastern Mediterranean Sea sapropel layers that archive episodes of past sea-floor anoxia. We reveal the following most advantageous (i.e., optimized for analytical accuracy and time efficiency) settings: (1) V, Cr, Ni at 20 kV with aluminum primary beam filter, (2) Cu, Zn, and U at 30 kV with ‘thick’ (125 μm) palladium primary beam filter, and (3) Mo at 50 kV with copper primary beam filter. For these trace elements, generally, ≥30 s of measurement are required for obtaining reliable data. Synthetic mixtures show that matrix effects, which are inherent to XRF analyses, are of particular importance for V. A correction for these matrix effects on V (e.g., using Compton scattering) may be necessary for samples with a large variability in carbonate content. XRF core-scanning measurements on synthetically, laminated sediments show that trace metals with contrasting atomic weights and related XRF penetration depths (V and Mo) can be determined at sub-mm resolution. We show that intensity results from the new XRF detector can be converted into concentrations using multivariate log-ratio calibration, allowing a fast quantitative prediction of sedimentary trace metal content using XRF core scanning.

Early Pleistocene (Calabrian) marine bottom oxygenation and palaeoclimate at the southern margin of the Central Anatolian Plateau

The Mediterranean Basin is a semi-enclosed basin highly sensitive to climate changes such as evaporation-precipitation processes and glacial-interglacial transitions. It is composed by two main basins, the Western Mediterranean and the Eastern Mediterranean, which are differently sensitive to the high latitude and low latitude climate interactions. Such differences could translate in different reactionsto climate changes recorded in the bottom sediments, i.e. the enhanced effects of the freshwater inputs on the bottom oxygenation in the Eastern Mediterranean. In this paper we investigate the palaeoenvironment and palaeoclimate derived from the study of Early Pleistocene (Calabrian) deep marine deposits cropping out along the southern margin of the Central Anatolian Plateau at the Gulnar East section (southern Turkey). Using benthic and planktonic foraminifers the bottom oxygenation and the sea surface temperature (SST) were evaluated through the calculation of the benthic foraminifera oxygen index (BFOI) and palaeoclimate curve. The results show that the marine epibathyal palaeonvironment in this Eastern Mediterranean area reacted to the palaeoclimate changes with the water mass stratification (warm periods) and/or with enhanced primary productivity (cool/cold periods) leading to the deposition of sapropel layers with different degrees of bottom oxygenation.