Connectivity with the ocean and climate strongly control the physical and chemical properties of restricted marine basins, sometimes leading to the formation of large evaporite accumulations known as salt giants. As a result of these processes, salinity, water oxygenation and nutrient availability may develop trends distinct from those of the global ocean, resulting in extreme salinity – from brackish to evaporitic – and driving ecosystems through specific patterns of origination and extinction. Reversely, the genesis and demise of such physico-chemically distinct water bodies changes global ocean circulation patterns, affects climate and leads to shifts in the location of global biodiversity hotspots. Our session mostly includes presentations on the Mediterranean, the Dead Sea, using modelling, sesimic stratigraphic, (bio)geochemical, sedimentologic and micropaleontological methods to investigate feedbacks between hydroclimate, tectonics and marine biota.
vPICO presentations: Fri, 30 Apr
Evaporite weathering and deposition are seldom in balance even on million-year time-scales with grand depositional events superimposed against a background of more slowly varying weathering. Despite such imbalance, biogeochemical models generally assume that evaporite weathering and deposition rates are equal on all time scales. Changes in evaporite dynamics through time will likely impact oxidant budgets through the sulfur cycle and we have shown this to have been especially significant during Proterozoic times. Recently, we proposed that imbalances between evaporite weathering and deposition can also affect climate through the process of carbonate sedimentation. Calcium sulfate weathering supplies calcium ions to the ocean unaccompanied by carbonate alkalinity, so that increased carbonate precipitation strengthens greenhouse forcing through transfer of carbon dioxide to the atmosphere. Conversely, calcium sulfate deposition weakens greenhouse forcing, while the high depositional rates of evaporite giants may overwhelm the silicate weathering feedback, causing several degrees of planetary cooling. Non-steady-state evaporite dynamics and related feedbacks have hitherto been overlooked as drivers of long-term carbon cycle change. In this talk, we illustrate the importance of evaporite deposition, in particular, by showing how a series of massive depositional events contributed to global cooling during the mid–late Miocene. Further studies are required to quantify gypsum deposition over time and its possible effects on deoxygenation of the surface environment, especially at times of mass extinction, as well as on climate.
How to cite: Shields, G. and Mills, B.: Evaporite dynamics and their effects on global climate and oxygen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15511, https://doi.org/10.5194/egusphere-egu21-15511, 2021.
Evaporation from porous rock is not only a significant part of the earth-atmosphere water balance but it also plays a crucial role in weathering processes. In the case of salt weathering, the evaporation rate directly influences the amount of precipitated aggressive salts. Evaporation also strongly affects frost, hydric and biogenic weathering, since they are influenced by water content and its temporal changes. Without proper quantification of the evaporation loss, it is not possible to thoroughly explain and/or predict the development of moisture content and its spatial distribution within natural rock outcrops. Despite its importance, the study of evaporation from porous rocks has seen little scientific focus so far. In our study (Slavík et al., 2020), we measured the evaporation rate from bare surfaces of sandstone under field microclimate on a roughly monthly interval for about one year. The measurement was performed using sandstone cores with a set depth of the vaporization plane (i.e. the area where most of the phase change from liquid to vapour occurs in the subsurface) and we used a simple Fick’s law of diffusion for calculations of the evaporation rate from the cores. The calculations required only a laboratory-measured water-vapour diffusion coefficient of the sandstone, in-situ seasonally measured vaporization plane depth, and logs of air humidity and temperature. The analysis of measured and calculated evaporation rate revealed that far the most important single factor influencing the evaporation rate is the depth of the vaporization plane. Other factors such as the microclimate characterised by temperature and relative humidity were of lesser importance and the calculated evaporation rate reasonably follows measured values with Pearson correlation coefficient r > 0.81. The experimental setup of evaporation rate measurement, for its simplicity and price, should find use in studies with high-number measuring sites or even locations with a risk of apparatus damage. Our measurements were performed in a humid continental climate and the suggested approach should be verified in more arid environments.
Figure: Goodness‐of‐fit between measured and calculated evaporation rate. Dashed line represents the identity line (calculated values equal to measured values).
This research was funded by the Czech Science Foundation [GA19-14082S].
References: Slavík, M., Bruthans, J., Weiss, T., Schweigstillová, J. (2020): Measurements and calculations of seasonal evaporation rate from bare sandstone surfaces: Implications for rock weathering. Earth Surface Processes and Landforms 45, 2965–2981.
How to cite: Weiss, T., Slavík, M., and Bruthans, J.: Evaporation rate from bare sandstone surfaces in humid climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15911, https://doi.org/10.5194/egusphere-egu21-15911, 2021.
As the only deep hypersaline, halite‐precipitating lake on Earth today, the Dead Sea is the
single modern analog for investigating the mechanisms by which large‐scale and thick salt deposits,
known as “salt giants”, have accreted in the geological record. We directly measure the hydroclimatic forcing
and the physical limnologic processes leading to halite sedimentation, the vertical thermohaline structure,
and salt fluxes in the Dead Sea. We demonstrate that changes in these forcing lead to strong seasonal
and regional variations in the stratification stability ratio, triggering corresponding spatiotemporal
variations in thermohaline staircase formation and diapycnal salt flux, and finally control the thickness of
the halite layer deposited. The observed staircase formation is consistent with the mean‐field γ instability,
causing layering in double‐diffusive convection. We show that double diffusion and thermohaline staircase
formation drive the spatial variability of halite deposition in hypersaline water bodies, underlying and
shaping “salt giants” basin architecture.
How to cite: Sirota, I., Ouillon, R., Mor, Z., Meiburg, E., Enzel, Y., Arnon, A., and Lensky, N.: Hydroclimatic Controls on Salt Fluxes and Halite Deposition in the Dead Sea and the Shaping of “Salt Giants”, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12510, https://doi.org/10.5194/egusphere-egu21-12510, 2021.
During the first phase of the Messinian Salinity Crisis, massive amounts of sulfate (SO42-) have been sequestred in the form of up to 200m thick gypsum deposits (Primary Lower Gypsum) in Mediterranean marginal basins. The sulfur isotopic composition of the sulfate ion of this unit (δ34SSO4) (on average 22.3 ‰) strongly suggests that gypsum was formed by concentration of marine sulfate. Interestingly, the preservation of sulfide globules within the gypsum and marls interbeds suggests that the basin sulfate was not only involved in gypsum formation but a fraction was also reduced through microbial sulfate reduction. Moreover, filamentous fossils interpreted to be the remnants of sulfide oxidizing bacterias are entrapped in this gypsum and indicate, together with the occurrence of sulfide globules and dolomite, that an active biogeochemical sulfur cycling was active at the time of Primary Lower Gypsum deposition. To investigate the role of this active sulfur cycling in Mediterranean marginal basins, we analyzed the multiple sulfur isotopic composition of sulfate and sulfide minerals (δ34S andΔ33S)from Primary Lower Gypsum of the Vena del Gesso basin (Italy). Whereas the isotopic composition of gypsum (δ34SSO4 from 21 to 24‰ and Δ33SSO4 from -0.001 to 0.049‰) display very homogenous values that are close to those of the Messinian ocean (δ34SMSC ~22±0.2‰ and Δ33SMSC~0.039±0.015), the analyzed reduced sulfur compounds display a wide range of variability with -36 to +9‰ in δ34S and -0.017 to 0.125‰ in Δ33S. This suggests huge hydrologically-driven redox variations during Primary Lower Gypsum deposition in the Vena del Gesso basin, possibly involving intermittent stratification of the water column and an active microbial cycling of sulfur.
How to cite: Guibourdenche, L., Cartigny, P., Dela Pierre, F., Natalicchio, M., and Aloisi, G.: Microbial sulfur cycling during the formation of Primary Lower Gypsum in Mediterranean marginals basins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14573, https://doi.org/10.5194/egusphere-egu21-14573, 2021.
Large deposits of gypsum accumulated in the marginal basins of the Mediterranean Sea during the Messinian Salinity Crisis. These form the marginal portions of the Mediterranean Salt Giant (MSG) that also occupies the deep, central Mediterranean basins. Although the marine, evaporitic origin of the MSG is undisputed, the analysis of gypsum fluid inclusions and of gypsum-bound water (d18OH2O and dDH2O) suggest that marginal basin gypsum formed from low- to moderate-salinity water masses (5 - 60 ‰), rather than from high-salinity brines (130 - 320 ‰), as expected during the evaporation of seawater. We present a new set of water isotope and fluid inclusion salinity data that extends the low salinity signature of gypsum to include five Mediterranean Sea marginal basins: Caltanissetta Basin (Sicily), Sorbas Basin (Spain), Piedmont Basin and Vena del Gesso Basin (northern Italy) and Catanzaro Trough (Southern Italy). With a simple geochemical model we explore the salinity-d18OH2O-dDH2O evaporation path and the 87/86Sr and d34SSO4 composition of the Mediterranean Sea subject to a variety of evaporation conditions and mixing ratios with continental runoff. This approach suggests that evaporation and mixing with continental runoff - including freshwater transiting via the Paratethys - cannot lead to the observed geochemical signature of MSC gypsum deposits. An alternative process that decouples the saturation state with respect to gypsum from salinity must have been active. We are exploring the possibility that the biogeochemical sulfur cycle leads to spatially and temporally localized gypsum supersaturation conditions via the production of SO42- by the oxidation and disproportionation of reduced sulfur compounds.
How to cite: Aloisi, G., Natalicchio, M., Guibourdenche, L., Caruso, A., and Dela Pierre, F.: Low-salinity Mediterranean gypsum deposits: chemical vs biological products, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12551, https://doi.org/10.5194/egusphere-egu21-12551, 2021.
Recent developments on analytical capabilities in the field of in-situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U-Pb geochronometers in low-U minerals such as carbonates (Roberts et al. 2020) or garnets (Millonig et al., 2020). The rapid development of the technique requires well-characterized, matrix-matched reference materials, which are essential for ion probes or LA-ICPMS due to potential matrix effects. However, given the unavailability of standards for some minerals, the use of non-matrix-matched standards, i.e. reference materials that are different to the sample, have been also addressed (Piccione et al., 2019).
In this contribution, we explored the possibility of using carbonate reference materials for in-situ U-Pb dating of sulphates. For that purpose, we selected samples from the Messinian Salinity Crisis because their ages are well established by cyclostratigraphy and thus can be compared with ages obtained by LA-ICPMS analysis. Data was acquired using a RESOLution 193 nm ArF excimer laser coupled to a (I) sector field ICP-MS (ElementXR) or (II) multicollector ICP-MS (Neptune Plus).
The majority of the samples (27 out of 32) failed due to the elevated common-Pb content and low 238U/204Pb ratios. Nevertheless, five of the samples showed greater amounts of U and U/Pb ratios of up to 600; therefore, regression lines could be drawn and ages are calculated with 5-10 % of uncertainty. These ages obtained are within error of the cyclostratigraphic ages already published (Vasiliev et al., 2017).
Millonig et al., (2020) Earth Planet. Sci. Lett. 552, 116589; Piccione et al. (2019) Geosphere 15 (6), 1958– 1972; Roberts et al. (2020) Geochronology 2, 33–61; Vasiliev et al. (2017) Palaeogeogr. Palaeoclimatol. Palaeoecol. 471, 120-133.
How to cite: Beranoaguirre, A., Vasiliev, I., and Gerdes, A.: Applicability of carbonate reference materials as matrix-matched standards for in-situ LA-ICPMS U-Pb dating of Sulphates , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5791, https://doi.org/10.5194/egusphere-egu21-5791, 2021.
Hydrochemistry of groundwater brines of the eastern part of the large playa deposit in the Makgadikgadi basin in northern Botswana has been analyzed. Brine samples were collected from 37 production and monitoring wells in this area. Brine samples for analysis were filtered to 0.45 and analyzed for major and minor anions and cations as well as trace species. The results of the hydrochemical analysis revealed that the major element chemistry of these samples from the area is dominated by Na and Cl with minor components of K, CO3, HCO3, and SO4, and depleted in Ca and Mg, which is typical of seawater or coastal water. The brine type is Na-Cl type. However, the exact mechanism of the genesis of the brines is still ambiguous, hence comparison curves of Na/C1 against seawater concentration factor (SCF) and Ca/Mg against (SCF) in order to ascertain the brine genesis geochemically were employed. The relationship between the current results to previous seawater freezing and evaporation experiments by other researchers indicated that the brines were formed by seawater evaporation. Observed variations in hydrogeochemistry and salinity with depth support the results of previous studies indicating downward infiltration of brackish waters and evaporative and/or mixing processes. With respect to minor and trace element analysis, A comparison of measured concentrations of trace elements to their concentration in seawater when normalized against the concentration of chloride, it can be seen that the saline groundwater brines in the area are enriched in a number of trace elements including W, Th, Se, Pb while depleted in Sr. Enrichments in all of these elements which would be expected to exhibit conservative behavior in the brines suggest that the origin of the brine is not restricted to the simple evaporation of seawater or but to a combination of end members enriched in these elements such as riverine and groundwater inputs.
How to cite: Motswaiso, F., Wang, J., Nakamura, K., Watanabe, N., and Komai, T.: The hydrochemical genesis of groundwater brines of the Eastern arm of the Makgadikgadi basin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14007, https://doi.org/10.5194/egusphere-egu21-14007, 2021.
The Adriatic basin represents one of several restricted basins located in the Mediterranean Area. It consists of the foreland of three different orogenic belts: the Dinarides to the East, active during the Eocene, the Southern Alps to the North, active since the Cretaceous time, and the Apennines to the West, active since the Paleogene. The Apennines had a primary role during the Messinian Salinity Crisis (MSC), conditioning the connection between the Adriatic basin, the Ionian basin, and the proto-Tyrrhenian basin. During the Messinian, the present Adriatic Sea was characterized by shallow water domains, where gypsum evaporites initially deposited and often successively incised or outcropped.
In the past 50 years, a massive dataset, composed of 2D multichannel seismic data and boreholes, was collected, covering almost the whole Adriatic basin in the Italian offshore. In this work, we interpreted the Plio-Quaternary base (PQb), based on available public datasets and on seismic profiles present in literature, which provided regional information from the northernmost Trieste Gulf (Northern Adriatic Sea) to the Otranto Channel (Southern Adriatic Sea). Here, we propose the PQb time-structural map, obtained by analyzing more than 600 seismic profiles. The PQb represents both the Messinian erosion and/or the top of the Messinian evaporites. It is characterized by a high-amplitude reflector, commonly called “horizon M” in the old literature. Principal findings concerning the Messinian event are summarized as below:
-The Northern Adriatic (Gulf of Trieste, Gulf of Venice, Po delta, Kvarner Area) reveals widespread channelized systems produced by the initial decrease of the sea level, followed by subaerial erosion, related to further sea level decrease. High-grade erosion involved the nearby Adriatic carbonate platform in the Croatian offshore, where deep valleys, filled with Last Messinian or post- Messinian sediments, cut through the limestones.
-The Central Adriatic (from the Po delta to the Gargano Promontory) displays a higher evaporites accumulation than the northern sector. Meanwhile, the Mid-Adriatic Ridge was already developing, along with the Apennine Chain, which was in a westernmost position. Erosional features in the deeper area are related to channelized systems, which followed the evaporites deposition. Meanwhile, also the Mid-Adriatic Ridge was affected by erosion.
-The Southern Adriatic (from the Gargano Promontory to the Otranto Channel) is characterized by the Mesozoic Apulia carbonate platform, covered by a thin Cenozoic sequence affected by subaerial erosion or non-deposition. The platform margin and the slope leading to the deepest South Adriatic basin, where a Messinian gypsum layer, also recorded in the Albanian and Croatian offshore, shows a lower level of upper erosion.
In general, we notice strongly variable thicknesses of the horizon M, which is related to submarine erosion (channels), subaerial erosion (discontinuous surfaces), non-deposition (possible unconformity), and tilting toward the surrounding chains (deepening horizons). In this work, we evaluate these different components from a regional point of view.
How to cite: Lanzoni, A., Del Ben, A., Forlin, E., Donda, F., and Zecchin, M.: Seismic evidence of the Messinian events in the Adriatic basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5785, https://doi.org/10.5194/egusphere-egu21-5785, 2021.
The Messinian Salinity Crisis (MSC) was caused and terminated by changes in the Atlantic-Mediterranean connectivity in the western end of the Alboran Basin, a complex tectonic area affected by the Iberia-Africa collision and the presence of a subducted lithospheric slab beneath the Betic-Rif orogen.
The isostatic, tectonic and erosional effects on surface topography work on different spatial and temporal scales, and their relative contributions to the changes in connectivity and subsequent evaporite deposition and sea-level drop are difficult to constrain.
We perform 2D-planform flexural isostatic modeling using the Messinian Erosion Surface imaged in the Alboran Basin to reconstruct the topography and vertical motions of this region since the end of the MSC. The results constrain the original depth of the Messinian erosional features to test their consistency against the various models proposed for Mediterranean sea-level changes during the MSC.
We apply Glacial Isostatic Adjustment theory to quantify the time response of these vertical motions to the large MSC-related mass shifts (salinification, evaporite deposition and a kilometer-scale sea-level drop), and their gravitational effects on sea-level in the Mediterranean. In particular, models for the Strait of Gibraltar allowus to identify the potential role of these effects as feedback mechanisms influencing the rates and duration of changes in the Atlantic-Mediterranean connectivity at the straits. We will explore the possible implications of these for the timing of the closure of the last Atlantic-Mediterranean seaway.
How to cite: Heida, H., Garcia-Castellanos, D., Jiménez-Munt, I., Estrada, F., Ercilla, G., Coulson, S., and Mitrovica, J.: Modelling the vertical motions of the Alboran Sea since the Messinian salinity crisis: Topographic reconstruction and glacial-isostatic sea-level effects , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10081, https://doi.org/10.5194/egusphere-egu21-10081, 2021.
The Nahr Menashe Unit (NMU), which forms the uppermost part of the Messinian succession, is one of the most cryptic and elusive sedimentary units present in the Levant basin (Eastern Mediterranean). We use a high-resolution 3D seismic dataset from offshore Lebanon to propose a new interpretation for its formation and evolution. The NMU varies laterally across the basin both in thickness and internal seismic characteristics. The variably coherent cyclic seismic packages affected by fracturing, faulting suggests that the NMU represent a reworked, layered evaporite succession interbedded with siliciclastics derived from both the Lebanon Highlands and the Latakia Ridge. Widespread semi-circular depressions, random linear imprints, passive surface collapsing and residual mound features within the NMU suggest that post depositional diagenetic and/or strong dissolution process often affected its evaporite-rich subunits. The well-known extended valley and tributary channel systems characterising the uppermost NMU shows mainly erosional rather than depositional features. Erosion started after deposition of NMU as a consequence of the maximum base level fall during the last phase of the Messinian Salinity Crisis (MSC). The channel and valley system were subsequently infilled by layered sediments here interpreted to represent post-MSC deep water marine reflooding. In conclusion, our analyses suggest the NMU can be interpreted as a mixed evaporite-siliciclastic system deposited in a shallow marine or marginal environment, which subsequently experienced fluvial erosion and later burial by transgressive/high-stand sediments.
How to cite: Kabir, S. M., Iacopini, D., Hartley, A., Maselli, V., and Oppo, D.: The role of the Nahr Menashe in the Messinian Salinity Crisis: formation, dissolution and fluvial incision of the top evaporite unit in the NE Levant Basin, Eastern Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10318, https://doi.org/10.5194/egusphere-egu21-10318, 2021.
The Late Miocene has been considered one of the most climatically stable periods of the Cenozoic, time span characterized by minor long-term cooling and ice growth. Especially, the Tortonian-Messinian Transition is recognized as a priority for paleoenvironmental reconstruction and climate modelling due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Here, we present stable oxygen (δ18O) and carbon (δ13C) isotopes measured on benthic and planktonic foraminifera from Potamida section (Crete Island, eastern Mediterranean). The δ18O results indicate a decoupling between the surface and the bottom water column starting before the Tortonian-Messinian boundary. The difference between planktonic and benthic oxygen isotope signals (Δδ18O) further provides an estimate of the degree of water column stratification during that time. The δ13C data indicate a generally trend towards lighter values as an excellent illustration of the Late Miocene Carbon Isotope Shift (LMCIS; 7.6-6.6 Ma) due to progressive restriction of the Mediterranean basin, with the exception of the 7.38-7.26 Ma time interval where significantly heavier δ13C values are documented in both records. Such changes in carbon cycle seem to be most pronounced in the planktonic foraminiferal record (surface waters) through a 6-cycle development indicative of a cyclic productivity pattern during the latest Tortonian. The entire record is substantiated by sea surface temperature (SST) estimates based on TEX86 biomarker based proxy. The reconstructed SST record shows that a warm phase characterized the late Tortonian sea surface (~27⁰C), time followed by a strong, steady cooling starting with earliest Messinian, when the SSTs dropped to values as low as 20⁰C. The outcome of the combined stable isotope and biomarker based SST data hint to increased salinity in the surface waters already before the Messinian, while at the Tortonian-Messinian Transition, the conditions in the surface waters changed towards cooler (~24⁰C) and normal salinity conditions.
How to cite: Besiou, E., Kontakiotis, G., Antonarakou, A., Mulch, A., and Vasiliev, I.: Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8853, https://doi.org/10.5194/egusphere-egu21-8853, 2021.
During the Late Miocene the Mediterranean Sea experienced severe disruption of its connectivity to the Atlantic Ocean, highlighted by a rapid sea-level drop, culminating to the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Such a paleoceanographic change, triggered by the cumulative effect of climate and tectonics, caused high-amplitude fluctuations in the hydrology of the entire basin, and further influenced the geological history of the Mediterranean Sea. Although a consistent pattern of the paleoclimate has started to emerge, we currently lack a continuous sea surface salinity (SSS) record linking the timing of sea surface temperature (SST) variations, sea-level fluctuations, and the overall environmental change, particularly for the pre-evaporitic period. Initial viewpoints of a linear and gradual salinity increase prior to the onset of the MSC have been recently revised and replaced by highly variable salinity-related patterns representative of the stepwise restriction of the Mediterranean Sea. Here we use the combined Tetra Ether (TEX86-) and/or alkenone unsaturation ratio (UK′37) based SSTs and oxygen isotopes (δ18O) from the cyclic marl-sapropel sedimentary succession of Agios Myron section (north-central Crete, Greece) to assess hydroclimate changes during that time, and we finally present the first record of SSS in the eastern Mediterranean Sea for the earliest Messinian (7.2–6.5 Ma). The relatively stable marine conditions after the Tortonian/Messinian boundary, expressed through a cool and fresh upper water column, significantly changed at ∼6.9 Ma, when an important reversal in the heart of the Messinian cooling trend supplemented by a coherent hypersaline water column took place. The observed SST and SSS patterns provide context for a two-fold evolution of this event (centered at 6.9–6.8 and 6.72 Ma), which finally led to the onset of a brine pool into the eastern Mediterranean basin. The transitional character of the following time interval (6.7–6.5 Ma) marks another important step in the basin restriction with a wider range of salinity fluctuations from highly saline to diluted conditions and enhanced water column stratification prior to the deposition of evaporites. Overall, this evolution supports the concept of a stepwise restriction of the Mediterranean Sea associated with substantial hydroclimate variability and increasing environmental (thermal and salinity) stress, and further confirms its position as a preferred laboratory for developing new conceptual models in paleoceanography, allowing the investigation and scale assessment of a phenomenon with high chances of representing a future analogue scenario.
How to cite: Kontakiotis, G., Butiseaca, G., Antonarakou, A., Karakitsios, V., Zarkogiannis, S. D., Besiou, E., Agiadi, K., Koskeridou, E., Thivaiou, D., Mulch, A., and Vasiliev, I.: The eastern Mediterranean pre-MSC brine pool as an analogue for future subtropical hydroclimate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8711, https://doi.org/10.5194/egusphere-egu21-8711, 2021.
Messinian Mediterranean (7.24‒5.33 Ma) was a highly dynamic environment governed by global climatic and regional tectonic activity. The impact of these two environmental factors is highly distinguishable especially during the latest Messinian (5.97–5.33 Ma), when the famous Messinian salinity crisis (MSC) affected the Mediterranean realm. However, the interplay between climate and tectonics is less studied for the earliest Messinian. Here we use biomarker analysis, coupled with compound-specific hydrogen (δ2H) and carbon isotopes (δ13C), to track changes in the hydrological budget, mean annual air temperature (MAAT), vegetation and reconstruct the sea-land climate conditions in Eastern Mediterranean between 7.2‒6.5 Ma. Our data from Agios Myron section on Crete (Greece) confirms a series of drastic environmental changes in the Eastern Mediterranean during the mentioned time interval. δ2H values of alkenones indicate highly evaporitic events accompanied by shifts in vegetation, from dominant >C3 plants to marked increasing dominance of C4, with recurrence of C3 vegetation at ~6.99 and 6.78 Ma respectively. The MAAT data indicate average values of 14⁰C and the overall trend suggests an orbitally paced continental climate, with maximum temperatures registered during eccentricity maxima. The reconstructed paleo-soil pH record follows a stepwise increasing trend towards slightly-alkaline soils, supporting an enhanced open vegetation contribution resulting from the ongoing continentalisation. These results provide new insights into the Messinian environmental conditions of the Mediterranean Sea, suggesting an ongoing restriction after 7 Ma, with multiple restrictive phases marked by increasing intensity until the final MSC event.
How to cite: Butiseaca, G.-A., van der Meer, M. T. J., Kontakiotis, G., Agiadi, K., Antonarakou, A., Mulch, A., and Vasiliev, I.: Multiple crises before the big crisis: Early Messinian Eastern Mediterranean paleoclimate reconstruction inferred from biomarkers and stable isotopes (Crete, Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5409, https://doi.org/10.5194/egusphere-egu21-5409, 2021.
Reconstructing paleoceanographic conditions for the entire water column remains challenging, due to the lack of proxies for seawater parameters below surface waters, which could be used to validate models. Fish otoliths and ostracods are used here to obtain biogeochemical proxy data of sea surface/bottom temperature and productivity, as well as the biological response of marine fishes to paleoenvironmental change. Our study area is located in the eastern Mediterranean Sea (Heraklion basin, Crete Island). During the Messinian age (specifically between 7.2 and 6.5 Ma), the Mediterranean–Atlantic connection was restricted leading to a strongly stratified water column. We study the sea surface and bottom conditions under these conditions.
Stable oxygen isotopes on ostracod valves (Bairdoppilata sp.) reflect the combined effect of bottom-water temperature and salinity changes. For fishes however, this depends on each species lifestyle. We analyzed two very common species: 1) Bregmaceros albyi, a surface-water pelagic species, and 2) Lesueurigobius friesii, a demersal fish dwelling on the sea bottom. Our hypothesis was that the stable oxygen isotopic ratios on B. albyi otoliths would reflect surface-water conditions, whereas those on L. friesii would correspond to bottom-water conditions. Furthermore, we obtained δ13C values for the same ostracod and otolith specimens. Stable carbon isotopic ratios in invertebrate shells indicate biological productivity, since carbon fractionation takes place as a single-step process during biomineralization. However, fish otolith aragonite mineralization is more complicated, involving more than one fractionation steps, and carbon is obtained from seawater, but also from diet. Therefore, otolith δ13C is considered a proxy of the fish’s field metabolic rate, reflecting its ability to continue to grow and reproduce despite environmental change.
Our results show that B. albyi δ18O values correlate well with those derived from planktonic foraminifera shells, whereas L. friesii δ18O is in agreement with ostracod values, thereby confirming our hypothesis. Moreover, ostracod and foraminifera δ13C follow the same decreasing pattern. However, otolith δ13C remains stable, even after 6.8 Ma, when high-amplitude salinity variations prevail. This suggests that fish maintained their capacity to grow and reproduce despite significant changes in seawater conditions at least until 6.5 Ma. However, whether this reflects their resilience to these environmental changes or an adaptation mechanism such as reducing their growth rate or shifting their trophic preferences remains a mystery.
How to cite: Agiadi, K., Thivaiou, D., Butiseaca, G., Kontakiotis, G., Besiou, E., Zarkogiannis, S., Antonarakou, A., Koskeridou, E., Mulch, A., and Vasiliev, I.: Seawater temperature, productivity and marine fish metabolism in the Messinian eastern Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12945, https://doi.org/10.5194/egusphere-egu21-12945, 2021.
In the late Miocene, the Mediterranean Basin became a restricted basin because of its progressive tectonic isolation from the Global Ocean. The almost complete halt of the Atlantic-Mediterranean water exchange about 6 Ma ago triggered the deposition of the Mediterranean Salt Giant during the Messinian salinity crisis (MSC; 5.97-5.33 Ma). The environmental conditions, which developed at the onset and during the MSC, are still debated since the evaporites buried beneath the modern Mediterranean seafloor are mostly inaccessible and the marginal successions contain scarce or no body fossils. Aiming to improve our knowledge on the environmental conditions at the onset of the MSC, we investigated the sedimentary record of intermediate palaeobathymetric settings (200-1000 m) from the Piedmont Basin (NW Italy) through a multidisciplinary approach (petrography, organic geochemistry). Shale/marl couplets deposited after the MSC onset are lateral time equivalents of shallow water (<200 m) shale/gypsum couplets deposited during the first phase of the crisis (5.97-5.60 Ma). Our results suggest that the MSC onset coincided with an intensification of water column stratification, most likely favoured by enhanced freshwater input due to moister climate conditions. No evidence of hypersaline conditions was found at the onset of the crisis, but rather normal marine conditions seem to have persisted at least in the upper water column, influenced by freshwater discharge. A stable chemocline apparently separated an upper water layer from a stagnant deeper-water body typified by reducing conditions. These physicochemical changes in the water column governed the sedimentary facies distribution during the first phase of the MSC.
How to cite: Sabino, M., Natalicchio, M., Birgel, D., Dela Pierre, F., and Peckmann, J.: Environmental change across the onset of the Messinian salinity crisis in the northern Mediterranean (Piedmont Basin, NW Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1475, https://doi.org/10.5194/egusphere-egu21-1475, 2021.
The Messinian Salinity Crisis (MSC), still highly discussed within the scientific community, affected the Mediterranean Sea between 5.97 and 5.33 Ma and led to the deposition of huge evaporite accumulations both in its marginal and deep basins. During this profound palaeoecological change, the connections between the Atlantic Ocean and Mediterranean Basin were extremely reduced or even non-existing creating an environment where evaporation was dominant. However, the isolation from the global ocean was not a sudden change but most probably a stepwise process. At 7.17 Ma the first signs of restriction are visible in the sedimentological and micropaleontological records all over the Mediterranean.
Particularly, several Italian, Greek and Cypriot locations register a reduced deep water marine ventilation to the sea floor since 7.17 Ma ago as reflected in the higher abundance of benthic low oxygen foraminifer species, indicators of stressed conditions like Bolivinia spp., Bulimina aculeata, Uvigerina peregrina. In these locations, the start of the progressive Mediterranean isolation coincides with the beginning of a more regular occurrence or even the first appearance of sapropel levels which further confirms the increasingly adverse conditions and increasingly dysoxygenated bottom waters. On the other hand, apart from the first opal-rich deposits in the Sorbas basin (Southern Spain) and the Messadit section (North-East Morocco), evidence from the Western Mediterranean is lacking and no studies have focused so far on the 7.17 Ma event.
In this view, we conducted a detailed benthic foraminifer and stable isotope study of West Alboran Sea Site 976 before and after the 7.17 Ma event. This new record highlights the imprint that the early Atlantic-Mediterranean gateway restriction had on the Mediterranean sedimentological record, in a location proximal to the Messinian Gateways. Here, even if anoxic bottom water conditions were never reached, the benthic foraminifer association, paired with the benthic foraminifer carbon isotope record suggest a perturbation of the bottom water circulation and a decrease in bottom water oxygen levels starting ~7.17 Ma. In addition, a comparison of Western-Eastern Mediterranean records enabled us to make assumptions regarding the Mediterranean scale circulation before and after the 7.17 Ma event.
How to cite: Bulian, F., Kouwenhoven, T. J., Sierro, F. J., and Krijgsman, W.: Geochemical and micropaleontological evidence of the Messinian Salinity Crisis preconditioning phase in the West Alboran Basin , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2126, https://doi.org/10.5194/egusphere-egu21-2126, 2021.
The fresh new cores 3AGN2S02 and 3AGN2S04 located in the deformed foredeep of the Gela Thrust System, locally known as Caltanissetta Basin, represent an opportunity for a better comprehension of the Messinian events, as well as for the reconstruction of the Sicilian evaporitic Basin architecture. The entire ‘early Messinian stage’ (7.2-5.96Ma) preceding the Messinian Salinity Crisis (MSC) has been already investigated in the Caltanissetta Basin. Even though the Tripoli Formation and ‘Calcare di Base’ (‘CdB’) have been widely studied for a long period of time, many aspects remain unclear. The ‘CdB’ has been commonly considered to represent the first evaporitic unit of the Messinian succession in Sicily. Different ages obtained in the underlying Tripoli deposits from various Sicilian outcrops display a diachronous onset of the MSC (Rouchy & Caruso, 2006). However, Manzi et al. (2011) propose an alternative interpretation for the ‘CdB’, suggesting that it does not belong exclusively to the onset of the MSC, but it is made of three carbonate facies belonging to different MSC stages. A detailed sedimentological, geochemical and petrographic study of the two cores allowed us to evidence the paleoceanographic changes that affected the central Mediterranean Sea during the transition from marine to restricted conditions, up to the onset of the MSC, and to observe the differences between the marginal and the deep basins of the Caltanissetta Basin, enhanced by the ongoing regional tectonics. Facies characterization made it possible to confirm the nature of the sediments of the cores, reflecting distinct depositional environments. A lithological transition passing from the Tripoli Formation to the complex ‘CdB’ carbonates alternating with shales is observed (3AGN2S04). This CdB appears to be laterally equivalent to gypsum and salts at site 3AGN2S02. In the brecciated facies of the ‘CdB’, evaporite pseudomorphs are also present, implying early stage diagenesis. Furthermore, our analyses gave us insights of strong oscillations in hypersaline conditions with freshwater inputs controlled by Milankovitch’s cycles. Moreover, the 3AGN2S04 core is characterized by the repetition of sedimentary successions due to the later development of a thrust system, which can be an important hint concerning the morphological and structural evolution of the Caltanissetta Basin. These new data are fundamental for stratigraphic reconstructions, comparing them with the already well-calibrated reference section of Falconara-Gibliscemi but also with other outcrops located in the various depocenters of the Caltanissetta Basin. The local transition from the uppermost part of the Tripoli cycles to the ‘CdB’ reflects the worsening of the marine connections, implying that during late Messinian broadly constant stressed environmental conditions existed in the central Mediterranean shelves. We conclude that since the onset of the MSC, marine inputs were not important enough to balance the effects of the climate fluctuations and the evaporation/precipitation budget in the individualized semi-closed settings.
How to cite: Tzevahirtzian, A., Caruso, A., Scopelliti, G., and Sulli, A.: The onset of the Messinian Salinity Crisis recorded by a new marginal basin succession in the Caltanissetta Basin (Sicily, IT)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5974, https://doi.org/10.5194/egusphere-egu21-5974, 2021.
Calcareous nannoplankton, one of the major contributors to marine primary production, not only responds quickly to variations in environmental conditions, but provides excellent means of first-order biostratigraphy. In our study we use early Pliocene sediments from the Cretan Sea (South Aegean; DSDP- Leg 42A, Site 378). The location of the record allows us to investigate formation processes of the Zanclean sapropelic layers in South Aegean Sea, and unravel the effects of monsoonal activity, as well as characterize any high latitude teleconnections of the area, prior to the mid-Pliocene warm period. The obtained nannofossil biostratigraphy provided the first-order bed-to-bed age control during the time interval of 5.08-3.98 Myrs, enabling the astronomical tuning of the marly–sapropelic cycles 12-59 to the target-curves.
Geochemical analysis (total organic carbon, oxygen, nitrogen, organic and carbonate carbon stable isotopes) were performed, revealing variations in carbon cycle and paleoceanographic conditions, as also variability in the redox conditions of the basin. Planktonic foraminifera δ18O and δ13C records are comparable to the global and Mediterranean Sea stacks, revealing warmer conditions in between approx. 5.08-4.9, in accordance to high summer insolation variation values. The quantification of the early Pliocene nannoplankton paleofluxes, indicated approximately two times higher average accumulation rates for the past export production during the sapropelic layers in respect to the non-sapropelic intervals; suggesting that primary productivity was a major component of the sapropelic formation procedures. Overall, calcareous nannofossil assemblage was dominated by Reticulofenestra spp. <5μm (up to 74%) followed by Florisphaera profunda (up to 64%). Other major species of the assemblage composition were Umbilicosphaera spp., Calcidiscus spp. and Helicosphaera spp. F. profunda showed an increase in paleofluxes within the sapropelic layers, coupled with relatively decreased accumulation rates of the upper photic zone taxa and high stratification index, thus suggesting an ecological depth-separation of the water column and a nutrient-rich lower photic zone.
We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – CLIMPACT’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments). E. Skampa has been granted with a scholarship from the State Scholarships Foundation. This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme « Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (ІΚΥ).
How to cite: Skampa, E., Triantaphyllou, M., Dimiza, M., Arabas, A., Gogou, A., and Baumann, K.-H.: Calcareous nannoplankton paleofluxes in the early Pliocene sapropels of the South Aegean Sea, NE Mediterranean: biogenic carbonate contribution and paleoecological implications , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14836, https://doi.org/10.5194/egusphere-egu21-14836, 2021.
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