Lithics and cut-marked mammal bones, excavated from the paleo-lake Marathousa 1 (MAR-1) sediments in the Megalopolis Basin, southern Greece, indicate traces of hominin activity occurring along a paleo-shoreline ca. 444,000 years (444 ka) ago. However, the local environment and climatic conditions promoting hominin activity in the area during the MIS12 glacial remain largely unknown. In order to reconstruct the paleo-environment including paleo-lake levels and governing paleo-climatic factors on a high temporal resolution, we analyzed a 6-meter-long sediment sequence from the archeological site MAR-1 and a Bayesian age model was computed for a better age constrain of the different sedimentary units. A multiproxy approach was applied using ostracods, sponge spicules, diatoms, grain sizes, total organic carbon, total inorganic carbon and conventional X-ray fluorescence analysis. The results from the site represent a protected region surrounded by high mountains under the constant influence of water, either as a shallow partly anoxic water body surrounded by reed belts (>463–457 ka, <434–427 ka), a riverine-lake deltaic system (∼457–448 ka), a floodplain (∼448–444 ka) or a seasonal freshwater pond (∼444–436 ka). The local changes of water levels resemble large trends and rhythms of regional records from the Mediterranean and appear to directly respond to sea surface temperature (SST) changes of the North Atlantic. In particular, when the SSTs are high, more moisture reaches the study area and vice versa. Additional water reaches MAR-1 through melting of the surrounding glaciers after brief warm phases during MIS12 in the Mediterranean realm, which leads to the formation of smaller fresh water ponds, where also the horizon of the excavated remains is placed. Such ponds, rich in ostracods and other microorganisms, provided mammals and humans valuable resources, such as potable water, a wide range of plant species and hunting opportunities. These deposits therefore bear a high archeological potential. The results from our study suggest that the Megalopolis Basin could have served as a refugium for hominins and other organisms due to its capacity to retain freshwater bodies during glacial and interglacial periods.
<p>In the fossil-rich sediments of the Megalopolis Basin, southern Greece, the remains of an ancient paleo-lake alternate between detrital units and lignite seams deposited during the Middle Pleistocene. The detrital sediments of MAR-1 (480-420 kyr) between two lignite seams are where lithics and elephant bones with cut-marks have been systematically excavated indicating hominin activity along a paleo-shoreline circa 440 kyr. Based on current knowledge, lignite seams formed during interglacials, while the silty-clay-rich deposits in between were deposited under glacial conditions. However, the paleoenvironmental and paleoclimatic conditions on shorter times-scales, leading to the preservation of hominin activity in the area, remain largely unknown. In order to reconstruct the paleo-environment including paleo-lake levels and thus sedimentation patterns and their governing paleo-climatic factors, we analyzed a high resolution 5-meter long sediment sequence from the archaeological site MAR-1. For the reconstruction, a multiproxy approach was applied using microfossils, grain-size, and geochemical analysis such as total organic carbon, total inorganic carbon, X-ray diffraction, and conventional X-ray fluorescence. Diatoms were often too corroded to be of use, most likely due to a combination of alkaline water conditions and the influence of silicate sponges. The results of the analyses revealed that MAR-1, located between lignite unit II and III, experienced multiple lake level oscillations mostly following insolation changes suggesting that several short-term wet-dry-wet cycles occurred during the investigated period, which must have impacted flora and fauna, including hominins, in the area. This research was conducted under the auspices of the Ephoreia of Paleoanthropology and Speleology, Greek Ministry of Culture, and was supported by the European Research Council (PaGE, CROSSROADS).</p>
<p>All hydrocarbon (HC) reservoirs experience some degree of leakage, so HCs will enter the overlying sediment. While strong leakage causes surface manifestations, minor leakage can remain undetected as the hydrocarbons are completely metabolized during their ascent to the sediment surface. However, even minor seepage affects the sediment&#8217;s geochemistry and microbiology as it adds electron donors. The PROSPECTOMICS project aims to use these sometimes minute microbiological and geochemical changes as a tool for HC prospecting.</p> <p>We recovered fifty 2-3 m long sediment cores in the Barents Sea from three potential HC seepage zones (HC zones) and two zones without seepage (REF zones) and sampled sediment and pore water with high spatial resolution.</p> <p>We measured sulfate reduction rates and quantified microbial cell abundance, and characterized the organic matter via FT-ICR-MS. We also quantified anions and cations in the pore water via ion chromatography and ICP-MS and determined alkalinity via titration.</p> <p>FT-ICR-MS and cell counts did not show any differences between HC zones and REF zones. Sulfate concentration profiles decrease linearly with depth and show a much steeper decline and greater variability in the HC zones than in the REF zones. The linear profiles imply the absence of active sulfate reduction within the cored depth intervals and a sink for sulfate at greater depth, most probably sulfate-driven anaerobic oxidation of methane (AOM). This would also explain the correlating linear increase in alkalinity. At some sites in the HC zones pore water sulfide profiles also increase linearly with depth whereas at other HC sites and at all REF sites, sulfide concentrations remain below our detection limit throughout the entire core.</p> <p>Using highly sensitive <sup>35</sup>SO<sub>4</sub><sup>2-</sup> radiotracer incubations, we were able to detect low rates of microbial sulfate reduction in the pmol*cm<sup>-3</sup>*d<sup>-1</sup> range in some single samples from deeper layers in HC cores. Thus, despite apparently linear pore water sulfate gradients indicating no net sulfate reduction, we observed minor but detectable microbial turnover of sulfate. Modeling of the sulfate reduction rate based on pore water concentration data also yielded rates in the same order of magnitude as the radiotracer measurements, confirming microbial activity.</p> <p>Looking at the pore water cation concentration profiles, manganese and calcium show different linear trends in the HC zones compared to REF zones. In HC zones, manganese decreases with depth, while in the REF zones, manganese concentrations increase. Calcium concentrations decrease at HC sites while they remain constant at REF sites. These findings can partly be explained by microbial activity and associated alteration of clays, potentially due to microbial reduction of structural metals, ion exchange processes and mineral dissolution and formation. Barium was only detected in the pore water of some cores originating from HC zones where it might have been released during sulfate reduction accompanied with destabilization of baryte.</p> <p>In summary, relative differences in pore water ion concentration trends and the occurrence of sulfate reduction may be indicators of HC seepage.</p>
<p>Bivalves offer outstanding potential as environmental archives. However, vital effects exert a strong control on the incorporation of many trace and minor elements into the shell so that their use as environmental proxies is currently limited. Furthermore, Sr and Mg show a strong relationship to the micrometer-sized shell architecture (shell microstructure), i.e., near growth lines, which are typically dominated by irregular simple/spherulitic prismatic microstructures, the concentrations of these elements are significantly higher than in portions between growth lines (= growth increments, which are microstructurally more complex). In contrast, Ba is uncoupled from the prevailing shell microstructure. To shed more light on these issues, we conducted a combined element chemical (in-situ analysis by means of LA-ICP-MS) and microstructural analyses (using SEM) of shells of <em>Arctica islandica</em> collected alive in NE Iceland.</p><p>According to our findings, (1) contemporaneous shell portions in the hinge and ventral margin (both belonging to the outer shell layer) within individual specimens showed nearly identical Sr/Ca and Mg/Ca values, but Ba/Ca was 1.5 &#8211; 2.5 times higher in the ventral margin than in the hinge. (2) In agreement with previous studies, Sr and Mg were strongly elevated near annual growth lines. (3) Along an isochronous transect from the inner portion of the outer shell layer near the myostracum toward the outer shell surface (in the ventral margin), Si/Ca values increased, on average, by 75% &#177; 11%, whereas Na/Ca values decreased by 7% &#177; 1%. Along this transect, the shell microstructure gradually changed from crossed-acicular to homogeneous suggesting that Si and Na are linked to the prevailing nanometer-sized shell architecture or underlying physicochemical processes controlling their formation. (4) In the hinge, Ba/Ca, Sr/Ca, Mn/Ca and Mg/Ca attained highest values along the axis of maximum growth, but gradually decreased in slower growing (contemporaneous) shell portions away from that axis. (5) In contemporaneous shell portions (in either the hinge or the ventral margin), the concentration of some elements varied significantly among specimens, whereas others showed little variability. For example, in similar and contemporaneous shell portions of different specimens, Na/Ca values exhibited only little variation (17.4 &#8211; 23.7 mmol/mol), whereas Sr/Ca and B/Ca differed more severely (0.3 &#8211; 1.6 mmol/mol and 0.04 &#8211; 0.07 mmol/mol, respectively; both within growth increments). Despite these inter-specimen chemical differences, the shell microstructure remained largely invariant.</p><p>Our findings firstly suggest that the extrapallial fluid, if it exists at all, is chemically inhomogeneous. This could result from differences in the efficiency of transmembrane ion transport or to differences in shell formation rate along the growing margin (e.g., faster growth in the outer portion of the outer shell layer than in portions closer to the myostracum). Secondly, chemical differences among specimens may be attributed to physiological differences. Thirdly, some elements such as Ba are uncoupled to microstructural properties, but co-vary strongly among specimens suggesting an environmental control on the uptake and incorporation of this element into the shell.</p>
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