Margarita D. Dimiza

Verification of the Algirosphaera robusta – Sphaerocalyptra quadridentata (coccolithophores) life-cycle association

Living coccolithophores were collected from eight stations along a transect in the gulf of Korthi (southeastern Andros island, Aegean Sea, Eastern Mediterranean) in August 2001. Samples were collected from 0–120 m water depth to determine the cell density, the species composition and the biogeographical (spatial and vertical) distribution of the coccolithophore biocommunities in coastal marine ecosystems. The studies revealed an impressive heterococcolith–holococcolith combination coccosphere (SEM micrograph) involving the species Algirosphaera robusta and Sphaerocalyptra quadridentata. In addition, a second association was observed by light microscopy. This discovery verifies the suggestions of Kamptner (1941) and provides strong proof on the assignment of these two ‘species’ in a common life cycle, increasing significantly our knowledge of life-cycle pairings ecology.

Holocene Climatic Optimum centennial-scale paleoceanography in the NE Aegean (Mediterranean Sea)

Combined micropaleontological and geochemical analyses of the high-sedimentation gravity core M-4G provided new centennial-scale paleoceanographic data for sapropel S1 deposition in the NE Aegean Sea during the Holocene Climatic Optimum. Sapropel layer S1a (10.2–8.0 ka) was deposited in dysoxic to oxic bottom waters characterized by a high abundance of benthic foraminiferal species tolerating surface sediment and/or pore water oxygen depletion (e.g., Chilostomella mediterranensis, Globobulimina affinis), and the presence of Uvigerina mediterranea, which thrives in oxic mesotrophic-eutrophic environments. Preservation of organic matter (OM) is inferred based on high organic carbon as well as loliolide and isololiolide contents, while the biomarker record and the abundances of eutrophic planktonic foraminifera document enhanced productivity. High inputs of terrigenous OM are attributed to north Aegean borderland riverine inputs. Both alkenone-based sea surface temperatures (SSTs) and δO18G. bulloides records indicate cooling at 8.2 ka (S1a) and ~7.8 ka (S1 interruption). Sapropelic layer S1b (7.7–6.4 ka) is characterized by rather oxic conditions; abundances of foraminiferal species tolerant to oxygen depletion are very low compared with the U. mediterranea rise. Strongly fluctuating SSTs demonstrate repeated cooling and associated dense water formation, with a major event at 7.4 ka followed by cold spells at 7.0, 6.8, and 6.5 ka. The prominent rise of the carbon preference index within the S1b layer indicates the delivery of less degraded terrestrial OM. The increase of algal biomarkers, labile OM-feeding foraminifera and eutrophic planktonic species pinpoints an enhanced in situ marine productivity, promoted by more efficient vertical convection due to repeated cold events. The associated contributions of labile marine OM along with fresher terrestrial OM inputs after ~7.7 ka imply sources alternative/additional to the north Aegean riverine borderland sources for the influx of organic matter in the south Limnos Basin, plausibly related to the inflow of highly productive Marmara/Black Sea waters.

Evidence for a possible life-cycle association between Syracosphaera protrudens (heterococcolithophore) and Syracosphaera pulchra HOL pirus-type (holococcolithophore)

An apparently unambiguous combination coccosphere from the Eastern Mediterranean (Aegean Sea, Greece) is documented involving Syracosphaera protrudens Okada & McIntyre, 1977 and Syracosphaera pulchra Lohmann, 1902 HOL pirus-type. This finding is difficult to interpret in terms of the current understanding of Syracosphaera taxonomy and adds evidence to the hypothesis of a distinctly complex Syracosphaera pulchra life cycle.

Coccolithophore community response along a natural CO2 gradient off Methana (SW Saronikos Gulf, Greece, NE Mediterranean)

A natural pH gradient caused by marine CO2 seeps off the Methana peninsula (Saronikos Gulf, eastern Peloponnese peninsula) was used as a natural laboratory to assess potential effects of ocean acidification on coccolithophores. Coccolithophore communities were therefore investigated in plankton samples collected during September 2011, September 2016 and March 2017. The recorded cell concentrations were up to ~50 x103 cells/l, with a high Shannon index of up to 2.8, along a pH gradient from 7.61 to 8.18, with values being occasionally <7. Numerous holococcolithophore species represented 60–90% of the surface water assemblages in most samples during September samplings. Emiliania huxleyi was present only in low relative abundances in September samples, but it dominated in March assemblages. Neither malformed nor corroded coccolithophores were documented. Changes in the community structure can possibly be related to increased temperatures, while the overall trend associates low pH values with high cell densities. Our preliminary results indicate that in long-termed acidified, warm and stratified conditions, the study of the total coccolithophore assemblage may prove useful to recognize the intercommunity variability, which favors the increment of lightly calcified species such as holococcolithophores.

Age Constraints and Paleoenvironmental Interpretation of a Borehole Sedimentary Sequence along the Eastern Part of the Corinth Isthmus, Greece

ABSTRACT Pallikarakis, A.; Triantaphyllou, M.V.; Papanikolaou, I.; Dimiza, M.D.; Reicherter, K., and Migiros, G., 2018. Age constraints and paleoenvironmental interpretation of a borehole sedimentary sequence along the eastern part of the Corinth Isthmus, Greece. Borehole Bh-3, located at the eastern part of the Corinth Isthmus (Greece) in a highly active extensional tectonic environment, is studied in detail. The lithology of the 70-m-long borehole is described, and 55 samples extracted from the core are analyzed for their micropaleontological content. Quantitative analysis of foraminiferal fauna assemblages, along with magnetic susceptibility measurements, indicates alternations between different paleoenvironments ranging from upper shoreface and fluvial-terrestrial to lagoon and shallow marine. The borehole site regional paleodepth was estimated, ranging from a few meters to ∼40 m on the basis of foraminiferal assemblages within the borehole, and the vertical stacking of the facies was interpreted as transgressive and regressive system tracts. Calcareous nannofossils found within the core, based on the presence of Emiliania huxleyi specimens, correlated with the glacioeustatic sea-level changes, and the uplift rate of the area indicated a post–240-ka age, corresponding to sea-level highstand marine isotope stages 7 to 5.