Coastal marine sediments receive intensive stress from urbanization and industrialization, which is manifested by increased contents of heavy metals and organic pollutants. Saronikos Gulf and the small embayment of Elefsis, stretch along the coast of the greater Athens and Pireaus port, the most urbanized and industrialized areas in Greece. Here we present the data of a 20-years geochemical record on grain-size, organic carbon, and major and trace elements contents of the Saronikos Gulf sediments. A total of 216 sediment samples were collected within the period of 1999 to 2018 from the four sub-sectors of the gulf, namely, the Elefsis Bay, the Inner, Outer, and Western (Megara and Epidavros basin) Saronikos Gulf. Additionally, at least one core was obtained from each sub-sector. Sediments deposited at pre-industrial periods were recognized by 14C and 210Pb datings, and served for establishing regionalized, background levels of metals. Factor analysis was conducted to reveal the inter-parametric relationships, thus their common sources, as well as transport and deposition pathways. Then, Enrichment Factors and the multi-elemental Modified Pollution Index (MPI) were calculated to assess the current environmental status of the sediments. Data of sampling sites with at least a five-year record, were assessed for temporal trends, to explore whether sustained, increasing or decreasing trends of the MPI are observed. The dataset and analyses presented here support the research article entitled Geochemistry of major and trace elements in surface sediments of the Saronikos Gulf (Greece): assessment of contamination between 1999 and 2018 by Karageorgis A.P., Botsou F., Kaberi H., and Iliakis S., https://doi.org/10.1016/j.scitotenv.2020.137046

Study to assess the quality of the excavated materials from the construction of an underground car parking in front of the exhibition center of Piraeus port. And the possible effects they will have on the marine ecosystem, in case of their disposal.

Study to assess the quality of the excavated materials from the construction of a fishing shelter in Sami, Kefalonia. And the possible effects they will have on the marine ecosystem, in case of their disposal.

Study to assess the quality of the excavated materials from the expansion and deepening of the existing port in Almiros Volou. And the possible effects they will have on the marine ecosystem, in case of their disposal.

Data were collected in the southern Western Black Sea (Bulgarian and Romanian territorial waters) for the Eurofleets+ PHYCOB cruise. This submission contains CTD and nutrient data. The main scientific objectives of the research cruise are: 1) To assess the presence of toxic microalgae in the plankton assemblage of the Western Black Sea. 2) To quantitatively determine the spatial distribution of toxic phytoplankton species and their corresponding toxins in the plankton. 3) To quantitatively describe the spatial distribution of toxic phytoplankton resting stages in surface sediments and determine hotspots of recruitment and bloom initiation. 4) To define correlations among hydrographic and/or meteorological conditions and occurrence of HAB species. 5) To characterize the plankton communities accompanying HAB species together with toxin analysis of size fractionated samples. 6) To identify heterotrophic dinoflagellates, ciliates, or other small zooplankton as possible toxin vectors. 7) To isolate toxic Black Sea microalgal species and establish monoclonal cultures for characterization of Black Sea strains. 8) To perform an interseasonal comparison of toxigenic plankton species by combining the data sets collected during the R/V Akademik cruise that was performed in May/June 2019 with our data from summer. 9) To compare the data set from the Western Black Sea to the Southern (North-) Western North Sea, Baltic Sea and West Greenland obtained during earlier expeditions for site comparisons.

The purpose of this publication is to give access to the analytic data set which has been used in a paper submitted to the journal Marine Geology (Torelli et al., submitted). This paper proposes a general study of the organic matter (OM) distribution within the recent Quaternary sediments of the Mozambique Channel (southern part of the east African margins). The study was conducted in the framework of the PAMELA (PAssive Margin Exploration LAboratory) research project (Bourillet et al., 2013). This study is mainly based on Rock-Eval 6 (RE6) analyses of samples collected during several marine surveys: Pamela-Moz01 (Olu, 2014), Pamela-Moz04 (Jouet and Deville, 2015) and Pamela-Moz08 (Khripounoff, 2016; Fig. 1). 394 RE6 analyses were performed on samples collected with the Küllenberg corer (recovered core length up to 12 m) of the R/V Atalante (Pamela-Moz01 survey) and the Calypso corer (recovered core length up to 33 m) of the R/V Pourquoi Pas? (Pamela-Moz04 survey), 11 RE6 analyses on samples collected with an interface multicorer (30-40 cm maximum penetration), and 101 RE6 analyses on samples collected with sediment traps in moorings located 47 m above seabed. We provide here the whole RE6 analyses (Table 1) and the correlation made between RE6 analyses and LECO elemental analyses concerning the total carbon (Tables 2 and 3). The analysis of samples collected with particle traps within the deep-water areas of the Mozambique Basin has shown that the OM is transported by turbidite and/or contour currents and deposited while preserving Total Organic Carbon (TOC) contents between 1.5 and 3%Wt. However, the sedimentary OM is largely oxidized (Oxygen Index > 300 mg CO2/g TOC) and only a small amount of TOC (< 0.5%Wt) is preserved within the recent sediments of the distal area of the Zambezi turbidite system at water depths below 2500 m. Interface sediments sampled to a maximum depth of 40 cm, have shown intermediate TOC values between those collected in the particle traps and those from piston cores suggesting that the degradation of the OM is mainly active at the water-sediment interface. This OM oxidation and degradation process in the deep-water domains of the Mozambique Basin is probably due to the conjugate effects of low sediment accumulation rate and high permeability of the coarse-grained sediments but also to important bottom currents that promote the remobilization and the rearrangement of fine grained sediments.   References   Bourillet, J.F., Ferry, J.N., Bourges, P., 2013. PAMELA, Passive Margins Exploration Laboratories. https://dx.doi.org/10.18142/236. Jouet, G., Deville, E., 2015. PAMELA-MOZ04 cruise, R/V Pourquoi Pas? https://doi.org/10.17600/15000700. Khripounoff, A., 2017. PAMELA-MOZ08 cruise, R/V Antea. https://doi.org/10.17600/17003900. Olu, K, 2014. PAMELA-MOZ01 cruise, R/V L'Atalante, https://dx.doi.org/10.17600/14001000. Torelli, M., Battani, A., Pillot, D., Kohler, E., Lopes De Azevedo, J., Kowalewski, I., Pastor, L., Brandily, C., Schmidt, S., Jouet, G., Deville, E. (Submitted to Marine Geology). Organic matter distribution in modern sediments of the Mozambique Channel: Evidence for widespread oxidation processes in the deep-water domains. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

We discuss vegetation and climate changes across western Europe over the last deglaciation, especially zooming on the Heinrich Stadial 1 (HS1) interval in the northern Bay of Biscay. Our study focuses on the marine palynological investigation of core MD13-3438, with new pollen analyses, here compared to a set of paleohydrographical marine proxies (including dinoflagellate cysts / dinocysts) obtained on the same core. We show that the recorded pollen signature is, at that time, tightly related to the fluvial dynamics of the ‘Fleuve Manche’ paleoriver, the latter being coupled with European Ice Sheet fluctuations, as well as influenced by fluvial deliveries from closer French rivers of the Atlantic coast. The onset of HS1 (18.2–16.7 ka BP), marked by enhanced ‘Fleuve Manche’ paleoriver seasonal runoff, is characterized by: i) two episodes of substantial fluvio-glacial input, concomitant with warmer summers and marked by increases of temperate forest pollen grain percentages; ii) and three episodes of moderate runoff, concomitant with extended colder winters and corresponding to increases of boreal forest pollen grain percentages. We suggest an important role of the variability of the North Atlantic atmospheric circulation in explaining those multidecadal changes in pollen sources recorded in the marine realm. When westerlies are deflected southward (respectively northward), they would bring higher humidity to the southern-western and closer (respectively northern-eastern and more distal) distributaries/rivers of the ‘Fleuve Manche’ paleoriver system, associated to moderate (respectively intense) runoff. Then, extreme cold and dry climate conditions are recorded at the onset of Heinrich Event 1 (16.7–15.6 ka BP) with marked occurrences of steppic pollen grains, followed by more humid conditions at the end of HS1, with mixed signatures of open-vegetation and temperate forest taxa. The wettest conditions are recorded during the Bølling-Allerød, concomitantly with the sea level rise and the advection of warm and salty waters by the North Atlantic Current to the study site. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

Pialassa Baiona is a temperate coastal lagoon connected with the Northwestern Adriatic Sea (44° 280 N and 44°310 E). Sediment cores and surface sediments were collected in two habitats within Pialassa Baiona: a) a salt marsh habitat characterized by the presence of saltmarsh vegetation, and b) a human impacted habitat close to anthropogenic source inputs. Cores were sampled by inserting one cylindrical Plexiglas hand corer (5-cm diameter, 50 cm long) into the sediment to a depth of 20-25 cm, and surface sediment samples (0–5 cm) were collected with a stainless-steel grab sampler. The cores were extruded in the field, sectioned into 1-2 cm intervals, and analyzed for total organic carbon (OC), total nitrogen (TN), carbon isotope ratio (d13C) and dry bulk density (upper 20 – 25 cm) and analyzed for organic carbon (OC), total nitrogen (TN), carbon isotope ratio (d13C) and dry bulk density. Organic carbon (OC), total nitrogen (TN), and carbon isotopes (d13C = [(13C/12C)sample/(13C/12C)standard - 1] × 1,000) were measured in sediment cores and surface sediments using a using a FINNIGAN Delta Plus XP mass spectrometer directly coupled to Thermo Fisher FLASH 2000 CHNS Elemental Analyzer. OC and TN content was expressed as the weight percentage of dried sediment, and carbon isotope results were reported in the standard delta notation with respect to the Vienna Pee Dee Belemnite. A ‘three-end member’ mixing model was used to estimate the relative contribution of the different organic matter (OM) sources: marine phytoplankton (FM), riverine-estuarine phytoplankton (FRE), and C3 saltmarsh plant material (FSM): d13Csample = d13CM x FM + d13CFE x FFE + d13CSM x FSM C/Nsample = C/NM x FM + C/NFE x FFE + C/NSM x FSM 1 = FM + FRE + FSM where FM, FRE and FSM are the relative contributions of marine phytoplankton, riverine-estuarine phytoplankton, and saltmarsh plant material, respectively. d13CM (-18.97‰) and C/NM (4.95), and d13CRE (-30.70‰,) and C/NRE (6.63) represent the end member POC signature recorded during distinct marine and estuarine phytoplankton blooms in the coastal lagoon (Guerra et al., 2013).The C3 saltmarsh plant end-member was selected on the basis of typical d13CSM (-20.2‰) and C/NSM (15.35) values for Juncus spp. (Gebrehiwet et al., 2008; Hughes and Sherr, 1983; J. I. Kelleway et al., 2017; Kemp et al., 2012, 2010; Lamb et al., 2006). References Gebrehiwet, T., Koretsky, C.M., Krishnamurthy, R. V., 2008. Influence of Spartina and Juncus on saltmarsh sediments. III. Organic geochemistry. Chem. Geol. 255, 114–119. https://doi.org/10.1016/j.chemgeo.2008.06.015 Guerra, R., Pistocchi, R., Vanucci, S., 2013. Dynamics and sources of organic carbon in suspended particulate matter and sediments in Pialassa Baiona lagoon (NW Adriatic Sea, Italy). Estuar. Coast. Shelf Sci. 135, 24–32. https://doi.org/10.1016/j.ecss.2013.06.022 Kelleway, J.I., Saintilan, N., Macreadie, P.I., Baldock, J.A., Ralph, P.J., 2017. Sediment and carbon deposition vary among vegetation assemblages in a coastal salt marsh. Biogeosciences 14, 3763–3779. https://doi.org/10.5194/bg-14-3763-2017 Kemp, A.C., Vane, C.H., Horton, B.P., Culver, S.J., 2010. Stable carbon isotopes as potential sea-level indicators in salt marshes, North Carolina, USA. Holocene 20, 623–636. https://doi.org/10.1177/0959683609354302 Kemp, A.C., Vane, C.H., Horton, B.P., Engelhart, S.E., Nikitina, D., 2012. Application of stable carbon isotopes for reconstructing salt-marsh floral zones and relative sea level, New Jersey, USA. J. Quat. Sci. 27, 404–414. https://doi.org/10.1002/jqs.1561 Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

During the 2007 MEDECO cruise of RV Pourquoi Pas ? (Sarrazin & Pierre, 2007), http://www.iso-analytical.co.uk/index.html). This data underlies the following paper: Carlier A., Ritt B., Rodrigues C.F., Sarrazin J., Olu K., Grall J. & Clavier J. (2010): Heterogeneous energetic pathways and carbon sources on deep eastern Mediterranean cold seep communities. Marine Biology 157 (11), 2545–2565 (2010), https://archimer.ifremer.fr/doc/00016/12684/ The dataset consists of two files: one containing the data itself, and one describing all used terms (measurements or metadata). Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

Contents and composition of microplastic-like particles have been analysed in ten sediment samples from the Danish part of the open North Sea and in the Inner Danish waters in 2015. The contents of microplastic-like particles in the size range 100-5000 µm were determined to be in the range of 192-3511 particles per kg dry weight sediment, dominated by blue and black coloured particles, mainly as fibres, and particle sizes < 300 µm were dominating.