19 research outputs found
Deep-Ocean dissolved organic matter reactivity along the Mediterranea Sea: does size matter?
Original research paperDespite of the major role ascribed to marine dissolved organic matter (DOM) in the global carbon
cycle, the reactivity of this pool in the dark ocean is still poorly understood. Present hypotheses,
posed within the size-reactivity continuum (SRC) and the microbial carbon pump (MCP) conceptual
frameworks, need further empirical support. Here, we provide field evidence of the soundness of the
SRC model. We sampled the high salinity core-of-flow of the Levantine Intermediate Water along its
westward route through the entire Mediterranean Sea. At selected sites, DOM was size-fractionated
in apparent high (aHMW) and low (aLMW) molecular weight fractions using an efficient ultrafiltration
cell. A percentage decline of the aHMW DOM from 68–76% to 40–55% was observed from the Levantine
Sea to the Strait of Gibraltar in parallel with increasing apparent oxygen utilization (AOU). DOM
mineralization accounted for 30±3% of the AOU, being the aHMW fraction solely responsible for this
consumption, verifying the SRC model in the field. We also demonstrate that, in parallel to this aHMW
DOM consumption, fluorescent humic-like substances accumulate in both fractions and protein-like
substances decline in the aLMW fraction, thus indicating that not only size matters and providing field
support to the MCP modelHOTMIX (grant number CTM2011–30010-C02 01-MAR and 02-MAR) and the project FERMIO (MINECO, CTM2014-57334-JIN), both co-financed with FEDER funds; (reference BES-2012- 056175) from the Spanish Ministry of Economy, Industry and Competitivenes; the project MODMED from CSIC (PIE, 201730E020) and CSIC Program “Junta para la Ampliación de Estudios” co-financed by the ESF (reference JAE DOC 040)Versión del editor2,92
Testing the association between psychosocial job strain and adverse birth outcomes - design and methods
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Comparative toxicity of azo dyes to two infaunal organisms (Hexagenia spp. and Tubifex tubifex) in spiked-sediment exposures
Genomic and enzymatic evidence for acetogenesis among multiple lineages of the archaeal phylum Bathyarchaeota widespread in marine sediments
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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