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Abstract
Due to its ever-increasing ocean inputs, fossil-based microplastics (MP) comprise a considerable constituent in the particulate organic carbon (POC) pool, which is instrumental in ocean biogeochemical cycling. Their distribution within the oceanic water column and the underpinning processes, however, remain unclear. Here we show that MP prevail throughout the water column of the eastern North Pacific Subtropical Gyre, comprising 334 #/m3 (84.5% of plastic particles <100 µm), with exponential relationships between concentrations and water depth in the upper 500-m layer and marked accumulation below this layer. Our results suggest that the biological carbon pump (BCP) strongly contributes to the water column MP redistribution in terms of polymer type, material density and particle size, which in turn could influence the efficiency of organic matter export to the deep sea. We further show that 14C-depleted plastic particles predictably are an emerging nonneglectable perturbation to radiocarbon signatures in the deep ocean through depletion of the 14C/C ratio in the POC pool. Our data provide insight into vertical MP flux and highlight the potential role of MP in alternating the marine particulate pool and interactions with the BCP.

9 páginas, 4 tablas, 9 figuras ; To better understand sources and transport of particulate material in the NW Iberian coastal upwelling system, a mooring line dotted with an automated PPS 4/3 sediment trap was deployed off Cape Silleiro at the base of the photic zone. The samples were collected from November 2008 through June 2012 over sampling periods of 4-12 days. Our study represents the first automated sediment trap database for the NW Iberian margin. The magnitude and composition of the settling material showed strong seasonal variability with the highest fluxes during the poleward and winter mixing periods (averages of 12.9±9.6 g m−2 d−1 and 5.6±5.6 g m−2 d−1 respectively), and comparatively lower fluxes (3.6±4.1 g m−2 d−1) for the upwelling season. Intensive deposition events registered during poleward and winter mixing periods were dominated by the lithogenic fraction (80±3%). They were associated to high energy wave-driven resuspension processes, due to the occurrence of south-westerly storms, and intense riverine inputs of terrestrial material from Minho and Douro rivers. On the other hand, during the spring - summer upwelling season, the share of biogenic compounds (organic matter, calcium carbonate (CaCO3), biogenic silica (bSiO2)) to downward fluxes was higher, reflecting an increase in pelagic sedimentation due to the seasonal intensification of primary production and negligible river inputs and wave-driven resuspended material. Otherwise, the large variations of biogenic settling particles were mainly modulated by upwelling intensity, which by means of upwelling filaments ultimately controlled the offshore transport of the organic carbon fixed by primary producers towards the adjacent ocean. Based on the average downward flux of organic carbon (212 mg C m−2 d−1) and considering an average primary production of 1013 mg C m−2 d−1 from literature, we estimated that about 21% of the fixed carbon is vertically exported during the upwelling season ; This study was sponsored by CAIBEX (CTM2007-66408-C02-01/MAR) and REIMAGE (CTM2011–30155–C03–03) projects funded by the Spanish Government, EXCAPA project (10MDS402013PR) supported by Xunta de Galicia, the EU FEDER funded projects RAIA (INTERREG 2009/2011; 0313/RAIA/E) and RAIA.co (INTERREG 2011/2013; 052/RAIA.co/1E) and the CALIBERIA project (PTDC/MAR/102045/2008) financed by Fundaçao para a Ciència e a Tecnologia (FCT-Portugal). D.Z. was funded by a postdoctoral fellowship (Plan I2C) from Xunta de Galicia (Spain) ; Peer reviewed

13 pages, 8 figures, 3 tables ; The production of transparent exopolymer particles (TEP) in response to several environmental variables was studied in 2 mesocosm experiments. The first (Expt 1) examined a gradient of 4 nutrient levels; the second (Expt 2) examined different conditions of silicate availability and zooplankton presence. Tanks were separated in 2 series, one subjected to turbulence and the other not influenced by turbulence. In tanks with nutrient addition, TEP were rapidly formed, with net apparent production rates closely linked to chl a growth rates, suggesting that phytoplankton cells were actively exuding TEP precursors. High nutrient availability increased the absolute concentration of TEP; however, the relative quantity of TEP produced was found to be lower, as TEP concentration per unit of phytoplankton biomass was inversely related to the initial nitrate dose. In Expt 1, an increase in TEP volume (3 to 48 μm equivalent spherical diameter) with nutrient dose was observed; in Expt 2, both silicate addition and turbulence enhanced TEP production and favored aggregation to larger TEP (>48 μm). The presence of zooplankton lowered TEP concentration and changed the size distribution of TEP, presumably by grazing on TEP or phytoplankton. For lower nutrient concentrations, the ratio of particulate organic carbon (POC) to particulate organic nitrogen (PON) followed the Redfield ratio. At higher nutrient conditions, when nutrients were exhausted during the post-bloom, a decoupling of carbon and nitrogen dynamics occurred and was correlated to TEP formation, with a large flow of carbon channeled toward the TEP pool in turbulent tanks. TEP accounted for an increase in POC concentration of 50% in high-nutrient and turbulent conditions. The study of TEP dynamics is crucial to understanding the biogeochemical response of the aquatic system to forcing variables such as nutrient availability and turbulence intensity ; This study was supported by EU project NTAP (EVK3-CT-2000-00022). Access to the Espeland Marine Biological Station of the Bergen Marine Food Chain Research Infrastructure was possible through Contract No. HPRI-CT-1999-00056 of the Improving Human Potential Programme of the European Union. F.P. held a Ramon y Cajal contract ; Peer Reviewed

AbstractTests OF FOUR types of filter media are presented, which show that granular activated carbon performs marginally less well than anthracite/sand or anthracite/sand/garnet in the removal of algae, particulate organic carbon, iron and turbidity. The lengths of run which are achieved by the two granular activated carbon filters are also shorter than those of the other two media. A three‐layer filter is better than the anthracite/sand filter for particulate organic carbon, iron and turbidity removal, and the filtrate contains lower mean concentrations of algae.