The biological carbon pump, which transports particulate organic carbon (POC) from the surface to the deep ocean, plays an important role in regulating atmospheric carbon dioxide (CO 2 ) concentrations. We know very little about geographical variability in the remineralization depth of this sinking material and less about what controls such variability. Here we present previously unpublished profiles of mesopelagic POC flux derived from neutrally buoyant sediment traps deployed in the North Atlantic, from which we calculate the remineralization length scale for each site. Combining these results with corresponding data from the North Pacific, we show that the observed variability in attenuation of vertical POC flux can largely be explained by temperature, with shallower remineralization occurring in warmer waters. This is seemingly inconsistent with conclusions drawn from earlier analyses of deep-sea sediment trap and export flux data, which suggest lowest transfer efficiency at high latitudes. However, the two patterns can be reconciled by considering relatively intense remineralization of a labile fraction of material in warm waters, followed by efficient downward transfer of the remaining refractory fraction, while in cold environments, a larger labile fraction undergoes slower remineralization that continues over a longer length scale. Based on the observed relationship, future increases in ocean temperature will likely lead to shallower remineralization of POC and hence reduced storage of CO 2 by the ocean.biological carbon pump | particulate organic carbon | remineralization | mesopelagic A tmospheric carbon dioxide (CO 2 ) levels are strongly influenced by the production, sinking, and subsequent remineralization of particulate organic carbon (POC) in the ocean (1), with the atmospheric concentration partially set by the depth at which regeneration occurs (2). Numerous studies have endeavored to describe the complex interactions that produce the typically observed depth profile of sinking POC flux attenuation as relatively simple mathematical forms (3-6), with perhaps the most commonly used being a power law equation:where f z is the flux at depth z, normalized to flux at some reference depth, z 0 , and b is the coefficient of flux attenuation (7). This relationship was originally derived from POC flux measurements from several eastern North Pacific locations, and an open ocean composite b value of 0.86 was calculated (7), a value which has since been used extensively in biogeochemical models (8) and to normalize fluxes measured in different regions and at different depths (9, 10). Regional variations in b, from 0.6 to 2.0, have since been demonstrated by deep-sea (>2,000 m) sediment trap studies (11,12). More recently, mesopelagic POC flux attenuation between 150 m and 500 m depth was measured in the Vertical Transport in the Global Ocean (VERTIGO) project at two contrasting sites in the North Pacific (13), using neutrally buoyant sediment traps (NBSTs) developed to improve the reliability of upper ocean ...

Concern over plastic pollution of the marine environment is severe. The mass-imbalance between the plastic litter supplied to and observed in the ocean currently suggests a missing sink. However, here we show that the ocean interior conceals high loads of small-sized plastic debris which can balance and even exceed the estimated plastic inputs into the ocean since 1950. The combined mass of just the three most-littered plastics (polyethylene, polypropylene, and polystyrene) of 32-651 µm size-class suspended in the top 200 m of the Atlantic Ocean is 11.6-21.1 Million Tonnes. Considering that plastics of other sizes and polymer types will be found in the deeper ocean and in the sediments, our results indicate that both inputs and stocks of ocean plastics are much higher than determined previously. It is thus critical to assess these terms across all size categories and polymer groups to determine the fate and danger of plastic contamination.

Plastics and other artificial materials pose new risks to the health of the ocean. Anthropogenic debris travels across large distances and is ubiquitous in the water and on shorelines, yet, observations of its sources, composition, pathways, and distributions in the ocean are very sparse and inaccurate. Total amounts of plastics and other man-made debris in the ocean and on the shore, temporal trends in these amounts under exponentially increasing production, as well as degradation processes, vertical fluxes, and time scales are largely unknown. Present ocean circulation models are not able to accurately simulate drift of debris because of its complex hydrodynamics. In this paper we discuss the structure of the future integrated marine debris observing system (IMDOS) that is required to provide long-term monitoring of the state of this anthropogenic pollution and support operational activities to mitigate impacts on the ecosystem and on the safety of maritime activity. The proposed observing system integrates remote sensing and in situ observations. Also, models are used to optimize the design of the system and, in turn, they will be gradually improved using the products of the system. Remote sensing technologies will provide spatially coherent coverage and consistent surveying time series at local to global scale. Optical sensors, including high-resolution imaging, multi-and hyperspectral, fluorescence, and Raman technologies, as well as SAR will be used to measure different types of debris. They will be implemented in a variety of platforms, from hand-held tools to ship-, buoy-, aircraft-, and satellite-based sensors. A network of in situ observations, including reports from volunteers, citizen scientists and ships of opportunity, will be developed to provide data for calibration/validation of remote sensors and to monitor the spread of plastic pollution and other marine debris. IMDOS will interact with other observing systems monitoring physical, chemical, and biological processes in the ocean and on shorelines as well as the state of the ecosystem, maritime activities and safety, drift of sea ice, etc. The synthesized data will support innovative multidisciplinary research and serve a diverse community of users.

11ocean can potentially increase carbon uptake and sequestration at depth. Nutrients can 12 enhance primary productivity, and mineral particles act as ballast, increasing sinking 26Flux of airborne desert dust into the surface ocean can increase the amount of 27 photosynthetically fixed carbon dioxide (CO2) by reducing nutrient limitation of primary 28 production and thus increase the flux of particulate organic carbon (POC) to the deep ocean 1 . 29Dense dust-derived lithogenic particles can also increase particle size through aggregation and (Fig.1). During this period, NOG was subjected to, on average, ten-fold higher dust deposition 65 compared to SOG (Fig. 2a), as inferred from dust concentration measurements over Barbados 13 66for NOG and modelled data 14, 15 for SOG (Methods). At both sites, the average surface 67 production rates derived from a Vertically Generalised Production Model (VGPM) 16 were 68 lower than much of the global ocean 17 , and on average 23% higher at NOG than at SOG ( (Fig. 2d, 3). The POC fluxes at NOG and SOG were significantly lower than the (refs 21, 22, 23, 24, 25 ). This coincides with higher fluxes of aerosol iron in autumn than 136We estimated the contribution of different nitrogen sources to δ 15 NPN at NOG and SOG 137 using a two-end member nitrogen mass-balance model 29 (see Methods and references therein). 138We assumed that the isotope budget of the mixed layer in the permanently oligotrophic gyres 145The dust-derived nitrogen endmember was assigned δ 15 N of -3.1‰ based on the average for a possible origin of particles from a specific trophic level (e.g. faecal pellets) and alteration 158 of δ 15 NPN due to isotopic fractionation during particle remineralisation and transformation in 159 the mesopelagic. However, regardless of these uncertainties, the isotope budgets suggest a large 166The unique presence of intact Trichodesmium colonies in the deep particles at NOG 167 (Fig. 4) during late summer at NOG (Fig. 3a). 180 Ballasting effect of dust 181Higher dust input significantly altered the composition of particles at NOG compared 182 to SOG (Fig. 2e). Dust-derived lithogenic material was the second largest contributor 183 (34.3±11.6%) to the total mass at NOG after calcite, whereas at SOG this value was 4.7±2.3%, 184 consistent with the difference in the amount of dust being deposited at each site (Fig. 2a). 185Although the seasonal signal of elevated dust flux at both sites was largely lost at 3000 m depth, following high dust input (Fig. 3a). Assuming that this temporal coherence was not accidental, Table 2). 197Overall, lithogenic material appears to be a more important ballast for POC in the central Table 2). The ballasting ability of lithogenic particles at NOG appears to be 215 confined to the summer-autumn period (Fig. 3a) when the surface fertilisation by dust was Jickells, T., An, Z., Andersen, K. K., Baker, A., Bergametti, G., Brooks, N., et al. 244 Global iron connections between desert dust, ocean biogeochemistry, and climate.