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ÁlvarezSalgado et al.  Outwelling versus Upwelling in NW Spain ÁlvarezSalgado et al.  Outwelling versus Upwelling in NW Spain3

), where labile DOM is produced from phytoplankton exudation and/or lysis and (2) the bottom nepheloid layer (at a rate of about 0.2 ppb eq tryptophan d

The input of new nitrogen into the euphotic zone constrains the export of organic carbon to the deep ocean and thereby the biologically mediated long-term CO2 exchange between the ocean and atmosphere. In low-latitude open-ocean regions, turbulence-driven nitrate diffusion from the ocean's interior and biological fixation of atmospheric N2 are the main sources of new nitrogen for phytoplankton productivity. With measurements across the tropical and subtropical Atlantic, Pacific and Indian oceans, we show that nitrate diffusion (171±190 μmol m−2 d−1) dominates over N2 fixation (9.0±9.4 μmol m−2 d−1) at the time of sampling. Nitrate diffusion mediated by salt fingers is responsible for ca. 20% of the new nitrogen supply in several provinces of the Atlantic and Indian Oceans. Our results indicate that salt finger diffusion should be considered in present and future ocean nitrogen budgets, as it could supply globally 0.23–1.00 Tmol N yr−1 to the euphotic zone.

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Net ecosystem production (NEP) rates of dissolved organic carbon (DOC) are estimated in a coastal upwelling system. The study site is a large coastal inlet (2.76 km 3 ) in the northern boundary (42-43ЊN) of the eastern North Atlantic upwelling system. The two-dimensional circulation pattern in the system is governed by an offshore Ekman transport quite variable in magnitude and direction. A mass balance of the short-timescale (2-4 d) changes in measured DOC profiles is performed to obtain the NEP rates. Microbial oxidation of imported labile DOC (8% of total DOC, recycling time Ͻ 5 d) at a maximum net rate of Ϫ37 mmol C m Ϫ2 d Ϫ1 occurred during a downwelling episode in the middle of the highly productive spring period. On the contrary, extensive export of labile DOC (Ͻ15% of total DOC, Ͻ 7 days) produced at net rates Ͼ42 mmol C m Ϫ2 d Ϫ1 took place during an upwelling episode in July, the middle of the upwelling season. This rate represents ϳ20% of the net primary production, demonstrating in the field the relative importance of horizontal offshore transport of labile DOC to the export of new production in upwelling systems. An autumn wind relaxation period results in dramatic changes in DOC standing stocks (Ϯ9 mol C L Ϫ1 ) caused by a conspicuous time segregation between sustained net phytoplankton production of labile DOC (ϩ15 mmol C m Ϫ2 d Ϫ1, 11 d) and subsequent rapid bacterial degradation (Ϫ63 mmol C m Ϫ2 d Ϫ1 , 3 d). Net horizontal export during this period was prevented by reduced offshore Ekman transport values, indicating that net DOC production is not always synonymous with net export. Finally, during the winter period, the large wind-driven net DOC horizontal exchange rates affected mainly the DOC standing stocks of no bioreactive materials in the system, whereas bacterial oxidation rates during this period reduced to less than Ϫ0.14 mmol C m Ϫ2 d Ϫ1 .Incorporation of the phytogenic bioreactive fractions of dissolved organic matter (DOM) in experimental (Carlson et al. 1994) and modeling (Anderson and Williams 1999) approaches to carbon cycling have advanced our understanding of the fate of primary production in the oceans. The bioreactive DOM with recycling times shorter than residence times in the study system-the labile fraction-will contribute to the regenerated production. The dimensions of the system (local to global) will dictate the timescales (days to months) involved. The bioreactive DOM with recycling times larger than residence times-the semilabile fractionwill contribute to the export production, which equals new production under steady-state conditions. Therefore, the early Eppley and Peterson (1979) concept of new production has been revisited because of the major contribution of DOM to organic matter export (Bronk et al. 1994). AcknowledgementsThe authors thank the captain and crew of the R/V Mytilus and the members of the IIM Group of Oceanography for their help during the sampling programme. M. V. González assisted us in the preparation of figures. Comments by K. Soetaert h...

Plastic debris is currently recognised as one of the major global threats to marine life. However, few data exist on the presence and abundance of microplastics (plastics < 5 mm in size) in marine mammals. This is the first record of the presence of microplastics in the digestive tracts of marine mammals on the Iberian Peninsula. This study made use of 35 samples of common dolphin stomach contents. Potassium hydroxide was used to digest the organic fraction in the stomach contents and to facilitate the retention of solid elements (microplastics and prey remains) from the samples. Microplastics were identified in all the samples analysed but their abundance varied greatly from one stomach to another. Most plastic items were small fibres although some fragments and a bead were also found. Although factors affecting accumulation of microplastics and their effect on common dolphins are unknown, the fact that all stomachs analysed contained microplastics is a cause for concern. Highlights-This is the first study that focuses on microplastics in the stomach contents of marine mammals in the NW Iberian Peninsula.-A specific protocol designed to obtain the microplastics, but also to preserve for diet analysis the hard structures of the dolphin prey, was used.-On average, 12 microplastics items were identified in each stomach contents analysed and their type, number and size are described in detail.