The nitrogen-isotope record preserved in Southern Ocean sediments, along with several geochemical tracers for the settling fluxes of biogenic matter, reveals patterns of past nutrient supply to phytoplankton and surface-water stratification in this oceanic region. Areal averaging of these spatial patterns indicates that reduction of the CO 2 'leak' from ocean to atmosphere by increased surface-water stratification south of the Polar Front made a greater contribution to the lowering of atmospheric CO 2 concentration during the Last Glacial Maximum than did the increased export of organic carbon from surface to deep waters occurring further north.The unstratified, nutrient-rich surface waters in the modern highlatitude ocean provide the main conduit for transferring deep-water CO 2 back into the atmosphere. This CO 2 'leak' to the atmosphere is particularly effective in the modern Southern Ocean, because of intensive vertical mixing and low nutrient utilization. Building on this observation, a series of papers 1-6 attributed the glacial lowering of atmospheric CO 2 either to enhanced biological removal of the nutrients and CO 2 in high-latitude surface waters resulting in higher sinking fluxes of organic matter (that is, higher export production), or to a lower supply rate of nutrients and CO 2 from intermediate waters produced by lower vertical mixing. But the extensive deepor intermediate-water anoxia predicted by these models, and the lack of palaeo-oceanographic evidence for increased export production in the glacial Southern Ocean, has led to the questioning of the validity of these models. Here we present new evidence which supports increased stratification south of the position of the modern Polar Front (MPF) during the Last Glacial Maximum as a mechanism that contributed to lower glacial atmospheric CO 2 and deep-water oxygen concentration.The sedimentary record of several palaeoproductivity proxies was recently presented as support for a large increase in the export flux of organic carbon in the Atlantic sector of the Southern Ocean, north of the position of the MPF, which could have contributed to lowering glacial atmospheric CO 2 as a result of Fe fertilization 7 . Here we combine a similar suite of geochemical proxies for palaeoproductivity and its fate with bulk-sediment d 15 N values to better constrain past changes in the nutrient balance of surface waters and its influence on atmospheric CO 2 . Bulk-sediment d 15 N provides a means of evaluating the fraction of surface nitrate utilized by phytoplankton [8][9][10][11] . By combining this information with export flux of nitrogen estimated from palaeoproductivity proxies, we constrain the supply rate of nitrate to surface waters. Our results indicate that, despite higher export flux of organic carbon in the Atlantic sector of the Southern Ocean north of the MPF during the last glacial period, the fraction of nitrate utilized by phytoplankton in this region did not increase, implying a sustained supply of nutrients (and thus CO 2 ) to surface waters. In...

Sr:Ca and Ba:Ca ratios in water from the Adour estuary show a clear relationship with the salinity of the surrounding water for salinities <20, while ratios are almost constant above this level of salinity. A positive relationship was observed for the Sr:Ca ratio, whereas it was inverse for the Ba:Ca ratio. These two elemental ratios were measured in the otoliths of the European eels (Anguilla anguilla L.) using femtosecond laser ablation linked to an ICP-MS (fs-LA-ICP-MS). There was a direct relationship between the elemental ratios recorded in eel otoliths and those found in water from fresh and marine areas, suggesting that Sr:Ca and Ba:Ca ratios in eel otoliths can be used as markers of habitat in this estuary. Continuous profiling allowed the determination of three behaviour patterns in terms of habitat: freshwater, estuary and migratory individuals. Finally, the above results support the simultaneous use of both ratios for a better understanding of the migratory contingents and also as a relevant method to avoid a misidentification of environmental migratory history due to the presence of vaterite crystal in the otolith matrix.

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