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[1] We produced gridded monthly sea-surface boundary conditions for the Atlantic Ocean at the Last Glacial Maximum (LGM) based on the sea-surface temperature reconstruction of the GLAMAP project. We used an ocean general circulation model (OGCM), subject to these sea-surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model, to study the differences in the distribution of the main water masses between the LGM and the present. Our global OGCM is characterized by high vertical resolution, low vertical diffusion, and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern Atlantic Ocean. According to a series of LGM experiments with an increasing sea-surface salinity anomaly in the Weddell Sea, the ventilated thermocline was colder than today by 2-3°C in the North Atlantic Ocean and, in the experiment with the largest anomaly (1.0 beyond the global anomaly), by 4-5°C in the South Atlantic Ocean. Its depth was reduced by 50 m on average, most notably in the tropics. In the North Atlantic Ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5°-10°, and the ventilation increased. In the South Atlantic Ocean the mixed layer and thermocline water masses were dominated by cold water originating from Drake Passage, and the import of warm water from the Indian Ocean was reduced to about 4 Sv or 40% of its modern value. Antarctic Intermediate Water was colder by 3-4°C and could be traced as far as 10°N. The meridional overturning rates of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) in the Atlantic Ocean were similar to those of the present-day experiment (9-10 Sv and 4 Sv, respectively). However, NADW cooled by 2.5°C and AABW by 1°C. AABW was near the freezing point of seawater at the surface and the saltiest water mass in the Atlantic Ocean, even saltier than NADW. We show that the differences between the LGM and the present-day experiments can be traced back to the changes in the subpolar and interhemispheric sea-surface density gradients.

We examined how seabirds might be used to study marine environmental variables, which necessitates knowing location and the value of the variable to be studied. Five systems can potentially be used for determination of location: VHF (Very High Frequency) telemetry, PTT (Platform Terminal Transmitters) telemetry, GLS (Global Location Service) geolocation methods, dead reckoning and GPS (Global Positioning System), each with its own advantages with respect to accuracy, potential number of fixes and size. Temperature and light were used to illustrate potential difficulties in recording environmental variables. Systems currently used on seabirds for measurement of temperature respond slowly to environmental changes; thus, they may not measure sea surface temperature adequately when contact periods with water bodies are too short. Light can be easily measured for light extinction studies, but sensor orientation plays a large role in determining recorded values. Both problems can be corrected. The foraging behaviour of seabirds was also examined in order to identify those features which would be useful for determination of marine environmental variables at a variety of spatial and temporal scales. Area coverage by birds is highly dependent on breeding phase and tends to be concentrated in areas where prey acquisition is particularly enhanced. The identification of these sites may be of particular interest to marine biologists. 'Plungers' and 'divers' are potentially most useful for assessment of variables deeper within the water column, with some divers spending up to 90% of their time sub-surface. Few seabirds exploit the water column deeper than 20 m, although some divers regularly exceed 50 m (primarily penguins and auks), while 2 species dive in excess of 300 m. The wide-ranging behaviour of seabirds coupled, in many instances, with their substantial body size makes them potentially excellent carriers of sophisticated environmental measuring technology; however, the ethical question of how much the well-being of birds can, and should, be compromised by such an approach needs to be carefully considered.

Recent efforts of the German paleoceanographic community have resulted in a unique data set of reconstructed sea-surface temperature for the Atlantic Ocean during the Last Glacial Maximum, plus estimates for the extents of glacial sea ice. Unlike prior attempts, the contributing research groups based their data on a common definition of the Last Glacial Maximum chronozone and used the same modern reference data for calibrating the different transfer techniques. Furthermore, the number of processed sediment cores was vastly increased. Thus the new data is a significant advance not only with respect to quality, but also to quantity. We integrate these new data and provide monthly data sets of global sea-surface temperature and ice cover, objectively interpolated onto a regular 1°x1° grid, suitable for forcing or validating numerical ocean and atmosphere models. This set is compared to an existing subjective interpolation of the same base data, in part by employing an ocean circulation model. For the latter purpose, we reconstruct sea surface salinity from the new temperature data and the available oxygen isotope measurements.

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Sedimentological evidence indicates metre‐scale, cyclic changes in global sea‐level during Mesozoic greenhouse climates; the cyclicity is thought to be due to Milankovitch forcing. The absence of continental ice‐caps requires other mechanisms than glacier build‐up to explain these variations. We propose that thermal expansion of the entire oceanic water column may partly explain the observed sea‐level variations on Milankovitch timescales. Using existing climate model results, we show that an increase in deep water temperature of ∼ 2°C and a corresponding sea‐level rise of 1.7 m by thermal expansion can be induced by Milankovitch forcing via increased formation of warm deep waters in low latitudes.

a b s t r a c tParticles sinking out of the euphotic zone are important vehicles of carbon export from the surface ocean. Most of the particles produce heavier aggregates by coagulating with each other before they sink. We implemented an aggregation model into the biogeochemical model of Regional Oceanic Modelling System (ROMS) to simulate the distribution of particles in the water column and their downward transport in the Northwest African upwelling region. Accompanying settling chamber, sediment trap and particle camera measurements provide data for model validation. In situ aggregate settling velocities measured by the settling chamber were around 55 m d À1. Aggregate sizes recorded by the particle camera hardly exceeded 1 mm. The model is based on a continuous size spectrum of aggregates, characterised by the prognostic aggregate mass and aggregate number concentration. Phytoplankton and detritus make up the aggregation pool, which has an averaged, prognostic and size dependent sinking. Model experiments were performed with dense and porous approximations of aggregates with varying maximum aggregate size and stickiness as well as with the inclusion of a disaggregation term. Similar surface productivity in all experiments has been generated in order to find the best combination of parameters that produce measured deep water fluxes. Although the experiments failed to represent surface particle number spectra, in the deep water some of them gave very similar slope and spectrum range as the particle camera observations. Particle fluxes at the mesotrophic sediment trap site off Cape Blanc (CB) have been successfully reproduced by the porous experiment with disaggregation term when particle remineralisation rate was 0.2 d À1 . The aggregation-disaggregation model improves the prediction capability of the original biogeochemical model significantly by giving much better estimates of fluxes for both upper and lower trap. The results also point to the need for more studies to enhance our knowledge on particle decay and its variation and to the role that stickiness play in the distribution of vertical fluxes.

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