Vertical distribution of large particulate matter in the Western Mediterranean Sea

The relationship between mesoscale hydrodynamics and the distribution of large particulate matter (LPM, particles larger than 200 ?m) in the first 1000 m of the Western Mediterranean basin was studied with a microprocessor-driven CTD-video package, the Underwater Video Profiler (UVP). Observations made during the last decade showed that, in late spring and summer, LPM concentration was high in the coastal part of the Western Mediterranean basin at the shelf break and near the continental slope (computed maximum: 149 ?g C/l between 0 and 100 m near the Spanish coast of the Gibraltar Strait). LPM concentration decreased further offshore into the central Mediterranean Sea where, below 100 m, it remained uniformly low, ranging from 2 to 4 ?g C/l. However, a strong variability was observed in the different mesoscale structures such as the Almeria-Oran jet in the Alboran Sea or the Algerian eddies. LPM concentration was up to one order of magnitude higher in fronts and eddies than in the adjacent oligotrophic Mediterranean waters (i.e. 35 vs. 8 ?g C/l in the Alboran Sea or 16 vs. 3 ?g C/l in a small shear cyclonic eddy). Our observations suggest that LPM spatial heterogeneity generated by the upper layer mesoscale hydrodynamics extends into deeper layers. Consequently, the superficial mesoscale dynamics may significantly contribute to the biogeochemical cycling between the upper and meso-pelagic layers.

Geochemistry, isotopic ratios, granulometry and Uk'37 derived SST of cores obtained during Poseidon cruise POS287, off Portugal

Continental and marine conditions during the last millennium off Porto, Portugal (the southern pole of the North Atlantic Oscillation, NAO), are reconstructed from a sediment archive through a high-resolution multiproxy study and instrumental evidence. Results show multidecadal variability and sea surface temperatures (SSTs) that correlate well with previously published land and sea-based Northern Hemisphere temperature records, and appear to be responding to long-term solar insolation variability. Precipitation was negatively correlated with the NAO, whereas strong flooding events occurred at times of marked climate cooling (AD 1100-1150 and 1400-1470) and transitions in solar activity. AD 1850 marks a major shift in the phytoplankton community associated with a decoupling of d18O records of 3 planktonic foraminifera species. These changes are interpreted as a response to a reduction in the summer and/or annual upwelling and more frequent fall-winter upwelling-like events. This shift's coincidence with a decrease in SST and the increase in coherence between our data and the Atlantic Multidecadal Oscillation (AMO) confirms the connection of the upwelling variability to the North Atlantic Ocean's surface and thermohaline circulation on a decadal scale. The disappearance of this agreement between the AMO and our records beyond AD 1850 and its coincidence with the beginning of the recent rise in atmospheric CO2 supports the hypothesis of a strong anthropogenic effect on the last ~150 yr of the climate record. Furthermore, it raises an important question of the use of instrumental records as the sole calibration data set for climate reconstructions, as these may not provide the best analogue for climate beyond AD 1730.