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Our current understanding of the silicon (Si) cycle in the ocean assumes that diatoms dominate not only the uptake of silicic acid, but also the production and recycling of biogenic silica (BSi), and that other organisms with siliceous skeletons, including sponges, radiolarians, and silicoflagellates, play a negligible role. In this study, we reexamine some aspects of the potential contribution by sponges and present in vitro evidence that BSi in the form of sponge spicules redissolves into silicic acid at far slower rates than those known for diatom frustules. We also show that the retention of Si by siliceous sponges in some sublittoral and bathyal environments is substantial and that sponge populations function as Si sinks. Additionally, by reanalyzing published information on sponge growth and BSi content, we estimate that BSi production rates by sublittoral sponges in Si-poor and Si-rich marine areas fall quite close to values known for diatom assemblages. Therefore, sponges may affect Si cycling dynamics and Si availability for diatoms, particularly in Si-depleted environments. Altogether, our data strongly suggest that the role of sponges in the benthopelagic coupling of the Si cycle is significant.

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Abstract.In the framework of the EU-funded MF-STEP project, autonomous drifting profilers were deployed throughout the Mediterranean Sea to collect temperature and salinity profile data and to measure subsurface currents. The realization of this profiler program in the Mediterranean, referred to as MedArgo, is described and assessed using data More than twenty drifting profilers were deployed from research vessels and ships-of-opportunity in most areas of the Mediterranean. They were all programmed to execute 5-day cycles with a drift at a parking depth of 350 m and CTD profiles from either 700 or 2000 m up to the surface. They stayed at the sea surface for about 6 h to be localised by, and transmit the data to, the Argos satellite system. The temperature and salinity data obtained with pumped Sea-Bird CTD instruments were processed and made available to the scientific community and to operational users in near-real time using standard Argo protocols, and were assimilated into Mediterranean numerical forecasting models.In general, the cycling and sampling characteristics chosen for the MedArgo profilers were found to be adequate for the Mediterranean. However, it is strongly advised to use GPS and global cellular phone telemetry or the future Argos bidirectional satellite system in order to avoid data compression and losses, for the continuation of the Mediterranean drifting profiler program.

Abstract. During the period 1998–2000, the Mediterranean Forecasting System Pilot Project, aiming to build a forecasting system for the physical state of the sea, has been carried out. A ship-of-opportunity programme sampled the Mediterranean upper ocean thermal structure by means of eXpendable Bathy-Thermographs (XBTs), along seven tracks, from September 1999 to May 2000. The tracks were designed to detect some of the main circulation features, such as the stream of surface Atlantic water flowing from the Alboran Sea to the Eastern Levantine Basin. The cyclonic gyres in the Liguro-Provenal Basin, the southern Adriatic and Ionian Seas and the anticyclonic gyres in the Levantine Basin were also features to be detected. The monitoring system confirmed a long-term persistence of structures (at least during the entire observing period), which were previously thought to be transient features. In particular, in the Levantine Basin anticyclonic Shikmona and Ierapetra Gyres have been observed during the monitoring period. In order to identify the major changes in the thermal structures and the dynamical implications, the XBT data are compared with historical measurements collected in the 1980s and 1990s. The results indicate that some thermal features are being restored to the situation that existed in the 1980s, after the changes induced by the so-called "Eastern Mediterranean Transient". Key words. Oceanography: physical (eddies and mesoscale processes; general circulation; instruments and techniques)

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