During Leg 15 of R/V Urania 1997 Cruise (Formia 18/11-Messina 11/12), 9 stations in the Ionian Sea (Figure 1) have been investigated with CTD-Rosette hydrological casts. The water samples collecting program was planned to obtain a temporal-spatial matrix of 72 samples in the upper 200 m photic zone (sampling depths: 5, 10, 25, 50, 80, 100, 150, 200 m). Additional samplings have been taken in 3 of the 9 stations every 500 meters depth for the whole water column to compare the composition, the density and the preservation of the calcareous biogenic particles in the water samples with the underlying sediment recovered. Water samples were collected by Niskin bottles (15 L) of the Rosette, interfaced with a Seabird CTD (continuous pressure, temperature, conductivity, oxygen, light attenuation, light scattering profiles). The aim of the research was to quantify the biogenic calcareous particles, focussing on coccospheres and coccoliths, along a W-E transect at different depths in the water column. For each water sampling depth, 6 to 12 liters of sea water were immediately filtered on board on Millipore polycarbonate and cellulose acetate filters (47 mm diameter, 0.45 µm pore size) using a vacuum filtration system. The filters were oven-dried at 40°C and stored in plastic boxes. The cellulose acetate filters are used for polarized light optical microscopy (LM) analyses and the polycarbonate filters for scanning electronic microscopy (SEM). The particle density and the taxonomic composition of both coccospheres and coccoliths was carried out using both LM and SEM. The results will be correlated with the physical and chemical data of the water column obtained with the CTD measurements and with the remote-sensing satellite data (Fig. 2 ;3).

Fig.1 CTD Rosette Stations

Fig. 2 - Chlor-a concentration (mg/m2) preliminary images edited by V.Barale, derived from New Ocean Color Sensors, HRPT Sea Wifs LAC data, processed by the Marine Environment Unit of the SAI (Space Applications Institute, JRC of the European Commission, Ispra, Italy. www.me.sai.jrc.it) using SEADAS .

CTD profile shows (Fig. 4) temperature, salinity, light attenuation, suspended particles concentration, dissolved oxygen concentration measurements on 9th December in the investigated station. Such data show the presence of two different water masses separated by a sharp thermo- and halocline: the surficial layer is homogeneous in both temperature and salinity and has a high concentration of suspended particles; beneath the thermocline, the water column is characterized by very gradual variations in T and S and by a general decreasing in particles concentration, notwithstanding the presence of some peaks of greater abundance.

Fig. 4 Station 12 CTD Profile (temperature, salinity, trasmittance, dissolved oxygen, suspended particles concentration).In red depth sampled.

Total concentration (number/l) of coccospheres and coccoliths at station 12 is shown in Fig. 5. Coccospheres reach their maximum concentration of 2 to 2,2 X 104 cells/l in the upper 25 m, then decrease to not more than 200 cells/l below 150 meters water depth. Coccoliths concentration profile is less regular, showing sharp variations, with a considerable peak at 50 m. At this depth, many reworked species are present, besides that ones, related to living coccolithophores, usually found in the other samples. Taxonomic composition of coccolithophores has been performed through S.E.M.(Scanning Electron Microscope) analysis and a total of 71 species (hetero- and holococcolithophores) has been identified; some of the most representative species recovered are shown in Fig. 7. The number of species (Fig. 6) is maximum at 5 m depth (43 species), still remains fairly high (about 30 species) in the upper 50 m, then largely decreases with depth.

Cell concentration of different species shows the existence of two different groups: upper photic zone (0-50 m) and lower photic zone (80-150 m) species, while at 200 m only the most resistant coccospheres species, sinked down from the overlying layers, are present. The upper group is dominated by E. huxleyi (50-60% , fig. 8 a, d), that is well represented also at higher depths, and includes delicate forms like D. tubifera, R. xiphos, besides Acanthoica spp., many species of Syracosphaera and a considerable amount of Holococcolithophores (Fig. 8 a,b,d,e). Also A. brasiliensis is present in the upper layer, but it reaches its maximum concentration at 50 m, and may therefore be considered an intermediate living species. At 80 m a dramatic change in scenario occours; new species are present that constitute up to 70% of the assemblage (Fig. 8 c,f): among these, F. profunda, G. flabellatus and A. bimurata are the most important. F. profunda reaches its maximum density of 2 x 103 cells/l at 80 m and mantains high values also at 100 m, then rapidly decreases with depth. Taxonomic composition of free coccoliths at different depths (not plotted) well follows coccospheres species distribution.

Fig. 8 a,b,c,d,e,f - Absolute and relative abundance of different coccolithophores species.