ALBERT

Description: Detailed study of associations of planktonic foraminifera in cores MD95-2043 and ODP 977, located in the Alboran Sea (Mediterranean Sea), has allowed the identification of 29 new faunal events,defined by abrupt changes in the abundances of Neogloboquadrina pachyderma (right and left coiling), Turborotalita quinqueloba, Globorotalia scitula, Globorotalia inflata, Globigerina bulloides and Globigerinoides ruber (white and pink varieties). The age model for ODP 977 was based on that of MD95-2043 [Cacho et al. (1999),Paleoceanogr. 14, 698-705], on the isotopic stratigraphy,and on two AMS 14C measurements. Sea Surface Temperatures (SSTs) were estimated for the last 54 kyr using the Modern Analog Technique (MAT) and were compared with the SSTs provided by the U37(k0) method. The U37(k0) record is very similar to the MAT annual mean temperature record for the last 8 kyr. However, for older times alkenone-derived temperatures are consistently higher than the annual MAT temperatures. This offset may be due to an underestimation of the SST provided by the planktonic foraminiferal method for glacial times, to an overestimation of the U37(k0) record, or to changes in the seasonal production of alkenones. Most of the variability in the fauna is related to the millennial variability of Heinrich and Dansgaard-Oeschger (D-O) events. During Heinrich events (HEs) and most of the other D-O stadials, G. bulloides, T. quinqueloba and G. scitula increased, while N. pachyderma (right coiling), G. inflata and G. ruber decreased. By contrast, N. pachyderma (left coiling) was only abundant in the HEs. The main component of the associations -N. pachyderma (right coiling) - follows a general trend similar to that of sea-level and delta18O. This species reached its highest abundance during the Last Glacial Maximum, when sea-level was at a lower position. The occurrence of a shallower nutricline owing to a shallowing of the interface between Atlantic inflowing and Mediterranean outflowing waters could have favoured the development of neogloboquadrinids in the vicinity of the Strait of Gibraltar.

Description: The composition and vertical distribution of planktonic ciliates within the surface layer was monitored over four diel cycles in May 95, during the JGOFS-France DYNAPROC cruise in the Ligurian Sea (NW Mediterranean). Ciliates were placed into size and trophic categories: micro- and nano-heterotrophic ciliates, mixotrophic ciliates, tintinnids and the autotrophic Mesodinium rubrum. Mixotrophic ciliates (micro and nano) represented an average of 46% of oligotrich abundance and 39% of oligotrich biomass; nano-ciliates (hetero and mixotrophic) were abundant, representing about 60 and 17% of oligotrich abundance and biomass, respectively. Tintinnid ciliates were a minor part of heterotrophic ciliates. The estimated contribution of mixotrophs to chlorophyll a concentration was modest, never exceeding 9% in discrete samples. Vertical profiles of ciliates showed that chlorophyll-containing ciliates (mixotrophs and autotrophs) were mainly concentrated and remained at the chlorophyll a maximum depth. In contrast, among heterotrophic ciliates, a portion of the population appeared to migrate from 20-30 m depth during the day to the surface at night or in the early morning. Correlation analyses of ciliate groups and phytoplankton pigments showed a strong relationship between nano-ciliates and zeaxanthin, and between chlorophyll-containing ciliates and chlorophyll a, as well as other pigments that were maximal at the chlorophyll a maximum depth. Total surface layer concentrations showed minima of ciliates during nightime/early morning hours.

Description: During FRUELA'95 cruise, seawater samples were collected at the Bransfield and Gerlache Straits for the analysis of dissolved organic carbon (DOC) profiles throughout the water column. An excess of DOC probably derived from phytogenic material was observed in the upper mixed layer (UML; average: +22±13 µmol C/l), compared to the constant concentration of refractory DOC below 400 m (44±4 µmol C/l). The average excess DOC concentration was higher than the particulate organic carbon concentration indicating the major contribution of DOC to carbon export in this area. However, large spatial variability of DOC in the upper mixed layer (52-102 µmol C/l) was observed: excess DOC contributed from 15% to 57% to the actual DOC concentration. Maximum average DOC concentrations in the UML were recorded in the Gerlache Strait (71 µmol C/l) and in the Gerlache-Bransfield confluence (80 µmol C/l), whereas minimum values were recorded in the Bransfield Strait (61 µmol C/l). Several shelf and slope stations showed a slight increase of DOC (5-10 µmol C/l) in the deep layer which might be related to organic matter release from the underlying sediments. Considering the net DOC release from phytoplankton, the low bacterial biomass and the reduced vertical DOC export, the DOC excess could build up in about 6 days for most of the sampling stations. The probable fate of the DOC excess is the eastwards horizontal transport by the Bransfield Current out of the study area.