Description of recent sediments of Nile Delta, Red Sea and Gulf of Aden (Table 1-3)

The study of textural, structural, chemical, and physical properties of fine-grained recent marine sediments leads to the conclusion that only a few compositional factors are responsible for significant changes in mass physical characteristics in the upper meters below sea bottom. Fossil-induced porosity increases water content and liquid limit. It also seems to have partially influenced the plastic limit and plasticity index of calcareous sandy silts from the Red Sea and the western Gulf of Aden so that they become similar to the montmorillonite rich prodelta clays from the Nile Delta. Diagrams based on liquid limit and plasticity loose their original meaning in these cases. Activity of sediments rich in microorganisms can be higher than that of montmorillonitic clay. The shear strength-depth relationship of normally consolidated sediments is surprisingly little influenced by changes in sand or clay content and clay mineralogy. Only high lime content, submarine erosion and beginning cementation increase the strength considerably. Erosional disconformities near the present surface can be deduced from the strength-depth curve when as little as 1 or 2 m sediment have been removed. Flat or irregular strength-depth curves indicate beginning cementation and probably discontinuous sedimentation, provided the composition of the material remains in some degree constant. In our samples diagenetic pyrite, but no recristallisation of carbonates could be detected under the microscope. Underconsolidation and excess pore-water pressure, factors which tend to foster submarine slides, mud lumps, and diapiric folding, seem to be restricted Varito areas with mainly rapidly deposited, homogeneous or layered sediments. But where an abundance of burrowing organisms increases the vertical permeability of the sediment, normal consolidation and stable deposits are to be expected, at least in the upper meters below the present surface. According to 14C-determinations on calcareous microorganisms the rate of deposition of the investigated sediments seems to range from 26 to 167 cm per 1000 years.

Net primary productivity, POC export, Th234 and U238 activities and abundance of autotrophs during U.S.C.G.C. Healy cruises HLY0802 and HLY0803

Seasonal patterns in the partitioning of phytoplankton carbon during receding sea ice conditions in the eastern Bering Sea water column are presented using rates of 14C net primary productivity (NPP), phototrophic plankton carbon content, and POC export fluxes from shelf and slope waters in the spring (March 30-May 6) and summer (July 3-30) of 2008. At ice-covered and marginal ice zone (MIZ) stations on the inner and middle shelf in spring, NPP averaged 76 ± 93 mmol C/m**2/d, and in ice-free waters on the outer shelf NPP averaged 102 ± 137 mmol C/m**2/d. In summer, rates of NPP were more uniform across the entire shelf and averaged 43 ± 23 mmol C/m**2/d over the entire shelf. A concomitant shift was observed in the phototrophic pico-, nano-, and microplankton community in the chlorophyll maximum, from a diatom dominated system (80 ± 12% autotrophic C) in ice covered and MIZ waters in spring, to a microflagellate dominated system (71 ± 31% autotrophic C) in summer. Sediment trap POC fluxes near the 1% PAR depth in ice-free slope waters increased by 70% from spring to summer, from 10 ± 7 mmol C/m**2/d to 17 ± 5 mmol C/m**2/d, respectively. Over the shelf, under-ice trap fluxes at 20 m were higher, averaging 43 ± 17 mmol C/m**2/d POC export over the shelf and slope estimated from 234Th deficits averaged 11 ± 5 mmol C/m**2/d in spring and 10 ± 2 mmol C/m**2/d in summer. Average e-ratios calculated on a station-by-station basis decreased by ~ 30% from spring to summer, from 0.46 ± 0.48 in ice-covered and MIZ waters, to 0.33 ± 0.26 in summer, though the high uncertainty prevents a statistical differentiation of these data.

Abundance of bacteria, cyanobacteria and nanoflagellates at sime series station DYNAPROC

The variability in microbial communities (abundance and biomass), bacterial production and ectoaminopeptidase activity, particulate and dissolved organic carbon (POC, DOC), and particulate and dissolved lipids was examined in spring 1995 in the northwestern Mediterranean, where a transition from the end of a bloom to pre-oligotrophic conditions was observed. Four time series of 36 h each and 4 h sampling intervals were performed at 5 m and at the chlorophyll maximum (30 m) between 11 and 31 May. Simultaneous measurements of pigments, abundance of hetero- and autotrophic flagellates, bacteria and POC enabled the estimation of living POC (defined as autotrophic-C plus heterotrophic-C biomass), and thus the detrital organic carbon. During the first 2 time series (11 to 15 May), the bacterial-C biomass was higher than the autotrophic-C biomass at 5 m (ratio 1.4 and 1.7), whereas the opposite trend was observed in the chlorophyll peak (ratio 0.7 for the first cycle). However, at the end of May, autotrophic-C biomass was equivalent to bacterial-C biomass at both depths studied. The detrital pool remained a more or less constant fraction of the POC (52, 53 and 47% on 11-12 May, 14-15 May and 30-31 May) at the chlorophyll peak, whereas it decreased significantly with time (62 to 53%) at 5 m. Relationships between bacterial activities and evolution of available resources were not systematically evidenced from our 36 h diel cycle data. Nevertheless, at the monthly scale, comparison of bacterial carbon demand (BCD) to potential carbon resources (detrital POC and DOC) showed that bacteria fed differently on the various pools. From ectoaminopeptidase turnover rates and detrital POC, the potential hydrolysis rate of detritus was calculated. Depending on the choice of conversion factors for bacterial production and estimates of hydrolysis turnover rates, it was shown that bacterial hydrolysis of detritus could be one of the DOC accumulation sources. We observed that the percentage of BCD supplied by detrital POC hydrolysis increased in the surface and decreased in the chlorophyll peak. An index of lipid degradation in POC, the lipolysis index, increased during the month at 5 m, also indicating a higher hydrolysis of POC. The opposite trend was observed in the chlorophyll maximum layer. The selective decrease in dissolved lipids in DOC in the chlorophyll maximum layer, particularly free fatty acids, also suggests that bacteria utilized increased fractions of carbon sources from the DOC. We concluded that partitioning between DOC and detritus as resources for bacteria can change during the rapid transition period from mesotrophy to oligotrophy in the northwestern Mediterranean.