Biomass and substrate utilization of cold adapted bacteria in Fram Strait and the Western Greenlad Sea

During the 'Polarstern' expedition ARK-IV/2 in June 1987, water samples from 8 stations were taken to study biomass and substrate utilization of cold adapted bacteria. Bacterial biomasses determined from acridine orange direct counts (AODC) were between 0.4 and 31.4 µ/g C/l, and ATP concentrations amounted from <0.1 to 40 ng/l. Colony counts on seawater agar reached only 0.1% of AODC, but with the MPN-method 1 to 10% of AODC were recorded. With 14C-glutamic acid or 14C-glucose as tracer substrate in oligotrophic broth containing 0.5 mg trypticase and 0.05 mg yeast extract per liter of seawater, obligately oligotrophic bacteria could be detected in one water sample. Although incubation was at 2 °C, only psychrotrophic bacteria showing growth temperatures between 1 and 30 °C were obtained. Organic substrate utilizations by 106 isolates were tested at 4 and 20 °C. Most carbohydrates, organic acids, alcohols, and alanine were assimilated at both temperatures, but arginine, aspartate and ornithine were utilized only at 20 °C by almost all strains.

Tintinnids of the western Arabian Sea

The results of an investigation of tintinnids from the western Arabian Sea are described. A total of 134 closing-net samples was obtained from 22 stations of the German "Meteor" expedition 1964/1965. Distribution charts of the dominant species of tintinnids from the study area are presented as well as a list of the world-wide distribution of these species as derived from the literature. Tintinnids were most abundant in the surface waters. The layer from 0 - 25 m yielded a maximum 94.3% and a minimum of 61.3% of the tintinnids present from 0 - 175 m; the mean was 80%. There was no significant difference in the vertical distribution between day and night stations nor was there any indication of the influence of the thermocline upon vertical distribution of tintinnids. TS-diagrams show different water types in the western Arabian Sea. Temperatur-salinity-tintinnid -diagrams indicate regional patterns in the distribution of various species of tintinnids. Some tintinnids can be used as indicator species: Climacocylis scalaria, Parundella lohmanni and Amphorella amphora were typical for the Somali Current whereas Rhabdonella apophysata and Branditella palliata indicated the presence of East African Coastal Current water. The concentration of tintinnids in the upper 25 m raged between 4,800 and 39,300 individuals/m**3 (mean 19,000/m**3). Plasma volume of tintinnids was calculated to permit comparison of different links in the food chain. There was a mean of 51 mm**3/m**2 in the upper layer, equivalent to a concentration of 2 mm**3/m**3. Carbon values were computed from the plasma volume of tintinnids, phytoplankton and larger zooplankton. The ratio of phytoplankton plus microzooplankton carbon to large zooplankton carbon was 1 : 0.8 in the Somali Current, 1 : 0.4 in the East African Coastal Current and 1 : 1.2 in the mixing zone of these current systems. Tintinnids are one of the first links in the food chain. It is very likely that a part of the organic detritus and of the nanoplankton is transfered to large herbivores or omnivores via tintinnids and other protozoans. This mechanism might be especially effective during seasons when large phytoplankters are not available in the ocean.

Sea surface temperature reconstruction for Mediterranean Sea samples

Alkenone unsaturation ratios and planktonic delta18O records from sediment cores of the Alboran, Ionian and Levantine basins in the Mediterranean Sea show pronounced variations in paleo-temperatures and -salinities of surface waters over the last 16,000 years. Average sea surface temperatures (SSTs) are low during the last glacial (averages prior to 13,000 years: 11-15°C), vary rapidly at the beginning of the Holocene, and increase to 17-18°C at all sites during S1 formation (dated between 9500 and 6600 calendar years). The modern temperature gradient (2-3°C) between the Mediterranean sub-basins is maintained during formation of sapropel S1 in the Eastern Mediterranean Sea. After S1, SSTs have remained uniform in the Alboran Sea at 18°C and have fluctuated around 20°C in the Ionian and Levantine Basin sites. The delta18O of planktonic foraminifer calcite decreases by 2 per mil from the late glacial to S1 sediments in the Ionian Basin and by 2.8 per mil in the Levantine Basin. In the Alboran Sea, the decrease is 1.7 per mil. Of the 2.8 per mil decrease in the Levantine Basin, the effect of global ice volume accounts for a maximum of 1.05 per mil and the temperature increase explains only a maximum of 1.3 per mil. The remainder is attributed to salinity changes. We use the temperature and salinity estimates to calculate seawater density changes. They indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during S1 time. Instead, it appears that intermediate and deep water formation may have shifted to the Ionian Sea approximately 2000 years before onset of S1 deposition, because surface waters were as cold, but saltier than surface water in the Levantine Basin during the Younger Dryas. Sapropel S1 began to form at the same time, when a significant density decrease also occurred in the Ionian Sea.

Planktonic foraminifera and sea surface temperature reconstruction of sediments from the Mediterranean Sea

Water exchange between the Black Sea and the Mediterranean Sea has been a major focus of the paleohydrography of the eastern Mediterranean. Glacial melt water released from the Black Sea is a potential factor in the formation of sapropel S1, an organic-rich sediment layer that accumulated during the Early Holocene. A high-resolution study done on sediments from the Marmara Sea, the gateway between the Mediterranean and the Black Sea, sheds light on the Holocene exchange processes. Past sea surface temperature and sea surface salinity (SSS) were derived from stable oxygen isotope ratios (delta18O) of foraminiferal calcite and alkenone unsaturation ratios (Uk'37). Heavy delta18O values and high SSS in the Marmara Sea suggest absence of low salinity water from the Black Sea during S1. The comparison with data from the Levantine Basin and southern Aegean Sea outlines gradients of freshening in the eastern Mediterranean Sea, whereby the major sources of freshwater were closer to the Levantine Basin. It is thus concluded that the Black Sea was not a major freshwater source contributing to formation of S1. Given the absence of a low salinity layer, the deposition of organic-rich sediments corresponding to S1 in the Marmara Sea is likely the result of the global transgression and the concomitant re-organization of biogeochemical cycles, leading to enhanced productivity as shown by Globigerina bulloides.

Calcareous dinoflagellate cysts and geochemistry of Mediterranean Sea sediments

Comparison of calcareous dinoflagellate cyst assemblages with Ba, Al, Mn, and Fe records from three sediment cores collected in the eastern Mediterranean Sea indicate that calcareous dinoflagellate cysts are generally resistant to postdepositional dissolution. Cyst association changes during and after sapropel S1 formation can therefore be closely related to variability in surface water productivity. Two groups of cysts are defined: those having highest abundances within the sapropelic and postsapropelic sediments. The temporal cyst distributions suggest increased freshwater input mainly from the Nile and a shallowing of the pycnocline as the most important processes increasing nutrient concentration in the photic zone, thus leading to increased productivity and organic carbon fluxes during sapropel formation. Furthermore, a general warming trend at the beginning of S1 formation and a slight salinity decrease are reconstructed.

Sedimentology and age determination on two cores from the eastern Mediterranean Sea

We present grain-size distributions of the terrigenous fraction of two sediment cores from the southeast Levantine Sea (SL112) and the northern Aegean Sea (SL148), spanning the time interval from the late glacial to the present. End-member modelling of the grain-size distribution allows discriminating between aeolian and fluvial transport of the sediments and helps to infer palaeoenvironmental conditions in the source areas. Sedimentary and depositional processes during the late glacial and Holocene were controlled by climatic variations of both the northern high latitudes and the African climate system. The sedimentation at site SL112 off Israel is dominated by the suspension load of the River Nile and aeolian dust from the Sahara. Variations in grain size reflect the early to mid- Holocene climate transition from the African Humid Period to recent arid conditions. This climate change was gradual, in contrast to the abrupt humidity change documented inWestern Saharan records. This implies a successive decrease in Nile river sediment supply due to a step-wise aridification of the headwaters. The grain-size data of SL112 show a humidity maximum at 5 kyr BP coincident with a regionally-restricted wet phase in the Levantine Sea. The sediments at the North Aegean site SL148 consist of riverine particles and low amounts of aeolian dust, probably derived from South European sources and with probably minor Saharan influence. The sedimentation processes are controlled by climate conditions being characterized by enhanced deposition of dust during the cold and dry glacial period and by decreased aeolian influx during the temperate and humid Holocene.

(Table 1) Heat flow data in the western Black Sea

Results of heat flow measurements are presented. On the basis of new data on structure of the sedimentary sequence, corrections are introduced that take account of effect of sedimentation. Diagrammatic maps of distribution of observed and deep-seated heat flow have been constructed. A hypothesis is offered that the regional zone of anomalously high heat-flow values on the northern continental slope has been controlled by processes of subsidence of an oceanic plate beneath its continental counterpart.