Based on the study of 10 sediment cores and 40 core-top samples from the South China Sea (SCS) we obtained proxy records of past changes in East Asian monsoon climate on millennial to bidecadal time scales over the last 220,000 years. Climate proxies such as global sea level, estimates of paleotemperature, salinity, and nutrients in surface water, ventilation of deep water, paleowind strength, freshwater lids, fluvial and=or eolian sediment supply, and sediment winnowing on the sea floor were derived from planktonic and benthic stable-isotope records, the distribution of siliciclastic grain sizes, planktonic foraminifera species, and the U K 37 biomarker index. Four cores were AMS-14 C-dated. Two different regimes of monsoon circulation dominated the SCS over the last two glacial cycles, being linked to the minima and maxima of Northern Hemisphere solar insolation. (1) Glacial stages led to a stable estuarine circulation and a strong O 2 -minimum layer via a closure of the Borneo sea strait. Strong northeast monsoon and cool surface water occurred during winter, in part fed by an inflow from the north tip of Luzon. In contrast, summer temperatures were as high as during interglacials, hence the seasonality was strong. Low wetness in subtropical South China was opposed to large river input from the emerged Sunda shelf, serving as glacial refuge for tropical forest. (2) Interglacials were marked by a strong inflow of warm water via the Borneo sea strait, intense upwelling southeast of Vietnam and continental wetness in China during summer, weaker northeast monsoon and high sea-surface temperatures during winter, i.e. low seasonality. On top of the long-term variations we found millennial-to centennial-scale cold and dry, warm and humid spells during the Holocene, glacial Terminations I and II, and Stage 3. The spells were coeval with published variations in the Indian monsoon and probably, with the cold Heinrich and warm Dansgaard-Oeschger events recorded in Greenland ice cores, thus suggesting global climatic teleconnections. Holocene oscillations in the runoff from South China centered around periodicities of 775 years, ascribed to subharmonics of the 1500-year cycle in oceanic thermohaline circulation. 102=84-year cycles are tentatively assigned to the Gleissberg period of solar activity. Phase relationships among various monsoon proxies near the onset of Termination IA suggest that summer-monsoon rains and fluvial runoff from South China had already intensified right after the last glacial maximum (LGM) insolation minimum, coeval with the start of Antarctic ice melt Wang et al. / Marine Geology 156 (1999) prior to the δ 18 O signals of global sea-level rise. Vice versa, the strength of winter-monsoon winds decreased in short centennial steps only 3000-4000 years later, along with the melt of glacial ice sheets in the Northern Hemisphere.

We present a new quantum mechanics/molecular mechanics (QM/MM) embedding approach for systems with directional polar covalent bonds. This “covalent elastic polarizable environment” (covEPE) scheme features a variational treatment of an energy expression that includes all degrees of freedom of both the QM region (the “cluster”) and the MM regions (the “environment”). The method completely and explicitly includes both the electrostatic and mechanical interactions between a QM model cluster and its environment. Monovalent pseudoatoms that represent real atoms of the material saturate the dangling bonds of the cluster; these pseudoatoms belong simultaneously to the QM and MM regions. For a correct description of a pure silica environment, we constructed a new force field of the shell-model type based on potential derived charges instead of formal charges. We implemented the covEPE approach in the density functional program ParaGauss and applied it to pure-silica and Al-containing chabazite, employing a generalized gradient approximation. These applications showed that calculated structural parameters and OH frequencies of bridging hydroxyl groups reproduce experimental data with good accuracy compared to other contemporary computational methods.

1. We studied variation in the composition of fatty acids in the seston of a small freshwater reservoir with changes in phytoplankton composition during four growth seasons. We focused on the dynamics of the x3 fatty acids because of their potential importance for zooplankton nutrition. 2. Total diatoms were related to the 20:5x3 fatty acid (eicosapentaenoic, EPA) content in seston. Among two dominant diatom genera, Cyclotella was not associated with EPA content. In contrast, there was a significant correlation between Stephanodiscus and the percentage contribution and content of EPA throughout the study. Hence, freshwater diatoms can differ strongly in content of the essential EPA. 3. We considered abundant cyanobacteria as a potential source of 18:3x3 fatty acid (linolenic, ALA) to aquatic food webs. Among four dominant cyanobacteria species, two (Anabaena flos-aquae and Planktothrix agardhii) showed significant correlation with the ALA content of the seston, while the other two (Aphanizomenon flos-aquae and Microcystis aeruginosa) did not. 4. Dinophyta had a relatively high level of 22:6x3 (docosahexaenoic, DHA) for freshwater species and can be also a source of EPA to aquatic food webs. 5. Our results show that various species of diatoms as well as cyanobacteria can be of contrasting nutritional value for zooplankton because of their different content of the essential PUFAs. Diatoms, which are low in EPA, could not be considered as a valuable food, while some field populations of cyanobacteria might be valuable sources of essential ALA.

We studied composition and concentrations of fatty acids (FAs) in benthos from pebbly littoral region of the Yenisei River in a sampling site near Krasnoyarsk city (Siberia, Russia) for 1 year from March 2003 to February 2004. Special attention was paid to major longchain polyunsaturated fatty acids (PUFAs) of the x3 family: eicosapentaenoic acid (EPA, 20:5x3) and docosahexaenoic acids (DHA, 22:6x3). In phytobenthos, which was dominated by diatoms, the annual maxima of EPA and DHA pool occurred in spring and early summer. In zoobenthos, EPA and DHA pool peaked in autumn, due mainly to an increase of the biomass of dominant taxa (gammarids) and to a moderate increase of the PUFA content per body weight. Seasonal peaks of EPA in overwintering insect larvae (chironomids and caddisflies) generally coincided with those of biomass of these larvae, while there was no such trend for amphipods and oligochaetes. In spring and early summer, the main part of x3 PUFA, 40-97% of total amount, in the littoral region was contained in biomass of producers, i.e., benthic microalgae, and in autumn it was transferred to primary consumers-benthic invertebrates, which contained~76-93% of total x3 PUFAs.

No abstract

We studied fatty acid (FA) composition of littoral microalgae in the fast-flowing oligotrophic river, the Yenisei, Siberia, monthly for 3 years. Seasonal dynamics of species composition had similar patterns in all the studied years. In springs, a pronounced dominance of filamentous green algae occurred, in summer and autumn diatoms were abundant, and in late autumn and winter epilithic biofilms consisted primarily of cyanobacteria and detritus. In general, FA composition of the algal periphytic community was dominated by 16:0, 16:1ω7, 20:5ω3, 14:0, and 18:3ω3 throughout the studied period. Several groups of FAs, which had peculiar seasonal dynamics, were differentiated by statistical analysis based on a method of correlation graphs. The seasonal changes in FA composition could be partly explained by the seasonal succession of species composition of the community. Besides, we found that populations of both diatom and green algae grown in summer at a higher water temperature were lower in polyunsaturated fatty acids than those in spring, at a lower temperature. Hence, we suppose that the regular seasonal dynamics of FA composition of the studied littoral microalgae was driven both by changes in species composition and by temperature adaptations of the algal populations. The highest content of essential polyunsaturated FAs, eicosapentaenoic and docosahexaenoic acids, in the spring "psychrophilic" populations of diatoms could make them of the higher nutritive value for zoobenthic primary consumers.

SUMMARY 1. We studied the composition of fatty acids (FAs) in the seston from two small freshwater reservoirs (Bugach and Lesnoi) with distinct periodicity of domination by cyanobacteria and eukaryotic algae during the growth season. 2. The diatoms in the both reservoirs were characterised by a high content of 14:0 and C16 unsaturated acids, whereas that of the essential FA 20:5ω3 [eicosapentanoic acid (EPA)] was low. The correlation between this polyunsaturated FA (PUFA) and diatom biomass was not significant in either reservoir. The percentage of 20:5ω3 in seston significantly correlated with the biomass of euglenophyta in Bugach and dinophyta in Lesnoi. Hence the diatoms, usually referred as a valuable food for zooplankton, were not an important source of the essential PUFA in these systems. 3. The dominant cyanobacteria in Bugach, and the green algae in Lesnoi, both contained the same marker acids: 18:3ω3 and 18:2ω6. Hence, a discrimination between these two phytoplanktonic groups on the basis of FA biomarkers may be difficult in some cases. 4. We found no significant correlation between the content of 20:5ω3 in seston and the biomass of the dominant daphniids in either reservoir. This is contrary to expectations, based on the literature, that EPA is generally important. Rather, the biomass of the two dominant Daphnia species in Bugach correlated strongly with the content of 18:3ω3 in the seston. The cyanobacteria were a probable source of this ω3 FA for Daphnia. We conclude that EPA is not always important for Daphnia populations although, in such cases, some other PUFA (e.g. 18:3ω3) might be related to their growth.

1. Arctic freshwaters are facing multiple environmental pressures, including rapid climate change and increasing land-use activities. Freshwater plankton assemblages are expected to reflect the effects of these stressors through shifts in species distributions and changes to biodiversity. These changes may occur rapidly due