(Table 3) Relative content of n-alkane groups in samples from hydrothermal fields of the Mid-Atlantic Ridge

Optimum conditions were selected for chromatographic separation of model mixtures of C12-C40 n-alkanes. For one of samples of hydrothermal deposits extraction conditions of hydrocarbons were studied and a sample preparation procedure was selected. The procedure was proposed to determine n-alkanes in samples of hydrothermal deposits by means of gas chromatography - mass spectrometry (GC-MS). Detection limit for n-alkanes was 3x10**-9 to 10**-8% depending on components. On the basis of the proposed procedure composition of n-alkanes was studied in samples of hydrothermal deposits collected at the Mid-Atlantic Ridge (Broken Spur, Lost City, and Rainbow hydrothermal fields). Analyses showed that samples contained C14-C35 n-alkanes. Concentrations of the n-alkanes were rather low and varied from 0.002 to 0.038 µg/g. Hypotheses concerning genesis of identified n-alkanes were offered.

Physiological responses of the marine diatom Thalassiosira pseudonana to increased pCO2 and seawater acidity

We studied the effects of elevated CO2 concentration and seawater acidity on inorganic carbon acquisition, photoinhibition and photoprotection as well as growth and respiration in the marine diatom Thalassiosira pseudonana. After having grown under the elevated CO2 level (1000 µatm, pH 7.83) at sub-saturating photosynthetically active radiation (PAR, 75 µmol photons/m**2/s) for 20 generations, photosynthesis and dark respiration of the alga increased by 25% (14.69 ± 2.55 fmol C/cell/h) and by 35% (4.42 ± 0.98 fmol O2/cell/h), respectively, compared to that grown under the ambient CO2 level (390 µatm, pH 8.16), leading to insignificant effects on growth (1.09 ± 0.08 (1/d))v 1.04 ± 0.07 (1/d)). The photosynthetic affinity for CO2 was lowered in the high-CO2 grown cells, reflecting a down-regulation of the CO2 concentrating mechanism (CCM). When exposed to an excessively high level of PAR, photochemical and non-photochemical quenching responded similarly in the low- and high-CO2 grown cells, reflecting that photoinhibition was not influenced by the enriched level of CO2. In T. pseudonana, it appeared that the energy saved due to the down-regulated CCM did not contribute to any additional light stress as previously found in another diatom Phaeodactylum tricornutum, indicating differential physiological responses to ocean acidification between these two diatom species.

(Appendix A) Relative abundance of Emiliania huxleyi in sediment cores of the North Atlantic

The coccolithophore species Emiliania huxleyi is characterized by a wide range of sizes, which can be easily distinguished in the light microscope. In this study we have quantified the abundance of large (coccoliths > 4 µm in maximum length) E. huxleyi specimens during the last 25 kyr in sedimentary records from eleven cores and drill sites in the NE Atlantic and W Mediterranean Sea, to prove its usefulness in the reconstruction of water mass dynamics and biostratigraphic potential. During the Last Glacial Maximum this large form, a cold-water indicator, was common in the NE Atlantic and Mediterranean, and its regional variation in abundance indicates a displacement of the climatic zones southwards in agreement with the development of ice sheets and sea ice in the Northern Hemisphere during this period. On the other hand, the gradient between northern and southern surface water masses in the Subtropical Gyre appears to have been more pronounced than at present, while the Portugal and Canary Currents were more intense. In the western Mediterranean basin temperatures were cooler than in the adjacent Atlantic, provoking a quasi-endemism of these specimens until the end of Heinrich Event 1. This may have been due to a restriction in the communication between the Atlantic and Mediterranean through the Strait of Gibraltar, the arrival of cold surface water and the amplification of cooling after the development of ice sheets in the Northern Hemisphere. During the deglaciation, large E. huxleyi specimens decreased in abundance at medium and low latitudes, but were still numerous close to the Subarctic region during the Holocene. In transitional waters this decrease to present day abundances occurred after Termination Ib. The abrupt change in abundance of this large E. huxleyi form is proposed as a new biostratigraphic event to characterize the Holocene in mid- to low-latitude water masses in the North Atlantic, although this horizon seems to be diachronous by 5 kyr from tropical to subarctic regions, in agreement with the gradual onset of warm conditions.