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[1] The Canadian Arctic Shelf Exchange Study (CASES) included the overwintering deployment of a research platform in Franklin Bay (70°N, 126°W) and provided a unique seasonal record of bacterial dynamics in a coastal region of the Arctic Ocean. Our objectives were (1) to relate seasonal bacterial abundance (BA) and production (BP) to physico-chemical characteristics and (2) to quantify the annual bacterial carbon flux. BAwas estimated by epifluorescence microscopy and BP was estimated from 3 H-leucine and 3 H-thymidine assays. Mean BA values for the water column ranged from 1.0 (December) to 6.8 Â 10 5 cells mL À1 (July). Integral BP varied from 1 (February) to 80 mg C m À2 d À1 (July). During winter-spring, BP was uncorrelated with chlorophyll a (Chl a), but these variables were significantly correlated during summer-autumn (r s = 0.68, p < 0.001, N = 38), suggesting that BP was subject to bottom-up control by carbon supply. Integrated BP data showed three distinct periods: fall-winter, late winter-late spring, and summer. A baseline level of BB and BP was maintained throughout late winter-late spring despite the persistent cold and darkness, with irregular fluctuations that may be related to hydrodynamic events. During this period, BP rates were correlated with colored dissolved organic matter (CDOM) but not Chl a (r s BP.CDOMjChl a = 0.20, p < 0.05, N = 176). Annual BP was estimated as 6 g C m À2 a À1 , implying a total BP of 4.8 Â 10 10 g C a À1 for the Franklin Bay region. These results show that bacterial processes continue throughout all seasons and make a large contribution to the total biological carbon flux in this coastal arctic ecosystem.

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We study the impact of the nucleation step on the final crystalline quality of 3C-SiC heteroepitaxial films grown on (111) and (100) oriented silicon substrates by low pressure chemical vapor deposition. The evolution of both the structural and morphological properties of 3C-SiC epilayers in dependence on the only nucleation parameters (propane flow rate and duration of the process) are investigated by means of x-ray diffraction, scanning electron, atomic force, and optical microscopies. At first, we show how the formation of interfacial voids is controlled by the experimental parameters, as previously reported, and we correlate the density of voids with the substrate sealing by using an analytical model developed by V. Cimalla et al. [Mater. Sci. Eng., B 46, 190 (1997)]. We show that the nucleation stage produces a more dense buffer layer in case of (111) substrates. Further, we investigate the impact of the nucleation parameters on the crystalline quality of 3C-SiC epilayers. Within our experimental setup, the crystalline quality of (100) oriented 3C-SiC films is more rapidly evolving than (111) films for low propane contents (0.025%–0.05% in hydrogen), whereas a common degradation of the crystalline quality is reported for both cases for the higher propane contents. In parallel, we investigate the morphological features of the epilayers. The (111) oriented epilayers are well coalesced irrespectively of the nucleation condition, contrarily to the (100) films. Finally, for both orientations we report on the dependence of the formation of double positioning domains (twins) on the nucleation conditions. Such defects can be suppressed within (111) films but not within (100) films. We highlight the role of the substrate sealing and discuss in what extent it can be responsible of the observations by reducing the contribution of the silicon outdiffusing and by allowing a more pronounced two-dimensional growth mode for (111) oriented 3C-SiC films.

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