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G. K. Rozenberg M. P. Pasternak G. R. Hearne C. A. McCammon 《Physics and Chemistry of Minerals》1997,24(8):569-573
?57Fe Mössbauer studies at room temperature and temperature-dependent resistance studies have been performed on a natural specimen of cubanite (CuFe2S3) in a diamond-anvil cell at pressures up to ~10 GPa. An insulator-metal phase transition occurs in the range 3.4–5.8 GPa coinciding with a previously observed structural transition from an orthorhombic to a hexagonal NiAs (B8) structure. The room temperature data shows that the metallization process concurs with a gradual transition from a magnetically ordered phase at low pressure to a nonmagnetic or paramagnetic phase at high-pressure. The change in magnetic behaviour at the structural transition may be attributed to a reduction of the Fe-S-Fe superexchange angle formed by edge-sharing octahedra occurring in the high-pressure phase. The non-magnetic or paramagnetic metallic phase at high pressure is retained upon decompression to ambient pressure-temperature conditions, indicative of substantial hysteresis associated with the pressure driven orthorhombic→hexagonal structural transition. The pressure evolution of both the 57Fe Mössbauer hyperfine interaction parameters and resistance behaviour is consistent with the transition from mixed-valence character in the low pressure orthorhombic structure to that of extended-electron delocalization in the hexagonal phase at high-pressure. 相似文献
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The role of the small-size (SF; 0.1–0.5 mm) and large-size (LF; 0.5–20.0 mm) fractions in the biomass and abundance of mesozooplankton
(0.1–20.0 mm) was assessed using the database of samples obtained during the cruises of RV Akvanavt in the northeastern Black Sea in November 2000 and October 2006. The mesozooplankton was collected by means of Juday nets
(37/50, filtering gauze 160 μm) and Niskin bottles in two areas: (1) the shelf and continental slope (30–1480 m depth) and
(2) the deep sea (depths of more than 1500 m). The plankton net was considerably less effective in collecting the SF of the
mesozooplankton (by a factor of 30–36) than the Niskin bottles. When comparing the SF and LF, we estimated the abundance and
biomass of the SF in the samples obtained with the Niskin bottles. The abundance of the SF in the deep-sea area was 2.5 times
lower compared to the shelf and continental slope, and the LF abundance was 5.0 times lower in the same way. The abundance
of the SF constituted 88% of the total mesozooplankton on the shelf and continental slope, and 78% in the deep-sea area. The
biomass of the SF was higher as well on the shelf and continental slope. Meroplankton played a significant role in the SF
zooplankton abundance (0.5 × 103 + 0.16 ind. m−3) in this area. The SF grazing impact was 10% of the total mesozooplankton grazing on the shelf and continental slope, and
17% in the deepsea area. Appendicularia and nauplii of copepods had the greatest contribution to the mesozooplankton grazing
among the SF group. 相似文献
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Drits A. V. Pasternak A. F. Kravchishina M. D. Arashkevich E. G. Sukhanova I. N. Flint M. V. 《Oceanology》2019,59(5):669-677
Oceanology - The role of plankton in the vertical flux in the East Siberian Sea was studied in the 69 cruise of the RV “Akademik Mstislav Keldysh” in September 2017. Vertical fluxes... 相似文献
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Camilla Svensen Lena Seuthe Yulia Vasilyeva Anna Pasternak Edmond Hansen 《Progress in Oceanography》2011,91(4):534-544
We investigated zooplankton distribution in September 2006/2007 at eight stations across Fram Strait in contrasting water masses ranging from cold Polar water to warm Atlantic water. Our main objectives were: (1) to describe the plankton community in the upper 200 m during autumn, and (2) to investigate the importance of small-sized copepods and protozooplankton in an arctic ecosystem when the majority of the large Calanus species had entered diapause. We sampled both with a WP-2 net and Go-Flo bottle and show that small copepods <1 mm are significantly undersampled using a WP-2 net with 90 μm mesh.Small copepods and protozooplankton made a significant contribution both in terms of abundance and total zooplankton biomass at all stations in September, when the large calanoid copepods had left the upper 200 m. The dominating group in the upper 60 m at all stations was Oithona spp. nauplii and their daily estimated grazing potential on the <10 μm phytoplankton ranged from 0.1% to 82% of the standing stock. Both Oithona copepodites and nauplii biomass showed a significantly positive relation with temperature, but not with potential food. Heterotrophic protozooplankton, on the other hand, were most likely bottom-up regulated by the availability of phytoplankton <10 μm. We hypothesise that Oithona nauplii and protozooplankton compete for food and conclude that there was a strong link between the zooplankton community and the microbial food web in Fram Strait. 相似文献
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RJM Crawford RM Randall TR Cook PG Ryan BM Dyer R Fox 《African Journal of Marine Science》2016,38(3):373-383
Numbers of Cape cormorants Phalacrocorax capensis breeding in South Africa decreased by nearly 50% from approximately 107 000 pairs in 1977–1981 to 57 000 pairs in 2010–2014. Although four colonies had >10 000 pairs in 1977–1981, there was just one such colony in 2010–2014. Almost all the decrease occurred after the early 1990s off north-west South Africa, between the Orange River estuary and Dassen Island. South of this, the number breeding in the two periods was stable, with some colonies being formed or growing rapidly in the 2000s. The proportion of South Africa’s Cape cormorants that bred south of Dassen Island increased from 35% in 1977–1981 to 66% in 2010–2014, with the opposite situation observed in the north-west. This matched a shift to the south and east in the distributions of two of the Cape cormorant’s main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax. In 2014, an apparent scarcity of prey in the north-west resulted in Cape cormorants attempting to take bait from hooks of fishing lines over an extended period, a behaviour not previously recorded. The number of Cape cormorants breeding in the south may be constrained by the absence of large islands between Dyer Island in the west and Algoa Bay in the east. If so, it may be possible to bolster the southern population through the provision of appropriate breeding habitat, such as platforms, or restricting human disturbance at suitable mainland cliff breeding sites. 相似文献
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