| 11. |
- Hetzinger, S., et al.
(författare)
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High-resolution analysis of trace elements in crustose coralline algae from the North Atlantic and North Pacific by laser ablation ICP-MS
- 2011
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Ingår i: Palaeogeography Palaeoclimatology Palaeoecology. - 0031-0182. ; 302:1-2, s. 81-94
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the trace elemental composition in the skeleta of two specimens of attached-living coralline algae of the species Clathromorphum compactum from the North Atlantic (Newfoundland) and Clathromorphum nereostratum from the North Pacific/Bering Sea region (Amchitka Island, Aleutians). Samples were analyzed using Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (IA-ICP-MS) yielding for the first time continuous individual trace elemental records of up to 69 years in length. The resulting algal Mg/Ca, Sr/Ca, U/Ca, and Ba/Ca ratios are reproducible within individual sample specimens. Algal Mg/Ca ratios were additionally validated by electron microprobe analyses (Amchitka sample). Algal Sr/Ca, U/Ca, and Ba/Ca ratios were compared to algal Mg/Ca ratios, which previously have been shown to reliably record sea surface temperature (SST). Ratios of Sr/Ca from both Clathromorphum species show a strong positive correlation to temperature-dependent Mg/Ca ratios, implying that seawater temperature plays an important role in the incorporation of Sr into algal calcite. Linear Sr/Ca-SST regressions have provided positive, but weaker relationships as compared to Mg/Ca-SST relationships. Both, algal Mg/Ca and Sr/Ca display clear seasonal cycles. Inverse correlations were found between algal Mg/Ca and U/Ca, Ba/Ca, and correlations to SST are weaker than between Mg/Ca, Sr/Ca and SST. This suggests that the incorporation of U and Ba is influenced by other factors aside from temperature. (C) 2010 Elsevier B.V. All rights reserved.
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| 12. |
- Larsen, A. Nylandsted, et al.
(författare)
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E center in silicon has a donor level in the band gap
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:10, s. 106402/1-106402/4
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Tidskriftsartikel (refereegranskat)abstract
- It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity-vacancy pair)-one of the most studied defects in semiconductors-has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.
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| 13. |
- Poulton, Alex J., et al.
(författare)
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Phytoplankton carbon fixation, chlorophyll-biomass and diagnostic pigments in the Atlantic Ocean
- 2006
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Ingår i: Deep-sea research. Part II, Topical studies in oceanography. - : Elsevier BV. - 0967-0645 .- 1879-0100. ; 53:14-16, s. 1593-1610
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Tidskriftsartikel (refereegranskat)abstract
- We have made daily measurements of phytoplankton pigments, size-fractionated (< 2 and > 2-mu m) carbon fixation and chlorophyll-a concentration during four Atlantic Meridional Transect (AMT) cruises in 2003-04. Surface rates of carbon fixation ranged from < 0.2-mmol C m(-3) d(-1) in the subtropical gyres to 0.2-0.5-mmol C m(-3) d(-1) in the tropical equatorial Atlantic. Significant intercruise variability was restricted to the subtropical gyres, with higher chlorophyll-a concentrations and carbon fixation in the subsurface chlorophyll maximum during spring in either hemisphere. In surface waters, although picoplankton (<-mu m) represented the dominant fraction in terms of both carbon fixation (50-70%) and chlorophyll-alpha (80-90%), nanoplankton (> 2-mu m) contributions to total carbon fixation (30-50%) were higher than to total chlorophyll-alpha (10-20%). However, in the subsurface chlorophyll maximum picoplankton dominated both carbon fixation (70-90%) and chlorophyll-alpha (70-90%). Thus, in surface waters chlorophyll-normalised carbon fixation was 2-3 times higher for nanoplankton and differences in picoplankton and nanoplankton carbon to chlorophyll-alpha ratios may lead to either higher or similar growth rates. These low chlorophyll-normalised carbon fixation rates for picoplankton may also reflect losses of fixed carbon (cell leakage or respiration), decreases in photosynthetic efficiency, grazing losses during the incubations, or some combination of all these. Comparison of nitrate concentrations in the subsurface chlorophyll maximum with estimates of those required to support the observed rates of carbon fixation (assuming Redfield stoichiometry) indicate that primary production in the chlorophyll maximum may be light rather than nutrient limited.
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