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| Fontorbe, Guillaume; Frings, Patrick J.; De La Rocha, Christina L.; Hendry, Katharine R.; Conley, Daniel J.. |
| The Paleocene‐Eocene Thermal Maximum (PETM, ca. 56 Ma) is marked by a negative carbon isotope excursion (CIE) and increased global temperatures. The CIE is thought to result from the release of 13C‐depleted carbon, although the source(s) of carbon and triggers for its release, its rate of release, and the mechanisms by which the Earth system recovered are all debated. Many of the proposed mechanisms for the onset and recovery phases of the PETM make testable predictions about the marine silica cycle, making silicon isotope records a promising tool to address open questions about the PETM. We analyzed silicon isotope ratios (δ30Si) in radiolarian tests and sponge spicules from the Western North Atlantic (ODP Site 1051) across the PETM. Radiolarian δ30Si... |
| Tipo: Text |
Palavras-chave: Paleocene‐Eocene Thermal Maximum; Silicon biogeochemical cycle; Silicon isotopes; Weathering. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00627/73939/73287.pdf |
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| Moriceau, Brivaela; Iversen, Morten H.; Gallinar, Morgane; Evertsen, Antti-jussi O.; Le Goff, Manon; Beker, Beatriz; Boutorh, Julia; Corvaisier, Rudolph; Coffineau, Nathalie; Donval, Anne; Giering, Sarah L. C.; Koski, Marja; Lambert, Christophe; Lampit, Richard S.; Le Mercier, Alain; Masson, Annick; Stibor, Herwig; Stockenreiter, Maria; De La Rocha, Christina L.. |
| The fraction of net primary production that is exported from the euphotic zone as sinking particulate organic carbon (POC) varies notably through time and from region to region. Phytoplankton containing biominerals, such as silicified diatoms have long been associated with high export fluxes. However, recent reviews point out that the magnitude of export is not controlled by diatoms alone, but determined by the whole plankton community structure. The combined effect of phytoplankton community composition and zooplankton abundance on export flux dynamics, were explored using a set of 12 large outdoor mesocosms. All mesocosms received a daily addition of minor amounts of nitrate and phosphate, while only 6 mesocosms received silicic acid (dSi). This resulted... |
| Tipo: Text |
Palavras-chave: Biogenic silica; POC; Marine snow; Zooplankton; Mesocosm; Bay of Hopavagen; Plankton community; Biological pump. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00469/58029/60433.pdf |
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| De La Rocha, Christina L.. |
| [ 1] The delta Si-30 and delta N-15(diatom) of diatom opal provide a view of nutrient utilization in past oceans and are used to formulate and test hypotheses concerning Southern Ocean productivity and fluctuations in atmospheric CO2 over glacial cycles. Water column profiles of the Si and N isotopic composition of nutrients and the delta N-15(diatom) of sediment core tops support the use of delta Si-30 and delta N-15(diatom) as tracers of silicic acid and nitrate utilization, but some issues remain concerning the use of these proxies for paleoceanographic reconstructions. If average marine delta Si-30 changes over time, it could contribute to the observed down core variations in delta Si-30. Reconstruction of deepwater delta Si-30 using opal from sponges... |
| Tipo: Text |
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| Ano: 2006 |
URL: https://archimer.ifremer.fr/doc/00496/60759/65122.pdf |
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| Laurenceau-cornec, Emmanuel C.; Trull, Thomas W.; Davies, Diana M.; De La Rocha, Christina L.; Blain, Stephane. |
| During the second KErguelen Ocean and Plateau compared Study (KEOPS2) in October-November 2011, marine snow was formed in roller tanks by physical aggregation of phytoplankton assemblages sampled at 6 stations over and downstream of the Kerguelen Plateau. Sinking velocities, morphology, bulk composition (transparent exopolymer particles, biogenic silica, particulate organic carbon), and phytoplankton contents were measured individually on 66 aggregates to identify controls on sinking velocities. Equivalent spherical diameters (ESD) ranged from 1 to 12 mm, and the particle aspect ratios, Corey shape factors, and fractal dimensions (D-F1 = 1.5, D-F2 = 1.8) were close to those of smaller natural aggregates (0.2 to 1.5 mm) collected in polyacrylamide... |
| Tipo: Text |
Palavras-chave: Sinking velocity Marine snow; Aggregation; Phytoplankton; Porosity. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00352/46275/46044.pdf |
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| Frings, Patrick J.; Clymans, Wim; Fontorbe, Guillaume; De La Rocha, Christina L.; Conley, Daniel J.. |
| The silicon isotope composition of biogenic silica (delta Si-30(BSi)) in the ocean is a function of the delta Si-30 of the available dissolved Si (DSi; H2SiO4), the degree of utilisation of the available DSi, and, for some organisms, the concentration of DSi. This makes delta Si-30(BSi) in sediment archives a promising proxy for past DSi concentrations and utilisation. At steady-state, mean delta Si-30(BSi) must equal a weighted average of the inputs, the majority of which are of continental origin. Variation in the functioning of the continental Si cycle on timescales similar to the residence time of DSi in the ocean (similar to 10 ka) may therefore contribute to downcore variability in delta Si-30(BSi) on millennial or longer time-scales. The direction... |
| Tipo: Text |
Palavras-chave: Global silicon cycle; Biogenic silica; Silicon isotopes; LGM; Palaeoceanography; Biogeochemical cycling. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00421/53252/54714.pdf |
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| De La Rocha, Christina L.; Bescont, Pierre; Croguennoc, Alice; Ponzevera, Emmanuel. |
| We report here the silicon isotopic composition (delta(30)Si) of dissolved silicon (DSi) from 42 surface water samples from the Drake Passage, the Weddell Gyre, other areas south of the Southern Boundary of the Antarctic Circumpolar Current (ACC), and the ACC near the Kerguelen Plateau, taken between the beginning of February and the end of March 2007. From the beginning to end of the cruise (ANTXXIII/9), DSi diminished in the Antarctic by 50 mu mol L(-1) while concentrations of nitrate + nitrite and phosphate showed no net decline, indicating that the high seasonal Si/N removal ratios well known for the Southern Ocean may be more related to the strength of the silicate pump in the Southern Ocean than to the instantaneous Si/N uptake ratio of diatoms. The... |
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| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00042/15372/12791.pdf |
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| Sutton, Jill N.; De Souza, Gregory F.; Garcia-ibiliez, Maribel I.; De La Rocha, Christina L.. |
| The stable isotope composition of dissolved silicon in seawater (δ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40–60°N) and Labrador Sea. Variations in δ30SiDSi below 500m were closely tied to the distribution of water masses. Higher δ30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower δ30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest δ30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the δ30SiDSi... |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00457/56881/58744.pdf |
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