Productivité et flux de carbone dans la mer du Labrador au cours des derniers 40 000 ans

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Hillaire-Marcel, Claude, Vernal, Anne de, Lucotte, Marc, Mucci, Alfonso, Bilodeau, Guy, Rochon, André, Vallières, Sylvain, Wu, Guoping
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1994
• Subjects: General Earth and Planetary Sciences; Mer du Labrador; Ice Sheet; Labrador Sea; Neogloboquadrina pachyderma; North Atlantic Deep Water; North Atlantic
• Online Access: http://dx.doi.org/10.1139/e94-012; http://www.nrcresearchpress.com/doi/pdf/10.1139/e94-012

Geochemical and micropaleontological analyses of Labrador Sea sediments allowed us to intercalibrate indicators of paleoproductivity and paleofluxes of carbon and to reconstitute biogeochemical fluxes, notably in relation to deep sea circulation changes (Western Boundary Undercurrent and North Atlantic Deep Water). Linear or logarithmic relations are observed between the subrecent fluxes of paleoproductivity indicators (coccoliths, diatoms, dinocysts, 230 Th), the 13 C content of left-coiling or sinistral Neogloboquadrina pachyderma, the modern surface water carbon production, and the rates of organic and inorganic carbon (C org , C inorg ) burial. All indicators increase by a factor of 10 2 to 10 3 in response to the evolution of paleosea-surface conditions since the last glacial maximum. Correlations are observed between authigenic C inorg , 230 Th, coccoliths, and 13 C content (left-coiling or sinistral Neogloboquadrina pachyderma), and also between authigenic C org , dinocysts, uranium, and sulfur. Relative C inorg /C org burial rates in the deep sediments (> 3000 m) allow us to calculate a net CO 2 production in the basin. The net CO 2 flux was slightly negative between ~ 20 and ~ 15 ka BP. It reached a first maximum at about 9 ka BP (~ 30 μmol∙cm −2 ∙a −1 CO 2 ) followed by a decrease at ~ 8 ka BP (~ 20 μmol∙cm −2 ∙a −1 ). Since about 7 ka BP, it stabilized at ~ 35 μmol∙cm −2 ∙a −1 . The minimum observed at about 8 ka BP corresponds to a significant rate of C org burial accompanied with a maximum flux of redox-sensitive indicators (uranium, sulfur). This event does not correspond to any change in sea-surface temperature or salinity, nor in deep circulation, but may be related to the reorganization of the atmospheric circulation during a major breakup stage of the Laurentide ice sheet. The close correlation between the change in CO 2 production in the Labrador Sea with variations of atmospheric CO 2 concentrations during the last 20 ka BP suggests that the production of biogenic carbonates in ...