Coccolithophore assemblages recovered from Integrated Ocean Drilling Program (IODP) Site U1313 are investigated to reconstruct the palaeoceanographic evolution of a sector of the North Atlantic during Marine Isotope Stage (MIS) 19 (~ 790–760 ka) at orbital, suborbital and millennial time-scales. The end of the glacial MIS 20 is marked by the arrival of cold waters, deriving from ice melting at higher latitudes, as recorded by Coccolithus pelagicus pelagicus. The MIS 19c is characterised by an extension of warmer North Atlantic Transitional Waters (NATW) reflecting the intensification of subtropical gyre influence on Site U1313, identified by an increase in warm species Umbilicosphaera sibogae. The influence on the site of cooler NATW is inferred from higher percentages of Gephyrocapsa margereli, which starts increasing from ~ 779 ka. Finally, the transition from MIS 19a to MIS 18 is characterised by a southward shift of the palaeoceanographic system due to a southward extension of the subpolar front, as indicated by an increase of cold subspecies C. pelagicus pelagicus. The evolution of the palaeoproductivity proxy records (number of coccoliths/g of sediment and Nannofossil Accumulation Rate — NAR) and the abundances of small Gephyrocapsa, G. margereli, U. sibogae and C. pelagicus pelagicus show that fluctuations in sea-surface productivity and alternations between cooling and warming phases occurred on the precessional timescale. Spectral analyses of U. sibogae, number of coccoliths/g of sediment and NAR indicate a significant concentration of variance close to half precession (~ 10 kyr); this reflects a nonlinear response of the mid-latitude North Atlantic surface ocean to low-latitude insolation forcing. Furthermore, millennial to multi-centennial instability in sea-surface dynamics is highlighted by spectral and wavelet analyses of U. sibogae, G. margereli and C. pelagicus pelagicus percentages, number of coccoliths/g of sediment and NAR, which reveal the occurrence of rapid events, related to stadial and interstadial-type conditions.
|Titolo:||Sea-surface dynamics and palaeoenvironmental changes in the North Atlantic Ocean (IODP Site U1313) during Marine Isotope Stage 19 inferred from coccolithophore assemblages|
|Data di pubblicazione:||2015|
|Appare nelle tipologie:||1.1 Articolo in rivista|