Holocene Paleohydrological Changes in the Southern Bay of Biscay: New Insights from Planktonic Microfossil Assemblages

English Abstract:

The Bay of Biscay is a region where significant shifts related to the North Atlantic Oscillation variation occur, a mechanism that is considered to be a major internal forcing for the climate variation during the Holocene, but still not too well constrained in this region. A core (PP10-07, 43°40.63’N; 02°13.69’W, water depth of 1472 m and 2004 cm long) collected at Capbreton canyon, with an exceptional sedimentation rate has enabled to recover a continuous and undisturbed Holocene climate signal, with a decadal to secular resolution. The present study was focused on studying cysts of dinoflagellates (dinocysts) with the aim to quantitatively reconstruct surface hydrological paleo-parameters and paleo-productivity, and therefore highlighting the Holocene signal of oceanographic changes in this area of the North East Atlantic. The ecological significance of the analysed dinocyst assemblages, besides showing evidence of high biodiversity, does not indicate any important movement of water masses. Most of the identified species are cosmopolitan and adapted to a wide range of surface temperature and salinity. These species are typical from the North Eastern Atlantic subtropical to temperate bioclimatic assemblages, with especially high occurrences of the intra-neritic species such as Lingulodinium machaerophorum, together with the cosmopolitan Operculodinium centrocarpum and Spiniferites ramosus. However, the quantitative reconstruction of the surface hydrological parameters and paleo-productivity through modern analogue technique derived from transfer functions highlights changes in temperature significantly differing from both the current average temperatures and the temperature signal given by foraminiferal data. Moreover, a relation between temperature variations and productivity at some times was observed, which could be as much associated with a cold or warm episode. Coupled to the detailed investigations made on the sedimentary context of the deposits, these palynological data derived from dinocyst assemblages allow us, for the first time in the Capbreton canyon area, to: (1) test the reliability of the marine palynological flora record in this atypical sedimentological environment, and (2) tentatively draw a coherent paleoceanographical pattern along the Holocene.