Sedimentological and palynological records since 10 ka BP along a proximal-distal gradient on the Armorican shelf (NW France) - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Quaternary Science Reviews Year : 2022

Sedimentological and palynological records since 10 ka BP along a proximal-distal gradient on the Armorican shelf (NW France)

Abstract

New findings acquired in Armorican shelf (core MD08-3204 CQ: Bay of Quiberon and core VK03-58bis: South Glénan islands) depict Holocene paleoenvironmental changes since 10 ka BP through a multi-proxy dataset including sedimentological and palynological data. First, grain-size analyses and AMS-14C dates show a common sedimentary history for both study cores. The slowdown of the relative sea level (RSL) rise was accompanied by a drop of the sedimentation rates between ∼8.3 and 5.7 ka BP; the rates had been relatively higher at the onset of the Holocene. This interval led to the establishment of a shell-condensed level, identified in core VK03-58bis by the "Turritella layer" and interpreted as a marker for the Maximum Flooding Surface. Palynological data (pollen and dinoflagellate cyst assemblages) acquired in core MD08-3204 CQ argue for an amplification of the fluvial influence since 5.7 ka BP; the establishment of the Highstand System Tract (i.e., mixed marine and fluviatile influences on the platform) then accompanied the slowdown of the RSL rise rates. On the shelf, the amplification of Anthropogenic Pollen Indicators (API) has been better detected since 4.2 ka BP, due not only to the increase of human impact but also due to a stronger fluvial influence on the shelf during the Late Holocene. Palynological data, recorded on the 8.5-8.3 ka BP interval along an inshore-offshore gradient, also demonstrate the complexity of the palynological signals such as i) the fluvial influence that promotes some pollen taxa (Alnus and Corylus) from proximal areas and ii) the macro-regionalization of palynomorph sources in distal cores. In addition, the comparison of palynological tracers, including API, over the last 7 kyrs BP, with South Brittany coastal and mid-shelf sites subject to northern vs. southern Loire catchment areas, shows a major hydro-climatic effect on the reconstructed palynological signals. Strengthened subpolar gyre (SPG) dynamics, combined with recurrent positive North Atlantic Oscillation (NAO) configurations, appear responsible for increased winter precipitation and fluvial discharge over northern Europe, as in Brittany. Conversely, weakened SPG intervals, associated with recurrent negative NAO-like modes, are characterized by intensified winter fluvial discharge over southern Europe. Interestingly, at an infra-orbital timescale, we record major peaks of API during periods of strengthened (/weakened) SPG dynamics in sites subject to detritic-organic matter inputs from Brittany (/Loire) watersheds.
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Dates and versions

insu-03824739 , version 1 (21-10-2022)

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Cite

Ophélie David, Aurélie Penaud, Muriel Vidal, Wiem Fersi, Clément Lambert, et al.. Sedimentological and palynological records since 10 ka BP along a proximal-distal gradient on the Armorican shelf (NW France). Quaternary Science Reviews, 2022, 293, ⟨10.1016/j.quascirev.2022.107678⟩. ⟨insu-03824739⟩
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