Sedimentological and palynological records since 8.5 ka BP along a proximal-distal gradient on the northern Bay of Biscay (NW Europe)

Date 2022-06
Author(s) David Ophélie1, 2, Penaud AurélieORCID1, Vidal MurielORCID1, Wiem FersiORCID1, Lambert ClémentORCID2, Goubert EvelyneORCID2, Herledan Maiwenn3, Stephan PierreORCID4, Pailler Yvan5, Bourillet Jean-FrancoisORCID1, Baltzer Agnès6
Affiliation(s) 1 : Univ. Brest, CNRS, Ifremer, Geo-Ocean, UMR 6538, F-29280 Plouzané, France
2 : Univ. Bretagne Sud, Univ. Brest, CNRS, Ifremer, Geo-Ocean, UMR 6538, F-56000 Vannes, France
3 : Univ. Lille, Laboratoire d’Océanologie et de Géosciences, UMR 8187, F-59655 Villeneuve d’Ascq, France
4 : CNRS, Littoral Environnement Télédétection Géomatique, UMR 6554, IUEM, F-29280 Plouzané, France
5 : Chaire Armerie, Univ. Brest, Inrap, Littoral Environnnement Télédétection Géomatique, UMR 6554, IUEM, F-29280 Plouzané, France
6 : Univ. Nantes, Laboratoire Géolittomer/IGARUN, UMR 6554, F-44300 Nantes, France
DOI 10.17882/86430
Publisher SEANOE
Keyword(s) Holocene, south-Brittany, pollen, dinoflagellate cysts, paleoenvironmental changes, Turritella layer, Anthropogenic Pollen Indicators (API), fluvial discharge

New results acquired in south-Brittany (MD08-3204 CQ core: Bay of Quiberon and VK03-58bis core: south Glénan islands) allow depicting Holocene paleoenvironmental changes from 8.5 ka BP to present through a multi-proxy dataset including sedimentological and palynological data. First, grain-size analyses and AMS-14C dates highlight a common sedimentary history for both study cores. The relative sea level (RSL) slowdown was accompanied by a significant drop of the sedimentation rates between ca. 8.3 and 5.7 ka BP, after being 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 grains 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 accompanying the slowdown of the RSL rise-rates. On the shelf, the amplification of Anthropogenic Pollen Indicators (API) is then better detected since 4.2 ka BP, not only due to human impact increase 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 signal such as i) the fluvial influence that promotes some pollinic taxa (i.e., Corylus, Alnus) 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, with south-Brittany coastal and mid-shelf sites subjected to northern vs. southern Loire catchment areas, allowed discussing a major hydro-climatic effect on the reconstructed palynological signals. Strengthened subpolar gyre dynamics (SPG), combined with recurrent positive North Atlantic Oscillation (NAO) configurations, appear responsible for increased winter precipitations and fluvial discharges over northern Europe, such as in Brittany. Conversely, weakened SPG intervals, associated with negative NAO-like modes, are characterized by intensified winter fluvial discharges over southern Europe. Interestingly, we record, at an infra-orbital timescale, major peaks of API during periods of strengthened (/weakened) SPG dynamics in sites subjects to Brittany watersheds (/Loire watersheds) inputs.

Licence CC-BY
Acknowledgements We thank the captain, the crew, and the scientific teams of cruises that collected both main study cores: MD08-3204 CQ core (BISCOT campaign onboard the Marion Dufresne; MD169/MICROSYSTEMS cruise, 2008; IPEV) and VK03-58bis core (Ifremer research project “Défi Golfe de Gascogne”; Vibarmor cruise, 2003 onboard the Côtes de la Manche). Palynological analysis of core VK03-58bis benefited credits by a CNRS-INSU project HCOG2 (2013-2014) “Forçages climatiques Holocène et répercussions Côtières et Océaniques dans le Golfe de Gascogne” (coord. A. Penaud) in the context of the LEFE-IMAGO research axis. Thanks to the QUIPALPLO project (coord. A. Baltzer), financed by OSUNA (Observatoire des Sciences de l’Univers de Nantes Atlantique), some palynological analyses have been realized during the M2 intership of M. Herlédan (2019/2020). Some dates were obtained thanks to French national ARTEMIS 14C-AMS facilities (2012, 2013, 2018, 2019) and the other ones were acquired within the Poznan Radiocarbon Laboratory and Beta Analytics. We would also like to thank Anne Véronique Walter-Simonnet (UMR 6249 Chrono-environnement; Bourgogne Franche-Comté University) who carried out the grain size analyses of the MD08-3204 CQ core and made them available to us. Authors thank the ZABrI (“Zone Atelier Brest Iroise”, CNRS-INEE) and the ArMeRIE program funded by the UBO (Univ Brest) for fruitful interdisciplinary exchanges about human dynamics and Holocene paleoenvironments. This work was supported by the ISblue project, Interdisciplinary graduate school for the blue planet (ANR-17-EURE-0015), co-funded by a grant from the French government under the program "Investissements d'Avenir".
File Size Format Processing Access
VK03-58bis core ("Grande Vasière, Glénan sector"): datations, grain size analyses (CaCO3 free) 42 KB XLS, XLSX Raw data Open access
MD08-3204 CQ core (Bay of Quiberon): datations, total grain size analyses, palynological data (pollen and dinocyst assemblages) 152 KB XLS, XLSX Raw data Open access
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David Ophélie, Penaud Aurélie, Vidal Muriel, Wiem Fersi, Lambert Clément, Goubert Evelyne, Herledan Maiwenn, Stephan Pierre, Pailler Yvan, Bourillet Jean-Francois, Baltzer Agnès (2022). Sedimentological and palynological records since 8.5 ka BP along a proximal-distal gradient on the northern Bay of Biscay (NW Europe). SEANOE.