Recherche d’indicateurs géomorphologiques de variation de l’orientation des houles sur les côtes françaises de l’Atlantique et de la Manche au cours des 25 dernières années, analyse des données et comparaison avec les données de l’atlas numérique de houle EDF-LNHE

Hénaff, Alain

doi:10.1051/lhb:2008006

Cited by 6 publications

(5 citation statements)

References 5 publications

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“…The altitude of the present high water spring tide (HWST) reaches 2.64 m NGF, while the tidal amplitude is 4.3 m (St Gwénolé harbour). Prevailing winds are commonly those of a Westerly nature, although during the 1960s and since 2002, meridian winds have been prevailing (Hénaff, 2008). The tidal platform is limited onshore by a rocky palaeocliff.…”

Section: Geological and Geomorphological Settingsmentioning

confidence: 99%

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Vliët-Lanoé¹,

Goslin²,

Hallégouët³

et al. 2014

The Holocene

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Our study aims to understand the recurring climatic conditions prevailing during the largest storms reaching NW France (Brittany). These storms are responsible for the breaching of coastal barriers and major flooding of lowlands. In a first part of our work, we examine the morphological impact and stratigraphic record of storm events along Western Brittany rocky coasts, with a special focus on the southern coast of the Bay of Audierne, the most exposed coast of the region. In a second paper ('Middle-to Late-Holocene Storminess in Brittany (NW France): Part II'), we shall focus on the chronology of storm events and their climate forcing conditions. Drilling transects and stratigraphic analyses were first undertaken to constrain chronology, strength and wind direction during the main Holocene storm events. New dates, observations and a relative sea-level (RSL) curve were then used to inform discussion of the necessary climatic and morphologic conditions leading to destructive storm events. Most recorded events appear to be linked with cooling episodes of the Holocene and a RSL close to present. Some storms are clearly responsible for breaching and dune building or remobilisation. We demonstrate that storm frequency and intensity appear to rise in a stepwise manner during the late Holocene. Maximum efficiency is reached during the 'Little Ice Age' with clustered events probably lasting several days, but major storms also occurred immediately prior to the 'Medieval Warm Period'. We suggest that recent coastal dune building from c. ad 1100 until now, despite a sea level close to present and continuously rising, may be a direct consequence of the restoration of beaches after periods of recurrent storminess. This building activity often occurred during dry negative North Atlantic Oscillation (NAO) events, in connection with the available sedimentary supply.

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Section: Geological and Geomorphological Settingsmentioning

confidence: 99%

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Vliët-Lanoé¹,

Goslin²,

Hallégouët³

et al. 2014

The Holocene

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“…During positive NAO modes, regional winds are mostly Westerlies (Pirazolli et al, 2004). During negative NAO modes, the prevailing winds are meridian (Hé naff, 2008), driven by the important oscillations of the jet stream. This is the main reason for some regional differences in dune formation, as related to the coastal orientation.…”

Section: Dynamical Context: Dune Disappearance In the Near Futurementioning

confidence: 99%

Holocene formation and evolution of coastal dunes ridges, Brittany (France)

Vliët-Lanoé

Goslin

Hénaff

et al. 2015

Comptes Rendus. Géoscience

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International audienceHolocene coastal dune formation under a continuously rising sea level (SL) is an abnormal response to increasing storm frequency. The aim of this work is to understand the coastal sedimentary budget and the present-day sand starvation, controlled by climate and man. Dating in Brittany shows that Aeolian deposition initiated from ca. 4000 cal BP, with the slowing down of the SL rise. Pre-historical dunes appeared here from ca. 3000 cal BP, without SL regression. After, further building phases recycled the same stock of sands. Historical dunes I developed from ca. 350 AD. Major storms between 900 and 1200 AD resulted in the construction of washover coastal ridges, the Historical dunes II. A part of the sand was evacuated offshore. From ca. 1350 AD, the pre-existing ridges are reworked forming the Historical dunes III, leading to rapid coastal erosion and inland drift. Holocene dunes with a rising SL constitute a temporary anomaly, mostly forced by man, soon erased by storms in Brittany

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“…Recurrence of negative NAO configurations may have persisted long enough (few winter months) to modify temporarily the wind pattern, such as those observed during the late 20th century (Visbeck et al, 2001) with dominant westerly winds in Brittany (Hénaff, 2008;Pirazzoli et al, 2004). Over longer timescales, colder (2310-2190 cal.…”

Section: Nao: From a Daily To A Millennial Signature?mentioning

confidence: 99%

“…At the Holocene timescale in NW Europe, drought and dune building would be associated with repeated centennial NAO negative modes and moderate storms (Lamb, 1995). Recurrence of negative NAO configurations may have persisted long enough (few winter months) to modify temporarily the wind pattern, such as those observed during the late 20th century (Visbeck et al, 2001) with dominant westerly winds in Brittany (Hénaff, 2008; Pirazzoli et al, 2004). Over longer timescales, colder (2310–2190 cal.…”

Section: State Of the Artmentioning

confidence: 99%

Middle- to late-Holocene storminess in Brittany (NW France): Part II – The chronology of events and climate forcing

Vliët-Lanoé¹,

Penaud²,

Hénaff³

et al. 2014

The Holocene

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This study focuses on the recurring climate conditions required for the largest storms occurring in NW France (Brittany). It is based on the analysed records of storm events along Western Brittany coast (see Part I). In this manuscript (Part II), storm recurrence is explored along with forcing mechanisms. Periods of more frequent storm events over the two last centuries are analysed first in order to link these events with possible forcing mechanisms (North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) modes) triggering the most destructive storms. Then, palaeostorm events are discussed at the Holocene scale, from 6000 yr BP to present, to verify the forcing mechanisms. Most recorded events appear to be linked with cooling episodes, mostly in winter, a transition to or from a negative winter NAO mode, a positive AMO mode. Extreme storms occur immediately prior to the 'Medieval Warm Period' (MWP). Maximum effects are reached prior to the onset of the MWP and during the Maunder and Dalton solar minima. Low storm activity occurred during the Spörer Minimum linked to an acceleration of the Atlantic Meridional Overturning Circulation (AMOC). Main storm triggers seem to correspond to a positive AMO mode with an unstable jetstream configuration driving a negative NAO. In this study, four specific weather configurations were defined to explain each type of recorded storminess. The strongest storms correspond to low AMO and decennial-negative NAO modes (e.g. 'Little Ice Age'), or high AMO in association with dominant low NAO modes, as during the early Middle Age and present-day period. Fresh or warm oceans in association with a positive NAO mode are stormy but with very low sting storms frequency. Although in agreement with the orbital forcing and the Holocene glacial history, increasing storm frequency and intensity is most probably partly biased by continuous sea-level rise and resulting erosion.

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Recherche d’indicateurs géomorphologiques de variation de l’orientation des houles sur les côtes françaises de l’Atlantique et de la Manche au cours des 25 dernières années, analyse des données et comparaison avec les données de l’atlas numérique de houle EDF-LNHE

Cited by 6 publications

References 5 publications

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Holocene formation and evolution of coastal dunes ridges, Brittany (France)

Middle- to late-Holocene storminess in Brittany (NW France): Part II – The chronology of events and climate forcing

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