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Salt marsh sedimentation over the past c. 120 years along the west Cotentin coast of Normandy (France): relationship to sea-level rise and sediment supply

Salt marsh sedimentation over the past c. 120 years along the west Cotentin coast of Normandy (France): relationship to sea-level rise and sediment supply
Salt marsh sedimentation over the past c. 120 years along the west Cotentin coast of Normandy (France): relationship to sea-level rise and sediment supply
Natural high sediment supply to a number of macrotidal estuaries along the western coast of the Cotentin Peninsula (Normandy, France) is resulting in estuarine infilling. A previously published aerial survey in one estuary shows salt marsh laterally expanding at a rate of $4400m^ {2}/y$. Five sediment cores collected from salt marshes in three estuaries (Havre de Carteret, Havre de Surville, and Havre de Lessay) are used to investigate the relationship between lateral and vertical salt marsh accretion, and sea level. The cores are chemostratigraphically correlated with reference to is established by 210Pb and 137Cs dating of one of the cores, providing a chronologyextending back to $1880\pm23$. Through this period, mean vertical accretion rates for single cores from interior planar salt marsh surface sites at Surville and Lessay are 7.7 and 6.3mm/y respectively. Three cores from Carteret were taken from a seaward sloping salt marsh, one each from low, middle and high marsh settings, yielding mean vertical accretion rates of 5.5, 4.4, and 4.1 mm/y respectively. These data are compared with a regional rise in relative mean sea level (msl) of 3.9mm/y determined from a tide gauge on the nearby island of Jersey from 1952-2001. The high marsh at Carteret appears to be accreting relative position to msl, as there is no significant upcore change in the faunas. A core from Surville, however, indicates salt marsh emergence, demonstrated by transitions from sandflat to salt marsh faunas. The low marsh core from Cateret reveals a recent acceleration in vertical accretion (8mm/y since $1975\pm5$) and may be related to an increase in sediment availability due to the cessation of intertidal sand mining. This study demonstrates the long-term emergence of the Cotentin salt marshes, but suggests no general increase in vertical accretion despite increased sediment supply from recent mining cessation. Rather, newly available sediments support enhanced accretion along the marsh edge and rapid development of new marsh surface through lateral accretion. This study is in close agreement with a previous study of stilt marsh deposition from the macrotidal Bay of Fundy (Canada) that states high marsh accretion reflects sea-level or hydrological changes, whilst low marsh accretion is greatly influenced by changes in sediment supply. For future studies, knowledge of these relationships enables the selection of sites according to the aims of the investigation.
FORAMINIFERA, SALT MARSHES, CHEMOSTRATIGRAPHY, SEDIMENTATION, FRANCE WATERS, LEAD ISOTOPES 210, NWEURCHAE, SEA LEVEL, CORES, CAESIUM ISOTOPES 137, GEOLOGY
0749-0208
609-620
Haslett, A.K.
d1a91ac7-386b-474d-832b-457b7d3e2782
Cundy, A.B.
994fdc96-2dce-40f4-b74b-dc638286eb08
Davies, C.F.C.
8db9d6e3-fabc-4454-a937-5ed52b3df1d7
Powell, E.
dddf79d5-e310-433d-bc8b-fe3b6ca04df2
Croudace, I.W.
24deb068-d096-485e-8a23-a32b7a68afaf
Haslett, A.K.
d1a91ac7-386b-474d-832b-457b7d3e2782
Cundy, A.B.
994fdc96-2dce-40f4-b74b-dc638286eb08
Davies, C.F.C.
8db9d6e3-fabc-4454-a937-5ed52b3df1d7
Powell, E.
dddf79d5-e310-433d-bc8b-fe3b6ca04df2
Croudace, I.W.
24deb068-d096-485e-8a23-a32b7a68afaf

Haslett, A.K., Cundy, A.B., Davies, C.F.C., Powell, E. and Croudace, I.W. (2003) Salt marsh sedimentation over the past c. 120 years along the west Cotentin coast of Normandy (France): relationship to sea-level rise and sediment supply. Journal of Coastal Research, 19 (3), 609-620.

Record type: Article

Abstract

Natural high sediment supply to a number of macrotidal estuaries along the western coast of the Cotentin Peninsula (Normandy, France) is resulting in estuarine infilling. A previously published aerial survey in one estuary shows salt marsh laterally expanding at a rate of $4400m^ {2}/y$. Five sediment cores collected from salt marshes in three estuaries (Havre de Carteret, Havre de Surville, and Havre de Lessay) are used to investigate the relationship between lateral and vertical salt marsh accretion, and sea level. The cores are chemostratigraphically correlated with reference to is established by 210Pb and 137Cs dating of one of the cores, providing a chronologyextending back to $1880\pm23$. Through this period, mean vertical accretion rates for single cores from interior planar salt marsh surface sites at Surville and Lessay are 7.7 and 6.3mm/y respectively. Three cores from Carteret were taken from a seaward sloping salt marsh, one each from low, middle and high marsh settings, yielding mean vertical accretion rates of 5.5, 4.4, and 4.1 mm/y respectively. These data are compared with a regional rise in relative mean sea level (msl) of 3.9mm/y determined from a tide gauge on the nearby island of Jersey from 1952-2001. The high marsh at Carteret appears to be accreting relative position to msl, as there is no significant upcore change in the faunas. A core from Surville, however, indicates salt marsh emergence, demonstrated by transitions from sandflat to salt marsh faunas. The low marsh core from Cateret reveals a recent acceleration in vertical accretion (8mm/y since $1975\pm5$) and may be related to an increase in sediment availability due to the cessation of intertidal sand mining. This study demonstrates the long-term emergence of the Cotentin salt marshes, but suggests no general increase in vertical accretion despite increased sediment supply from recent mining cessation. Rather, newly available sediments support enhanced accretion along the marsh edge and rapid development of new marsh surface through lateral accretion. This study is in close agreement with a previous study of stilt marsh deposition from the macrotidal Bay of Fundy (Canada) that states high marsh accretion reflects sea-level or hydrological changes, whilst low marsh accretion is greatly influenced by changes in sediment supply. For future studies, knowledge of these relationships enables the selection of sites according to the aims of the investigation.

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More information

Published date: 2003
Keywords: FORAMINIFERA, SALT MARSHES, CHEMOSTRATIGRAPHY, SEDIMENTATION, FRANCE WATERS, LEAD ISOTOPES 210, NWEURCHAE, SEA LEVEL, CORES, CAESIUM ISOTOPES 137, GEOLOGY
Organisations: Geochemistry

Identifiers

Local EPrints ID: 399506
URI: http://eprints.soton.ac.uk/id/eprint/399506
ISSN: 0749-0208
PURE UUID: f6a1ae2d-e6df-4220-9249-6a093a8e4326
ORCID for A.B. Cundy: ORCID iD orcid.org/0000-0003-4368-2569

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Date deposited: 17 Aug 2016 15:06
Last modified: 09 Jan 2022 03:49

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Contributors

Author: A.K. Haslett
Author: A.B. Cundy ORCID iD
Author: C.F.C. Davies
Author: E. Powell
Author: I.W. Croudace

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