Abstract
About a decade ago, a large field of pockmarks (individual features up to 30 m in diameter and <2 m deep) was discovered in water depths of 15–40 m in the Bay of Concarneau in southern Brittany along the French Atlantic coast, covering an overall area of 36 km2 and characterised by unusually high pockmark densities in places reaching 2,500 per square kilometre. As revealed by geophysical swath and subbottom profile data ground-truthed by sediment cores collected during two campaigns in 2005 and 2009, the confines of the pockmark field show a spectacular spatial association with those of a vast expanse of tube mats formed by a benthic community of the suspension-feeding amphipod Haploops nirae. The present study complements those findings with subbottom chirp profiles, seabed sonar imagery and ultrasonic backscatter data from the water column acquired in April 2011. Results show that pockmark distribution is influenced by the thickness of Holocene deposits covering an Oligocene palaeo-valley system. Two groups of pockmarks were identified: (1) a group of large (>10 m diameter), more widely scattered pockmarks deeply rooted (up to 8 ms two-way travel time, TWTT) in the Holocene palaeo-valley infills, and (2) a group of smaller, more densely spaced pockmarks shallowly rooted (up to 2 ms TWTT) in interfluve deposits. Pockmark pore water analyses revealed high methane concentrations peaking at ca. 400 μl/l at 22 and 30 cm core depth in silty sediments immediately above Haploops-bearing layers. Water column data indicate acoustic plumes above pockmarks, implying ongoing pockmark activity. Pockmark gas and/or fluid expulsion resulting in increased turbidity (resuspension of, amongst others, freshly settled phytoplankton) could at least partly account for the strong spatial association with the phytoplankton-feeding H. nirae in the Bay of Concarneau, exacerbating impacts of anthropogenically induced eutrophication and growing offshore trawling activities. Tidally driven hydraulic pumping in gas-charged pockmarks represents a good candidate as large-scale short-term triggering mechanism of pockmark activation, in addition to episodic regional seismic activity.
Similar content being viewed by others
References
Baltzer A, Tessier B, Nouzé H, Bates R, Moore C, Menier D (2005) Seistec seismic profiles: a tool to differentiate gas signatures. Mar Geophys Res 26:235–245
Baltzer A, Bates R, Mokeddem Z, Clet-Pellerin M, Walter-Simonnet A-V, Bonnot-Courtois C, Austin WEN (2010) Using seismic facies and pollen analyses to evaluate climatically driven change in a Scottish sea loch (fjord) over the last 20 ka. In: Howe JA, Austin WEN, Forwick M, Paetzel M (eds) Fjord systems and archives. Geol Soc Lond Spec Publ 344:355–369
Baltzer A, Ehrhold A, Cordier C, Clouet H, Souron A, Cagna R, Gillier A (2011) Origine des pockmarks en surface des vasières à Haploops (Crustacé amphipode) de la Baie de Concarneau à partir des dernière données acquises lors de la campagne avec la vedette Haliotis en 2011. In: Ext Abstr Vol 13th ASF Congress, 16–18 November 2011, Dijon. Association des Sédimentologistes Français, Paris, publ no 68, pp 17–18
Baltzer A, Ehrhold A, Rigolet C, Dubois S, Cordier C (2013) Etude d’un champ de pockmarks associé à un peuplement de Haploops dans la Baie de Concarneau: apport de la prospection géophysique THR. In: Carhambar, Cartographie des habitats marins benthiques. Edition Ifremer-AAMP, pp 64–68. http://www.carhambar.org
Béchennec F, Guennoc P, Guerrot C, Lebret P, Thieblemont D (1997) Notice explicative, carte géologique de France, 1/50000 feuille Concarneau (382). BRGM, Orléans
Bøe R, Rise L, Ottesen D (1998) Elongate depressions on the southern slope of the Norwegian Trench (Skagerrak): morphology and evolution. Mar Geol 146:191–203
Boudreau P, Algar C, Johnson BD, Coudrace I, Reed A, Furukawa Y, Dorgan KM, Jumars PA, Grader AS, Gardiner BS (2005) Bubble growth and rise in soft sediments. Geology 33:517–520
Bouysse P, Le Calvez Y (1967) Etude des fonds marins compris entre Penmarc’h et Groix (Sud-Finistère). Bull BRGM 2:39–69
Bouysse P, Chateauneuf JJ, Ters M (1974) Présence d’Ypresien, niveau transgressif et taux de sédimentation flandriens (Bretagne méridionale) en baie de Vilaine. C R Acad Sci Paris 279:1421–1424
Brothers LL, Kelley JT, Belknap DF, Barnhardt WA, Koons PO (2011a) Pockmarks: self-scouring seep features? In: Proc 7th Int Conf Gas Hydrates, 17–21 July 2011, Edinburgh
Brothers LL, Kelley JT, Belknap DF, Barnhardt WA, Andrews BD, Landon Maynard M (2011b) More than a century of bathymetric observations and present-day shallow sediment characterization in Belfast Bay, Maine, USA: implications for pockmark field longevity. Geo-Mar Lett 31:237–248. doi:10.1007/s00367-011-0228-0
Brothers LL, Kelley JT, Belknap DF, Barnhardt WA, Andrews BD, Legere C, Clarke JH (2012) Shallow stratigraphic control on pockmark distribution in north temperate estuaries. Mar Geol 329–331:34–45
Chronis C, Piper D, Anagnostou G (1991) Late Quaternary evolution of the Gulf of Patras. Mar Geol 97:191–209
Cuylaerts M, Naudts L, Casier R, Khabuev AV, Belousov OV, Kononov EE, Khlystov O, De Batist M (2012) Distribution and morphology of mud volcanoes and other fluid flow-related lake-bed structures in Lake Baikal, Russia. Geo-Mar Lett 32:383–394. doi:10.1007/s00367-012-0291-1
Diez R, Garcia-Gil S, Durán R, Vilas F (2007) Gas charged sediments in the Ría de Arousa: short- to long-term fluctuations? Estuar Coast Shelf Sci 71:467–479
Dutertre M, Hamon D, Chevalier C, Ehrhold A (2013) The use of the relationships between environmental factors and benthic macrofaunal distribution in the establishment of a baseline for coastal management. ICES J Mar Sci 70:294–308
Ehrhold A, Hamon D, Guillaumont B (2006) The REBENT monitoring network, a spatially integrated, acoustic approach to surveying nearshore macrobenthic habitats: application to the bay of Concarneau (South Brittany, France). ICES J Mar Sci 63:1604–1615
Ehrhold A, Blanchet A, Hamon D, Chevalier C, Gaffret JD, Alix AS (2007) Réseau de surveillance Benthique, Région Bretagne: approche sectorielle subtidale: identification et caractérisation des habitats benthiques du secteur Concarneau. Rapport Ifremer
Fader GBJ (1991) Gas-related sedimentary features from the eastern Canadian continental shelf. Cont Shelf Res 11(8/10):1123–1153
Fannin NGT (1980) The use of regional geological surveys in the North Sea and adjacent areas in the recognition of offshore hazards. In: Ardus DA (ed) Offshore site investigation. Graham & Trotman, London, pp 5–21
Ferrín A, Durán R, Diez R, García-Gil S, Vilas F (2003) Shallow gas features in the Galician Rías Baixas (NW Spain). Geo-Mar Lett 23:207–214. doi:10.1007/s00367-003-0158-6
Field ME, Jennings AE (1987) Seafloor gas seeps triggered by a northern California earthquake. Mar Geol 77:39–51
Floodgate GD, Judd AD (1992) The origin of shallow gas. Cont Shelf Res 12(10):1145–1156
García-García A, Vilas F, García-Gil S (1999) A seeping sea-floor in a Ria environment: Ria de Vigo (NW Spain). Environ Geol 38(4):296–300
Garcia-Gil S (2003) A natural laboratory for shallow gas: the Rías Baixas (NW Spain). Geo-Mar Lett 23:215–229. doi:10.1007/s00367-003-0159-5
Garcia-Gil S, Vilas-Martin F, Muñoz A, Acosta J, Uchupi E (2002) Quaternary sedimentation and thermal diapirism in the Ria de Pontevedra (Galicia), Northwest Spain. J Coastal Res 15(4):1083–1090
Glémarec M, Grall J (2003) Effets biogènes sur la sédimentation en baie de Concarneau. Cah Nantais 59:123–130
Gontz AM, Belknap DF, Kelley JT (2002) Seafloor features and characteristics of the Black Ledges area, Penobscot Bay, Maine, USA. J Coast Res Spec Issue 36:333–339
Granin NG, Radziminovich NA, Granina LZ, Blinov VV, Gnatovskiy RY (2012) Freshening of near-bottom waters in Lake Baikal triggered by the Mw6.2 Kultuk earthquake of August 2008. Geo-Mar Lett 32:453–464. doi:10.1007/s00367-012-0302-2
Guyomarc’h JP, Le Foll F (2011) Milieux côtiers, ressources marines et société. Ceser Bretagne, www.ceser-bretagne.fr
Hammer Ø, Webb KE, Depreiter D (2009) Numerical simulation of upwelling currents in pockmarks, and data from the Inner Oslofjord, Norway. Geo-Mar Lett 29:269–275. doi:10.1007/s00367-009-0140-z
Harrington PK (1985) Formation of pockmarks by pore-water escape. Geo-Mar Lett 5:193–197. doi:10.1007/BF02281638
Hasiotis T, Papatheodorou G, Kastanos N, Ferentinos G (1996) A pockmark field in the Patras Gulf (Greece) and its activation during the 14/7/93 seismic event. Mar Geol 130:333–344
Hasiotis T, Papatheodorou G, Ferentinos G (2002) A string of large and deep gas-induced depressions (pockmarks) offshore Killini peninsula, western Greece. Geo-Mar Lett 22:142–149. doi:10.1007/s00367-002-0106-x
Hily C, Le Loc’h F, Grall J, Glémarec M (2008) Soft bottom macrobenthic communities of North Biscay revisited: long-term evolution under fisheries-climate forcing. Estuar Coast Shelf Sci 78:413–425
Hovland M, Judd AG (1988) Seabed pockmarks and seepages. Graham & Trotman, London
Hovland M, Gardner JV, Judd AG (2002) The significance of pockmarks to understanding fluid flow processes and geohazards. Geofluids 2:127–136
Hovland M, Jensen S, Indreiten T (2012a) Unit pockmarks associated with Lophelia coral reefs off mid-Norway: more evidence of control by ‘fertilizing’ bottom currents. Geo-Mar Lett 32:545–554. doi:10.1007/s00367-012-0284-0
Hovland M, Jensen S, Fichler C (2012b) Methane and minor oil macro-seep systems—their complexity and environmental significance. Mar Geol 332(334):163–173
Josenhans HW, King LH, Fader GB (1978) A side-scan sonar mosaic of pockmarks on the Scotian shelf. Can J Earth Sci 15:831–840
Judd AG, Hovland M (2007) Seabed fluid flow: the impact on geology, biology and the marine environment. Cambridge University Press, Cambridge
Kelley JT, Dickson SM, Belknap DF, Barnhardt WA, Henderson M (1994) Giant sea-bed pockmarks: evidence for gas escape from Belfast Bay, Maine. Geology 22:59–62
Khandriche A, Werner F (1995) Freshwater induced pockmarks in Bay of Eckernförde, western Baltic. In: Mojski JE, Malecka J (eds) Proc 3rd marine geological conf “The Baltic”. Panstwowy Instytut Geologiczny, Warsaw, pp 155–164
King LH, MacLean B (1970) Pockmarks on the Scotian shelf. Geol Soc Am Bull 81:3141–3148
Marinaro G, Etiope G, Lo Bue N, Favali P, Papatheodorou G, Christodoulou D, Furlan F, Gasparoni F, Ferentinos G, Masson M, Rolin J-F (2006) Monitoring of a methane-seeping pockmark by cabled benthic observatory (Patras Gulf, Greece). Geo-Mar Lett 26:297–302. doi:10.1007/s00367-006-0040-4
Menier D, Reynaud JY, Proust JN, Guillaucheau F, Guennoc P, Bonnet S, Tessier B, Goubert E (2006) Basement control on shaping and infilling of valleys incised at the southern coast of Brittany, France. SEPM Spec Publ 85:37–55
Menier D, Tessier B, Proust JN, Baltzer A, Sorrel P, Traini C (2010) The Holocene transgression as recorded by incised valley infilling in a rocky coast context with a low sediment supply (southern Brittany, western France). Bull Soc Geol Fr 181(2):115–128
Muir Wood R (1994) Earthquakes, strain-cycling and the mobilization of fluids. In: Geofluids: origin, migration and evolution of fluids in sedimentary basins. Geol Soc Lond Spec Publ 78:85–98
Nelson H, Thor DR, Sanstrom MW, Kvenvolden KA (1979) Modern biogenic gas-generated craters (“sea-floor pockmarks”) on the Bering Shelf, Alaska. Bull Geol Soc Am 90(1):1144–1152
Pau M, Gisler G, Hammer Ø (2014) Experimental investigation of the hydrodynamics in pockmarks using particle tracking velocimetry. Geo-Mar Lett 34:11–19. doi:10.1007/s00367-013-0348-9
Pickrill RA (1993) Shallow seismic stratigraphy and pockmarks of a hydrothermally influenced lake, Lake Rototoiti, New Zealand. Sedimentology 40:813–828
Pilcher R, Argent J (2007) Mega-pockmarks and linear pockmark trains on the West African continental margin. Mar Geol 244:15–32
Pinot JP (1974) Le pré-continent breton, entre Penmarc’h, Belle-île et l’escarpement continental, étude géomorphologique. Impram, Lannion
Proust JN, Menier D, Guillocheau F, Guennoc P, Bonnet S, Rouby S, Le Corre C (2001) Les vallées fossiles de la baie de Vilaine: nature et évolution du prisme sédimentaire côtier du Pleistocène armoricain. Bull Soc Geol Fr 172(6):737–749
Quemart P (1993) Granulométrie par diffraction laser: application aux sédiments marins. Rapport SHOM
Rigolet C, Le Souchu P, Caisey X, Dubois SF (2011) Group sweeping: feeding activity and filtration rate in the tubiculous amphipod Haploops nirae (Kaim-Malka, 1976). J Exp Mar Biol Ecol 406(1/2):29–37
Rigolet C, Dubois S, Droual G, Caisey X, Thiébaut E (2012) Life history and secondary production of the amphipod Haploops nirae (Kaim-Malka, 1976) in the Bay of Concarneau (South Brittany). Estuar Coast Shelf Sci 113:259–271
Rigolet C, Thiébaut E, Dubois SF (2014a) Food web structures of subtidal benthic muddy habitats: evidence of microphytobenthos contribution supported by an engineer species. Mar Ecol Prog Ser (in press). doi:10.3354/meps10685
Rigolet C, Dubois SF, Thiébaut E (2014b) Benthic control freaks: effects of the tubiculous amphipod Haploops nirae on the specific diversity and functional structure of benthic communities. J Sea Res 85:413–427
Rogers JN, Kelley JT, Belknap DF, Gontz A, Barnhardt WA (2006) Shallow-water pockmark formation in temperate estuaries: a consideration of origins in the western gulf of Maine with special focus on Belfast Bay. Mar Geol 225(1/4):45–62
Scanlon KM, Knebel HJ (1989) Pockmarks in the floor of Penobscot Bay, Maine. Geo-Mar Lett 9:53–58. doi:10.1007/BF02262818
Soter S (1999) Macroscopic seismic anomalies and submarine pockmarks in the Corinthe-Patras Rift, Greece. Tectonophysics 308:275–290
Souron A (2009) Sédimentologie des vasières subtidales à Haploops spp. sur les fonds à pockmarks de Bretagne sud. Mémoire de Master2, Institut Universitaire Européen de la Mer, Plouzané
Sultan N, Marsset B, Ker S, Marsset T, Voisset M, Vernant AM, Bayon G, Cauquil E, Adamy J, Colliat JL, Drapeau D (2010) Hydrate dissolution as a potential mechanism for pockmark formation in the Niger delta. J Geophys Res 115, B08101. doi:10.1029/2010JB007453
Tessier C (2006) Caractérisation et dynamique des turbidités en zone côtière: l’exemple de la région marine Bretagne Sud. Thèse, Université de Bordeaux
Ulyanova M, Sivkov V, Kanapatskij T, Sigalevich P, Pimenov N (2012) Methane fluxes in the southeastern Baltic Sea. Geo-Mar Lett 32:535–544. doi:10.1007/s00367-012-0304-0
Van Vliet-Lanoë B, Bonnet S, Hallegouët B, Laurent M (1997) Neotectonic and seismic activity in the Armorican and Cornubian Massifs: regional stress field with glacio-isostatic influence? J Geodyn 24(1/4):219–239
Wever THF, Lühder R, Voβ H, Knispel U (2006) Potential environmental control of free shallow gas in the seafloor of Eckernförde Bay. Mar Geol 225:1–4
Whiticar MJ (1982) The presence of methane bubbles in the acoustically turbid sediments of Eckernförde Bay, Baltic Sea. In: Fanning KA, Manheim FT (eds) The dynamic environment of the ocean floor. Lexington Books, Lexington, pp 219–235
Wildish DJ, Akagi HM, McKeown DL, Pohle GW (2008) Pockmarks influence benthic communities in Passamaquoddy Bay, Bay of Fundy, Canada. Mar Ecol Prog Ser 357:51–66
Acknowledgements
We would like to thank the REBENT monitoring program for benthic habitats, the Brittany region, and the Total Foundation for Biodiversity and the Sea for their funding. We are particularly grateful to the crews of the R/V Côte d’Aquitaine and R/V Haliotis for their help during the cruises, and to Jean-Claude Caprais for technical assistance in conducting methane analyses. The article benefitted from constructive feedback from L.L. Brothers, an anonymous reviewer, the guest editor C. Pierre and the journal editors.
Author information
Authors and Affiliations
Corresponding author
Additional information
Responsible guest editor: C. Pierre
Rights and permissions
About this article
Cite this article
Baltzer, A., Ehrhold, A., Rigolet, C. et al. Geophysical exploration of an active pockmark field in the Bay of Concarneau, southern Brittany, and implications for resident suspension feeders. Geo-Mar Lett 34, 215–230 (2014). https://doi.org/10.1007/s00367-014-0368-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00367-014-0368-0