High frequency Barium profiles in shells of the Great Scallop iPecten maximus/i: a methodical long-term and multi-site survey in Western Europe

摘要

Skeletal barium/calcium ([Ba]/[Ca])_shell ratios were measured everythird daily striae in 39 flat valves of the Great Scallop Pecten maximus collected intemperate coastal environments of Western Europe. A methodical evaluation ofthe ([Ba]/[Ca])_shell ratio was performed for the first time anddemonstrates that ([Ba]/[Ca])_shell profiles are reproducible forseveral scallop individuals from the same population (2-year old; 3shells/year), over a 7-year period (1998–2004), and from different coastalenvironments in France (42–49° N). As previously determined in the shellsof other bivalve species, ([Ba]/[Ca])_shell profiles generally exhibiteda background ratio punctuated by two transient maxima occurring in early andlate summer. Background partition coefficient (D_Ba=0.11±0.03,in 2000) was similar to that previously reported in P. maximus shells, suggesting adirect shell uptake of dissolved seawater Ba (Gillikin et al.,2008). The 7-year survey in the Bay of Brest of the high frequency([Ba]/[Ca])_shell profiles in the scallop's shell was exploited tobetter constrain both the occurrence and the amplitude of the summer Barelative enrichments as influenced by environmental processes. Seawater Bacontents in 2000 underlined significant particulate Ba inputs at thesediment water interface (SWI) during ([Ba]/[Ca])_shell peak events.These Ba inputs are thus suggested to be subsequently induced by a pelagicbiogenic process, which mainly occurs under summer post-bloom conditions inrelationship to the cycling of particulate organic matter and associated Ba.The long term survey reveals that such pelagic Ba cycling processes areresponsible for particulate Ba inputs to the sediment water interface (SWI).Subsequent indirect Ba uptake by the bivalve results in higher([Ba]/[Ca])_shell ratios, in that archived Ba within the shell cannot beused as a direct paleo productivity tracer. Our methodical approach, basedon a multi-year and multi-site-survey of ([Ba]/[Ca])_shell ratio inScallop bivalves, allows us to establish the potential application of suchhigh frequency archives for further biogeochemical and ecologicalinvestigations of bivalves in the coastal environment.