Barium and molybdenum records in bivalve shells: Geochemical proxies for phytoplankton dynamics in coastal environments?

Abstract

Barium : calcium and molybdenum : calcium ratios were investigated in shells of the tropical scallop Comptopallium radula. Three juvenile specimens were harvested alive in the southwest lagoon of New Caledonia after a 1-yr hydrological survey. Calcite samples representing a few hours of biomineralization were laser-ablated along the maximal growth axis and analyzed for Ba and Mo content with an inductively coupled plasma mass spectrometer. Absolute dates of shell precipitation assigned on the basis of periodic formation of shell growth patterns led to the accurate reconstruction of ontogenetic variations of elemental ratios with subweekly resolution. Interindividual variability of Ba : Ca and Mo : Ca time series was low, indicating an environmental control on the incorporation of these elements within shells. Both profiles were characterized by a background level punctuated by sharp peaks. The ingestion of diatoms enriched in Ba (adsorbed on iron oxyhydroxides associated with the frustules) is the most likely cause of the formation of Ba : Ca peaks. Some contribution of diatom-associated barite is also possible. In every instance, Ba : Ca would possibly be a proxy for the timing and magnitude of diatom blooms. Among all the theories that could be advanced to explain the occurrence of Mo : Ca peaks, the most plausible appears to be the ingestion of phytoplankton cells grown on NO { 3 , and therefore containing high levels of Mo required for the activity of nitrate reductase. If this is so, then Mo : Ca could be a new proxy for nitrate uptake by phytoplankton in coastal ecosystems, helping to reconstruct the balance between new and regenerated production in paleoenvironments.

Spring molybdenum enrichment in scallop shells: a potential tracer of diatom productivity in temperate coastal environments (Brittany, NW France)

“…Barats et (Thébault et al, 2009). Our data may support these assumptions, but none of these pathways can be completely demonstrated.…”

“…This statement also agrees with the Mo concentration in phytoplankton cell data obtained from experimental culture on various genera and species which did not show Mo cell enrichment under controlled growing conditions Quigg et al, 2003). Mo cell enrichment would however, be induced by environmental and physiological conditions such as light limitation (Finkel et al, 2006) or nitrate utilization (Thébault et al, 2009). This last hypothetic process could be conclusive for the Bay of Brest exhibiting significant nitrate inputs from human activities (Ragueneau et al, 2002).…”

“…The variations of trace element shell concentrations provide significant and highly detailed historical information (Freitas et al, 2005(Freitas et al, , 2006Lorrain et al, 2005;Barats, 2006;Barats et al, 2007Barats et al, , 2008. For example, manganese (Mn) concentrations along the shell were recently demonstrated to be mainly governed by concentrations of dissolved Mn at the SWI (sediment water interface) being themselves controlled by freshwater inputs and benthic release (Freitas et al, 2006;Barats et al, 2008 Gillikin et al, 2008;Thébault et al, 2009).…”

Reconstructing past upwelling intensity and the seasonal dynamics of primary productivity along the Peruvian coastline from mollusk shell stable isotopes

“…Lorrain et al [2004] showed that in scallop shells, these ontogenetic d 13 C trends were due to increasing contribution of respired carbon with the body size. An influence of food availability was also suggested by Van der Putten et al [2000] because of decreasing d 13 C values associated with Mn and Ba peaks which are believed to be related to phytoplankton blooms [Stecher et al 1996;Gillikin et al, 2006b;Thébault et al, 2009]. However, the majority of the shell d …”

Local-scale variation in trace elemental fingerprints of the estuarine bivalve Austrovenus stutchburyi within and between estuaries

“…It has previously been demonstrated that differences in the incorporation of elements to bivalve shell vary between larval and recruited shell (Zacherl et al 2009). It has also been found that the diet of individuals may influence the uptake of elements into bivalve shell (Thebault et al 2009 Table 2 possible that prodissoconch shell initially consists primarily of amorphous calcium carbonate (ACC), which later transitions to aragonite (Weiss et al 2002). Both differences in the structure of ACC as well as changes as this precursor transitions to aragonite have the potential to prevent comparisons being made between prodissoconch and settled shell material (Weiss et al 2002).…”