Ba/Ca variations in the modern intertidal bean clam Donax gouldii: An upwelling proxy?

The discovery and calibration of high resolution paleoceanographic proxies is necessary to extend historic climate records and to understand regional climate variability. Chemical variations of skeletal remains have emerged as an often reliable recorder of environmental conditions. Specifically, Ba/Ca ratios have been correlated to temperature, salinity, seawater Ba/Ca, and phytoplankton biomass, although, many of these relationships appear taxon- and location-specific. To assess the sub-weekly Ba/Ca variations in the intertidal shallow-burrowing bivalve Donax gouldii, specimens were collected from the Southern California Bight, skeletal growth increments were cross-dated based on tidal-driven growth patterns, and skeletal aragonite Ba/Ca was determined using laser ablation inductively coupled plasma mass spectrometry. Cross-dated growth among specimens revealed a simultaneous, large, and transient Ba/Ca peak in all shells. The timing of peak Ba/Ca was compared to a suite of locally measured physical and biological data, including temperature, salinity, density, nitrate, silicate, chlorophyll, diatom abundance, dinoflagellate abundance, and phytoplankton community composition. Based on cross-dated chronologies, Ba/Cashell is significantly correlated with Chl a from six and nine days prior and nutrients (nitrate, phosphate, silicate, and nitrite) from three days prior. In this system diatom abundance was not related to Ba/Cashell. Transiently higher seawater Ba/Ca resulting from upwelling may be reflected in peak Ba/Cashell, however the exact mechanisms leading to population wide Ba/Ca peaks remains enigmatic.