Quantitative assessment of the salinity gradient within the estuarine systems in the southern Bay of Biscay using benthic foraminifera

In order to assess quantitatively the foraminiferal response to the relative distance from the estuary mouth (RDEM) in the estuarine systems from the southern Bay of Biscay, a foraminifera-based transfer function has been developed using two models based on a modern dataset of 88 samples and 41 species obtained from six estuaries in northern Spain. We consider the RDEM of the foraminiferal assemblages as a proxy for salinity. The relationship between observed and foraminifera-predicted RDEM illustrates the strong performance of the transfer function (rjack2 ranges from 0.73 to 0.76). These results indicate that precise reconstructions of former RDEM are possible. In fact, the transfer functions have relatively low root-mean-square errors of prediction (expressed as a percentage of the range of the modern environmental gradient sampled), ∼11%, which is comparable to other foraminifera-based transfer functions from the northern Atlantic Ocean. This is even more important considering that it is of a regional significance and that the sampling was performed randomly to minimize sample autocorrelation and the possible correlation among the different variables controlling the foraminiferal distribution (e.g., elevation and salinity).