Development of a foraminifera-based transfer function in the Basque marshes, N. Spain: Implications for sea-level studies in the Bay of Biscay

In order to reconstruct former sea level we have developed a foraminifera-based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four Basque marshes in Northern Spain. The relationship between observed and foraminifera-predicted elevation illustrated the strong performance of the transfer function (r²_jack ranges from 0.74 to 0.81). These results indicated that precise reconstructions of former sea levels are possible (error ranges from 0.11 to 0.19 m). The transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core. We placed the foraminifera-based reconstructions into a temporal framework using ¹³⁷Cs, Pb concentrations, and ²¹⁰Pb-derived sediment accumulation rates. The resulting relative sea-level curve is in good agreement with regional tide-gauge data. Both instrumental data and microfossil records suggest a rate of relative sea-level rise of approximately 2 mm yr^{- 1} for the 20th century.