FORAMINIFERAL STUDIES FOR DEPICTING THE RECENT SEA-LEVEL CHANGE: COMPARING MARSHES FROM EAST TO WEST NORTH ATLANTIC COASTS

Vertical foraminiferal distribution in temperate marshes is argued to resolve relative sea-level determinations within ±5 cm. Although sea-level rise and marsh accretion are not exactly in balance, high marshes lie close to the hypothetical equilibrium state. Therefore, estimating sea-level rise from sedimentary sequences of marsh peat has received increasing attention. While USA east coast marshes present long peat sequences dominated by organic deposition their counterparts in Europe are profoundly different. Although superior reconstructions of former sea level have been confined to eastern N. America, European marshes can also provide relevant information to assess the recent sea-level change. We present here results of the potential use of marsh sites from both Delaware Bay (west N. Atlantic) and northern Spain (east N. Atlantic). While in the Delaware marshes we have studied infaunal distribution and performed field experiments to assess the impact of bioturbation, in the European marshes we have developed a transfer function in order to evaluate the faunal response to tidal elevation and studied four short cores to assess the reconstruction of the recent environmental and sea-level change. Bioturbation in the Delaware marshes is relatively low for high, intermediate and low marsh and dominates in summer; however, burial rates are rapid although mixed layer thickness is large for intermediate and low marsh plots. These results show a very good temporal resolution for the high and intermediate marsh plots, as well as for the low marsh when burial rates are around 10 mm yr-1. Infaunal distributions support these results. In the Spanish marshes the transfer function presented a strong performance (r2jack = 0.87). Indeed, these results indicated that precise reconstructions of former sea levels are possible (RMSEPjack = 0.27 m). We dated all four cores using 137Cs and 210Pb-derived sediment accumulation rates. However, only one presented more the 200 years of continuous marsh record whereas the others present at least a 100 years record. These results support the use of marsh sediments for high resolution sea-level studies at both sides of the Atlantic, although extensive site specific knowledge is needed. Acknowledgements: This is a contribution to the UNESCO06/08, GIU06/10 and IGCP 495 projects.