Sea surface temperature proxy comparison for the Pliocene North Sea

Abstract

The Pliocene (5.3 – 2.6 Ma) is seen as a good analogue for the climate of the near future, due to slightly higher global temperatures (i.e. 2-3 °C) and similar atmospheric CO2 concentrations (400 ppm) compared to the present. However, reliable data are needed to validate models that make projections of future climate. In this study, we have used sediments from a core in the coastal North Sea to test and compare three sea surface temperature (SST) proxies based on biomarkers: i.e. UK’37, TEX86H and LDI, on their ability to reconstruct SSTs of the Pliocene North Sea. The SSTs are compared with the continental mean air temperature record of the same site produced using biomarkers (branched GDGTs). The influence of sea level changes and terrestrial input are also investigated. The SST proxy comparison demonstrates that the UK’37 and LDI proxies respond to the same driver, i.e. temperature, but to a different extent, probably due to different production seasons of the biomarkers used in the proxies. The TEX86H proxy shows trends not consistent with the other two SST proxies, and is therefore assumed not reliable in this setting. Large fluctuations in SSTs are seen, most likely caused by changes in the configuration of the North Atlantic current. Finally, comparison of the marine and terrestrial climates shows that they are decoupled. The mechanism for this decoupling could be a result of regional ocean currents influencing marine climate, while the terrestrial climate largely follows global climate fluctuations.