Biomarker paleo-proxy affected by modern processes in the South China Sea: UK37 as an example

The scientific question in this paper is focused on how water column processes of particulate matter affect geochemical indicator such as UK37 paleo-SST proxy. Based on UK37 index of sinking particles collected by time-series sediment traps in four stations as well as surface sediment samples in South China Sea (SCS), we attempt to explore the how geochemical parameter such as UK37 paleo-SST proxy affected by modern processes. Results show that sea surface temperature (SST) estimated by UK37 in settling particulate matter differs from the upper layer remote sensing temperature data in most cases and decoupling of particulate matter UK37 signals between upper and deep traps was also found in some cases. Coccolith living depth fluctuation in the euphotic zone could cause a lower estimated SST than remote SST, while advection of particle could cause an opposite effect. On the other hand, the variation of UK37 index during particle settling in the water column is unconspicuous, implying a weak effect of Particulate Organic Matter (POM) degradation on the estimation of UK37 temperature. Contemporary, the SST estimated by UK37 in surface sediment shows a good correlation with annual average temperature from upper layer in the SCS, suggesting a long term sediment record (decadal to millennial) may smooth the short term and local fluctuations of environment signals. In conclusion, although the UK37 index is a good proxy to study the paleotemperature of SCS, the study of modern processes are still of great significance.