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

Abstract:

The scientific question in this paper is focused on how water column processes of particulate matter affect geochemical indicator such as U^K₃₇ paleo-SST proxy. Based on U^K₃₇ 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 U^K₃₇ paleo-SST proxy affected by modern processes. Results show that sea surface temperature (SST) estimated by U^K₃₇ in settling particulate matter differs from the upper layer remote sensing temperature data in most cases and decoupling of particulate matter U^K₃₇ 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 U^K₃₇ index during particle settling in the water column is unconspicuous, implying a weak effect of Particulate Organic Matter (POM) degradation on the estimation of U^K₃₇ temperature. Contemporary, the SST estimated by U^K₃₇ 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 U^K₃₇ index is a good proxy to study the paleotemperature of SCS, the study of modern processes are still of great significance.