南海沉降颗粒物U37K＇指标的影响因素初探

INFLUENCING FACTORS OF U37K＆#39; INDEX IN SINKING PARTICLES IN THE SOUTH CHINA SEA

根据南海不同海区的时间序列沉降颗粒物的U37K＇指标及基于该指标估算的海表温度（Sea Surface Temperature,简称SST）,试图探讨现代过程对地球化学古环境参数的改造.结果表明,通过沉降颗粒物中U37K＇估算的SST与卫星测算的SST在大多数时段并不一致.其中,颗粒物的侧向运动可能会使得U37K＇估算的SST与遥感SST不一致,而颗石藻的层位效应可能使U37K＇估算的SST低于遥感SST.另外,沉降过程中U37K＇指标并无明显的改变,表明有机质沉降过程中的降解作用对U37K＇温度估算影响较小.然而已有的研究表明,南海表层沉积物U37K＇估算的SST与上层多年平均的实测温度有较好的相关性,表明代表几十至几百年的表层沉积物,能够对短时间和局地的差异进行＂平滑＂.综上所述,局部的差异（捕获器样品）并不与全局的变化趋势（表层沉积物）相矛盾,U37K＇指标仍是研究南海古温度的良好替代指标,但为提高U37K＇估算温度和解释现象的可靠性,现代过程的研究仍然有重要意义.

The U37K＇ index derived from alkenone produced by haptophytes has been wildly used to reconstruct the paleosea surface temperature （SST）. In this study, the alkenone concentration and U37K＇ index of sinking particulate matter collected by time series sediment trap in the South China Sea （SCS） from 1995 to 1999 were analyzed, to discuss potential modification of U37K＇ index by modern oceanic processes. The sediment traps were deployed at four sites, namely SCS-N station （18.5°N, 116.0°E） in the northern basin, SCS-C station （14.7°N, 115.1°E） in the central basin, SCS-SW station （11.9°N, 110.0°E） in the southwestern basin and SCS-NE station （17.3°N, 119.5°E） in the northeastern basin, respectively. The SST estimated by U37K＇ index of sinking particle varied from 18.6℃ to 29.3℃, which are highly differed from the SST derived from remote sensing. Also there was decoupling of SST derived from shallow and deep trap particles during the same periods. The discrepancies were mainly attributed to the advection of sinking particle, which is related to the upper ocean circulation of the SCS basin. Moreover, the variability in living depth of originated algae of alkenone could also account for a lower SST from u37K＇ index than that from remote sensing. On the other hand, no significant change of U37K＇ index of particles during settling process in the water column suggested few effect of organic matter degradation on U37K＇ index. However, a good correlation between the SST estimated by U37K＇ of surface sediment and the annual average temperature from the upper layer （30m） in the SCS suggested a long term sediment record （decadal to millennial） may smooth the short term and local fluctuations of environment signals. Although the U37K index is a good proxy to study the paleo-temperature of SCS, more attention should be paid to quantify the modification of biomarker proxy by physical and biogeochemical processes in the future.