A four-year record of UK'37- and TEX86-derived sea surface temperature estimates from sinking particles in the filamentous upwelling region off Cape Blanc, Mauritania

Lipid biomarker records from sinking particles collected by sediment traps are excellent tools to study the seasonality of biomarker production as well as processes of particle formation and settling, ultimately leading to the preservation of the biomarkers in sediments. Here we present records of the biomarker indices UK'37 based on alkenones and TEX86 based on isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs), both used for the reconstruction of sea surface temperatures (SST). These records were obtained from sinking particles collected using a sediment trap moored in the filamentous upwelling zone off Cape Blanc, Mauritania, at approximately 1300 water depth during a four-year time interval between 2003 and 2007. Mass and lipid fluxes are highest during peak upwelling periods between October and June. The alkenone and GDGT records both display pronounced seasonal variability. Sinking velocities calculated from the time lag between measured SST maxima and minima and corresponding index maxima and minima in the trap samples are higher for particles containing alkenones (14-59 m/d) than for GDGTs (9-17 m/d). It is suggested that GDGTs are predominantly exported from shallow waters by incorporation in opal-rich particles. SST estimates based on the UK'37 index faithfully record observed fluctuations in SST during the study period. Temperature estimates based on TEX86 show smaller seasonal amplitudes, which can be explained with either predominant production of GDGTs during the warm season, or a contribution of GDGTs exported from deep waters carrying GDGTs in a distribution that translates to a high TEX86 signal.由沉积物捕集器（sediment trap）采集的沉降颗粒中的脂质生物标志物记录，是研究生物标志物生产季节动态、颗粒形成与沉降过程，最终实现生物标志物在沉积物中保存机制的优良研究工具。本文报道了基于烯酮类化合物（alkenones）的UK'37生物标志物指数，以及基于类异戊二烯甘油二烷基甘油四醚（isoprenoid glycerol dialkyl glycerol tetraethers, GDGTs）的TEX86指数的观测记录，二者均用于海表温度（sea surface temperatures, SST）的重建。这些记录取自2003至2007年四年监测时段内，在毛里塔尼亚布兰科角外丝状上升流区、水深约1300米处锚定的沉积物捕集器所采集的沉降颗粒。质量通量与脂质通量在10月至次年6月的上升流峰值期达到最高水平。烯酮类与GDGTs的观测记录均呈现显著的季节变异性。通过实测海表温度极值与捕集器样品中对应生物标志物指数极值之间的时间滞后计算得到的沉降速率，含烯酮类颗粒（14~59米/天）高于GDGTs颗粒（9~17米/天）。研究表明，GDGTs主要通过结合在富蛋白石颗粒中从浅水区向外输出。基于UK'37指数的海表温度估算值，准确记录了研究时段内观测到的海表温度波动。基于TEX86的温度估算值呈现更小的季节振幅，这可通过两种机制解释：其一为GDGTs主要在暖季产生；其二为从深水区输出的GDGTs贡献了信号，这类GDGTs的分布对应较高的TEX86信号。