Alkenones in the Mediterranean Sea

Time-series of downward alkenone fluxes have been investigated at 200 m depth over a one year sediment trap experiment, in the Northwestern Mediterranean Sea. Alkenone flux maxima occurred in autumn and to a lesser extent in May, during the spring bloom. Temperature estimates calculated from the UK'37 index revealed that alkenone producers preferentially develop in subsurface waters (at about 50 m) in spring, whereas the autumn alkenone production occurred upper in the water column (around 30 m). Examination of the core-top UK'37 index values at various sites of the Northwestern Mediterranean basin, suggested that the spring bloom period do not significantly imprint the temperatures recorded in the sediments. The sedimentary temperature estimates would rather reflect annually integrated SST, with a major influence of the autumnal post-bloom development of the coccolithophores in the euphotic zone.本研究针对地中海西北部海域开展了为期一年的沉积物捕获器实验（sediment trap experiment），对200米水深处的下沉烯酮通量（downward alkenone fluxes）进行了时序监测与分析。研究结果显示，烯酮通量峰值集中出现于秋季，春季水华（spring bloom）期间的5月仅存在相对较弱的通量峰值。基于UK'37指数（UK'37 index）计算得到的温度估算结果表明：春季时，烯酮生产者主要在约50米的次表层水体中繁衍，而秋季的烯酮生产则集中在水柱上层约30米处。对地中海西北部盆地多个站位的表层沉积物岩芯UK'37指数值进行分析后可知，春季水华期并未在沉积物记录的温度中留下显著印记。沉积物的温度估算结果实则反映的是年际整合的海表温度（sea surface temperature，SST），其主要受秋季透光带（euphotic zone）内颗石藻（coccolithophores）水华后发育过程的显著影响。