Alkenones and TEX86 temperature proxies for core-top sediments from the southern Adriatic Sea@en

The Mediterranean Sea is at the transition between temperate and tropical air masses and as such of importance for studying climate change. The Gulf of Taranto and adjacent SW Adriatic Sea are at the heart of this region. Their sediments are excellently suited for generating high quality environmental records for the last millennia with a sub-decadal resolution. The quality of these records is dependent on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment. Here, we examine and calibrate the UK'37 and TEX86 lipid-based temperature proxies in 48 surface sediments and relate these to ambient sea surface temperatures and other environmental data. The UK'37-based temperatures in surface sediments reflect winter/spring sea surface temperatures in agreement with other studies demonstrating maximum haptophyte production during the colder season. The TEX86-based temperatures for the nearshore sites also reflect winter sea surface temperatures. However, at the most offshore sites, they correspond to summer sea surface temperatures. Additional lipid and environmental data including the distribution of the BIT index and remote-sensed chlorophyll-a suggest a shoreward increase of the impact of seasonal and spatial variability in nutrients and control of planktonic archaeal abundance by primary productivity, particle loading in surface waters and/or overprint by a cold-biased terrestrial TEX86 signal. As such the offshore TEX86 values seem to reflect a true summer signal to the effect that offshore UK'37 and TEX86 reconstruct winter and summer temperature, respectively, and hence provide information on the annual temperature amplitude.地中海地处温带气团与热带气团的过渡地带，因此在气候变化研究中具有重要意义。塔兰托湾（Gulf of Taranto）及毗邻的亚得里亚海南部海域正是该区域的核心区域。其表层沉积物极佳地适配于重建近千年来分辨率达亚十年级的高质量环境记录。这类环境记录的质量，取决于对转移函数的精准校准——该函数用于将沉积脂质信号转化为局地环境参数。本研究对48个表层沉积物中基于脂质的UK'37温度代用指标（UK'37）与TEX86温度代用指标（TEX86）进行了校准与检验，并将其与实际海表温度及其他环境数据建立关联。与其他研究结论一致，基于UK'37的表层沉积物温度结果反映了冬/春季海表温度，这印证了定鞭金藻（haptophyte）在寒冷季节生产力达到峰值的观点。近岸站点的TEX86温度结果同样对应冬季海表温度；但在离岸最远的站点，TEX86温度则对应夏季海表温度。额外的脂质与环境数据，包括BIT指数（BIT index）分布与遥感叶绿素-a（chlorophyll-a）数据，表明营养盐的季节与空间变异的影响、浮游古菌（planktonic archaeal）丰度受初级生产力、表层水体颗粒物负荷的调控，以及受冷偏向性陆地TEX86信号的叠加影响均呈现向岸递增的趋势。因此，离岸区域的TEX86数值似乎能反映真实的夏季温度信号，换言之，离岸区域的UK'37与TEX86可分别重建冬季与夏季温度，进而提供年温度振幅的相关信息。