17The Mediterranean Sea is at the transition between temperate and tropical air masses and as 18 such of importance for studying climate change. The Gulf of Taranto and adjacent SW 19 Adriatic Sea are at the heart of this region. Their sediments are excellently suited for 20 generating high quality environmental records for the last millennia with a sub-decadal 21resolution. The quality of these records is dependent on a careful calibration of the transfer 22 functions used to translate the sedimentary lipid signals to the local environment. Here, we 23 examine and calibrate the U K" 37 and TEX 86 lipid-based temperature proxies in 48 surface 24 sediments and relate these to ambient sea surface temperatures and other environmental data. 25The U K" 37 -based temperatures in surface sediments reflect winter/spring sea surface 26 *Manuscript Click here to view linked References 2 temperatures in agreement with other studies demonstrating maximum haptophyte production 27 during the colder season. The TEX 86 -based temperatures for the nearshore sites also reflect 28 winter sea surface temperatures. However, at the most offshore sites, they correspond to 29 summer sea surface temperatures. Additional lipid and environmental data including the 30 distribution of the BIT index and remote-sensed chlorophyll-a suggest a shoreward increase 31 of the impact of seasonal and spatial variability in nutrients and control of planktonic archaeal 32 abundance by primary productivity, particle loading in surface waters and/or overprint by a 33 cold-biased terrestrial TEX 86 A valid and powerful method to better understand short-term environmental and climate 44 change is to study the past. The interactions between atmosphere and ocean are complex so 45 deciphering them requires quantitative and reliable proxies for key environmental parameters 46 such as temperature, air pressure, sea level and the precipitation-evaporation budget. This is 47 also valid for the Mediterranean climate, which is especially sensitive to climate change due 48 to its location between the subtropical high-pressure belt and mid-latitude westerlies (e.g., 49 Trigo et al., 1999; Xoplaki et al., 2003 Xoplaki et al., , 2004. 50As Sea Surface Temperature (SST) is an important factor in the Earth"s climate, its 51 reconstruction is essential for an understanding of past climate change. The commonly used 52 geochemical temperature proxies include  18 O and Mg/Ca ratios of planktonic foraminifera 53 (Erez & Luz, 1983; Nürnberg et al., 1996; Elderfield & Ganssen, 2000), the U K" 37 from 54 alkenones synthesized by haptophytes (Prahl & Wakeham, 1987) and the TEX 86 based on 55 archaeal isoprenoidal tetraether lipids (Schouten et al., 2002; Kim et al., 2008). 56The U K" 37 exploits the observation that the abundance of the diunsaturated C 37 methyl 57 alkenone, relative to the total of di-and triunsaturated C 37 methyl alkenones in surface waters 58 and algal cultures increases with increasing water temperature. These alkenones are produced 59 by a...

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Biosynthesis of C29 sterols, enhancing eukaryotic temperature resistance, evolved during the global Neoproterozoic glaciations.

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