长链1,13-和1,15-二醇是在海洋环境中普遍存在的脂质,和长链二醇指数(LDI),根据它们的分布,以前曾被引入作为海面温度的代理。长链1,13-和1,15-二醇的主要生物来源仍然未知,但是我们对来自地中海的悬浮颗粒物进行的脂质和23S核糖体RNA(23SrRNA)的组合分析表明,这些脂质是由海洋eustigmattryte类群产生的,该类群起源于目前已知的eustigmattrytes多样化之前。18SrRNA数据证实了早期分枝的海洋eustigmaturtes的存在,在全球范围内发生。LDI记录与其他古温度代理之间的差异通常归因于代理相关生物发生的季节之间的差异。我们的结果,结合来自表层沉积物的可用LDI数据,表明LDI主要记录混合层深度时最热月份的温度,盐度,营养浓度低。LDI可能不适用于Proboscia硅藻贡献1,13-二醇的地区,但这可以通过C281,12二醇的增加贡献来认识。淡水输入也可能影响温度和LDI之间的相关性,但是相对的C321,15-二醇丰度有助于识别和纠正这些影响。当考虑到这些因素时,LDI的校准误差为2.4°C。作为最温暖季节温度的明确代表,LDI可以解锁重要且以前无法获得的古气候信息,从而大大改善我们对过去气候条件的了解。
Long chain 1,13- and 1,15-diols are lipids which are omnipresent in marine environments, and the Long chain Diol Index (
LDI), based on their distributions, has previously been introduced as a proxy for sea surface temperature. The main biological sources for long chain 1,13- and 1,15-diols have remained unknown, but our combined lipid and 23S ribosomal RNA (23S rRNA) analyses on suspended particulate matter from the Mediterranean Sea demonstrate that these lipids are produced by a marine eustigmatophyte group that originated before the currently known eustigmatophytes diversified. The 18S rRNA data confirm the existence of early-branching marine eustigmatophytes, which occur at a global scale. Differences between LDI records and other paleotemperature proxies are generally attributed to differences between the seasons in which the proxy-related organisms occur. Our results, combined with available
LDI data from surface sediments, indicate that the
LDI primarily registers temperatures from the warmest month when mixed-layer depths, salinity, and nutrient concentrations are low. The
LDI may not be applicable in areas where Proboscia diatoms contribute 1,13-diols, but this can be recognized by enhanced contributions of C28 1,12 diol. Freshwater input may also affect the correlation between temperature and the
LDI, but relative C32 1,15-diol abundances help to identify and correct for these effects. When taking those factors into account, the calibration error of the
LDI is 2.4 °C. As a well-defined proxy for temperatures of the warmest seasons, the LDI can unlock important and previously inaccessible paleoclimate information and will thereby substantially improve our understanding of past climate conditions.