Earthworm secreted calcite granules - constructing a new terrestrial palaeo-environment thermometer and quantifying carbon sequestration potential

本研究旨在确定蚯蚓分泌方解石颗粒中C、O同位素组成在不同温度和二氧化碳浓度下的变化。我们将研究是否发生了系统的同位素变化，可以用来解释颗粒形成过程中的地球温度和二氧化碳水平，并将我们的数据应用于来自一系列考古遗址的颗粒：Silbury (4130-4395 BP), Boxgrove（中更新世），Laacher See (12900 BP), Odiham Castle（公元1207-1216年）和Ventnor （11690 BP）。我们将制作一个独特的环境解释工具，地质考古学家可以用它来解释过去人类活动时期的环境状况。这是因为颗粒每天都在排泄，通过分析颗粒的范围，我们可以得到在日期剖面/序列中每天经历的温度范围。这对于理解过去的高分辨率气候序列具有巨大的潜力。蚯蚓分泌方解石颗粒。迄今为止，我们在NERC资助下的研究表明，陆生蚓每天平均每只蚯蚓产生0.8毫克碳酸钙，产生直径达2毫米的颗粒。我们的溶解实验表明，蚯蚓分泌的方解石与无机产生的方解石的溶解速度相同，模型表明，与我们的颗粒大小相同的方解石颗粒可以在体积pH值低至5.4的土壤中存活1000 - 10000年。此外，还从Silbury和Boxgove沉积物中回收了颗粒。来自锡尔伯里的那些用14C测定了4130 - 4395年BP，我们用u系列测年法测定了4670年BP。显然蚯蚓分泌的方解石颗粒可以在土壤中存活很长一段时间。在我们的初步工作的支持下，这增加了一种令人兴奋的可能性，即测定单个颗粒的年代并测量它们的碳氧同位素，以解释它们形成时的环境条件。单个颗粒含有足够高浓度的U和低浓度的Th，因此可以应用U系列测年法。它们具有C和O同位素特征，表明它们来自土壤有机质、大气气体和土壤水的混合物。由于它们含有大气氧的成分，它们的同位素特征应该随温度而波动。我们将在三种不同的土壤中以不同的温度和二氧化碳浓度的阶因安排培养陆生草-所有可能的温度和二氧化碳浓度的组合将被调查。我们将在30天、60天、90天和120天后对颗粒进行取样，以确认同位素已达到稳定状态。我们预计，这将是在以往的研究基础上，调查C掺入颗粒的情况。我们的系统和颗粒的不同组分的同位素组成的差异将根据温度绘制，以确定同位素组成与温度之间的关系。我们将通过在相同的3种土壤中培养陆生草来确定颗粒中大气、水和有机物C和O的相对比例。我们将在已知不同同位素组成的水分含量的环境二氧化碳条件下进行实验。为了降低成本，我们将使用中东和美国的矿泉水。我们将在30、60、90和120天后再次对颗粒进行取样。我们将使用混合图3来确定我们的颗粒中不同C和O源的相对比例。最后，我们将对我们的项目合作伙伴（English Heritage, Boxgrove）捐赠的颗粒进行U/Th测年和C和O分析，并利用我们之前实验中得出的关系来解释颗粒形成过程中的环境条件。这将有助于解释这些重要的考古遗址。

This proposal seeks to determine the variation of C and O isotope compositions in earthworm secreted calcite granules under different temperatures and concentration of carbon dioxide. We will investigate whether systematic isotopic variation occurs that can be used to interpret terrestrial temperature & carbon dioxide levels during granule formation, and apply our data to granules from a range of archaeological sites: Silbury (4130-4395 BP), Boxgrove (Mid Pleistocene), Laacher See (12900 BP), Odiham Castle (1207-1216 AD) and Ventnor (11690 BP). We will produce a unique environmental interpretation tool that Geoarchaeologists can use to interpret environmental conditions during periods of past human activity. This is because granules are excreted on a daily basis and by analysing a range of granules this will give us the daily temperature ranges experienced during the dated profile/sequence. This has enormous potential for understanding past high resolution climate sequences Earthworms secrete granules of calcite. Our NERC funded investigations to date suggest that Lumbricus terrestris earthworms produce granules of up to 2 mm diameter at an average rate of 0.8 mg of CaCO3 per earthworm per day. Our dissolution experiments indicated that earthworm secreted calcite dissolves at the same rate as inorganically produced calcite and modelling suggests that calcite grains the same size as our granules can survive for 1000 - 10000 years in soils of bulk pH as low as 5.4. In addition granules have been recovered from Silbury and Boxgove sediments. Those from Silbury have been dated using 14C as 4130 - 4395 years BP and 4670 years BP by ourselves using U-series dating Clearly earthworm secreted calcite granules can survive for significant periods of time in soils. This raises the exciting possibility, supported by our preliminary work, of dating individual granules and measuring their C & O isotopes to interpret the environmental conditions during their formation. Individual granules contain sufficiently high concentrations of U and low concentrations of Th that U-series dating can be applied. They have C and O isotopic signatures indicative of derivation from a mixture of soil organic matter, atmospheric gases and soil water. As they contain a component of atmospheric oxygen their isotopic signature should fluctuate with temperature We will investigate isotope dynamics of the granules in several ways 1. We will culture L. terrestris in three different soils at different temperatures and carbon dioxide concentrations in a factorial arrangement - all possible combinations of temperature and carbon dioxide concentration will be investigated. We will sample granules after 30, 60, 90 and 120 days to confirm that isotopic steady state has been achieved. We anticipate that this will be the case on the basis of previous studies investigating C incorporation into granules. Differences in the isotopic compositions of the various components of our system and granules will be plotted against temperature to determine a relationship between isotopic composition and temperature 2. We will confirm the relative proportions of atmospheric, aqueous and organic matter C and O present in the granules by culturing L. terrestris in the same 3 soils. We will conduct the experiments at ambient carbon dioxide conditions with known moisture contents of different isotopic compositions. To keep costs down we will use Middle Eastern and American mineral waters. Again we will sample granules after 30, 60, 90 and 120 days. We will determine the relative proportions of our different C and O sources in our granules using mixing diagrams 3. Lastly we will perform U/Th dating and C and O analyses on granules donated by our project partners (English Heritage, Boxgrove) and interpret environmental conditions during granule formation using the relationships derived in our previous experiments. This will help interpret these important archaeological sites.