Lucassen Friedrich, Pritzkow Wolfgang, Rosner Martin, Sepúlveda Fernando, Vásquez Paulina, Wilke Hans, Kasemann Simone A
Department of Geosciences and MARUM-Center for Marine Environmental Sciences, Universität Bremen, Bremen, Germany.
Department of Analytical Chemistry and Reference Materials, Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany.
PLoS One. 2017 Jun 8;12(6):e0179440. doi: 10.1371/journal.pone.0179440. eCollection 2017.
Seabird excrements (guano) have been preserved in the arid climate of Northern Chile since at least the Pliocene. The deposits of marine organic material in coastal areas potentially open a window into the present and past composition of the coastal ocean and its food web. We use the stable isotope composition of nitrogen and carbon as well as element contents to compare the principal prey of the birds, the Peruvian anchovy, with the composition of modern guano. We also investigate the impact of diagenetic changes on the isotopic composition and elemental contents of the pure ornithogenic sediments, starting with modern stratified deposits and extending to fossil guano. Where possible, 14C systematics is used for age information. The nitrogen and carbon isotopic composition of the marine prey (Peruvian anchovy) of the birds is complex as it shows strong systematic variations with latitude. The detailed study of a modern profile that represents a few years of guano deposition up to present reveals systematic changes in nitrogen and carbon isotopic composition towards heavier values that increase with age, i.e. depth. Only the uppermost, youngest layers of modern guano show compositional affinity to the prey of the birds. In the profile, the simultaneous loss of nitrogen and carbon occurs by degassing, and non-volatile elements like phosphorous and calcium are passively enriched in the residual guano. Fossil guano deposits are very low in nitrogen and low in carbon contents, and show very heavy nitrogen isotopic compositions. One result of the study is that the use of guano for tracing nitrogen and carbon isotopic and elemental composition in the marine food web of the birds is restricted to fresh material. Despite systematic changes during diagenesis, there is little promise to retrieve reliable values of marine nitrogen and carbon signatures from older guano. However, the changes in isotopic composition from primary marine nitrogen isotopic signatures towards very heavy values generate a compositionally unique material. These compositions trace the presence of guano in natural ecosystems and its use as fertilizer in present and past agriculture.
至少从上新世以来，海鸟粪便（鸟粪）就一直保存在智利北部的干旱气候中。沿海地区海洋有机物质的沉积物有可能为了解现代和过去沿海海洋的组成及其食物网打开一扇窗口。我们利用氮和碳的稳定同位素组成以及元素含量，将鸟类的主要猎物秘鲁鳀鱼与现代鸟粪的组成进行比较。我们还研究了成岩变化对纯鸟源沉积物的同位素组成和元素含量的影响，从现代分层沉积物开始，一直延伸到化石鸟粪。在可能的情况下，利用碳-14系统来获取年龄信息。鸟类海洋猎物（秘鲁鳀鱼）的氮和碳同位素组成很复杂，因为它显示出随纬度有强烈的系统变化。对一个代表了至今数年鸟粪沉积的现代剖面的详细研究揭示，氮和碳同位素组成朝着随年龄（即深度）增加而变重的值发生系统变化。只有现代鸟粪最上面、最年轻的层显示出与鸟类猎物的成分相似性。在这个剖面中，氮和碳通过脱气同时损失，而磷和钙等非挥发性元素在残留鸟粪中被动富集。化石鸟粪沉积物的氮含量非常低，碳含量也低，并且显示出非常重的氮同位素组成。该研究的一个结果是，利用鸟粪追踪鸟类海洋食物网中氮和碳的同位素及元素组成仅限于新鲜材料。尽管在成岩过程中有系统变化，但从较老的鸟粪中获取可靠的海洋氮和碳特征值的希望渺茫。然而，从原始海洋氮同位素特征向非常重的值的同位素组成变化产生了一种成分独特的物质。这些组成可以追踪自然生态系统中鸟粪的存在及其在现在和过去农业中作为肥料的使用情况。
