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Earthworm-produced calcite granules: a new terrestrial palaeothermometer?
In this paper we show for the first time that calcite granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water δ18O values. Earthworms were cultivated in an orthogonal combination of two different (granule-free) soils moistened by three types of mineral water and kept at three temperatures (10, 16 and 20 ºC) for an acclimatisation period of three weeks followed by transfer to identical treatments and cultivation for a further four weeks. Earthworm-secreted calcite granules were collected from the second set of soils. δ18O values were determined on individual calcite granules (δ18Oc) and the soil solution (δ18Ow). The δ18Oc values reflect soil solution δ18Ow values and temperature, but are consistently enriched by 1.51 (±0.12) ‰ in comparison to equilibrium in synthetic carbonates. The data fit the equation 1000 ln α = [20.21 ± 0.92] (103 T-1) - [38.58 ± 3.18] (R2 = 0.95; n = 96; p < 0.0005). As the granules are abundant in modern soils, buried soils and archaeological contexts, and can be dated using U-Th disequilibria, the developed palaeotemperature relationship has enormous potential for application to Holocene and Pleistocene time intervals
Multiple nutritional strategies of hydrothermal vent shrimp (Rimicaris hybisae) assemblages at the Mid-Cayman Rise
Alvinocaridid shrimp occurring in dense assemblages close to vigorously venting orifices are characteristic of many vent fields on the Mid-Atlantic Ridge, Central Indian Ridge, and Mid-Cayman Rise. Episymbiotic bacteria of these shrimp are exposed to vent fluids enriched in inorganic nutrients (carbon dioxide, sulfide) that, together with dissolved oxygen in the surrounding seawater, sustain autotrophic growth and supply nourishment to the shrimp. Enigmatically, conspecific shrimp may also be found sparsely distributed in the periphery of a vent field, where there is little visual evidence of vent fluid flux. We tested the null hypothesis that nourishment sources were identical for the central (dense) and peripheral shrimp assemblages, using gut content and stable isotope analyses. Rimicaris hybisae were sampled from central and peripheral assemblages at the Von Damm Vent Field (Mid-Cayman Rise). Guts of centrally aggregated shrimp contained a white material inferred to be bacteria, while peripheral individuals contained this white material and/or pieces of crustacean exoskeletons. C, N, and S isotopic compositions of shrimp muscle tissues were significantly different between central and peripheral shrimp assemblages, and little overlap in isotopic space was found. A comparison of δ13C and δ34S values of gut contents and abdominal tissues revealed that abdominal tissue composition reflects the shrimp's source of nourishment. Slight but significantly elevated δ15N values in peripheral shrimp, together with crustacean exoskeleton fragments in the gut, suggest facultative carnivory in peripherally aggregated shrimp. The lower δ13C and δ34S values in individuals from the peripheral assemblages are also consistent with a mixotrophic diet. We conclude that central and peripheral assemblages of R. hybisae have different nourishment sources, with central assemblages relying on episymbionts, while peripheral assemblages have diverse nourishment sources comprising bacteria and Crustacea