Depositional continuity of seasonally laminated tufas: Implications for δ¹⁸O based palaeotemperatures

A ~100 ka old laminated tufa (freshwater carbonate) deposit from central Greece was studied for evidence of a seasonal origin of the laminae. Annual laminar couplets (6 mm thick) consist of dense β bands of spring– early summer calcified cyanobacterial bushes and porous α bands of autumn precipitated calcite on unclustered cyanobacterial filaments. This is evidence of likely seasonal palaeoclimate during the last interglacial in Greece. δ<sup>18</sup>O variability is explained by seasonal changes in stream water temperature; however, the total range in δ<sup>18</sup>O translates to ~6 °C (±1 °C) almost certainly underestimating the likely actual range of ~17 °C. As abrupt changes in δ<sup>18</sup>O inferred temperatures (from warming to cooling and vice versa) occur exactly on sharp petrographic lamina boundaries, we infer that mid-summer and mid-winter precipitates are missing. We suggest that when stream conditions (summer drying and winter cold) are unsuited to cyanobacterial substrate development, no tufa build-up occurs. Laminated tufas are thus incomplete records of annual tufa formation, as are the δ18O based palaeoclimate records they preserve. They require careful petrographic study linked to high resolution sampling for δ<sup>18</sup>O to ensure that palaeotemperature ranges are not seriously underestimated

Is it really organic? - multi-isotopic analysis as a tool to discriminate between organic and conventional plants

Novel procedures for analytical authentication of organic plant products are urgently needed. Here we present the first study encompassing stable isotopes of hydrogen, carbon, nitrogen, oxygen, magnesium and sulphur as well as compound-specific nitrogen and oxygen isotope analysis of nitrate for discrimination of organically and conventionally grown plants. The study was based on wheat, barley, faba bean and potato produced in rigorously controlled long-term field trials comprising 144 experimental plots. Nitrogen isotope analysis revealed the use of animal manure, but was unable to discriminate between plants that were fertilized with synthetic nitrogen fertilizers or green manures from atmospheric nitrogen fixing legumes. This limitation was bypassed using oxygen isotope analysis of nitrate in potato tubers, while hydrogen isotope analysis allowed complete discrimination of organic and conventional wheat and barley grains. It is concluded, that multi-isotopic analysis has the potential to disclose fraudulent substitutions of organic with conventionally cultivated plants