Glacial terminations as southern warmings without northern control

The change from a glacial to an interglacial climate is paced by variations in Earth’s orbit. However, the detailed sequence of events that leads to a glacial termination remains controversial. It is particularly unclear whether the northern or southern hemisphere leads the termination. Here we present a hypothesis for the beginning and continuation of glacial terminations, which relies on the observation that the initial stages of terminations are indistinguishable from the warming stage of events in Antarctica known as Antarctic Isotopic Maxima, which occur frequently during glacial periods. Such warmings in Antarctica generally begin to reverse with the onset of a warm Dansgaard–Oeschger event in the northern hemisphere. However, in the early stages of a termination, Antarctic warming is not followed by any abrupt warming in the north. We propose that the lack of an Antarctic climate reversal enables southern warming and the associated atmospheric carbon dioxide rise to reach a point at which full deglaciation becomes inevitable. In our view, glacial terminations, in common with other warmings that do not lead to termination, are led from the southern hemisphere, but only specific conditions in the northern hemisphere enable the climate state to complete its shift to interglacial conditions

Agricultural production in the 1st millennium BCE in Northwest Iberia: results of carbon isotope analysis

This work presents the first results of carbon isotope (δ13C) analysis of seeds (Triticum dicoccum, Triticum aestivum/durum, Triticum cf. spelta and Hordeum vulgare L.) from archaeological contexts from the settlement sites of A Fontela and Castrovite in Northwest Iberia, which cover a chronological range between 1050 cal BC and 25 cal AD. In addition, 142 present-day wheat seeds from 16 plots cultivated in 2014 and 2015 across this region were analysed. The results obtained for A Fontela and Castrovite were − 23.6‰ (between − 25.3 and − 21.4) and − 24.0‰ (between − 26.6 and − 21.8), respectively. Taking into account changes in the isotope composition of atmospheric carbon (δ13Catm), the Δ13C values were 17.5‰ (A Fontela) and 18.0‰ (Castrovite). In Castrovite, differences between storage facilities were detected, which could be related to the exploitation of different areas for cultivation, possibly indicating a family-based organization of agricultural production.This work was supported by a FPU grant at the Spanish Ministerio de Educación, Cultura y Deporte (AP2012-1353) and part of this research is included in the PhD Thesis of Adrián Mora-González “Irrigación y secano en el Mediterráneo Occidental (III-I milenio A.N.E.): un estudio isotópico”. This research has been conducted within the framework of the HAR2015-66009-P “Arqueología y Química. Reconstruyendo los hábitos alimenticios en la cultura de El Argar” funded by the Spanish Ministerio de Economía y Competitividad, the Project RNM-8011 and the research groups RNM309 and HUM274 (Junta de Andalucía). The archaeobotanical studies of A Fontela and Castrovite were undertaken in the project “Paleoenvironment and Paleoeconomics during the 1st millennium BC”. We also thank Xulio Carballo Arceo, Josefa Rey Castiñeira and Cliodhna Ni Lionain for valuable comments on a draft of the text, leading to measurable improvements