Holocene changes in moisture source and temperature revealed by the oxygen isotopic composition of fossil Daphnia ephippia in Sierra Nevada, southern Spain

• Oxygen isotopes of Daphnia were used as a proxy for autumn snapshots of water isotopic composition. • Long-term changes were controlled by the moisture source and the summer insolation. • Before the 4.2 event, depleted values reflected a predominant Atlantic influence. • A peak at 7.2 cal kyr BP was forced by higher summer temperatures at HTM. • After the 4.2 event, enriched values reflected a more Mediterranean influence. The study of oxygen isotopes in chitin and its use as a paleoclimatic proxy is still under development. The low oxygen content of chitin and the low sample weight of fossils have hindered this research topic, even though there is evidence of a strong correlation between the oxygen isotopic composition of chitin and the isotopic composition of the host water. In order to further this research we present a paleoclimatic reconstruction based on δ 18 O of cladoceran remains from the lake sediments of Laguna de Río Seco, Sierra Nevada, Spain. Here, modern water isotopic data were used as a modern analogue to establish an important influence on evaporative enrichment as the ice-free season advances. The oxygen isotope signal from Daphnia resting eggs was used as a proxy for autumn snapshots of the water isotopic composition at millennial time scales. Long-term changes were controlled by the moisture source and the summer insolation. Between deglaciation and 4.2 kyr BP, δ 18 O measurements exhibited generally depleted values only interrupted by a peak at ∼ 7.2 kyr BP, concurrent with a temperature maximum inferred from earlier quantitative reconstructions. A predominantly Atlantic moisture source and changes in the evaporation related to seasonality explained the isotopic variability at that time. From 4.2 kyr BP onwards, a notable enrichment in this isotopic signal occurred, which was consistent with greater influence of a Mediterranean precipitation source and higher evaporation at lower lake levels. This new isotope record provides a unique application of paleoclimates from cladocerans, which goes beyond the taxonomic and numerative methodology traditionally used in subfossil cladoceran analysis.