Late Glacial temperature, anoxia, and primary production in Lago di Mezzano, Central Italy

Abstract

In the North Atlantic domain, the Late Glacial period (19–11.8 cal ka BP) is characterized by rapid, high-amplitude climatic changes. The amplitude of temperature change in the Central Mediterranean region remains debated because reconstructions are limited and often contradictory. We present a chironomid-inferred temperature record from Lago di Mezzano, Central Italy, covering the Late Glacial. The chironomid record is contextualized with high-resolution multi-proxy data to elucidate the effects of changing primary production, sediment composition, and oxygen availability on chironomid assemblages. During the Oldest Dryas (>14.8 cal ka BP), reconstructed July air temperatures averaged ~12 °C. Temperatures increased in two steps, reaching ~16.8 °C (14.5–14.1 cal ka BP) and, finally, a plateau at ~17.5 °C during the Allerød and the Younger Dryas (13.9–12.0 cal ka BP). This warming is gradual and is paralleled by increasing primary production and the gradual extension of hypolimnetic anoxia. During the Younger Dryas, we observe low primary production, an increase in the siliciclastic fraction, and a shift in chironomid assemblages. This chironomid assemblage shift does not translate into significant summer cooling, suggesting that, while the Younger Dryas climatic reorganization affected catchment hydrology and erosion (Ti, K), the impact of the associated AMOC-slowdown on Central Italian summer temperatures was insignificant. Reconstructed absolute temperatures appeared “too cold” considering the geographical location of Mezzano. This discrepancy may stem from extensive cold, deep lake habitats in Mezzano and the edge effects of the applied transfer function. Habitat preferences of most chironomid taxa matched trophic and anoxic gradients during the Late Glacial.