Meltwater events and the Mediterranean reconnection at the Saalian–Eemian transition in the Black Sea

The last glacial–interglacial transition or Termination I (T I) is well documented in the Black Sea, whereas little is known about climate and environmental dynamics during the penultimate Termination (T II). Here we present a multi-proxy study based on a sediment core from the SE Black Sea covering the penultimate glacial and almost the entire Eemian interglacial ( ( 133.5 ± 0.7 ) – ( 122.5 ± 1.7 )   ka BP ). Proxies comprise ice-rafted debris (IRD), O and Sr isotopes as well as Sr/Ca, Mg/Ca, and U/Ca ratios of benthic ostracods, organic and inorganic sediment geochemistry, as well as TEX86 and UK′37 derived water temperatures. The ending penultimate glacial (MIS 6, 133.5 to 129.9 ± 0.7   ka BP ) is characterised by mean annual lake surface temperatures of about 9 °C as estimated from the TEX86 palaeothermometer. This period is impacted by two Black Sea melt water pulses (BSWP-II-1 and 2) as indicated by very low Sr/Caostracods but high sedimentary K/Al values. Anomalously high radiogenic 87Sr/86Srostracod values (max. 0.70945) during BSWP-II-2 suggest a potential Himalayan source communicated via the Caspian Sea. The T II warming started at 129.9 ± 0.7   ka BP , witnessed by abrupt disappearance of IRD, increasing δ18Oostracod values, and a first TEX86 derived temperature rise of about 2.5 °C. A second, abrupt warming step to ca. 15.5 °C as the prelude of the Eemian warm period is documented at 128.3 ka BP. The Mediterranean–Black Sea reconnection most likely occurred at 128.1 ± 0.7   ka BP as demonstrated by increasing Sr/Caostracods and U/Caostracods values. The disappearance of ostracods and TOC contents > 2 % document the onset of Eemian sapropel formation at 127.6 ka BP. During sapropel formation, TEX86 temperatures dropped and stabilised at around 9 °C, while UK′37 temperatures remain on average 17 °C. This difference is possibly caused by a habitat shift of Thaumarchaeota communities from surface towards nutrient-rich deeper and colder waters located above the gradually establishing halo- and redoxcline.