Benthic ostracode δ13C as sensor for early Holocene establishment of modern circulation patterns in Central Europe

Shells from adult specimen of the benthic ostracodes Limnocytherina sanctipatricii and Leucocythere mirabilis selected from a 8.7 m long piston core provide continuous stable oxygen and carbon records for the past approximately 16 ka. Oxygen isotopes from both species show identical values and track the general North Atlantic and European temperature history since deglaciation in great detail. Values of ostracode δ18O values suggest that about 16 cal ka the average annual air temperatures were about 11 °C colder than today. Carbon isotopic values from both species of ostracodes are similar during the Lateglacial and early Holocene, and show an overall decrease from −4‰ to −7‰ that is probably related to an increase in photosynthetic productivity in the water column, as suggested by an increase in organic carbon, delivering 13C-depleted organic matter to the bottom waters (carbon pump). About 9 cal ka only L. mirabilis δ13C values decreased about −2.5‰ within 300 years. Higher δ13C variability and ecological evidence suggests that L. mirabilis represents a summer signal, whereas L. sanctipatricii displays a more subdued annual average. After about 7 cal ka another −1.5% decrease for both species, accompanied by an increase in magnetic susceptibility, a decrease in carbonate content, and more positive bulk carbonate isotope values followed, suggesting higher detrital-clastic input into the lake