Muted multidecadal climate variability in central Europe during cold stadial periods

Here, we present a near-annual-resolution climate proxy record of central European temperature reconstructed from the Eifel maar lakes of Holzmaar and Auel in Germany spanning the past 60,000 years. The lake sediments reveal a series of previously undocumented multidecadal climate cycles of around 20- to 150-years that persisted through the last glacial cycle. The periodicity of these cycles suggests that they are related to the Atlantic multidecadal climate oscillations found in the instrumental record and in other climate archives during the Holocene. Our record shows that multidecadal variability in central Europe was strong during all warm interstadials, but was substantially muted during all cold stadial periods. We suggest that this decrease in multidecadal variability was the result of the atmospheric circulation changes associated with the weakening of the AMOC and the expansion of North Atlantic sea ice cover during the coldest parts of the last ice age.

Organic carbon was determined by measuring the reflectance for each wavelength of the visible light as percent relative to a white color standard. Absorption forms a pronounced minimum in the wavelength range of 640 nm – 730 nm in cores both from Holzmaar and Auel. Reflectivity in this wavelength band (I-Band, 660 – 670 nm, i.e. the red part of the spectrum), was shown to relate to sediment concentrations of chlorophyll a and its degradation products.The absorption at 670 nm was calibrated in the first study versus organic carbon and chlorine content, both of which revealed a significant relation to the “In situ Reflectance Spectroscopy – ISRS” absorption at 670 nm, which is subtracted from the interpolated value between 640 and 730 nm. The ISRS670 detects accordingly chlorophyll a, b, and c and also Bacteriochlorophyll c and d (Green sulfur bacteria) as well as their derivates and can be applied to detect trends in total aquatic paleoproduction in both ocean and lake sediments.