Description: The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.

Description: Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on 10Be records from ice cores and 14C time-series from tree rings, all including archive-specific limitations. We present the first 10Be record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, 10Be deposition using a new approach based on regression analyses between our 10Be record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our 10Be record, but cannot be the main explanation for major 10Be excursions. Corrected for these environmental influences, our 10Be record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in 10Be from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.

Description: Beryllium 10 concentrations (10Becon) were measured at annual resolution from varved sediment cores of Lakes Tiefer See (TSK) and Czechowskie (JC) for the period 1983–2009 (∼solar cycles 22 and 23). Calibrating the 10Becon time-series against complementing proxy records from the same archive as well as local precipitation and neutron monitor data, reflecting solar forced changes in atmospheric radionuclide production, allowed (i) identifying the main depositional processes and (ii) evaluating the potential for solar activity reconstruction. 10Becon in TSK and JC sediments are significantly correlated to varying neutron monitor counts (TSK: r=0.5r=0.5, p=0.05p=0.05, n=16n=16; JC: r=0.46r=0.46, p=0.03p=0.03, n=22n=22). However, the further correlations with changes in organic carbon contents in TSK as well as varying organic carbon and detrital matter contents in JC point to catchment specific biases in the 10Becon time-series. In an attempt to correct for these biases multiple regression analysis was applied to extract an atmospheric 10Be production signal (10Beatmosphere). To increase the signal to noise ratio a 10Be composite record (10Becomposite) was calculated from the TSK and JC 10Beatmosphere time-series. 10Becomposite is significantly correlated to variations in the neutron monitor record (r=0.49r=0.49, p=0.01p=0.01, n=25n=25) and matches the expected amplitude changes in 10Be production between solar cycle minima and maxima. This calibration study on 10Be from two sites indicates the large potential but also, partly site-specific, limitations of 10Be in varved lake sediments for solar activity reconstruction.

Description: Time-series of varve properties and geochemistry were established from varied sediments of Lake Woserin (north-eastern Germany) covering the recent period AD 2010–1923 and the mid-Holocene time-window 6400–4950 varve years before present (vyr BP) using microfacies analyses, x-ray fluorescence (µ-XRF) scanning, microscopic varve chronology, and 14C dating. The microscopic varve chronology was compared with a macroscopic varve chronology for the same sediment interval. Calcite layer thickness during the recent period is significantly correlated to increases in local annual precipitation (r = 0.46, p = 0.03) and reduced air-pressure (r = −0.72, p 〈 0.0001). Meteorologically consistent with enhanced precipitation at Lake Woserin, a composite 500 hPa anomaly map for years with 〉1 standard deviation calcite layer thickness depicts a negative wave train air-pressure anomaly centered over southern Europe, with north-eastern Germany at its northern frontal zone. Three centennial-scale intervals of thicker calcite layers around the mid-Holocene periods 6200–5900, 5750–5400, and 5300–4950 vyr BP might reflect humid conditions favoring calcite precipitation through the transport of Ca2+ ions into Lake Woserin, synchronous to wetter conditions in Europe. Calcite layer thickness oscillations of about 88 and 208 years resemble the solar Gleissberg and Suess cycles suggesting that the recorded hydroclimate changes in north-eastern Germany are modified by solar influences on synoptic-scale atmospheric circulation. However, parts of the periods of thicker calcite layers around 5750–5400 and 5200 vyr BP also coincide with enhanced human catchment activity at Lake Woserin. Therefore, calcite precipitation during these time-windows might have further been favored by anthropogenic deforestation mobilizing Ca2+ ions and/or lake eutrophication.

Description: Several climate oscillations have been reported from the early Holocene superepoch, the best known of which is the Preboreal oscillation (PBO). It is still unclear how the PBO and the number of climate oscillations observed in Greenland ice cores and European terrestrial records are related to one another. This is mainly due to uncertainties in the chronologies of the records. Here, we present new, high-resolution 10Be concentration data from the varved Meerfelder Maar sediment record in Germany, spanning the period 11 310–11 000 years BP. These new data allow us to synchronize this well-studied record, as well as Greenland ice core records, with the IntCal13 timescale via radionuclide wiggle matching. In doing so, we show that the climate oscillations identified in Greenland and Europe between 11 450 and 11 000 years BP were not synchronous but terminated and began, respectively, with the onset of a grand solar minimum. A similar spatial anomaly pattern is found in a number of modeling studies on solar forcing of climate in the North Atlantic region. We further postulate that freshwater delivery to the North Atlantic would have had the potential to amplify solar forcing through a slowdown of the Atlantic meridional overturning circulation (AMOC) reinforcing surface air temperature anomalies in the region.

Description: Timescale uncertainties between paleoclimate reconstructions often inhibit studying the exact timing, spatial expression and driving mechanisms of climate variations. Detecting and aligning the globally common cosmogenic radionuclide production signal via a curve fitting method provides a tool for the quasi-continuous synchronization of paleoclimate archives. In this study, we apply this approach to synchronize 10Be records from varved sediments of Tiefer See and Lake Czechowskie covering the Maunder, Homeric and 5500 a BP grand solar minima with 14C production rates inferred from the IntCal13 calibration curve. Our analyses indicate best fits with 14C production rates when the 10Be records from Tiefer See were shifted for 8 (−12∕ + 4) (Maunder Minimum), 31 (−16∕ + 12) (Homeric Minimum) and 86 (−22∕ + 18) years (5500 a BP grand solar minimum) towards the past. The best fit between the Lake Czechowskie 10Be record for the 5500 a BP grand solar minimum and 14C production was obtained when the 10Be time series was shifted 29 (−8∕ + 7) years towards present. No significant fits were detected between the Lake Czechowskie 10Be records for the Maunder and Homeric minima and 14C production, likely due to intensified in-lake sediment resuspension since about 2800 a BP, transporting "old" 10Be to the coring location. Our results provide a proof of concept for facilitating 10Be in varved lake sediments as a novel synchronization tool required for investigating leads and lags of proxy responses to climate variability. However, they also point to some limitations of 10Be in these archives, mainly connected to in-lake sediment resuspension processes.

Description: Our study on the exact timing and the potential climatic, environmental, and evolutionary consequences of the Laschamps Geomagnetic Excursion has generated the hypothesis that geomagnetism represents an unrecognized driver in environmental and evolutionary change. It is important for this hypothesis to be tested with new data, and encouragingly, none of the studies presented by Picin et al. undermine our model.