Description: Highlights • Previous age estimates of the Laacher See Eruptions (LSE) around 12,900 years are still diverging and imprecise. • The combination of dendrochronology, wood anatomy, and 14C measurements holds the potential to establish a precise LSE date. • An absolute calendric date of the LSE would improve the synchronization of European Late Glacial to Holocene archives. Abstract The precise date of the Laacher See eruption (LSE), central Europe’s largest Late Pleistocene volcanic event that occurred around 13,000 years ago, is still unknown. Here, we outline the potential of combined high-resolution dendrochronological, wood anatomical and radiocarbon (14C) measurements, to refine the age of this major Plinian eruption. Based on excavated, subfossil trees that were killed during the explosive LSE and buried under its pyroclastic deposits, we describe how a firm date of the eruption might be achieved, and how the resulting temporal precision would further advance our understanding of the environmental and societal impacts of this event. Moreover, we discuss the relevance of an accurate LSE date for improving the synchronization of European terrestrial and lacustrine Late Glacial to Holocene archives.

Description: Radiocarbon (14C), as a consequence of its production in the atmosphere and subsequent dispersal through the carbon cycle, is a key tracer for studying the Earth system. Knowledge of past 14C levels improves our understanding of climate processes, the Sun, the geodynamo, and the carbon cycle. Recently updated radiocarbon calibration curves (IntCal20, SHCal20, and Marine20) provide unprecedented accuracy in our estimates of 14C levels back to the limit of the 14C technique (~55,000 years ago). Such improved detail creates new opportunities to probe the Earth and climate system more reliably and at finer scale. We summarize the advances that have underpinned this revised set of radiocarbon calibration curves, survey the broad scientific landscape where additional detail on past 14C provides insight, and identify open challenges for the future.

Description: Compound-specific radiocarbon dating often requires working with small samples of 〈 100 µg carbon (µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6-151 µgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F14C. There was an inverse linear relationship between the measured F14C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We used Bayesian methods to fit linear regression lines between F14C and 1/mass for the fossil and modern standards. The intersection points of these lines were used to infer F14Cblank and mblank and their associated uncertainties. We estimated 4.88±0.69 μgC of procedural blank with F14C of 0.714±0.077 for n-alkanoic acids, and 0.90±0.23 μgC of procedural blank with F14C of 0.813±0.155 for lignin phenols. These F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.

Description: Centennial and millennial scale variability of Southern Ocean temperature is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variability instead coming mainly from ice core records. Here we present a high-resolution (~ 60 year) record of diatom abundance from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka BP (calibrated kiloyears before present). The results show the dominant species are Fragilariopsis kerguelensis and Thalassiosira lentiginosa, with accompanying species typical of the Polar Front Zone and Permanent Open Ocean Zone. Species associated with warmer temperatures were most abundant in the period 12-9.5 ka BP, while species associated with lower temperatures were abundant at 14.2-9.5 ka BP.

Description: Centennial and millennial scale variability of Southern Ocean temperature is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variability instead coming mainly from ice core records. Here we present a high-resolution (~ 60 year), diatom-based sea-surface temperature (SST) reconstruction from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka BP (calibrated kiloyears before present). During the late deglaciation, the new SST record shows cool temperatures at 14.2–12.9 ka BP and gradual warming between 12.9–11.6 ka BP in phase with atmospheric temperature evolution. This supports that the temperature of the Southern Ocean during the deglaciation was linked with a complex combination of processes and drivers associated with reorganisations of atmospheric and oceanic circulation patterns. Specifically, we suggest that Southern Ocean surface warming coincided, within the dating uncertainties, with the reconstructed slowdown of the Atlantic Meridional Overturning Circulation (AMOC), rising atmospheric CO2 levels, changes in the southern westerly winds and enhanced upwelling. During the Holocene the record shows warm and stable temperatures from 11.6–8.7 ka BP followed by a slight cooling and greater variability from 8.7 to 1 ka BP, with a quasi-periodic variability of 200–260 years as identified by spectral analysis. We suggest that the increased variability during the mid to late Holocene may reflect the establishment of centennial variability in SST connected with changes in the high latitude atmospheric circulation and Southern Ocean convection, as identified in models.

Description: Benthic foraminifera assemblage data for marine sediment core DA17-NG-ST03-039G retrieved in the Westwind Trough on the Northeast Greenland Shelf. The marine gravity core was collected during the NorthGreen2017 cruise on board the research vessel RV Dana. The data covers the period 13.3 to 3.9 cal ka BP. The benthic foraminifera assemblage data was carried out in order to reconstruct the oceanographic development on the Northeast Greenland shelf.

Description: Accelerator mass spectrometer measurement results of C14 age in tree rings from 13 different dendrochronoligically dated trees from England and Switzerland spanning the last almost all of the last millenium. The Sun provides almost all of the external forcing to the Earth system, so that its variability is of considerable interest for geoscience. Observational records of solar activity cover only the last about 400 yr. Beyond that, cosmogenic nuclides stored in tree rings (14C) or ice cores (10Be, 36Cl) are used as proxies for solar activity extending back by many thousands of years1-3. Major drawbacks of cosmogenic nuclide based solar reconstructions are the presence of weather-induced noise (10Be in ice cores) and/or low temporal resolution of long, precisely dated records (14C in tree rings). Here, we present a continuous, annually resolved 14C record from absolutely dated tree rings covering nearly all of the last millennium (969-1933 AD). The high resolution and high precision 14C record reveals the presence of the eleven-year solar Schwabe cycle over the past millennium. Statistical analysis of the Schwabe cycle shows a positive correlation of its amplitude with reconstructed solar modulation. The record further confirms the 993 AD solar energetic particle event and reveals two new candidate events (1052 AD and 1279 AD) indicating that strong solar events are probably more common than previously thought.

Description: Accelerator mass spectrometer measurement results of C14 age in tree rings from 13 different dendrochronoligically dated trees from Ireland and the Alps, United states and Siberia, spanning from 7220-7122 BCE and 5300-5190 BCE. The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as 14C, 10Be and 36Cl have been found. Analyzing annual 14C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric 14C corresponding to 7176 and 5259 BCE. The ~2% increases of atmospheric 14C recorded for both events exceed all previously known 14C peaks but after correction for the geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which threaten modern infrastructure.