Florian Adolphi’s research while affiliated with University of Bremen and other places

Establishing accurate chronological frameworks is imperative for reliably identifying lead–lag dynamics within the climate system and enabling meaningful intercomparisons across diverse paleoclimate proxy records over long time periods. Robust age models provide a solid temporal foundation for establishing correlations between paleoclimate records. One of the primary challenges in constructing reliable radiocarbon-based chronologies in the marine environment is to determine the regional marine radiocarbon reservoir age correction. Calculations of the local marine reservoir effect (ΔR) can be acquired using independent 14C dating methods, such as synchronization with other well-dated archives. The cosmogenic radionuclide 10Be offers such a synchronization tool. Its atmospheric production rate is controlled by the global changes in the cosmic ray influx, caused by variations in solar activity and geomagnetic field strength. The resulting fluctuations in the meteoric deposition of 10Be are preserved in sediments and ice cores and can thus be utilized for their synchronization. In this study, for the first time, we use the authigenic 10Be/9Be record of a Laptev Sea sediment core for the period 8–14 kyr BP and synchronize it with the 10Be records from absolutely dated ice cores. Based on the resulting absolute chronology, a benthic ΔR value of +345 ± 60 14Cyears was estimated for the Laptev Sea, which corresponds to a marine reservoir age of 848 ± 90 14Cyears. The ΔR value was used to refine the age–depth model for core PS2458-4, establishing it as a potential reference chronology for the Laptev Sea. We also compare the calculated ΔR value with modern estimates from the literature and discuss its implications for the age–depth model.

Arctic permafrost stores vast amounts of terrestrial organic matter (terrOM). Under warming climate conditions, Arctic permafrost thaws, releasing aged carbon and potentially impacting the modern carbon cycle. We investigated the characteristics of terrestrial biomarkers, including n-alkanes, fatty acids, and lignin phenols, in marine sediment cores to understand how the sources of terrOM transported to the ocean change in response to varying environmental conditions such as sea-level rise, sea ice coverage, inland climate warming, and freshwater input. We examined two sediment records from the western Laptev Sea (PS51/154 and PS51/159) covering the past 17.8 kyr. Our analyses reveal three periods with high mass accumulation rates (MARs) of terrestrial biomarkers, from 14.1 to 13.2, 11.6 to 10.9, and 10.9 to 9.5 kyr BP. These MAR peaks revealed distinct terrOM sources, likely in response to changes in shelf topography, rates of sea-level rise, and inland warming. By comparing periods of high terrOM MAR in the Laptev Sea with published records from other Arctic marginal seas, we suggest that enhanced coastal erosion driven by rapid sea-level rise during meltwater pulse 1A (mwp-1A) triggered elevated terrOM MAR across the Arctic. Additional terrOM MAR peaks coincided with periods of enhanced inland warming, prolonged ice-free conditions, and freshwater flooding, which varied between regions. Our results highlight regional environmental controls on terrOM sources, which can either facilitate or preclude regional terrOM fluxes in addition to global controls.

Establishing accurate chronological frameworks is imperative for reliably identifying lead-lag dynamics within the climate system and enabling meaningful inter-comparisons across diverse paleoclimate proxy records over long time periods. Robust age models provide a solid temporal foundation for establishing correlations between paleoclimate records. One of the primary challenges in constructing reliable radiocarbon-based chronologies in the marine environment is to determine the regional marine radiocarbon reservoir age correction. Calculations of the local marine reservoir effect (ΔR) can be acquired using 14C-independent dating methods, such as synchronization with other well-dated archives. The cosmogenic radionuclide 10Be offers such a synchronization tool. Its atmospheric production rate is controlled by the global changes in the cosmic ray influx, caused by variations in solar activity and geomagnetic field strength. The resulting fluctuations in the meteoric deposition of 10Be are preserved in sediments and ice cores and can thus be utilized for their synchronization. In this study, for the first time, we use the authigenic 10Be/9Be record of a Laptev Sea sediment core for the period 8–14 kyr BP and synchronize it with the 10Be records from absolutely dated ice cores. Based on the resulting absolute chronology, a benthic ΔR value of +345 ± 60 14C years was estimated for the Laptev Sea, which corresponds to a marine reservoir age of 848 ± 90 14C years. The ΔR value was used to refine the age-depth model for core PS2458-4, establishing it as a potential reference chronology for the Laptev Sea. We also compare the calculated ΔR value with modern estimates from the literature and discuss its implications for the age-depth model.

Carbon cycle models used to calculate the marine reservoir age of the non-polar surface ocean (called Marine20) out of IntCal20, the compilation of atmospheric 14C, have so far neglected a key aspect of the millennial-scale variability connected with the thermal bipolar seesaw: changes in the strength of the Atlantic meridional overturning circulation (AMOC) related to Dansgaard/Oeschger and Heinrich events. Here we implement such AMOC changes in the carbon cycle box model BICYCLE-SE to investigate how model performance over the last 55 kyr is affected, in particular with respect to available 14C and CO2 data. Constraints from deep ocean 14C data suggest that the AMOC in the model during Heinrich stadial 1 needs to be highly reduced or even completely shutdown. Ocean circulation and sea ice coverage combined are the processes that almost completely explain the simulated changes in deep ocean 14C age, and these are also responsible for a glacial drawdown of ∼60 ppm of atmospheric CO2. We find that the implementation of abrupt reductions in AMOC during Greenland stadials in the model setup that was previously used for the calculation of Marine20 leads to differences of less than ±100 14C yrs. The representation of AMOC changes therefore appears to be of minor importance for deriving non-polar mean ocean radiocarbon calibration products such as Marine20, where atmospheric carbon cycle variables are forced by reconstructions. However, simulated atmospheric CO2 exhibits minima during AMOC reductions in Heinrich stadials, in disagreement with ice core data. This mismatch supports previous suggestions that millennial-scale changes in CO2 were probably not driven directly by the AMOC, but rather by biological and physical processes in the Southern Ocean and by contributions from variable land carbon storage.

Plain Language Summary The cosmogenic radionuclide beryllium‐10 (¹⁰Be) deposition in natural archives can be used to reconstruct solar and geomagnetic changes in the past. Understanding how ¹⁰Be deposition reflects atmospheric production rate changes is crucial for these applications. However, this relationship remains debated. To address this issue, we use two state‐of‐the‐art global models, GEOS‐Chem 14.1.1 and ECHAM6.3‐HAM2.3, along with the latest beryllium production model (CRAC: Be). When responding to solar modulation, both models indicate that ¹⁰Be deposition corresponds proportionally to global production rate changes, with a minor latitudinal bias. However, during geomagnetic modulation, ¹⁰Be deposition changes significantly compared to global production rate changes. ¹⁰Be deposition also shows varying hemispheric responses to geomagnetic modulation, attributed to the asymmetric production between hemispheres. For the extreme solar proton event in 774/5 CE, ¹⁰Be shows a higher deposition flux increase in the polar regions compared to the tropics. These findings underscore the need to account for atmospheric mixing on ¹⁰Be deposition from different locations, especially for the changes due to the geomagnetic field variations.

The cosmogenic radionuclides 7Be and 10Be are useful tracers for atmospheric transport studies. Combining 7Be and 10Be measurements with an atmospheric transport model can not only improve our understanding of the radionuclide transport and deposition processes but also provide an evaluation of the transport process in the model. To simulate these aerosol tracers, it is critical to evaluate the influence of radionuclide production uncertainties on simulations. Here we use the GEOS-Chem chemical transport model driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis to simulate 7Be and 10Be with the state-of-the-art production rate from the CRAC:Be (Cosmic Ray Atmospheric Cascade: Beryllium) model considering realistic spatial geomagnetic cutoff rigidities (denoted as P16spa). We also perform two sensitivity simulations: one with the default production rate in GEOS-Chem based on an empirical approach (denoted as LP67) and the other with the production rate from the CRAC:Be but considering only geomagnetic cutoff rigidities for a geocentric axial dipole (denoted as P16). The model results are comprehensively evaluated with a large number of measurements including surface air concentrations and deposition fluxes. The simulation with the P16spa production can reproduce the absolute values and temporal variability of 7Be and 10Be surface concentrations and deposition fluxes on annual and sub-annual scales, as well as the vertical profiles of air concentrations. The simulation with the LP67 production tends to overestimate the absolute values of 7Be and 10Be concentrations. The P16 simulation suggests less than 10 % differences compared to P16spa but a significant positive bias (∼18 %) in the 7Be deposition fluxes over East Asia. We find that the deposition fluxes are more sensitive to the production in the troposphere and downward transport from the stratosphere. Independent of the production models, surface air concentrations and deposition fluxes from all simulations show similar seasonal variations, suggesting a dominant meteorological influence. The model can also reasonably simulate the stratosphere–troposphere exchange process of 7Be and 10Be by producing stratospheric contribution and 10Be/7Be ratio values that agree with measurements. Finally, we illustrate the importance of including the time-varying solar modulations in the production calculation, which significantly improve the agreement between model results and measurements, especially at mid-latitudes and high latitudes. Reduced uncertainties in the production rates, as demonstrated in this study, improve the utility of 7Be and 10Be as aerosol tracers for evaluating and testing transport and scavenging processes in global models. For future GEOS-Chem simulations of 7Be and 10Be, we recommend using the P16spa (versus default LP67) production rate.

10Be is produced by the interaction between galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the Earth's atmospheric constituents. The flux of GCRs is modulated by the varying strength of the magnetic fields of the Earth and the Sun. Measurement of 10Be concentrations from polar ice cores is thus a valuable tool to reconstruct the variations in the geomagnetic field and solar activity levels. The interpretation of 10Be records is, however, complicated by non-production-related effects on the 10Be deposition rate caused by climate- or weather-induced variability. Furthermore, volcanic eruptions have been proposed to lead to short-term 10Be deposition enhancements. In this study, we test the use of excess meltwater from continuous flow analysis (CFA) to measure 10Be, allowing less time-consuming and more cost-effective sample preparation. We compare two records obtained from CFA and discrete samples from the East Greenland Ice core Project (EGRIP) S6 firn core, reaching back to 1900 CE. We find that the two records agree well and that the 10Be record from CFA samples agrees as well as the discrete samples with other records from Greenland. Furthermore, by subtracting the theoretically expected GCR-induced signal, we investigate the high-frequency variability in the 10Be records from Greenland and Antarctica after 1951 CE, focusing on SEP events and volcanic eruptions. Finally, we use the 10Be records from Greenland and Antarctica to study the 11-year solar cycles, allowing us to assess the suitability of the CFA samples for the reconstruction of solar activity. This result opens new opportunities for the collection of continuous 10Be records with less time-consuming sample preparation, while saving an important portion of the ice cores for other measurements.

Here we present the high-resolution continuous flow analysis (CFA) data from the top 479 m of the East Greenland Ice coring Project (EGRIP) ice core covering the past 3.8 kyr. The data consist of 1 mm depth-resolution profiles of calcium, sodium, ammonium, nitrate, and electrolytic conductivity as well as decadal averages of these profiles. The nominally 1 mm data represent an oversampling of the record as the true resolution is limited by the analytical setup to approximately 1 cm. Alongside the data we provide a description of the measurement setup, procedures, the relevant references for the specific methods as well as an assessment of the precision of the measurements, the sample-to-depth assignment, and the depth and temporal resolution of the data set. The error in absolute depth assignment of the data may be on the order of 2 cm; however, relative depth offsets between the records of the individual species are only on the order of 1 mm. The presented data have sub-annual resolution over the entire depth range and have already formed part of the data for an annually layer-counted timescale for the EGRIP ice core used to improve and revise the multi-core Greenland ice-core chronology (GICC05) to a new version, GICC21 . The data are available in full 1 mm resolution and decadal averages on PANGAEA (10.1594/PANGAEA.945293, ).

Cosmogenic radionuclides (e.g., ¹⁰Be) from ice cores are a powerful tool for solar reconstructions back in time. However, superimposed on the solar signal, other factors like weather/climate and volcanic influences on ¹⁰Be can complicate the interpretation of ¹⁰Be data. A comprehensive study of ¹⁰Be records over the recent period, when atmospheric ¹⁰Be production and meteorological conditions are relatively well‐known, can improve our interpretation of ¹⁰Be records. Here we conduct a systematic study of the production and climate/volcanic signals in Antarctica and Greenland ¹⁰Be records, including a new ¹⁰Be record from the East GReenland Ice‐core Project site. Greenland and Antarctica records show significant decreasing trends (5%–6.5%/decade) for 1900–1950, which is comparable with the expected production rate inferred from sunspot observations. By comparing ¹⁰Be records with reanalysis data and atmospheric circulation patterns, ¹⁰Be records from Southern/Southeastern Greenland are significantly correlated with the Scandinavia pattern. Stacking ¹⁰Be records from different locations can enhance the production signal. However, this approach is not always straightforward as uncertainties in some records can lead to a weaker solar signal. A strategy can be employed to select records for the bipolar stack by comparing Greenland records with Antarctica records, assuming the shared signal is a production signal. Finally, we observe significant increases (36%–64%) in ¹⁰Be depositions in Greenland related to the Agung eruption. This large increase in Greenland ¹⁰Be records after the Agung eruption, could be partly explained by the enhanced air mass transport from mid‐latitudes coinciding with the decreased precipitation en‐route.