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10 Be 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 10 Be 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 10 Be records is, however, complicated by non-production-related effects on the 10 Be deposition rate caused by climate- or weather-induced variability. Furthermore, volcanic eruptions have been proposed to lead to short-term 10 Be deposition enhancements. In this study, we test the use of excess meltwater from continuous flow analysis (CFA) to measure 10 Be, 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 10 Be 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 10 Be records from Greenland and Antarctica after 1951 CE, focusing on SEP events and volcanic eruptions. Finally, we use the 10 Be 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 10 Be records with less time-consuming sample preparation, while saving an important portion of the ice cores for other measurements. [ABSTRACT FROM AUTHOR]

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,). [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Cosmogenic radionuclides (e.g., 10Be) from ice cores are useful proxies for reconstructing the solar variability in the past. However, besides the solar signal, there are also atmospheric and volcanic signals in 10Be records measured from ice cores. It is important to understand those signals before we can reliably apply 10Be records for solar reconstructions. A study of 10Be records over the recent period, when atmospheric 10Be production and meteorological conditions are relatively well‐known, can improve our interpretation of polar 10Be records. In this study, we conduct a systematic study of the production and climate/volcanic signals in 14 10Be records, including a new 10Be record from East GReenland Ice‐core Project site. We find that simply averaging all available 10Be records to strengthen the solar signal in the composite record is not always straightforward as uncertainties (e.g., regional climate effects) in some records can weaken the solar signal. For example, 10Be records from Central and Southern Greenland are influenced by the atmospheric circulation pattern (Scandinavia pattern). Finally, we find a large increase in 10Be (>30%) depositions in Greenland after the Agung eruption, which could be partly explained by enhanced air mass transport from mid‐latitudes coinciding with decreased precipitation en‐route. Key Points: A systematic analysis of production, climate, and volcanic signals in 14 polar 10Be records over the last 100 yearsThe stacking method is not always straightforward to enhance the solar signal in 10Be records due to uncertainties in some 10Be records10Be records from Central and Southern Greenland are influenced by the Scandinavia pattern [ABSTRACT FROM AUTHOR]

Here we present the high-resolution CFA data from the top 479m of the East Greenland Ice coring Project (EGRIP) ice core covering the past 3.8 thousand years. The data consists of 1mm-depth-resolution profiles of calcium, sodium, ammonium, nitrate and electrolytic conductivity as well as decadal averages of these profiles. 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 nominally 1-mmdata represents an oversampling of the record as the true resolution is limited by the analytical setup to approximately 1 cm. The error of absolute depth assignment of the data may be on the order of 1 cm, however relative depth offsets between the records of the individual species is only on the order of 1mm. The presented data has sub-annual resolution over the entire depth range and has already formed part of the data for an annually layer-counted time scale for the EGRIP ice core used to improve and revise the multi-core Greenland ice-core chronology (GICC05) to a new version, GICC21 (Sinnl et al., 2021). The data is available in full 1-mm resolution and decadal averages on PANGAEA (https://doi.org/10.1594/PANGAEA.945293 (Erhardt et al., 2022b)). [ABSTRACT FROM AUTHOR]

Between 15 and 27 kyr b2k (thousands of years before 2000 CE) during the last glacial, Greenland experienced a prolonged cold stadial phase, interrupted by two short-lived warm interstadials. Greenland ice-core calcium data show two periods, preceding the interstadials, of anomalously high atmospheric dust loading, the origin of which is not well understood. At approximately the same time as the Greenland dust peaks, the Chinese Hulu Cave speleothems exhibit a climatic signal suggested to be a response to Heinrich Event 2, a period of enhanced ice-rafted debris deposition in the North Atlantic. In the climatic signal of Antarctic ice cores, moreover, a relative warming occurs between 23 and 24.5 kyr b2k that is generally interpreted as a counterpart to a cool climate phase in the Northern Hemisphere. Proposed centennial-scale offsets between the polar ice-core timescales and the speleothem timescale hamper the precise reconstruction of the global sequence of these climatic events. Here, we examine two new 10 Be datasets from Greenland and Antarctic ice cores to test the agreement between different timescales, by taking advantage of the globally synchronous cosmogenic radionuclide production rates. Evidence of an event similar to the Maunder Solar Minimum is found in the new 10 Be datasets, supported by lower-resolution radionuclide data from Greenland and 14 C in the Hulu Cave speleothem, representing a good synchronization candidate at around 22 kyr b2k. By matching the respective 10 Be data, we determine the offset between the Greenland ice-core chronology, GICC05, and the Antarctic chronology for the West Antarctic Ice Sheet Divide ice core (WDC), WD2014, to be 125 ± 40 years. Furthermore, via radionuclide wiggle-matching, we determine the offset between the Hulu speleothem and ice-core timescales to be 375 years for GICC05 (75–625 years at 68 % confidence) and 225 years for WD2014 (- 25–425 years at 68 % confidence). The rather wide uncertainties are intrinsic to the wiggle-matching algorithm and the limitations set by data resolution. The undercounting of annual layers in GICC05 inferred from the offset is hypothesized to have been caused by a combination of underdetected annual layers, especially during periods with low winter precipitation, and misinterpreted unusual patterns in the annual signal during the extremely cold period often referred to as Heinrich Stadial 1. [ABSTRACT FROM AUTHOR]

During solar storms, the Sun expels large amounts of energetic particles (SEP) that can react with the Earth's atmospheric constituents and produce cosmogenic radionuclides such as 14C, 10Be and 36Cl. Here we present 10Be and 36Cl data measured in ice cores from Greenland and Antarctica. The data consistently show one of the largest 10Be and 36Cl production peaks detected so far, most likely produced by an extreme SEP event that hit Earth 9125 years BP (before present, i.e., before 1950 CE), i.e., 7176 BCE. Using the 36Cl/10Be ratio, we demonstrate that this event was characterized by a very hard energy spectrum and was possibly up to two orders of magnitude larger than any SEP event during the instrumental period. Furthermore, we provide 10Be-based evidence that, contrary to expectations, the SEP event occurred near a solar minimum. Cosmogenic radionuclides from ice cores and tree rings indicate that an extreme solar proton event has hit Earth about 9200 years ago. Contrary to expectations, the event occurred during a quiet phase of the Sun within the 11 year solar cycle. [ABSTRACT FROM AUTHOR]

Ice-core timescales are vital for the understanding of past climate; hence they should be updated whenever significant amounts of new data become available. Here, the Greenland ice-core chronology GICC05 was revised for the last 3835 years by synchronizing six deep ice cores and three shallow ice cores from the central Greenland ice sheet. A new method was applied by combining automated counting of annual layers on multiple parallel proxies and manual fine-tuning. A layer counting bias was found in all ice cores because of site-specific signal disturbances; therefore the manual comparison of all ice cores was deemed necessary to increase timescale accuracy. After examining sources of error and their correlation lengths, the uncertainty rate was quantified to be 1 year per century. The new timescale is younger than GICC05 by about 13 years at 3835 years ago. The most recent 800 years are largely unaffected by the revision. Between 800 and 2000 years ago, the offset between timescales increases steadily, with the steepest offset occurring between 800 and 1100 years ago. Moreover, offset oscillations of about 5 years around the average are observed between 2500 and 3800 years ago. The non-linear offset behavior is attributed to previous mismatches of volcanic eruptions, to the much more extensive dataset available to this study, and to the finer resolution of the new ice-core ammonium matching. By analysis of the common variations in cosmogenic radionuclides, the new ice-core timescale is found to be in alignment with the IntCal20 curve (Reimer et al., 2020). [ABSTRACT FROM AUTHOR]

Differences between 10Be records from Greenland and Antarctica over the last 100 years have led to different conclusions about past changes in solar activity. The reasons for this disagreement remain unresolved. We analyze a seasonally resolved 10Be record from a firn core (North Greenland Eemian Ice Drilling [NEEM] ice core project) in Northwestern Greenland for 1887–2002. By comparing the NEEM data to 10Be data from the NGRIP and Dye3 ice cores, we find that the Dye3 data after 1958 are significantly lower. These low values lead to a normalization problem in solar reconstructions when connecting 10Be variations to modern observations. Excluding these data strongly reduces the differences between solar reconstructions over the last 2,000 years based on Greenland and Antarctic 10Be data. Furthermore, 10Be records from polar regions and group sunspot numbers do not support a substantial increase in solar activity for the 1937–1950 period as proposed by previous extensions of the neutron monitor data. Key Points: Summer NEEM 10Be concentrations are generally higher than winter 10Be concentrations due to the stratospheric intrusionErroneous Dye 3 10Be data can bias solar activity estimates for the past toward too low10Be and sunspot data suggest higher solar activity than extensions of the neutron monitor data before 1951 [ABSTRACT FROM AUTHOR]

Northern Hemispheric high-latitude climate variations during the last glacial are expected to propagate globally in a complex way. Investigating the evolution of these variations requires a precise synchronization of the considered environmental archives. Aligning the globally common production rate variations of the cosmogenic radionuclide 10Be in different archives provides a tool for such synchronizations. Here, we present a 10Be record at <40-y resolution along with subdecadal proxy records from one Black Sea sediment core around Greenland Interstadial 10 (GI-10) ~41 ka BP and the Laschamp geomagnetic excursion. We synchronized our 10Be record to that from Greenland ice cores based on its globally common production rate variations. The synchronized environmental proxy records reveal a bipartite climate response in the Black Sea region at the onset of GI-10. First, in phase with Greenland warming, reduced sedimentary coastal ice rafted detritus contents indicate less severe winters. Second, and with a lag of 190 (± 44) y, an increase in the detrital K/Ti ratio and authigenic Ca precipitation point to enhanced regional precipitation and warmer lake surface temperatures. We explain the lagged climatic response by a shift in the dominant mode of atmospheric circulation, likely connected with a time-transgressive adjustment of the regional thermal ocean interior to interstadial conditions. [ABSTRACT FROM AUTHOR]

The research area of climate field reconstructions has developed strongly during the past 20 years, motivated by the need to understand the complex dynamics of the earth system in a changing climate. Climate field reconstructions aim to build a consistent gridded climate reconstruction of different variables, often from a range of climate proxies, using either statistical tools or a climate model to fill the gaps between the locations of the proxy data. Commonly, large-scale climate field reconstructions covering more than 500 years are of annual resolution. In this method study, we investigate the potential of seasonally resolved climate field reconstructions based on oxygen isotope records from Greenland ice cores and an isotope-enabled climate model. Our analogue-type method matches modeled isotope patterns in Greenland precipitation to the patterns of ice core data from up to 14 ice core sites. In a second step, the climate variables of the best-matching model years are extracted, with the mean of the best-matching years comprising the reconstruction. We test a range of climate reconstructions, varying the definition of the seasons and the number of ice cores used. Our findings show that the optimal definition of the seasons depends on the variability in the target season. For winter, the vigorous variability is best captured when defining the season as December–February due to the dominance of large-scale patterns. For summer, which has weaker variability, albeit more persistent in time, the variability is better captured using a longer season of May–October. Motivated by the scarcity of seasonal data, we also test the use of annual data where the year is divided during summer, that is, not following the calendar year. This means that the winter variability is not split and that the annual data then can be used to reconstruct the winter variability. In particularly when reconstructing the sea level pressure and the corresponding main modes of variability, it is important to take seasonality into account, because of changes in the spatial patterns of the modes throughout the year. Targeting the annual mean sea level pressure for the reconstruction lowers the skill simply due to the seasonal geographical shift of the circulation modes. Our reconstructions based on ice core data also show skill for the North Atlantic sea surface temperatures, in particularly during winter for latitudes higher than 50 ∘ N. In addition, the main modes of the sea surface temperature variability are qualitatively captured by the reconstructions. When testing the skill of the reconstructions using 19 ice cores compared to the ones using eight ice cores, we do not find a clear advantage of using a larger data set. This could be due to a more even spatial distribution of the eight ice cores. However, including European tree-ring data to further constrain the summer temperature reconstruction clearly improves the skill for this season, which otherwise is more difficult to capture than the winter season. [ABSTRACT FROM AUTHOR]

The last glacial period is characterized by a number of millennial climate events that have been identified in both Greenland and Antarctic ice cores and that are abrupt in Greenland climate records. The mechanisms governing this climate variability remain a puzzle that requires a precise synchronization of ice cores from the two hemispheres to be resolved. Previously, Greenland and Antarctic ice cores have been synchronized primarily via their common records of gas concentrations or isotopes from the trapped air and via cosmogenic isotopes measured on the ice. In this work, we apply ice core volcanic proxies and annual layer counting to identify large volcanic eruptions that have left a signature in both Greenland and Antarctica. Generally, no tephra is associated with those eruptions in the ice cores, so the source of the eruptions cannot be identified. Instead, we identify and match sequences of volcanic eruptions with bipolar distribution of sulfate, i.e. unique patterns of volcanic events separated by the same number of years at the two poles. Using this approach, we pinpoint 82 large bipolar volcanic eruptions throughout the second half of the last glacial period (12–60 ka). This improved ice core synchronization is applied to determine the bipolar phasing of abrupt climate change events at decadal-scale precision. In response to Greenland abrupt climatic transitions, we find a response in the Antarctic water isotope signals (δ18O and deuterium excess) that is both more immediate and more abrupt than that found with previous gas-based interpolar synchronizations, providing additional support for our volcanic framework. On average, the Antarctic bipolar seesaw climate response lags the midpoint of Greenland abrupt δ18O transitions by 122±24 years. The time difference between Antarctic signals in deuterium excess and δ18O , which likewise informs the time needed to propagate the signal as described by the theory of the bipolar seesaw but is less sensitive to synchronization errors, suggests an Antarctic δ18O lag behind Greenland of 152±37 years. These estimates are shorter than the 200 years suggested by earlier gas-based synchronizations. As before, we find variations in the timing and duration between the response at different sites and for different events suggesting an interaction of oceanic and atmospheric teleconnection patterns as well as internal climate variability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Variations in galactic cosmic rays reaching the Earth's atmosphere produce globally synchronous variations in the production rates of cosmogenic radionuclides. In consequence, they leave their imprint in tree-ring 14 C and ice-core 10 Be records. By identifying this signal and correcting for the known geochemical influences on the radionuclides, it is possible to compare and synchronize the tree-ring chronology and the Greenland ice-core time scale. Here, we compare the IntCal13 and the GICC05 time scales for the last 14,000 years via identification and synchronization of the common short-term variations in the ice-core 10 Be and tree-ring 14 C records most likely induced by variations in the solar modulation of galactic cosmic rays. We conclude that systematic time-scale differences have to be accounted for if ice-core and 14 C-dated records are compared on decadal time scales. These are mostly within the uncertainties of the time scales and the method proposed here. However, for large parts of the mid to late Holocene (i.e. after 7000 yrs BP) the best agreement between ice-core 10 Be and tree-ring 14 C records is obtained for time shifts outside the stated errors of the respective time scales. A transfer function is proposed that can be applied to synchronize the GICC05 ice-core time scale to the radiocarbon time scale. [ABSTRACT FROM AUTHOR]

Several deep Greenland ice cores have been retrieved, however, capturing the Eemian period has been problematic due to stratigraphic disturbances in the ice. The new Greenland deep ice core from the NEEM site (77.45°N, 51.06°W, 2450 m.a.s.l) recovered a relatively complete Eemian record. Here we discuss the cosmogenic 10Be isotope record from this core. The results show Eemian average 10Be concentrations about 0.7 times lower than in the Holocene which suggests a warmer climate and approximately 65–90% higher precipitation in Northern Greenland compared to today. Effects of shorter solar variations on 10Be concentration are smoothed out due to coarse time resolution, but occurrence of a solar maximum at 115.26–115.36 kyr BP is proposed. Relatively high 10Be concentrations are found in the basal ice sections of the core which may originate from the glacial-interglacial transition and relate to a geomagnetic excursion about 200 kyr BP. [ABSTRACT FROM AUTHOR]

We analyse the 8200yr BP cold event by comparing the high-resolution 10Be record from the GRIP ice core from Central Greenland with the well-known tree ring record. By transferring the absolute dated tree ring chronology to the ice core time scale, we show that the coldest phase in the GRIP record occurred around 8150yr BP. Furthermore, this method allows us to disentangle production and climate effects on 10Be and 14C with important implications for the reconstruction of past solar activity, and changes in the carbon cycle and 10Be transport. We show that, in principle, it is possible to infer changes in ocean circulation by comparing 10Be and 14C records. However, the duration of the 8200yr BP event is too short to assign unambiguously a significant change in atmospheric 14C concentration to changes in the global ocean circulation. Based on the comparison of 10Be with climate records, one could argue that the 8200yr BP cold event is triggered by a change towards lower solar activity. However, this link is questioned by the fact that around this period there are other similar and even stronger changes in solar activity that have no apparent connection to climate changes. [Copyright &y& Elsevier]

Abstract: A new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on 14C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1ka age difference between GICC05 and SFCP04 and a more than 0.5ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on 14C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties. [Copyright &y& Elsevier]

The geomagnetic dipole moment (GDM) modulates the production rates of cosmogenic radionuclides via the shielding of galactic cosmic rays. Therefore, it is possible to use this linkage to reconstruct past changes in the GDM based on cosmogenic radionuclide records from natural archives such as ice cores. Here we present a GDM reconstruction based on 10Be and 36Cl data from two Greenland ice cores from 11.7 ka to 108 ka b2k (before A.D. 2000). We find that the cosmogenic radionuclide records reflect a mixture of climate and production effects that require separation to evaluate the changes in the GDM. To minimize climate-related variations on isotope data, we applied a multi-linear correction method by removing common variability between 10Be and 36Cl and climate parameters (accumulation rates, δ18O and ion data) from radionuclide records. The resulting "climate corrected" radionuclide data are converted to GDM using a theoretical production model. Comparison of "climate corrected" radionuclides based GDM reconstructions with independent paleomagnetic-derived GDM records shows a good agreement. Furthermore, the "climate correction" leads to an improved agreement with GDM reconstructions than simply using radionuclide fluxes, lending support to the validity of our correction method to isolate production rate changes from ice core radionuclide records. With this correction method, we can extend the GDM reconstructions based on the cosmogenic radionuclides in ice cores to a period when there is a strong climate signal in the data. • We present a new continuous 10Be record from the NEEM ice core for 11.7–108 ka. • We found changing relationships between 10Be and climate data. • We reduced the climate signal in 10Be and 36Cl data using a multi-linear model. • The radionuclide-based dipole reconstructions agree well with independent records. [ABSTRACT FROM AUTHOR]

• We present a first continuously seasonally resolved 10Be record over 1951–2002. • The post-production effects on NEEM ice 10Be is quantified. • The tropopause pressure represents an important factor influencing NEEM 10Be. • A multi-linear correction method is proposed to reduce the climate bias. 10Be in ice cores has been instrumental for reconstructing past changes in solar activity prior to direct observations. For a robust use of these records, it is pivotal to understand the 10Be transport and deposition. However, there are only few high-resolution seasonal 10Be data longer than one full solar cycle (11 years) that could enable a quantification of the influences of atmospheric circulation and deposition processes on the 10Be signal in ice. Here we present a seasonally resolved 10Be data set covering the neutron monitor period (1951–2002) from a firn core connected to the NEEM (North Greenland Eemian Ice Drilling) project. The results suggest that both summer and winter 10Be reflect the production signal induced by solar modulation of galactic cosmic rays. However, superimposed on this solar signal we find additional meteorologically driven influences on 10Be transport and deposition. We found that the tropopause pressure over 30°N represents an important factor influencing NEEM 10Be concentrations on seasonal and annual scales. 10Be deposited in summer also correlates significantly with the tropopause pressure over Greenland suggesting a direct contribution of stratospheric intrusions during summer to the 10Be deposition in Greenland. To correct for these transport/deposition influences, we apply a first-order correction to the 10Be data using a multi-linear regression model. The "climate-corrected" 10Be data shows a comparable skill for reconstructing production rate changes as the 10Be composite record from five different ice cores in Greenland. The results suggest that the correction approach can be a complementary method to the stacking to better isolate the production rate signal from the 10Be data when only limited data are available. [ABSTRACT FROM AUTHOR]

Irreversible shifts of large-scale components of the Earth system (so-called 'tipping elements') on policy-relevant timescales are a major source of uncertainty for projecting the impacts of future climate change. The high latitudes are particularly vulnerable to positive feedbacks that amplify change through atmosphere-ocean-ice interactions. Unfortunately, the short instrumental record does not capture the full range of past or projected climate scenarios (a situation particularly acute in the high latitudes). Natural archives from past periods warmer than present day, however, can be used to explore drivers and responses to forcing, and provide data against which to test models, thereby offering insights into the future. The Last Interglacial (129–116,000 years before present) — the warmest interglacial of the last 800,000 years — was the most recent period during which global temperatures were comparable with low-end 21st Century projections (up to 2 °C warmer, with temperature increase amplified over polar latitudes), providing a potentially useful analogue for future change. Substantial environmental changes happened during this time. Here we synthesise the nature and timing of potential high-latitude tipping elements during the Last Interglacial, including sea ice, extent of the boreal forest, permafrost, ocean circulation, and ice sheets/sea level. We also review the thresholds and feedbacks that likely operated through this period. Notably, substantial ice mass loss from Greenland, the West Antarctic, and possibly sectors of the East Antarctic drove a 6–9 m rise in global sea level. This was accompanied by reduced summer sea-ice extent, poleward-extended boreal forest, and reduced areas of permafrost. Despite current chronological uncertainties, we find that tipping elements in the high latitudes all experienced rapid and abrupt change (within 1–2 millennia of each other) across both hemispheres, while recovery to prior conditions took place over multi-millennia. Our synthesis demonstrates important feedback loops between tipping elements, amplifying polar and global change during the Last Interglacial. The high sensitivity and tight interconnections between polar tipping elements suggests that they could exhibit similar thresholds of vulnerability in the future, particularly if the aspirations of the Paris Agreement are not met. • We review potential high-latitude tipping elements during the Last Interglacial. • These include ice sheets, sea ice, ocean circulation, permafrost and boreal forest. • Rapid and abrupt polar change occurred within 1–2 millennia across both hemispheres. • Feedback loops produce tight interconnections between polar tipping elements. [ABSTRACT FROM AUTHOR]

The sections of Greenland and Antarctic ice cores covering last glacial period have previously been synchronized primarily by their common records of gas concentrations and cosmogenic isotopes. Here, we apply annual layer counting and matching of volcanic peak patterns to synchronize the onsets and terminations of Greenland Interstadials (GI) in Marine Isotope Stage 3 (MIS3, 25-60 ka). Based on the identification of more than 50 significant bipolar volcanic events throughout MIS3, most abrupt climate events can be synchronized between the two Hemispheres at decadal precision. Layer counting has been performed in the Greenland NGRIP and the Antarctic EDML ice cores using high-resolution records of chemical impurities, dust, and visual grey scale intensity. The time scales obtained from layer counting are not always in agreement with existing ice core chronologies. Volcanic peak patterns have been identified in all available acidity records from the Greenland GRIP, GISP2, NGRIP, and NEEM and the Antarctic EDML (Atlantic sector), EDC (East Antarctic plateau), and WDC (West Antarctica) ice cores. The obtained volcanic synchronizations within Greenland and within Antarctica are in agreement with existing volcanic synchronizations. The bipolar volcanic synchronization is supported by cosmogenic record patterns at several of the major GI onsets and it is in accord with the cosmogenic synchronization at around the geomagnetic Laschamp event (41 ka). The bipolar volcanic synchronization is offset from the NGRIP-WDC methane synchronization by up to 150 years, generally pushing the Antarctic record towards older ages at the GI onsets. The general Antarctic response to a GI onset is a direct warming at the EDC and WDC sites that peaks within a century and a less significant cooling at the EDML site, possibly attributed to a northward shift of the southern hemisphere westerly winds. This pattern is however not consistent among all GI onsets and in particular the weaker GI events show deviating Antarctic response patterns. Several of the sharp Greenland climate transitions in MIS3 are associated with periods of strong volcanism suggesting that volcanism may work as a trigger of abrupt climate change. Other abrupt transitions are not associated with volcanism and many strong volcanic events do not show a response in the climate records. Overall, the bipolar volcanic synchronization gives strong support for the suggested bipolar seesaw mechanism. [ABSTRACT FROM AUTHOR]

Studying sub-annual 10Be records is vital for the understanding of the isotope distribution inice cores and related interpretations of the changes in solar activity and climate.However, such high-resolution data from Greenland are scarce and cover less thanone full solar cycle (11yr). Here we present a seasonally resolved 10Be data setcovering the neutron monitor period (1951-2002) from a firn core connected to theNEEM (North Greenland Eemian Ice Drilling) project. The result suggests that bothsummer and winter 10Be reflect the production signal induced by solar modulation ofgalactic cosmic rays, although some mismatch to the solar signal partly disturbs fullagreement between the records. We found that the NEEM summer and winter 10Beis influenced by different climate conditions and, therefore, consideration of theannual 10Be deposition minimizes the seasonal noise. We also found that the varyingtropopause height over 30˚ N represents a main factor controlling the NEEM 10Bedata on a seasonal and annual scales. Exceptionally low tropopause height mayhave contributed to a peak in winter 10Be deposition in 1983 which is not directlyassociated with the 10Be production rate. Summer 10Be data also correlates significantlywith the tropopause height over the Greenland suggesting a direct contribution ofsummer stratospheric 10Be intrusion to the 10Be deposition in Greenland. The resultsuggests that summer 10Be deposition may be more influenced by stratospheric 10Beintrusions than winter 10Be. To adjust for these climate biases, we apply a first-ordercorrection to 10Be data using a multi-linear regression model. The climate-corrected10Be data indicate better correlations with the production rate than the original10Be data. Furthermore, a 10Be composite record from 5 ice cores in Greenlandincluding the NEEM ice core data also shows the exceptional 10Be deposition duringthe early 1980s. This feature suggests a regional climate influence on Greenland10Be that can be difficult to correct for by construction of a composite record usingGreenland ice core data only. This study shows that long term seasonally resolved 10Berecords may provide a better understanding of climate factors influencing the 10Bedeposition in ice cores and improve reconstructions of past changes in solar activity. [ABSTRACT FROM AUTHOR]

Solar cosmic rays, which are mainly accelerated in shocks driven by coronal massejections, can represent a challenge to our technological society. Instrumental data onthese events only date back to the advent of neutron monitors in the 1940s and ofsatellite measurements. However, the atmospheric production rates of the cosmogenicradionuclides 10Be, 14C, and 36Cl have been shown to be enhanced by particularlyextreme and rare solar events. Of these three nuclides, the production rate of 36Clhas been proposed to have the greatest sensitivity to protons accelerated duringsolar events. Yet, no continuous and high resolution measurements of ice-core 36Clare available. Here we present two such 36Cl records from the NGRIP and Dye-3ice cores, both of which are from Greenland, that we investigate for hints of solarstorms for the past six hundred years. We observe several potential increases thatcould be linked to solar storms including one that occurs simultaneously in bothice cores and around the period of an extreme geomagnetic storm that took placein September 1909. We also consider the different thresholds in energy spectraand fluence for solar cosmic rays to be detectable in ice-core 36Cl and 10Be data.Finally, we show that there was no significant enhancement in 36Cl concentration dataaround the Carrington event of 1859 CE. Accordingly, we infer an upper limit to theflux of solar energetic protons related to the event, assuming they did hit Earth. [ABSTRACT FROM AUTHOR]

It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores, enabling reconstructions of past flora and fauna. We show that high-altitude southern Greenland, currently lying below more than 2 kilometers of ice, was inhabited by a diverse array of conifer trees and insects within the past million years. The results provide direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections.