Displays

Global changes in climate, especially in mean temperature, receive increasing public as well as scientific attention under the current warming trend. However, the probability of extreme events and their societal impact is also governed by changes in climate variability. Improving the understanding of changes in both and their relationship is crucial for projecting reliable climate change scenarios. Model-data comparisons between general circulation models and speleothem paleoclimate archives, with δ¹⁸O as a temperature and precipitation proxy, have been suggested to test and validate the capability of different climate models.

Speleothems are precisely date-able and provide well preserved (semi-)continuous climate signals in the lower and mid-latitudes, providing a suitable archive to assess a model’s capability to simulate climate variability on time scales longer than those observable. However, the δ¹⁸O measured in speleothem calcite does not directly represent temperature or precipitation but results from multivariate, non-linear processes on top of the dominant meteoric controls on δ¹⁸O in precipitation.

Here, we evaluate correlations and networks between different records and power spectral densities across a speleothem database for the past millennium (850-2000CE), testing for representativity of individual records for the time period. Similarity measures are applied to proxy records and to the local climate variables obtained from three isotope-enabled HadCM3 simulations to evaluate simulation biases across different parameters and to distinguish main climate drivers for individual records or regions. The proxy records show strong damping of variability on shorter time scales compared to simulations down-sampled to record-resolution, acting like simple filter processes with realistic time scales for karst transit times.

Based on the evidence from proxies and models for the past 1000 years, we test for realistic parameter constraints and sufficient complexity of a speleothem proxy system model to represent low-latitude changes in climate variability on interannual to centennial timescales.

How to cite: Buehler, J., Kirschner, M., Roesch, C., Holloway, M. D., Sime, L., and Rehfeld, K.: Comparison of isotopic signatures in speleothem records and model simulations for the past millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8982, https://doi.org/10.5194/egusphere-egu2020-8982, 2020.

Recent changes and variability in climate conditions leave a significant footprint on the distribution and properties of sea ice, as it is sensitive to environmental variations. We investigate the rapidly transforming region of the Western Antarctic Peninsula (WAP) focusing on the conditions and development of sea ice in the pre-satellite era. For this study on past sea ice cover we apply the novel proxy IPSO₂₅ (Ice Proxy for the Southern Ocean with 25 carbon atoms; Belt et al., 2016). Three sampling sites were selected to cover areas near the Antarctic mainland, in the Bransfield Basin (2000 m depth) and the deeper shelf under an oceanographic frontal system. Analysis of short cores (multicores) resolving the last 200 years (based on ²¹⁰Pb_ex dating) focused on geochemical bulk parameters, biomarkers (highly branched isoprenoids, GDGTs, sterols) and diatoms. These results are compared to multiple climate archives and modelled data. This multiproxy based approach provides insights on changes in spring sea ice cover, primary production regimes, subsurface ocean temperature (SOT based on TEX^L₈₆) and oceanographic as well as atmospheric circulation patterns. While environmental proxies preserved in two cores near the coast and in the Bransfield Basin reflect the properties of water masses from the Bellingshausen Sea and Weddell Sea, respectively, data from the third core at the deeper shelf depict mixed signals of both water masses. Our study reveals clear evidence for warm and cold periods matching with ice core records and other marine sediment data at the WAP. We observe a general decrease in SOT and an increase in sea ice cover overprinted by high decadal fluctuations. Trends in SOT seem to be decoupled from atmospheric temperatures in the 20^th century, and this is supported by previous studies (e.g. Barbara et al., 2013), and may be related to the Southern Annual Mode. We consider numerical modelling of sea ice conditions, sea surface temperature and SOT for further support of our findings.

References:

Barbara, L., Crosta, X., Schmidt, S. and Massé, G.: Diatoms and biomarkers evidence for major changes in sea ice conditions prior the instrumental period in Antarctic Peninsula, Quat. Sci. Rev., 79, 99–110, doi:10.1016/j.quascirev.2013.07.021, 2013.

Belt, S. T., Smik, L., Brown, T. A., Kim, J. H., Rowland, S. J., Allen, C. S., Gal, J. K., Shin, K. H., Lee, J. I. and Taylor, K. W. R.: Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25, Nat. Commun., 7, 1–10, doi:10.1038/ncomms12655, 2016.

How to cite: Vorrath, M.-E., Cárdenas, P., Rebolledo, L., Shi, X., Müller, J., Lange, C. B., Mollenhauer, G., Muñoz, P., Martínez Méndez, G., Geibert, W., and Esper, O.: Multiproxy climate and sea ice reconstruction of the industrial era at the Western Antarctic Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-525, https://doi.org/10.5194/egusphere-egu2020-525, 2020.

The Interdecadal Pacific Oscillation (IPO) is a nominally 15-30 year climate mode that has been identified through analysis of tropical and extratropical Pacific sea surface temperatures over the past 150 years. It is still unclear whether the IPO is a true oscillation or whether it is simply the low frequency response of the climate system to forcing (natural and potentially anthropogenic), principally ENSO. Regardless of this, the IPO as it is currently known has clear climate impacts, one example being hydroclimate variability in Australia. In positive phases of the IPO, drought risk is heightened due to a reduction in the likelihood of large, recharging La Nina-derived rainfall events. Conversely, in IPO negative phases, flood risk in Australia is greatly increased due to an increased likelihood of such rain events.

Previous work derived a 1000 year, accurately dated reconstruction of the IPO from multiple palaeoclimate archives from the Law Dome ice core in East Antarctica. This reconstruction provided a long-term reconstruction with which to assess the true risk of drought- and flood-prone epochs in Australia. Subsequently, an entirely independent reconstruction of the IPO was developed using SE Asian tree rings by Buckley et al. in 2019, also spanning most of the last millennium. The fidelity the two reconstructions display with respect to the instrumental IPO record and with each other suggests both are faithfully representing IPO variability. Here we present an IPO reconstruction that doubles the temporal span of existing reconstructions to cover the last 2000 years using newly analysed and dated material from the Law Dome ice core. This new, longer reconstruction identifies important features of Pacific decadal variability that have significant implications for understanding hydroclimate epochs across not only Australasia, but the Pacific region as a whole.

How to cite: Vance, T., Kiem, A., Roberts, J., Jong, L., Plummer, C., Curran, M., Moy, A., and van Ommen, T.: An annually dated Interdecadal Pacific Oscillation reconstruction spanning the last two millennia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6218, https://doi.org/10.5194/egusphere-egu2020-6218, 2020.

Sea surface temperatures in the eastern equatorial Pacific exert powerful influence on the climate beyond the tropics through strong atmosphere-ocean coupling. Records of eastern Pacific sea surface temperatures are of vital importance for identifying the linkages between short-term climate variability and long-term climate trends. Here we reconstruct eastern equatorial Pacific sea surface temperature and salinity from paired trace metal and stable isotope analyses in foraminifera from a sediment core near the Galápagos Islands. Sea surface temperatures are correlated with reconstructed Northern and Southern hemisphere temperature records suggesting a common origin. We propose that this temperature signal originates in the extra-tropics and is transmitted to the eastern Pacific surface via its source waters. We find exceptions to this cooling during the Little Ice Age and during the last century, where notable sea surface temperature increases are observed. We calculate δ¹⁸O_sw from paired stable isotope and trace element analyses and derive salinity, which reveals a significant trend toward fresher surface waters in the eastern equatorial Pacific. The overall trend toward cooler and fresher sea surface conditions is consistent with longer-term trends from both the Eastern and Western Pacific.

How to cite: Rustic, G., Koutavas, A., and Marchitto, T.: Cooling and freshening of the eastern equatorial Pacific over the last 2000 years , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12476, https://doi.org/10.5194/egusphere-egu2020-12476, 2020.

The South Pacific Convergence Zone (SPCZ) is the largest driver of precipitation variability over South Pacific island communities during the austral warm season influencing the severity and duration of drought and the frequency of tropical cyclones. The SPCZ is known to exhibit variability on a range of timescales, from intra-seasonal to multidecadal variations, modulated by the Interdecadal Pacific Oscillation (IPO). Despite its climatic and societal importance, determining the causes of low frequency variability in the SPCZ has been hampered by the short instrumental data record, with most comprehensive analyses since the satellite era. Here we report the first paleoclimate reconstruction of the SPCZ, allowing climate variability in the South Pacific region to be explored back to 700 CE. Our 1300-year reconstruction of the SPCZI (South Pacific Convergence Zone Index; the difference between mean sea level pressure between Apia, Samoa and Suva, Fiji) is based on a trans-Pacific network of precisely dated tree-ring proxies. Capturing SPCZ teleconnections from both sides of the Pacific has produced a robust, unbiased reconstruction with excellent reconstruction skill over the entire period. El Niño-Southern Oscillation periodicities (∼3-7 years) are pervasive throughout the SPCZI reconstruction. Multidecadal periodicities wax and wane, apparently coinciding with the timing of the Medieval Climate Anomaly (c. 1000-1200 CE) and Little Ice Age (1300-1700 CE). We discuss some of the drivers of SPCZI variability including global dimming events. Our reconstruction helps improve our understanding of past hydroclimatic behaviour in the southwest Pacific and can be used to validate general circulation model projections for Pacific Island communities in the twenty-first century.

How to cite: Higgins, P., Palmer, J., Turney, C., Andersen, M., and Cook, E.: A 1300-year reconstruction of the South Pacific Convergence Zone using a Pacific-wide tree-ring network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11844, https://doi.org/10.5194/egusphere-egu2020-11844, 2020.

Tree-ring chronologies are the main source for annually resolved and absolutely dated temperature reconstructions of the last millennia and thus for studying the intriguing problem of climate impacts. Here we focus on central Europe and compare the tree-ring based temperature reconstruction with reconstructions from harvest dates, long meteorological measurements, and historical model data. We find that all data are long term persistent, but in the tree-ring based reconstruction the strength of the persistence quantified by the Hurst exponent is remarkably larger (h = 1.02) than in the other data (h = 0.52 − 0.69), indicating an unrealistic exaggeration of the historical temperature variations. We show how to correct the tree-ring based reconstruction by a mathematical transformation that adjusts the persistence and leads to reduced amplitudes of the warm and cold periods. The new transformed record agrees well with both the observational data and the harvest dates-based reconstructions and allows more realistic studies of climate impacts. It confirms that the present warming is unprecedented.

How to cite: Ludescher, J., Bunde, A., Büntgen, U., and Schellnhuber, H. J.: Setting the tree-ring record straight, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19795, https://doi.org/10.5194/egusphere-egu2020-19795, 2020.

The production of 10Be in the atmosphere in the high latitudes is modulated by solar variability. Time-series records of 10Be from ice cores therefore provide important information on variations in solar activity through time, which is fundamental to understanding climate variability. However, deposition of 10Be to the ice surface is also influenced by variability in atmospheric circulation and deposition processes, and thus, many 10Be ice core records remain difficult to interpret.

South Pole is arguably the best available location for minimizing the influence of variable atmospheric circulation on 10Be deposition. The single existing 10Be record from South Pole covers the last millennium and ends in CE 1982.

We present a new South Pole 10Be record from the late Holocene, together with examplary measurements from the last glacial period, complemented by climate modeling experiments of atmospheric 10Be production, transport and deposition physics. Our continuous one-meter resolution record covers so far the last three millennia. The data from the last millennium agree well with the existing 10Be record by Raisbeck et al. (1990). The 10Be data from the South Pole ice core matches the historic sunspot records strikingly, providing a robust calibration between sunspot number and 10Be deposition. The coincident timing of major shifts in sunspot number and 10Be provides an independent confirmation of the South Pole ice core timescale.

Independently, our model simulations of both internannual variablity and glacial vs. interglacial 10Be production, transport and deposition indicate that 10Be in South Pole snow is robust even to significant climate changes, suggesting that the measured 10Be primarily reflect changes of solar activity over that period. In turn, our model-data comparison allows to evaluate potential shifts in solar activity through the late Holocene, and during the glacial-interglacial transition.

How to cite: Schaefer, J. M., Steig, E. J., and Ding, Q.: Be-10 measurements and modeling results from the South Pole ice core – here comes the sun!, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12153, https://doi.org/10.5194/egusphere-egu2020-12153, 2020.

Global climate change is projected to exacerbate regional droughts across much of the globe by the end of the 21^stcentury, while increases in precipitation extremes are projected to increase regional flood risk. Trends consistent with these changes have already been observed across the contiguous United States (US). Instrumental records indicate a 20^th-century trend towards drier soil moisture conditions over a large portion of the western US and wetter conditions over the eastern US, termed here as the east-west US aridity gradient. If these trends continue through the end of the 21^st century, there would be significant consequences for human and ecological health, socioeconomics, water resources, and agriculture in both the semi-arid southwestern and flood-prone eastern US. A greater understanding of the spatiotemporal nature of terrestrial water variability across the US is critical to mitigate its impacts and inform policy decisions in the coming decades.

Using empirical orthogonal functions (EOFs) of instrumental summer (JJA) drought and soil moisture indices with a normalized Varimax rotation, we identify multiple independent regional soil moisture modes across the contiguous US. Modes in the northeastern and midwestern US contribute to wetting in the eastern US and a mode in the southwestern US contributes to drying in the western US, collectively increasing the east-west aridity gradient during the 20^th century. The gradient has been studied previously, but its recent observed trend has not been contextualized within the natural range of variability in the paleoclimate record. Such a contextualization would improve our understanding of the underlying drivers of the modern trend and help benchmark future climate change projections. Here, we seek to (1) determine the timescales that the aridity gradient has been most active, (2) contextualize and evaluate the spatial characteristics and physical mechanisms of the aridity gradient trend within its natural range of climate variability, and (3) evaluate the relative roles of anthropogenic climate change and natural climate variability on the recent gradient trend.

The modes impacting the observed US aridity gradient are also apparent in multiple paleoclimate data products that span the past millennium (e.g., tree ring-reconstructed North American Drought Atlas, multi-proxy Paleo Hydrodynamics Data Assimilation product), although spatial characteristics of these modes vary through time. Using these products, we find that the recent observed multidecadal trend toward wetting in the east and drying in the west was abnormal relative to the last millennium. During 1956-2005, the mean soil-moisture difference between the east and west US was larger than during any other 50-year period since the end of the Medieval Warm Period (1201-1250 CE). Additional work will decompose the effects of temperature and precipitation on soil moisture trends and variability through time and relate the reconstructions to last-millennium CMIP5/CMIP6 climate simulations to assess model ability to simulate the reconstructed range of multi-annual to decadal hydroclimatic variability across the US. We will also assess climate projections to investigate the potential contribution of anthropogenic climate trends to the strengthened aridity gradient observed over the past century, providing insights into how this gradient may trend in future decades.

How to cite: Bishop, D., Williams, P., Seager, R., Cook, E., Peteet, D., Cook, B., and Rao, M.: Placing the east-west United States aridity gradient in a millennial context, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6120, https://doi.org/10.5194/egusphere-egu2020-6120, 2020.

South America hydrological cycle is highly dependent on the water vapor transport advected from tropical-equatorial Atlantic, Southern Pacific as well as the polar advections. While the Pacific contribution in the continental water budget is basically restricted to the western Andes region, the Atlantic Ocean and others mechanism – as advection in Amazonas basin – play a great role in modulating precipitation over the continent. Besides, modes of climatic variability, such as ENSO, have an important role in pluviosity distribution patterns and respectively intensity, influencing the availability of water resources from mountainous regions, vital to ecosystems and to economy and human wellbeing. Intense droughts and floods observed continentally during the modern epoch have pointed to the need of better understanding the regional climate related issue. Recent paleoclimate advances, especially the creation of high-standard regional proxy record databases, allow describing the South American climate from a new perspective. Here we present an effort of the South American PAGES 2k paleo-community LOTRED-SA to build a South America hydrology robust and unique multiproxy database. We present a spatial and temporal approach of the South American hydro-climate reconstruction based on more than 360 available databases in an attempt to unravel their changes and impacts. Following a multi-proxy approach, we expect to better describe duration and location of wet and dryer climate regimes at most important climate spatial domains, and modes patterns on South America, during each period; as well as their predominant variability base on high resolution records (tree rings, speleothems, lake, marine and ice cores). we combine here the use of different proxy records and spatial-temporal approach, owing to consolidate interpretations of the hydrological cycles in South America.

How to cite: Briceño-Zuluaga, F. J., Nogueira, J., Evangelista, H., Apaéstegui, J., Sifeddine, A., Carlo Espinosa, J., Neukom, R., Von Gunten, L., Gonzalez Arango, C., Khodri, M., Monteiro, H. L., Prestes, A., Pereira de Souza Echer, M., Ledru, M.-P., Valdez, J., Cruz, F. W., Strikis, N., and Dias, P.: Unraveling South American spatial precipitation patterns, intensity and variability through a multi-proxy approach for the past 2 kyr, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22649, https://doi.org/10.5194/egusphere-egu2020-22649, 2020.

Sub-decadal to annual climate oscillations are particularly relevant to human climate perception, including such well-known phenomena as the seasonal monsoons and El Niño-Southern Oscillation (ENSO). To assess the variability of these oscillations in the past, proxies for climate parameters that are influenced by these oscillations (e.g., temperature, precipitation) and geologic materials with a temporal resolution able to record them are both needed. However, even in settings where these two criteria are met, the sample size needed for laboratory analysis can limit temporal resolution.

We utilize a novel mass spectrometry imaging technique to measure and map distributions of climate-relevant biomarkers (e.g., GDGTs, alkenones) from intact sediment core surfaces in sub-mm increments, unlocking the ability to reconstruct sub-annual paleoclimate. These same sediment sample surfaces are analyzed with micro-XRF mapping to enable congruent examination of complementary elemental- and biomarker-derived paleoenvironmental proxies at ultra-high spatial resolution, both down-core and along-lamination.

We applied our biomarker and elemental mapping techniques to annually-laminated Pakistan Margin (northeastern Arabian Sea) sediment core SO90-58KG, spanning 1790-1993 CE. Laminated Pakistan Margin marine sediments are excellent archives of past climate and oceanographic conditions that are influenced by the summer (Southwest) and winter (Northeast) monsoons of India. We measured alkenones and GDGTs at 200 µm resolution, and elemental abundances at 50 µm resolution. Reconstructed sea surface temperatures (SSTs) were calculated from alkenone (U^K'₃₇) and GDGT (CCaT) ratios, respectively, with sample resolution up to four points per year. Principal component analysis was applied to the elemental measurements. The first principal component (PC1) is associated with siliciclastic elements (Al, Si, K, Ti, Fe), and is used as a proxy for sub-annual precipitation-driven river runoff.

Reconstructed SSTs for both biomarker proxies contain congruent trends, and align with the annual range of instrumental measurements (23 to 30 °C). The annual cycles in SST, with low temperatures driven by mixing during the winter monsoon, are prominent in the time series and highly significant in their power spectra. Using this annual cycle in SST and our paired elemental measurements, we determine the season(s) of river runoff. PC1 is typically highest when SST is low, suggesting runoff/deposition usually occurs during the winter monsoon, consistent with precipitation from westerly storms. However, some years contain PC1 peaks that occur in-phase with warm SSTs, suggesting expansion of summer monsoon rainfall west of Karachi during these years. This work demonstrates the cutting edge of high-resolution paleoclimate science, and provides new insights into the variability of the Indian monsoon from its sensitive western edge.

How to cite: Napier, T. J., Wӧrmer, L., Wendt, J., Lückge, A., and Hinrichs, K.-U.: Influences of the seasonal Indian monsoons, 1790-1993 CE: Sub-annual sea surface temperature and precipitation reconstructed from laminated Pakistan Margin sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20153, https://doi.org/10.5194/egusphere-egu2020-20153, 2020.

The subtropical dry zones, including the broader Mediterranean region, are likely to experience considerable changes in hydroclimate in a warming climate. An expansion of the atmosphere’s meridional overturning circulation, the Hadley circulation, over recent decades has been reported, with implications for regional hydroclimate. Yet, there exists considerable disagreement in magnitude and even sign of these trends among different metrics that measure various aspects of the Hadley circulation, as well as discrepancies in trends between different analysis periods and reanalysis products during the 20^th century. In light of these uncertainties, it is therefore of interest to explore variability and trends in subtropical hydroclimate and its dominant driver, the Hadley Circulation. We focus on the North Atlantic sector and explore variability in the Azores High, the manifestation of the Hadley Circulation’s downward branch, and hydroclimate across the Iberian Peninsula using a combination of observational/reanalysis products, state-of-the-art climate model simulations, and hydroclimatically-sensitive stalagmite records over the past 1200 yr. The Last Millennium Ensemble (LME) with the Community Earth System Model provides thirteen transient simulations covering the period 850 to 2005 A.D. with prescribed external forcing (e.g. greenhouse gas, solar, volcanic, land use, orbital, and aerosol) and smaller subsets with individual forcing only. The LME is shown to accurately simulate the variability and trends in the Azores High when compared to observational records from the 20^th century. We evaluate variability in the Azores High (e.g., size, intensity, position) in relation to other key metrics that measure different aspects of the Hadley circulation throughout the course of the last millennium, as well as during key periods, such as the Little Ice Age or Medieval Climate Anomaly. The smaller subsets of LME simulations with individual forcing factors (e.g., solar, volcanic) allow for an attribution of past changes in regional hydroclimate to external drivers. Results from the climate model simulations are compared with hydroclimate reconstructed from stalagmites from Portuguese caves.

How to cite: Ummenhofer, C., Cresswell-Clay, N., Thatcher, D., Wanamaker, A., and Denniston, R.: Variability of the Azores High and regional hydroclimate over the past millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19571, https://doi.org/10.5194/egusphere-egu2020-19571, 2020.

The spatial and temporal variability of droughts in the Euro-Mediterranean area during the last two millennia has been analyzed by comparing the Old World Drought Atlas (OWDA) dentrochronological based reconstruction and 13 simulations including a complete set of natural and anthropogenic forcings from the Community Earth System Model- Last Millennium Ensemble (CESM-LME). The OWDA represents scPDSI estimates, whereas for the CESM-LME soil moisture is used. A clustering into regions of objectively different behavior is achieved through rotation of principal components and the resulting regionalizations of the OWDA and the CESM-LME are compared.

The resulting regions from the reconstructions and model are overall consistent. Some regions are coincident in both and in some cases model regions are a combination of the reconstructed ones. The resulting classification is also robust across the model ensemble, although It is found that the definition of some hydroclimatic regions shows some sensitivity to internal variability.

The temporal variability of drought within each region is analyzed. Differences are found in the level of low frequency variability among regions with implications for the probability of having long intense droughts in different areas. Megadroughts have been found to exist both in the reconstructions and in the simulations and their occurrence suggest rather internal variability dependances rather than responses to external forcing.

How to cite: González-Rouco, F., López-Cayuela, M. A., Navarro, J., García-Bustamante, E., García-Cantero, N., Melo-Aguilar, C., and Steinert, N.: European drought during the last two millennia from reconstructions and model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19963, https://doi.org/10.5194/egusphere-egu2020-19963, 2020.

Grain was the most important food source for a majority of the population in early modern Europe (c. 1500–1800). The price level and volatility had huge societal effects: high prices tended to increase mortality, decrease fertility as well as affect overall consumption patterns. To what extent climate variability influenced the long-term grain price evolution in early modern Europe has for a long time been a matter of debate. Recent advances in high-resolution palaeoclimatology and historical climatology have made it possible to reassess the grain price–climate relationship in time and space with unprecedented detail (Esper et al. 2017). We analyse the climate signal in 56 multi-centennial long series of annual prices of barley, oat, rye, and wheat across Europe. The grain price–climate relationship in regional clusters of grain price data is analysed using both tree-ring based temperature reconstructions, documentary-based temperature reconstructions, tree-ring based drought reconstructions, and early temperature and precipitation instrumental data, considering possible different climate responses in each grain type and different seasonal targets. In addition, we systematically investigate whether, and to what extent, the imprints of variations in solar forcing, including possible lag effects, can be detected in the grain prices.

We find a highly significant and persistent negative temperature–price relationship (i.e., cold = high prices and vice versa) across all of Europe and for all four grain types using both temperature reconstructions and instrumental temperature data. Excluding the Thirty Years’ War (1618–1648) and the period following the French Revolution (1789), this relationship is as strong as r = –0.41 between the annual average of all the 56 included European grain price series and the reconstructed June–August temperature for the previous year. The correlations to drought and precipitation are, on the other hand, mainly insignificant and inconsistent in time and space. The evidence for the existence of the effect of solar forcing variations on early modern European grain prices is not strong, although we can detect statistically significant grain price–solar forcing relationships for certain regions. In conclusion, we find much stronger evidence than hitherto reported for long-term temperature imprints on historical grain prices in Europe, implying that temperature variability and change have been a more important factor in European economic history, even in southern Europe, than commonly acknowledged.

Reference:

Esper J., et al., 2017. Environmental drivers of historical grain price variations in Europe. Clim. Res. 72: 39–52.

How to cite: Charpentier Ljungqvist, F., Thejll, P., Christiansen, B., Seim, A., Hartl, C., and Esper, J.: The significance of climate and solar variability on historical European grain prices, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11257, https://doi.org/10.5194/egusphere-egu2020-11257, 2020.

Biogeochemical proxy records from Icelandic lake sediment reflect large-scale shifts in North Atlantic Holocene climate and highlight the impact that North Atlantic Ocean- and atmospheric circulation has on Iceland’s local climate. Following Early Holocene warmth, millennial-scale cooling has been modulated by centennial-scale climate change, culminating in the transition to the Little Ice Age (ca. 1300-1900 CE). Although the long-term cooling trend is presumably driven by variations in Earth’s orbit and the concomitant decline in Northern Hemisphere summer insolation, the centennial-scale variability has been linked to variations in solar irradiance, the strength of the Atlantic Meridional Overturning Circulation, volcanism coupled with sea ice/ocean related feedbacks and internal modes of atmospheric variability. One manifestation of these regional climate changes on Iceland is the intensification of soil erosion, resulting in the degradation of its eco-systems and landscape. In recent millennia, persistent and severe soil erosion has also been linked to human impact on the environment following the settlement ~874 CE, rapid population growth and the poorly consolidated nature of tephra dominated soils. However, against the argument that the onset of severe soil erosion coincided with human settlement are composite landscape stability proxies extracted from the high-resolution, precisely-dated lake sediment cores. These data suggest event-dominated landscape instability and soil erosion began in the Middle to Late Holocene with an intensification of landscape instability around ~500 CE, several centuries before the acknowledged settlement of Iceland, after which soil erosion continue to increase. In order to statistically identify abrupt and persistent changes within our landscape stability proxy records, we performed an analysis that targets mean regime shifts in individual time series. The first clear regime shift occured around ~500 CE, with a second large shift ~1200 CE. In order to provide a causal explanation for these regime shifts, we looked to a new 2 ka fully coupled climate transient simulation using CESM1, with forcing data from PMIP4, including insolation, volcanic aerosols, land-cover, and GHG. The CESM results show a ~0.5°C reduction in summer temperature in the first millennium CE, consistent with increased landscape instability and soil erosion in Iceland.  A second phase of persistent summer cooling in the model occurs after 1150 CE, with stronger cooling after 1450 CE, reaching a minimum shortly after 1850 CE, ~1°C lower than at the start of the experiment. Orbitally driven declines in summer insolation appear to be the dominant forcing early in the first millennium CE, with volcanism and solar irradiance reductions increasingly important after 500 CE and in the second millennium CE, but positive feedbacks from sea ice and the overturning circulation are necessary to explain the magnitude of peak LIA cooling when soil erosion is at its greatest in Iceland. Collectively, our initial results suggest that natural variations in regional climate and volcanism are likely responsible for soil erosion prior to human impact, with intensification of these processes following settlement particularly during the cooling associated with the Little Ice Age.

How to cite: Geirsdóttir, Á., Harning, D., Andrews, J., Miller, G., Zhong, Y., and Jahn, A.: Climate, volcanism and human impact on Iceland’s landscape during the last two millennia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4141, https://doi.org/10.5194/egusphere-egu2020-4141, 2020.

We present high temporal (near-annually) resolved δ¹⁸O values from absolutely dated stalagmite record that represents the Indian Summer Monsoon (ISM) rainfall variations for the Indian subcontinent spanning from 207 AD to 2014 AD. This rainfall reconstruction shows ISM varaitions for four major global climatic periods viz., Roman Warm Period (RWP), Dark Ages Cold Period (DACP), Medieval Warm Period (MWP) and Little Ice Age (LIA). Cave records from different patrs of the sub-continent synchronously show enhanced precipitation during DACP. This wet period was forced by Solar-induced El-NiNo Southern Oscillation (ENSO) and Tibetan Plateau Temperature. Cliamtic conditions were wetter during LIA than that during MWP, as the former witnessed more number of wet monsoon years. However, MWP witnessed the strongest and the weakest monsoon years in the last two millennia. The direct influence of Soalr activity on the position of Inter Tropical Convergance zone (ITCZ) might have caused the observed ISM variability of MWP. Altough ISM shows largest variability during MWP, the overall monsoon state was moving towards wetter conditions, forced by ENSO. Solar induced forcings on ENSO influenced ISM during LIA. Our results suggest of non-stationary dynamical forcings over ISM during different periods in the last two millennia.

How to cite: Gandhi, N., Reddy A., P., Krishnan, R., and Yadava, M. G.: Indian Monsoon Rainfall Variability and associated Climatic forcings in the last two millennia inferred by a Stalagmite from the peninsular India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-89, https://doi.org/10.5194/egusphere-egu2020-89, 2020.

Changes in marine primary productivity (MPP) over the 21st century are expected to occur under the prevailing climate change scenario. For better understanding of past climate variability, we reconstructed MPP at high resolution (~1-2 years) for the past 2000 years analyzing biogenic silica and total organic carbon (TOC %) on a sediment core collected from Soledad Basin (25°N, 112°W), Baja  California, Mexico. Located in the Eastern Tropical North Pacific, this suboxic basin is ideal for palaeoceanographic reconstructions due to its high sedimentation rate (2 mm/year), which allow us to reconstruct past changes in the ocean and climate at high resolution. Our results show an increasing trend in the variability of MPP for the past 2000 years: biogenic silica content does not show a well-defined trend, but rather it is dominated by strong multidecadal and prominent centennial-scale cycles while TOC (%) shows a slight increasing trend towards the present, starting at least 2000 years ago. Spectral analysis confirms the presence of multidecadal to centennial cycles. These results will be discussed in the context of the Anthropocene and natural climate variability.

How to cite: Treinen-Crespo, C., Carriquiry, J., Villaescusa, J., and Repiso-Terrones, E.: 2000 years of marine primary productivity in the Eastern Tropical North Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-903, https://doi.org/10.5194/egusphere-egu2020-903, 2020.

Variability in global wave climate has been observed to occur in response to climate changes influencing the wave-generating zones. This highlights the need for an improved understanding of long-term wave-climate cycles, considering the multi-decadal variability of the atmospheric patterns and large-scale climate drivers. In this study, a novel use of the morphology of former shorelines preserved in beach-foredune ridges was applied to reconstruct changes in predominant wave directions in the Subtropical South Atlantic during the Late Holocene. A 3km wide semi-continuous sequence of beach-foredune ridges preserved within the Pinheira Strandplain (Santa Catarina State, Brazil) was mapped in order to extract the orientation of the former shorelines and derive a 3000-year record of inferred mean wave direction. The mean wave direction series was compared to ~1000 years of decadal means of mid-latitude mean sea-level pressure gradients (∆MSLP) and zonal westerly wind velocities estimated from the CESM1-CAM5 “Last Millennium Ensemble (LME)”, and to 2000 years of air-surface temperature anomalies for Southern Hemisphere. Results showed that multi-centennial cycles of oscillation in predominant wave direction occurred in accordance with stronger (weaker) South Atlantic mid-latitude mean sea-level pressure and zonal westerlies winds, favouring wave generation zones in higher (lower) latitudes and consequent southerly (easterly) wave climate dominance. It was identified the Southern Annular Mode as the main climate driver responsible for these changes, responding for 43% of the variance in the Subtropical South Atlantic atmospheric patterns in the last 1000 years. Long-term variations in interhemispheric air-surface temperature offsets, coincident with oscillations in wave direction, may have influenced wave-generation patterns similarly to the seasonal behaviour observed over recent decades. Periods of relatively warmer Southern Hemisphere (SH) as compared with Northern Hemisphere (NH) (e.g., during 400–800 CE and the Little Ice Age) favours the predominance of easterly wave energy flux along the eastern South American coast, whereas periods with equivalent NH-SH temperature anomalies (e.g., Medieval Warm Period) or with colder relative SH (last ~150 years) support an increase in the influence of the southerly wave energy flux over the South Atlantic. These results provide a novel geomorphic proxy for paleoenvironmental reconstructions and present new insights into the role of multi-decadal to multi-centennial climate variability on controlling coastal ocean wave climate.

How to cite: Da Silva, A. P., Klein, A. H. D. F., Fetter Filho, A. F. H., Hein, C., Mendez, F., Broggio, M., and Dalinghaus, C.: Beach-foredune ridges as proxies for climate-induced wave direction changes in South Atlantic during Late Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-941, https://doi.org/10.5194/egusphere-egu2020-941, 2020.

Explosive volcanism imposes impulse-like radiative forcing on the climate system, providing a natural experiment to study the climate response to perturbation. Previous studies have identified disagreements between paleoclimate reconstructions and climate model simulations (GCMs) with respect to the magnitude and recovery from volcanic cooling, questioning the fidelity of GCMs, reconstructions, or both. Using the paleoenvironmental data assimilation framework of the Last Millennium Reanalysis, this study investigates the causes of the disagreements, using both real and simulated data. We demonstrate that the disagreement may be resolved by assimilating tree-ring density records only, by targeting growing-season temperature instead of annual temperature, and by performing the comparison at proxy locales. Our work suggests that discrepancies between paleoclimate models and data can be largely resolved by accounting for these features of tree-ring proxy networks.

How to cite: Zhu, F., Emile-Geay, J., Hakim, G., King, J., and Anchukaitis, K.: Resolving the differences in the simulated and reconstructed climate response to volcanism over the last millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2477, https://doi.org/10.5194/egusphere-egu2020-2477, 2020.

The mismatch between oceanic proxy data and climate model results over the past millennia has been a long-lasting challenge. Although both are valuable sources of paleoclimate information, there is a strong discrepancy in variance between models and proxies, so that they cannot be compared directly. In addition, local sea-surface temperature (SST) reconstructions are often inconsistent among proxy types. We first performed several offline data assimilation experiments with different standardized SST proxy datasets using the climate models LOVECLIM and CESM in order to investigate the effect of proxy selection on local and regional reconstructions over the Common Era (0-2000 CE). All experiments work technically at the local scale, but the spatial pattern of the reconstructions vary with the type(s), number and density of proxies, and, where there is no proxy, the choice of the model. We then developed empirical scaling factors based on independent SST observations to correct for the discrepancy between model and proxy amplitude. While it is essential to scale proxies, scaling the model leads to complications because of the biases in the sea ice extent. Data assimilation of scaled proxies results in coherent SST reconstructions at the scale of the North Atlantic, with timing and amplitude that are in agreement with those given by forced models. Finally, results are compared to online data assimilation experiments.

How to cite: Goosse, H., Gilson, G., Klein, F., Lenoir, G., de Vernal, A., Evans, M. N., and Saenger, C.: Data assimilation of oceanic proxies in the North Atlantic over the Common Era, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2926, https://doi.org/10.5194/egusphere-egu2020-2926, 2020.

Energy exchanges among climate subsystems are of critical importance the climate sensitivity of the Earth's system to greenhouse gases, to quantify the magnitude and evolution of the Earth's energy imbalance, and to project the evolution of future climate. Thus, ascertaining the magnitude and change of the Earth's energy partition within climate subsystems has become urgent in recent years.

Here, we provide new global estimates of changes in ground surface temperature, ground surface heat flux and continental heat storage derived from geothermal data using an expanded database and new techniques. Results reveal markedly higher changes in ground heat flux and heat storage within the continental subsurface than previously reported, with land temperature changes of 1K and continental heat gains of around 12 ZJ during the last part of the 20th century relative to preindustrial times. Half of the heat gain by the continental subsurface since 1960 occurred in the last twenty years.

How to cite: Cuesta-Valero, F. J., García-García, A., Beltrami, H., González-Rouco, J. F., and García-Bustamante, E.: Long-Term Global Ground Heat Flux and Continental Heat Storage from Geothermal Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3138, https://doi.org/10.5194/egusphere-egu2020-3138, 2020.

We here present new ²³⁰Th-dated stalagmite multi-proxy records from Toirano cave (44˚ N, 8˚E), northern Italy, characterized by a semi-arid Mediterranean climate with humid winters and dry summers. Eleven U-Th ages was used to build the regional hydroclimate evolution over the past 800 years. Sr/Ca and Ba/Ca records show a similar pattern with an increasing trend at the end of Medieval Warm Period (MWP; 950-1250 C.E.) and a decreasing trend at the inception of Little Ice Age (LIA; 1300 to 1800 C.E). The temperature effect on the Sr partition coefficient in calcite is negligible and no significant influence of deposition rate on Sr/Ca and Ba/Ca is observed. The high degree of co-variation between the two records (r = 0.91; n = 212) suggest the variation should be mainly governed by prior calcite precipitation (PCP). Dry conditions lead to a longer water residence time in the epikarst, enhanced CO₂ degassing and decreasing drip rate, resulting in high Sr/Ca and Ba/Ca ratios due to the preferential removal of Ca during PCP. Our results suggest a dry period during the transition of MCA and LIA in our region.

How to cite: Shen, C.-C. (., Hu, H.-M., Michel, V., Valensi, P., Mii, H.-S., Spötl, C., Starnini, E., Zunino, M., Watanabe, T., Watanabe, T., Tsai, H.-C., Sung, W.-H., and Chien, W.-Y.: Stalagmite geochemical proxy-inferred precipitation records over the past 800 years in northern Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4028, https://doi.org/10.5194/egusphere-egu2020-4028, 2020.

Extreme precipitation in Europe over summer time is one type of climate extreme with strongest impact on societies, at present and over the past centuries. In contrast to mean and extreme temperatures, it is still unclear to what extant the external forcing may modulate the intensity and frequency of this type of hydrological extremes. This contribution focuses on the identification of the impact of external forcing on European extreme precipitation over the past millennium in one small ensembles of simulations with the Earth System model MPI-ESM-P and in the Large Millennium Ensemble with the model CESM.

Both models realistically simulate the meteorological conditions that give rise to sustained (over several days) strong precipitation, compared to present conditions. The analysis of both ensembles indicates that the role of the external forcing over the past millennium has been weak at most, with individual members of the ensemble providing different timings for period with high and low probability of extreme summer precipitation in this region. This conclusion is also valid for mean summer precipitation.

This result confirms the evidence obtained from analysis of proxy records, mostly palaeoclimatological records but also historical evidence. This analysis indicates that the frequency and intensity of extreme summer precipitation has been so far independent of the mean climate state.

How to cite: Zorita, E.: Extreme summer precipitation in Central Europe over the past millennium: role of external forcing in enseble of simulations with Earth System models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4191, https://doi.org/10.5194/egusphere-egu2020-4191, 2020.

Sea surface temperature (SST) of the Caribbean Sea exerts a strong control on the amount of precipitation on the adjacent land. However, a clear understanding of the regional climate development on centennial timescales is missing due to scarcity of SST records. To fill this gap, we generated a new high-resolution proxy dataset of the last 1800 years from the Tobago Basin, a region that is presently affected by both Atlantic and Pacific climate variability on one hand, and by the South Atlantic circulation on the other hand. Our dataset is comprised of Mg/Ca and alkenone-derived SSTs, stable isotopes, element composition of bulk sediment and planktic foraminiferal assemblages. Our Mg/Ca-based reconstruction suggests significant SST variability over the past 1800 years CE, particularly during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The MCA encompasses an abrupt 2 °C SST reduction between 1050-1100 years CE, which coincided with a distinct episode of precipitation minima in the region and was followed by a century of warm and wet MCA conditions. A 1 °C cooling also characterized the onset of the LIA between 1400-1550 years CE, which was associated with a reduction in water column stratification inferred from stable isotopes and foraminiferal assemblage data. The initial LIA cooling was followed by a robust 1 °C SST rise between 1550-1750 years CE. This warming trend is also supported by alkenone-derived SSTs. Our reconstructed SST variability across the LIA may help to explain the occurrence of alternating dry and wet conditions on the Caribbean islands.

How to cite: Zhuravleva, A., Bauch, H., Mohtadi, M., and Fahl, K.: SST Variability in the Southeastern Caribbean Sea over the Past 1800 Years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5232, https://doi.org/10.5194/egusphere-egu2020-5232, 2020.

The Indonesian and South China Sea throughflows play an important role in global ocean circulation as the only low-latitude pathway for the exchange of heat and salt between the Pacific and Indian oceans. This transport is modulated by different climate systems including the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) and the East Asian Monsoon. The interactions of these climate systems across the Southeast Asian region are still being understood, particularly the role of sea surface salinity (SSS) in inhibiting flow from the Makassar Strait into the Indian Ocean.

Reconstructions of SSS from corals provide an opportunity to study long-term trends in climate and ocean circulation. Coral records from north and south of the Luzon Strait, the Makassar Strait, and Lombok Strait for the period 1926 to 2010 are examined to evaluate their shared variability. Principal component analysis synthesizes these records for the boreal winter (December to March) and boreal summer (June to September). The first and second principal components or empirical orthogonal functions (EOF) describe over 55% of the shared variance in both seasons. In the winter, the EOF of both modes correlates to PDO and the first EOF correlates to the Indian Ocean Dipole (IOD). A high-pass filter of the first EOF for <10 years per cycle for the winter and summer significantly correlates to ENSO and IOD respectively. While several sites individually correlate with ENSO and PDO, no individual SSS record correlates to the IOD. This consistent relationship of the IOD to the winter EOF indicates a regional influence on salinity variance that is not identified locally. One hypothesis to explain IOD’s regional influence is that the interaction of the IOD and ENSO through the atmospheric bridge or the Madden Julian Oscillation (MJO) is influencing the region. Spectral analysis, and climatic and oceanographic models will be used to further investigate this connection.

How to cite: Kannad, A., Goodkin, N. F., Murty, S. A., Ramos, R. D., Samanta, D., and Gordon, A. L.: Paleoclimate drivers of the Indonesian and South China Sea throughflows, the curious case of the IOD, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6484, https://doi.org/10.5194/egusphere-egu2020-6484, 2020.

Mega-droughts are notable manifestations of the American Southwest, but not so much of the European climate. By using long-term hydrological and meteorological observations, as well as paleoclimate reconstructions, we show that central Europe has experienced much longer and severe droughts during the Spörer Minimum (~AD 1400 – 1500) and Dalton Minimum (~AD 1770 – 1850), than the ones observed during the 21^st century. These two mega-droughts appear to be linked with a weak state of the Atlantic Meridional Overturning Circulation (AMOC) and enhanced winter atmospheric blocking activity over the British islands and western part of Europe, associated with reduced solar forcing and explosive volcanism. In contrast with these mega-droughts, present-day extreme dry events in Europe are mainly related to high temperature levels. Since numerical simulations indicate a future slowdown of AMOC in a globally warming world, we argue that these two forcing factors for droughts, weakening ocean circulation and temperature increase, could interfere constructively in the future. Consequently, this will potentially lead to an increase in the frequency of hot and dry summers, especially over the central part of Europe, posing enormous challenges to governments and society.

How to cite: Ionita-Scholz, M., Dima, M., Nagavciuc, V., Scholz, P., and Lohmann, G.: Components of past cold mega-droughts and modern warm dry events in central Europe could interfere constructively in the future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7159, https://doi.org/10.5194/egusphere-egu2020-7159, 2020.

Ice cores are key archives in the quest to reconstruct and understand past climate variability. They are generally found in polar and high latitude regions, but caves in the Carpathian Mountains (East-central Europe) host several glaciers thousands of years old. Here, we present a reconstruction of summer and winter air temperatures during the last millennium based on the d¹⁸O and d²H values measured in ice cores drilled in the glaciers hosted by Focul Viu (FV) and Scărișoara Ice Caves (SIC), both in the Western Carpathians (East-Central Europe, Romania). In order to understand the climatic signal locked in the two cores, we analyzed the stable isotope composition of the rainfall water, which was subsequently compared with that of the cave ice. Accordingly, d¹⁸O in ice in SIC is a proxy for late-autumn through early winter air temperature, while that in FV for summer air temperatures. The analysis of d¹⁸O values indicate that on centennial scales, air temperature variability during the last 1000 years was controlled by changes during the winter season, summer temperatures being relatively constant (on these time scales). Contrary, short-term variability (decadal to multi-decadal) was well expressed in both seasons. In summer, the main controlling factors seem to be changes in solar radiation and possibly in the strength of the Atlantic Multidecadal Oscillation, while in winter, the strength of the Siberian High could have acted as the main forcing factor.

How to cite: Bădăluță, C.-A. and Perșoiu, A.: Late Holocene climate variability in the Western Carpathians (East-Central Europe) reconstructed from ice cores records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7411, https://doi.org/10.5194/egusphere-egu2020-7411, 2020.

Variability in Sea Surface Temperature (SST) is one of the prime sources of intra-annual variability, and also an important boundary condition for Atmospheric General Circulation Models (AGCMs). In many AGCM simulations, SST and Sea Ice Concentration (SIC) are prescribed. While SSTs are specified according to observations available in recent period of instrumental records (1850 – present), SIC depends on climatological averages with less variability prior to the inception of satellite measurements. This limits our understanding of large-scale climate variations in the past.

In this study, we augment multi-proxy reconstructed annual mean temperature of Neukom et al. (2019) with intra-annual variability from HadISST (v2.0), for 850 years (1000 – 1849). Intra-seasonal variability, such as the phase-locking of El-Nino Southern Oscillation, Indian Ocean Dipole and Tropical Atlantic SST indices to annual-cycle, are utilized. The intra-annual component of HadISST and SST indices estimated from the multi-proxy reconstructed annual mean, are used to develop grid-based multivariate linear regression models using the Frisch-Waugh-Lovell theorem, in a monthly stratified approach. Furthermore, we introduce a scaling technique to ensure homogeneous mean and variance, similar to that of the target. SST observations obtained from ship measurements by ICOADS before 1850, will be integrated in an off-line data assimilation approach.

Similarly, we reconstruct SIC via analogue resampling of HadISST SIC (1941 – 2000), for both hemispheres. We pool our analogues in four seasons, comprising of 3 months each, such that for each month within a season, there are 180 possible analogues. The best analogues are selected based on correlation coefficients between reconstructed SST and its target.

How to cite: Samakinwa, E. and Brönnimann, S.: Global monthly sea surface temperature and sea ice reconstruction for historical simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8744, https://doi.org/10.5194/egusphere-egu2020-8744, 2020.

Explosive volcanic eruptions are able to affect significantly the atmosphere for 2‐3 years. During this time, volcanic products (mainly H2SO4) with high residence 
time are stored in the stratosphere/troposphere, and eventually deposited onto polar ice caps; snow layers may thus record signals providing a history of past 
volcanic events. A high resolution sulphate concentration profile along a 197 m long ice core drilled at GV7 (Northern Victoria Land) was obtained by Ion Chromatography. The relatively high accumulation rate (241±13 mm we yr^-1) and the 5‐cm resolution allowed a preliminary counted age scale. The obtained stratigraphy covers roughly the last millennium and 24 major volcanic eruptions were identified, dated and 
ascribed to a source volcano. The deposition flux of volcanic sulfate was calculated and the results were compared with data from other Antarctic ice cores at regional and continental scale. Our results show that the regional variability is of the same order of magnitude 
of the continental scale.

How to cite: Traversi, R., Becagli, S., Severi, M., Nardin, R., Caiazzo, L., Amore, A., Frezzotti, M., and Stenni, B.: Volcanic fluxes over the last millennium as recorded in the GV7 ice core (Northern Victoria Land, Antarctica), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10616, https://doi.org/10.5194/egusphere-egu2020-10616, 2020.

Mid-latitude, cave-hosted temperate ice is increasingly scrutinised for its palaeoclimatic potential. Findings of dendrochronologically dated wood trunks and radiometrically dated woody macrofossils demonstrate that underground ice accumulations records may locally span several millenia. The cave geometries conducive to underground firn accumulation were additionally shown to favour the preservation of a winter signal, making cave-hosted ice an attractive and complementary archive to existing and largely summer-biased proxy records. Proxy derivation from these ice accumulations first requires the establishment of firn accumulation/ablation chronologies from stratigraphic mapping and radiometric dating of organic inclusions. Decadal to centennial trends in accumulation/ablation recorded by the ice stratigraphy thus provide insight in past variations of solid precipitation .

Preliminary results from several well-dated ice caves of the Northern Calcareous Alps in Austria suggest local preservation of ice since ca. 3600-3300 BC. Inclusion-rich unconformities in the ice stratigraphy from these alpine caves mark short breaks in firn accumulation between 250 BC and 250 AD and longer hiatuses during Late Antiquity and the 8^th and 9^th century AD. The majority of dated ice sequences testify the onset of rapid ice accumulation from the 11^th and 12^th century AD onwards and build up throughout the 'Litte Ice Age'.

How to cite: Racine, T., Spötl, C., and Reimer, P.: Establishing past firn accumulation records from ice caves of the European Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10959, https://doi.org/10.5194/egusphere-egu2020-10959, 2020.

Although most simulation models published have concluded that coastal upwelling will intensify in three of the most productive marine ecosystems of the world, the results seem contradictory for the California Current System (CCS). These contradictory results may be due to the fact that instrumental records are too short to yield reliable predictions. Because of this, we opted to test this hypothesis by studying the sedimentary record of Soledad basin, in Baja California, Mexico, using geochemical proxies to reconstruct at ultra-high resolution the history of productivity and sea surface temperature during the last two millennia, with particular emphasis on the Anthropocene. Our results indicate that SST (alkenones and TEX-86) do not show a cooling trend during the Anthropocene, but rather multidecadal cycles related to PDO. Likewise, primary productivity organic biomarkers [i.e., alkenone concentration (C37 Total) as a proxy for phytoplankton productivity, etc] show an increasing trend that started 2000 years ago with prominent multidecadal cycles, but without any observable trend taking place during the Anthropocene. An interesting feature of the organic matter record is the increasing amplitude of the cycles towards the present, starting 2000 years ago. Primary productivity is probably controlled by large scale mesoscale eddies developing at the southern Baja California margin.

How to cite: Carriquiry, J., Treinen-Crespo, C., Villaescusa, J., Pearson, A., and Barbara, L.: The impact of global warming on the upwellings and primary productivity at the southern limb of the California Current, Baja California, Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11271, https://doi.org/10.5194/egusphere-egu2020-11271, 2020.

The past two thousand years is a key interval for climate science because this period encompasses both the era of human-induced global warming and a much longer interval when changes in Earth's climate were governed principally by natural drivers. This earlier 'pre-industrial' period is particularly important for two reasons. Firstly, we now have a growing number of well-dated, climate sensitive proxy data with high temporal resolution that spans the full period. Secondly, the pre-industrial climate provides context for present-day climate change, sets real-world targets against which to evaluate the performance of climate models, and allows us to address other questions of Earth sciences that cannot be answered using only a century and a half of observational data. 

Here, we first provide several perspectives on the concept of a 'pre-industrial climate'. Then, we highlight the activities of the PAGES 2k Network, an international collaborative effort focused on global climate change during the past two thousand years. We highlight those aspects of pre-industrial conditions (including both past climate changes and past climate drivers) that are not yet well constrained, and suggest potential areas for research during this period that would be relevant to the evolution of Earth's future climate.

How to cite: Eggleston, S. S., Bothe, O., Abram, N., Konecky, B., Linderholm, H., Martrat, B., McGregor, H., Phipps, S., and St. George, S.: Global climate changes during the most recent two millennia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13378, https://doi.org/10.5194/egusphere-egu2020-13378, 2020.

Climate and vegetation history of Upper Dnieper region (Western Russia) is investigated poorly while archaeological studies provide evidences of human activities during last 3 millennia. Our study presents vegetation reconstruction based on pollen analysis of sediments extracted from two sites in Smolensk region. The first site is located in Katynka river bassin and pollen analysis of extracted buried soil, alluvium and peat sediments demonstrates vegetation dynamics in archaeologically rich area over 5 millennia. The second site is located in 50 km from to the west from Smolensk and in 15 km to east from the Russian-Belarus state border. The analysis of extracted peat sediments presents regional history of vegetation. The aim of our study is to compare data obtained from both sites and to estimate climate and human influence on vegetation during last two millennia when activities associated with agriculture changed Dnieper valley landscape significantly.

The first results of pollen analysis data of the first site allow to register significant human impact on vegetation 2.0-0.8 ka BP. Before that period pollen of indigenous forest trees dominates in spectra while since 2.0 ka BP pollen compassion changes dramatically and pollen of Betula and Pinus is in majority in so-called “Gnezdovo soil” lay. Medieval lays of sapropel contains mostly pollen of Pinus with admixture of Betula and Alnus. Taxonomic diversity and presence of meadow herbs, weeds and cultivated taxa pollen increases significantly (up to 30%). Dynamics of pollen composition in specimens from the second site allows us to register slow processes of indigenous vegetation recovery over last 3 centuries approximately. Modern analogue technique applied on pollen data and analysis of historical data makes possible to separate impacts of climate and human on vegetation of the past and to reconstruct the climate of last two millennia.

The study was funded by RFBR, project number 19-34-90172.

How to cite: Lavrenov, N., Ershova, E., Zhuravkova, M., and Krenke, N.: Vegetation history of Western Russia (Upper Dnieper, Smolensk region): Climate and human impact on landscape in last two millennia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14384, https://doi.org/10.5194/egusphere-egu2020-14384, 2020.

The meteorological station at University of Graz, Austria has been recently recognised as WMO "Centennial Station", with measurements taken at
the same location going back to the year 1891. Combined with data from nearby downtown stations (in particular at the former location of the University) the record extends back to the year 1836 - in this form the data are currently used in the HISTALP dataset. This record can, however, be extended at least four decades back in time:

Mr. Rospini, a man of great interest in natural sciences (and later his son and grandsons) measured  temperature and pressure three times per day (morning, noon and evening) in the historic center of Graz - close to the former location of the University. Measurements apparently started as early as 1781, and have been continuously published in the "Grätzer Zeitung" from 1795 onwards. So far, we have been able to compile an almost uninterrupted
record since 1797 (with just a few weeks missing in total), and we are trying to fill the remaining gaps for the two previous years. Temperatures are given in Réaumur, recorded at 7, 15 and 22 (confirmed for 1823, very likely for the time before). For the year 1837 we performed a consistency check, comparing our recently retrieved data with those from the University (which are used in the HISTALP dataset), yielding an annual mean offset of just +0.2 °C.

With those subdaily measurements, we cannot only extend the climate record, but we can also attempt to analyse particularly interesting years. Using the temperature recorded at 15:00 as proxy for the maximum temperature, we could identify the extremely warm Summer of 1834, with at least 35 days, where the temperature maximum was 30 °C or higher. Since we slightly underestimate the true number of “Hot Days” with this approach, we can assume that this summer was not too different from the record Summer of 2003, where our meteorological station recorded 41 “Hot Days” (with actual maximum temperature measurements). The second highest value in the “official” time series was obtained in 2015 with 34 “Hot Days”. The year 1816, on the other hand, was indeed a "year without summer" - also in Graz, with just 11 days reaching a temperature of 25 °C or more.

How to cite: Foelsche, U., Kraml, E., and Besser, B.: Subdaily instrumental data from Graz, Austria, starting in 1795, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17966, https://doi.org/10.5194/egusphere-egu2020-17966, 2020.

How to cite: Khodri, M., Feng, Y., Li, L., Sicre, M.-A., and Lebas, N.: Influence of external forcings on the hydroclimate conditions in the Europe-Mediterranean Region over the Common Era : a model/data approach , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19746, https://doi.org/10.5194/egusphere-egu2020-19746, 2020.

The mid of the 6^th century is an outstanding period and started with an unusual cold period that lasted several years to decades, due to the 536/540 CE double eruption event, with the strongest decadal volcanic forcing in the last 2000 years. Evidence from multiple tree ring records from the Alps to the Altai Mountains in Russia identified a centennial cooling lasting from 536 up to 660 CE. A previous Earth System Model (ESM) study with reconstructed volcanic forcing covering 535-550 CE like conditions already found that the double eruption led to a global decrease in temperature and an increase in Arctic sea-ice for at least a decade. However, the simulations were too short to fully investigate the multi-decadal cooling event and the atmospheric forcing from this double volcanic eruption alone may not be enough to sustain such a prolonged cooling. To better understand forced versus internal decadal climate variability in the first millennium we have performed mid 6^th century ensemble simulations with the MPI-ESM1.2 for the 520-680 CE period. The ensemble consists of 10 realizations, which were branched of the MPI-ESM1.2 PMIP4 Past2k run, including the evolv2k volcanic forcing.

Here, we present results of this new set of the 6^th-7^th century MPI-ESM simulations in comparison to paleo-proxies. Summer surface temperatures are analyzed and compared with available tree-ring data, which fits very well for the entire 160 year period. As part of the VIKINGS project, special focus is placed on the impact of the 536/540 CE double volcanic eruption event on the surface climate in the Northern Hemisphere, in particular Scandinavia, Northern Europe and Siberia. The goal is to also compare the model data with new tree-ring and lake sediment proxies from southeastern Norway. Detailed comparison with proxy data will allow us to better understand the regional and seasonal climate variations of the 6^th-7^th century. Duration, strength and the possible mechanism for a long lasting volcanic induced cooling will be discussed.

How to cite: van Dijk, E., Timmreck, C., Jungclaus, J., Lorenz, S., Bajard, M., Bostic, J., and Krüger, K.: Impact of the 536/540 CE double volcanic eruption event on the 6th-7th century climate using model and proxy data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19943, https://doi.org/10.5194/egusphere-egu2020-19943, 2020.

The analysis of subsurface temperature measurements from boreholes is a well established approach for reconstructing last millennium (LM) surface air temperature (SAT). It is based on the assumption that SAT variations are strongly coupled to ground surface temperature (GST) variations and transferred to the subsurface by thermal conduction. We have evaluated the long-term SAT-GST coupling over the LM using an ensemble of both full- and single-forcing simulations form the Community Earth System Model-Last Millennium Ensemble (CESM-LME). Such a premise is explored by investigating the evolution of the long-term SAT–GST relationship. The results indicate that SAT–GST coupling is strong at global and above multi-decadal timescales in CESM-LME. However, at local to regional scales this relationship experiences considerable long-term changes mostly after the end of the 19th century. Land use land cover (LULC) changes stand as the main driver for locally and regionally decoupling SAT and GST, due to the changes in the energy fluxes at the surface. Snow cover feedbacks due to the influence of GHG forcing are also important for corrupting the long-term SAT–GST coupling. These processes may represent a source of bias for SAT reconstructions from GST borehole profiles. In light of these findings, we subsequently assessed the potential effects on SAT reconstructions from the borehole method in pseudo-proxy experiments that make use of the same set of simulations from the CESM-LME. First, a heat-conduction forward model has been used to estimate subsurface temperature-anomaly profiles using simulated GST as boundary conditions. Subsequently, singular value decomposition inversion (SVD) has been applied to reconstruct LM GST variations from the simulated profiles. We implemented and ideal scenario in which it is assumed the existence of borehole logs at every model grid point. Further, this scenario considers that all boreholes are logged homogenously at the same time. In addition, we implemented a more realistic approach in which the real-world spatio-temporal distribution of the global borehole network is considered. Results show that the SVD inversion is able to retrieve the long-term GST variations over the LM when an appropriated coverture of borehole logs is available. However, due to the limited spatio-temporal distribution of the actual borehole network, there is a lost in the accuracy to retrieve the simulated GST 20th century trends, with the temporal logging of the BTPs as the main sampling issue. Furthermore, in the surrogate reality of the CESM-LME the SAT-GST decoupling, due to the influence of LULC and GHG forcings, leads to a slightly underestimation of SAT warming during the industrial period across the CESM-LME. The level of impact is, however, highly depended on the realization of internal variability.

How to cite: Melo Aguilar, C., González Rouco, F., García Bustamante, E., Steinert, N., Navarro, J., Roldan Gómez, P., and Jungclaus, J.: Analysis of methodological and physical bias on borehole temperature reconstructions from a pseudo-proxy approach., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20483, https://doi.org/10.5194/egusphere-egu2020-20483, 2020.

Improved knowledge of greenhouse gas-climate feedbacks is required to understand past and future climate changes. Atmospheric nitrous oxide (N₂O) is of concern for its potential role in global warming and future stratospheric ozone destruction. Existing ice core N₂O records for the Holocene have not been sufficiently consistent to allow an examination of small changes on sub-millennial time scales. Here, we present new high-resolution and high-precision N₂O records obtained from the Greenland NEEM (North Greenland Eemian Ice Drilling) and Antarctic Styx Glacier ice cores. Our reconstruction shows, for the first time, a centennial-scale variability of ~10 ppb during the last 2000 years.  Comparisons with proxy records suggest that centennial- to millennial-scale variations in N₂O are driven, to a large extent, by changes in tropical and subtropical land hydrology and marine productivity.

How to cite: Ryu, Y., Ahn, J., Yang, J.-W., Brook, E., Timmermann, A., Blunier, T., Hur, S., and Kim, S.-J.: Millennial-scale variations in atmospheric N2O during the past 2000 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20714, https://doi.org/10.5194/egusphere-egu2020-20714, 2020.