CL1.1

EDI
Studying the climate of the last two millennia

This session aims to place recently observed climate change in a long-term perspective by highlighting the importance of paleoclimate research spanning the past 2000 years. We invite presentations that provide insights into past climate variability, over decadal to millennial timescales, from different paleoclimate archives (ice cores, marine sediments, terrestrial records, historical archives and more). In particular, we are focussing on quantitative temperature and hydroclimate reconstructions, and reconstructions of large-scale modes of climate variability from local to global scales. This session also encourages presentations on the attribution of past climate variability to external drivers or internal climate processes, data syntheses, model-data comparison exercises, proxy system modelling, and novel approaches to producing multi-proxy climate field reconstructions.

Convener: Sarah S. EgglestonECSECS | Co-conveners: Stella AlexandroffECSECS, Hugo Beltrami, Steven Phipps, Andrea Seim
vPICO presentations
| Fri, 30 Apr, 09:00–12:30 (CEST)

Session assets

Session materials

vPICO presentations: Fri, 30 Apr

Chairpersons: Steven Phipps, Sarah S. Eggleston
09:00–09:05
09:05–09:07
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EGU21-10979
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ECS
Sarah S. Eggleston, Steven Phipps, Oliver Bothe, Helen V. McGregor, Belen Martrat, Hans Linderholm, Bronwen Konecky, Nerilie Abram, and Scott St. George

The past two thousand years is a key interval for climate science. 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 and unforced variability. Since 2009, the Past Global Changes (PAGES) 2k Network has brought together hundreds of scientists from around the world to reconstruct and understand the climate of the Common Era using open and collaborative approaches to palaeoclimate science, including virtual meetings. The third phase of the network will end in December 2021. Here we highlight some key outputs of PAGES 2k and present the major themes and scientific questions emerging from recent surveys of the community. We explore how these might boost a new phase of PAGES 2k or a successor project(s). This year we will further reach out to the community through Town Hall consultations, vEGU and other meetings, and a PAGES 2k global webinar series. The aim of these activities is to foster development of post-2021 community-led PAGES initiatives that connect past and present climate.

How to cite: Eggleston, S. S., Phipps, S., Bothe, O., McGregor, H. V., Martrat, B., Linderholm, H., Konecky, B., Abram, N., and St. George, S.: Advancing community-led research into the climate of the Common Era, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10979, https://doi.org/10.5194/egusphere-egu21-10979, 2021.

09:07–09:09
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EGU21-6663
Mikhail A. Lokoshchenko

Better understanding of current climate changes needs a full knowledge about regional specific of thermal conditions at the end of Little Ice Age. So, the earliest available meteorological data are important. First regular daily qualitative meteorological observations were taken in Moscow city from 1657 to 1675. Episodic short series of instrumental measurements were made there for the first time in 1731; regular daily measurements started in 1779 when one of Mannheim network stations was founded in Moscow.

         All known old data series of the air temperature T measurements in Moscow since 1779 were collected and analyzed. Mannheim station existed there from 1779 to 1797 but average values of T are available from issues of Ephemerides Societatis Meteorologicae Palatinae only for the period 1779–1792. High accuracy of measurements at Mannheim network is confirmed by high correlation co-efficient between monthly-averaged T values in Moscow and at closest stations (Warsaw and St. Petersburg): up to 0.82-0.84 on separate months.

         Different methodical questions (unknown location of the station, unknown conditions of thermometer installation, its height and shading, an accuracy of its calibration, etc.) were studied. As a result it was found that the most probable error due to thermometer installation close to the northern building wall is ±0.1÷0.2 ºС; the error of daily-averaged T due to unknown height of measurements is ±0.1 ºС; the calibration accuracy in Mannheim was about ±0.1 ºС. Thus, a total error of T on average of a day in the 18th century was not higher than ±0.3÷0.4 ºС. Probably it was even less because separate components of the error may be multidirectional. For the first time mean-annual T in Moscow was received for 1783, and the most probable values were estimated for 1784 and 1785 using the data of the closest Mannheim station (Saint-Petersburg) for separate months with data gaps. The end of Little Ice Age manifeted at extremely low minimal values of T: up to –31 ˚R (–38.8 ˚С) in December 17th, 1788. However, thermal conditions from June to September changed only a bit since the 18th century till nowadays (differences are not statistically significant with the 0.95 confidence probability).  

         Later measurements in Moscow were renewed since 1808 and broken again in August of 1812 due to Napoleon’s invasion and terrible Moscow fire. For the first time unknown data series of everyday measurements which were made by Ivan Lange in 1816–1817 were found and studied. As is known the famous 1816 ‘Year Without a Summer’ was noted almost all over the World by extremely cold summer as probable result of Mount Tambora eruption in 1815. Nevertheless, it was found that summer of 1816 in Moscow was comparatively cool but not extremely cold: monthly-averaged T there was 15.7, 17.3 and 14.5 ˚С in June, July and August, respectively, and 15.8 ˚С on average of the summer. Thus, 1816 occupies only 27th place among the coldest summers in the city during 216 years.

         Author is thankful to the memory of his late PhD student Ekaterina L. Vasilenko.

How to cite: Lokoshchenko, M. A.: Climate of Moscow at the end of Little Ice Age, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6663, https://doi.org/10.5194/egusphere-egu21-6663, 2021.

09:09–09:11
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EGU21-11953
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ECS
Thomas Pliemon, Ulrich Foelsche, Christian Rohr, and Christian Pfister

Based on copies of the original data (source: Oeschger Center for Climate Change Research) we perform climate reconstructions for Paris between 1665 - 1709. The focus lies on the following meteorological variables: temperature, cloudiness, direction of movement of the clouds, precipitation and humidity. Apart from humidity, these meteorological variables were measured three times a day over the entire period from Louis Morin. Temperature and humidity were measured with instruments, whereas cloud cover, direction of movement of the clouds and precipitation were measured in a descriptive manner. In addition to the quantitative temperature measurements, conclusions about synoptic air movements over Europe are possible due to the additional meteorological variables. The Late Maunder Minimum is characterised by cold winters and moderate summers. Winter is characterised by a lower frequency of westerly direction of movement of the clouds. This reduction of advection from the ocean leads to cooling in Paris and also to less precipitation in winter. This can be seen very strongly between the last decade of the 17th century (cold) and the first decade of the 18th century (warm). A lower frequency of westerly direction of movement of the clouds can also be seen in summer, but the influence is stronger in winter than in summer. However, this reduction leads to moderate/warm temperatures in summer. So unusually cold winters in the Late Maunder Minimum can be attributed to a lower frequency of westerly direction of movement of the clouds.

How to cite: Pliemon, T., Foelsche, U., Rohr, C., and Pfister, C.: Analysis of Subdaily Meteorological Measurements by Louis Morin in the Late Maunder Minimum 1665 – 1709 in Paris, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11953, https://doi.org/10.5194/egusphere-egu21-11953, 2021.

09:11–09:13
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EGU21-15903
Elin Lundstad, Yuri Brugnera, and Stefan Brönnimann

This work describes the compilation of global instrumental climate data with a focus on the 18th and early 19th centuries. This database provides early instrumental data recovered for thousands of locations around the world. Instrumental meteorological measurements from periods prior to the start of national weather services are designated “early instrumental data”. Much of the data is taken from repositories we know (GHCN, ISTI, CRUTEM, Berkeley Earth, HISTALP). In addition, many of these stations have not been digitized before. Therefore,  we provide a new global collection of monthly averages of multivariable meteorological parameters before 1890 based on land-based meteorological station data. The product will be form as the most comprehensive global monthly climate data set, encompassing temperature, pressure, and precipitation as ever done. These data will be quality controlled and analyzed with respect to climate variability and they be assimilated into global climate model simulations to provide monthly global reconstructions. The collection has resulted in a completely new database that is uniform, where no interpolations are included. Therefore, we are left with climate reconstruction that becomes very authentic. This compilation will describe the procedure and various challenges we have encountered by creating a unified database that can later be used for e.g. models. It will also describe the strategy for quality control that has been adopted is a sequence of tests.

How to cite: Lundstad, E., Brugnera, Y., and Brönnimann, S.: Global Instrumental Meteorological Database Before 1890 – a useful overview, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15903, https://doi.org/10.5194/egusphere-egu21-15903, 2021.

09:13–09:15
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EGU21-589
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ECS
Francisco José Cuesta-Valero, Almudena García-García, Hugo Beltrami, J. Fidel González-Rouco, and Elena García-Bustamante

Energy exchanges among climate subsystems are of critical importance to determine the climate sensitivity of the Earth's system to changes in external forcing, to quantify the magnitude and evolution of the Earth's energy imbalance, and to make projections of future climate. Additionally, climate phenomena sensitive to land heat storage, such as permafrost stability and sea level rise, are important due to their impacts on society and ecosystems. 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 developed in the last two decades. This new dataset contains 253 recent borehole profiles that were not included in previous estimates of global continental heat storage. In addition, our analysis considers additional sources of uncertainty that were not included in previous borehole studies. Results reveal markedly higher changes in ground heat flux and heat storage within the continental subsurface during the second half of the 20th century than previously reported, with a land mean temperature increase of 1 K and continental heat gains of around 12 ZJ relative to preindustrial times. Half of the heat gained by the continental subsurface since 1960 have occurred in the last twenty years. These results may be important for estimates of climate sensitivity based on energy budget constrains, as well as for the evaluation of global transient climate simulations in terms of the Earth’s heat inventory and energy-dependent subsurface processes. Our estimate of land heat storage is included in the new assessment of the components of the Earth’s heat inventory recently released (von Schuckmann et al. 2020), together with the oceans, the atmosphere and the cryosphere.

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 2021, online, 19–30 Apr 2021, EGU21-589, https://doi.org/10.5194/egusphere-egu21-589, 2021.

09:15–09:17
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EGU21-9222
Hugo Beltrami, Fracisco José Cuesta-Valero, Almudena García-García, Stephan Gruber, and Fernando Jaume-Santero

The surface temperature response to changes in our planet’s external forcing is larger at higher latitudes, a phenomenon known as polar amplification. The Arctic amplification has been particularly intense during the last century, with arctic-wide paleoclimatic reconstructions and state-of-the-art model simulations revealing a twofold arctic warming in comparison with the average global temperature increase. As a consequence, Arctic ground temperatures respond with rapid warming, but this response varies with snow cover and permafrost processes. Thus, changes in arctic ground temperatures are difficult to reconstruct from data, and to simulate in climate models.

Here, we reconstruct the ground surface temperature histories of 120 borehole temperature profiles above 60ºN for the last 400 years. Past surface temperature evolution from each profile was estimated using a Perturbed Parameter Inversion approach based on a singular value decomposition method. Long-term surface temperature climatologies (circa 1300 and 1700 CE) and quasi-steady state heat flow are also estimated from linear regression through the depth range 200 to 300 m of each borehole temperature profile. The retrieved temperatures are assessed against simulated ground surface temperatures from five Past Millennium and five Historical experiments from the Paleoclimate Modelling Intercomparison Project Phase III (PMIP3), and the fifth phase of the Coupled Model Intercomparison Project (CMIP5) archives, respectively.

Preliminary results from borehole estimates and PMIP3/CMIP5 simulations reveal that changes in recent Arctic ground temperatures vary spatially and are related to each site’s earlier thermal state of the surface. The magnitudes of ground warming from data and simulations differ with large discrepancies among models. As a consequence, a better understanding of freezing processes at and below the air-ground interface is necessary to interpret subsurface temperature records and global climate model simulations in the Arctic.

How to cite: Beltrami, H., Cuesta-Valero, F. J., García-García, A., Gruber, S., and Jaume-Santero, F.: Assessing Arctic Ground Surface Temperatures from Borehole Temperatures and Paleoclimatic Model Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9222, https://doi.org/10.5194/egusphere-egu21-9222, 2021.

09:17–09:19
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EGU21-8323
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ECS
Bernhard Hofer, Natalie A. Krivova, Sami K. Solanki, Robert Cameron, Chi-Ju Wu, and Ilya G. Usoskin

Historical solar irradiance is a critical input to climate models. As no direct measurements are available before 1978, reconstructions of past irradiance changes are employed instead. Such reconstructions are based on the knowledge that solar irradiance on time scales of interest to climate studies is modulated by the evolution of the solar surface magnetic structures, such as sunspots and faculae. This calls for historical records or proxies of such features. The longest direct, and thus mostly used, record is the sunspot number. It allows a reasonable description of the emergence and evolution of active regions, which are larger magnetic regions containing sunspots. At the same time, a significant amount of the magnetic flux on the Sun emerges in the form of the so-called ephemeral magnetic regions, which are weaker short-lived bipolar regions that do not contain sunspots. Due to their high frequency, ephemeral regions are an important source of the irradiance variability, especially on time scales longer than the solar cycle. Difficulties in their proper accounting are a main reason for the high uncertainty in the secular irradiance variability. Existing models either do not account for their evolution at all or link them linearly to active regions. We use a new, more realistic model of the ephemeral region emergence, relying on recent independent solar observations, as input to a surface flux transport model (SFTM) to simulate the evolution of the magnetic field in such regions. The latter can then be used to reconstruct the solar irradiance since the Maunder minimum.

How to cite: Hofer, B., Krivova, N. A., Solanki, S. K., Cameron, R., Wu, C.-J., and Usoskin, I. G.: Accounting for small bipolar magnetic regions in solar irradiance reconstructions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8323, https://doi.org/10.5194/egusphere-egu21-8323, 2021.

09:19–09:21
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EGU21-1893
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ECS
Jinheum Park, Qiuhong Jin, Jieun Choi, and Jungjae Park

This study presents a reconstruction of climate change in central Korea during the last 3,000 years, using a core from a montane peatland of Yongneup. Multiple proxies of pollen, macrocharcoal, and geochemistry were analysed to provide three findings as follows: First, abrupt climate events at ca. 2.8 and 2.3 ka BP possibly accompanied dry summer as well as cold and arid winter seasons on the Korean peninsula. The first macrocharcoal analysis on the peninsula indicates increased wildfire activities during these dry periods. Next, a weakening of summer monsoon during El Niño-like phases was clearly found during the late Holocene. This confirms previous findings of a dominant oceanic influence on hydroclimate variability on the Korean peninsula. Finally, changes in temperature were likely synchronous with a global trend, indicated by the total organic content (TOC) and arboreal pollen percentages. Due to its location at a high-altitude, the environment of Yongneup has possibly sensitively responded to fluctuations in temperature. Altogether, these findings suggest that temperature and precipitation changes on the Korean peninsula have been separately influenced by insolation and oceanic circulations, respectively.

How to cite: Park, J., Jin, Q., Choi, J., and Park, J.: Late-Holocene climate variability of coastal East Asia reconstructed from the Yongneup fen in central Korea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1893, https://doi.org/10.5194/egusphere-egu21-1893, 2021.

09:21–09:23
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EGU21-2789
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ECS
Joanna Tindall, Jonathan Holmes, Ian Candy, Melanie Leng, Kira Rehfeld, Louise Sime, Irene Malmierca Vallet, Thierry Fonville, Pete Langdon, and David Sear

Late Holocene climatic variations pre-1850 CE are associated with volcanic and solar forcing (Schurer et al., 2013).  Whilst these variations are recorded in speleothems and ice-cores, these archives are often spatially restricted leaving gaps in our knowledge about short-term climate variability in a range of regions. Here, we investigate the potential of using the high-resolution δ18O analysis of lake carbonates formed within artificially constructed water bodies dating back to the Medieval period. Whilst the isotopic analysis of lake carbonates is a well-established Quaternary palaeoclimate proxy (Leng and Marshall, 2004) it has received less attention as a tool for climate reconstruction over the historic period. In this study we use the δ18O analysis of winter calcifying ostracod species from lake sediments recovered from Medieval fishponds from the town of Alresford, in southern England, combined with a programme of monitoring within the present-day water body to establish the hydrology and thermal regime of the system. This analysis shows that over the studied interval (the end of the Medieval period through to the 20th century) the lake system underwent regular inter-annual/decadal isotopic shift of relatively high magnitude (1-2‰).

In order to investigate whether these high magnitude δ18O fluctuations are explainable by climatic variability or are a result of intra-lake processes we provide a data-model comparison. This approach allows an understanding of the likely mechanistic drivers of climatic change as well as testing if proxy observations are consistent with modelled outputs (Evans et al., 2013). This study compares the δ18O ostracod record with a synthetic δ18Ocarbonate record derived from the Millennium Data iHadCM3 runs for the period 1200 CE to 1850 CE. The iHadCM3 model generates modelled values for temperature and δ18Oprecipitation on an annual and monthly basis. These data were used to produce a synthetic δ18Ocarbonate record on both an annual and seasonal basis using Kim and O’Neil's (1997) equation that describes the relationship between temperature, δ18Ocarbonate and δ18Olakewater.

The preliminary outputs of this proxy-model output comparison demonstrate that the magnitude of δ18Ocarbonate variability predicted by the model data is similar to the magnitude of change recorded in the proxy data. This suggests that these variations are real and driven by climatic rather than catchment-specific processes. Ongoing work aims to disentangle primary climate drivers of interannual δ18O change, at this site, using δ18O enabled climate model simulations. Our approach of considering what drives interannual δ18O changes over the last few hundred years, in these lacustrine settings, will help enable more robust palaeoclimatic reconstructions from these records.

References: Evans, M.N. et al., (2013), QSR, 76, pp.16–28.; Kim, S.-T. and O’Neil, J.R. (1997) Geochimica et Cosmochimica Acta, 61(16), pp.3461–3475; Leng, M.J. and Marshall, J.D. (2004) QSR, pp.811–831; Schurer, A.P. et al., (2013) Journal of Climate, 26(18), pp. 6954–6973.

How to cite: Tindall, J., Holmes, J., Candy, I., Leng, M., Rehfeld, K., Sime, L., Malmierca Vallet, I., Fonville, T., Langdon, P., and Sear, D.: Oxygen isotopic evidence of climate variability in southern England since the Medieval Period., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2789, https://doi.org/10.5194/egusphere-egu21-2789, 2021.

09:23–09:25
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EGU21-3748
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ECS
Georgina Falster, Bronwen Konecky, Sloan Coats, Samantha Stevenson, and Midhun Madhavan

Changes in the strength of the Pacific Walker circulation (PWC) can have a significant impact on global mean surface temperatures, as well as regional temperature, precipitation, and extreme weather events far beyond the tropical Pacific. Understanding PWC variability is therefore important for constraining future climate. But observational records of the PWC are short, and single-site proxy records for changes in the strength of the PWC during the last millennium offer contrasting interpretations. This leaves a critical gap in our understanding of PWC variability on the decadal to centennial timescales relevant to future climate change.

Falster et al. (in prep.) demonstrated that the PWC is strongly imprinted in modern global precipitation δ18O (δ18OP). This relationship arises via multiple complementary mechanisms, including but not limited to ENSO dynamics. We exploit this relationship to reconstruct changes in the strength of the PWC over the past millennium, using six different statistical and machine learning reconstruction methods in conjunction with a globally-distributed network of palaeo-δ18OP records (Konecky et al. 2020). Although δ18OP from a relatively small number of locations explains a large proportion of PWC variance in the calibration interval, we use a larger network of sites because larger networks are less susceptible to non-stationary teleconnections or non-signal biases than individual sites or smaller networks. 

Preliminary results indicate that reconstructed PWC variability is coherent across methods, particularly for the past 400 years. Our reconstructions are also robust to both the calibration window used, and the particular palaeo-δ18OP records included in the reconstruction. This provides confidence that our network comprises sufficient proxy timeseries i.e. that we successfully extracted the common underlying climate signal (the PWC) from site-specific information inherent in individual palaeo-δ18OP records. Thus, we are confident that our reconstruction of changes in the strength of the PWC through the last millennium is robust, and it will therefore help to constrain the PWC’s long-term internal variability and sensitivity to external forcing.


References:

Falster, G. M., B. Konecky, M. Madhavan, S. Coats, S. Stevenson. 2021. “Imprint of the Pacific Walker circulation in global precipitation δ18O”. In preparation for Journal of Climate

Konecky, B. L., N. P. McKay, O. V. Churakova (Sidorova), L. Comas-Bru, E. P. Dassié, K. L. DeLong, G. M. Falster, et al. 2020. “The Iso2k Database: A Global Compilation of Paleo-δ18O and δ2H Records to Aid Understanding of Common Era Climate.” ESSD. https://doi.org/10.5194/essd-2020-5.

How to cite: Falster, G., Konecky, B., Coats, S., Stevenson, S., and Madhavan, M.: Pacific Walker circulation variability during the last millennium reconstructed from a network of water isotope proxy records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3748, https://doi.org/10.5194/egusphere-egu21-3748, 2021.

09:25–09:27
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EGU21-6292
Katherine Scharer, Jenifer Leidelmeijer, Matthew Kirby, Nicole Bonuso, and Devin McPhillips

In tectonically active regions, sedimentary records are overprinted by landscape response to climate, fire, and local earthquakes.  We explore this issue using a new paleoclimate record developed at the Pallett Creek paleoseismic site in southern California USA, a recently incised distal fan located along the San Andreas Fault at the base of a 35 km2 catchment in the San Gabriel Mountains.  To date, we have analyzed 6 m of section, spanning the last 1300 yr, for grain size, total organic material (TOM), carbon/nitrogen (C/N) ratios, magnetic susceptibility, and charcoal count. Existing C-14 dates (Scharer et al., 2011) inform rates of sediment deposition and charcoal accumulation (CHAR). Additional dating and macrofossil analysis is ongoing.  Sedimentological variability within the section is dominated by two general units. Unit 1 is characterized by high % clay, % silt, and % TOM, while Unit 2 is distinctly coarser with higher % sand and lower % TOM.  Pulses of high CHAR occur from 1150-1260 yr BP and during the Little Ice Age (100-500 yr BP) and are associated with high sedimentation rates (0.3-2 cm/yr), while only a few relatively weak fire episodes are recorded in the Medieval Climate Anomaly (700-1000 yr BP), despite similarly high sedimentation rates (0.6 cm/yr).  Ten earthquakes documented at the site (Sieh et al., 1989) occurred about every 135 years and impart no obvious short-term impact on sedimentation rates, perhaps reflecting the distance between the site and steeper portions of the drainage network (>4 km) likely to produce mass wasting.  Overall, the landscape response of this large, integrated catchment appears to reflect a stronger influence of fire and climate than earthquakes. Future work will focus on the impact of the fire episodes on sediment delivery and resultant paleoearthquake ages.

How to cite: Scharer, K., Leidelmeijer, J., Kirby, M., Bonuso, N., and McPhillips, D.: Impact of fires, earthquakes, and climate on catchment response since 600 CE, Pallett Creek, San Gabriel Mountains, Southern California USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6292, https://doi.org/10.5194/egusphere-egu21-6292, 2021.

09:27–09:29
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EGU21-8550
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ECS
Léo Chassiot, Emmanuel Chapron, Elisabeth Michel, Vincent Favier, Vincent Jomelli, Joanna Charton, Deborah Verfaillie, and Xavier Crosta

The strength and the location of Southern Hemisphere winds (SHW) define an annular mode (SAM), a major component of interannual climatic variability in the Southern Hemisphere. SAM has a significant impact on mid-latitude westerly winds, but also acts on the meridional moisture transport over the Southern Ocean (for example, in the case of atmospheric rivers), with dramatic consequences on the cryosphere at high latitudes. Assessment of past, present and future changes in the SAM is essential for understanding climate variations and impacts at high latitudes. To date, Holocene proxy-based reconstructions of SAM are limited to South America, Australia/New Zealand, and Antarctica. In opposite, the paucity of SAM-related records for the Southern Indian Ocean presently limits our understanding of the spatial and temporal extent of SHW behavior in this region.

To this aim, we present a series of 30-m long marine records retrieved from a fjord fed by glacial melt of the Ampere glacier belonging to the Cook Ice Cap in the Kerguelen Archipelago (49˚20’S, 69˚20’E). A new chronological framework, based on Bayesian modelling of 50 radiocarbon ages along with 137Cs and 210Pb measures, allows reconstructing 4 kyrs of sediment discharge related to glacier variability. Sedimentological and geochemical analyses from XRF and GEOTEK core scanners highlight (i) a regional tephra at 950 cal BP; (ii) regular occurrences of floods during the LIA; and (iii) a background sedimentation related to glacial flour inputs through hypo- and hyperpycnal flows favoring very high sedimentation rates (1-2 cm.a-1) in the fjord. Phases of glacier advances and retreats linked to moisture transport by SHW are reflected by fluctuations in sedimentological and geochemical signals, and correlated with moraines dating on land. Over the past 4 kyrs, four cycles of glacier advances/retreats can be evidenced, reflecting wet/dry periods in response to shifts in the position and changes in magnitude of the SHW, associated with moisture transport and precipitation in the Southern Indian Ocean. On centennial timescales, wet/dry periods inferred from Kerguelen are in-phase with Holocene SAM-related records from South America and Tasmania over the last 2 kyrs, suggesting the long-term glacier dynamic at Kerguelen is also related to a centennial expression of SAM.

Acknowledgments : Marion Dufresne Crew, ARTEMIS program, UGA-ARCA.

How to cite: Chassiot, L., Chapron, E., Michel, E., Favier, V., Jomelli, V., Charton, J., Verfaillie, D., and Crosta, X.: Marine records of Holocene glacier variability in the Kerguelen Islands (South Indian Ocean): sedimentology, chronology, and paleoclimatic drivers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8550, https://doi.org/10.5194/egusphere-egu21-8550, 2021.

09:29–09:31
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EGU21-13653
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ECS
Sven Pallacks, Patrizia Ziveri, Belen Martrat, Graham P. Mortyn, Michael Grelaud, Ralf Schiebel, Alessandro Incarbona, Jordi Garcia-Orellana, and Griselda Anglada-Ortiz

The increase in anthropogenic induced warming over the last two centuries is impacting marine environments. Marine planktic calcifying organisms interact sensitively to changes in sea surface temperatures (SST), and the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly (MCA) to present. Reconstructed SSTs are in good agreement with other results, tracing temperature changes through the Common Era, and show a clear 20th century warming signal. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides) a common group of marine calcifying zooplankton. The abundance ratios between these species show the switch between winter / spring surface productivity and deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of North Atlantic Oscillation (NAO), and, to lesser extent, by the Atlantic Multidecadal Oscillation (AMO). In the industrial era, starting from about 1800 Common Era (CE), this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles and influences are being overprinted by human influences.

How to cite: Pallacks, S., Ziveri, P., Martrat, B., Mortyn, G. P., Grelaud, M., Schiebel, R., Incarbona, A., Garcia-Orellana, J., and Anglada-Ortiz, G.: Planktic Foraminifera changes in the western Mediterranean Anthropocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13653, https://doi.org/10.5194/egusphere-egu21-13653, 2021.

09:31–09:33
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EGU21-14756
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ECS
Shah Parth, James M Russell, and Nicolas Waldmann

There is a major knowledge gap in the past climate oscillation of the Arabian desert, especially during the past two millennium. Reliable continuous continental records that archives at high resolution past environmental variability are useful sentinels of paleoclimate changes. Reliable interpretation from climatic proxies retrieved from lake records are crucial for identifying periodicities and the onset of climatic events and evaluating inter-annual and decadal trends driven by shifting of the Intertropical Convergence Zone (ITCZ). A multiproxy approach is presented for a ~3.3 m composite core from a karst lake located in Gayal el Bazal, southern Yemen. Sedimentary proxies, including grain size distribution and magnetic susceptibility (MS) coupled with geochemistry (XRF), provide an initial picture of centennial-scale environmental changes over the southern Arabian desert. The chronology of the core was anchored by five radiocarbon (14C) dates of terrestrial plants (wood) extracted from sediment samples and indicates the core extends to ~800 AD. Our data provides a snapshot for better understanding the impact of Indian Ocean monsoon variability at an exceptional resolution for a region that lacks sufficient information. Our data indicates that during the ‘Little Ice Age’ (~1500-1800 AD) was arid relative to the warm conditions that prevailed during the Medieval Warming Period (~800 to 1200 AD). The arid phase was marked by high Ca/(Al, Fe, Ti) values, increased inorganic carbon content, decreased MS values, and gypsum precipitation. Furthermore, end-member mixing analyses (EMMA) derived from the grain-size distribution corroborates the production of carbonate sand probably due to an increase in flash floods occurring concurrently with low lake levels under generally dry conditions. Aridity during the Little Ice Age is consistent with evidence and theory for weakened boreal summer monsoons during intervals of northern hemisphere cooling. Overall, this study will provide insight into the monsoon variability and a record for understanding the interactions between northward migrations of the ITCZ and tropical monsoonal dynamics during the late Holocene. In the context of current climate change and increasing population pressure, a deeper understanding of their long-term hydrological variability, this study is highly essential to satisfactorily forecast the sustainability of lakes as a resource in a warming world.

How to cite: Parth, S., Russell, J. M., and Waldmann, N.: Reconstructing 1200 years of hydroclimate variability in the southern margins of the Arabian Desert, inferred from an ancient lake in southern Yemen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14756, https://doi.org/10.5194/egusphere-egu21-14756, 2021.

09:33–09:35
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EGU21-13949
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ECS
Rachel Walter and the PAGES CoralHydro2k

Corals are distributed throughout the tropical oceans, making them useful for resolving climate information covering time before the satellite era when instrumental data is often scarce. Coral δ18O has been used to reconstruct changes in both sea surface temperature (SST) and hydrology, while coral Sr/Ca is thought to mainly record SST. Coral δ18O data, when used in conjunction with Sr/Ca, can therefore be used to reconstruct seawater δ18O (δ18Osw), an indicator of the local precipitation-evaporation balance as well as other surface ocean hydrological changes. Coral Sr/Ca-SST relationships are critical for reconstructing δ18Osw from paired Sr/Ca and δ18O records, but vary across existing literature. Some of this variation is due to existing natural differences between corals, but variation also stems from differences in calibration methods or SST products used to determine the Sr/Ca-SST relationship. Such methodological differences complicate the comparison of results across studies and slow efforts to create a global picture of reconstructed tropical ocean hydroclimate.

Here, we use the PAGES CoralHydro2k database - a collection of 45 paired coral Sr/Ca-δ18O records and 70 coral δ18O records - to assess different methodological choices such as SST product and regression method and develop a calibration framework to use as a set of “best practices” moving forward. We also examine the sensitivity of δ18Osw to our calibration framework and to existing δ18Osw calculation methods. The PAGES CoralHydro2k project aims to leverage its coral database and apply these best practices and insights to a global reconstruction of tropical marine hydrology over the past 200 years.

How to cite: Walter, R. and the PAGES CoralHydro2k: Assessing the impact of Sr/Ca-SST calibrations on coral-based seawater δ18O reconstructions - First results from PAGES CoralHydro2k, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13949, https://doi.org/10.5194/egusphere-egu21-13949, 2021.

09:35–10:30
Break
Chairpersons: Andrea Seim, Hugo Beltrami, Francisco José Cuesta-Valero
11:00–11:02
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EGU21-571
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ECS
Zhiqiang Lyu, Hugues Goosse, and Quentin Dalaiden

Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although the changes over recent decades are well studied, the short instrumental record limits our ability to determine if such asymmetric patterns are common for Antarctica and the processes at their origin. Here, we will focus on the years 0-1000 CE as some ice core records display very contrasted trends during this period. Furthermore, the climate models are unable to reproduce the warming displayed in some reconstructions from 1 to 500 CE over East Antarctica. In order to understand the origin of these apparent incompatibilities and investigate the effect of proxy selection on regional reconstructions over 0-1000 CE, we performed several offline data assimilation experiments based on different groups of d18O records and the isotope-enabled general circulation models (iCESM). When assimilating different d18O data sets, large differences appear in the pattern of temperature trend over 0-500 CE, but the patterns over 500-1000 CE are more consistent among the various experiments. This implies that the spatial pattern of temperature trend over 0-500 CE is still uncertain because of this high sensitivity on the choice of the proxies to constrain the model results, while the pattern over 500-1000 is more robust, with the greater cooling over West Antarctica than East Antarctica. This pattern over 500-1000 CE relates to the intensifying of the low pressure centered in the Amundsen Sea, which induces enhanced southerly flow through most of WAIS.

How to cite: Lyu, Z., Goosse, H., and Dalaiden, Q.: Spatial patterns of multi-centennial temperature trend in Antarctica over 0-1000 CE: insights from ice core records and modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-571, https://doi.org/10.5194/egusphere-egu21-571, 2021.

11:02–11:04
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EGU21-3756
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ECS
Danielle Udy, Tessa Vance, Anthony Kiem, Neil Holbrook, and Mark Curran

Weather systems in the southern Indian Ocean drive synoptic-scale precipitation, temperature and wind variability in East Antarctica, sub-Antarctic islands and southern Australia.  Over seasonal to decadal timescales, the mean condition associated with combinations of these synoptic weather patterns (e.g., extratropical cyclones, fronts and regions of high pressure) is often referred to as variability in the westerly wind belt or the Southern Annular Mode (SAM). The westerly wind belt is generally considered to be zonally symmetric around Antarctica however, on a daily timescale this is not the case. To capture the daily variability of regional weather systems, we used synoptic typing (Self-Organising Maps) to group weather patterns based on similar features, which are often lost when using monthly or seasonal mean fields. We identified nine key regional weather types based on anomaly pattern and strength. These include four meridional nodes, three mixed nodes, one zonal node and one transitional node. The meridional nodes are favourable for transporting warm, moist air masses to the subantarctic and Antarctic region, and are associated with increased precipitation and temperature where the systems interact with the Antarctic coastline.  These nodes have limited association with the SAM, especially during austral spring.  In contrast, the zonal and mixed nodes were strongly correlated with the SAM however, the regional synoptic representation of SAM positive conditions is not zonally symmetric and is represented by three separate nodes.  These different types of SAM positive conditions mean that the commonly used hemispheric Marshall index often fails to capture the regional variability in surface weather conditions in the southern Indian Ocean. Our results show the importance of considering different synoptic set ups of SAM conditions, particularly SAM positive, and identify conditions that are potentially missed by SAM variability (e.g., extreme precipitation events). Our results are particularly important to consider when interpreting SAM or westerly wind belt reconstructions in the study region (from ice cores, tree rings, or lake sediments).  Here we present a case study using the synoptic typing results to enhance our understanding of the Law Dome (East Antarctica) ice core record, focussing on links to large scale modes of climate variability and Australian hydroclimate.  These results enhance the usefulness of ice core proxies in coastal East Antarctica and assist with determining where and how it is appropriate to use coastal East Antarctic ice core records for reconstructions of large scale modes of climate variability (e.g. SAM and ENSO) and remote hydroclimate conditions.

How to cite: Udy, D., Vance, T., Kiem, A., Holbrook, N., and Curran, M.: Synoptic climatology of southern Indian Ocean and paleoclimate proxy interpretation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3756, https://doi.org/10.5194/egusphere-egu21-3756, 2021.

11:04–11:06
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EGU21-8661
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ECS
Yannick Heiser, Janica Bühler, Mathieu Casado, and Kira Rehfeld

Stable water isotope ratios (δ18O) measured in e.g. ice-cores or speleothems have long been established as temperature proxies and are used to reconstruct past climate variability but still require more quantification on spatial and temporal scales. The high resolution ice-core archives are mainly found in polar and alpine regions, whereas the speleothem records mostly grow in caves in low to mid-latitudes. To bridge between the archives, models are needed to compare the climate variability stored in both ice-cores and speleothems, which will help to evaluate future projections of climate variability.

Here, we compare a transient isotope enabled simulation from the Hadley Center Climate Model version 3 (iHadCM3) [1, 2] to polar ice-core records from the iso2k database [3] for the last millennium (LM, 850-1850 CE). We analyze time-averaged isotope ratios and their variability on decadal to centennial timescales to systematically evaluate the offsets and correlation patterns between simulated and recorded isotopes to specific climatic drivers. For better comparability between speleothem and ice core-archives, we also include non-polar ice core records, as well as monitored precipitation δ18O from a global database.

We find the time-averaged δ18O offsets between the simulation and ice-core records to be fairly small for most of the polar ice-core sites, indicating a low simulation climate offset.
As expected, we find the simulated δ18O variability to be higher in the polar regions of ice-core locations, compared to the simulated variability at speleothem cave locations. Recorded δ18O variability is also generally higher as stored in ice-cores, compared to that stored in speleothems. Both speleothems and ice-core records show damping effects on decadal time scales, which can in part be attributed to the temporal resolution of the individual records. This comparison of different proxy archives to isotope-enabled GCM output shows a promising way to evaluate the model’s capability to resolve δ18O variability.

[1]  Bühler, J. C. et al. Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium. Climate of the Past: Discussions 1–30 (2020).

[2]  Tindall, J. C., Valdes, P. J. & Sime, L. C. Stable water isotopes in HadCM3: Isotopic signature of El Niño-Southern Oscillation and the tropical amount effect. Journal of Geophysical Research Atmospheres 114, 1–12 (2009).

[3] Konecky, B. L. et al. The Iso2k database: A global compilation of paleo-δ18O and δ2H records to aid understanding of Common Era climate. Earth System Science Data 12, 2261–2288 (2020).

How to cite: Heiser, Y., Bühler, J., Casado, M., and Rehfeld, K.: Comparison of isotopic signatures in ice core and speleothem records to an isotope enabled climate model simulation for the last millennium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8661, https://doi.org/10.5194/egusphere-egu21-8661, 2021.

11:06–11:08
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EGU21-12729
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ECS
Anouk Vlug, Fabien Maussion, Ben Marzeion, Matthias Prange, and Kristin Richter

The mass loss of glaciers and ice caps is one of the major contributors to sea-level rise over the past 120 years. Different climate forcings, both natural and anthropogenic, have an influence on the climate and therefore on glacier mass balance. Glaciers have a slow and delayed response to climate change, and at any point in time, their properties are therefore also a result of past climate changes. In this context, we present global glacier simulations over the last millennium. For these simulations, the Open Global Glacier Model was forced with the fully forced, single forced and control simulations of the Community Earth System Model Last Millennium Ensemble. These simulations show how different climate forcings, i.e., volcanic, greenhouse gasses, solar, orbital, land use & land cover and ozone-aerosol, impact the climatic mass balance, both individually and combined. These influences are then analyzed over time and regionally. In addition to addressing the role of the different forcings, we present the contribution of natural vs anthropogenic forcings on glacier mass balance over the last millennium.

How to cite: Vlug, A., Maussion, F., Marzeion, B., Prange, M., and Richter, K.: The contribution of different climate forcings on the global glacier climatic mass balance over the last millennium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12729, https://doi.org/10.5194/egusphere-egu21-12729, 2021.

11:08–11:10
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EGU21-15684
Sea ice changes in the Chukchi Sea over the Industrial Era based on biomarkers
(withdrawn)
Youcheng Bai, Marie-Alexandrine Sicre, Jian Ren, Bassem Jalali, Hongliang Li, Long Lin, Zhongqiang Ji, Liang Su, Qingmei Zhu, Haiyan Jin, and Jianfang Chen
11:10–11:12
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EGU21-15966
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ECS
Diana Vladimirova, Elizabeth Thomas, and on behalf of CLIVASH2k

Trends in sea ice extent and atmospheric circulation around Antarctica have exhibited large variability over recent decades. Direct observations such as satellite data cover the past four decades only. Thus, a comparison with paleoclimate archives is essential to understand the natural and anthropogenic components of these recent changes. We have initiated a data call within CLIVASH2k community (http://pastglobalchanges.org/science/wg/2k-network/projects/clivash) to collect all available sodium (Na+) and sulfate (SO42-) concentration and fluxes from Antarctic ice cores. We aim to improve our understanding of large-scale sea-ice variability and atmospheric circulation over the past 2000 years. In this respect, ice cores are a unique archive.

Here we present the new database, which builds on previous efforts by the PAGES community in gathering snow accumulation (Thomas et al. 2017) and stable water isotope data (Stenni et al. 2017).  To date, 88 published and 14 unpublished records have been submitted, 10 of which span the full 2000 years. The data, especially 2000 years-long records are equally distributed over the Antarctic continent and all coastal regions are well represented.  The new data will allow us to investigate interannual and decadal-to-centennial scale variability in sea ice extent and atmospheric circulation and its regional differences over the past 2000 years.

How to cite: Vladimirova, D., Thomas, E., and CLIVASH2k, O. B. O.: Compiling a chemistry database from Antarctic ice cores records spanning the past 2000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15966, https://doi.org/10.5194/egusphere-egu21-15966, 2021.

11:12–11:14
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EGU21-15355
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ECS
Zeynab Foroozan, Jussi Grießinger, Kambiz Pourtahmasi, and Achim Bräuning

Knowledge about the long-term hydroclimatic variability is essential to analyze the historic course and recent impact of climate change, especially in semi-arid and arid regions of the world. In this study, we present the first tree-ring δ18O chronology for the semi-arid parts of northern Iran based on juniper trees. We were able to reconstruct past hydroclimatic variability for the past 500 years. The highly significant correlation between tree-ring δ18O and spring precipitation indicates the primary influence of spring moisture availability on δ18O variations. The thereof derived precipitation reconstruction reveals short and long-term variability of precipitation intensity, duration, and frequency of dry/wet events. During the past 500 years, the driest period occurred in the 16th century, whereas the 18th century was comparably wet. A gradual decline in the reconstructed spring precipitation is evident since the beginning of the 19th century, culminating in the continuing drought of the 20th century. An analysis of dry/wet years indicated that over the last three centuries, the occurrence of years with a relatively dry spring is increasing. In contrast, more humid spring conditions are decreasing. However, the overall frequency of the occurrence of extreme events increased over the past five centuries. In addition, past hydrological disasters recorded in Persian history were well represented in our reconstruction. Correlations between our reconstructed precipitation record and large-scale circulation systems revealed no significant influence of large-scale climatic drivers on spring precipitation variations in north Iran, which therefore seem to be mostly controlled by a regional climate forcing.

How to cite: Foroozan, Z., Grießinger, J., Pourtahmasi, K., and Bräuning, A.: A multi-century spring precipitation history for northern Iran derived from tree-ring δ18O , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15355, https://doi.org/10.5194/egusphere-egu21-15355, 2021.

11:14–11:16
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EGU21-7550
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ECS
Tom De Mil, Matthew Salzer, Charlotte Pearson, Valerie Trouet, and Jan Van den Bulcke

Great Basin Bristlecone pine (Pinus longaeva) is known for its longevity. The longest continuous tree-ring width chronology covers more than 9000 years. Tree-ring width of upper treeline bristlecone pine trees is influenced by summer temperature variability at decadal to centennial scales, but to infer a temperature signal on interannual scales, Maximum Latewood Density (MXD) is a better proxy. Here, we present a preliminary MXD chronology to investigate the temperature signal in upper treeline and lower elevation bristlecone pines. MXD was measured with an X-ray Computed Tomography toolchain in 24 dated cores,  with the oldest sample dating back to 776 CE. Ring and fibre angles were corrected and two MXD chronologies for different elevations were developed, which will be used to study climate-growth relationships and the effect of elevation on them. Future scanning will allow constructing a 5000+ year-long MXD chronology from upper treeline sites, which will provide an annual-resolution North American temperature record covering the mid-to-late Holocene.

How to cite: De Mil, T., Salzer, M., Pearson, C., Trouet, V., and Van den Bulcke, J.: Maximum latewood density records of Great Basin Bristlecone pine (Pinus Longaeva) from the White Mountains, California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7550, https://doi.org/10.5194/egusphere-egu21-7550, 2021.

11:16–11:18
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EGU21-8995
Olga Churakova (Sidorova), Marina Fonti, Rolf Siegwolf, Tatyana Trushkina, Eugene Vaganov, and Matthias Saurer

We use an interdisciplinary approach combining stable isotopes in tree rings, pollen data, ice cores from temperature-limited environment in the Siberian north and developed a comprehensive description of the climatic changes over the past 1500 years. We found that the Climatic Optimum Period was warmer and drier compared to the Medieval one, but rather similar to the recent period. Our results indicate that the Medieval Warm period in the Taimyr Peninsula started earlier and was wetter compared to the northeastern part of Siberia (northeastern Yakutia). Summer precipitation reconstruction obtained from carbon isotopes in tree-ring cellulose from Taimyr Peninsula significantly correlated with the pollen data of the Lama Lake (Andreev et al. 2004) and oxygen isotopes of the ice core from Severnaya Zemlya (Opel et al. 2013) recording wetter climate conditions during the Medieval Warm period compared to the northeastern part of Siberia. Common large-scale climate variability was confirmed by significant relationship between oxygen isotope data in tree-ring cellulose from the Taimyr Peninsula and northeastern Yakutia, and oxygen isotope ice core data from Severnaya Zemlja during the Medieval Warm period and the recent one. Finally, we showed that the recent warming on the Taimyr Peninsula is not unprecedented in the Siberian north. Similar climate conditions were recorded by stable isotopes in tree rings, pollen, and ice core data 6000 years ago. On the northeastern part of Siberia newly developed a 1500-year summer vapor pressure deficit (VPD) reconstruction showed, that VPD increased recently, but does not yet exceed the maximum values reconstructed during the Medieval Warm period. The most humid conditions in the northeastern part of Siberia were recorded in the Early Medieval period and during the Little Ice Age. However, the increasing VPD under elevated air temperature in the last decades affects the hydrological regime of these sensitive ecosystems by greater evapotranspiration rates. Further VPD increase will significantly affect Siberian forests most likely leading to drought even under additional access of thawed permafrost water.

This work was supported by the FP7-PEOPLE-IIF-2008 - Marie Curie Action: "International Incoming Fellowships" 235122 and "Reintegration Fellowships" 909122 “Climatic and environmental changes in the Eurasian Subarctic inferred from tree-ring and stable isotope chronologies for the past and recent periods” and the Government of Krasnoyarsk Kray and Russian Foundation for Basic Research and Krasnoyarsk Foundation 20-44-240001 “Adaptation of conifer forests on the north of the Krasnoyarsk region (Taimyr Peninsula) to climatic changes after extreme events over the past 1500 years“ awarded to Olga V. Churakova (Sidorova).

How to cite: Churakova (Sidorova), O., Fonti, M., Siegwolf, R., Trushkina, T., Vaganov, E., and Saurer, M.: Response of Siberian trees to climatic changes over the past 1500 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8995, https://doi.org/10.5194/egusphere-egu21-8995, 2021.

11:18–11:20
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EGU21-10485
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ECS
Guobao Xu, Meko Matthew, Lara Klippel, Isabel Dorado-Liñán, and Valerie Trouet

The jet stream configuration over the Atlantic Ocean and the European continent substantially affects climatic extremes in Western Eurasia by transporting heat and vorticity. However, how the Europe-Atlantic jet configuration varies and how it affects European climate on the long time-scales are still unclear. We compiled a network of tree-ring width, blue intensity, and maximum density chronologies from Europe to explore past variability in the summer Europe-Atlantic Jet stream and its influence on regional climate. By combining five regional chronologies, we were able to reconstruct July-August jet stream latitude (JSL) PC2 variability over the past millennium (978-2010 CE) for the Europe-Atlantic domain (30°W to 40°E). Our reconstruction explains 40% of summer JSL PC2 variability over the instrumental period (1948-2010 CE) with strong skill. Our millennial-long reconstruction shows that summer JSL is a relevant driver of the temperature, precipitation, and drought dipoles observed between Northwestern and Southern Europe. Positive summer JSL PC2 values (northward jet position) generally lead to a strengthening of the European summer climate dipole, while negative values (southward jet position) lead to a weak or insignificant dipole mode. Our summer JSL reconstruction shows large variability and a high occurrence rate of extremes over the 20th century, as well as 1200-1350 CE Medieval Climate Anomaly (MCA). The high occurrence rate of summer JSL extremes corresponds to periods with increased number of climatic extremes. Our results suggest that the summer JSL contributes to the European climate dipole both in a long-term context and in its extremes. We also reveal that the occurrence rate of summer JSL extremes is double during the 20th century compared to other periods, especially for the negative extremes, which might be related to anthropogenic warming. Our results suggest a high occurrence rate of summer JSL extremes during the 20th century, leading to more climatic extremes in Europe, as well as a prevailing northward summer JSL position resulting in a weakening climatic dipole.

How to cite: Xu, G., Matthew, M., Klippel, L., Dorado-Liñán, I., and Trouet, V.: Europe-Atlantic jet caused dipole mode of European climate and increased climatic extremes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10485, https://doi.org/10.5194/egusphere-egu21-10485, 2021.

11:20–11:22
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EGU21-5405
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ECS
Woon Mi Kim, Richard Blender, Michael Sigl, Christoph Raible, and Martina Messmer

Torrential rainfall and floods have had devastating impacts on civilizations throughout history. Thus, understanding long-term characteristics of extreme precipitation is necessary to identify physical mechanisms involved in such events and to be able to assess, not only the past, but also the present and future risk of extreme precipitation for society. However, the scarce spatial and temporal distribution of existing datasets on extreme precipitation complicates a detailed study of such events in the paleo climate context.  

In this study, we employ the newly produced seamless simulations from the Community Earth System Model v1.2.2 that covers the period from 1501 BC to 1849 AD to analyze the daily extreme precipitation before the preindustrial period. We explore the statistical characteristics of extreme precipitation and their association with natural external forcing, such as changes in the orbital parameters, solar cycle, insolation, and volcanic eruptions. For this, we applied to the simulations an extreme value analysis  by adopting a peak-over-threshold method (Coles et al., 2001). The 99th percentile of daily precipitation anomalies with respect to 1501BC - 1849AD are taken as the extreme values and these extremes are fitted to the Generalized Pareto Distribution to create time-stationary and covariate models (GPD models) at each grid point.  

The stationary GPD model shows that over the mid-latitudes, high scale and negative shape parameters predominate in the Pacific while the opposite condition occurs in the Atlantic sector. Over the Southern Ocean, low scale and negative shape parameters are more common. The covariate GPD models indicate some connection between the external forcing and extreme precipitation. The changes in the orbital parameters are slightly connected to the extreme precipitation over the tropical Atlantic and southern Indian oceans. Among all the forcing, the volcanic eruptions are the most influential in the extreme precipitation during the past 3350 years. The return periods of extreme precipitation decrease over the tropical Pacific, and the mid-latitude oceans and lands after volcanic eruptions, indicating that such eruptions likely increase the occurrence of extreme precipitation in these regions. Over the regions where a decrease in extreme precipitation is followed after the eruptions, such as India, Australia, and eastern Asia, the return periods decrease after volcanic eruptions.  

Overall, our study provides a long-term continuous view on the global extreme precipitation, which elucidates some complementary information to the currently available proxy and instrumental observations on extreme precipitation events. 

 

Coles, S., Bawa, J., Trenner, L., & Dorazio, P. (2001). An introduction to statistical modeling of extreme values (Vol. 208, p. 208). London: Springer. 

How to cite: Kim, W. M., Blender, R., Sigl, M., Raible, C., and Messmer, M.: Statistical Characteristics of Global Daily Extreme Precipitation during the last 3350 years (1501BC – 1849 AD) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5405, https://doi.org/10.5194/egusphere-egu21-5405, 2021.

11:22–11:24
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EGU21-1692
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ECS
Devika Varma, Gert-Jan Reichart, and Stefan Schouten

For more than a decade TEX86 and UK’37, derived from ratios of biomarker lipids have widely been used as organic paleotemperature proxies. Yet, these proxies, especially TEX86, have several uncertainties associated with factors such as depth and seasonal biases which are complicating its application as an annual mean sea-surface temperature (SST) proxy. To constrain this impact, we performed a relatively simple modelling exercise where we use instrumental temperature and nutrient data from 40 locations across the globe to predict theoretical proxy values and compare them with measured core-top proxy values.

The model first uses instrumental nutrient and temperature data, and probability density functions to predict the theoretical depth occurrence of the source organisms of the two proxies. Additionally, seasonal bias was introduced by predicting seasonal occurrences using instrumental nutrient and chlorophyll data. This was used to calculate the depth- and season weighed temperature signal annually deposited in the sediment, which in turn was converted to theoretical proxy values using culture or mesocosm calibrations. This showed, as expected, that depth and seasonal biases introduced scatter in the correlation between theoretical proxy values and annual mean SST but still highly significant for both UK’37 (r2= 0.96), and TEX86 (r2= 0.77). We find that the theoretical proxy values are much lower than measured proxy value for TEX86, which tentatively suggests that TEX86 might in fact be coming from shallower depths or that the mesocosm calibration is incorrect. Our model for UK’37 results in theoretical values similar to measured values except for low temperature locations. This might suggest an influence of seasonal bias towards more warmer summer seasons which is more pronounced in high latitudes than in tropics.

How to cite: Varma, D., Reichart, G.-J., and Schouten, S.: Depth and seasonal biases in organic temperature proxies: a modelling study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1692, https://doi.org/10.5194/egusphere-egu21-1692, 2021.

11:24–11:26
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EGU21-12106
Johann Jungclaus, Eduardo Alastrue de Asenjo, Alexandre Cauquoin, Shih-Wei Fang, Myriam Khodri, Stephan Lorenz, Rumi Ohgaito, Teffy Sam, Claudia Timmreck, Matthew Toohey, Martin Werner, Kohei Yoshida, Davide Zanchettin, and Qiong Zhang

The Common Era (CE, i.e. the two millennia before the industrialization) is among the periods selected by the Paleo Model Intercomparison Project (PMIP) for transient experiments contributing to PMIP4. For PMIP4, novel estimates and updates of external forcing have been compiled (Jungclaus et al., GMD, 2017).  In addition to the Tier-1 category simulation “past1000” for the period 850 CE to 1849 CE, the Tier-3 “past2k” experiment covers the entire CE. After serious delays, the ESGF is now being filled by modeling groups running the transient simulations.

Here we provide an overview of the simulations, discuss the range of applied models, and present first results of common analyses from past1000 and subsequent historical simulations. We discuss the long-term climate evolution, the range of internally-generated and externally-forced variability and specific aspects of the response to volcanic forcing.

Another focus is the presentation of the first MPI-ESM ‘past2k’ simulations and their extension to include water isotopes in MPI-ESM-WISO. These simulations extend the pool of current ESM simulations into the 1st millennium CE and represent an important basis to assess the models’ response to external forcing and improved model-data comparison. We analyze regional trends and variations over the last 2000 years in comparison with PAGES2k reconstructions.

 

How to cite: Jungclaus, J., Alastrue de Asenjo, E., Cauquoin, A., Fang, S.-W., Khodri, M., Lorenz, S., Ohgaito, R., Sam, T., Timmreck, C., Toohey, M., Werner, M., Yoshida, K., Zanchettin, D., and Zhang, Q.: Transient simulations over the Common Era in PMIP4/CMIP6, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12106, https://doi.org/10.5194/egusphere-egu21-12106, 2021.

11:26–11:28
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EGU21-16004
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ECS
Julián Villamayor and Myriam Khodri

The Sahel region is extremely sensible to alterations in its characteristic precipitation regime, associated with the West African Monsoon (WAM). In fact, the WAM presents strong variability at several timescales which has focused the attention of many works that mainly attribute such changes to variations in the sea surface temperature, the emerging increase of greenhouse gases concentration and to alterations in land use. However, the impact of large volcanic eruptions has been just tentatively addressed. This work aims at shedding more light on the influence of large volcanic eruptions on Sahel rainfall relying on past1000 simulations, covering the last millennium, of the IPSL-CM6A-LR model. The results show the mechanisms involved and the differences between tropical and high-latitude eruptions.

How to cite: Villamayor, J. and Khodri, M.: Sahel droughts induced by large volcanic eruptions over the last millennium in IPSL-CM6A-LR model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16004, https://doi.org/10.5194/egusphere-egu21-16004, 2021.

11:28–11:30
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EGU21-16519
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ECS
Francisco José Cuesta-Valero, Almudena García-García, Hugo Beltrami, Eduardo Zorita, and Fernando Jaume Santero
Estimates of climate sensitivity from Atmosphere-Ocean Coupled General Circulation Model (GCM) simulations present a large spread despite the continued improvements in climate modeling since the 1970s. This variability is partially caused by the dependence of several long-term feedback mechanisms on the reference climate state. However, it is difficult to provide a reference to assess the climatology of preindustrial control simulations as there are no long-term preindustrial observations.
In the ground, recent changes in ground surface temperature are observed at shallow depths as perturbations to the quasi-steady state geothermal regime. However, if undisturbed by recent surface temperature changes, the deep ground temperatures vary linearly as a function of depth, and the extrapolation of this linear behavior to the surface can be interpreted as the past long-term surface temperature climatology.
We assemble a new gridded database of past long-term ground surface temperatures (LoST database) obtained from 514 borehole temperature profiles measured across North America, and we explore its use as a potential reference for the evaluation of GCM preindustrial control simulations and past millennium simulations. All temperature profiles are truncated at 300 m depth, allowing to estimate the ground surface climatology for the period 1300-1700 of the common era. We compare the LoST database with observations from the CRU database, as well as with five past millennium simulations and five preindustrial control simulations from the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3) and the fifth phase of the Coupled Model Intercomparison Project (CMIP5) archives. Our results suggest that LoST temperatures could be employed as a reference to narrow down the spread of surface temperature climatologies on GCM preindustrial control and past millennium simulations.

How to cite: Cuesta-Valero, F. J., García-García, A., Beltrami, H., Zorita, E., and Jaume Santero, F.: Long-term Surface Temperature (LoST) Database as a Complement for Transient and Control Preindustrial Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16519, https://doi.org/10.5194/egusphere-egu21-16519, 2021.

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