Displays

Terrestrial climate archives provide a rich array of information on regional climate dynamics that often can link to global climate change.  A range of new metal and coupled isotope proxies is helping to unlock the most information from terrestrial archives and this paleoclimate information. The Jordon-Arava valley, tectonically active since the early Neogene, is one of the world’s largest pull-apart basins.  Throughout the Pleistocene to the Holocene, the valley contained a series of lacustrine water bodies.  As the valley is located on the boundary between the African-Arabian deserts and the Mediterranean regional climatic zone, studies of past conditions in these lacustrine bodies allows the reconstruction of changes in the regional hydrological cycle.  Lacustrine sediments, such as those found in the Jordon-Arava valley, record paleoclimatic information similar to that found within marine sedimentary archives and often at much higher resolution, from millennial to even annual timescales. The Lisan Formation is a 40-80m thick Pleistocene marl, which was deposited in Lake Lisan, which existed over the last glacial cycle in the Jordan-Arava Valley. The Lisan Formation contains a significant quantity of annually-precipitated primary aragonite, which has not recrystallised to calcite, allowing for direct U-Th dating, which has led to an exceptional age model for the Lisan Formation.

Here we discuss the measurement of the sulfur and oxygen isotopic composition of gypsum in the Lisan formation, as well as the generation of sulfur nodules within the formation that are not found in the sediment cores of the Dead Sea. We use this data to explore how sediment diagenesis, relating to changes in biogeochemistry, changes as a function of climate change over the last glacial cycle. We then present the calcium isotopic composition of the gypsum and interbedded aragonite, and show how the aragonite calcium isotopic composition covaries with lake level, and thus offers profound insight into the regional hydrological cycle in the Jordon-Arava Valley.

How to cite: Turchyn, A., Bradbury, H., and Torfstein, A.: Changes in biogeochemistry recorded in the Lisan formation and the Dead Sea Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12712, https://doi.org/10.5194/egusphere-egu2020-12712, 2020.

Throughout the last 65,000 years, there have been several brief periods of increased temperatures and precipitation over the eastern Sahara.  These periods have been constrained by numerous proxies including: palaeodischarge and sediment-load estimates of the Nile River, cave speleothems, dust fluxes, fossil groundwater, marine sediments, and reconstructed palaeolake level fluctuations. These climate disturbances are widely considered to have affected both the migration patterns of anatomically modern humans and Holocene human settlements.

However, these proxies can not be directly translated into precipitation intensity which would have had a profound impact on human activities, as intense precipitation events would make settlements next to rivers hazardous places to live. Here we reconstruct the paleoenvironmental conditions of six palaeoriver channel systems preserved over a ca 40’000 km² area in southern Egypt using geochronological, palaeohydrological and sedimentological techniques. These palaeorivers deposits are currently topographically inverted due to wind deflation. Despite previous attempts at dating these river channels using Acheulean artifacts and pottery shards collected from within the channel bodies, their age remains contentious between the middle Pleistocene to Holocene. Here we provide refined age constraints using Optically Stimulated Luminescence (OSL) coupled with Carbon-14 dating. Our results show that these rivers record at least 8 episodes of fluvial deposition distributed between 53 ± 7 ka and 1 ± 0.25 ka ago.

In addition, we estimate, using channel geometry (width and height) and median grain size (D₅₀), the palaeoslope, palaeovelocity, and palaeodischarge of these ancient inverted channels. Combining these parameters with estimates of palaeodrainage areas (based on digital elevation models (derived from ALOS PALSAR data) and Hack’s law) allows us to assess palaeoprecipitation rates in the range of 50 ± 10 mm/h during the incision of these palaeorivers. These rates indicate relatively intense periods of precipitation and important sediment transport periods during the early to mid-Holocene pluvial period in the Sahara compared with previous pluvial periods. Our results show that during these warmer and wetter periods the precipitation occurred in intense periods, which we suggest created hazardous environments close to the rivers and thus causing forcing human migration away from the rivers into the West and North. This, therefore, gives a plausible mechanism for the dispersal of human settlements from the South of Egyptian Sahara to the North-West 8,500 to 5,300 years ago.

How to cite: Zaki, A. S., King, G. E., Haghipour, N., Herman, F., Giegengack, R., Schuster, M., Gupta, S., Watkins, S. E., Khairy, H., Ahmed, S., Eltayeb, S. A., El-wakil, M., and Castelltort, S.: New palaeoclimate record from ancient river channels in the eastern Sahara: Implications for climate impact on human dispersals during the late Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12189, https://doi.org/10.5194/egusphere-egu2020-12189, 2020.

For millions of people living in the humid neotropics seasonally predictable rainfall is crucial for agricultural success and food security.  Understanding long-term stability and volatility of seasonal rainfall distributions should be of concern to researchers and policy makers. However, reconstructions of paleorainfall seasonality in the neotropics have been constrained by a lack of precisely dated and sub-annually resolved records. We present a 1,600-year rainfall paleoseasonality reconstruction from speleothem sample Yok G, from Yok Balum Cave located in southern Belize, Central America. Yok G grew continuously from 400 C.E. to 2,006 C.E. and its age is constrained by 52 U-series dates with a mean error of ~7 years. The isotope record consists of 7,151 δ¹⁸O and δ¹³C measurements at ~0.22-year resolution allowing us to detect the presence and amplitude of annual wet-dry cycles. In Belize rainfall distribution and seasonality controls are currently dominated by the annual migration of the intertropical convergence zone (ITCZ) with marked meridional contrast.  The Yok G record suggest distinct changes in seasonality at multi-centennial intervals.  The earliest portion of the record (400-~850 C.E.) shows little intra-annual seasonal variation, the period from ~850-1400 C.E. has highly variable annual oscillations and periods of low seasonality, while the period from 1,400-2,006 C.E. shows well developed seasonal signals.  Element ratios (Mg/Ca, Sr/Ca, and U/Ca) are used to assess Prior Carbonate Precipitation in the epikarst system.  We review these changes and the isotopic record from Yok G and discuss tools for interpreting the stability and volatility in seasonal rainfall distributions and possible implications for past and modern agricultural societies. 

How to cite: Prufer, K., Breitenbach, S., Baldini, J., Braun, T., Ray, E., Baldini, L., Polyak, V., Lechleitner, F., Marwan, N., Kennett, D., and Asmerom, Y.: A 1,600 year record of paleoseasonality from the neotropics of Central America and its implications for rainfall predictability in agricultural societies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18100, https://doi.org/10.5194/egusphere-egu2020-18100, 2020.

The Younger Dryas (YD, GS-1) is the latest of the canonical millennial-scale stadials of the last glacial period. Proxy data from terrestrial archives point to a climate dominated by extreme seasonality and continentality across Europe. YD summers were characterised by large meridional temperature gradients and remained quite warm despite the prominent slowdown of the Atlantic Meridional Overturning Circulation. The few available winter proxy records point to cold and dry winters.

In the Alps, the YD was characterised by the last major glacier advance and the development of rock glaciers. Dating these cryogenic geomorphological features, however, is associated with substantial uncertainties. A new type of secondary carbonate archive (coarsely crystalline cryogenic cave carbonates, or CCC_coarse) has received increasing attention as a promising quantitative cryogenic indicator for the shallow subsurface environment. CCC_coarse are found in karst caves and their formation is directly linked to thawing of perennial cave ice and U-series disequilibrium methods allow to date these events at high precision.

CCC_coarse formed during the YD were found in three caves covering an approximately 170 km-long SW-NE transect. The entrance of Cioccherloch cave is located at 2245 m in the Dolomites; Frauenofen opens in the Tennengebirge at 1635 m, while the third cave, Großes Almbergloch, is situated in Totes Gebirge at an elevation of 1475 m. The thermal regime in Cioccherloch reflects the ambient mean annual air temperature, while the cave microclimate of Frauenofen and Großes Almbergloch is partially influenced by cold air intrusions in winter.

²³⁰Th dating of twenty-two CCC_coarse samples demonstrates that perennial ice was present in these caves during the first part of the YD, and Großes Almbergloch, Cioccherloch and Frauenofen warmed to 0°C at 12.32 ±0.09, 12.20 ±0.09, and 12.01 ±0.04 ka BP (weighted means), respectively, initiating slow thawing of cave ice bodies. Due to the partial cold trap behaviour of Frauenofen and Großes Almbergloch, a delay in cave ice demise and thus CCC_coarse formation is likely. This and the higher elevation could explain the centennial lag observed in CCC_coarse deposition in Frauenofen compared to Großes Almbergloch.

The change in the thermal condition of these caves commencing at ~12.3 ±0.1 ka BP is attributed to a change in the winter climate in the Alps, from dry to snow-rich and/or from extremely cold to milder winters. A snowpack could effectively insulate the shallow subsurface from the YD winter coldness, allowing the subsurface to slowly warm. The timing of this warming of the subsurface coincides with the mid-YD transition recorded in other archives across Europe (e.g., Meerfelder Maar, central Germany; El Soplao cave, northern Spain) and corroborates the hypothesis of a northward movement of the Westerlies during the mid-YD, bringing warmer air and moisture to the Alps. Our study also demonstrates that the interpretation of CCC_coarse data requires a sound understanding of the cave geometry and the resulting mode of air exchange, since both the onset of perennial ice build-up and the eventual thawing may lag the atmospheric forcing outside the cave.

How to cite: Koltai, G., Spötl, C., and Cheng, H.: Changing winter conditions in the Alps during the Younger Dryas cold period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12049, https://doi.org/10.5194/egusphere-egu2020-12049, 2020.

The Holocene climate and its thermal optimum (HTM) are poorly studied in the boreal forests of the northwestern Urals region, particularly in the Republic of Komi. The objective of this study is to provide robust reconstructions of the Holocene climate (temperatures and precipitation) of the Vychegda River basin. The temperature reconstruction is based on pollen assemblages and GDGTs (Glycerol Dialkyl Glycerol Tetraethers). This first study of GDGTs in this area corresponds to a preliminary step for the calibration of this proxy in peats. Higher temperatures and precipitation are recorded between 7000 and 4000 cal. yr BP (mean annual temperatures around 3°C and precipitation between 600 and 700 mm per year. This climatic optimum is in agreement with previous pollen-based climate reconstructions, and climate patterns in the neighboring Russian and Fennoscandia (Komi Republic - previous study-, Arctic Russia, Siberia and Northern Europe, Andreev and Klimanov, 2000; Golubeva, 2008; Seppä et al., 2009a; Novenko et al., 2019). These results, in conjunction with the reconstruction of fire activity and vegetation dynamics in this region, led to a better understanding of the crossed influences of these factors. In particular, vegetation is mainly controlled by climate during the first part of the Holocene, while a threshold is reached on fire frequency after 3500 cal. yr BP and this parameter has a greater impact on vegetation than climate. Over the past 600 years, the intensification of human activities led to overexploitation of the forest and an increase in its fire activity.

How to cite: Barhoumi, C., Joannin, S., Ali, A. A., Ménot, G., Golubeva, Y., Subetto, D., Kryshen, A., Drobyshev, I., and Peyron, O.: Holocene climate in Northern Urals (Komi Republic, Russia): a multi-proxy approach based on pollen and brGDGTs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21994, https://doi.org/10.5194/egusphere-egu2020-21994, 2020.

Globally, lakes and reservoirs are vital sources of fresh water. In temperate zones like the Great Lakes region, Canada, it is not known if climate warming will increase or decrease effective moisture, or affect water availability. The links between effective moisture and primary production are also unclear. To test for possible linkages, we have reconstructed the ~900-year history of effective moisture and primary production in a small, kettle lake (Barry Lake, Ontario, Canada). To reconstruct the history of effective moisture at Barry Lake, we measured the carbon (δ¹³C) and oxygen (δ¹⁸O) isotope ratios of marl and shelly fauna in two ~900-year sediment core records, tightly constrained by radiocarbon and lead-210 dates. To reconstruct primary production, we analyzed the carbon (δ¹³C_TOC) and nitrogen (δ¹⁵N_TN) isotope ratios, total organic carbon to total nitrogen (TOC:TN) ratios and chlorophyll-a concentrations of the sediments. Analyses of n-alkane relative abundances further refined our understanding of the history of primary production in Barry Lake and confirmed the predominately autochthonous origin of the sediment organic matter.  

Relative to present conditions, we determined that effective moisture was lower during the Medieval Warm Period (MWP: AD 1000- 1300) and higher during the Little Ice Age (LIA: AD 1450- 1650). Despite these differences, primary production remained unchanged until AD ~1917. After AD ~1917, primary production accelerated, reaching levels unprecedented across the entire record. A 4 ‰ increase in δ¹⁵N_TN is coincident with this rise in primary production. This change may be related to the introduction of organic fertilizer from nearby agricultural fields. A rise in the relative abundance of nC₁₇ at AD ~1917 suggests that the proliferation of algae was responsible for the increase in primary production. Our findings suggest that primary production was insensitive to climate change on the scale of the LIA and MWP, but highly sensitive to nutrient loading. The fact that modern indicators of effective moisture are within the natural range of variation observed over the last ~900 years suggests that modern climate warming has not altered the hydrologic regime of Barry Lake beyond baseline conditions. Comparisons of our hydroclimatic record with similar records from the region confirm this finding. In short, our research demonstrates that, in small lakes like Barry Lake, primary production is primarily driven by nutrient loading rather than changes in effective moisture related to moderate oscillations in hydroclimate.  

How to cite: Doyle, R., Liu, Z., Walker, J., Hladyniuk, R., Moser, K., and Longstaffe, F.: Primary production in a kettle lake (Canada) was not driven by effective moisture over the last ~900 years , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1150, https://doi.org/10.5194/egusphere-egu2020-1150, 2020.

Reconstructing precipitation, hydrology and flooding under different climatic states has multiple benefits: it informs us on the history of the climate system and its subcomponents; it allows assessing the capacity of current modeling tools to capture key features of climate and the hydrological cycle under a set of different forcings; in the case of warmer past periods, it can offer a perspective of possible changes in a future warmer climate. We present our study of the hydroclimate of the Last Interglacial (LIG; ca. 125,000 years ago), a period that was slightly warmer than the present. We show that an ensemble of climate models of the latest generation (PMIP4/CMIP6) is broadly able to reproduce a wetter LIG climate (compared to the pre-industrial) in vast areas of the boreal hemisphere, as reconstructed from existing proxies from different types of archive. Based on the results of those climate simulations, we forced a global hydrological model (PCR-GLOBWB), and therefore a global river routing model (CaMa-Flood), to reconstruct the hydrology and river hydrodynamics of the Last Interglacial. We show that runoff and river discharge anomalies of the LIG are generally larger where precipitation is higher, but that in many regions the warmer temperatures imply decreased runoff and discharge also where precipitation is higher. Many main river basins show changes in the seasonality of discharge, and a slight anticipation in the day of the year when half of the water mass is discharged. Unfortunately, comparison to geological evidence of discharge is limited by the low availabilty of proxy data. Finally, we report changes in the global patterns of flooding for several return periods, and suggest mechanisms by which the LIG climate impacted those patterns.

How to cite: Scussolini, P. and the Last Interglacial Floods: Global hydroclimate of the Last Interglacial: precipitation, river discharge, floods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19247, https://doi.org/10.5194/egusphere-egu2020-19247, 2020.

Peatlands are natural geoarchives which record within organic deposits a picture of the past environmental changes. Depending on the preserved proxy, we are able to reconstruct various aspects of palaeoenvironmental changes, e.g. using pollen (vegetation composition), plant macrofossils (local vegetation changes), testate amoebae and zoological remains (hydrological changes) or XRF scanning (geochemical changes). Here, we investigated changes in land use and climate of western Russia using a range of biotic and abiotic proxies. This part of Europe is characterized by a continental climate, which makes this region very sensitive to climate change, in particular to precipitation fluctuations. Furthermore, in the last two centuries strong human impact in that area has been noticed.  

The Serteya kettle hole mire (55°40'N 31°30'E) is situated in the Smolensk Oblast in Western Dvina Lakeland. Study site is located close to the range of plant communities belonging to the hemiboreal zone, making it an ideal position to trace the plant succession of Eastern Europe. Preliminary dating of the material proves that the average rate of biogenic deposits in the reservoir was approx. 1 m per 600 years. The majority of the European peatlands was in some sense transformed as a result of drainage and land use practices in their basins. Serteya kettle hole mire allowed us to accurately track how a small ecosystem responds to palaeoenvironmental changes. Preliminary results will show the major fluctuations of the mire hydrology accompanied by the changes in the land use in the region. Our goal is also to determine the resistance and resilience of peat bogs to disturbances.

How to cite: Mroczkowska, A., Kittel, P., Marcisz, K., Dolbunova, E., Gauthier, E., Kublitsky, Y. A., Lamentowicz, M., Mazurkevich, A., Płóciennik, M., Tjallingii, R., Kramkowski, M., Łuców, D., and Słowiński, M.: A great response from small ecosystem – the last 500 years of history of a kettle hole mire in W Russia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-495, https://doi.org/10.5194/egusphere-egu2020-495, 2020.

Paleoclimate studies in different temporal and spatial scales provide important information on long-term statistics required to test hypotheses about climate changes. Comprehensive high-quality data sets and a solid understanding of dynamic climate processes in different temporal variations are essential to evaluate the sensitivity of the climatic system. Moreover, these data sets and dynamic analyses can help to distinguish the variability of natural and anthropogenic factors, reducing uncertainties about the magnitude and impact of future global climate changes. A common way to conduct paleoclimatic studies is through high resolution multiproxy lake sediments. Lake environments have been increasingly used in recent years to infer past fluctuations in climate, and many studies that comprise different locations and timescales demonstrate the great value of lakes as paleoclimatic archives. Because lake sediments are continental indicators sensitive to environmental changes, they can be used to reconstruct climate parameters, such as past rainfall, area management and environmental or limnological lake conditions. Changes of rainfall quantity can be recorded in lake archives by the variation of sedimentary input, which is related to changes in drainage basin and erosion rate. Beside of sedimentary input, lake sediments also exhibit physical and chemical changes in water bodies which, in turn, induce transformation in geochemical composition caused by changes in runoff or other allocated components. Thus, there is a variation in the proxies used in the studies, both in relation to the type of proxy used and the relationship used. In this context, we made a compilation of paleoclimatic studies on lake sediments (about 350 lakes), focusing on the main proxies used. Our study shows that there has been a change in the major proxies used along decades and with the emergence of new analysis techniques. In addition, we notice that lake characteristics (e.g., shape, geomorphological context, formation, etc.) have directly influence the proxies used and the quality of the information obtained. This compilation provides a database with an analysis of several lakes around the world, which can help future works and enable the identification of commonly used proxies according to the different variables that should be used, promoting more objective analyzes.

How to cite: Bianchini, P., Yokoyama, E., and Prado, L.: Paleoclimatic reconstruction studies in lake sediments: major proxies, technical evolution and database, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5311, https://doi.org/10.5194/egusphere-egu2020-5311, 2020.

The application of novel paleotemperature proxies such as the carbonate clumped isotope (∆47) paleothermometer and GDGT-derived TEX₈₆ temperature index offer insight into the continental record of ancient temperatures. While standardizing laboratory protocols has enhanced each methodology, the modern calibrations necessary to fully exploit their application in ancient environments lag. As the application of clumped isotopes and GDGTs in ancient lacustrine deposits expands, it is essential to describe the limitations and utility of each technique in modern environments. 

This study employs biweekly monitoring and water sampling of a temperate lake, Green Lake, Fayetteville, NY, USA, for water, lipids, and calcite, to explore how isotope- and GDGT-based proxies record seasonal changes in temperature. In addition to monitoring water temperature, we analyzed samples collected at depths between 0.5 and 15 m below the lake surface from May to October 2019 for carbon and oxygen isotopes, clumped isotopes, and GDGTs. Water samples were analyzed for hydrogen, oxygen isotopes, and ionic chemistry. The results allow for a comparison of the water column-derived lacustrine record of the clumped isotope paleothermometer of calcite, oxygen isotope paleothermometer of calcite, and GDGT-derived temperature indices. 

Previous work shows the majority of calcite precipitated annually in the water column grows rapidly during summer warming, so we expected proxy temperatures to reflect summer water temperatures at the depth of sampling. Over the May to October sampling period surface water temperatures were 14 to 25 °C, with the highest temperatures measured July 11. At 15 m below the surface water temperature ranged from 10 to 13°C. Temperatures calculated using the fractionation relation from Kim and O’Neil (1997), and preliminary calcite and water ẟ¹⁸O values from various depths are within uncertainty but 0 to 5°C cooler than measured water column temperatures at the time and depth of sampling. Carbonate ∆47 proxy temperatures, though the majority fall within uncertainty, suggest systemic temperature offset 6 to 19 °C hotter than the water column. It is currently unclear if calcite sampled from a given depth is locally formed or if it settles from higher in the water column, where temperatures are higher. Additional data are needed to test the hypothesis that higher ẟ¹⁸O and lower ∆47 values for carbonate reflect disequilibrium effects. 

Future work will extend the dataset and make proxy temperature comparisons to sediment cores to create an empirical temperature transfer function between seasonal information and recorded core temperatures.  A suite of soxhlet extracted lipid samples await HPLC analysis to confirm the existence of GDGTs in these samples. With the ensemble of data, we will clarify: 1) how seasonality of the proxy record relates to mean annual air temperature; 2) the correspondence between T(∆47) values and observed water column temperatures; and 3) which GDGT-temperature indices, TEX₈₆, TEX₈₆’, along with the BIT index, accurately describe temperature within the water column. The results of this study will provide constraints on how to interpret temperature signals recovered from the lacustrine record, and the utility of a multi-proxy approach.

How to cite: Wiesner, M., Hoke, G., Bhattacharya, T., Junium, C., Huntington, K., and Schauer, A.: Calibration of multiple paleotemperature proxies in modern lacustrine carbonate and lipids, Green Lake, New York, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11938, https://doi.org/10.5194/egusphere-egu2020-11938, 2020.

Sediments from lakes are a useful climate archive that provides information about past climate changes and human impact. It is well-known that abrupt climate change can be the trigger of the collapse or migrations of past civilizations. To have a better understanding of the migration of the Yamnaya civilization, located west of the Black Sea at ~5.5-5 cal kyr BP, we hypothesize that past climate changes acts as a driver of this migration. To test this we focus on a sedimentary record retrieved from the Mocearu lake that is located at 780 m a.s.l. in the Buzau mountains (eastern Carpathians, Romania). The record has a length of 7 m and covers the last ~6.5 cal kyr BP based on AMS radiocarbon dates. To reconstruct vegetation, environment and climate during the Middle and Late Holocene, we use complementary techniques: pollen, inorganic (XRF-analysis) and organic geochemistry based on lipid biomarkers (brGDGTs). The reconstruction has been carried out with higher resolution during the Middle Holocene, with the objective of finding evidence of the climatic changes that may have occurred around 5 cal kyr BP. Based on preliminary radiocarbon dating, the climatic reconstruction (based on brGDGTs) shows an increase in temperature from ~6 to 5.5 cal kyr BP, followed by a prominent decrease ~5.3-5 cal kyr BP.

How to cite: Ramos-Roman, M. J., Seppä, H., Magyari, E., De Jonge, C., Veres, D., Heyd, V., Eglinton, T. I., and Develle, A.-L.: Multi-proxy approach to reconstruct Middle and Late Holocene paleoenvironment and climate in the eastern Carpathians., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13592, https://doi.org/10.5194/egusphere-egu2020-13592, 2020.

3-hydroxy or beta-hydroxy fatty acids produced by Gram-negative bacteria are a novel proxy for assessment of the environmental changes. These compounds composed of lipopolysaccharide (LPS) of Lipid A, a core polysaccharide region, and an O-antigen polysaccharide chain. The improved method for the 3-hydroxy fatty acids extraction was proposed in this study. The 12 soil samples collected from the eastern US border along the coastline from Maine to Florida were generally processed by acid hydrolysis, methylation, total lipid extraction, and solid-phase chromatography, respectively. Fatty acids eventually can be separated from the main part of LPS and combined with a methyl group. However, in the stage of acid hydrolysis, the temperature was decreased to 55 °C, and heating time was extended in order to prevent the broken of volatile compounds and diminish the relative abundance of 3-OH fatty acids. The higher abundance of interested 3-OH fatty acids for the environmental reconstruction can potentially be extracted by this improvement than the classical protocol. This research will be further compared in terms of cost, experimental time and completeness of data between these two methods.

How to cite: Panbut, C.: An improved extraction method of 3-oh fatty acids for environmental reconstruction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4018, https://doi.org/10.5194/egusphere-egu2020-4018, 2020.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a class of biomarker lipids that can be conserved over long timescales in lake sediments. Produced throughout the lake water column before settling and incorporation in the sedimentary archive, they are used to reconstruct lake water temperature changes through time. However, it is not clear how degradation and/or production of these compounds in the surface sediments influences the brGDGT signal and the reconstructed temperature record.

Here we present the core lipid (“fossil”) and intact polar lipid (“recently produced”) signal of brGDGT lipids in 8 short cores collected in 4 Swiss lakes, covering a eutrophic gradient. In eutrophic conditions (Lake Baldegg), a clear subsurface (20-35 cm blf) maximum in intact polar lipids is observed (15-20%), whereas the most surficial sediments (0-2 cm blf) show the lowest percentage of IPL lipids (<5%). Our data indicates that tetramethylated brGDGT lipids are produced in the subsurface. As the bacterial community has been reconstructed in all cores, using 16S rRNA gene distribution, we observe that this production is coeval with an increase in the relative abundance of OTUs in the phyla Acetothermia, Aminicenantes, Caldiserica and Spirochaetes. Hexamethylated brGDGTs are encountered in increased amounts in most surficial sediments (0-2 cm bsf), but are degraded further downcore. Both degradation and in-situ production cause the reconstructed temperatures based on the surface sediments to be 2 ℃ colder than those from the subsurface.

In sediments where degradation and subsurface production of brGDGT lipids occurs, this has the potential to impact paleoclimate reconstructions. A colder MBT’_5ME signal in surface sediments has indeed been observed in several studies (i.e. Tierney et al., 2012; Miller et al., 2018, Martin et al., 2020). Furthermore, a distinct brGDGT signal in surface sediments has a possible impact on existing lacustrine calibration datasets, as these are based on surface sediments.

References:

Tierney et al. (2012), GCA 77, p561-581. Miller et al. (2018), CoP 14 (11), p1653-1667. Martin et al. (2020), QSR 228, 106109.

How to cite: De Jonge, C., Fiskal, A., Han, X., and Lever, M.: Biomarker (brGDGT) degradation and production in lacustrine surface sediments: Implications for paleoclimate reconstructions. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12592, https://doi.org/10.5194/egusphere-egu2020-12592, 2020.

Fifteen samples were collected from coal mines Mae Than basins located in Lampang Province, Northern Thailand to investigate organic geochemical characterization which can provide organic matter input, thermal maturity and depositional environment. The total organic carbon (TOC) content of the coal samples ranges from 30.12 to 73.71 wt. %, while shales and mudstones value between 5.98 – 24.87 wt. %. The extractable organic matter (EOM) content of all samples, which is yielded from bitumen extraction, values in the range of 1,256 and 16,421 ppm indicating good to excellent hydrocarbon generation potential. The organic geochemical data were studied by using Gas-chromatography Mass-spectrometry (GC-MS) providincg biomarker and non-biomarker data. The thermal maturity of studied samples is represented as immature stage due to ratio of Ts/(Ts+Tm) and homohopane isomerization. The distribution of normal alkanes is predominantly long-chain normal alkanes with odd-numbered carbon. The high Carbon Preference Index (CPI) value of samples indicates terrestrial organic matter input. The depositional environment of the study area can be interpreted that the coal formation is occurred within an oxidizing condition with the majority of higher plant input, whereas shale and mudstone is slightly more anoxic-aquatic environment.

How to cite: Chaiseanwang, P. and Chenrai, P.: Organic geochemical characteristics of coal deposits in Mae Than coal mine, Lampang Province, Thailand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12894, https://doi.org/10.5194/egusphere-egu2020-12894, 2020.

Several lake sediment studies have investigated the Holocene climate history in Mongolia using pollen, organic and inorganic elemental analyses. However, these studies come to very different conclusions. Isotope analyses, particularly compound-specific carbon, hydrogen and oxygen isotopic composition of leaf wax n-alkanes (δ¹³C_wax, δ²H_wax) and hemicellulose sugars (δ¹⁸O_sugar) are increasingly used for paleoenvironmental and -hydrological reconstructions and might have great potential to address the controversies in Mongolia.

Here we present a regional calibration of δ¹³C_wax, δ²H_wax and δ¹⁸O_sugar on topsoils along a distinct climate gradient in semi-arid/arid Mongolia. δ¹³C_wax significantly correlates with aridity indicating variations in water use efficiency. The apparent fractionation (Ɛ_app) of δ²H_wax and δ¹⁸O_sugar is nearly constant at -131 ± 13‰ for Ɛ_n-C29/p, -148 ± 11‰ for Ɛ_n-C31/p and 40.8 ± 1.9‰ for Ɛ_sugar/p, respectively. δ²H_wax (n-C₂₉ and n-C₃₁) and δ¹⁸O_sugar thus, reflect the isotopic composition of precipitation, which in turn is controlled by atmospheric circulation systems bringing moisture to continental Mongolia, i.e. the interaction between the Westerlies and the Asian Summer Monsoon. Therefore, we applied regionally calibrated δ¹³C_wax, δ²H_wax and δ¹⁸O_sugar isotopes, as well as well-established sedimentological and geochemical proxies and δ¹³C_org, δ¹³C_carb, δ¹⁸O_carb on a 160 cm long gravity core from Lake Telmen (Central Mongolia) that covers 4,110 ⁺³⁵⁰/_‑340 cal. a BP.

Low terrestrial input (e.g. low Al, Fe, K, Sr) suggests decreased runoff and points to overall dryer conditions in the area around Lake Telmen between 4,110 ⁺³⁵⁰/_‑340 and 3,040 ⁺⁶¹⁰/_‑400 cal. a BP. Those findings are in line with positive δ²H_n-C23, δ¹⁸O_sugar and δ¹⁸O_carb, which indicate enhanced lake water evaporation. From 3,040 ⁺⁶¹⁰/_‑400 to 1,360 ⁺²³⁰/_‑220 cal. a BP, high terrestrial input and more negative δ²H_n-C23, δ¹⁸O_sugar and δ¹⁸O_carb values indicating more humid conditions. This is in line with seismic results which reveal distinct subaqueous cliffs and an extreme lake level rise beginning at ~ 2,000 cal. a BP. Drier conditions and low lake levels occurred between 1,360 ⁺²³⁰/_‑220 and 700 ⁺²¹⁰/_‑180 cal. a BP and are indicated by low Ca/Mg ratios and a distinct enrichment in ¹³C_wax, ²H_wax,¹⁸O_sugar and ¹⁸O_carb. From 700 ⁺²¹⁰/_‑180 cal. a BP onwards, drier conditions continue but the terrestrial input increases possibly reflecting anthropogenic impact.

How to cite: Struck, J., Bliedtner, M., Strobel, P., Daut, G., Schumacher, J., Bittner, L., Plessen, B., Glaser, B., Klaes, B., Bazarradnaa, E., Salazar, G., Szidat, S., Zech, M., and Zech, R.: Calibration and paleohydrological application of compound-specific isotope analyses (δ13Cwax, δ2Hwax and δ18Osugar) in semi-arid/arid Mongolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16577, https://doi.org/10.5194/egusphere-egu2020-16577, 2020.

The study of climate variability in especially sensitive areas is crucial for a better understanding of the response of Earth’s different components to abrupt changes and envisage future climate responses. In this regard, the southern Iberian and western Mediterranean regions have demonstrated hemispheric-scale teleconnections during the last glacial period. Long-records from continental sedimentary archives are scarce, and the Padul wetland represents one of the longest and most continuous continental record in this area, detecting climate variability at centennial to millennial-scale from the Pleistocene to the Holocene. The applicability of organic-based proxies in this organic rich continental archive is a promising tool because the variations in different biomarkers are closely related to biological sources and environmental factors such as temperature. Particularly interesting from a paleoclimatic point of view are glycerol dialkyl glycerol tetraethers (GDGTs), which are membrane lipids from Bacteria and Archaea, ubiquitous in a range of natural archives, including wetlands. Previous works have demonstrated their applicability as a significant past continental air temperature proxy, where the distribution of bacterial branched GDGTs (brGDGTs) is correlated with mean annual air temperature (MAAT) and soil pH. Here we present a first quantification of past temperatures using brGDGTs in the Padul sedimentary record. Preliminary results have evidenced substantial variations in derived-MAAT and distribution of the different brGDGTs during the last 36 kyr that are consistent with abrupt climate periods, such as Henrich Stadial 1 and the Holocene onset. Nevertheless, different absolute MAAT values using the peat-specific calibration and the mineral soil calibration have been obtained and they need to be evaluated.

How to cite: Rodrigo-Gámiz, M., García-Alix, A., Jiménez-Moreno, G., Camuera, J., Ramos-Román, M. J., Torney, J. L., Sachse, D., and Anderson, R. S.: Quantification of past temperature variability during the last 36 kyr using organic-derived proxies in the Padul wetland, southern Iberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18370, https://doi.org/10.5194/egusphere-egu2020-18370, 2020.

Hydrogen isotope ratios (²H/¹H) of plant waxes and other lipids preserved in sediments are increasingly used as a paleohydrologic proxy for past water isotopes. The relationship between precipitation ²H/¹H ratios and those of plant waxes in surface sediments is linearly correlated at a global scale. However, there are large residuals in this relationship, and the offsets in ²H/¹H ratios for the same compound produced by different species growing at the same site, as well as for different compounds produced within the same plant, can approach the magnitude of continental scale variability in precipitation isotopes. This indicates that lipid ²H/¹H ratios are influenced by significant factors besides the ²H/¹H ratios of local precipitation. One possibility is that plant metabolic responses to stresses such as drought cause changes in ²H/¹H fractionation during lipid synthesis.

In order to assess the effects of drought on ²H/¹H fractionation during plant lipid synthesis, we grew Pachira aquatica seedlings in controlled growth chamber conditions, with half of the individual plants experiencing drought conditions (soil moisture content reduced to ~10%) and half serving as well-watered controls (soil moisture content ~25%). We used position-specific ¹³C-pyruvate labeling to assess if there were changes in lipid production under drought, and focused on a diverse range of compounds including palmitic acid, n-C₂₉ and n-C₃₁-alkanes, phytol, squalene, and sitosterol. We also measured natural abundance ²H/¹H ratios from the same compounds and from cryogenically extracted leaf water to quantify biosynthetic H isotope fractionation (ε_Bio).

Biosynthetic ²H/¹H fractionation spanned a 150‰ range among compounds, with palmitic acid being the least ²H-depleted compound (ε_Bio = -140 ± 10‰) and phytol being the most ²H-depleted compound (ε_Bio = -317 ± 7‰). These fractionation factors did not change under drought, although ¹³C-pyruvate labeling indicated that the compounds were being actively produced. There was no change in the production rate of any compound under drought, however. Differential incorporation of ¹³C depending on whether the 1^st or 2^nd carbon in pyruvate was labeled showed clear distinctions among compound classes, with the acetogenic compounds only becoming enriched from the C2 label, and isoprenoids using roughly equal proportions of carbon from each position. These results suggest that under this level of drought stress, Pachira aquatica did not make any changes to its lipid metabolism, and lipid ²H/¹H ratios were therefore unperturbed. If replicated in additional plants types and under more severe drought, this result is encouraging for the use of plant lipid ²H/¹H ratios as robust paleohydroclimate tracers.  

How to cite: Ladd, S. N., Nelson, D. B., Bamberger, I., Daber, E., Kahmen, A., Schubert, C. J., and Werner, C.: Drought does not affect hydrogen isotope fractionation during lipid biosynthesis by the tropical plant Pachira aquatica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19361, https://doi.org/10.5194/egusphere-egu2020-19361, 2020.

There is a growing trend in using structural analyses to investigate temporal changes in ecosystem system architecture. System architecture defines the organisation of taxa within a system and how this may affect system response to stress. Over the Holocene, in areas with little/no human impact, the climate has been a key driver of ecosystem change, including post-glacial to early/mid-Holocene warming, subsequent neoglacial cooling, and rapid climate change events such as the 8.2 kyr event. This study aims to investigate whether Holocene climate change is a driver for structural change in temperature-sensitive organisms, such as chironomids, in high latitude lakes. These areas are at risk from rapidly rising global temperatures, with warmer temperatures already recorded and predicted to continue rising in high latitude areas. Increased temperatures can create stress on ecologically sensitive environments where many organisms are adapted to cooler temperatures. Three sets of analyses - beta diversity, compositional disorder, and network skewness - are applied to Norwegian chironomid sequences to investigate ecosystem structural change during the Holocene.

How to cite: Mayfield, R., Langdon, P., Dearing, J., Doncaster, P., and Wang, R.: Structural ecosystem change in Holocene chironomid assemblages, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-992, https://doi.org/10.5194/egusphere-egu2020-992, 2020.

Past climate states can be used to test climate models for present-day changes and future responses. Past states can be reconstructed from fossil assemblages, and WA-PLS (weighted averaging–partial least squares) is one of the most widely used statistical methods to do this. However, WA-PLS has a marked bias. Whatever biotic indicator is being used, reconstructed climate values are artificially compressed and biased towards the centre of the range used for calibration.

Here we developed an improvement of the method, derived rigorously from theory. It makes three assumptions:

a) the theoretical abundance of each taxon follows a Gaussian (unimodal) curve with respect to each climate variable considered;

b) the abundances of taxa are compositional data, so they sum to unity and follow a multinomial distribution;

c) the best estimate of the climate value at the site to be reconstructed maximizes the log-likelihood function – in other words, it minimizes the difference between theoretical and actual abundances as assessed by the likelihood criterion.

The best estimate of the climate value is approximated by a tolerance-weighted version of the weighted average in which the abundances of taxa are weighted by the inverse square of their tolerances (a measure of the range of environments in which a taxon is found). WA-PLS thus corresponds to the special case when all taxon tolerances are equal. The fact that this special case is far from reality generally is part of the the cause of the “compression and bias”. The new method can be applied using the existing functions for WA-PLS in the R package rioja. We show that it greatly reduces the compression bias in reconstructions based on a large modern pollen data set from Europe, northern Eurasia and the Middle East.

How to cite: Liu, M., Prentice, I. C., Braak, C. T., and Harrison, S.: A theory of palaeoclimate reconstruction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8457, https://doi.org/10.5194/egusphere-egu2020-8457, 2020.

Switches of temperature-precipitation correlation in northern Hemisphere extra-tropics

Future precipitation response to warming remains uncertain because climate models poorly reproduce observed changes of temperature-precipitation correlations. However, restricting model validations to the observational period may yield to misleading conclusions due to the complexity of the involved processes. Our analyses of Holocene proxy-based temperature-precipitation correlations from 1500 northern Hemisphere extratropic pollen records portrayed significant latitudinal dependance, temporal changes from the early to late Holocene as well as differences between short and long time-scales. These observed variations were found to be mostly consistent with patterns simulated by Holocene transient climate simulations. Our results suggest that the strength of positive temperature-precipitation correlations in high-latitudes is sensitive to the background temperature while monsoonal subtropics reflect spatial shifts of circulation systems; and correlation sign switches in mid-latitudes relate to changes of westerlies strength. We conclude that regional and continental climate change on land is more complex than the expected “wetter climate in a warmer world” assumption which holds well at the global scale. On the other hand, long-term projections of precipitation may be better than previously thought as major processes seem to be already implemented correctly in general circulation models.

How to cite: Herzschuh, U., Boehmer, T., Herbert, R., Laepple, T., Telford, R., Cao, X., Dallmeyer, A., and Kruse, S.: Switches of Holocene temperature-precipitation correlations in northern Hemisphere extra-tropics comparing proxy and model data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20282, https://doi.org/10.5194/egusphere-egu2020-20282, 2020.

Speleothems are secondary mineral deposits found in caves. They can grow continuously over 1,000-10,000 years and the ²³⁰Th/U method allows accurate dating back to 500,000 years.[1] Stable conditions in caves preserve organic matter, making speleothems highly valuable climate archives. The high interest in expanding the range of organic proxies in speleothems requires highly sensitive analytical techniques. Novel trace analysis methods for lignin and levoglucosan in speleothems were established according to principles of "Green Chemistry" [2] and applied to flowstone samples from different caves in New Zealand during the Holocene.

Lignin is the second most abundant biopolymer after cellulose. It consists of three monomers, which are included into the polymer in different ratios, depending on the type of vegetation. It is found in speleothems and quantification in timely consecutive layers allows drawing conclusions on changing types and amount of vegetations above the caves, which are influenced by climate conditions like temperature and rainfall.[3] To analyse the monomeric composition, lignin has to be degraded by an alkaline oxidation. Thereby the monomers are oxidized into lignin oxidation products which are then analysed by uHPLC-ESI-HRMS. To date, lignin degradation was conducted using Cu(II)O as a catalyst, which was replaced by CuSO₄, eliminating the solid, toxic Cu(II)O waste, and highly reducing the amount of artefacts and used chemicals during sample preparation. The new method was successfully applied to the flowstone samples but posed further questions on the transport of lignin through the soil into the speleothem.[4],[5]   

The other proxy of interest was levoglucosan, an anhydrosugar formed by cellulose combustion. For temperature studies in speleothems carbon isotopes are used which can be influenced by e.g. fire events. Therefore, it is necessary to introduce a proxy, which prevents falsely positive or negative temperature trends. Extraction of levoglucosan was conducted using graphitized carbon black and chromatographic separation by a hydrophilic interaction liquid chromatography, using a post-column flow to increase the ionization efficiency in the ESI ion source. Levoglucosan analysis was introduced into the existing workflow, without interfering with lignin analysis, and thereby a multi-proxy approach was developed. This work showed that levoglucosan is present in speleothems in quantifiable amounts. It was detected in two of the study sites, showing no correlation to lignin. A plant-based origin of levoglucosan was ruled out, suggesting a fire-related entry into the speleothem.

[1] Baker, A., et al. (2008). International Journal of Speleology, 37 (3), 193-206; [2] Anastas, P., Eghbali, N. (2010), Chemical Society Reviews, 39, 301-312; [3] Hedges, J., Mann, D. (1979). Geochimica et Cosmochimica Acta, 43 (11), 1803-1807; [4] Heidke, I., Scholz, D., Hoffmann, T. (2018). Biogeosciences, 15 (19), 5831-5845; [5] Yan, G., Kaiser, K. (2018). Analytical Chemistry , 90 (15), 9289-9295

How to cite: Beschnitt, A. and Hoffmann, T.: Application of novel trace analysis methods for lignin and levoglucosan in flowstone samples from New Zealand during the Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2397, https://doi.org/10.5194/egusphere-egu2020-2397, 2020.

Secondary mineral deposits in caves like stalagmites, stalactites, or flowstones are valuable paleoclimate archives. Advantages of organic trace analysis in such deposits are stable conditions in a cave, protecting compounds from external influences, as well as the possibility to precisely date samples up to 600,000 years using the uranium/thorium method.[1]

Lignin, a biopolymer, is one of the main constituents of higher plants and consists of three monomeric units: sinapyl-, coniferyl-, and coumaryl alcohol. Lignin can be degraded into its monomeric units by alkaline CuSO₄-oxidation. The oxidized monomer units can be analysed by UHPLC-ESI-HRMS with limits of quantification in the ng/g range. By determination of the ratios among different oxidation products in a speleothem, conclusions can be drawn on the type of vegetation above the cave. [2,3]

Levoglucosan, an anhydrosugar, naturally only originates from the combustion of cellulose and can thus be used as a biomass burning marker. Analysis of levoglucosan in sediments shows good correlation with traditional burning markers like black charcoal. [4] Mannosan and galactosan, stereoisomers of levoglucosan, are formed during the combustion of hemicellulose. Literature suggests that the ratio of levoglucosan to its isomers rather than absolute levoglucosan concentrations should be considered when characterizing burning events. [5] To date, no data on levoglucosan or its isomers in speleothems is published.

As the anhydrosugars are highly polar molecules, extraction and analysis with traditional reversed phase systems proved difficult. An optimized sample preparation to access both lignin and levoglucosan in speleothems is presented. Furthermore, a HILIC-UHPLC-ESI-HRMS method was developed to analyze the lignin oxidation products (LOPs) and anhydrosugars.

The methods were applied to a flowstone from a cave of the Dolomites in Southern Tyrol.

[1] D. Scholz, D. Hoffmann, Quat. Sci. J. 57 (2008) 52–76 [2] C.N. Jex et al. Quat. Sci. Rev. 87 (2014) 46–59. [3] G. Yan, K. Kaiser, Anal. Chem. 90 (2018) 9289–9295. [4] V. O. Elias et al. Geochim. et Cosmochim. Acta 65 (2001) 267-272. [5] D. Fabbri et al. Atmos. Env. 43 (2009) 2286–2295

How to cite: Homann, J., Beschnitt, A., and Hoffmann, T.: Trace analysis of levoglucosan and lignin-phenols in speleothems by HILIC-UHPLC-ESI-HRMS: A new method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2413, https://doi.org/10.5194/egusphere-egu2020-2413, 2020.

An improved understanding of medium and short-term changes in temperature and rainfall in the East Mediterranean is necessary for a comprehensive description of the regional climate regime. In particular, it can help advancing current climate models and predictions. A new paleoclimate record from Cyprus gives new insights into climatic variations during MIS 6 and 5 for this region. A 66 cm long speleothem from Pentadactylos cave in the Kyrenia range (800 m asl) was extensively dated with the U/Th method and investigated for petrography, fluid inclusions, stable and clumped isotopes. The stalagmite grew from 174.6 ± 0.7 to 112.2 ± 0.5 ka BP. The growth rate varies from 31 to 5 mm/ka during the early-MIS6 and evolving from 123 to 18 mm/ka at the end-MIS6. The onset of MIS5e is marked by a high growth rate (125 mm/ka) until growth decreased drastically after 122 ka. Growth rate and stalagmite diameter as well as δ¹⁸O and δ¹³C curves are positively correlated. We interpret the δ¹⁸Oc signal as being controlled by effective infiltration and thus rainfall amount. Climate conditions during early-MIS6 were highly variable (δ¹⁸O_c) on a millennial-scale with several short-lived wet episodes during sapropel 6. From 141 to 132 ka, δ¹⁸O_c suggests general dry/cold conditions with low bio-pedological activity, followed by a growth stop during H11. The δ¹⁸O values during the Eemian wet period in Cyprus are driven by the source effect (sapropel 5). Stable conditions during MIS 5e were rather short: ~2 ka, as shown in the δ¹³C signal. After 122 ka, a slow deterioration of the soil cover coupled with low rainfall amounts during the glacial inception period show rather a regional decoupling phase. Fluid inclusions show a clear shift (4-5‰) in δ¹⁸O_w between end-MIS 6 and MIS 5e. Clumped isotopes measurements indicate kinetic effects between calcite and water of up to ~1‰. After correction for kinetics using Δ₄₇, an estimate for the MIS6-5 temperature shift in the East-Mediterranean is >10°C.

How to cite: Nehme, C., Verheyden, S., Kluge, T., Weissbach, T., Nader, F., Gucel, S., Charalambidou, I., Cheng, H., Edwards, L., and Claeys, P.: Speleothem record from Pentadactylos cave (Cyprus): high-resolution insight into climatic variations during MIS 6 and MIS 5, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11105, https://doi.org/10.5194/egusphere-egu2020-11105, 2020.

Despite intensive research efforts by archaeologists, geomorphologists, and palaeoclimatologists, the climatic and environmental changes accompanying the societal changes in the wider Indus/Thar region c. 4000 years ago remain puzzling. In particular, rainfall seasonality might be an important determinant for societal well-being. A major hurdle to a more detailed understanding of climate-human interaction is the relative scarcity of well-dated and highly resolved proxy records.

We present a multi-proxy record from aragonitic stalagmite DHAR-1 collected in Dharamjali Cave, Uttarakhand, India, that spans c. 1600 years between c. 4.25 and 2.6 ka BP.  The stalagmite has been dated with 13 U/Th dates with average uncertainties of <18 years (2σ). In addition to c. 1600 oxygen and carbon isotope samples, element ratios (X/Ca) were measured using high resolution μXRF and laser ablation ICPMS at 25 μm resolution.  

The DHAR-1 record represents the most precisely dated speleothem record to date from northern India, covering the mid-Holocene 4.2 ka BP event and the millennium thereafter. The attained sub-decadal to seasonal resolution allows robust assessment of both regional and local hydrological changes, and changes in amount and temporal distribution of summer and winter rainfall. 

The speleothem record reveals decadal-scale trends that can be related to changes in seasonality. The δ¹⁸O record reveals a 220-year period of weakened ISM from 4.2 to 3.98 ka BP. A contemporaneous increase in δ¹³C, and decrease in U/Ca, Ba/Ca, and Sr/Ca point to increased prior aragonite precipitation (PAP) resulting from increased aridity above the cave extending throughout the dry season. The ISM intensified after c. 3.7 ka BP while dry seasons remained dry, with a resultant increase in seasonality. Lower PAP after c. 3.4 ka BP can be interpreted as sign of reduced rainfall seasonality.

We compare the results with available records from the wider region, and discuss potential implications of the suggested changes in seasonality for agriculture-based societies.

How to cite: Giesche, A., Breitenbach, S. F. M., Marwan, N., Hartland, A., Plessen, B., Adkins, J. F., Haug, G. H., French, A., Petrie, C. A., and Hodell, D. A.: Rainfall seasonality changes in northern India across the 4.2 ka event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16898, https://doi.org/10.5194/egusphere-egu2020-16898, 2020.

The cation-to-Ca ratio in natural carbonate minerals is routinely used by the geoscientific community in order to reveal information about the conditions occurred during mineral formation in the geological past. Environmental reconstruction, however, relies on our understanding on the mechanisms controlling mineral growth but also on the physico-chemical properties of cations. In this respect experimental studies and laboratory calibrations of elemental ratios in synthetic carbonates provide important insights on the interpretation of the chemical signatures in natural samples. This holds especially truth for the chemical and isotopic signals of carbonates forming in continental environments that are characterized by the absence of bio-induced precipitation, low concentration of solutes in the forming fluid and slow growth rates (e.g. speleothems). In this study, we examine the incorporation of Li in aragonite, owing to its use as a temperature proxy and its importance in paleo-weathering reconstruction. Our preliminary results suggest that aragonite growth rate is likely the most important parameter controlling Li content in the forming phase. This finding comes in excellent agreement with the recent study by Füger et al. (2019). In addition, the experimental work suggest that temperature is also affecting the distribution of Li in aragonite but to a lesser extent than growth rate. It is anticipated that once completed this work will provide the fundamental knowledge needed for adequate interpretation of Li partitioning in aragonite and significantly improve our ability to interpret Li signatures in natural carbonates.

References: Füger et al. 2019. Effect of growth rate and pH on lithium incorporation in calcite, Geochim. Cosmochim. Acta., 248, 14-24.

How to cite: Mavromatis, V., Brazier, J.-M., and Goetschl, K.: Controls of Li incorporation in aragonite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3527, https://doi.org/10.5194/egusphere-egu2020-3527, 2020.

Carbonate minerals record, through their chemical and isotopic composition, the environmental conditions occurring at the time of their formation. Thus, the incorporation of traces/impurities in CaCO₃ minerals calcite and aragonite, have been widely studied over the last five decades in order to provide the fundamental knowledge needed for the use of these traces in paleoenvironmental reconstructions. The processes controlling the uptake of traces in natural samples, however, are manifold and hard to distinguish from each other. Thus, experimental co-precipitation studies on synthetic material under strictly controlled abiotic conditions can provide fundamental understanding on the effect of each process involved in the chemical signatures of natural carbonates. In this study, we explore the incorporation of Cu in calcite and its potential as proxy of reactive fluid composition. This transition metal commonly occurs complexed with organic ligands in natural waters, however, it exhibits very high affinity for calcite. Our experiments were performed at pH 6.3 and 8.3, with varying growth rate ranging between 10^-8.5 and 10^-7.6 (mol/m²/s). Our first results highlight that the partitioning coefficient of Cu is positively correlated to the calcite growth rate at both pH conditions, indicating an increase of Cu entrapment at higher growth rate. These new preliminary findings could bring fundamental understanding of Cu incorporation in calcite and highlight the potential of Cu partitioning coefficient as a proxy of mineral growth rate.

How to cite: Brazier, J.-M., Götschl, K., Dietzel, M., and Mavromatis, V.: Parameters controlling the incorporation of Cu in calcite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3603, https://doi.org/10.5194/egusphere-egu2020-3603, 2020.

The concept of seasonal changes is traditionally understood as a consecutive follow-up of four seasons, spring, summer, autumn, and winter (in the mid-latitudes); or wet/ dry season alteration (in low latitudes). Intuitively, the term ‘seasonality’ usually refers to temperature or moisture gradients throughout a year. These gradients determine the composition and dynamics of natural ecosystems and agricultural strategies; as such seasonality is a key parameter when describing modern and past climatic and environmental conditions. Consequently, changes in seasonality are often called for as the ultimate driving force of observed changes, but there is more to them than meets the eye. Most importantly there is an essential and often overlooked aspect of external, orbitally-driven seasonality, and internal, regional-to-local responses to these changes.

What does ‘increased’ or ‘decreased’ seasonality actually mean? Can we quantify this change? And is the amplitude all that matters? What about temporal distribution? Does temperature and precipitation always respond symmetrically and harmonically? My contribution is aimed at raising awareness, caution and precision when referring to seasonality changes. Come to my poster and let’s discuss it!

How to cite: Kwiecien, O.: What we talk about when we talk about seasonality? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4240, https://doi.org/10.5194/egusphere-egu2020-4240, 2020.

Occasionally, there is an interest in groundwater flows over many millennia. The input parameter requirement of numerical groundwater flow models and their calculation times limit their usefulness for such studies.

Analytical models require considerable simplifications of the properties and geometry of aquifers and of the forcings. On the other hand, they do not appear to have an inherent limitation on the duration of the simulated period. The simplest models have explicit solutions, meaning that the hydraulic head at a given time and location can be calculated directly, without the need to incrementally iterate through the entire preceding time period like their numerical counterparts.

We developed an analytical solution for a simple aquifer geometry: a strip aquifer between a no flow boundary and a body of surface water with a prescribed water level. This simplicity permitted flexible forcings: The non-uniform initial hydraulic head in the aquifer is arbitrary and the surface water level can vary arbitrarily with time. Aquifer recharge must be uniform in space but can also vary arbitrarily with time.

We also developed a modification that verifies after prescribed and constant time intervals if the hydraulic head is such that the land surface is covered with water. This excess water then infiltrates in areas where the groundwater level is below the surface and the remainder is discharged into the surface water. The hydraulic head across the aquifer is modified accordingly and used as the initial condition for the next time interval. This modification models the development of a river network during dry periods. The increased flexibility of the model comes at the price of the need to go through the entire simulation period one time step at a time. For very long time records, these intervals will typically be one year.

Given the uncertainty of the aquifer parameters and the forcings, the models are expected to be used in a stochastic framework. We are therefore working on a shell that accepts multiple values for each parameter as well as multiple scenarios of surface water levels and groundwater recharge rates, along with an estimate of their probabilities. The shell will generate all possible resulting combinations, the number of which can easily exceed 10000, then runs the model for each combination, and computes statistics of the average hydraulic head and the aquifer discharge into the surface water at user-specified times.

A case study will tell if this endeavor is viable. We will model the aquifer below the mountain range north of Salalah in Oman, which separates the desert of the Arabian Peninsula from the coastal plain at its southern shore. Rainfall estimates from the isotopic composition of stalactites in the area indicate distinct dry and wet periods in the past 300 000 years. In combination with estimated sea level fluctuations over that period, this provides an interesting combination of forcings. We examine the dynamics of the total amount of water stored in the aquifer, and of the outflow of water from the aquifer into the coastal plain.

How to cite: de Rooij, G. H. and Mueller, T.: Groundwater modelling for time periods of up to hundreds of thousands of years., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5177, https://doi.org/10.5194/egusphere-egu2020-5177, 2020.

Palaeohydrological studies usually focus on extreme events and long-term changes as observed from floodplain archives. As a consequence, the information that is obtained inheritely reflects palaeohydrological conditions from a specific compartment of the hydrological system only, namely the discharge area which acts as a drain for runoff and groundwater. In contrast, palaeohydrological conditions in recharge areas, outside the floodplains, are less well understood and documented.

Aeolian drift sands are a typical feature in the European sand belt, and reflect phases of human induced and climatically modulated Holocene landscape instability. As the European sand belt is characterised by shallow phreatic groundwater tables in climates with a precipitation surplus, we might theoretically expect aeolian activity to interfere with a fluctuating groundwater table and/or precipitation events. The aim of this presentation is to explore the possibilities and limitations of four types of palaeohydrological proxy that were retrieved from a variety of different sites in drift sand landscapes in NE Belgium (Campine area): (1) soil horizon morphology of buried podzols, (2) deflation surfaces, (3) drift sand depositional facies and (4) palaeobotanical remains in organic-rich sediment.

The palaeohydrological information that these proxies contain will be discussed according to various characteristics. These include the continuity of the archive (continuous or discontinuous), the resolution (high resolution or integrated proxy), and whether the proxy is indicative for outcropping groundwater or precipitation events.

Podzol soil horizon morphology is an indicator of the average highest groundwater table position over a time period of several thousands of years prior to landscape instability and sand drifting, and can thus be qualified as an integrated proxy. Overblown deflation surfaces can only be used as an upper limit of the highest palaeo-groundwater table in between podzolisation and drift sand deposition, and can be qualified as a discontinuous low-resolution proxy. Drift sand depositional facies is a highly discontinuous proxy but can be used to verify whether deposition took place in dry, wet or standing water environments, with or without the influence of significant precipitation events and/or running water. Undoubtedly, palaeobotanical remains (macrobotanical and pollen) in overblown peat and peaty sand from the deepest parts of the drift sand landscape offer the highest resolution in terms of chronology (century to decades) and highest reliability in terms of water source tracing (outcropping groundwater vs precipitation).

Proxy verification mainly relies on fragmentary historical information derived from maps covering the last 250 years. Most importantly, when different proxies are available at the same site, they usually show strong internal consistency. A good example is the presence of peat with aquatic palaeobotanical remains in the deepest parts of the landscape where the underlying podzol soil also shows hydromorphic features and the overlying drift sand contains elements that are typical for deposition in wet environments.

We conclude that the above outlined complementary set of palaeohydrological proxies is a promising tool to reconstruct past hydrology in drift sand landscapes from the European sand belt.

How to cite: Beerten, K., van der Meer, W., Hebinck, K., Schurmans, M., and Bastiaens, J.: Reconstructing past hydrology from drift sand archives: possibilities and limitations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18227, https://doi.org/10.5194/egusphere-egu2020-18227, 2020.

Alluvial river long profiles continually adjust to their water discharge (Q_w) and sediment supply (Q_s). Q_w and Q_s are in turn functions of local climatic and tectonic conditions. Hence, changes in the prevailing tectonic or climatic conditions will trigger adjustments to channel long profiles, either by channel incision into previously deposited sediments or by sediment deposition. Because fluvial terraces are abandoned floodplains that preserve ancient river elevation profiles formed from past Q_s and Q_w, they store information on past climatic or tectonic conditions. 

In NW Argentina, reconstructions of Pleistocene climate are sparse due to the limited availability of paleo-climatic records, such as stable isotope data from speleothems or lake cores. However, many intermontane basins within the Southern Central Andes of NW Argentina are characterized by multiple generations of fluvial-fill terraces, some of which date back several tens to hundreds of thousands of years. Here, we show that these geomorphic units provide an opportunity to extract information about paleo-climatic conditions. 

A combination of several geochronological techniques has revealed the history of a >200-m-thick fluvial-fill terrace sequence within the Quebrada del Toro. The terrace sequence experienced alternating episodes of incision and aggradation since at least 500 ka. Subsequent terrace surfaces appear to have formed following a cyclicity of ca. 100 kyr. From detrital sediment within those fill terraces, past Q_s could be reconstructed for times of sediment aggradation based on cosmogenic ¹⁰Be concentrations. The analyses revealed that over the last ~500 kyr Q_s has varied at most by a factor of 4, but overall has been relatively constant. As the slope of a river channel (and likewise, the slope of a well preserved terrace surface) is a function of incoming Q_s and Q_w, combining data of terrace slope and past Q_s allowed us to reconstruct past Q_w for the times represented by the ages of the terrace surfaces, which mark the onset of river incision. The analyses revealed that during these times, Q_w was 10 to 80% higher than today. The results are in line with the few existing quantitative estimates of past precipitation changes in the Central Andes, but have the advantage of extending further back in time. Moreover, the widespread occurrence of fluvial-fill terraces throughout the Central Andes offers the opportunity to reconstruct past Q_w with high spatial resolution, offering a new perspective regarding the impact of past climate changes on the sediment-routing system through space and time.

How to cite: Tofelde, S., Schildgen, T., Wickert, A., Strecker, M., and Alonso, R.: Reconstructions of past sediment and water discharges from fluvial-fill terraces in the southern Central Andes of NW Argentina, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4887, https://doi.org/10.5194/egusphere-egu2020-4887, 2020.