| 1. |
- Adroit, Benjamin, et al.
(författare)
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Patterns of insect damage types reflect complex environmental signal in Miocene forest biomes of Central Europe and the Mediterranean
- 2021
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Ingår i: Global and Planetary Change. - Amsterdam : Elsevier. - 0921-8181 .- 1872-6364. ; 199
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystems are defined by the community of living organisms and how they interact together and with theirenvironment. Insects and plants are key taxa in terrestrial ecosystems and their network determines the trophicstructure of the environment. However, what drives the interactions between plants and insects in modern andfossil ecosystems is not well understood. In this study, we analyzed insect damage richness and frequency in 5000 fossil leaves deposited during the early Miocene at 20–17 Ma along a latitudinal gradient from Europe (twolocalities in Czech Republic) to Turkey (one locality) in a temperate climate setting. Damage frequency wasmainly linked with abiotic factors (temperature, precipitation seasonality) whereas damage richness was mainlylinked with biotic factors (plant richness, biome). Univariate analysis of insect damage types consistently suggested closer trophic similarity between the Mediterranean and either the one or the other Central European plant assemblage. In contrast, multivariate analysis of all insect damage types indicated closer similarity between the two Central European sites highlighting the importance of biogeographic legacy and geographic closeness to the plant-insect interaction patterns. Our results underscore the high complexity of the herbivory network andcall for careful interpretations of plant-insect interaction patterns in palaeoecological studies. Finally, comparing the trophic similarity between different localities using total evidence plots as done in this work might be apromising complementary method in comparative studies of plant-insect interactions.
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| 2. |
- Bohm, Katja, et al.
(författare)
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Neogene global climate change and East Asian dust sources : Combined rutile geochemistry and zircon U Pb analysis from the northern Chinese Loess Plateau
- 2023
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Ingår i: Global and Planetary Change. - : Elsevier. - 0921-8181 .- 1872-6364. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- During the late Neogene, global climate underwent a long-term transition to cooler climates that culminated in the Quaternary icehouse conditions. In the East Asian terrestrial realm, atmospheric dustiness increased, and the volume of aeolian dust deposits expanded significantly. The Neogene Red Clay deposits, located on the Chinese Loess Plateau (CLP), provide an exceptional geologic archive to investigate pre-Quaternary climates and environments. Constraining the provenance of the Red Clay is crucial for unravelling the links between late Neogene Central-East Asian climate, tectonics and desertification. However, Red Clay provenance is highly debated and data are scarce. In this study, we have used a multi-proxy approach at a high sampling resolution to study the provenance of the c. 7–2.6 Ma Baode Red Clay. Our data consist of joint detrital zircon U-Pb ages and detrital rutile trace element geochemistry of the Baode Red Clay, and of a massive rutile geochemistry dataset from 14 potential dust source areas. The data indicate that the Mio-Pliocene and Plio-Pleistocene global climate transitions were coupled with gradual dust provenance shifts. We propose these shifts indicate the intensification of East Asian winter monsoon and/or enhanced Central-East Asian drying as a response to global cooling. We also identify temporary Pliocene provenance changes that interrupt the long-term winter monsoon -controlled dust transport at c. 4 Ma and c. 3.5 Ma. Several indicators point to dust transport by the westerly jet at c. 4 Ma, possibly caused by a shift in the jet position as a response to global cooling, and/or enhanced wet deposition caused by intensified summer monsoon. Alternatively, the role of the paleo-Yellow River should be investigated further. We infer the 3.5 Ma provenance signal was caused by increased Yellow River -transported material from eroding Northeastern Tibetan Plateau and/or western CLP. Implications of our results not only shed light on the links between late Cenozoic global climate change and Central-East Asian dust cycle, but also provide detailed information to further investigate the late Neogene regional geomorphology and its effects on dust emission, transport, and deposition. Our combined rutile-zircon analysis also verifies that a multi-proxy single-grain approach that targets different types of primary source rocks is needed for reliable provenance analysis of the CLP dust.
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| 3. |
- Dalton, April S., et al.
(författare)
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The marine δ18O record overestimates continental ice volume during Marine Isotope Stage 3
- 2022
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Ingår i: Global and Planetary Change. - Amsterdam : Elsevier. - 0921-8181 .- 1872-6364. ; 212, s. 103814-103814
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Tidskriftsartikel (refereegranskat)abstract
- There is disagreement in the Quaternary research community in how much of the marine δ18O signal is driven by change in ice volume. Here, we examine this topic by bringing together empirical and modelling work for Marine Isotope Stage 3 (MIS 3; 57 ka to 29 ka), a time when the marine δ18O record indicates moderate continental glaciation and a global mean sea level between −60 m and −90 m. We compile and interpret geological data dating to MIS 3 to constrain the extent of major Northern Hemisphere ice sheets (Eurasian, Laurentide, Cordilleran). Many key data, especially published in the past ~15 years, argue for an ice-free core of the formerly glaciated regions that is inconsistent with inferences from the marine δ18O record. We compile results from prior studies of glacial isostatic adjustment to show the volume of ice inferred from the marine δ18O record is unable to fit within the plausible footprint of Northern Hemisphere ice sheets during MIS 3. Instead, a global mean sea level between −30 m and − 50 m is inferred from geological constraints and glacial isostatic modelling. Furthermore, limited North American ice volumes during MIS 3 are consistent with most sea-level bounds through that interval. We can find no concrete evidence of large-scale glaciation during MIS 3 that could account for the missing ~30 m of sea-level equivalent during that time, which suggests that changes in the marine δ18O record are driven by other variables, including water temperature. This work urges caution regarding the reliance of the marine δ18O record as a de facto indicator of continental ice when few geological constraints are available, which underpins many Quaternary studies.
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| 4. |
- Drobyshev, Igor
(författare)
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352 years long fire history of a Siberian boreal forest and its primary driving factor
- 2021
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 207
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Tidskriftsartikel (refereegranskat)abstract
- Fire is a major disturbance agent in the boreal forest, affecting the structure, dynamics and biogeochemical cycles in this biome. In the Asian section of boreal forest, the records of long-term fire history are few that limits our understanding of factors forcing regional fire dynamics. We presented an annually-resolved 352 year (1666-2017) fire chronology based on fire scars of Scots pine (Pines sylvestris L.) and Siberian larch (Larix sibirica Ledeb) from the Transbaikal area in the southeastern Siberia. Fire activity showed an increasing trend from 1720 to 1929 (R-2 = 0.80, P < 0.0001), and a significant decreasing trend from 1920 to 2010 (R-2 = 0.62, P < 0.001). We assessed the potential relationships between drought (as represented by the Palmer Drought Severity Index, PDSI, and the Monthly Drought Code, MDC), ocean-atmosphere circulation and forest fire by Superposed epoch analyses, cross-wavelet analysis and Granger causality analysis. Increased fire activity was associated with stronger drought from previous winter to current summer of fire event years and positive Arctic Oscillation (AO) before and during major fire season (February and April to May), as revealed by superposed epoch analysis. Granger causality pointed to the significant role of drought in driving forest fires. Our findings provide insights into the climate drivers of forest fire activity and its prediction in the Transbaikal region.
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| 5. |
- Harper, David A.T., et al.
(författare)
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Early Cambrian brachiopod-dominated shell concentrations from North-East Greenland: Environmental and taphonomic implications
- 2021
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 204, s. 103560-103560
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of a series of thin but persistent early Cambrian (Cambrian Age 4) brachiopod shell concentrations extending along a transect of some 150 km in NE Greenland, indicates the ability of the group to form widespread, skeletal pavements very early in the history of the phylum, its gregarious behaviour and ability to harness available nutrients. These extensive shell pavements within the Bastion Formation mark biological events within the basin, the abundance of shells perhaps associated with oscillating redox conditions prompting the dissolution of phosphate and its spread across the shelf. The shells were subsequently reworked and deposited by episodic distal storm surges with some winnowing.
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| 6. |
- Költringer, Chiara, et al.
(författare)
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Quaternary sediment sources and loess transport pathways in the Black Sea - Caspian Sea region identified by detrital zircon U-Pb geochronology
- 2022
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Ingår i: Global and Planetary Change. - : Elsevier. - 0921-8181 .- 1872-6364. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- Constraining the controls on the distribution of sediment at a continental scale is a critical step in understandinglong-term landscape and climate evolution. In particular, understanding of the role of rivers in wider sedimentrouting and impacts on aeolian loess formation on a continental scale remains limited. Extensive Quaternaryloess deposits are present on the East European Plain and in the Black Sea - Caspian Sea region and are associatedwith major rivers draining numerous surrounding cratonic and orogenic hinterland areas. Coupled with this,complex changes in local and global sea level have affected the extent and drainage of the Caspian Sea and theBlack Sea, and Quaternary glaciations have impinged on the northern margin of the East European Plain. Thissuggests that sediment routing and loess formation may show complex patterns and controls. Here, we applyU–Pb dating of detrital zircons from fluvial, marine and aeolian (dominantly loess) sedimentary records on theEast European Plain and in the Black Sea - Caspian Sea region. This shows a strong control of large rivers on thedistribution of sediments at a continental scale in the region, through long-distance transport of several 1000 km,sourced from continental and mountain glacier areas prior to marine or atmospheric reworking and trans-portation. Strong spatial variability in zircon U–Pb data from loess deposits on the East European Plain revealsmultiple diverse sources to the different individual loess sections, whereas no significant temporal variability inloess source is detected during the Late Pleistocene of the Lower Volga loess in South Russia. While the sedimentsupply from glacial areas via rivers plays an important role for the provenance of East European Plain loessdeposits, our data indicate that the stark spatial diversity in loess provenance on the East European Plain is oftendriven by the input of multiple local sources. Similar to the loess, marine sediments from different basins of theBlack Sea and the Caspian Sea also show significant spatial variability. This variability is controlled by the ba-thymetry of the seas, leading to sedimentary intermixing by sea currents within, but not between differentseparated sea basins. A direct comparison of marine and aeolian sediments at the same depositional site suggeststhat although loess and marine sediments are both dominantly sourced from river sediments containing fartravelled sedimentary material, local sources play a more important role in many loess deposits.
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| 7. |
- Niezgodzki, Igor, et al.
(författare)
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Simulation of Arctic sea ice within the DeepMIP Eocene ensemble : Thresholds, seasonality and factors controlling sea ice development
- 2022
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 214
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Tidskriftsartikel (refereegranskat)abstract
- The early Eocene greenhouse climate maintained by high atmospheric CO2 concentrations serves as a testbed for future climate changes dominated by increasing CO2 forcing. In particular, the early Eocene Arctic region is important in the context of future CO2 driven climate warming in the northern polar region and associated shrinking Arctic sea ice. Here, we present early Eocene Arctic sea ice simulations carried out by six coupled climate models within the framework of the Deep-Time Model Intercomparison Project (DeepMIP). We find differences in sea ice responses to CO2 changes across the ensemble and compare the results with available proxy-based sea ice reconstructions from the Arctic Ocean. Most of the models simulate seasonal sea ice presence at high CO2 levels (≥ 840 ppmv = 3× pre-industrial (PI) level of 280 ppmv). However, the threshold when sea ice permanently disappears from the ocean varies considerably between the models (from <840 ppmv to >1680 ppmv). Based on a one-dimensional energy balance model analysis we find that the greenhouse effect likely caused by increased atmospheric water vapor concentration plays an important role in the inter-model spread in Arctic winter surface temperature changes in response to a CO2 rise from 1× to 3× the PI level. Furthermore, differences in simulated surface salinity in the Arctic Ocean play an important role in the control of local sea ice formation. These differences result from different implementations of river run-off between the models, but also from differences in the exchange of waters between a brackish Arctic and a more saline North Atlantic Ocean that are controlled by the width of the gateway between both basins. As there is no geological evidence for Arctic sea ice in the early Eocene, its presence in most of the simulations with 3× PI CO2 level indicates either a higher CO2 level and/or an overly weak polar sensitivity in these models.
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| 8. |
- Perić, Zoran M., et al.
(författare)
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Detailed luminescence dating of dust mass accumulation rates over the last two glacial-interglacial cycles from the Irig loess-palaeosol sequence, Carpathian Basin
- 2022
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Ingår i: Global and Planetary Change. - : Elsevier. - 0921-8181 .- 1872-6364. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- Mineral dust records distant from dust sources are crucial in establishing wider atmospheric dust loads in the past. However, detailed, independent chronologies for loess-palaeosol sequences distant from local dust sources are still rare in Europe. In this study we present a high-resolution OSL and pIRIR(290) chronology and multi-proxy investigation of the Irig loess-palaeosol sequence (LPS), Vojvodina, Serbia. Our results show that 4-11 mu m quartz is a reliable dosimeter only up to similar to 59 ka (179 Gy), after which the OSL ages underestimate the expected ages based on stratigraphy. The pIRIR 290 signal displays generally good luminescence behaviour and resultant ages show good agreement with the expected stratigraphic ages, although with apparent 15 kyr and 35 kyr age underestimations at the L2-52 and 52-L3 boundaries, respectively. The calculated dust mass accumulation rates (MAR) reveal large fluctuations during the last two glacial-interglacial cycles. During the penultimate glacial, the highest MARs were observed between 171 and 181 ka, subsequently decreasing rapidly during MIS 5. During the last glacial period, dust MARs display maximum values during MIS 2 and MIS 4, while the lowest dust input was observed during the Holocene, followed by MIS 3. Dust MAR and grain-size shifts appear to lead changes in magnetic susceptibility by several kyr. Our results imply that changes in dust availability and wind dynamics occurred prior to changes in climate-controlled soil moisture conditions at the Irig LPS. Moreover, our results reveal a close coupling of the dust MAR and grain-size variations during the Mid-Late Pleistocene. These patterns suggest that the Irig site is likely representative of regional dust dynamics, which separates it from more source proximal loess sites, such as those close to major rivers, which are likely more affected by local dust availability and river discharge.
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| 9. |
- Piao, Jinling, et al.
(författare)
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Northward extension of the East Asian summer monsoon during the mid-Holocene
- 2020
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 184
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Forskningsöversikt (refereegranskat)abstract
- Previous studies based on multiple paleoclimate archives suggested that during the mid-Holocene (MH, similar to 6000 years before present day), the East Asian summer monsoon (EASM) had a prominent intensification and northward extension. However, current climate model simulations with orbital forcing alone present an underestimation of the magnitude of changes in the EASM. In the current work, we show that considering a vegetated and dust-reduced Sahara in the MH can significantly strengthen the EASM intensity and expand its northernmost boundary northward compared to the results with orbital forcing alone. The vegetation change over the Sahara is the dominant factor for the variation in the EASM, while the dust reduction plays a smaller role. The vegetated Sahara causes a westward shift of the Walker circulation, accompanied with enhancement of the western Pacific subtropical high (WPSH), which then results in a strengthened EASM. On one hand, the change in the Walker circulation induces decreased rainfall over the western equatorial Pacific, intensifying the WPSH through the Gill-Matsuno response. On the other hand, the shift in the Walker circulation is associated with a stronger local Hadley circulation, reinforcing the WPSH. Finally, our results show that the westward expansion of the WPSH is mainly caused by the local strengthening of the Hadley circulation.
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| 10. |
- Salonen, J. Sakari, et al.
(författare)
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Uncovering Holocene climate fluctuations and ancient conifer populations : Insights from a high-resolution multi-proxy record from Northern Finland
- 2024
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Ingår i: Global and Planetary Change. - 0921-8181 .- 1872-6364. ; 237
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Tidskriftsartikel (refereegranskat)abstract
- A series of abrupt climate events linked to circum-North Atlantic meltwater forcing have been recognised in Holocene paleoclimate data. To address the paucity of proxy records able to characterise robustly the regional impacts of these events, we retrieved a sub-centennial resolution, well-dated core sequence from Lake Kuutsjarvi, northeast Finland. By analysing a range of paleo-environmental proxies (pollen, plant sedimentary ancient DNA, plant macrofossils, conifer stomata, and non-pollen palynomorphs), and supported with proxy-based paleotemperature and moisture reconstructions, we unravel a well-defined sequence of vegetation and climate dynamics over the early-to-middle Holocene. The birch-dominated pioneer vegetation stage was intersected by two transient tree-cover decrease events at 10.4 and 10.1 thousand years ago (ka), likely representing a two-pronged signal of the 10.3 ka climate event. Our data also show a clear signal of the 8.2 ka climate event, previously not well recorded in the European Arctic, with a collapse of the pine-birch forest and replacement by juniper developing in tight synchrony with Greenland isotopic proxies over 8.4-8.0 ka. Supported by climate modelling, severe winter cooling rather than summer might have been driving vegetation disruptions in the early Holocene. The Kuutsjarvi data indicate an early arrival of Norway spruce (Picea abies) by 9.2 ka (pollen, DNA, and stoma finds), as well as the first evidence for Holocene presence of larch (Larix) in Finland, with pollen finds dating to 9.6-5.9 ka.
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