The 100 and 400 kyr eccentricity cycles are present in many Mesozoic and Cenozoic records but appear especially prominent during the warmer intervals. Their occurrence in deep marine records of these intervals demonstrates that astronomical forcing not only impacts the regional environment but also alters climate conditions and carbon cycle dynamics on a global scale. Yet, the pathways by which regional insolation changes amplify to global scale climate perturbations remain poorly understood, particularly in greenhouse climates where climate-sensitive ice sheets are absent. Here, we present the first-ever Earth system model simulations that closely replicate the 100 kyr climate-carbon cycles in an ice-free world, using only insolation forcing as a driver. Subtle changes in nutrient fluxes and marine organic carbon burial have the potential to drastically alter the ocean buffering capacity – a key mechanism that amplifies astronomical climate variability via the preferential partitioning of carbon to atmospheric CO2. The presence of extensive oxygen minimum zones, where the interplay between sedimentary nutrient (phosphate) regeneration and terrestrial nutrient runoff regulates organic carbon burial, lies at the foundation of the mechanism presented here.
How to cite: Vervoort, P., Greene, S. E., Ridgwell, A., Hülse, D., and Kirtland Turner, S.: Astronomical (paleo)climate forcing amplified by oxygen minimum zone dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16994, https://doi.org/10.5194/egusphere-egu25-16994, 2025.
Geological proxies indicate that early Archean Earth was not in a permanent snowball state. Otherwise, we have limited data on its atmospheric composition, how volatile cycling operated, its evolving land-sea mask, topography and ocean bathymetry, etc. At the same time Archean climate studies provide a relatively large and underexplored parameter space for full complexity General Circulation Models (GCMs). Here we model the climate of the Archean at 3.8Ga when the amount of exposed land is likely very small (e.g. Cawood et al. 2022). The ROCKE-3D (R3D; Way et al. 2017) GCM is used. It is a full-complexity fully coupled atmosphere, land and ocean model. In contrast to previous studies we utilize a full complexity atmosphere, a coupled fully dynamic ocean, and dynamic sea ice. R3D is a child of the Goddard Institute for Space Studies GCM Model_E that is used for climate change studies (Schmidt et al. 2013). We model day lengths of 12 and 18 hours in an aquaplanet setup. We use an N2 dominated atmosphere with differing amounts of CO2 and CH4 (being careful to avoid ratios that lead to climate cooling hydrocarbon hazes). Surface pressures of 1, 0.5 and 0.25 bar are modeled, given various Archean pressure proxy constraints (e.g. Som et al. 2016). We use a solar spectrum from 3.8Ga with a reduction of ~25% from modern day insolation. Perhaps unsurprisingly we discover that the tipping point from a temperate state (similar to modern day Earth) versus a snowball state is very sensitive to greenhouse gas amounts and total atmospheric pressure. We see differences in latitudinal ice extent dependent upon day length (12 vs 18 hours) for otherwise similar parameters, and that the dynamics of the climate is similar to recent work by Feulner et al. (2022). This work, alongside others such as Charnay et al. (2017) and Feulner et al. (2023) provide a clear path to explaining why the Faint Young Sun paradox may finally be put to rest.
References:
Cawood et al. (2022) RG, 60, e2022RG000789; Charnay et al. (2017) EPSL 474, 97; Feulner et al. (2023) ESD 14, 533-547; Schmidt et al. (2013) JAMES, 6, 141-184; Som et al. (2016) NatGeo 9, 448; Way et al. (2017) ApJS. 231, 12.
How to cite: Way, M., Wolf, E., and Wilmes, S.-B.: Killing the Faint Young Sun Paradox: An exploration of Eoarchean climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3193, https://doi.org/10.5194/egusphere-egu25-3193, 2025.
The Devonian period (419–359 million years ago) was characterized by significant climatic changes, including Oceanic Anoxic Events (OAEs) and mass extinctions. A potential link between these events and long-term astronomical cycles influencing Earth’s climate has been suggested, yet the mechanisms connecting these processes remain unclear.
To investigate this link, an emulator-based framework has been developed to simulate atmospheric conditions during the Devonian. The emulator, trained on an ensemble of snapshot simulations using HadSM3 (a General Circulation Model), captures the spatial effects of climatic precession, eccentricity, obliquity, and pCO2 on runoff and temperature. This approach provides a computationally efficient alternative to traditional GCMs and has been integrated into the recent GEOCLIM7 model, which combines a geographically distributed model of vertical weathering profile with a biogeochemical ocean box model. Vegetation distribution is estimated using FLORA, a fast model accounting for temperature, runoff, and insolation to determine potential biomass. Steady-state oceanic circulation fields are provided by cGENIE, a model of intermediate complexity. Dynamic feedbacks are incorporated as pCO2 levels are passed between the box model and the emulator, enabling the simulation of associated climate fields.
These results offer insights into the potential role of vegetation and astronomical cycles, such as eccentricity and precession in triggering oceanic anoxia, and allow for a critical evaluation of existing hypotheses on the mechanisms underlying these events.
How to cite: Sablon, L., Maffre, P., Gérard, J., Huygh, J., Da Silva, A.-C., and Crucifix, M.: Exploring the Connections between Vegetation, Orbital Forcing, and Anoxia in the Devonian with a Hierarchical Model Framework, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16931, https://doi.org/10.5194/egusphere-egu25-16931, 2025.
The Devonian period, spanning from 419 to 359 million years ago, was marked by a warmer-than-present climate and recurring ocean anoxic events (OAEs), with evidence increasingly suggesting a link between these events and astronomical forcing. Our study aims to investigate how astronomical forcing can initiate ocean anoxic events, revealing the spatial manifestation of these perturbations and assessing whether they remain regionally confined or escalate into global-scale phenomena. To this end, we employed the Earth System Model of Intermediate Complexity (EMIC) cGENIE, forced with spatially distributed continental reactive phosphorus fluxes. The coupling is performed offline with the dynsoil module of GEOCLIM, itself coupled to a statistical emulator of the Devonian climate, trained on a general circulation model (namely HadSM3). This coupling ensures the effects of more complex processes related to astronomical forcing that EMICs can hardly resolve. cGENIE is run transiently over a 1 Myr astronomical solution, crossing a 2.4 Myr eccentricity node, allowing us to capture the dynamic interplay between astronomical cycles and ocean oxygenation, mainly through the alteration of weathering. By exploring multiple variations of this astronomical solution, we aim to disentangle the respective contributions of individual astronomical parameters to the perturbation of the system. Furthermore, two experimental setups characterized by different atmospheric pCO2 levels, one high (2000 ppm) and another low (500 ppm), are considered, enabling us to investigate the impact of astronomical forcing under both "warm" and "cold" Devonian climate scenarios.
How to cite: Gérard, J., Crucifix, M., Sablon, L., Da Silva, A.-C., Huygh, J., and Pohl, A.: Astronomical forcing and anoxia during the Devonian: Insights from Earth system modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8832, https://doi.org/10.5194/egusphere-egu25-8832, 2025.
Several studies have revealed that the Eocene fine-grained sedimentary rocks in Bohai Bay Basin is driven by astronomical forces. However it is still not clarified how orbital cycles specifically control the deposition of fine-grained sedimentary rocks and the coupling relationship of paleoclimate- paleolake- sedimentation. In this study, a combination of core and thin section observation, X-ray diffraction, ICP-MS analysis, total organic carbon (TOC) content analysis and cyclostratigraphy analysis were conducted on the lacustrine shale of the Eocene Shahejie Formation (Es4u to Es3l) in the Dongying Depression of Bohai Bay Basin, in order to recognize the Milankovitch cycles and explore the controlling effect of eccentricity, obliquity and precession on the deposition of the lacustrine shale as well as the paleoclimate evolution. The related achievements are as follows: 1. Through pre-processing, sliding window spectrum analysis and multi-taper method (MTM) of the natural gamma ray data of the well NY1, good orbital signals were recognized. And through correlation coefficient method (COCO), the study interval is divided into two sections according to the change of accumulating rates. Filtered eccentricity, obliquity and precession signal curves were obtained for both sections. 2. For the lower Section, obliquity is the main controlling factor for shale deposition and precession is the secondary controlling factor. When obliquity reaches its maximum, the content of dolomite and clay in Shahejie Formation increases, while the content of calcite decreases and TOC also increases. At this point the laminar combinations are mainly dolomite/calcite lamina and organic-rich clay lamina. When obliquity reaches its minimum, the content of calcite increases, the content of dolomite and clay decreases and TOC decreases. At this point the laminar combinations are mainly calcite lamina and clay silt mixed lamina. 3. For the upper Section, eccentricity is the main controlling factor for shale deposition and precession is the secondary controlling factor. When eccentricity reaches its maximum, the content of clay and quartz in Shahejie Formation increases, while the content of carbonate minerals decreases and TOC also increases. At this point the laminar combinations are mainly calcite lamina and organic-rich clay silt lamina. When eccentricity reaches its minimum, the content of clay and quartz decreases, the content of carbonate minerals increases and TOC decreases. At this point the laminar interface is usually blurry. 4. According to a series of geochemistry data analysis, the chemical weathering index (CIA) for the lower section is relatively low, the Mg/Ca ratio and Ni/Co ratio are relatively high, which indicates that the paleo-environment was arid and reductive. For the upper section, CIA is relatively high and the Mg/Ca ratio and Ni/Co ratio are relatively low, indicating a humid and less reductive paleo-environment. The coupling relationship of paleoclimate- paleolake- sedimentation experienced a transition from the lower section to the upper section of the study interval, which is consistent with the shift from obliquity driven to eccentricity driven. The intensification of East Asia monsoons might be responsible for this transition.
How to cite: Liang, C., Han, Y., and Cao, Y.: Recognition and Responses of Milankovitch Cycles in Eocene Shahejie Formation, Dongying Depression, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3783, https://doi.org/10.5194/egusphere-egu25-3783, 2025.
The intricate rhythms of changes in Earth’s axial tilt (obliquity) and orbit (eccentricity) are strongly imprinted on records of past climate. Some of our best-dated records of astronomically paced changes in climate and continental glaciation come from deep-sea benthic foraminiferal oxygen isotope records (δ18Ob). However, even these data present major questions about the mechanisms linking Earth’s climate to its astronomical configuration, particularly the importance of eccentricity- and obliquity-paced changes in climate. We studied striking site-to-site disagreement over the frequency of change in δ18Ob, which violates the first principles of oxygen isotope systematics, and inferred Antarctic ice volume for the late Oligocene and early Miocene (Oligo-Miocene) interval.
We present a new, finely resolved δ18Ob record for ~26.4 to 21.8 million years ago from International Ocean Drilling Program (IODP) Site U1406 in the northwest Atlantic Ocean. Our new record shows clear variability at both obliquity and eccentricity frequencies, but not in equal measures. A comparison of our record to other δ18Ob records for the time interval shows a remarkably consistent global imprint of eccentricity on δ18Ob whereas the obliquity signal is inconsistent between sites, indicating that eccentricity was the primary pacemaker of land ice volume. Our results also show that the larger eccentricity-paced early Antarctic ice ages were vulnerable to rapid termination. These findings imply that the self-stabilizing hysteresis effects of large land-based early Antarctic ice sheets were strong enough to maintain ice growth despite consecutive insolation-induced polar warming episodes. However, rapid ice age terminations indicate resistance to melting was weaker than simulated by numerical models and regularly overpowered, sometimes abruptly.
How to cite: van Peer, T. E., Liebrand, D., Taylor, V. E., Brzelinski, S., Wolf, I., Bornemann, A., Friedrich, O., Bohaty, S. M., Xuan, C., Lippert, P. C., and Wilson, P. A.: Eccentricity pacing and rapid termination of the early Antarctic ice ages, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12088, https://doi.org/10.5194/egusphere-egu25-12088, 2025.
As the Earth and the other planets orbit around the Sun, the Solar System itself revolves around the center of the Milky Way, our Galaxy. The Milky Was is far from being a static and homogeneous environment. On large scales, the stars, the gas, and the dust are organized into a rotating spiral structure that extend from the center into the galactic disk. On smaller scales, the environment between the stars, also known as the interstellar medium (ISM), is continuously shaped by different events and mechanism, like supernovae explosions, stellar winds, Galactic shear, magnetic fields, etc.
The Solar System, located at about 27’000 light-years from the center of the Milky Way, completes a full orbit around the Galactic center in about 225 million years (Myr). The constantly evolving environment, combined with the Sun’s peculiar velocity relative to the average velocity of the surrounding gas and stars, causes the Solar System to “sail” various Galactic environments with different gas densities.
Encounters with dense gas regions, such as gas clouds or supernova shock fronts, can compress the heliosphere, exposing parts of the Solar System to the ISM. These encounters also increase the influx of interstellar dust into the Solar System and Earth's atmosphere. A greater influx of dust would result into the decrease of the amount of sunlight reaching Earth and, by bringing radioactive elements from the supernovae, might also cause radionuclides anomalies in geological records.
Recently, by the means of new astronomical data provided by the Gaia mission, the 3D structure of the environment surrounding the Sun has been unveiled. This has led to the identification of previously unknown Galactic structures, such as the Radcliffe Wave. This raises the question of whether the Sun has encountered any of these structures.
In our work, we study the passage of the Solar System through the Radcliffe Wave gas structure over the past 30 Myr. We find that the Solar System’s trajectory intersected the Radcliffe Wave in the Orion star forming region. We have constrained the timing of this event to between 18.2 and 11.5 Myr ago, with the closest approach occurring between 14.8 and 12.4 Myr ago.
Notably, this period is synchronous with the Middle Miocene Climate Transition on Earth, providing an interdisciplinary link with paleoclimatology. We also estimate the potential impact of the crossing of the Radcliffe Wave on climate on Earth and suggest possible future developments for this work. As the crossing could also lead to anomalies in radionuclide abundances, we highlight its importance for the field of geology and nuclear astrophysics.
How to cite: Maconi, E., Alves, J., Swiggum, C., Ratzenböck, S., Großschedl, J., Köhler, P., Miret-Roig, N., Meingast, S., Konietzka, R., Zucker, C., Goodman, A., Lombardi, M., Knorr, G., Lohmann, G., Forbes, J., Burkert, A., and Opher, M.: The Solar System's Passage through the Radcliffe Wave during the Middle Miocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3465, https://doi.org/10.5194/egusphere-egu25-3465, 2025.
Growing evidence indicates a rapid expansion of the Western Pacific Warm Pool (WPWP), characterized by annual sea surface temperatures exceeding 28°C. This expansion is seen both in area and upper ocean heat content (OHC) over the past few decades, potentially increasing typhoon activity, coral bleaching. Ecological disruptions are expected if OHC continues to rise. To better understand future changes, paleo-records offer valuable insights for assessing potential scenarios. Most previous studies in the region have focused on surface reconstructions or shorter timescales, with limited data extending beyond 0.5–0.3 million years (Ma).
In this study, we present reconstructions of surface and subsurface temperatures based on planktonic foraminiferal Mg/Ca ratios (Globigerinoides ruber and Neogloboquadrina dutertrei) from the central and southwestern margins of the WPWP for the last 1.75 Ma. Our data were obtained from core MD97-2140 (2°02’ N, 141°46’ E) and ODP Hole 1115B (9°11’ S, 151°34’ E), respectively. Our findings reveal distinct glacial/interglacial (G/IG) cycles in OHC at both sites, underscoring the significant influence of global climate boundary conditions on the WPWP. Across the middle Pleistocene transition (MPT), as the dominant climate periodicity shifted from 41-kyr to 100-kyr cycles, changes in the periodicities and amplitudes of G/IG OHC variations were also observed. Notably, OHC in both central and southwestern WPWP regions has been declining since approximately 0.8 Ma, driven primarily by a gradual subsurface cooling of 2–3°C. During “warmer-than-present” periods, such as Marine Isotope Stages 5e, 11, and 31, OHC exceeded Holocene averages.
Our findings indicate that ocean circulation and greenhouse gas forcing play a more significant role in driving OHC changes than direct orbital-induced insolation forcing. However, the long-term stability of surface SSTs in both central and southern marginal warm pool regions does not clearly support a sustained decline in greenhouse gas radiative forcing, suggesting the existence of more complex feedback mechanisms that require further exploration. This research helps refine energy budget estimates and improve the calibration of numerical models. Additionally, it emphasizes the importance of subsurface water circulation in connecting the WPWP to climate systems in mid- and high-latitude regions.
How to cite: Lo, L., Tsai, Y.-H., Godad, S. P., Lee, S.-Y., de Garidel-Thoron, T., Chu, C.-S., Shen, C.-C., Löwemark, L., Mii, H.-S., and Chang, Y.-P.: Significant ocean heat content reduction caused by subsurface cooling after 0.8 Ma in the central and southern margins of the Western Pacific Warm Pool, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3028, https://doi.org/10.5194/egusphere-egu25-3028, 2025.
To investigate the climate effect of astronomical forcing on several timescales, we have performed transient simulations covering the last 800,000 years with LOVECLIM1.3, an Earth system model of intermediate complexity. Our results show that, in addition to changes on orbital timescale, slow-varying insolation could trigger abrupt changes and multi-centennial variability in the Atlantic meridional overturning circulation (AMOC).
The insolation-induced abrupt changes and multi-centennial variability of AMOC are particularly pronounced at the end of interglacials. When summer insolation in the Northern Hemisphere (NH) high latitudes decreases to a threshold, it triggers a strong, abrupt weakening of the AMOC and consequently an abrupt cooling in the NH. The mechanism involves sea ice-ocean feedbacks in the Northern Nordic Sea and the Labrador Sea. During glacial times, the insolation-induced high frequency oscillations of AMOC could be strongly modulated by both reduced CO2 concentration and enhanced NH ice sheets through their additional effects on the sea ice-ocean system.
The timing of the simulated abrupt events at the end of interglacials is highly consistent with that observed in marine and terrestrial records, especially in high-resolution, absolutely-dated speleothem records from Asia and Europe. This validates the model results and provides a plausible explanation for the abrupt cooling events observed at the end of interglacials in many proxy records. Our preliminary results from ice sheet simulations show that the insolation-induced cooling plays an essential role on the regrowth of NH ice sheets at the glacial inception. The next insolation threshold will occur in 50,000 years, implying an exceptionally long interglacial ahead naturally speaking.
How to cite: Yin, Q., Wu, Z., Berger, A., Goosse, H., Liang, M.-Q., and Liu, W.: Insolation induced abrupt changes and multi-centennial variability of AMOC , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16876, https://doi.org/10.5194/egusphere-egu25-16876, 2025.
Earth's continents assemble into supercontinents and subsequently disperse in cycles of 400 – 600 million years. The next supercontinent is predicted to form in about 250 million years. Previous studies of future supercontinent climate have focused on surface climate and atmospheric circulation only, so this study explores how small changes in astronomical forcing―future increased solar radiation and longer day lengths―could impact ocean circulation and climate. We simulated two scenarios using present-day or future astronomical forcing for one of the possible future continental arrangements, Aurica, using the fully-coupled climate model ROCKE-3D. Future orbital forcing leads to a 4.4°C rise in global surface temperatures and a shift towards an ice-free state. Ocean circulation transitions from a gyre-dominated state to an overturning circulation with deep water formation at subpolar latitudes, similar to present-day Earth's ocean circulation. This change in ocean circulation state is driven by interactions between the atmospheric circulation, altering rainfall and evaporation patterns, and changes in the transport of salt in the oceans. Our work adds to a growing body of evidence that, for the same continental configurations, multiple stable ocean circulation states may exist. We also emphasise that fully-coupled climate models (i.e., atmosphere and oceans) are needed to understand deep-time climate states.
How to cite: Wilmes, S.-B., Way, M., Taylor, A., and Green, M.: The Climate of Earth's Next Supercontinent: Stable Ocean Circulation States, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11061, https://doi.org/10.5194/egusphere-egu25-11061, 2025.
Posters on site: Tue, 29 Apr, 14:00–15:45 | Hall X5
The Early Carboniferous successions in the Namur-Dinant Basin (NDB) in Belgium spans the transition from the Devonian Greenhouse to the Late Paleozoic Ice Age (LPIA). Sections in the basin have been extensively studied, resulting in the establishment of a stratigraphic framework. The role of orbital forcing on sedimentary cycles during the Tournaisian-Visean interval remains unclear. Although cyclic patterns have been visually identified [1], detailed cyclostratigraphic analysis has yet to be conducted.
Our primary objective is to enhance the astrochronological framework of this period, contributing to a precise geologic timescale calibration and a deeper understanding of Early Carboniferous paleoclimate variability. Additionally, this research seeks to improve our estimates of the Earth Precession and Obliquity rates. This will allow to estimate the Earth-Moon distance during a period when a critical change in the Earth-Moon system occurred [2], but still lacking cyclostratigraphic data.
To achieve this, we selected The Salet Road section in the NDB, a 30-meter-thick stratotype for the Moliniacian regional substage, characterized by alternating thick and thinly bedded black limestone facies. We sampled and measured at an unprecedented high resolution of 1 cm. Initial results are promising, showing the imprint of ~2.5 eccentricity cycles (405-kyr). The findings are expected to clarify the influence of orbital forcing on sedimentary processes and expand the global relevance of NDB stratigraphy during this period.
[1] Poty. "The Dinantian (Mississippian) succession of southern Belgium and surrounding areas: stratigraphy improvement and inferred climate reconstruction." Geologica Belgica 19.1-2 (2016).
[2] Farhat et al. "The resonant tidal evolution of the Earth-Moon distance." Astronomy & Astrophysics 665 (2022): L1.
How to cite: Boukhalfa, D., Omar, H., Arts, M., Huygh, J., Crucifix, M., Denayer, J., and Da Silva, A.-C.: Deciphering Orbital Frocing and Paleoclimate dynamics in the Early Carboniferous: Cyclostratigraphy of the Salet Road section, Belgium, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19356, https://doi.org/10.5194/egusphere-egu25-19356, 2025.
Extreme global warming events, such as that one expected for the shared socio-economic pathway (SSP) 8.5 in upcoming centuries, induce significant hydrological cycle changes characterized mainly by wet-wetter (wet-becomes-wetter) hydroclimates. However, hydroclimate changes of dry areas associated with increased temperatures are poorly understood and the occurrence of dry-drier (dry-becomes-drier) or dry-wetter (dry-becomes-wetter) conditions remains elusive. Early Eocene hothouse climates offer alternatives to assess the response of dry regions to global warming, which allows to better understand hydroclimate variability drivers in geological timescales and likely improve predictions about hydrological cycle variability under an extreme SSP 8.5-like global warming state. Here, we study the proto-Mediterranean Contessa Road (Italy) section, which contains records of a series of early Eocene carbon cycle perturbations. We used geochemical and rock magnetic data to reconstruct proto-Mediterranean hydroclimate variability, and found that orbital forcing and global warming controlled the hydrological cycle. Precession-driven insolation changes led to generation of dry/wet cycles, which occurred over superimposed aridification trends caused by short-lived (~200 kyr) carbon cycle perturbations and long-term (~6 Ma) global warming. Short-lived events caused hydroclimate perturbations that took ~24-27 kyr to recover from peak to pre-event conditions. These observations suggest that anthropogenic global warming can cause widespread aridification with impacts that exceed societally relevant timescales.
How to cite: Piedrahita, V., Roberts, A., Rohling, E., Heslop, D., Zhao, X., Galeotti, S., Florindo, F., Grant, K., and Li, J.: Dry hydroclimates in the early Eocene hothouse world, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4679, https://doi.org/10.5194/egusphere-egu25-4679, 2025.
The behavior of the global climate system on scales from years to centuries is related to several mechanisms, including solar forcing and the El Niño-Southern Oscillation (ENSO). Pre-Quaternary archives are rare, however, due to limited stratigraphic resolution and the accuracy of datings. A middle Eocene lacustrine shale in the Bohai Bay Basin (E China) shows annual laminae that allow establishing its astronomical and varve chronology. Principal component analysis of the sediments in the cored material, their magnetic susceptibility and grayscale scans as well as analysis of the varve thickness in thin sections jointly reveal variations between a warm/dry and a cold/wet climate on the scale of centuries (~200–240 years, ~350 years), probably corresponding with cycles in solar activity. In situ δ13C and δ18O values of the light carbonate laminae show, in combination with varve-thickness data, that algal blooming and carbonate production show ~2.1–8.7 year cycles that could be ascribed to ENSO activity. The data also suggest that solar forcing controlled the ENSO intensity in the area of the Bohai Bay Basin during the middle Eocene.
How to cite: Han, Y., Cao, Y., and Liang, C.: Recognition and response of ENSO signals in the middle Eocene Bohai Bay Basin lake (E China) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3765, https://doi.org/10.5194/egusphere-egu25-3765, 2025.
The late Permian to Triassic (~ 260-201 Ma) is one of the hottest periods in the last 500 Ma, witnessing dramatic changes in the environment on the Pangea supercontinent, extensive low mid latitude dusty desert formation and the development of a strong monsoonal regime (Ruffell & Hounslow 2006). However, one aspect of Permo-Triassic climate that is relatively unexplored is the extent to which orbital forcing drove terrestrial environmental change in the monsoon and desert areas. The terrestrial mudstone deposits of the Aylesbeare and Mercia Mudstone groups formed under a dusty desert environment crop out along the southwest coast of England (Hounslow and Gallois, 2023) and potentially provide a means to address this gap.
Here we apply dual frequency magnetic susceptibility and analysis of its frequency dependence on mudstones of the Aylesbeare and Mercia Mudstone groups in order to constrain the environmental controls on these parameters and reconstruct Permo-Triassic environmental changes. We sample for these parameters at closely spaced regular intervals and use the new magnetostratigraphic timescale of Hounslow and Gallois (2023) to ascertain variations in these parameters with both age and depth. Both bulk magnetic susceptibility at low frequency (976 Hz) and frequency dependence show considerable variation, which correspond to stratigraphic alternations between green-grey silty mudstones and red mudstones, potentially reflecting wider scale changes in water table level and humidity. Evidence from temperature‐dependent magnetic susceptibility experiments suggested prevailing of magnetite in all types of sequences with hematite evidence in a red mudstone. We propose a model where changes in a dissolution of iron oxides due to climatically driven water table level changes explains these variations in the mudstones. Spectral and wavelet analysis reveals clear orbital periodicities in the proxy data, implying orbital control on water table in these desert environments, potentially via distal monsoon precipitation. Notably, there are substantial changes in the importance of key orbital parameters in the data through time, implying strong sensitivity of this hyper-arid climate to external boundary conditions.
References
Ruffell, A. & Hounslow, M., 2006: In P. F. Rawson, & P. Brenchley (Eds.), The Geology of England & Wales. Geological Society of London; 295-325.
Hounslow, M. & Gallois, R., 2023: Magnetostratigraphy of the Mercia Mudstone Group (Devon, UK): implications for regional relationships and chronostratigraphy in the Middle to Late Triassic of Western Europe. Journal of the Geological Society 180, jgs2022-173.
How to cite: Netsyk, M., Stevens, T., Arnqvist, J., Niezabitowska, D., Almqvist, B., Hounslow, M. W., and Gallois, R.: Magnetic susceptibility of Permian-Triassic terrestrial mudstone of southern Britain: features and application for paleoenvironment reconstruction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8979, https://doi.org/10.5194/egusphere-egu25-8979, 2025.
The dominant periodicity of the late Pleistocene glacial-interglacial cycles is roughly 100 kyr, rather than other major orbital periods such as 19, 23, 41, and 400 kyr. Various models explain this fact through distinct dynamical mechanisms, which include synchronization of self-sustained oscillations and resonance in mono- or multi-stable systems. However, the variety of proposed models and dynamical mechanisms could obscure the essential factor for realizing the 100-kyr periodicity.
In this study, we propose the hypothesis that the ice-sheet climate system responds to orbital forcing at the 100-kyr periodicity because the intrinsic timescale of the system is closer to 100 kyr than to other major orbital periods. We support this hypothesis with analyses and sensitivity studies of several simple ice age models with contrasting mechanisms.
How to cite: Crucifix, M., Mitsui, T., Ditlevsen, P., and Boers, N.: 100-kyr glacial-interglacial cycles seen as a timescale matching problem, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18358, https://doi.org/10.5194/egusphere-egu25-18358, 2025.
The response of mean annual sea surface temperature (MASST) to orbital insolation forcing has remained not well understood. Here, we study the MASST response to orbital forcing in a climate model simulation of the last 200,000 years. Our results show that SST responds nearly linearly to insolation across most of the tropics and high latitudes, with the MASST dominated by obliquity variability. In the mid-latitude and the eastern equatorial Pacific, however, SST response is nonlinear such that the MASST is dominated precession variability. The nonlinear MASST response can be biased towards winter or summer SST, caused by the rectification of the seasonal insolation forcing by cloud albedo or mixed layer depth.
How to cite: Kong, X., Liu, Z., Yan, M., Wen, Q., Bova, S., Rosenthal, Y., Ning, L., Liu, J., and Xie, F.: Linear and Nonlinear Responses of Annual Mean Sea Surface Temperature to Orbital Forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4028, https://doi.org/10.5194/egusphere-egu25-4028, 2025.
For a century, the hemispheric summer insolation is proposed as a key pacemaker of astronomical climate change. In high latitudes, these climate changes are characterized by cyclical expansion and retreat of ice sheets. While the low-latitude climate changes are featured by strong variations in the hydrological cycle, with dominant precessional variations. Existing studies argued that precession determines the inter-hemispheric summer insolation difference, thus regulating the North-South seesaw of the ITCZ. However, an increasing number of geologic records, especially those absolutely dated ones, reveal that terrestrial precipitation shows asynchronous precessional evolutions that are very often out of phase with the summer insolation. The underlying mechanism, despite being highly debated, however, remains unclear. In this study, we proposed that the astronomically driven low-latitude hydrological cycle is paced by shifting perihelion, rather than the Northern (or Southern) Hemisphere summer insolation. Precession of the Earth’s rotation axis alters the occurrence season and latitude of perihelion. When perihelion occurs, increasing insolation raises the moist static energy over land faster than over ocean due to differing thermal inertia. This thermodynamically moves the tropical convergence precipitation from the ocean to the land, contributing to enhancing the terrestrial precipitation over the latitudinal rain belt. As perihelion shifts towards different latitudes and seasons at different precessional phases, this leads to asynchronous terrestrial precipitation maxima at different latitudes. We present both model simulations and geological records to support our hypothesis. Our results suggest that the insolation in individual seasons is equally important in shaping the orbital scale climate changes at low latitudes. This offers new insight into the Milankovitch theory.
How to cite: Yang, H., Shi, X., Wang, X., Liu, Q., Zhong, Y., Liu, X., Sun, Y., Cai, Y., Liu, F., Lohmann, G., Werner, M., Jian, Z., Pinho, T. M. L., Cheng, H., Lu, L., Liu, J., Yang, Q., Hu, Y., Zhang, J., and Chen, D.: Astronomical driven low-latitude hydrological cycle not paced by summer insolation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2066, https://doi.org/10.5194/egusphere-egu25-2066, 2025.
The East Asian monsoon (EAM) and the Australian monsoon (AUM) are two subsystems of the Asian-Australian monsoon system. The EAM and AUM can be linked dynamically through the cross-equatorial outflow, in addition to their own distinct responses to external forcing. Despite previous studies on their relationships for different timescales, their relationship at the orbital timescale has remained poorly explored. In a set of simulations, we demonstrate that the Australian Summer Monsoon (AUSM) precipitation varies out-of-phase to the East Asian Summer Monsoon (EASM) at precession timescale due to the local insolation. At the same time scale, the relation between the AUSM and the East Asian winter monsoon (EAWM) is weak. The weak relation is due to the precession induced inter-hemispheric insolation gradient, which weakens the cross-equatorial flow and thus the dynamical links between the AUSM and the EAWM
How to cite: Yan, M., Liu, Z., Wang, B., Kong, X., Ning, L., Wen, Q., and Liu, J.: The response of AUSM to precession forcing and its relation to EASM and EAWM , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3901, https://doi.org/10.5194/egusphere-egu25-3901, 2025.
Climatic fingerprint of Heinrich (H) events was characterized by widespread megadroughts over the Asian summer monsoon (ASM) region accompanied by systemic weakening of the ASM. However, recent studies of hydroclimate proxies suggest huge spatial discrepancies in precipitation over the ASM region during some H events, characterized by increased precipitation in the Yangtze River Valley contrasting with the prevalent megadroughts across the whole ASM region. The mechanism responsible for the spatial discrepancies in precipitation and the relationship between local precipitation and the ASM intensity remain elusive. In this study, we investigate the response of the ASM circulation and precipitation to orbital forcing during six H events based on simulations with a coupled atmosphere-ocean general circulation model. The results show that changes in insolation alone can induce spatial discrepancies in precipitation over the ASM region during the H events. During the H1, 3, 4, 5, 6 events, the amplification of the land-sea pressure contrast in response to a positive interhemispheric insolation gradient (30◦N-30◦S) during boreal summer intensifies moisture transport from the adjacent oceans to the ASM region. The ensuing moisture divergence, combined with anomalous downdrafts, results in decreased precipitation in the South Asian Summer Monsoon (SASM) region, but converse scenario for the East Asian Summer Monsoon (EASM) region. During the H2 event, the increased precipitation across the Yangtze River Valley sharply contrasts the widespread drought over the ASM region, attributing to an anticyclone anomaly over the subtropical Western North Pacific and a cyclone anomaly over Japan and Korea. Moisture budget analysis shows that the dynamic effect, especially the vertical term, rather than the thermodynamic effect, is the dominant control of precipitation changes over the ASM region. Our results also suggest that despite the synchronous variation in the strength of the EASM and SASM in response to orbital forcing, the EASM should not be regarded as an eastward and northward extension of the SASM. Furthermore, our model simulates a weak correlation between the monsoon intensity and precipitation in the SASM region in response to orbital forcing, calling for caution in employing precipitation to reconstruct SASM intensity on orbital time scale.
How to cite: Liang, M., Yin, Q., Sun, Y., Zhang, C., Berger, A., Lyu, A., Liu, W., and Wu, Z.: Distinct response of Asian summer monsoon circulation and precipitation toorbital forcing during six Heinrich events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8041, https://doi.org/10.5194/egusphere-egu25-8041, 2025.
Many geological datasets exhibit distinct lithological cycles at high-frequencies (e.g., ~30 kyr, ~15 kyr, ~13 kyr) that often lack a definitive explanation for their origin. While such cycles are frequently hypothesized to be tied to astronomical forcing, the identification of periodicities alone is insufficient to confirm their astronomical origin. This challenge underscores the need for robust analytical frameworks capable of probing the underlying forcing mechanisms of these cycles. Recently, amplitude variations are the standard tool to assess the possible orbital origin of quasi-cyclic sediment sequences. Bi-coherence spectral analysis, a technique commonly used to identify nonlinear interactions and energy transfer between frequencies in complex systems, offers a promising complementary approach for addressing this issue. By assessing the coherence between two primary frequencies and their interaction-generated secondary frequency in the astronomical solutions, bi-coherence spectra provide insights into the complex relationships between orbital cycles. Here, we utilize bi-coherence analysis as a tool to evaluate whether specific periodicities observed in geological records stem from nonlinear interactions consistent with astronomical forcing. We test this approach using several datasets from the Quaternary to the Paleozoic and assess Milanković and sub-Milanković frequencies. This study proposes a novel test for the astronomical origin of cycles in geological records.
How to cite: Zhang, Y., Zeeden, C., Fang, Q., and Wu, H.: Can bi-coherence spectral analysis be used as test for the astronomical origin of sedimentary cycles?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11086, https://doi.org/10.5194/egusphere-egu25-11086, 2025.
