Climate response to orbital forcing

The pacing of the global climate system by orbital variations is clearly demonstrated in the timing of e.g. glacial-interglacial cycles. The mechanisms that translate this forcing into geoarchives and climate changes continue to be debated. We invite submissions that explore the climate system response to orbital forcing, and that test the stability of these relationships under different climate regimes or across evolving climate states (e.g. mid Pleistocene transition, Pliocene-Pleistocene transition, Miocene vs Pliocene, and also older climate transitions). Submissions exploring proxy data and/or modelling work are welcomed, as this session aims to bring together proxy-based, theoretical and/or modelling studies focused on global and regional climate responses to astronomical forcing at different time scales in the Phanerozoic.

Co-organized by SSP2
Convener: Stefanie Kaboth-BahrECSECS | Co-conveners: Anne-Christine Da SilvaECSECS, Mingsong Li, Huanchun Wu, Christian ZeedenECSECS
vPICO presentations
| Thu, 29 Apr, 15:30–17:00 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Stefanie Kaboth-Bahr, Christian Zeeden, Anne-Christine Da Silva
Anqi Lyu, Qiuzhen Yin, Michel Crucifix, and Youbin Sun

The East Asian summer monsoon (EASM) is an important component of the climate system and it influences about one-third of the world’s population. Numerous paleoclimate records and climate simulations have been used to study its long-term evolution and response to different forcings. The strong regional dependence of the EASM variation questions the relative role of ice sheets and insolation on the EASM precipitation in different sub-regions in East Asia. A Gaussian emulator, which was generated and calibrated by interpolating the outputs of 61 snapshot simulations performed with the model HadCM3, is used to quantitatively assess how astronomical forcing, CO2 and northern hemisphere ice sheets affect the variation of the summer precipitation over the last 800 ky. Our results show that in the north of 25°N of the EASM domain, the variation of the summer precipitation is dominated by precession and insolation. This leads to strong 23-ky cycles in the summer precipitation. However, in the southern part (south of 25°N), the impact of ice volume becomes more important, leading to strong 100-ky cycles. Ice sheets influence the summer precipitation in the south mainly through its control on the location of the Intertropical Convergence Zone (ITCZ) which is very sensitive to ice volume. ITCZ is shifted significantly to the south under large ice sheets conditions. Therefore, the region under control of the ITCZ is more sensitive to the influence of ice volume than other regions. Our results also show that obliquity and CO2 have relatively small effect on the summer precipitation as compared to precession and ice sheets.

How to cite: Lyu, A., Yin, Q., Crucifix, M., and Sun, Y.: Diverse Regional Sensitivity of Summer Precipitation in East Asia to Ice Volume, CO2 and Astronomical Forcing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1051,, 2021.

Romain Vaucher, Shahin E. Dashtgard, Chorng-Shern Horng, Christian Zeeden, Antoine Dillinger, Yu-Yen Pan, Romy Ari Setiaji, Wen-Rong Chi, and Ludvig Löwemark

The Pleistocene was a phase of global cooling of the Earth through which glacial-interglacial cycles occurred, and the growth and decay of the ice-sheets resulted in quasi-cyclic sea-level fluctuations driven by orbital forcing. Despite that summer insolation is mostly controlled by precession, the records of the glacial cycles showcase a significant periodicity of ~41 kyrs during the Early Pleistocene forced by Earth’s obliquity (tilt) that varies the latitudinal distribution of insolation especially in high latitudes. The dominance of obliquity over precession in marine archives is commonly attributed to the in-phase effect of obliquity-related insolation versus the opposite-phased influence of precession, which may cancel out the summer insolation signal received by the southern and northern hemispheres.

Here, we present a clastic shallow marine record from the Cholan Formation (Early Pleistocene; Taiwan). Facies analysis indicates that quasi-cyclic deposition occurred in shoreface to offshore environments in the paleo-Taiwan Strait. The magnetobiostratigraphic framework indicates that the studied section occurs in the lower part of the Matuyama subchron (1.925 - 2.595 Ma) close to the lower limit of the Olduvai (1.925 Ma) normal polarity subchron. Comparison of the stratigraphy to a d18O isotope record of benthic foraminifera and orbital curves of precession and obliquity at the time of sediment accumulation reveals a good correlation between depositional cycles and the Northern Hemisphere summer insolation, demonstrating precession dominated sea-level fluctuations during the Early Pleistocene. These results underpin recent findings suggesting that d18O isotope records of benthic foraminifera have a more significant precession signal than previously described. This study also demonstrates that shallow-marine stratigraphic successions in high-accommodation and high-sedimentation basins can be outstanding climate archives, possibly even preserving sediment flux responding to half-precession cycles.

How to cite: Vaucher, R., Dashtgard, S. E., Horng, C.-S., Zeeden, C., Dillinger, A., Pan, Y.-Y., Setiaji, R. A., Chi, W.-R., and Löwemark, L.: Insolation-paced sea level during the Early Pleistocene, Taiwan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1433,, 2021.

Harald Yndestad


A possible relation between plants period oscillations and the Earth´s temperature variability reveals deterministic variations in the Earth´s temperature variability. This study is based on a deterministic solar-lunar model, a wavelet spectrum analysis of global temperature data series from 1850 and a wavelet spectrum analysis of Greenland temperature (GISP-2) from 2000BC.


The results reveal a period- and phase-relation between the Jovian planets, Total Solar Irradiation variability from 1700, global sea temperature variability from 1850 and Greenland temperature variability from 2000B.C. in a multidecadal spectrum of 4480 years. The results are explained by interference between accumulated solar-forced and lunar-forced periods in oceans. The climate response from solar-lunar forced periods explain Grand Solar minimum periods from 1000A.D. the Little Ice Age from 1640 to 1850, the Deep Freeze minimum at 1710 A.D. and the global temperature growth from 1850 to 2000. The solar-lunar model computes a modern global maximum temperature at 2030A.D. and an upcoming Grand Solar minimum at 2062A.D. and an upcoming deep temperature minimum at 2070A.D.


Keywords: Solar-lunar interference; Deep solar minima; Earth’s temperature variability; Global temperature minima.


How to cite: Yndestad, H.: Jovian Planets influence on the Earth’s Temperature Variability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1499,, 2021.

Peng Gao and Junsheng Nie

The middle Piacenzian period is the closest sustained warm interval and a possible analog to the future climate. It is well known that global ice volume exhibits dominant 41-kyr cyclicities. However, high resolution terrestrial paleoenvironmental records are scare. Here we present a 3.6 kyr terrestrial environmental variation record from Teruel Basin of Spain and compare the results with the East Asian monsoon records. The Spain results show dominant 41-kyr cycles during the early Piacenzian (3.3-3.15 Ma) when eccentricity was at minimum, but the 41-kyr cycles weakens during the late Piacenzian 3.15-2.95 Ma when eccentricity got increased, suggesting direct forcing by insolation. This pattern is different from the monsoonal records from China, which demonstrates persistent 20-kyr cycles during the entire middle Piacenzian. The strong 41-kyr cycles in westerly region during the early Piacenzian may originate from its higher latitude and higher sensitivity to insolation gradient forcing.

How to cite: Gao, P. and Nie, J.: Diverse manifestations of insolation forcing of environmental changes during the middle Piacenzian, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1733,, 2021.

Jie Huang and Michael Sarnthein

Glacial-to-interglacial variations in East Asian summer and winter monsoon are widely ascribed to orbital and/or global ice-sheet forcing. However, the relative impact of orbital and millennial-scale factors on Pleistocene variations in East Asian monsoon still remain controversial. To better constrain the differential response of seasonal monsoon winds over the last million years we present paired records of siliciclastic silt grain sizes, pollen, minerals, and geochemical tracers obtained from high-sedimentation rate deposits at ODP Sites 1144 and 1146 in the northern South China Sea. The proxy records show that loess-style dust supply of winter monsoon was dominant and fluvial input reduced during peak glacials over the last 900 kyr, moreover, during Heinrich stadials, while fluvial mud marked interglacial regimes as result of enhanced summer monsoon, then completely superimposing the weakened dust input of winter monsoon. A dominating superposition of fluvial mud on top of eolian dust, however, also prevailed during the initial part of most glacial stages during and after the Mid-Pleistocene Transition (MPT), in part possibly modulated by long-term groundwater reserves and/or unknown climate forcings linked to the southern Hemisphere. Prior to the MPT, during glacial stages 24–32, prolonged groundwater reserves and/or a more limited extent of northern-Hemisphere ice sheets, or unknown southern Hemisphere forcing may have controlled an ongoing interglacial-style humid climate in East Asia. In summary, our findings suggest that variations of sediment signals of seasonal East Asian monsoon variability in part may have been more sensitive to secondary factors of groundwater storage, plant cover as well as to the redistribution of insolation energy amongst various climate subsystems than to direct orbital and/or northern ice-sheet forcing.

How to cite: Huang, J. and Sarnthein, M.: One million years of seasonal seesaw in East Asian monsoon winds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1914,, 2021.

David De Vleeschouwer and Maximilian Vahlenkamp

Carbonate-rich middle Eocene sedimentary sequences are relatively scarce, hampering the reconstruction of paleoclimate dynamics within this high-CO2 world. Nevertheless, the Newfoundland Ridge (North-Atlantic Ocean) hosts a unique sedimentary archive of middle Eocene paleoceanographic change at astronomical 104-year resolution. International Ocean Discovery Program (IODP) Sites U1408 and U1410 exhibit well-defined lithologic alternations between calcareous ooze and clay-rich intervals, occurring at the obliquity beat and associated with changing intensities of Northern Component Water (NCW) formation (Vahlenkamp et al., 2018). These lithological variations are captured by the calcium-iron ratio (Ca/Fe) proxy as a measure of carbonate content. Yet, the asymmetric shape of the Ca/Fe cycles immediately reflects a strong non-linear response to the sinusoidal obliquity forcing. To explore the causes of this non-linearity, we built a simple physically-motivated and time-dependent model that simulates the sedimentary response at IODP Sites U1408 and U1410 between 46 and 42 million years ago.  

dy/dt = 1/T (bx – y)

The orbital input x constitutes of an insolation gradient during boreal winter (more specifically at winter solstice), as NCW formation is a high northern latitude winter process that depends on the Atlantic interhemispheric temperature gradient (Karas et al., 2017; Vahlenkamp et al., 2018). The latitudes between which the insolation gradient x is calculated is not user-prescribed but part of the parametrization of the model. Two further parameters define the model. The characteristic time constant T accelerates (T < 1) or slows the response to the forcing (T > 1), whereas the base of the exponential-response term b determines the degree of non-linearity in the system. We explored this four-space first with a coarse and then with a finer mesh, and found that the optimum model lies in the neighbourhood of the following values: latitudinal gradient between 63°N and 31°S, T = 4.94 kyr, b = 2.13. The corresponding system reproduces the asymmetric shape of the Ca/Fe cycles, while also exhibiting precession-obliquity interference patterns that occur in the proxy series. These kind of simple modelling efforts hold the potential to refine our mechanistic understanding of the Earth System response to astronomical forcing in the deep and warmer-than-present geologic past.

Karas et al. (2017) Pliocene oceanic seaways and global climate. Scientific Reports 7: 39842

Vahlenkamp et al. (2018) Astronomically paced changes in deep-water circulation in the western North Atlantic during the middle Eocene. Earth and Planetary Science Letter 484: 329 – 340.



How to cite: De Vleeschouwer, D. and Vahlenkamp, M.: Modelling the sedimentary response to orbital variations. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2174,, 2021.

Ze Zhang, Zhixiang Wang, and Chunju Huang

The Pliocene - Pleistocene period (3.6-1.8 Ma) was a significant global cooling time, from very warm, equable climates to high-amplitude glacial-interglacial cycles. The origin of glaciers in the Northern Hemisphere, and the mechanisms by which glacial cycles have expanded since the late Pliocene, remain a subject of ongoing discussion. The studies of the Pliocene orbital scale climate evolution mainly are focused on marine sediments and loess-paleosoil sequences, however, there are few records of continental lacustrine facies during this period. Here we present a 37.6 m high-resolution Sanmen lacustrine sequences during the Pliocene-Pleistocene transition period that indicates the astronomically controlling East Asian climate transition and the Sanmen paloelake evolution. The Rb/Sr series evolution was divided into two parts for astronomical analysis based on the obvious changes observed in curve shape and Evolutionary spectral analysis through the section: 7.4-19 and 19-45 m. Based on evaluation of average accumulation rates from paleomagnetic results, the dominated ~99-cm cycles in the 7.4 to 19 m intervals represent ~41 kyr obliquity cycles. The 19 to 45 m intervals show obvious cycles at ~232-cm, interpreting as ~100 kyr eccentricity. Astronomical tuning combined with paleomagnetic results has been used to establish the 3.83-2.32 Ma high-precision astronomical scale. Rb/Sr series reveals that ~100 kyr eccentricity was the dominant control on lake expansion for Sanmen paleolake evolutionary before 2.75 Ma, after that, dominant obliquity control. Based on re-established the meridional sea surface temperature (SST) gradient between polar Atlantic borehole ODP 982 and the equatorial Atlantic borehole ODP 662, results show that the meridional sea surface temperature gradients increased significantly at 2.75 Ma, with cyclicity changing from the dominant ~140 kyr and ~95 kyr cycles to ~41 kyr at 2.75 Ma, and is coeval with our Rb/Sr record in the Weihe Basin. Crossspectral analysis show that the Rb/Sr and meridional SST gradient are strongly coherent and almost in-phase at these primary orbital periods in the past between 3.83-2.32 Ma. Thus, we conclude that the reorganization of the East Asian climate system at ~2.75 Ma, which coincided with the expansion of Arctic ice sheet, was a response to a dramatic cooling of the global climate and obliquity-driven changes in meridional SST gradients.

How to cite: Zhang, Z., Wang, Z., and Huang, C.: Orbital-scale climatic record in the North China across the Pliocene-Pleistocene transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2697,, 2021.

Grainne ONeill and Anthony Broccoli

Glacial cycles are driven by cyclical changes in Earth’s three orbital parameters: obliquity, precession, and eccentricity.  A common interpretation of Milankovitch’s orbital theory suggests that June insolation at 65°N is the dominant forcing in driving glacial cycles. This places emphasis on precession which has the greatest effect on June insolation at 65°N. However, there is abundant evidence for the importance of obliquity in driving glacial cycles. We compare the relative strengths of obliquity and precession on climate to further explore the possibility that obliquity could be more important than common interpretations of Milankovitch’s orbital theory would suggest. We use a set of coupled atmosphere-ocean general circulation model simulations to produce time series of key climate variables. Such variables include snowfall and positive degree-days (the sum of mean daily temperature for all days above 0°C), which are proxies for accumulation and ablation, respectively. We focus our analysis on glacial inception in Scandinavia and Baffin Island, the locations where the Scandinavian and Laurentide ice sheets were initiated. We show that obliquity causes changes in positive degree-days of larger magnitude than those of precession in both Scandinavia and Baffin Island. Snowfall is dominated by obliquity in Scandinavia and by precession in Baffin Island. The location dependence of the importance of obliquity and precession may have implications for deglaciation which occurred at lower latitudes than the inception locations. Additionally, our positive degree-day time series were most closely represented by Milankovitch’s caloric summer insolation metric than June insolation at 65°N.

How to cite: ONeill, G. and Broccoli, A.: Examining the relative effects of obliquity and precession on variables important for glacial inception in Scandinavia and Baffin Island using linear reconstructions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3159,, 2021.

Christopher Lepre, Owen Yazzie, and Paul Olsen

Late Triassic records of the orbital pacing of climate are well documented from the stratigraphy of lake basins and marine facies. However, fewer studies have focused on detecting orbital climate signals preserved by fluvial depositional environments, home to terrestrial life. The sedimentary Chinle Formation of the Colorado Plateau (southwestern USA) is a succession of Late Triassic largely red beds that preserves numerous vertebrate fossils, including evidence of the Adamanian–Revueltian tetrapod faunal transition. Floodplain mudstones showing pedogenic features alternate on various thickness scales with channel sandstones. We assessed the cyclostratigraphy of red bed color for a ~250-m-thick interval of the Chinle Formation dated to 209-216 Ma using a scientific drill core from the Petrified Forest National Park, Arizona, 1A. Diffuse reflectance spectroscopy demonstrates that red bed color in this core derives from the mineral hematite, probably formed in response to the wetting and drying of soils under monsoonal rainfall. The magnetochronology and high-precision U-Pb detrital zircon dates of the core, and the astrochronostratigraphic polarity time scale of the Newark-Hartford basins are used to provide an age model for our spectral analyses and cyclostratigraphy. From the red-green and yellow-blue time series, we identified evidence of the long eccentricity, Jupiter-Venus cycle (405 kyr), longer-period grand eccentricity cycles including the Mars-Earth cycle, and possibly the Mars-Earth inclination cycle. There are also hints at higher frequency cycles. Although the relative amount of 405 kyr power is a fraction of the total variability, there is significant coherence between the Newark Basin depth rank record and the Chinle color at the 405 kyr and the ~100 kyr cycles. Our findings support previous interpretations that color and hematite variations formed during the Late Triassic and are unrelated to a younger diagenetic component of the red beds. Fluvial accumulation of the Chinle sediments was not as discontinuous as other studies have suggested, allowing for a reconstruction of orbital climate changes that may have affected the development of terrestrial ecosystems in Western Equatorial Pangaea.

How to cite: Lepre, C., Yazzie, O., and Olsen, P.: Orbital pacing of redox cycles suggested by red bed color of the Late Triassic Chinle Formation, Arizona, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3696,, 2021.

Jan Landwehrs, Georg Feulner, Matteo Willeit, Benjamin Sames, and Michael Wagreich

The Mesozoic era (~252—66 Ma) is traditionally considered as a prolonged greenhouse period, witnessing the breakup of the Pangaean supercontinent. Orbital cycles have, for example, been invoked as drivers of e.g. Pangaean „Megamonsoon“ variability and eustatic sea level cycles in the Mesozoic.

We aim to contribute to a more comprehensive understanding of orbital effects on Mesozoic climates by employing the newly developed CLIMBER-X Earth System Model. Here, we primarily use its coupled atmosphere, ocean, sea ice and vegetation modules, but also include preliminary tests with dynamic carbon cycle and ice-sheets. We present first results from a set of transient climate simulations of four Mesozoic timeslices representative for Triassic, Jurassic, Early Cretaceous and Late Cretaceous boundary conditions (e.g. paleogeography and solar luminosity). The simulations each cover ~100,000 years and are driven by changing precession, obliquity, and eccentricity.

We would like to use the opportunity to discuss this approach and associated questions with the community. For example: Would changing paleogeography and climate background state have modified the response to orbital forcings? Could eustatic sea level cycles have been caused by orbitally-driven redistribution of water between the ocean and land water storages or should orbitally-forced ice sheets also have played a role in the alleged Mesozoic greenhouse? Which connections can be established to proxy records?

How to cite: Landwehrs, J., Feulner, G., Willeit, M., Sames, B., and Wagreich, M.: Transient Climate Simulations of Orbital Effects on Mesozoic Climates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4093,, 2021.

Mengmeng Cao, Zhixiang Wang, Ze Zhang, and Anguo Xiao

Mineral dust is one of the environmental component for forcing the global climatic change, and not only influences the amount of solar radiation incoming the earth surface, but affects atmospheric CO2 concentrations in the past through wind transport to ocean and subsequent biological pumping. Mineral dust is one of the important driving factors for variations of atmospheric CO2 content in Quaternary glacial-interglacial cycles. Here, we reconstruct the interaction between the Asian dust flux (as a representative of the global dust flux), the cryosphere system (δ18Obenthic), and the global carbon cycle since 4 Ma using phase analysis, power decomposition analysis, obliquity sensitivity calculation and evolutionary spectral analysis. The evolutionary spectra show that orbital-scale variability of mineral dust, δ18Obenthic and δ13Cbenthic are very similar over the past 4 Ma, except the interval time of 3-2 Ma that shows higher obliquity energy (higher O/T values) of the δ18Obenthic and δ13Cbenthic data. Therefore, we suggest that the Asian and/or global dust is acted as a transmitter transporting the periodic signals stored in the Arctic ice sheet to deep-sea δ13Cbenthic. This is why δ13Cbenthic data have very similar changes with the Arctic ice sheets on the orbital scale. Sharp increase of global dust flux after 1.6 Ma resulted in a significant weakening of the 405 kyr long eccentricity power of δ13Cbenthic series because Arctic ice sheet signals strongly inhibit the influences of low-latitude solar insolation variations on deep-sea δ13Cbenthic system. In addition, we suggest that strengthened global drought and increases of dust fluxes since late Miocene probably forced the anti-phase relationship between δ18Obenthic and δ13Cbenthic around 6 Ma, rather than the expansion of Arctic ice sheet. Our results highlight the close coupling between dust fluxes and the global carbon cycle, with deeply influencing marine productivity and land surface processes.

Keywords: mineral dust; deep sea oxygen isotope (δ18Obenthic ); deep sea carbon isotope(δ13Cbenthic); orbital  periods ; inland Asia

How to cite: Cao, M., Wang, Z., Zhang, Z., and Xiao, A.: Mineral dust coupled with climate-carbon cycle on orbital timescales over the past 4 Ma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4242,, 2021.

Meng Wang, Mingsong Li, David B. Kemp, and Slah Boulila

Projecting future anthropogenic sea-level rise requires a comprehensive understanding of the mechanistic links between climate and short-term sea-level changes under a warming climate. Two different hypotheses, glacioeustasy and groundwater aquifer eustasy, have been proposed to explain short-term, high amplitude sea-level oscillations during past greenhouse intervals. However, the aquifer eustasy hypothesis – supported by subjective evidence of sequence stratigraphy in the Late Triassic greenhouse, has never been rigorously tested. Here we test these competing hypotheses using a recently proposed, objective approach of sedimentary noise modeling for both sea- and lake-level reconstructions for the first time. Sedimentation rate estimates and astronomical calibration of multiple paleoclimate proxies from the lacustrine Newark Basin and the marine Austrian Alps enable the construction of a highly resolved astronomical time scale for the Late Triassic. Using this timescale, sedimentary noise modeling for both lacustrine and marine successions is carried out through the Late Triassic. Lake level fluctuations reconstructed by sedimentary noise modeling and principal component analysis revealed that million-year scale lake-level variations were linked to astronomical forcing with periods of ~3.3 Myr, ~1.8 Myr, and ~1.2 Myr. Our objective water-depth reconstructions demonstrate that lake-level variations in the Newark Basin correlate with sea-level changes in the Austrian Alps, rejecting the aquifer eustasy hypothesis and supporting glacioeustasy as the sea-level driver for the Late Triassic. This study thus emphasizes the importance of high-resolution, objective reconstruction of sea- and lake-levels and supports the hypothesis that fluctuations in continental ice mass drove sea-level changes during the Late Triassic greenhouse.

How to cite: Wang, M., Li, M., Kemp, D. B., and Boulila, S.: Glacial-driven sea-level changes in the Late Triassic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6117,, 2021.

Miranda Margulis-Ohnuma, Jessica Whiteside, and Paul Olsen

Gravitational interactions among masses in the solar system are recorded in Earth’s paleoclimate history because variations in the geometry of Earth’s orbit and axial orientation modulate solar insolation. However, astronomical models prior to ca. 60 Ma are unreliable due to the unpredictable nature of orbital chaos in the solar system, and therefore such models must be constrained using geological data. Here, we use natural gamma radioactivity and other environmental proxies from paleo-tropical Late Triassic lake deposits of the Newark Rift Basin of eastern North America, previously shown to be paced by variations in axial precession and orbital eccentricity and stratigraphically constrained by U-Pb dating, to explore hitherto undescribed strong variations in orbital inclination in the 201–206 Ma interval (lacustrine, upper Passaic Formation), where lake level variations are particularly muted. We identify the Earth-Saturn 173 kyr orbital inclination cycle and use it to tune the sequence because it exhibits high theoretical stability and metronomic behavior due to the very large mass of Saturn. We tune separately to long-eccentricity as well, with similar effect. Slight, complimentary offsets in the other inclination and eccentricity periods revealed by the Earth-Saturn (s3-s6) and Venus-Jupiter (g2-g5) tunings are apparent that may be due to chaotic variations of the secular fundamental frequencies in the nodal and perihelion orbital precessions of Earth and Venus, respectively. The surprising strength of the inclination cycles in this specific sequence suggest an additional modulating effect of the Earth System on expression of the components of orbital pacing of climate, as well a mechanism to more fully constrain the secular fundamental frequencies of the solar system beyond the ca. 60 Myr limit of predictability that chaos imposes on astronomical solutions.

How to cite: Margulis-Ohnuma, M., Whiteside, J., and Olsen, P.: Strong inclination pacing of climate in Late Triassic low latitudes revealed by the Earth-Saturn tilt cycle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6638,, 2021.

Pepijn Bakker, Auk de Haas, Brett Metcalfe, and Didier Roche

Measurements of δ18O on planktonic foraminifera represent an important geological archive. In the study of climate change on orbital time-scales, δ18O is used either as a proxy for temperature change, to construct age models through pattern matching, to deduce the drivers of climate change by looking at frequency power spectra or all of the above. The validity of these approaches hinges on a two-step assumption, namely that the signal of the orbital cycles is transferred unaltered from 1) solar radiation that reaches the top of the atmosphere, insolation, to the sea surface, and 2) from the sea surface translated into the δ18O composition of the foraminiferal shell. The complexity of these two steps make it difficult to validate the assumptions behind these major paleoclimatological approaches. In this research we aim to disentangle the problem, here focussing only on the latter part: how do species-specific living habitats of foraminifera in the water column and throughout the year shape the δ18O response were the Earth’s surfce climate to perfectly reflect the orbital forcing(s). To this end we combine an isotope-enabled climate model (iLOVECLIM) with a foraminifera growth model and investigate the response of δ18O from three species of foraminifera (Globigerinoides ruber, Neogloboquadrina pachyderma, and Globigerina bulloides) to obliquity and precessional cycles.

Our results show that the planktonic foraminifera δ18O response to astronomical forcings is dominated by annual mean changes in sea-surface temperature, thus corroborating a key assumption underlying many geological climate reconstructions. However, in various places changes in the depth habitat, temperature-dependent growth rates, seasonality and δ18O of the sea water dominate the foraminifera δ18O signal. Because of these modulations, planktonic foraminifera δ18O time series can have very different characteristics compared to the orbital forcings, including limited spatial coherence as well as limited inter-species coherence at a single location.

How to cite: Bakker, P., de Haas, A., Metcalfe, B., and Roche, D.: Modulated orbital cycles in planktonic foraminifera δ18O, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7746,, 2021.

Matthias Sinnesael, Andrew R. Millard, and Martin R. Smith

The lower Cambrian successions of Southern Morocco (West Gondwana) feature some of the oldest trilobites and archaeocyaths fossil remains in the world, as well as some of the largest carbon isotope excursions of the Phanerozoic. Combined with multiple state-of-the-art U-Pb radio-isotopic constraints, these sections are key references for lower Cambrian stratigraphy. We suggest that some of the regularly alternating lithological sequences, which show various orders of nested cyclicity, carry a signal of astronomical climate forcing. In agreement with a U-Pb Bayesian age model, the primary lithological alternation corresponds with the precession astronomical cycle while clear amplitude modulation patterns reflect a short-term eccentricity imprint. Both small- and large-scale features are laterally continuous at great distances. Changes in lithology may have been primary controlled by changes in terrigenous input. This integrated astrochronological age model has the potential to result in unprecedented early Cambrian timescales for major paleoenvironmental changes like the appearance of key fossils and large carbon isotope excursions. Often, lower Cambrian and Precambrian strata lack classical stratigraphical tools like good index fossils or magnetostratigraphy. In comparison with younger strata, the combined use of high-quality radio-isotopic dating and high-precision astrochronology might be even more crucial to disentangle important events in the early evolution of life and climate on our planet.

How to cite: Sinnesael, M., Millard, A. R., and Smith, M. R.: Astrochronology for the oldest Cambrian trilobites in Moroccan West Gondwana, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9782,, 2021.

Boris Theofanis Karatsolis, Bryan Lougheed, David De Vleeschouwer, and Jorijntje Henderiks

The late Miocene to early Pliocene was a time of global cooling, albeit in a warmer-than present climate state. Increased marine primary productivity characterizes this interval, often referred to as the late Miocene-early Pliocene biogenic bloom (~9-3.5 Ma). To explain its manifestation, paleoceanographers often involve ocean gateway or monsoon-related mechanisms, formulating hypotheses of increased or redistributed nutrients in the ocean. However, the exact cause-and-effect chains remain obscure, since important diachronicity is observed across ocean basins for the main phase and the termination of this event. Here, we compile proxy data for late Miocene to Pliocene paleoproductivity from all major ocean basins, including calcareous and siliceous plankton groups. By systematically evaluating the age-depth model accuracies of previously published records we demonstrate that a globally synchronous and long-sustained reduction in primary productivity was initiated with a sharp decline between 4.6 and 4.4 Ma. Our compilation supports that relatively rapid processes (~200 kyr) influenced nutrient availability towards the end of the biogenic bloom. By evaluating different mechanisms influencing the ocean nutrient budget on such time scales, we propose orbital forcing as an important candidate to have tipped the balance towards a less productive ocean. We show that this decline in productivity coincided with a prolonged period of low orbital eccentricity and a shift towards lower-amplitude obliquity. This specific astronomical configuration prevents the development of extreme seasonal contrasts which could lead to reduced nutrient supply to the ocean due to decreased riverine influx.

How to cite: Karatsolis, B. T., Lougheed, B., De Vleeschouwer, D., and Henderiks, J.: Long-term, sustained reduction in ocean productivity initiated at 4.6-4.4 Ma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10071,, 2021.

Jaime Yesid Suarez Ibarra, Cristiane Fraga Frozza, Sandro Monticelli Petró, Pamela de Lara Palhano, and Maria Alejandra Gómez Pivel

Paleoceanographic studies reconstructing surface paleoproductivity and benthic conditions allow us to measure the effectiveness of the biological pump, an important mechanism in the global climate system. In order to assess surface productivity changes and their effect on the sea-floor environment, a multiproxy paleoceanographic analysis was conducted on the core SAT-048A (1542 m.b.s.l.), recovered from the continental slope of the southernmost Brazilian continental margin, western South Atlantic. We assessed sea surface productivity using different planktonic foraminiferal proxies: (1) the relative abundances of the species Globigerina bulloides and Globigerinita glutinata and (2) the δ13C signal of shells of the species Globigerinoides ruber ruber. To assess the organic matter (OM) flux to the seafloor, the foraminiferal planktonic:benthic ratio and the δ13C signal of shells of the benthic foraminifer Uvigerina spp. were used. To study dissolution effects occurring at the sea-floor, the Fragmentation Intensity (i.e., the proportion of fragments and broken foraminiferal shells), the number of planktonic foraminiferal tests per gram of dry sediment, and the CaCO3 and Sand contents of the sediment were measured. Superimposed on the climate-induced changes related to the last glacial-interglacial transition, the reconstruction indicates paleoproductivity changes synchronized with the precessional cycle. From the reconstructed data, it was possible to identify the glacial and postglacial stages: surface productivity, flux to the seafloor, and dissolution rates of planktonic foraminiferal tests where high during the glacial and low during the postglacial. Furthermore, within the glacial, enhanced productivity was associated with higher insolation values, which can be explained by increased NE summer winds that strengthened the Brazil Current transport and, in turn, promoted meandering and upwelling of the nutrient rich South Atlantic Central Water. Changes in the Atlantic Meridional Overturning Circulation and the reorganization of bottom water masses may change the CO32- saturation levels and, consequently, influence carbonate preservation. However, the δ13C values from shells of Uvigerina spp. are different from present-day δ13C values from dissolved inorganic carbon for the Upper Circumpolar Deep Water and the North Atlantic Deep Water, which is likely linked to varying OM fluxes. Future studies (e.g., εNd in benthic Foraminifera) must quantify the effect of the reorganization of the bottom water masses on the dissolution of the planktonic foraminiferal tests, to better understand the effect of the biological pump removing carbon from the seawater and its subsequent sequestration in the seafloor sediments.

How to cite: Suarez Ibarra, J. Y., Fraga Frozza, C., Monticelli Petró, S., de Lara Palhano, P., and Gómez Pivel, M. A.: Orbital cycle-related benthic-pelagic fluctuations in Foraminifera during the last glacial-interglacial interval in the western South Atlantic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10245,, 2021.

Gaelle Leloup and Didier Paillard

A correct understanding of the human perturbation on the carbon cycle is a fundamental prerequisite of future climate modelling on large timescales.

However, « classical » carbon cycle theories barely take into account the « organic » part of the carbon cycle and are not able to reproduce past δ13C data.

Analysis of sediment data reveals the presence of cycles in the δ13C record. A 400 kyr cycle has been observed at several time periods, from the Eocene to present [1-4]. Moreover, longer cycles have been observed : 2.4, 4.6 and 9 Myr [5-8]. The 9 Myr cycle is present since the start of the Mesozoic. These periodicities seem linked to eccentricity periods.

By forcing astronomically the (net) organic matter burial in a carbon cycle conceptual model, Paillard [9] reproduced 400 kyr and 2.4 Myr cycles in δ13C.

The net organic matter burial has a key role on δ13C, as terrestrial and marine biology preferentially use 12C during photosynthesis. Therefore if the burial of (12C rich) organic matter is relatively more important, the δ13C of the superficial system will decrease, and inversely.

However, this conceptual model was not able to explain longer term cycles at 4.6 and 9 Myr.

Here, we develop a new conceptual model based on Paillard [9], which includes the role of oxygen. Indeed, oxygen also influences the organic matter burial.

With this new conceptual model coupling carbon and oxygen cycle, it is possible to obtain 400 kyr, 2.4 Myr, but also longer cycles.


References :

[1] Sexton et al, 2011, Eocene global warming events driven by ventilation of oceanic dissolved organic carbon

[2] Pälike et al, 2006 The Heartbeat of the Oligocene Climate System

[3] Billups et al, 2004 Astronomic calibration of the late Oligocene through early Miocene geomagnetic polarity time scale

[4]Wang et al, 2010, Obscuring of long eccentricity cyclicity in Pleistocene oceanic carbon isotope records

[5] Boulila et al, 2012, A ~9 myr cycle in Cenozoic δ13C record and long-term orbital eccentricity modulation: Is there a link?

[6] Ikeda et al, 2014, 70 million year astronomical time scale for the deep-sea bedded chert sequence (Inuyama, Japan): Implications for Triassic–Jurassic geochronology.

[7] Martinez et al, 2015, Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic

[8] Sprovieri M, et al. (2013) Late Cretaceous orbitally-paced carbon isotope stratigraphy from the Bottaccione Gorge (Italy).

[9] Paillard, 2017, The Plio-Pleistocene climatic evolution as a consequence of orbital forcing on the carbon cycle.

How to cite: Leloup, G. and Paillard, D.: An attempt to understand δ13C cycles with a simple conceptual model., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11364,, 2021.

Qiang Fang, Huaichun Wu, Shuzhong Shen, Junxuan Fan, Linda Hinnov, Shihong Zhang, and Tianshui Yang

Late Paleozoic deglaciation is the Earth’s first icehouse-to-greenhouse transition in a vegetated world, but the climatic and biological responses to this transition have not yet been fully addressed. We conducted cyclostratigraphic analysis on the magnetic susceptibility from a deep marine carbonate succession in South China, to reconstruct the astrochronology of the late Early Permian, and to decipher evolutionary responses to astronomically forced climate changes in a marine diversity time series. Our results indicates that the minima of ~1.8 m.y. short orbital eccentricity amplitude modulation cycles led to seasonally stable precipitation patterns and a constant input of nutrients, which spurred marine biodiversity during this deglaciation. Synchronizing global biotic and abiotic records reveals that peaks of marine biodiversity occurred during nodes of ~1.3 m.y. obliquity amplitude modulation cycles, when ice sheet expansion triggered enhanced precipitation and organic carbon burial during icehouse conditions (290−285.1 Ma). Starting at 285.1 Ma, the insolation-biodiversity relationship began to change, paced by glacial termination and tropical aridification. With the transition to greenhouse conditions (~279.1−272 Ma), obliquity nodes became associated instead with terrestrial aridity and marine anoxia, and suppression of marine speciation. Our results bring into focus a pattern of shifting dynamics involving Earth’s astronomical parameters, climate change and marine biodiversity for icehouse and greenhouse worlds in the late Paleozoic Era.

How to cite: Fang, Q., Wu, H., Shen, S., Fan, J., Hinnov, L., Zhang, S., and Yang, T.: Astronomically paced marine biological evolution during the Late Paleozoic icehouse-to-greenhouse transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13809,, 2021.

Teuntje P. Hollaar, Sarah B. Baker, Stephen P. Hesselbo, Jean-Francois Deconinck, Luke Mander, Micha Ruhl, and Claire M. Belcher

Fire regimes are changing due to anthropogenic climatic drivers and fuel management challenges in all regions of Earth. However, the planet is also subject to natural background variability due to Earth’s orbital parameters (Milkankovitch cycles). To date no studies have assessed a sedimentary record that is sufficiently long or has a resolution that is high enough to assess both long eccentricity and precessional forcings on fire.  Here we present a ~350,000 yr record of wildfire activity, using fossil charcoal from Jurassic sediments.

The studied interval is part of the astronomically constrained Upper Pliensbachian of the Mochras borehole, Cardigan Bay Basin. The site was located within the Laurasian Seaway, south of the Viking Corridor that linked the north-western Tethys Ocean to the Boreal Sea, at a palaeolatitude of ~35°N. Clear lithological couplets of carbonate-rich and TOC-enhanced beds are observed, which show an orbital control on deposition. High resolution macrocharcoal (>125 um) and microcharcoal (10-125 um) abundance data have been obtained at a ~2 ky resolution over the studied interval. Charcoal data are coupled to estimates of variations in the hydrological cycle using clay mineral analyses, along with palynofacies and elemental analyses, and lithological and biogeochemical signatures.

We show that fire activity was strongly increased during (1) a period of maximum eccentricity (405,000 yr cycle) and (2) inferred maximum in seasonal contrast due to precession (20,000 yr cycles). In these periods with a strong seasonality, charcoal abundance indicates enhanced wildfire activity. This is coupled to a more seasonal pattern of rainfall as indicated by the relative abundance of smectite versus kaolinite. We argue that the shift to a more seasonal climate would have led to the increase in dry-adapted conifer forests. Conifers have biochemical and morphological traits that make them particularly flammable whether dry or live.This climate induced change in vegetation contributed to increased wildfire activity in the seasonal dry periods.

Increase in wildfire activity on an orbital time scale indicates that currently wildfires should be suppressed as Earth is close to an eccentricity minimum, such that man may have counteracted a relatively fire limited period.

How to cite: Hollaar, T. P., Baker, S. B., Hesselbo, S. P., Deconinck, J.-F., Mander, L., Ruhl, M., and Belcher, C. M.: Long and short orbital forcing of Jurassic wildfires., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15594,, 2021.