Astronomical component estimation (ACE v.1) by time-variant sinusoidal modeling

Accurately deciphering periodic variations in paleoclimate proxy signals is essential for cyclostratigraphy. Classical spectral analysis often relies on methods based on (fast) Fourier transformation. This technique has no unique solution separating variations in amplitude and frequency. This characteristic can make it difficult to correctly interpret a proxy's power spectrum or to accurately evaluate simultaneous changes in amplitude and frequency in evolutionary analyses. This drawback is circumvented by using a polynomial approach to estimate instantaneous amplitude and frequency in orbital components. This approach was proven useful to characterize audio signals (music and speech), which are non-stationary in nature. Paleoclimate proxy signals and audio signals share similar dynamics; the only difference is the frequency relationship between the different components. A harmonic-frequency relationship exists in audio signals, whereas this relation is non-harmonic in paleoclimate signals. However, this difference is irrelevant for the problem of separating simultaneous changes in amplitude and frequency. Using an approach with overlapping analysis frames, the model (Astronomical Component Estimation, version 1: ACE v.1) captures time variations of an orbital component by modulating a stationary sinusoid centered at its mean frequency, with a single polynomial. Hence, the parameters that determine the model are the mean frequency of the orbital component and the polynomial coefficients. The first parameter depends on geologic interpretations, whereas the latter are estimated by means of linear least-squares. As output, the model provides the orbital component waveform, either in the depth or time domain. Uncertainty analyses of the model estimates are performed using Monte Carlo simulations. Furthermore, it allows for a unique decomposition of the signal into its instantaneous amplitude and frequency. Frequency modulation patterns reconstruct changes in accumulation rate, whereas amplitude modulation identifies eccentricity-modulated precession. The functioning of the time-variant sinusoidal model is illustrated and validated using a synthetic insolation signal. The new modeling approach is tested on two case studies: (1) a Pliocene-Pleistocene benthic delta O-18 record from Ocean Drilling Program (ODP) Site 846 and (2) a Danian magnetic susceptibility record from the Contessa Highway section, Gubbio, Italy

Reconstructing seasonality through stable-isotope and trace-element analyses of the Proserpine stalagmite, Han-sur-Lesse cave, Belgium : indications for climate-driven changes during the last 400 years

Fast-growing speleothems allow for the reconstruction of palaeoclimate down to a seasonal scale. Additionally, annual lamination in some of these speleothems yields highly accurate age models for these palaeoclimate records, making these speleothems valuable archives for terrestrial climate. In this study, an annually laminated stalagmite from the Han-sur-Lesse cave (Belgium) is used to study the expression of the seasonal cycle in northwestern Europe during the Little Ice Age. More specifically, two historical 12-year-long growth periods (ca. 1593-1605 CE and 1635-1646 CE) and one modern growth period (1960-2010 CE) are analysed on a sub-annual scale for their stable-isotope ratios (delta C-13 and delta O-18) and trace-element (Mg, Sr, Ba, Zn, Y, Pb, U) contents. Seasonal variability in these proxies is confirmed with frequency analysis. Zn, Y and Pb show distinct annual peaks in all three investigated periods related to annual flushing of the soil during winter. A strong seasonal in-phase relationship between Mg, Sr and Ba in the modern growth period reflects a substantial influence of enhanced prior calcite precipitation (PCP). In particular, PCP occurs during summers when recharge of the epikarst is low. This is also evidenced by earlier observations of increased delta C-13 values during summer. In the 17th century intervals, there is a distinct antiphase relationship between Mg, Sr and Ba, suggesting that processes other than PCP, i.e. varying degrees of incongruent dissolution of dolomite, eventually related to changes in soil activity and/or land-use change are more dominant. The processes controlling seasonal variations in Mg, Sr and Ba in the speleothem appear to change between the 17th century and 1960-2010 CE. The Zn, Y, Pb, and U concentration profiles; stable-isotope ratios; and morphology of the speleothem laminae all point towards increased seasonal amplitude in cave hydrology. Higher seasonal peaks in soil-derived elements (e.g. Zn and Y) and lower concentrations of host-rock-derived elements (e.g. Mg, Sr, Ba) point towards lower residence times in the epikarst and higher flushing rates during the 17th century. These observations reflect an increase in water excess above the cave and recharge of the epikarst, due to a combination of lower summer temperatures and increased winter precipitation during the 17th century. This study indicates that the transfer function controlling Mg, Sr and Ba seasonal variability varies over time. Which process is dominant - either PCP, soil activity or dolomite dissolution - is clearly climate driven and can itself be used as a palaeoenvironment proxy

The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls

Cyclostratigraphy is an important tool for understanding astronomical climate forcing and reading geological time in sedimentary sequences, provided that an imprint of insolation variations caused by Earth’s orbital eccentricity, obliquity and/or precession is preserved (Milankovitch forcing). Numerous stratigraphic and paleoclimate studies have applied cyclostratigraphy, but the robustness of the methodology and its dependence on the investigator have not been systematically evaluated. We developed the Cyclostratigraphy Intercomparison Project (CIP) to assess the robustness of cyclostratigraphic methods using an experimental design of three artificial cyclostratigraphic case studies with known input parameters. Each case study is designed to address specific challenges that are relevant to cyclostratigraphy. Case 1 represents an offshore research vessel environment, as only a drill-core photo and the approximate position of a late Miocene stage boundary are available for analysis. In Case 2, the Pleistocene proxy record displays clear nonlinear cyclical patterns and the interpretation is complicated by the presence of a hiatus. Case 3 represents a Late Devonian proxy record with a low signal-to-noise ratio with no specific theoretical astronomical solution available for this age. Each case was analyzed by a test group of 17-20 participants, with varying experience levels, methodological preferences and dedicated analysis time. During the CIP 2018 meeting in Brussels, Belgium, the ensuing analyses and discussion demonstrated that most participants did not arrive at a perfect solution, which may be partly explained by the limited amount of time spent on the exercises (∼4.5 hours per case). However, in all three cases, the median solution of all submitted analyses accurately approached the correct result and several participants obtained the exact correct answers. Interestingly, systematically better performances were obtained for cases that represented the data type and stratigraphic age that were closest to the individual participants’ experience. This experiment demonstrates that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions and, importantly, that it is a trainable skill. Finally, we emphasize the importance of an integrated stratigraphic approach and provide flexible guidelines on what good practices in cyclostratigraphy should include. Our case studies provide valuable insight into current common practices in cyclostratigraphy, their potential merits and pitfalls. Our work does not provide a quantitative measure of reliability and uncertainty of cyclostratigraphy, but rather constitutes a starting point for further discussions on how to move the maturing field of cyclostratigraphy forward

Globally distributed iridium layer preserved within the Chicxulub impact structure

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide

Data for: The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls

Supplementary materials for Submission: Sinnesael et al., Earth-Science Reviews "The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls "

Data for: The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls

Supplementary materials for Submission: Sinnesael et al., Earth-Science Reviews "The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls "

Timing and Pacing of the Late Devonian Mass extinction event regulated by eccentricity and obliquity

The Late Devonian envelops one of Earth’s big five mass extinction events at the Frasnian–Famennian boundary (374 Ma). Environmental change across the extinction severely affected Devonian reef-builders, besides many other forms of marine life. Yet, cause-and-effect chains leading to the extinction remain poorly constrained as Late Devonian stratigraphy is poorly resolved, compared to younger cataclysmic intervals. In this study we present a global orbitally calibrated chronology across this momentous interval, applying cyclostratigraphic techniques. Our timescale stipulates that 600 kyr separate the lower and upper Kellwasser positive δ13C excursions. The latter excursion is paced by obliquity and is therein similar to Mesozoic intervals of environmental upheaval, like the Cretaceous Ocean-Anoxic-Event-2 (OAE-2). This obliquity signature implies coincidence with a minimum of the 2.4 Myr eccentricity cycle, during which obliquity prevails over precession, and highlights the decisive role of astronomically forced “Milankovitch” climate change in timing and pacing the Late Devonian mass extinction

Cosmogenic 3^3He anomaly K1 vs. the early Campanian isotopic event (ECE) as recorded in pelagic limestones of the Umbria-Marche succession (Italy)

International audienceIn this paper, we report on a biostratigraphic, magnetostratigraphic, and stable isotope (δ$^{13}$C and $^3$He) analysis across three pelagic limestone sections of the Campanian Scaglia Rossa Formation exposed in the classic Bottaccione Gorge at Gubbio (Umbria region), near the village of Furlo, and near the town of Apiro (both in the Marche region), all located in the Umbria-Marche basin of the northeastern Apennines of central Italy. These sections record the coincidental occurrence of an extraterrestrial $^3$He ($^3$He$_{ET}$) anomaly known as K1 and a negative shift in the δ$^{13}$C record known as the early Campanian event. Cyclostratigraphic spectral analysis of the Furlo section based on a high-resolution magnetic susceptibility record in these pelagic limestones revealed that the regular orbitally forced Milankovitch cycles are somewhat disturbed or blurred through the interval of the coincident $^3$He$_{ET}$ K1 anomaly and the early Campanian event isotopic anomaly, suggesting a causal effect resulting from the enhanced influx of extraterrestrial material (i.e., interplanetary dust particles and a myriad of small meteorite impacts). This would have altered the transparency of the atmosphere, causing a short-lived climate change event

Precession-driven climate cycles and time scale prior to the Hirnantian glacial maximum

Paleozoic astrochronologies are limited by uncertainties in past astronomical configurations and the availability of complete stratigraphic sections with precise, independent age control. We show it is possible to reconstruct a robust Paleozoic ~104-yr-resolution astrochronology in the well-preserved and thick Upper Ordovician reference record of Anticosti Island (Canada). The clear imprint of astronomical cycles, including ~18 k.y. precession, potential obliquity, and short and long eccentricity, constrains the entire Vauréal Formation (~1 km thick) to only ~3 m.y. in total, representing ~10 times higher accumulation rates than previously suggested. This ~104 yr resolution represents an order of magnitude increase in the current standard temporal resolution for the Katian and even allows for the detection of sub-Milankovitch climate-scale variability. The loss of a clear precession signal in the uppermost Vauréal Formation might be related to contemporaneous global cooling prior to the Hirnantian glacial maximum as indicated by the δ18O record. Complementary to the study of cyclostratigraphy of longer and often simplified records, it is important to recognize stratigraphic hiatuses and complexities on the ~104 yr scale to achieve robust sub-eccentricity-scale Paleozoic astrochronologies

7 α-methyl-19-nortestosterone vs. testosterone implants for hypogonadal osteoporosis: A preclinical study in the aged male orchidectomized rat model

Overt male hypogonadism induces not only osteoporosis but also unfavourable changes in body composition, which can be prevented by testosterone (T) replacement. In this preclinical study, the potential of synthetic androgen 7α-methyl-19-nortestosterone (MENT) as alternative treatment for male hypogonadism was evaluated in comparison with T. Eleven-month-old male rats were orchidectomized (orch) and left untreated for 2-months. Subsequently, the effects of 4-month MENT (12μg/day) and T (72μg/day) treatment on bone, muscle and fat were analysed using microcomputed tomography, dual-energy X-ray absorptiometry, dynamic bone histomorphometry and muscle fibre typing. At the onset of treatment, orch rats were clearly hypogonadal. This was evidenced by significant reductions of androgen-sensitive organ weight, lean mass, cortical thickness and trabecular bone volume compared with sham-operated aged-matched controls (sham). MENT and T restored weight of androgen-sensitive organs to a similar extent, with a superior anabolic action of MENT on levator ani muscle. Both androgens not only fully rescued hypogonadal loss of lean mass but also restored muscle fibre type composition and trabecular bone volume. Cortical bone loss was similarly prevented by MENT and T, but without full recovery to sham. Both androgens stimulated periosteal bone formation, but with a stronger effect of T. By contrast, MENT more strongly suppressed endocortical bone formation and bone turnover rate and reduced fat mass and serum leptin to a greater extent than T. MENT and T are both effective replacement therapies to stimulate bone and muscle in hypogonadal rats, with stronger lipolytic action of MENT