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Cyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High-resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well-suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408–U1410 are highly complex with several hiatuses. Here, we built a two-site composite and constructed a conservative age-depth model to provide a reliable chronology for this rhythmic, highly resolved (<1 kyr) sedimentary archive. Astronomical components (g-terms and precession constant) are extracted from proxy time-series using two different techniques, producing consistent results. We find astronomical frequencies up to 4% lower than reported in astronomical solution La04. This solution, however, was smoothed over 20-Myr intervals, and our results therefore provide constraints on g-term variability on shorter, million-year timescales. We also report first evidence that the g4–g3 “grand eccentricity cycle” may have had a 1.2-Myr period around 41 Ma, contrary to its 2.4-Myr periodicity today. Our median precession constant estimate (51.28 ± 0.56″/year) confirms earlier indicators of a relatively low rate of tidal dissipation in the Paleogene. Newfoundland Ridge drift sediments thus enable a reliable reconstruction of astronomical components at the limit of validity of current astronomical calculations, extracted from geologic data, providing a new target for the next generation of astronomical calculations.

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 ty

North Atlantic Deep Water (NADW) currently redistributes heat and salt between Earth’s ocean basins, and plays a vital role in the ocean-atmosphere CO2 exchange. Despite its crucial role in today’s climate system, vigorous debate remains as to when deep-water formation in the North Atlantic started. Here, we present datasets from carbonate-rich middle Eocene sediments from the Newfoundland Ridge, revealing a unique archive of paleoceanographic change from the progressively cooling climate of the middle Eocene. Well-defined lithologic alternations between calcareous ooze and clay-rich intervals occur at the ∼41-kyr beat of axial obliquity. Hence, we identify obliquity as the driver of middle Eocene (43.5–46 Ma) Northern Component Water (NCW, the predecessor of modern NADW) variability. High-resolution benthic foraminiferal δ18O and δ13C suggest that obliquity minima correspond to cold, nutrient-depleted, western North Atlantic deep waters. We thus link stronger NCW formation with obliquity minima. In contrast, during obliquity maxima, Deep Western Boundary Currents were weaker and warmer, while abyssal nutrients were more abundant. These aspects reflect a more sluggish NCW formation. This obliquity-paced paleoceanographic regime is in excellent agreement with results from an Earth system model, in which obliquity minima configurations enhance NCW formation.

The middle Eocene (47.8-38 Ma) marks the transition from the early Cenozoic greenhouse into the late Cenozoic icehouse climate. The early Cenozoic was characterized by warm temperatures, high atmospheric CO2 concentration ( 1000 ppm) and a non-existent or minor cryosphere. The climatic cooling towards the major glaciation of Antarctica is only partially covered by sedimentary records from scientific deep-sea drilling, which allow for high- resolution paleoceanographic studies. In the context of anthropogenic CO2 emissions and consequent global warming, the study of the nature and causes of climatic variability and the role of the ocean in the climate system during greenhouse climate is one of the fundamental challenges of paleoclimatology. Studying past times of extreme warmth and elevated CO2 enables us to anticipate the magnitude and potential consequences of future climate change. To understand the sequence of climatic, biotic and tectonic events before, during and after the ...

The middle Eocene (47.8-38 Ma) marks the transition from the early Cenozoic greenhouse into the late Cenozoic icehouse climate. The early Cenozoic was characterized by warm temperatures, high atmospheric CO2 concentration ( 1000 ppm) and a non-existent or minor cryosphere. The climatic cooling towards the major glaciation of Antarctica is only partially covered by sedimentary records from scientific deep-sea drilling, which allow for high- resolution paleoceanographic studies. In the context of anthropogenic CO2 emissions and consequent global warming, the study of the nature and causes of climatic variability and the role of the ocean in the climate system during greenhouse climate is one of the fundamental challenges of paleoclimatology. Studying past times of extreme warmth and elevated CO2 enables us to anticipate the magnitude and potential consequences of future climate change. To understand the sequence of climatic, biotic and tectonic events before, during and after the ...

The middle Eocene (47.8-38 Ma) marks the transition from the early Cenozoic greenhouse into the late Cenozoic icehouse climate. The early Cenozoic was characterized by warm temperatures, high atmospheric CO2 concentration ( 1000 ppm) and a non-existent or minor cryosphere. The climatic cooling towards the major glaciation of Antarctica is only partially covered by sedimentary records from scientific deep-sea drilling, which allow for high- resolution paleoceanographic studies. In the context of anthropogenic CO2 emissions and consequent global warming, the study of the nature and causes of climatic variability and the role of the ocean in the climate system during greenhouse climate is one of the fundamental challenges of paleoclimatology. Studying past times of extreme warmth and elevated CO2 enables us to anticipate the magnitude and potential consequences of future climate change. To understand the sequence of climatic, biotic and tectonic events before, during and after the ...