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Astronomical cycles are strongly expressed in marine geological records, providing important insights into Earth system dynamics and an invaluable means of constructing age models. However, how various astronomical periods are filtered by the Earth system and the mechanisms by which carbon reservoirs and climate components respond, particularly in absence of dynamic ice sheets, is unclear. Using an Earth system model that includes feedbacks between climate, ocean circulation, and inorganic (carbonate) carbon cycling relevant to geological timescales, we systematically explore the impact of astronomically modulated insolation forcing and its expression in model variables most comparable to key paleoceanographic proxies (temperature, the δ¹³C of inorganic carbon, and sedimentary carbonate content). Temperature predominately responds to short and long eccentricity and is little influenced by the modeled carbon cycle feedbacks. In contrast, the cycling of nutrients and carbon in the ocean generates significant precession power in atmospheric CO₂, benthic ocean δ¹³C, and sedimentary wt% CaCO₃, while inclusion of marine sedimentary and weathering processes shifts power to the long eccentricity period. Our simulations produce reducedpCO₂and dissolved inorganic carbon (DIC) δ¹³C at long eccentricity maxima and, contrary to early Cenozoic marine records, CaCO₃preservation in the model is enhanced during eccentricity‐modulated warmth. Additionally, the magnitude of δ¹³C variability simulated in our model underestimates marine proxy records. These model‐data discrepancies hint at the possibility that the Paleogene silicate weathering feedback was weaker than modeled here and that additional organic carbon cycle feedbacks are necessary to explain the full response of the Earth system to astronomical forcing.

 

As the world warms, there is a profound need to improve projections of climate change. Although the latest Earth system models offer an unprecedented number of features, fundamental uncertainties continue to cloud our view of the future. Past climates provide the only opportunity to observe how the Earth system responds to high carbon dioxide, underlining a fundamental role for paleoclimatology in constraining future climate change. Here, we review the relevancy of paleoclimate information for climate prediction and discuss the prospects for emerging methodologies to further insights gained from past climates. Advances in proxy methods and interpretations pave the way for the use of past climates for model evaluation—a practice that we argue should be widely adopted. 

Chert, porcelainite, and other siliceous phases are exceptionally common in Atlantic sedimentary records of the early Eocene, but the origins of these facies remain enigmatic. The early Eocene was also the warmest interval of the entire Cenozoic Era, punctuated by numerous discrete warming events termed “hyperthermals,” the largest of which is termed the Paleocene‐Eocene Thermal Maximum (~56 Ma). Here we present new and published lithologic and carbon isotope records of silica‐bearing lower Eocene sediments and suggest a link between the ubiquitous Atlantic cherts of that time period and hyperthermal events. Our data demonstrate that many of these Atlantic siliceous horizons coincide with negative carbon isotope excursions (a hallmark of hyperthermal events), including a previously unrecognized record of the Paleocene‐Eocene Thermal Maximum in the South Atlantic. Hyperthermal‐associated silica burial appears to be focused in the western middle to high latitudes of both the North and South Atlantic, with no association between siliceous facies and hyperthermal events found in the Pacific. We also present a new model of the coupled carbon and silica cycles (LOSiCAR) to demonstrate that enhanced silicate weathering during these events would require a rapid increase in total marine silica burial. Model experiments that include previously suggested transient reversals in the pattern of deep‐ocean circulation during hyperthermals demonstrate that such a mechanism can explain the apparent focusing of elevated silica burial into the Atlantic. This combination—a silicate weathering feedback in response to global warming along with a circulation‐driven focusing of silica burial—represents a new mechanism for the formation of deep‐sea cherts in lower Eocene Atlantic sedimentary records and may be relevant to understanding chert formation in other intervals of Earth history.