New constraints on Early Eocene hyperthermals; Terrestrial I1 and I2 hyperthermals solve the relation between marine and continental carbon isotope excursion magnitudes.
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During the Early Eocene (~56-46 Ma), the Earth`s climate underwent a series of events that led to relative rapid global warming. The events, or hyperthermals, comprehended a relative fast temperature rise linked to extreme greenhouse conditions. Those greenhouse conditions were fueled by carbon injection to the atmosphere, but the origin of the carbon is still unclear. The occurrence of the hyperthermals is in pace with eccentricity related orbital forcing. Continental hyperthermal carbon isotope excursions magnitudes from paleosol carbonate are found to be consistently higher than their marine equivalents. The relation of how carbon isotope excursion magnitudes are recorded during hyperthermals between the continental and marine records is not resolved. Solving this relation would be an important step towards the understanding of the origin of the injected carbon. Until now, a lack of documented continental hyperthermals hamper the understanding of this relation. We present a carbonate isotope record from paleosol carbonate nodules from the Bighorn Basin, Wyoming. Our section shows, for the first time, the I1 and I2 hyperthermals with δ13C magnitude excursions of respectively -2.7‰ and -1.8‰. Further, we constrain a cyclostratigraphic framework containing short and long eccentricity, and precession signals. With this framework we relate our section to the marine realm and show that the cyclostratigrapic framework for both realms are similar. Paleomagnetic study shows a major polarity change, the C24n/C24r reversal boundary, to be present in the short eccentricity maximum after hyperthermal H2. Scaling of five marine and continental hyperthermals inhibits an exponential relation, implying that the same process or processes underlie all of the hyperthermals. Therefore, we exclude hypotheses that do not fit this requirement and causes that do not include orbital forcing.