CYCLICITY AND COMPARISON OF TERRESTRIAL AND MARINE ISOTOPE RECORDS FROM THE EARLY EOCENE CLIMATIC OPTIMUM

The Early Eocene Climatic Optimum (EECO) has been identified as a potential analog to projections of future warm climates. As the nearest “super greenhouse” period to the modern, the EECO offers a natural laboratory to explore climate variation and cyclicity in both terrestrial and marine realms during warm periods. Reconciling climate records between the marine and terrestrial realms for important climatic events has historically been a difficult task. Differing carbon cycle dynamics between such disparate environments can hamper the ability to accurately align isotope records and describe key patterns. Previous work using “wiggle matching” to visually align records lacks statistical robustness, while dynamic time warping (DTW) accounts for differences in sedimentation rate between sites by allowing the stretching or compressing of candidate records, and utilizes a many-to-one peak matching methodology that can help match peaks with differing shapes between records.

Here we utilize DTW to align and compare new carbon isotope records from the Green River Formation (GRF; terrestrial) and existing records from ODP Site 1263 (marine), both of which cover the same period during the EECO (~49-52 Ma). In the GRF record, δ¹³C values range from -0.65‰ to 5.38‰ with an average of 2.20‰ and δ¹⁸O values range from -18.89‰ to -0.48‰ with an average of -3.31‰. There is no long-term trend in either δ¹³C or δ¹⁸O, though the carbon values appear to oscillate between approximately 0 and -5‰ every ~100m. The ODP 1263 and the warped GRF records show good alignment (87% cross-correlation, 62% overlap) when DTW is applied to the normalized time series. Spectral analysis of the tuned ODP 1263 and GRF records reveals significant power at frequencies corresponding to eccentricity in both records. High correlation between the terrestrial and marine records in addition to similar Milankovitch pacing indicate that the terrestrial and marine realms were in phase with each other during the EECO. We conclude that the terrestrial and marine realms reacted in similar ways to carbon cycle perturbations during the EECO, and that these perturbations were influenced by changes in insolation on (long) eccentricity timescales.