![]() Thus, middle Eocene MATs were 17–20 ☌ warmer, CMMTs 27–31 ☌ warmer, WMMTs 7–8 ☌ warmer, and MAP 3–5 times higher than present. The present-day climate for Yellowknife (62.45°N, 114.40°W), the nearest long-term climate station situated 300 km southwest of the Giraffe locality, has a MAT of −4.3 ☌, CMMT of -25.6 ☌, WMMT of 17.0 ☌, and MAP of 289 mm (1981–2010 climate normals htpp://.ca). Reconstructed mean annual precipitation (MAP) ranges from 1257 to 1292 mm, with a mean uncertainty of 310 mm. Mutual climate range (MCR) analysis (e.g., Ballantyne et al., 2010 Thompson et al., 2012 see the methods description in Appendix DR1) of these pollen assemblages using nearest living relatives yields reconstructed mean annual temperatures (MATs) of 12.5–16.3 ☌ (mean ± 1σ = 14.5 ± 1.3 ☌), coldest month mean temperatures (CMMTs) of 0.5–4.5 ☌ (3.4 ± 1.7 ☌), and warmest month mean temperatures (WMMTs) of 23.5–25.0 ☌ (24.5 ± 0.8 ☌) ( Figs. Paleoclimate of the Latest Middle Eocene Subarctic Glass fission track dating ( Westgate et al., 2013) of both tephra beds gives a weighted mean age (☑σ) of 37.84 ± 1.99 Ma (Table DR1 and Appendix DR1). Two rhyolitic tephra beds are present in the core directly below the lacustrine-to-peat transition ( Fig. The common sampling interval over which we estimate the mean climate state and CO 2 concentration includes multiple samples from 7 m of vertical equivalent thickness ( Fig. assuming reasonable accumulation rates and only moderate compaction. We analyzed a 21 m section (vertical equivalent depth) of peat in core BHP 99-01, representing ∼20 k.y. Both facies have remarkable preservation of aquatic and terrestrial plant fossils ( Wolfe et al., 2006 Doria et al., 2011). 1), together representing the progressive infilling of the maar basin. #Metasequoia 4.5 archive#Furthermore, paleoclimate and CO 2 reconstructions are not commonly derived from the same sedimentary archive this complicates assessment of proxy-model mismatch and frustrates efforts to understand the sensitivity of past equilibrium climate response to greenhouse gas forcing.Įxploration drill core BHP 99-01 (see Appendix DR1 in the GSA Data Repository 1) captures ≥50 vertical-equivalent meters of lacustrine sediment overlain by 32 m of peat ( Fig. Climate models struggle with these critical early Cenozoic intervals because unrealistically high CO 2 forcing is required to produce the temperature responses implied by proxies, particularly for the sparse network of terrestrial high-latitude sites ( Lunt et al., 2012a). ![]() Observations from the Arctic Ocean suggest that ice rafting may have been initiated by the middle Eocene (e.g., Tripati et al., 2008), in apparent conflict with the warmth implied by the terrestrial biota (e.g., Eberle and Greenwood, 2012). The subsequent cooling trend of the middle and late Eocene ( Pagani et al., 2005) is also relevant because atmospheric CO 2 concentrations dovetail the range projected for the coming century ( Maxbauer et al., 2014 Jagniecki et al., 2015 Anagnostou et al., 2016 Steinthorsdottir et al., 2016), ultimately crossing the threshold necessary to maintain continental ice sheets (∼500 ppm Royer, 2006). Estimates of regional climate sensitivity, expressed as ∆MAT per CO 2 doubling above preindustrial levels, converge on a value of ∼13 ☌, underscoring the capacity for exceptional polar amplification of warming and hydrological intensification under modest CO 2 concentrations once both fast and slow feedbacks become expressed.Įfforts to understand climate response to sustained greenhouse gas forcing commonly focus on periods of peak Cenozoic warmth during the Paleocene–Eocene thermal maximum and early Eocene (e.g., Zachos et al., 2008 Lunt et al., 2012a). ![]() Reconstructed MATs are more than 6 ☌ warmer than those produced by Eocene climate models forced at 560 ppm CO 2. ![]() Metasequoia stomatal indices and gas-exchange modeling produce median CO 2 concentrations of ∼630 and ∼430 ppm, respectively, with a combined median estimate of ∼490 ppm. Mutual climatic range and oxygen isotope analyses of botanical fossils reveal a humid-temperate forest ecosystem with mean annual temperatures (MATs) more than 17 ☌ warmer than present and mean annual precipitation ∼4× present. 38 Ma) terrestrial sediments in the posteruptive sediment fill of the Giraffe kimberlite in subarctic Canada. We reconstruct temperature, precipitation, and CO 2 from latest middle Eocene (ca. Eocene paleoclimate reconstructions are rarely accompanied by parallel estimates of CO 2 from the same locality, complicating assessment of the equilibrium climate response to elevated CO 2. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |