Publication Date:
2015-09-15
Description:
The mid-Pliocene warm period (MPWP, 3.3–2.9 Ma), with reconstructed atmospheric p CO 2 of 350–450 ppm, represents a potential analogue for climate change in the near future. Current highly cited estimates place MPWP maximum global mean sea level (GMSL) at 21 ± 10 m above modern, requiring total loss of the Greenland and marine West Antarctic Ice Sheets and a substantial loss of the East Antarctic Ice Sheet, with only a concurrent 2–3 °C rise in global temperature. Many estimates of Pliocene GMSL are based on the partitioning of oxygen isotope records from benthic foraminifera ( 18 O b ) into changes in deep-sea temperatures and terrestrial ice sheets. These isotopic budgets are underpinned by the assumption that the 18 O of Antarctic ice ( 18 O i ) was the same in the Pliocene as it is today, and while the sensitivity of 18 O b to changing meltwater 18 O has been previously considered, these analyses neglect conservation of 18 O/ 16 O in the ocean-ice system. Using well-calibrated 18 O-temperature relationships for Antarctic precipitation along with estimates of Pliocene Antarctic surface temperatures, we argue that the 18 O i of the Pliocene Antarctic ice sheet was at minimum 1–4 higher than present. Assuming conservation of 18 O/ 16 O in the ocean-ice system, this requires lower Pliocene seawater 18 O without a corresponding change in ice sheet mass. This effect alone accounts for 5%–20% of the 18 O b difference between the MPWP interglacials and the modern. With this amended isotope budget, we present a new Pliocene GMSL estimate of 9–13.5 m above modern, which suggests that the East Antarctic Ice Sheet is less sensitive to radiative forcing than previously inferred from the geologic record.
Print ISSN:
0091-7613
Electronic ISSN:
1943-2682
Topics:
Geosciences
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