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Abstract Peak Neogene warmth and minimal polar ice volumes occurred during the Miocene Climatic Optimum (MCO, ca. 16.95–13.95 Ma) followed by cooling and ice sheet expansion during the Middle Miocene Climate Transition (MMCT, ca. 13.95–12.8 Ma). Previous records of northern high-latitude sea surface temperatures (SSTs) during these global climatic transitions are limited to Atlantic sites, and none resolve orbital-scale variability. Here, we present an orbital-resolution alkenone SST proxy record from the subpolar North Pacific that establishes a local maximum of SSTs during the MCO as much as 16 °C warmer than modern with rapid warming initiating the MCO, cooling synchronous with Antarctic ice sheet expansion during the MMCT, and high variability on orbital time scales. Persistently cooler North Pacific SST anomalies than in the Atlantic at equivalent latitudes throughout the Miocene suggest enhanced Atlantic northward heat transport under a globally warm climate. We conclude that a global forcing mechanism, likely elevated greenhouse gas concentrations, is the most parsimonious explanation for synchronous global high-latitude warmth during the Miocene.
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Sea ice feedbacks cause more greenhouse cooling than greenhouse warming at high northern latitudes on multi-century timescales
Abstract In contrast to surface greenhouse warming, surface greenhouse cooling has been less explored, especially on multi-century timescales. Here, we assess the processes controlling the pacing and magnitude of the multi-century surface temperature response to instantaneously doubling and halving atmospheric carbon dioxide concentrations in a modern global coupled climate model. Over the first decades, surface greenhouse warming is larger and faster than surface greenhouse cooling both globally and at high northern latitudes (45–90° N). Yet, this initial multi-decadal response difference does not persist. After year 150, additional surface warming is negligible, but surface cooling and sea ice expansion continues. Notably, the equilibration timescale for high northern latitude surface cooling (∼437 years) is more than double the equivalent timescale for warming. The high northern latitude responses differ most at the sea ice edge. Under greenhouse cooling, the sea ice edge slowly creeps southward into the mid-latitude oceans amplified by positive lapse rate and surface albedo feedbacks. While greenhouse warming and sea ice loss at high northern latitudes occurs on multi-decadal timescales, greenhouse cooling and sea ice expansion occurs on multi-century timescales. Overall, this work shows the importance of multi-century timescales and sea ice processes for understanding high northern latitude climate responses.
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- Award ID(s):
- 2233420
- PAR ID:
- 10596583
- Publisher / Repository:
- Environmental Research: Climate
- Date Published:
- Journal Name:
- Environmental Research: Climate
- Volume:
- 3
- Issue:
- 4
- ISSN:
- 2752-5295
- Page Range / eLocation ID:
- 041003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/2752-5295/ad8026
