English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

. The Eocene–Oligocene transition (EOT) was a climate shift from a largely ice-free greenhouse worldto an icehouse climate, involving the first major glaciation of Antarctica and global coolingoccurring ∼34 million years ago (Ma) and lasting ∼790 kyr. The change ismarked by a global shift in deep-sea δ18O representing a combination ofdeep-ocean cooling and growth in land ice volume. At the same time, multiple independent proxiesfor ocean temperature indicate sea surface cooling, and major changes in global fauna and florarecord a shift toward more cold-climate-adapted species. The two principal suggested explanationsof this transition are a decline in atmospheric CO2 and changes to ocean gateways,while orbital forcing likely influenced the precise timing of the glaciation. Here we review andsynthesise proxy evidence of palaeogeography, temperature, ice sheets, ocean circulation andCO2 change from the marine and terrestrial realms. Furthermore, we quantitativelycompare proxy records of change to an ensemble of climate model simulations of temperature changeacross the EOT. The simulations compare three forcing mechanisms across the EOT: CO2decrease, palaeogeographic changes and ice sheet growth. Our model ensemble results demonstratethe need for a global cooling mechanism beyond the imposition of an ice sheet or palaeogeographicchanges. We find that CO2 forcing involving a large decrease in CO2 ofca. 40 % (∼325 ppm drop) provides the best fit to the available proxy evidence,with ice sheet and palaeogeographic changes playing a secondary role. While this large decrease isconsistent with some CO2 proxy records (the extreme endmember of decrease), thepositive feedback mechanisms on ice growth are so strong that a modest CO2 decreasebeyond a critical threshold for ice sheet initiation is well capable of triggering rapid ice sheetgrowth. Thus, the amplitude of CO2 decrease signalled by our data–model comparisonshould be considered an upper estimate and perhaps artificially large, not least because thecurrent generation of climate models do not include dynamic ice sheets and in some cases may beunder-sensitive to CO2 forcing. The model ensemble also cannot exclude the possibilitythat palaeogeographic changes could have triggered a reduction in CO2.

The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons