| 1. |
- Ao, Hong, et al.
(författare)
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Orbital climate variability on the northeastern Tibetan Plateau across the Eocene-Oligocene transition
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The first major build-up of Antarctic glaciation occurred in two consecutive stages across the Eocene-Oligocene transition (EOT): the EOT-1 cooling event at similar to 34.1-33.9Ma and the Oi-1 glaciation event at similar to 33.8-33.6Ma. Detailed orbital-scale terrestrial environmental responses to these events remain poorly known. Here we present magnetic and geochemical climate records from the northeastern Tibetan Plateau margin that are dated precisely from similar to 35.5 to 31Ma by combined magneto- and astro-chronology. These records suggest a hydroclimate transition at similar to 33.7Ma from eccentricity dominated cycles to oscillations paced by a combination of eccentricity, obliquity, and precession, and confirm that major Asian aridification and cooling occurred at Oi-1. We conclude that this terrestrial orbital response transition coincided with a similar transition in the marine benthic delta O-18 record for global ice volume and deep-sea temperature variations. The dramatic reorganization of the Asian climate system coincident with Oi-1 was, thus, a response to coeval atmospheric CO2 decline and continental-scale Antarctic glaciation. Marine records indicate a greenhouse to icehouse climate transition at similar to 34 million years ago, but how the climate changed within continental interiors at this time is less well known. Here, the authors show an orbital climate response shift with aridification on the northeastern Tibetan Plateau during this time.
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| 2. |
- Pagani, Mark, et al.
(författare)
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The Role of Carbon Dioxide during the Onset of Antarctic Glaciation
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Earth’s modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted to environmental conditions that led to the glaciation of Antarctica ∼34 million years ago. Rapid Antarctic glacia- tion reflects a “tipping point” in Earth’s climate history and provides a target to investigate the contributing role of atmospheric carbon dioxide during climate change. For this study, we reconstruct CO2 trends using the alkenone- CO2 methodology, as well as changes in coccolithophore cell size, and show that CO2 declined just prior to-, and in association with, major Antarctic ice accumulation. We further show that CO2 estimates from Subantarctic and Antarctic sites do not reflect average atmospheric CO2 levels and yield spurious global CO2 trends if included in alkenone compilations. Substantial atmosphere-ocean CO2 disequilibrium evolved throughout the Southern Oceans, in conjunction with enhanced upwelling rates elsewhere, and potentially contributed to an apparent rise in atmospheric CO2 just prior to the CO2 decline associated with Antarctic glaciation. Our results imply high "Earth system" climate sensitivity to CO2, with sea-ice expansion and increased albedo playing an important role in enhancing global cooling.
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| 3. |
- Pagani, Mark, et al.
(författare)
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The Role of Carbon Dioxide During the Onset of Antarctic Glaciation
- 2011
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 334:6060, s. 1261-1264
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Tidskriftsartikel (refereegranskat)abstract
- Earth's modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation similar to 33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth's climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO(2)) during major climatic change. Previously published records of alkenone-based CO(2) from high-and low-latitude ocean localities suggested that CO(2) increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO(2) levels, biasing long-term trends. Our results show that CO(2) declined before and during Antarctic glaciation and support a substantial CO(2) decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO(2) thresholds.
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