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  • Miocene  (2)
  • Arctic Ocean circulation  (1)
  • English  (3)
  • 1
    Publication Date: 2023-11-23
    Description: Based on inferences from proxy records the Miocene (23.03–5.33 Ma) was a time of amplified polar warmth compared to today. However, it remains a challenge to simulate a warm Miocene climate and pronounced polar warmth at reconstructed Miocene CO〈sub〉2〈/sub〉 concentrations. Using a state‐of‐the‐art Earth‐System‐Model, we implement a high‐resolution paleobathymetry and simulate Miocene climate at different atmospheric CO〈sub〉2〈/sub〉 concentrations. We estimate global mean surface warming of +3.1°C relative to the preindustrial at a CO〈sub〉2〈/sub〉 level of 450 ppm. An increase of atmospheric CO〈sub〉2〈/sub〉 from 280 to 450 ppm provides an individual warming of ∼1.4°C, which is as strong as all other Miocene forcing contributions combined. Substantial changes in surface albedo are vital to explain Miocene surface warming. Simulated surface temperatures fit well with proxy reconstructions at low‐ to mid‐latitudes. The high latitude cooling bias becomes less pronounced for higher atmospheric CO〈sub〉2〈/sub〉 concentrations. At such CO〈sub〉2〈/sub〉 levels simulated Miocene climate shows a reduced polar amplification, linked to a breakdown of seasonality in the Arctic Ocean. A pronounced warming in boreal fall is detected for a CO〈sub〉2〈/sub〉 increase from 280 to 450 ppm, in comparison to weaker warming for CO〈sub〉2〈/sub〉 changes from 450 to 720 ppm. Moreover, a pronounced warming in winter is detected for a CO〈sub〉2〈/sub〉 increase from 450 to 720 ppm, in contrast to a moderate summer temperature increase, which is accompanied by a strong sea‐ice concentration decline that promotes cloud formation in summer via enhanced moisture availability. As a consequence planetary albedo increases and dampens the temperature response to CO〈sub〉2〈/sub〉 forcing at a warmer Miocene background climate.
    Description: Key Points: At a CO〈sub〉2〈/sub〉 level of 450 ppm, a Miocene simulation shows a global mean surface warming of +3.1°C relative to the preindustrial state. Atmospheric CO〈sub〉2〈/sub〉 increase from 280 to 450 ppm causes a warming of ∼1.4°C, which is as strong as all other forcing factors combined. At higher atmospheric CO〈sub〉2〈/sub〉 levels, the Miocene climate shows a reduced polar amplification linked to a breakdown of seasonality in the Arctic.
    Description: Alfred Wegener Institute
    Description: Helmholtz Centre for Polar and Marine Research
    Description: https://doi.org/10.1594/PANGAEA.943430
    Description: https://github.com/FESOM/fesom2/
    Description: https://mpimet.mpg.de/en/science/modeling-with-icon/code-avilability
    Keywords: atmospheric CO2 ; Miocene ; Miocene temperature change ; polar amplification ; climate modeling ; Miocene bathymetry
    Language: English
    Type: doc-type:article
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  • 2
    Publication Date: 2021-10-01
    Description: A regional seismic survey on the southeastern Lomonosov Ridge (LR) and adjacent basins provides constraints on the coupled evolution of ocean circulations, depositional regime, and tectonic processes. First, Mesozoic strata on the LR, its faulted flanks and the initial Amundsen Basin were covered with syn-rift sediments of Paleocene to early Eocene age. Numerous vertical faults indicate differential compaction of possibly anoxic sediments deposited in the young, still isolated Eurasian Basin. The second stage, as indicated by a prominent high-amplitude-reflector sequence covering the ridge, was a time of widespread changes in deposition conditions, likely controlled by the ongoing subsidence of the LR and gradual opening of the Fram Strait. Episodic incursions of water masses from the North Atlantic probably were the consequences and led to the deposition of thin sedimentary layers of different lithology. The third stage is marked by continuous deposition since the early Miocene (20 Ma). At that time, the ridge no longer posed an obstacle between the Amerasia and Eurasia Basins and pelagic sedimentation was established. Drift bodies, sediment waves, and erosional structures indicate the onset of circulation. Faulting on the ridge slope has led to a series of terraces where sediment drifts have accumulated since the early Miocene. It is suggested that ongoing sagging of the ridge and currents may have shaped the steep sediment free flanks of the terraces. Lastly, a sequence of high-amplitude reflectors marks the transition to the early Pliocene large-scale Northern Hemisphere glaciations.
    Keywords: 551.46 ; 622.15 ; Amundsen Basin ; Arctic Ocean ; Arctic Ocean circulation ; Lomonosov Ridge ; Marine Seismics ; Seismostratigraphy
    Language: English
    Type: map
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  • 3
    Publication Date: 2021-10-25
    Description: Changes in ocean gateway configuration can induce basin-scale rearrangements in ocean current characteristics. However, there is large uncertainty in the relative timing of the Oligocene/Miocene subsidence histories of the Greenland-Scotland Ridge (GSR) and the Fram Strait (FS). By using a climate model, we investigate the temperature and salinity changes in response to the subsidence of these two key ocean gateways during early to middle Miocene. For a singular subsidence of the GSR, we detect warming and a salinity increase in the Nordic Seas and the Arctic Ocean. As convection sites shift to the north of Iceland, North Atlantic Deep Water (NADW) is formed at cooler temperatures. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface can cause a cooling in the southern high latitudes. These characteristic responses to the GSR deepening are independent of the FS being shallow or deep. An isolated subsidence of the FS gateway for a deep GSR shows less pronounced warming and salinity increase in the Nordic Seas. Arctic temperatures remain unaltered, but a stronger salinity increase is detected, which further increases the density of NADW. The increase in salinity enhances the contribution of NADW to the abyssal ocean at the expense of the colder southern source water component. These relative changes largely counteract each other and cause a negligible warming in the upwelling regions of the Southern Ocean.
    Keywords: 551.46 ; Gateway subsidence ; Miocene ; Fingerprints ; Greenland-Scotland Ridge ; Fram Strait ; Temperature and salinity change
    Language: English
    Type: map
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