Impact of atmospheric CO2 and Atlantic-Arctic gateway evolution on Miocene climate and ocean circulation changes

• Main Author: Hossain, Akil
• Other Authors: Jokat, Wilfried, Lohmann, Gerrit
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2022
• Subjects: Miocene Climate; atmospheric CO2; Atlantic-Arctic Gateway; Ocean circulation; Earth System Modelling; temperature and salinity change; Greenland-Scotland-Ridge; Fram Strait; Arctic Ocean; 550; 550 Earth sciences and geology; ddc:550; Arctic; Greenland; Southern Ocean; Atlantic Arctic; Atlantic-Arctic; Greenland-Scotland Ridge; Iceland; NADW; Nordic Seas; North Atlantic Deep Water; North Atlantic; Sea ice
• Online Access: https://media.suub.uni-bremen.de/handle/elib/6098; https://doi.org/10.26092/elib/1672; https://nbn-resolving.org/urn:nbn:de:gbv:46-elib60980

The Miocene (23.03–5.33 Ma) was a time period with a warmer climate than today. During this period, changes in ocean gateways and atmospheric CO2 levels largely control ocean circulation and climate changes. However, the underlying ocean processes and dynamics are poorly understood and it remains a challenge to simulate Miocene climate key characteristics such as pronounced polar warming and a reduced meridional temperature gradient. By applying state-of-the-art fully coupled atmosphere-ocean-sea-ice model approaches Miocene climate conditions at different atmospheric CO2 concentrations are simulated and thermohaline changes in response to the subsidence of Atlantic-Arctic gateways for various Greenland-Scotland Ridge (GSR) and Fram Strait (FS) configurations are investigated. For a singular subsidence of the GSR, warming and a salinity increase in the Nordic Seas and the Arctic Ocean is detected. 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 or widening 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 cause a negligible warming in the upwelling regions of the Southern Ocean. For a sill depth of ~1500 m, ventilation of the Arctic Ocean is achieved due to enhanced import of saline Atlantic water through a FS width of ~105 km. Moreover, at this width and depth, a modern-like three-layer stratification in the Arctic Ocean is detected. ...