ALBERT

Description: Herein, we publish the simulated global annual mean temperature (THO), salinity (SAO), ice compactness (SICOMO), Atlantic Meridional Overturning Circulation (AMOC), Global Meridional Overturning Circulation (GMOC), zonal velocity (UKO), meridional velocity (VKE), 10m u-velocity (u10), 10m v-velocity (v10), mixed layer depth (zmld), horizontal barotropic streamfunction (PSIUWE) and sealevel (ZO) over a time period of 100 years retrieved from equilibrium climate simulations for the Miocene (~23-15 Ma) and use different Greenland-Scotland Ridge (GSR) and Fram Strait (FS) sill depths as a representative for different tectonic settings that occur during the subsidence interval and utilized in the publication by Hossain et al. (2020). The climate data has been produced with COSMOS (ECHAM5/JSBACH/MPIOM/OASIS3), utilized at a resolution of T31 in the atmosphere (19 hybrid sigma-pressure levels) and a resolution of GR30 (bipolar orthogonal curvilinear grid, formal resolution of ~3.0°x1.8°) in the ocean (40 z-coordinate levels). The model setup refers to boundary conditions (incl. changes in orography, bathymetry, physical land surface characteristics, ice sheets, atmospheric CO2) representative for the Miocene. Details on setup and identifiers of Miocene model simulations can be found in Table 1 and Supplementary Table 1 of Hossain et al., 2020.

Description: Herein, we publish the simulated global annual mean sea surface temperature (THO), surface air temperature (SAT) over a time period of 100 years retrieved from equilibrium climate simulations for the Last Glacial Maximum (~21 ka BP). We investigate the range of temperature variability that occurs in response to uncertainties in the boundary conditions of Laurentide ice sheet (LIS). We performed LGM simulations, applying six different LIS reconstructions (ICE-6g, GLAC-1a, ANU, Gowan, Licciardi and PMIP3) in a fully coupled atmosphere-ocean-sea-ice model. The model data has been used in the publication by Hossain et al., 2021. The climate data has been produced with Consortium for Small-scale Modeling (COSMOS; ECHAM5/JSBACH/MPIOM/OASIS3), utilized at a resolution of T31 in the atmosphere with 19 vertical layers and a resolution of GR30 (~3.0°x1.8°) in the ocean with 40 vertical layers. The model setup refers to boundary conditions (terrestrial topography, ocean bathymetry), greenhouse gas concentrations (CO2 = 185 ppm; CH4 = 350 ppb; N2O = 200 ppb) and orbital forcing representative for the LGM and are imposed in accordance with the PMIP3 protocol. We also run COSMOS using PI boundary conditions (ice-sheet topography, orbital forcing, greenhouse gas concentrations and ocean bathymetry). Details on setup and identifiers of LGM model simulations can be found in Table S1 of Hossain et al., 2021.

Description: Herein, we publish the simulated global annual mean surface air temperature (SAT), sea surface temperature (SST), sea surface salinity (SSS), sea ice cover (seaice), surface albedo (albedo) and total cloud cover (aclcov) over a time period of 100 years retrieved from equilibrium climate simulations for the Middle Miocene and Preindustrial. We simulate Miocene and Preindustrial climate states at different atmospheric CO2 concentrations. The model data has been used in the publication by Hossain et al., 2022. The climate data has been produced with AWI Earth System Model (AWI-ESM2.1; ECHAM6/JSBACH/MPIOM2/ OASIS3‐MCT), utilized at a spectral resolution of T63 (~1.88° x 1.88°) in the atmosphere with 47 vertical layers. FESOM2 uses the COREII mesh. The Miocene model setup is based on the combined high-resolution (0.1° x 0.1°) global bathymetry and topography (Middle Miocene; ~14 Ma) of Paxman et al. (2019), Hochmuth et al. (2020) and Straume et al. (2020). The model setup refers to boundary conditions (incl. changes in orography, bathymetry, physical land surface characteristics, ice sheets, atmospheric CO2) representative for the Miocene and Preindustrial. Details on setup and identifiers of Miocene and Preindustrial model simulations can be found in Table 1 of Hossain et al., 2022.

Description: Herein, we publish the simulated global annual mean sea surface salinity (SAO), sea surface temperature (THO), ice compactness (SICOMO), zonal velocity (UKO), meridional velocity (VKE) and Atlantic Meridional Overturning Circulation (AMOC) over a time period of 100 years retrieved from equilibrium climate simulations for the Miocene (~23-15 Ma). We investigate the sensitivity of stratification in the Arctic Ocean to the widening of Fram Strait (FS) and different levels of atmospheric CO2 concentrations. The model data has been used in the publication by Hossain et al., 2020. The climate data has been produced with COSMOS (ECHAM5/JSBACH/MPIOM/OASIS3), utilized at a resolution of T31 in the atmosphere with 19 vertical layers and a resolution of GR30 (~3.0°x1.8°) in the ocean with 40 vertical layers. The model setup refers to boundary conditions (incl. changes in orography, bathymetry, physical land surface characteristics, ice sheets, atmospheric CO2) representative for the Miocene. Details on setup and identifiers of Miocene model simulations can be found in Table 1 of Hossain et al., 2020.

Description: We present climate model output for various atmosphere and ocean quantities that illustrate the impact of three different types of forcing on global climate characteristics during mid-Pliocene (~3.3 - 3.0 Million years before present, Ma BP) and early to Mid-Miocene (~23-15 Ma BP): -geography, including setups for modern, mid-Pliocene, and early to Mid-Miocene -carbon dioxide, ranging from Pre-Industrial (280 parts per million by volume, ppmv) to 840 ppmv -strength of ocean mixing via enhancement of respective mixing parameters, ranging from the unperturbed state to mild (five times), intermediate (ten times), and strong (twenty-fife times) enhancement of vertical mixing. The data provided with this data publication has been employed by the authors in the manuscript "Effects of CO2 and ocean mixing on Miocene and Pliocene temperature gradients" (revised for publication in the journal Paleoceanography and Paleoclimatology, special issue "The Miocene: The Future of the Past") for a comparative study of the effects of carbon dioxide and ocean mixing on various climate characteristics. Here we provide all climate output that has been employed towards creating analyses presented in that publication. Data is provided at the resolution employed for generating analyses for the manuscript. Atmosphere model output provided at native model resolution (T31, ~3.75°x3.75° horizontally). Ocean output provided at a regular grid (the native grid of the ocean model is curvilinear with a formal resolution of 3.0°x1.8° horizontally). Sea ice cover provided at a resolution of 1.0°x1.0°. Zonal mean of ocean potential temperature over all model levels provided at a latitudinal resolution of 1°, vertically discretized on native ocean model levels (40 pressure levels of non-linear spacing). Depth of the ocean mixed layer, sea surface temperature, and total heat flux across the atmosphere ocean interface given at resolutions of 0.5°x0.5° resolution. Data at higher resolutions is provided towards retaining more details of the coastlines and of ocean gateway regions.

Description: Over the Last Glacial Maximum (LGM, ~21ka BP), the presence of vast Northern Hemisphere ice-sheets caused abrupt changes in surface topography and background climatic state. While the ice-sheet extent is well known, several conflicting ice-sheet topography reconstructions suggest that there is uncertainty in this boundary condition. The terrestrial and sea surface temperature (SST) of the LGM as simulated with six different Laurentide Ice Sheet (LIS) reconstructions in a fully coupled Earth System Model (COSMOS) have been compared with the subfossil pollen and plant macrofossil based and marine temperature proxies reconstruction. The terrestrial reconstruction shows a similar pattern and in good agreement with model data. The SST proxy dataset comprises a global compilation of planktonic foraminifera, diatoms, radiolarian, dinocyst, alkenones and planktonic foraminifera Mg/Ca-derived SST estimates. Significant mismatches between modeled and reconstructed SST have been observed. Among the six LIS reconstructions, Tarasov’s LIS reconstruction shows the highest correlation with reconstructed terrestrial and SST. In the case of radiolarian, Mg/Ca, diatoms and foraminifera show a positive correlation while dinocyst and alkenones show very low and negative correlation with the model. Dinocyst-based SST records are much warmer than reconstructed by other proxies as well as Pre-industrial (PI) temperature. However, there are large discrepancies between model temperatures and temperature recorded by different proxies. Eight different PMIP3 models also compared with temperature proxies reconstruction which show mismatches with the proxy records might be due to misinterpreted and/or biased proxy records. Therefore, it has been speculated that considering different habitat depths and growing seasons of the planktonic organisms used for SST reconstruction could provide a better agreement of proxy data with model results on a regional scale. Moreover, it can reduce model-data misfits. It is found that shifting in the habitat depth and living season can remove parts of the observed model-data mismatches in SST anomalies.

Description: Changes in ocean gateway configuration are known to induce basin-scale rearrangements in ocean characteristics throughout the Cenozoic. However, there is large uncertainty in the relative timing of the subsidence histories of ocean gateways in the northern high latitudes. By using a fully coupled General Circulation Model we investigate the salinity and temperature changes in response to the subsidence of two key ocean gateways in the northern high latitudes during early to middle Miocene. Deepening of the Greenland-Scotland Ridge causes a salinity increase and warming in the Nordic Seas and the Arctic Ocean. While warming this realm, deep water formation takes place at lower temperatures due to a shift of the convection sites to north off Iceland. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface causes a cooling in the southern high latitudes. These characteristic impacts in response to the Greenland-Scotland Ridge deepening are independent of the Fram Strait state. Subsidence of the Fram Strait for a deep Greenland-Scotland Ridge causes less pronounced warming and salinity increase in the Nordic Seas. A stronger salinity increase is detected in the Arctic while temperatures remain unaltered, which further increases the density of the North Atlantic Deep Water. This causes an enhanced contribution of North Atlantic Deep Water to the abyssal ocean and on the expense of the colder southern source water component. These relative changes largely counteract each other and cause little warming in the upwelling regions of the Southern Ocean.

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.

Description: The tectonic opening of the Fram Strait (FS) was critical to the water exchange between the Atlantic Ocean and the Arctic Ocean, and caused the transition from a restricted to a ventilated Arctic Ocean during early Miocene. If and how the water exchange between the Arctic Ocean and the North Atlantic influenced the global current system is still disputed. We apply a fully coupled atmosphere–ocean–sea-ice model to investigate stratification and ocean circulation in the Arctic Ocean in response to the opening of the FS during early-to-middle Miocene. Progressive widening of the FS gateway in our simulation causes a moderate warming, while salinity conditions in the Nordic Seas remain similar. On the contrary, with increasing FS width, Arctic temperatures remain unchanged and salinity changes appear to steadily become stronger. For a sill depth of ~ 1500 m, we achieve ventilation of the Arctic Ocean due to enhanced import of saline Atlantic water through an FS width of ~ 105 km. Moreover, at this width and depth, we detect a modern-like three-layer stratification in the Arctic Ocean. The exchange flow through FS is characterized by vertical separation of a low-salinity cold outflow from the Arctic Ocean confined to a thin upper layer, an intermediate saline inflow from the Atlantic Ocean below, and a cold bottom Arctic outflow. Using a significantly shallower and narrower FS during the early Miocene, our study suggests that the ventilation mechanisms and stratification in the Arctic Ocean are comparable to the present-day characteristics.