scholarly journals Tropical seaways played a more important role than high latitude seaways in Cenozoic cooling

2011 ◽  
Vol 7 (3) ◽  
pp. 801-813 ◽  
Author(s):  
Z. Zhang ◽  
K. H. Nisancioglu ◽  
F. Flatøy ◽  
M. Bentsen ◽  
I. Bethke ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Drake Passage ◽  
Central American ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
The West ◽  
Early Eocene Climatic Optimum ◽  
Tectonic Events

Abstract. Following the Early Eocene climatic optimum (EECO, ~55–50 Ma), climate deteriorated and gradually changed the earth from a greenhouse into an icehouse, with major cooling events at the Eocene-Oligocene boundary (∼34 Ma) and the Middle Miocene (∼15 Ma). It is believed that the opening of the Drake Passage had a marked impact on the cooling at the Eocene-Oligocene boundary. Based on an Early Eocene simulation, we study the sensitivity of climate and ocean circulation to tectonic events such as the closing of the West Siberian Seaway, the deepening of the Arctic-Atlantic Seaway, the opening of the Drake Passage, and the constriction of the Tethys and Central American seaways. The opening of the Drake Passage, together with the closing of the West Siberian Seaway and the deepening of the Arctic-Atlantic Seaway, weakened the Southern Ocean Deep Water (SODW) dominated ocean circulation and led to a weak cooling at high latitudes, thus contributing to the observed Early Cenozoic cooling. However, the later constriction of the Tethys and Central American Seaways is shown to give a strong cooling at southern high latitudes. This cooling was related to the transition of ocean circulation from a SODW-dominated mode to the modern-like ocean circulation dominated by North Atlantic Deep Water (NADW).

scholarly journals Tropical seaways played a more important role than high latitude seaways in Cenozoic cooling

2011 ◽  
Vol 7 (2) ◽  
pp. 965-996 ◽  
Author(s):  
Z. Zhang ◽  
K. H. Nisancioglu ◽  
F. Flatøy ◽  
M. Bentsen ◽  
I. Bethke ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Drake Passage ◽  
Central American ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
The West ◽  
Early Eocene Climatic Optimum ◽  
Tectonic Events

Abstract. Following the Early Eocene climatic optimum (EECO, ~55–50 Ma), climate deteriorated and gradually changed the earth from a greenhouse into an icehouse, with major cooling events at the Eocene-Oligocene boundary (~34 Ma) and the Middle Miocene (~15 Ma). It is believed that the opening of the Drake Passage had a marked impact on the cooling at the Eocene-Oligocene boundary. Based on an Early Eocene simulation, we study the sensitivity of climate and ocean circulation to the tectonic events such as the closing of the West Siberian Seaway, the deepening of the Arctic-Atlantic Seaway, the opening of the Drake Passage, and the constriction of the Tethys and Central American seaways. The opening of the Drake Passage, together with the closing of the West Siberian Seaway, and the deepening of the Arctic-Atlantic Seaway, weakens the Southern Ocean Deep Water (SODW) dominated ocean circulation and leads to a weak cooling at high latitudes, thus contributing to the observed Early Cenozoic cooling. However, the later constriction of the Tethys and Central American Seaways is shown to give a strong cooling at southern high latitudes. This cooling is related to the transition of ocean circulation from a SODW-dominated mode to the modern-like ocean circulation dominated by North Atlantic Deep Water (NADW).

scholarly journals Paleobotanical proxies for early Eocene climates and ecosystems in northern North America from middle to high latitudes

2020 ◽  
Vol 16 (4) ◽  
pp. 1387-1410 ◽  
Author(s):  
Christopher K. West ◽  
David R. Greenwood ◽  
Tammo Reichgelt ◽  
Alexander J. Lowe ◽  
Janelle M. Vachon ◽  
...  
Keyword(s):  
North America ◽  
Climate Models ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
Early Eocene Climatic Optimum ◽  
Northern Half ◽  
Thermal Maximum ◽  
High Precipitation

Abstract. Early Eocene climates were globally warm, with ice-free conditions at both poles. Early Eocene polar landmasses supported extensive forest ecosystems of a primarily temperate biota but also with abundant thermophilic elements, such as crocodilians, and mesothermic taxodioid conifers and angiosperms. The globally warm early Eocene was punctuated by geologically brief hyperthermals such as the Paleocene–Eocene Thermal Maximum (PETM), culminating in the Early Eocene Climatic Optimum (EECO), during which the range of thermophilic plants such as palms extended into the Arctic. Climate models have struggled to reproduce early Eocene Arctic warm winters and high precipitation, with models invoking a variety of mechanisms, from atmospheric CO2 levels that are unsupported by proxy evidence to the role of an enhanced hydrological cycle, to reproduce winters that experienced no direct solar energy input yet remained wet and above freezing. Here, we provide new estimates of climate and compile existing paleobotanical proxy data for upland and lowland midlatitude sites in British Columbia, Canada, and northern Washington, USA, and from high-latitude lowland sites in Alaska and the Canadian Arctic to compare climatic regimes between the middle and high latitudes of the early Eocene – spanning the PETM to the EECO – in the northern half of North America. In addition, these data are used to reevaluate the latitudinal temperature gradient in North America during the early Eocene and to provide refined biome interpretations of these ancient forests based on climate and physiognomic data.

scholarly journals Paleobotanical proxies for early Eocene climates and ecosystems in northern North America from mid to high latitudes

2020 ◽  
Author(s):  
Christopher K. West ◽  
David R. Greenwood ◽  
Tammo Reichgelt ◽  
Alex J. Lowe ◽  
Janelle M. Vachon ◽  
...  
Keyword(s):  
North America ◽  
Climate Models ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
Early Eocene Climatic Optimum ◽  
Northern Half ◽  
Thermal Maximum ◽  
High Precipitation

Abstract. Early Eocene climates were globally warm, with ice-free conditions at both poles. Early Eocene polar landmasses supported extensive forest ecosystems of a primarily temperate biota, but also with abundant thermophilic elements such as crocodilians, and mesothermic taxodioid conifers and angiosperms. The globally warm early Eocene was punctuated by geologically brief hyperthermals such as the Paleocene-Eocene Thermal Maximum (PETM), culminating in the Early Eocene Climatic Optimum (EECO), during which the range of thermophilic plants such as palms extended into the Arctic. Climate models have struggled to reproduce early Eocene Arctic warm winters and high precipitation, with models invoking a variety of mechanisms, from atmospheric CO2 levels that are unsupported by proxy evidence, to the role of an enhanced hydrological cycle to reproduce winters that experienced no direct solar energy input yet remained wet and above freezing. Here, we provide new estimates of climate, and compile existing paleobotanical proxy data for upland and lowland mid-latitudes sites in British Columbia, Canada, and northern Washington, USA, and from high-latitude lowland sites in Alaska and the Canadian Arctic to compare climatic regimes between mid- and high latitudes of the early Eocene – spanning the PETM to the EECO – of the northern half of North America. In addition, these data are used to reevaluate the latitudinal temperate gradient in North America during the early Eocene, and to provide refined biome interpretations of these ancient forests based on climate and physiognomic data.

scholarly journals Paleocene-Eocene volcanic segmentation of the Norwegian-Greenland seaway reorganized high-latitude ocean circulation

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Jussi Hovikoski ◽  
Michael B. W. Fyhn ◽  
Henrik Nøhr-Hansen ◽  
John R. Hopper ◽  
Steven Andrews ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
High Latitude ◽  
Seismic Reflection ◽  
Arctic Region ◽  
Climatic Conditions ◽  
The Arctic ◽  
Early Eocene ◽  
Subaerial Exposure ◽  
Thermal Maximum ◽  
Volcanic Facies

AbstractThe paleoenvironmental and paleogeographic development of the Norwegian–Greenland seaway remains poorly understood, despite its importance for the oceanographic and climatic conditions of the Paleocene–Eocene greenhouse world. Here we present analyses of the sedimentological and paleontological characteristics of Paleocene–Eocene deposits (between 63 and 47 million years old) in northeast Greenland, and investigate key unconformities and volcanic facies observed through seismic reflection imaging in offshore basins. We identify Paleocene–Eocene uplift that culminated in widespread regression, volcanism, and subaerial exposure during the Ypresian. We reconstruct the paleogeography of the northeast Atlantic–Arctic region and propose that this uplift led to fragmentation of the Norwegian–Greenland seaway during this period. We suggest that the seaway became severely restricted between about 56 and 53 million years ago, effectively isolating the Arctic from the Atlantic ocean during the Paleocene–Eocene thermal maximum and the early Eocene.

scholarly journals Influence of the Central American Seaway and Drake Passage on ocean circulation and neodymium isotopes: A model study

2014 ◽  
Vol 29 (12) ◽  
pp. 1214-1237 ◽  
Author(s):  
Patrik L. Pfister ◽  
Thomas F. Stocker ◽  
Johannes Rempfer ◽  
Stefan P. Ritz
Keyword(s):  
Ocean Circulation ◽  
Drake Passage ◽  
Central American ◽  
Neodymium Isotopes ◽  
Model Study ◽  
Central American Seaway

scholarly journals North Atlantic deep water formation and AMOC in CMIP5 models

Ocean Science ◽  
2017 ◽  
Vol 13 (4) ◽  
pp. 609-622 ◽  
Author(s):  
Céline Heuzé
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Deep Water ◽  
Deep Convection ◽  
The Arctic ◽  
Subpolar Gyre ◽  
Deep Water Formation ◽  
Nordic Seas ◽  
Water Formation

Abstract. Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turn, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecasting Arctic oceanic warming and its consequences for the global ocean circulation, cryosphere and marine life.

scholarly journals Inter-hemispheric seasonal comparison of Polar Amplification using radiative forcing of quadrupling CO<sub>2</sub> experiment

2019 ◽  
Author(s):  
Fernanda Casagrande ◽  
Ronald Buss de Souza ◽  
Paulo Nobre ◽  
Andre Lanfer Marquez
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Models ◽  
Initial Conditions ◽  
The Arctic ◽  
Climate Simulation ◽  
Polar Regions ◽  
High Latitudes ◽  
Polar Amplification

Abstract. The numerical climate simulation from Brazilian Earth System Model (BESM) are used here to investigate the response of Polar Regions to a forced increase of CO2 (Abrupt-4xCO2) and compared with Coupled Model Intercomparison Project 5 (CMIP5) simulations. Polar Regions are described as the most climatically sensitive areas of the globe, with an enhanced warming occurring during the cold seasons. The asymmetry between the two poles is related to the thermal inertia and the coupled ocean atmosphere processes involved. While in the northern high latitudes the amplified warming signal is associated to a positive snow and sea ice albedo feedback, for southern high latitudes the warming is related to a combination of ozone depletion and changes in the winds pattern. The numerical experiments conducted here demonstrated a very clear evidence of seasonality in the polar amplification response. In winter, for the northern high latitudes (southern high latitudes) the range of simulated polar warming varied from 15 K to 30 K (2.6 K to 10 K). In summer, for northern high latitudes (southern high latitudes) the simulated warming varies from 3 K to 15 K (3 K to 7 K). The vertical profiles of air temperature indicated stronger warming at surface, particularly for the Arctic region, suggesting that the albedo-sea ice feedback overlaps with the warming caused by meridional transport of heat in atmosphere. The latitude of the maximum warming was inversely correlated with changes in the sea ice within the model’s control run. Three climate models were identified as having high polar amplification for cold season in both poles: MIROC-ESM, BESM-OA V2.5 and GFDL-ESM2M. We suggest that the large BIAS found between models can be related to the differences in each model to represent the feedback process and also as a consequence of the distinct sea ice initial conditions of each model. The polar amplification phenomenon has been observed previously and is expected to become stronger in coming decades. The consequences for the atmospheric and ocean circulation are still subject to intense debate in the scientific community.

scholarly journals Early Eocene vigorous ocean overturning and its contribution to a warm Southern Ocean

2020 ◽  
Author(s):  
Yurui Zhang ◽  
Thierry Huck ◽  
Camille Lique ◽  
Yannick Donnadieu ◽  
Jean-Baptiste Ladant ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Heat Transport ◽  
Southern Hemisphere ◽  
Ocean Circulation ◽  
Deep Water ◽  
Atmospheric Co2 ◽  
Early Eocene ◽  
Deep Water Formation ◽  
Overturning Circulation ◽  
Water Formation

Abstract. The early Eocene (~ 55 Ma) is the warmest period, and most likely characterized by the highest atmospheric CO2 concentrations, of the Cenozoic era. Here, we analyze simulations of the early Eocene performed with the IPSL-CM5A2 coupled climate model set up with paleogeographic reconstructions of this period from the DeepMIP project, with different levels of atmospheric CO2, and compare them with simulations of the modern conditions. This allows us to explore the changes of the ocean circulation and the resulting ocean meridional heat transport. At a CO2 level of 840 ppm, the Early Eocene simulation is characterized by a strong abyssal overturning circulation in the Southern Hemisphere (40 Sv at 60º S), fed by deep water formation in the three sectors of the Southern Ocean. Deep convection in the Southern Ocean is favored by the closed Drake and Tasmanian passages, which provide western boundaries for the build-up of strong subpolar gyres in the Weddell and Ross seas, in the middle of which convection develops. The strong overturning circulation, associated with the subpolar gyres, sustains the poleward advection of saline subtropical water to the convective region in the Southern Ocean, maintaining deep-water formation. This salt-advection feedback mechanism works similarly in the present-day North Atlantic overturning circulation. The strong abyssal overturning circulation in the 55 Ma simulations primarily results in an enhanced poleward ocean heat transport by 0.3–0.7 PW in the Southern Hemisphere compared to modern conditions, reaching 1.7 PW southward at 20° S, and contributing to maintain the Southern Ocean and Antarctica warm in the Eocene. Simulations with different atmospheric CO2 levels show that the ocean circulation and heat transport are relatively insensitive to CO2-doubling.

scholarly journals An inter-hemispheric seasonal comparison of polar amplification using radiative forcing of a quadrupling CO<sub>2</sub> experiment

2020 ◽  
Vol 38 (5) ◽  
pp. 1123-1138
Author(s):  
Fernanda Casagrande ◽  
Ronald Buss de Souza ◽  
Paulo Nobre ◽  
Andre Lanfer Marquez
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Models ◽  
Cold Season ◽  
Coupled Processes ◽  
The Arctic ◽  
Polar Regions ◽  
High Latitudes ◽  
Polar Amplification

Abstract. The numerical climate simulations from the Brazilian Earth System Model (BESM) are used here to investigate the response of the polar regions to a forced increase in CO2 (Abrupt-4×CO2) and compared with Coupled Model Intercomparison Project phase 5 (CMIP5) and 6 (CMIP6) simulations. The main objective here is to investigate the seasonality of the surface and vertical warming as well as the coupled processes underlying the polar amplification, such as changes in sea ice cover. Polar regions are described as the most climatically sensitive areas of the globe, with an enhanced warming occurring during the cold seasons. The asymmetry between the two poles is related to the thermal inertia and the coupled ocean–atmosphere processes involved. While at the northern high latitudes the amplified warming signal is associated with a positive snow– and sea ice–albedo feedback, for southern high latitudes the warming is related to a combination of ozone depletion and changes in the wind pattern. The numerical experiments conducted here demonstrated very clear evidence of seasonality in the polar amplification response as well as linkage with sea ice changes. In winter, for the northern high latitudes (southern high latitudes), the range of simulated polar warming varied from 10 to 39 K (−0.5 to 13 K). In summer, for northern high latitudes (southern high latitudes), the simulated warming varies from 0 to 23 K (0.5 to 14 K). The vertical profiles of air temperature indicated stronger warming at the surface, particularly for the Arctic region, suggesting that the albedo–sea ice feedback overlaps with the warming caused by meridional transport of heat in the atmosphere. The latitude of the maximum warming was inversely correlated with changes in the sea ice within the model's control run. Three climate models were identified as having high polar amplification for the Arctic cold season (DJF): IPSL-CM6A-LR (CMIP6), HadGEM2-ES (CMIP5) and CanESM5 (CMIP6). For the Antarctic, in the cold season (JJA), the climate models identified as having high polar amplification were IPSL-CM6A-LR (CMIP6), CanESM5(CMIP6) and FGOALS-s2 (CMIP5). The large decrease in sea ice concentration is more evident in models with great polar amplification and for the same range of latitude (75–90∘ N). Also, we found, for models with enhanced warming, expressive changes in the sea ice annual amplitude with outstanding ice-free conditions from May to December (EC-Earth3-Veg) and June to December (HadGEM2-ES). We suggest that the large bias found among models can be related to the differences in each model to represent the feedback process and also as a consequence of each distinct sea ice initial condition. The polar amplification phenomenon has been observed previously and is expected to become stronger in the coming decades. The consequences for the atmospheric and ocean circulation are still subject to intense debate in the scientific community.

scholarly journals Thermohaline Fingerprints of the Greenland-Scotland Ridge and Fram Strait Subsidence Histories

2020 ◽  
Author(s):  
Akil Hossain ◽  
Gregor Knorr ◽  
Gerrit Lohmann ◽  
Michael Stärz ◽  
Wilfried Jokat
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
North Atlantic Deep Water ◽  
The Arctic ◽  
Fram Strait ◽  
High Latitudes ◽  
Nordic Seas ◽  
Basin Scale ◽  
Salinity Increase

&lt;p&gt; &lt;span&gt;&lt;span&gt;Changes in ocean gateway configuration are known to induce basin-scale rearrangements in ocean characteristics throughout the Cenozoic. &lt;/span&gt;&lt;span&gt;However, there is large uncertainty in the relative timing of the &lt;/span&gt;&lt;span&gt;subsidence histories of ocean gateways in the northern high latitudes. By using a fully coupled General Circulation &lt;/span&gt;&lt;span&gt;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. &lt;/span&gt;&lt;span&gt;Deepening of the Greenland-Scotland Ridge &lt;/span&gt;&lt;span&gt;causes a salinity increase and warming in the Nordic Seas and the Arctic Ocean. &lt;/span&gt;&lt;span&gt;While warming this realm, deep water formation takes place at lower temperatures due to a shift of the convection sites to north off Iceland. &lt;/span&gt;&lt;span&gt;The associated deep ocean cooling and &lt;/span&gt;&lt;span&gt;upwelling of deep waters to the Southern Ocean surface causes a cooling in the southern high latitudes.&lt;/span&gt; &lt;span&gt;These characteristic impacts in response to the &lt;/span&gt;&lt;span&gt;Greenland-Scotland Ridge&lt;/span&gt;&lt;span&gt; deepening are independent of the &lt;/span&gt;&lt;span&gt;Fram Strait&lt;/span&gt;&lt;span&gt; state.&lt;/span&gt; &lt;span&gt;Subsidence of the Fram Strait for a deep Greenland-Scotland Ridge causes &lt;/span&gt;&lt;span&gt;less pronounced warming and salinity increase&lt;/span&gt;&lt;span&gt; in &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;Nordic Seas. &lt;/span&gt;&lt;span&gt;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 &lt;/span&gt;&lt;span&gt;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 &lt;/span&gt;&lt;span&gt;warming in the upwelling regions of the Southern Ocean.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

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