scholarly journals The role of East-Tethys seaway closure in the middle Miocene climatic transition (ca. 14 Ma)

2013 ◽  
Vol 9 (2) ◽  
pp. 2115-2152
Author(s):  
N. Hamon ◽  
P. Sepulchre ◽  
V. Lefebvre ◽  
G. Ramstein
Keyword(s):  
Middle Miocene ◽  
Ice Sheet ◽  
Circulation Model ◽  
Water Source ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
Climatic Transition ◽  
The Impact ◽  
Final Closure ◽  
Middle Miocene Climatic Transition

Abstract. The middle Miocene climatic transition (MMCT, approximately 14 Ma) is a key period in Cenozoic cooling and cryospheric expansion. Despite it is well documented in isotopic record, the causes of the MMCT are still a matter of debate. Among various hypotheses, some authors suggested that it was linked with the final closure of the East-Tethys seaway and subsequent oceanic circulation reorganisation. The aim of the present study is to quantify the impact of varying East-Tethys seaway depths on middle Miocene ocean and climate, in order to better understand its role in the MMCT. We present four sensitivity experiments with a fully coupled ocean-atmosphere generalized circulation model. Our results indicate the presence of a warm and salty water source in the northern Indian Ocean when the East-Tethys is deep-open (4000 or 1000 m), which corresponds to the Tethyan Indian Saline Water (TISW) described on the basis of isotopic studies. This water source is absent in the experiments with shallow (250 m) and closed East-Tethys, inducing strong changes in the latitudinal density gradient and ultimately the reinforcement of the Antarctic Circumpolar Current (ACC). Moreover, when the East-Tethys seaway is shallow or closed, there is a westward water flow in the Gibraltar Strait that strengthens the Atlantic meridional overturning circulation (AMOC) compared to the experiments with deep-open East-Tethys. Our results therefore suggest that the shoaling and final closure of the East-Tethys seaway played a major role in the oceanic circulation reorganisation during the middle Miocene. The results presented here provide new constraints on the timing of the East-Tethys seaway closure, and particularly indicate that, prior to 14 Ma, a deep-open East-Tethys should have allow the formation of TISW. Moreover, whereas the final closure of this seaway likely played a major role in the MMCT, we suggest that it was not the only driver of the global cooling and Antarctica ice sheet growth. Here, we propose that the initiation of the MMCT may have been an atmospheric pCO2 drawdown and that the oceanic Changes due to the East-Tethys seaway closure amplified the response of global climate and East-Antarctic Ice Sheet.

scholarly journals The role of eastern Tethys seaway closure in the Middle Miocene Climatic Transition (ca. 14 Ma)

2013 ◽  
Vol 9 (6) ◽  
pp. 2687-2702 ◽  
Author(s):  
N. Hamon ◽  
P. Sepulchre ◽  
V. Lefebvre ◽  
G. Ramstein
Keyword(s):  
General Circulation ◽  
Middle Miocene ◽  
Ice Sheet ◽  
Water Source ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
Climatic Transition ◽  
The Impact ◽  
Final Closure ◽  
Middle Miocene Climatic Transition

Abstract. The Middle Miocene Climatic Transition (MMCT, approximately 14 Ma) is a key period in Cenozoic cooling and cryospheric expansion. Despite being well documented in isotopic record, the causes of the MMCT are still a matter of debate. Among various hypotheses, some authors suggested that it was due the final closure of the eastern Tethys seaway and subsequent oceanic circulation reorganisation. The aim of the present study is to quantify the impact of varying Tethys seaway depths on middle Miocene ocean and climate, in order to better understand its role in the MMCT. We present four sensitivity experiments with a fully coupled ocean-atmosphere general circulation model. Our results indicate the presence of a warm and salty water source in the northern Indian Ocean when the eastern Tethys is deep open (4000 or 1000 m), which corresponds to the Tethyan Indian Saline Water (TISW) described on the basis of isotopic studies. This water source is absent in the experiments with shallow (250 m) and closed Tethys seaway, inducing strong changes in the latitudinal density gradient and ultimately the reinforcement of the Antarctic Circumpolar Current (ACC). Moreover, when the Tethys seaway is shallow or closed, there is a westward water flow in the Gibraltar Strait that strengthens the Atlantic Meridional Overturning Circulation (AMOC) compared to the experiments with deep-open Tethys seaway. Our results therefore suggest that the shoaling and final closure of the eastern Tethys seaway played a major role in the oceanic circulation reorganisation during the middle Miocene. The results presented here provide new constraints on the timing of the Tethys seaway closure and particularly indicate that, prior to 14 Ma, a deep-open Tethys seaway should have allowed the formation of TISW. Moreover, whereas the final closure of this seaway likely played a major role in the reorganisation of oceanic circulation, we suggest that it was not the main driver of the global cooling and Antarctica ice-sheet expansion during the MMCT. Here we propose that the initiation of the MMCT was caused by an atmospheric pCO2 drawdown and that the oceanic changes due to the Tethys seaway closure amplified the response of global climate and East Antarctic Ice Sheet.

scholarly journals Assessing the impact of Laurentide Ice Sheet topography on glacial climate

2014 ◽  
Vol 10 (2) ◽  
pp. 487-507 ◽  
Author(s):  
D. J. Ullman ◽  
A. N. LeGrande ◽  
A. E. Carlson ◽  
F. S. Anslow ◽  
J. M. Licciardi
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Ice Sheet ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Laurentide Ice Sheet ◽  
Global Circulation Model ◽  
Northeastern Asia ◽  
The Impact ◽  
Ice Sheet Topography

Abstract. Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets caused profound changes in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotope-enabled fully coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition. We present this comparison at two equilibrium time slices: the LGM, when differences in ice-sheet topography are maximized, and 14 ka, when differences in maximum ice-sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic Meridional Overturning Circulation and warmer surface air temperatures, particularly over northeastern Asia and the North Pacific. These up- and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over northeastern Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may significantly impact the results of paleoclimate simulations and their ability to successfully simulate past climates, with implications for estimating climate sensitivity to greenhouse gas forcing utilizing past climate states.

scholarly journals Assessing the impact of Laurentide Ice-Sheet topography on glacial climate

2013 ◽  
Vol 9 (3) ◽  
pp. 3239-3306 ◽  
Author(s):  
D. J. Ullman ◽  
A. N. LeGrande ◽  
A. E. Carlson ◽  
F. S. Anslow ◽  
J. M. Licciardi
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Northeast Asia ◽  
Ice Sheet ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Laurentide Ice Sheet ◽  
Global Circulation Model ◽  
The Impact ◽  
Ice Sheet Topography

Abstract. Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets provides a profound change in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotope-enabled fully-coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition. We present this comparison at two equilibrium time slices: the LGM, where differences in ice sheet topography are maximized, and 14 ka, where differences in maximum ice sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic meridional overturning circulation and warmer surface air temperatures, particularly over Northeast Asia and the North Pacific. These up and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over Northeast Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may greatly impact the results of paleoclimate simulations and their ability to successfully simulate past climates, with implications for estimating climate sensitivity to greenhouse gas forcing utilizing past climate states.

Tracking ice-sheet dynamics by detrital feldspar Pb-isotope and 87Rb/87Sr dating during the Middle Miocene Climatic Transition, Weddell Sea, Antarctica

2021 ◽  
Author(s):  
Roland Neofitu ◽  
Chris Mark ◽  
Suzanne O'Connell ◽  
Samuel Kelley ◽  
Delia Rösel ◽  
...  
Keyword(s):  
Deep Sea ◽  
Middle Miocene ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Provenance Analysis ◽  
Pb Isotope ◽  
Iceberg Calving ◽  
Climatic Transition ◽  
The Antarctic ◽  
Middle Miocene Climatic Transition

<p>Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ<sup>18</sup>O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT will be an important tool for forecasting effects of anthropogenic climate change.</p><p>Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (Kfs only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), combining in-situ Sr-isotope fingerprinting with <sup>87</sup>Rb/<sup>87</sup>Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, which was recovered from the Weddell Sea; as this is located ca. 750 km from the continental rise, in 4671.3 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14 to 14.4 Ma.</p><p>We discuss the implications of our results in terms of location of active iceberg calving sites and further consider the viability of our multi-proxy provenance approach to the Antarctic offshore.</p><p>Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).</p><p>Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.</p><p>Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.</p>

scholarly journals Does a difference in ice sheets between Marine Isotope Stages 3 and 5a affect the duration of stadials?

2021 ◽  
Author(s):  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Akira Oka ◽  
Takahito Mitsui ◽  
Fuyuki Saito
Keyword(s):  
Sea Ice ◽  
Recovery Time ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Surface Cooling ◽  
Glacial Ice ◽  
Formation Region ◽  
Background Climate ◽  
The Impact

Abstract. Glacial periods undergo frequent climate shifts between warm interstadials and cold stadials on a millennial time-scale. Recent studies have shown that the duration of these climate modes varies with the background climate; a colder background climate and lower CO2 generally results in a shorter interstadial and a longer stadial through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, the duration of stadials was shorter during the Marine Isotope Stage 3 (MIS3) compared with MIS5, despite the colder climate in MIS3, suggesting potential control from other climate factors on the duration of stadials. In this study, we investigated the role of glacial ice sheets. For this purpose, freshwater hosing experiments were conducted with an atmosphere–ocean general circulation model under MIS5a, MIS3 and MIS3 with MIS5a ice sheet conditions. The impact of ice sheet differences on the duration of the stadials was evaluated by comparing recovery times of the AMOC after freshwater forcing was reduced. Hosing experiments showed a slightly shorter recovery time of the AMOC in MIS3 compared with MIS5a, which was consistent with ice core data. We found that larger glacial ice sheets in MIS3 shortened the recovery time. Sensitivity experiments showed that stronger surface winds over the North Atlantic shortened the recovery time by increasing the surface salinity and decreasing the sea ice amount in the deepwater formation region, which set favourable conditions for oceanic convection. In contrast, we also found that surface cooling by larger ice sheets tended to increase the recovery time of the AMOC by increasing the sea ice thickness over the deepwater formation region. Thus, this study suggests that the larger ice sheet in MIS3 compared with MIS5a could have contributed to the shortening of stadials in MIS3, despite the climate being colder than that of MIS5a, when the effect of surface wind played a larger role.

Impact of Accurate Geoid Fields on Estimates of the Ocean Circulation

2007 ◽  
Vol 24 (8) ◽  
pp. 1464-1478 ◽  
Author(s):  
Detlef Stammer ◽  
Armin Köhl ◽  
Carl Wunsch
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Formal Proof ◽  
Meridional Overturning Circulation ◽  
Dynamic Topography ◽  
Model Errors ◽  
Geoid Model ◽  
Meridional Heat Transport ◽  
The Impact

Abstract The impact of new geoid height models on estimates of the ocean circulation, now available from the Gravity Recovery and Climate Experiment (GRACE) spacecraft, is assessed, and the implications of far more accurate geoids, anticipated from the European Space Agency’s (ESA) Gravity and Ocean Circulation Explorer (GOCE) mission, are explored. The study is based on several circulation estimates obtained over the period 1992–2002 by combining most of the available ocean datasets with a global general circulation model on a 1° horizontal grid and by exchanging only the EGM96 geoid model with two different geoid models available from GRACE. As compared to the EGM96-based solution, the GRACE geoid leads to an estimate of the ocean circulation that is more consistent with the Levitus temperature and salinity climatology. While not a formal proof, this finding supports the inference of a substantially improved GRACE geoid skill. However, oceanographic implications of the GRACE model are only modest compared to what can be obtained from ocean observations alone. To understand the extent to which this is merely a consequence of a not-optimally converged solution or if a much more accurate geoid field could in principle play a profound role in the ocean estimation procedure, an additional experiment was performed in which the geoid error was artificially reduced relative to all other datasets. Adjustments occur then in all elements of the ocean circulation, including 10% changes in the meridional overturning circulation and the corresponding meridional heat transport in the Atlantic. For an optimal use of new geoid fields, improved error information is required. The error budget of existing time-mean dynamic topography estimates may now be dominated by residual errors in time-mean altimetric corrections. Both these and the model errors need to be better understood before improved geoid estimates can be fully exploited. As is commonly found, the Southern Ocean is of particular concern.

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