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.
The Central American Seaway played a pivotal role in shaping global climate throughout the late Cenozoic. Recent geological surveys have provided new constraints on timing of the seaway shoaling, ...while neodymium isotopic (εNd) data measured on fossil teeth, debris, and ferromanganese crusts have helped define the history of water masses in the region. Here we provide the first 3‐D simulations of εNd responses to the shoaling seaway. Our model suggests that a narrow and shallow seaway is sufficient to affect interoceanic circulation, that inflow/outflow balance between the Caribbean and the Antilles responds nonlinearly to sill depth, and that a seaway narrower than 400 km is consistent with an active Atlantic meridional overturning circulation during the late Miocene. Simulated εNd values in the Caribbean confirm that inputs from radiogenic Pacific waters in the Caribbean decrease as the seaway shoals. Despite model limitations, a comparison between our results and εNd values recorded in the Caribbean helps constrain the depth of the Central American Seaway through time, and we infer that a depth between 50 and 200 m could have been reached 10 Ma ago.
Key Points
Model/data comparison of epsilon Nd suggests a shallow CAS during the Miocene
CAS throughflow depends on seaway geometry and atmospheric coupling
Ocean circulation responds nonlinearly to CAS shoaling
A century ago, the pioneering book published in 1924 Die Klimate der geologischen Vorzeit explained by plate motion the evolution of vegetation revealed in sedimentary records. Nevertheless, they did ...not invoke climate changes. In the second part of the 20th century, the intricate relationship between tectonics, long‐term carbon cycle, and climate was depicted by Walker (1981). Since these major steps, climate modeling of the Earth system kept on improving and including more and more components and processes to enable the investigation of deep time periods using general circulation model that can account for atmosphere and ocean dynamics. Here we illustrate long but drastic climate changes clearly related with tectonics, through three different examples: (1) the crucial role of paleogeography (continental distribution) to explain the drawdown of atmospheric carbon dioxide and the huge glaciation associated that occurred during the Neoproterozoic period; (2) the shrinkage of large epicontinental Paratethys that covered a large part of Eastern Europe and Western Asia and its impact on both monsoonal systems (African and Asian) since 40 Ma; and (3) the large impact of mountain range uplifts since Eocene both in Asia (Tibetan Plateau and Himalaya) and in Africa (buildup of the rift), on atmosphere and ocean dynamics. These studies not only allow for testing the ability of Earth system models to capture long‐term changes of Earth climate, but they also pinpoint the pivotal role tectonics played in shaping the long‐term evolution of atmospheric CO2 and monsoon patterns.
Plain Language Summary
For the celebration of the 50th anniversary of the publication of the pioneering papers that established the basis of plate tectonic, this paper was solicited to illustrate the close relation between tectonics and climate. Amongst the large spectrum of interactions that depict how tectonics modified the climate at geological time steps, we choose to illustrate two major issues: (1) How the “tryptic” climate/long‐term carbon cycle/tectonics explains the extraordinary glacial episode (717–635 Ma) occurring during Neoproterozoic era? (2) How major tectonic events (i.e., the slow shrinkage of a huge epicontinental sea and the uplift of large mountains ranges in Asia and Africa) drastically changed the climate and shaped the pattern of present‐day monsoons systems. This paper is the result of long‐standing collaboration with many researchers from different countries.
Key Points
Relationships between paleogeographic configurations, climate, hydrological cycle and erosionto assess atmospheric CO2 changes
Evaluations of climatic impact of uplifts (Tibetan Plateau and African rift) and epicontinental shrinkage (Paratethys) on Cenozoic climates
Impacts on Tibetan Plateau uplift on Pacific and Atlantic meridional ocean circulationthrough Cenozoic
Large parts of the Sahara were vegetated during the early to mid Holocene. Several positive feedbacks, most notably related to vegetation, have been shown to have favored the northward migration of ...the desert boundary. During this period, numerous lakes and wetlands existed in the Sahara region and might have acted as a local moisture source. However, earlier model studies of the effects of open water surfaces on the mid‐Holocene North African climate suggested that these were weak and did not contribute significantly to this northward migration of the North African climate zones. Using a state‐of‐the‐art climate model, we suggest that the effect of open‐water surfaces on the mid‐Holocene North African climate might have been much stronger than previously estimated, regionally more than doubling the simulated precipitation rates. It is thus possible that this effect, combined to other known positive feedbacks, favored the appearance of the “Green Sahara”.
Key Points
Open‐water surfaces lead to increased precipitation rates in North Africa
This provides a major positive feedback to the mid‐Holocene
Climate models should take this effect into account
Given the growing evidence for megalakes in the geological record, assessing their impact on climate and vegetation is important for the validation of palaeoclimate simulations and therefore the ...accuracy of model–data comparison in lacustrine environments. Megalake Chad (MLC) occurrences are documented not only for the mid-Holocene but also for the Mio-Pliocene (Schuster et al., 2009). At this time, the surface covered by water would have reached up to ~350 000 km2 (Ghienne et al., 2002; Schuster et al., 2005; Leblanc et al., 2006), making it an important evaporation source, possibly modifying climate and vegetation in the Chad Basin. We investigated the impact of such a giant continental water area in two different climatic backgrounds within the Paleoclimate Model Intercomparison Project phase 3 (PMIP3): the late Pliocene (3.3 to 3 Ma, i.e. the mid-Piacenzian warm period) and the mid-Holocene (6 kyr BP). In all simulations including MLC, precipitation is drastically reduced above the lake surface because deep convection is inhibited by overlying colder air. Meanwhile, convective activity is enhanced around MLC because of the wind increase generated by the flat surface of the megalake, transporting colder and moister air towards the eastern shore of the lake. The effect of MLC on precipitation and temperature is not sufficient to widely impact vegetation patterns. Nevertheless, tropical savanna is present in the Chad Basin in all climatic configurations, even without MLC presence, showing that the climate itself is the driver of favourable environments for sustainable hominid habitats.
For a long time, evaporitic sequences have been interpreted as indicative of an arid climate. Such systematic interpretations led to the suggestion that the Central segment of the South Atlantic ...(20-0°) was characterized by an arid climate during the upper Aptian. Indeed, synchronous to this period that corresponds to the rifting and to the opening of this part of the South Atlantic, a large evaporitic sequence spreads out from the equator to 20° S. Using the fully ocean atmosphere coupled model FOAM, we test the potential for the Aptian geography to produce an arid area over the Central segment. Sensitivity to the altitude of the rift shoulders separating the Africa and the South America cratons, to the water depth of the Central segment and to the drainage pattern have been performed. Using seawater salinity as a diagnostic, our simulations show that the southern part of the Central segment is characterized by very high salinity in the case of catchment areas draining the water out of the Central segment. Conversely, whatever the boundary conditions used, the northern part of the Central segment remains humid and salinities are very low. Hence, we conclude that the evaporites deposited in the southern part of the Central segment may have been controlled by the climate favouring aridity and high saline waters. In contrast, the evaporites of the northern part can hardly be reconciled with the climatic conditions occurring there and may be due to hydrothermal sources. Our interpretations are in agreement with the gradient found in the mineralogical compositions of the evaporites from the North to the South, i.e. the northern evaporites are at least 4 times more concentrated than the southern one.
Only few well-dated records document the evolution of Southeast Asian paleoenvironments during the Cenozoic. Here we analyse continental pollen assemblages from Late Oligocene and Miocene fossil ...sites of Thailand. In agreement with previous studies, palynoflora from the Oligocene suggests warm temperate forested habitats at 24-26 Ma, whereas Middle Miocene assemblages are made of thermophilous taxa. This change can be linked to the major climate reorganization that brought warmer and wetter conditions over Southeast Asia around 22 Ma. This study also provides the first submillional records from the Middle Miocene of Thailand. Thirteen samples of lignite layers from the sivaladapid-bearing Mae Moh site, dated between 13.3 and 13.1 Ma, and six samples from the hominoid-bearing Chiang Muan deposit, dated between 12.4 and 12.2 Ma, document oscillations between tropical woodlands and grasslands in northern Thailand. These pollen records likely reflect climate variations linked to insolation variations. Late Miocene palynological assemblages from Khorat, northeastern Thailand, document fluviolacustrine paleoenvironments alternatively covered by thermophilous trees and grasslands. These records show that both sivaladapids and early hominoids from Thailand have evolved in tropical environments with high variability in the vegetation cover.
The Asian monsoons are triggered by complex interactions between the atmosphere, Asian and African orography, and the surrounding oceans, resulting in highly seasonal climate and specific regional ...features. It was thought that the Asian monsoon was established during the Neogene, but recent evidence for monsoon-like precipitation seasonality occurring as early as the Paleogene greenhouse period challenges this paradigm. The possible occurrence of monsoons in a climatic and paleogeographic context very different from the present-day questions our understanding of the drivers underpinning this atmospheric phenomenon, in particular with regard to its dependence on geography. In this study, we first take advantage of the wealth of new studies to tentatively draw an up-to-date picture of Asian tectonic and paleoenvironmental evolution throughout the Cenozoic. We then analyze a set of 20 paleoclimate simulations spanning the late Eocene to latest Miocene (∼ 40–8 Ma) in order to better understand the evolution of the distinct Asian monsoon subsystems. At odds with the traditional view of a monsoonal evolution driven mainly by Himalayan-Tibetan uplift, our work emphasizes the importance of peripheral mountain ranges in driving the evolution of Asian climate. In particular, the uplift of East African and Anatolian-Iranian mountain ranges, as well as the emergence of the Arabian Peninsula, contribute to shaping the modern South Asian summer monsoon. We also suggest that East Asian monsoon establishment and the aridification of inland Asia are driven by a combination of factors including increasing continentality, the orographic evolution of the Tibetan Plateau, Mongolia, Tian Shan and Pamir, and pCO2 decrease during the Cenozoic.
•Monsoon-like rainfall regime in Paleogene eastern Asia is triggered by the proto-Tibetan Plateau uplift.•Increasing continentality, due to the retreat of the Paratethys Sea and the emergence of the Arabian Platform above sea level, are instrumental in the establishment of surface temperature gradients that promote moist air advection from the Indian Ocean towards Asia in summer.•The Anatolian-Iranian and East African landforms contribute to reinforcing the Somali Jet that brings moisture to Southeastern Asia in summer.•The uplift of the Mongolian Plateau drives the formation of the Siberian High in winter, which broadly reinforces the East Asian winter monsoon and induces aridification of the Gobi region.•The uplift of the Tian Shan and Pamir mountain ranges blocks the westerly moisture flux, forces the northward migration of the Jet Stream in summer, and enhances inland Asian aridification. Their effect on the South Asian monsoon is likely dependent on the paleoelevation of neighboring landforms, especially the Anatolian-Iranian Plateau.
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