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

Abstract

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 pCO 2 drawdown and that the oceanic changes due to the Tethys seaway closure amplified the response of global climate and East Antarctic Ice Sheet.

Boundary conditions for the Middle Miocene Climate Transition (MMCT v1.0)

“…In view of the variable configuration of the Tethys/Paratethys across the Middle Miocene, it would be recommendable to test different Tethys/Paratethys configurations when performing Middle Miocene experiments with GCMs, although such testing can be limited by model constraints: seas disconnected from the global ocean can produce freshwater imbalance in GCMs and narrow ocean passages require high resolution ocean grids to allow ocean flux calculation (Rosenbloom et al, 2011). Some studies, indeed, suggest that the Tethys passage closure might have played a role in Middle Miocene atmosphere and ocean circulation patterns (Ramstein et al, 1997;Hamon et al, 2013).…”

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

“…Here, we will purely focus on the influence of ice sheets on the climate, in particular the relation between CO 2 and temperature, during this time. Earlier studies using more complex stand-alone ice sheet models and coupled ice sheet-climate models have, for example, determined the CO 2 thresholds for the glaciation of Antarctica (DeConto and Pollard, 2003;Langebroek et al, 2010;Ladant et al, 2014;Gasson et al, 2014) and the Northern Hemisphere (DeConto et al, 2008;Hamon et al, 2013). Furthermore, they have investigated the hysteresis in the relation between ice volume and CO 2 (Pollard and DeConto, 2005) and the behaviour of the Antarctic ice sheet during the Oligocene and Plio-Pleistocene (Pollard and DeConto, 2009 ice sheets and the climate.…”

“…We recognise that our simulation of CO 2 may be improved in subsequent studies that include geological processes that are still missing in our model set-up. For instance, tectonics leading to mountain uplift (Kutzbach et al, 1993) and closure of sea ways (Kennett, 1977;Toggweiler and Bjornsson, 2000;Hamon et al, 2013), erosion (Wilson et al, 2012;Gasson et al, 2015;Stap et al, 2016b), and vegetation changes (Knorr et al, 2011;Liakka et al, 2014;Hamon et al, 2012) may have affected the climate system during the past 38 Myr. Here, we will purely focus on the influence of ice sheets on the climate, in particular the relation between CO 2 and temperature, during this time.…”

IODP workshop: developing scientific drilling proposals for the Argentina Passive Volcanic Continental Margin (APVCM) – basin evolution, deep biosphere, hydrates, sediment dynamics and ocean evolution

“…Following the MCO, more complex oceanic circulation patterns developed during the midMiocene Climatic Transition (MMCT) from about 14.2 to 13.8 Ma. Possible important events that occurred at that time include the emplacement of large volcanic complexes (such as the Columbia River Basalts, CRB), which would have affected pCO 2 (Armstrong McKay et al, 2014), the Andean uplift with an impact on atmospheric circulation and weathering patterns Grützner et al, 2011 and, and the closing of the Tethys seaway, which changed global ocean circulation patterns (Hamon et al, 2013). Climate deterioration continued into the late Miocene, leading to the initiation and growth of the West Antarctic Ice Sheet (Shevenell et al, 2004).…”