Hydrologic cycling over Antarctica during the middle Miocene warming

Lake geochemistry reveals marked environmental change in Southwest China during the Mid Miocene Climatic Optimum

“…The shift between Zones 1 and Zone 2 could reflect the cooling event Mi-2, although this event is dated around 16.0 Ma [58]. Alternatively, a ''peak warmth'' centred around 15.6 Ma has been described from the Pacific Ocean and Antarctica [2,6,8]. It is therefore possible that the boundary between Zones 1 and 2 is related to the end of the ''peak warmth''.…”

“…In Antarctica, a palynological study and leaf wax geochemistry revealed a warmer and wetter climate than today, and demonstrated that Antarctica could support a tundra vegetation [7,8]. In China, a lithological study conducted in the northeast Tibetan Plateau and a palynological investigation in Tian Shan (northwest China) show evidence of a warm and wet period during the MMCO [9,10], demonstrating that the lower latitude continental areas were also affected by the MMCO.…”

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“…Site AND-2A recovered a ~20 to 14 Ma sequence interpreted to reflect TAM tidewater outlet glaciers overriding and/or calving near the site Passchier et al, 2011). At 15.7 Ma, a diatomite with abundant pollen, algae, and other biomarkers suggests a warmer than present (mean surface temperature of ~10°C) climate during the MMCO (Feakins et al, 2012;Warny et al, 2009). At 300 mbsf, a 300 ky disconformity is thought to be equivalent to Unconformity RSU4, suggesting a shelf-wide advance of the marine-based ice sheet during the MMCT (Figures F6, F8) (De Santis et al, 1999;Passchier et al, 2011).…”

“…Following the O/M glaciation, both near-and far-field proxy records indicate a period of sustained (~3°C warmer than present) (You et al, 2009) warmth and carbon cycle reorganization (e.g., Foster et al, 2012;Vincent and Berger, 1985), referred to as the Middle Miocene Climatic Optimum (MMCO; ~17-15 Ma) (Flower and Kennett, 1994;Shevenell et al, 2004). During the MMCO, polar amplification of temperature is suggested (Feakins et al, 2012;Lewis et al, 2008;Shevenell et al, 2004;Warny et al, 2009) but not yet successfully modeled (e.g., You et al, 2009). The MMCO was immediately followed by an interval of Antarctic ice growth and cooling, termed the Middle Miocene Climate Transition (MMCT; 14.2-13.8 Ma), as observed in both far-field benthic foraminifer δ 18 O records and ice-proximal data ( Figure F1) (Cramer et al, 2009;Flower and Kennett, 1994;Holbourn et al, 2007;Kennett, 1977;Shevenell et al, 2008Shevenell et al, , 2004Zachos et al, 2001) and is believed to have resulted in the extinction of the Antarctic tundra vegetation (Lewis et al, 2008).…”

Southern Exposure: New Paleoclimate Insights From Southern Ocean and Antarctic Margin Sediments

“…teX 86 -derived temperatures are compared with local insolation (blue and purple), antarctic ice core (green), and sub-antarctic sea surface temperatures (SSts; red and blue) from the pacific Sector of the Southern ocean, revealing similarities on orbital and millennial timescales (see Shevenell et al, 2011, for details (Savin et al, 1975;Kennett, 1977;Flower and Kennett, 1994;Shevenell et al, 2004 (Figure 2; Flower, 1999;Zachos et al, 2001;Pagani et al, 2005;Kurschner et al, 2008). Because a definitive link between ice growth and atmospheric CO 2 concentrations has yet to be established for the middle Miocene (Flower, 1999;Pagani et al, 1999) Shevenell et al, 2004Shevenell et al, , 2008Verducci et al, 2009;Majewski and Bohaty, 2010), the Ross Sea region (Naish et al, 2007;Warny et al, 2009;Harwood et al, 2008Feakins et al, 2012), the Antarctic Peninsula (J.B. Anderson et al, 2011), and the McMurdo Dry Valleys (Lewis et al, 2008) (Shevenell et al, 2004) and benthic (Shevenell et al, 2008) foraminifer CaCO 3 suggest the presence of warm waters around Antarctica was only slightly higher than present ( Figure 5; Shevenell et al, 2008;Lear et al, 2010). Although ice growth began at 15.5 Ma, about two million years prior to the node in Earth's orbital parameters identified at ~ 13.84 Ma (Holbourn et al, 2005), Southern Ocean surface cooling did not commence until 14.2 Ma, when SSTs cooled 6-7°C in a stepwise fashion, reaching a minimum at 13.8 Ma (Shevenell et al, 2004).…”