Palynomorphs from a sediment core reveal a sudden remarkably warm Antarctica during the middle Miocene

Abstract

An exceptional triple palynological signal (unusually high abundance of marine, freshwater,\ud and terrestrial palynomorphs) recovered from a core collected during the 2007 ANDRILL\ud (Antarctic geologic drilling program) campaign in the Ross Sea, Antarctica, provides constraints\ud for the Middle Miocene Climatic Optimum. Compared to elsewhere in the core, this\ud signal comprises a 2000-fold increase in two species of dinofl agellate cysts, a synchronous fi vefold\ud increase in freshwater algae, and up to an 80-fold increase in terrestrial pollen, including\ud a proliferation of woody plants. Together, these shifts in the palynological assemblages\ud ca. 15.7 Ma ago represent a relatively short period of time during which Antarctica became\ud abruptly much warmer. Land temperatures reached 10 C (January mean), estimated annual\ud sea-surface temperatures ranged from 0 to 11.5 C, and increased freshwater input lowered\ud the salinity during a short period of sea-ice reduction

Progressive Cenozoic cooling and the demise of Antarctica’s last refugium

“…3 and Table S4). The concentrations of Nothofagidites and Podocarpidites pollen are not nearly as high as those recovered during the Mid Miocene Climatic Optimum (approximately 15.7 Ma) recorded in the Ross Sea (26), but the similarities in assemblage indicate that the climate must have included intervals of warmer austral summer temperatures (10°C warm month mean) in protected areas to allow flowering of these alpine species. Radiometric ages of volcanic tephra associated with pristinely preserved plant remains from the Dry Valleys (Transantarctic Mountains, East Antarctica) show the last vestiges of tundra life in that region disappeared earlier, prior to 13.85 Ma (25).…”

“…(fusca gp.) and a few podocarpaceous conifer pollen, along with tundra taxa (identified as such in Ross Sea assemblages) (24,25,26), such as Caryophyllaceae (Colobanthus-type) and Poaceae (grasses), plants that grow today on the Antarctic Peninsula, plus moss species (Fig. 3 and Table S4).…”

Stratigraphic calibration of Oligocene–Miocene organic-walled dinoflagellate cysts from offshore Wilkes Land, East Antarctica, and a zonation proposal

“…Studies on Oligocene-Neogene dinocyst assemblages have been carried out on sediment cores from Prydz Bay (Hannah, 2006;Warnaar, 2006;Houben et al, 2013), Cape Roberts (Hannah et al, 1998(Hannah et al, , 2000(Hannah et al, , 2001a, within the Cenozoic Investigation in the Western Ross Sea (CIROS) program (Hannah, 1994(Hannah, , 1997, the Antarctic Geological Drilling (ANDRILL) program in the Ross Sea (Warny et al, 2009), and Ocean Drilling Program (ODP) Site 696 in the Weddell Sea (Warnaar, 2006;Houben et al, 2013). Further north in the Southern Ocean, dinocyst records have been generated from ODP Site 1168 (Brinkhuis et al, 2003a) and Deep Sea Drilling Project (DSDP) Site 511 (Goodman and Ford Jr., 1983;Houben et al, 2011).…”

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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).…”