Initial Expansion of C₄ Vegetation in Australia During the Late Pliocene

Abstract

Since the late Miocene, plants using the C4 photosynthetic pathway have increased to become major components of many tropical and subtropical ecosystems. However, the drivers for this expansion remain under debate, in part because of the varied histories of C4 vegetation on different continents. Australia hosts the highest dominance of C4 vegetation of all continents, but little is known about the history of C4 vegetation there. Carbon isotope ratios of plant waxes from scientific ocean drilling sediments off north‐western Australia reveal the onset of Australian C4 expansion at ~3.5 Ma, later than in many other regions. Pollen analysis from the same sediments reveals increasingly open C3‐dominated biomes preceding the shift to open C4‐dominated biomes by several million years. We hypothesize that the development of a summer monsoon climate beginning in the late Pliocene promoted a highly seasonal precipitation regime favorable to the expansion of C4 vegetation.

Timing and Pacing of Indonesian Throughflow Restriction and Its Connection to Late Pliocene Climate Shifts

“…This sea level highstand also marks the termination of the~0.5 ‰ offset between the isotopic values of site 763 and U1463 (De Vleeschouwer et al, 2018), indicating that the LC again reached Site 763A by~3.2 Ma. These results imply a link between the observed paleooceanographic changes and the end of the Australian Humid Interval and the beginning of the Transitional Interval at 3.3 Ma (Andrae et al, 2018;Christensen et al, 2017;Di Nezio et al, 2016;Krebs et al, 2011;Sniderman et al, 2016) Interval 5 "Post M2 glacial/interglacial : the final interval reflects the response of local oceanographic conditions to increased glacial/interglacial amplitudes and seasonality after MIS M2 (De Vleeschouwer et al, 2018;Lisiecki & Raymo, 2005). TG2 and TG3 alternate on an orbital scale showing cooler and more open marine TG2 dominantly occurring during ETP maxima in glacial times (Figures 4c and 4e).…”

“…This sea level highstand also marks the termination of the ~0.5 ‰ offset between the isotopic values of site 763 and U1463 (De Vleeschouwer et al, ), indicating that the LC again reached Site 763A by ~3.2 Ma. These results imply a link between the observed paleooceanographic changes and the end of the Australian Humid Interval and the beginning of the Transitional Interval at 3.3 Ma (Andrae et al, ; Christensen et al, ; Di Nezio et al, ; Krebs et al, ; Sniderman et al, )…”

Equilibrium and non‐equilibrium phases in the radiation ofHakeaand the drivers of diversity in Mediterranean‐type ecosystems

“…; Andrae et al. ). Of an increasing number of MTE clades investigated, many (including Hakea ) appear to have started their radiation within an MTE, supporting the “time for speciation” model (Valente et al.…”

“…Non-equilibrium explanations for MTE diversity typically involve one or more of three scenarios: (1) there has been a greater time for lineages to accumulate diversity in MTEs because these regions are older than other temperate biomes ("time for speciation"); (2) MTEs have had reduced extinction rates (Hopper 2009;Hopper et al 2016); or (3) MTE lineages or environments have features that have promoted increased speciation rates (Hopper and Gioia 2004;Linder 2005;Sauquet et al 2009;Schnitzler et al 2011;Reyes et al 2015). After rainforests, the Mediterranean biome may be the oldest of Australia's biomes, with recent estimates suggesting the development of a Mediterranean-type climate from 30 million years ago (Lamont and He 2017), whereas temperate forests probably did not become widespread until 25 to 15 million years ago (Byrne et al 2011), and modern woodland, grassland, savannah, and arid ecosystems until eight to three million years ago (Hill and Creek 2004;Beerling and Osborne 2006;Byrne et al 2008;Bowman et al 2010;Andrae et al 2018). Of an increasing number of MTE clades investigated, many (including Hakea) appear to have started their radiation within an MTE, supporting the "time for speciation" model (Valente et al 2009;Cardillo and Pratt 2013;Cook et al 2015;Cardillo et al 2017;Skeels and Cardillo 2017).…”

Toward a Robust Plio‐Pleistocene Chronostratigraphy for ODP Site 762

“…But Stuut et al (2019) place the onset of the aridification in Australia~300 kyr earlier (~3.8 Ma) at Site 762. The authors ascribe the difference to insufficient time resolution at Site 763 (Andrae et al, 2018) or to the fact that the Site U1463 records (Auer et al, 2019) do not extend far enough back in time. Finally, Stuut et al (2019) argue that the smoothed wireline K wt.% long-term Pliocene record at Site U1463 (Christensen et al, 2017) may be too imprecise to pinpoint this shift.…”