OFR 151.pdf - CRC LEME

Other events occurring during the Early Pliocene are the closure of the Isthmus of Panama
between 4.4-3.2 Ma (Coates et al. 1992), constriction of the Indonesian Seaway to warm
water transport between the Pacific and Indian Oceans (Srinivasan and Sinha 1998), sea levels
up to 25-35 m above present (Cronin and Dowsett 1993), and growth of forest species at 82 0 N
in Greenland, some 2500 km north of the modern Arctic treeline (Funder et al. 1985).
Diatom evidence indicates that between 3.1-2.9 Ma, the Antarctic Polar Front lay some 6 0 S
south of its present position – implying SSTs between 55-60 0 S were up to 3-4 0 C warmer than
at present (Barron 1996). These events almost certainly were linked, directly or indirectly.
For example, mechanisms proposed to account for the poleward transport of heat (and
enhanced moisture supply) needed to allow forest species to grow at 82 0 N include
intensification of the Gulf Stream following closure of the Isthmus of Panama (Willard et al.
1993), and altered intermediate and deep water circulation (Kwiek and Ravelo 1999): Raymo
et al. (1996) and Billups et al. (1998) suggest a combination of increased atmospheric CO2
and enhanced thermohaline circulation. As yet, the relative contribution of these and tectonic
and palaeogeographic factors is unclear (Crowley 1996).
7.1.7 Plio-Pleistocene bipolar glaciation [