Samples from deep-ocean sediments from ODP Site 646 in the Labrador Sea) are dominated by Pinus pollen, with Picea subdominant and Abies, Betula, Alnus, Quercus, Sciadopitys, and Tsuga present in most samples (see also de Vernal, this volume). These assemblages were compared to modern samples using the Modern Analog Technique (MAT) of dissimilarity coefficients, and the closest modern analogs are from Newfoundland and Nova Scotia. If the source area for pollen at Site 646 was Labrador or Quebec, as suggested by present wind patterns, then these data indicate a northward expansion of the northern hardwood forest into Labrador and Quebec and indicate that Pliocene temperatures in those regions were at least 3.5° C warmer than today with higher precipitation levels.
Pollen assemblages from the shallow-marine sediments of the Yorktown Formation in southeastern Virginia are dominated by Pinus with Quercus, Carya, and Sciadopitys pollen commonly present. The closest modern analogs are from North Carolina and South Carolina, indicating Pliocene temperatures about 2° C warmer than today and higher precipitation levels. The Pinecrest Beds of southwestern Florida also are dominated by Pinus pollen, with Quercus and taxodiaceous pollen abundant. These assemblages are analogous to modern assemblages from sites along the coast of Florida that represent the longleaf/slash pine forests that cover much of the Atlantic Coastal Plain and indicate no significant differences between Pliocene and modern temperatures or precipitation in this subtropical region.
The presence of vegetation characteristic of temperatures much warmer than present at high latitudes grading southward to present-day temperatures at low latitudes is similar to patterns shown by marine invertebrates in both degree and timing of change. Comparison of the marine and terrestrial records indicate that they responded to climate forcing mechanisms in phase with each other. The relatively greater amplification of temperatures at subarctic sites is consistent with predictions by general circulation models using increased meridional heat transport as the mechanism for middle Pliocene warming in the northern hemisphere. Further research on lower latitude and southern hemisphere sites should help determine whether Pliocene circulation patterns in southern oceans differed appreciably from those of today and whether they exerted similar controls on terrestrial vegetation.