A colder, wetter climatic phase which followed the more continental climate of sub-Boreal times. The change from sub-Boreal to sub-Atlantic conditions in Britain began about 2850 bp and roughly coincided with the transition from Bronze to Iron Age cultures. The sub-Atlantic marks a period of renewed peat growth on bog surfaces that in late sub-Boreal times were sufficiently dry and humified (see humification) to support heath vegetation (e.g. Calluna vulgaris, ling or heather). This renewed peat growth gives a major recurrence surface, the Grenz horizon, which at one time was considered to define the boundaries between Godwin pollen zones VIIb and VIII. Radiocarbon dating has shown that there are many such recurrence horizons, however, and this use of Godwin pollen zones is now obsolete. See pollen zone.
Subjects: Plant Sciences and Forestry.