Pollen zones are a system of subdividing the last glacial period and Holocene paleoclimate using the data from pollen cores. The sequence provides a global chronological structure to a wide variety of r, such as geologists, climatologisists, geographers and archaeologists, who study the physical and cultural environment of the last 15,000 years.
Pollen zone Wikipedia
The palynological aspects of the system were first investigated extensively by the Swedish palynologist Lennart von Post in the years before the First World War. By analysing pollen in core samples taken from peat bogs, von Post noticed that different plant species were represented in bands through the cores.
The differing species and differing quantities of the same species are caused by changes in climate. Von Post was able to confirm the Blytt-Sernander climatic sequence showing fluctuations between warmer and colder periods across thousands of years. He used local peat sequences combined with varve dating to produce a regional climatic chronology for Scandinavia.
In 1940 Harry Godwin began applying von Post's methods to pollen cores from the British Isles to produce the wider European sequence accepted today. It basically expanded the Blytt-Sernander further into the late Pleistocene and refined some of its periods. Following the Second World War, the technique spread to the Americas.
Currently scientists are focusing a repertory of several different methods on core samples in peat, ice, lake and ocean bottoms, and sediments to achieve "high resolution" dating not possible to only one method: Carbon dating, Dendrochronology, isotope ratios on a number of gases, studies of insects and molluscs, and others. While often doubting the utility of the modified Bytt-Sernander, they seem to confirm and expand it all the more.