Subboreal

The Subboreal is the second before last climatic period of the Holocene. It lasted from 3710 to 450 BCE.

History and stratigraphy

The composite scientific term Subboreal, i. e. below the Boreal, is derived from the Latin sub (below, under) and the Greek Βορέας - Boreas, the God of the North Wind. It was first introduced in 1889 by Rutger Sernander to distinguish it from Axel Blytt's Boreal, established in 1876. The Subboreal replaces the Atlantic and is followed by the Subatlantic.

The Subboreal is equivalent to W. H. Zagwijn's pollen zones IVa and IVb and T. Litt's pollen zone VIII. In the pollen scheme of Fritz Theodor Overbeck it occupies pollen zone X.

In paleoclimatology the Subboreal is divided into an Older Subboreal and a Younger Subboreal. Historically the Subboreal is equivalent to most of the Neolithic and the entire Bronze Age which started 4200 to 3800 years ago.

Dating

The beginning of the Subboreal is usually defined as 3710 years BCE or 5660 years BP. This lower limit is flexible, as some authors prefer to use 4400 BCE or 6350 BP or like in northwestern Poland even 4830 BC or 6780 BP, whereas others use 5000 calendar years or 3050 BCE. The upper limit of the Subboreal (and therefore the beginning of the Subatlantic) is also flexible and can be attributed to the interval 1170 to 830 BCE, but is usually fixed at 450 BCE. In varve years the Subboreal corrsponds to the interval 5660 till 2750 years BP.

Blytt–Sernander system

The Blytt-Sernander classification, or sequence, is a series of north European climatic periods or phases based on the study of Danish peat bogs by Axel Blytt (1876) and Rutger Sernander (1908). The classification was incorporated into a sequence of pollen zones later defined by Lennart von Post, one of the founders of palynology.

Description

Layers in peat were first noticed by Heinrich Dau in 1829. A prize was offered by the Royal Danish Academy of Sciences and Letters to anyone who could explain them. Blytt hypothesized that the darker layers were deposited in drier times; the lighter, in moister times, applying his terms Atlantic (warm, moist) and Boreal (cool, dry). In 1926 C.A. Weber noticed the sharp boundary horizons, or Grenzhorizonte, in German peat, which matched Blytt’s classification. Sernander defined subboreal and subatlantic periods, as well as the late glacial periods. Other scientists have since added other information.

The classification was devised before the development of more accurate dating methods, such as C-14 dating and oxygen isotope ratio cycles. Currently geologists working in different regions are studying sea levels, peat bogs and ice core samples by a variety of methods, with a view toward further verifying and refining the Blytt-Sernander sequence. They find a general correspondence across Eurasia and North America.