Subboreal

This article's lead section may be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. (May 2021)

Preceded by the Pleistocene
Holocene Epoch
Oak-hornbeam forest at Žernov, Czech Republic.
ages (official) ka ) Northgrippian (8.236–4.2† ka) Meghalayan (4.2 ka–present)
Blytt–Sernander stages/ages Preboreal (10.3†–9† ka) Boreal (9–7.5† ka) Atlantic (7.5–5† ka) Subboreal (5–2.5† ka) Subatlantic (2.5 ka–present) *Relative to year 2000 (b2k). †Relative to year 1950 (BP/Before "Present").
v t e

The Subboreal is a climatic period, immediately before the present one, of the Holocene. It lasted from 3710 to 450 BCE.

Etymology

The composite scientific term Subboreal, meaning "below the Boreal," is derived from the

The Subboreal followed the Atlantic and was followed by the Subatlantic. The Subboreal is equivalent to W. H. Zagwijn's pollen zones IVa and IVb^[3] and T. Litt's pollen zone VIII.^[4] In the pollen scheme of Fritz Theodor Overbeck, it occupies pollen zone X.

In

The Subboreal is usually defined as 5660 to 3710 years BP. The lower limit is flexible, as some authors prefer to use 4400 BCE, or 6350 BP[5] in northwestern Poland, even 4830 BC, or 6780 BP,^[6] And 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 1170 to 830 BCE,^[7] but it is usually fixed at 450 BCE. In varve years, the Subboreal corresponds to 5660 to 2750 years BP.^[8]

The boundary between the older and the younger Subboreal is considered to be 1350 BCE.

Climatic evolution

The climate was generally drier and slightly cooler (by about 0.1 °C) than in the preceding Atlantic but still warmer than today. The temperatures were 0.7 °C higher than during the following Subatlantic. Consequently, in Scandinavia the lower limit of glaciers was 100 to 200 m higher than during the Subatlantic.^[9] On the whole, the oscillating temperatures slightly receded in the course of the Subboreal by about 0.3 °C.^{[citation needed]}

In the

The Levant shows a similar climatic evolution.[15] The dry conditions prevailing in Mesopotamia around 4200 years BP probably resulted in the downfall of the Akkadian Empire.^[16]

Carbon dioxide

Levels of carbon dioxide had reached at the beginning of the Subboreal its Holocene minimal value of 260 ppm. During the Subboreal, it started rising and reached 293 ppm at the end of the period.^[17] As a comparison, today's value is over 400 ppm.^[18]

Vegetation history

In

The relatively-dry climate during the subboreal furthered the spreading of heath plants (Ericaceae).

Sea level

Like in the Atlantic period, the global sea level kept on rising during the Subboreal but at a much slower rate. The increase amounted to about 1 m, which corresponds to a rate of 0.3 mm per year. At the end of the Subboreal, the sea level was about 1 m below the current value.

Evolution in the Baltic

In the