Late Holocene climate change: The benthic foraminifer record from the Skagerrak.

The climate of the past 4,000 years

Climate fluctuations during the upper Holocene had significant influence on man. These climatic periods include: SBO = Subboreal Climate Optimum: until ca. 900 BC. Warm. SAP = climate deterioration ('pessimum') of the Subatlantic: until ca. 300-400 BC. Cool. RO = Climate optimum of Roman times: until ca. 300-400 AD. Warm and dry. May have supported the Roman empire. VW = Climate deterioration at the time of the general south migration of Germanic tribes in Europe: until ca. 700 AD. Cool and wet. MWP = Medieval Warm Period: until ca. 1400 AD. Warm summers, mild winters (average temperature more than 1K higher than today). Period of the Vikings: settlements in Greenland and Labrador. LIA = Little Ice Age: until 1900. First phase cool and stormy, second phase cold, third phase cool and stormy. 100,000s of flood victims in Germany. Doom of the Vikings. Plague, wars, harvest failures. Temperatures 0.6K below today (locally much more!). MO = Modern Climate Optimum: 1930-1950ies.

High resolution granulometric and stable oxygen isotope data from the Skagerrak (NE North Sea) suggest a tight coupling of atmospheric and water mass circulation during the Late Holocene. Climate periods can be pinpointed and characterized by fluctuations in current strengths and water mass properties, which are dependant on prevailing wind directions. Generally, colder climate intervals are characterized by stronger bottom current velocities, caused by a predominant zonal atmospheric circulation pattern. Warmer phases are marked by weaker bottom currents, resulting from a predominant meridional type circulation.

The benthic foraminifer record

Calcareous benthic foraminifera from four cores from the southern flank of the Skagerrak (NE North Sea) were investigated in order to estimate the response of this fossil group to climate fluctuations during the upper part of the Holocene. Q-mode factor analyses were carried out for the most abundant taxa (reference list). The results reveal C. laevigata, H. balthica, M. barleeanus, G. turgida, B. marginata, and U. peregrina as most common/important taxa. In the upper part of all cores B. skagerrakensis shows a significant increase and dominates the foraminifer fauna in cores from greater water depth. The data suggest no direct relation between the fluctuations of foraminifer assemblages and climate change.

However, climate forced fluctuations in the strength of the water-circulation caused considerable changes in the foraminifer assemblages. Three major assemblages were used for environmental analysis: H. balthica dominated assemblages were identified as indicators for stagnant conditions. They characterize the oldest core sections, most probably the Holocene climate optimum. C. laevigata assemblages seem to indicate increasing current strength, a process that is often associated with deteriorating climatic conditions. B. skagerrakensis appears to have a certain relation to unsta-ble water masses, and probably a tolerance for increasing polution of the North Sea since the advent of modern industrialization.

HASS, H.C. (1997): The benthic foraminiferal response to late Holocene climate change over northern Europe.- In: Hass, H.C. & Kaminski, M.A. (eds.) (1997): Micropaleontology and Paleoceanology of the North Atlantic.- Grzybowsky Foundation Special Publication, 5, 199-216.

HASS, H.C. (1997): Recent and subrecent agglutinated foraminifera in four box cores from the Skagerrak (NE North Sea).- In: Hass, H.C. & Kaminski, M.A. (eds.) (1997): Micropaleontology and Paleoceanology of the North Atlantic.- Grzybowsky Foundation Special Publication, 5, 217-226.

HASS, H.C. (1995): Sedimentologische und mikropalŠontologische Untersuchungen zur Entwicklung des Skagerraks (NE Nordsee) im SpŠtholozŠn.- GEOMAR Report, 34, 115 pp.