A paleoclimate record through the past millennium from the Skagerrak based on grain-size data

The Skagerrak

The Skagerrak is a current-controlled sedimentary basin between the North and Baltic Seas. It forms the deepest part (> 700 m water depth) of the Norwegian Trench and is the westernmost part of a narrow strait which guides the water-mass exchange between the two epicontinental seas. Being highly sensitive to wind forcing, current velocities may be extreme in the shallower areas off northern Jutland (Fonselius, 1990) due to strong westerlies, whereas they decelerate again further east. The brackish Baltic Current enters the Skagerrak via the mouth of the Kattegat. In the inner Skagerrak water masses turn around and slowly leave the Skagerrak in the form of the north-headed Norwegian Coastal Current. A deep counter current to the Norwegian Coastal Current injects highly saline Atlantic water into the Skagerrak deep (Dahl, 1978).

Strong westerlies, emerging from the Northern Hemisphere main westerly wind stream (MWWS) are likely to amplify current intensities, while easterly wind directions can hamper the water mass circulation in the Skagerrak. Changes in current energies can be traced by the granulometric composition of the sediments. Earlier investigations regarding the movement of the cyclone tracks (northwards during warm and southwards during cold periods; see e.g. LAMB, 1969) can be confirmed: the Medieval Warm Period (ca. 800/1000-1350 AD) is characterized by generally finer sediments indicating lower bottom current energies. Thus, minor wind-forcing and a northern position of the MWWS can be inferred. During the Little Ice Age (ca. 1350-1900 AD) the southward movement of the MWWS as far south as the Skagerrak system and probably further south is suggested resulting in a stormy first phase, a calm but cold main phase and again a stormy last phase. Similar processes may have affected the area of the Skagerrak during the entire Holocene.

The images show the interpreted positions of the main westerly wind stream and the associated cyclone tracks during the past centuries and millennia. If the high latitudes are affected by a future warming trend similar to the mid and lower latitudes, storm frequencies and strengths over middle Europe should decrease under future global warming. The pressure gradient over the North Atlantic maybe decreasing and the cyclones would be weaker and located further to the north.

HASS, H.C. (1999): Sedimentation rates and late Holocene climate change: a case study from the Skagerrak (NE North Sea).- in: Bruns, P. & Hass, H.C. (Hrsg.) (1999): On the determination of sediment accumulation rates. Geo Research Forum 5, Trans Tech Publications, ZŸrich (CH), 197-208.

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

HASS, H.C. (1996): Northern Europe climate variations during Late Holocene: evidence from marine Skagerrak.- Palaeogeography, Palaeoclimatology, Palaeoecology 123, 121-145.

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

HASS, H.C. & KAMINSKI, M.A. (1994): Change in atmospheric and oceanic circulation reflected in North Sea sediments during the late Holocene.- Zentralblatt für Geologie und Paläontologie Teil I, H.1/2, 51-65 pp.

HASS, H.C. (1993): Depositional processes under changing climate: Upper Subatlantic granulometric records from the Skagerrak (NE-North Sea).- Marine Geology 111, 361-378.