The salt industry on the Danish Kattegat island of Læsø (1150–1652): Hypersaline source, climatic dependence, and environmental impact

Abstract

Around 1,700 ruins of Medieval salt production huts have been identified on the island of Lrese. It has been uncertain what the production's raw material was, how important the production was, when and why the industry expanded and declined, and what the industry's natural causes and environmental effects were. It is shown that present-day settings of hypersaline groundwater accumulations are comparable to the palaeo-settings of the Medieval salt production and that up to I 35 production huts were simultaneously active during more than 400 years from the production began around I I 50-I 200 until the industry culminated around I 585 and completely ceased only a few decades later. The growth and decline in number of active production huts seems clearly related to climatically induced control of the length of accessible coastal stretches where hypersaline groundwater could be formed During the I 7'h century's reinforcement of the Little lee Age the length of productive stretches fell to less than I 5% of the length they had around I 585. Thus, the industry's

Absolute sea levels and isostatic changes of the eastern North Sea to central Baltic region during the last 900 years

“…(v) the tidal range is extremely small; (vi) the vertical relief of beach ridges and swales is invariably less than 25 cm; (vii) a GIA during the late Holocene of more than 1.0 mm a -1 (Ekman et al 1996;Eronen et al 2001;Påsse & Andersson 2005;Khan et al 2006), which through this study can be measured precisely; and (viii) additional local tectonic and regional relaxation uplift (Hansen 1977(Hansen , 1995(Hansen , 2010 that can be precisely quantified by this study.…”

“…; Påsse & Andersson ; Khan et al . ), which through this study can be measured precisely; and (viii) additional local tectonic and regional relaxation uplift (Hansen , , ) that can be precisely quantified by this study.…”

“…The unique setting of the southern part of the Læsø archipelago in terms of sea‐level reconstruction includes (i) several series of chronologically ordered, well‐separated palaeo‐shorelines consisting of low, sandy and alongshore‐coherent beach ridges in still uncultivated surroundings (Hansen , ); (ii) rates of coastal progradation between 0.5 and 2.6 m a −1 , which has resulted in the formation of numerous conformable beach ridges over the last 900 years (Hansen ); (iii) a wide sandy shoreface with an extremely gentle slope, ∼0.03° (1:2000); (iv) a low‐energy wave regime – waves are unable to transport pebbles, and the swash zone is vertically narrow (extending to ∼30 cm above MSL) and well defined, enabling precise measurement of palaeo‐shoreliness; (v) the tidal range is extremely small; (vi) the vertical relief of beach ridges and swales is invariably less than 25 cm; (vii) a GIA during the late Holocene of more than 1.0 mm a −1 (Ekman et al . ; Eronen et al .…”

“…This 37‐cm difference is caused by two mechanisms: (i) increasing age to the SW, causing more geological uplift to the SW than to the NE owing to the tectonic tilting of the area (see below); and (ii) propagation of the beach ridge to the NE and thus more time for sedimentary growth to the SW. The age difference between SW and NE parts of the beach ridge is considered to be less than ∼ 30 years, corresponding to the average age difference of the area's beach ridges (Hansen ).…”

“…Similarly, palaeo-shorelines formed during the last millennium at southern Laesø are elevated up to 2.5 m above MSL, while contemporary shorelines at comparable isostatic isobases in northern Jutland and western Sweden are found no higher than 1.5 m above MSL (cf. Mörner 1969;Hansen 1977Hansen , 1980Hansen , 1986Hansen , 1995Hansen , 2010Christensen 2001;Clemmensen et al 2001).…”