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Post-Glacial History of Sea-Level and Environmental Change in the Southern Baltic Sea

Kortekaas, Marloes LU (2007) In LUNDQUA Thesis 57.
Abstract
A new palaeoenvironmental record of the post-glacial history of the southern Baltic Sea (~14 ka to present) is presented. During this period, large water level and salinity changes occurred in the Baltic Basin due to opening and closing of connections to the North Atlantic. Previous attempts to establish a detailed chronology for these palaeoenvironmental changes have been conducted mainly in coastal settings, where organic material for 14C dating is abundant. Many of these records are, however, discontinuous due to large water level fluctuations. In the relatively deep water of the Arkona Basin (45 m deep) in the southern Baltic Sea the sediment record is expected to be more or less continuous, but lack of organic material for 14C dating... (More)
A new palaeoenvironmental record of the post-glacial history of the southern Baltic Sea (~14 ka to present) is presented. During this period, large water level and salinity changes occurred in the Baltic Basin due to opening and closing of connections to the North Atlantic. Previous attempts to establish a detailed chronology for these palaeoenvironmental changes have been conducted mainly in coastal settings, where organic material for 14C dating is abundant. Many of these records are, however, discontinuous due to large water level fluctuations. In the relatively deep water of the Arkona Basin (45 m deep) in the southern Baltic Sea the sediment record is expected to be more or less continuous, but lack of organic material for 14C dating has impeded previous studies.



Here, palaeoenvironmental change in the Arkona Basin is reconstructed on the basis of geochemical, sedimentological, mineral magnetic and palaeontological investigations. Additionally, independent physically based chronological control is, for the first time, obtained using Optically Stimulated Luminescence (OSL) dating on fine quartz sand from a ~10.86 m long sediment core. Tests of luminescence characteristics confirmed the suitability of the material for OSL dating and the ages agree well with the available AMS 14C ages on shells; in contrast, bulk sediment 14C ages are generally ~1000 years too old. Stratigraphic marker horizons in this deep basin are now absolutely dated, allowing comparison and testing of existing models of post-glacial Baltic Sea regional development.



Glacial varved clay was deposited during the Baltic Ice Lake stage and a sand layer representing the Baltic Ice Lake drainage to the North Atlantic is dated to ~11.6 ka. This event is followed by a period of low water level and enhanced influence from the Oder River. A period of very rapid sedimentation occurs between ~10.9 and ~10.4 ka and is attributed to the Ancylus Lake transgression. A first anomalous slightly brackish water inflow is recorded at ~9.8 ka, but there is no clear evidence for fully brackish conditions until ~6.5 ka. At that time, the lithologic change to clay gyttja represents a distinct shift in the circulation mode, with the onset of a high-productivity, brackish circulation system in the southern Baltic. Post-depositional diffusion of sulphur from the clay gyttja most likely explains the presence of greigite (Fe3S4) concretions in the underlying silty clay unit.



With this new chronology an anomaly appears between the classical model of the Littorina transgressions with brackish conditions starting ~8.5 ka, supported by studies in coastal lagoons, and our first clear brackish/marine influence occurring as late as ~6.5 ka based on studies performed in the deeper basins. This implies that the circulation system of the present Baltic Sea, with fully brackish conditions and the Danish-German Straits as the dominant inflow areas, only started from ~6.5 ka onwards. (Less)
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author
opponent
  • Professor Knudsen, Karen-Luise, Aarhus University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
kartografi, klimatologi, Geofysik, fysisk oceanografi, physical oceanography, meteorology, Sedimentologi, Stratigrafi, Stratigraphy, Baltic Sea, geokemi, Petrologi, mineralogi, geochemistry, mineralogy, Petrology, greigite, mineral magnetics, sea-level changes, Holocene, Littorina transgression, geomorphology, pedology, cartography, climatology, meteorologi, Geophysics, Sedimentology, Optically Stimulated Luminescence (OSL), Fysisk geografi, geomorfologi, marklära, Physical geography
in
LUNDQUA Thesis
volume
57
pages
34 pages
publisher
Department of Geology, Lund University
defense location
Pangea, Geocentrum II, Sölvegatan 12, SE-22362 Lund, Sweden
defense date
2007-03-30 14:15
ISSN
0281-3033
ISBN
978-91-86746-84-1
language
English
LU publication?
yes
id
305edcd3-a017-4faa-9e8a-f5f3e6b8396c (old id 548242)
date added to LUP
2007-09-05 10:10:06
date last changed
2016-09-19 08:44:59
@phdthesis{305edcd3-a017-4faa-9e8a-f5f3e6b8396c,
  abstract     = {A new palaeoenvironmental record of the post-glacial history of the southern Baltic Sea (~14 ka to present) is presented. During this period, large water level and salinity changes occurred in the Baltic Basin due to opening and closing of connections to the North Atlantic. Previous attempts to establish a detailed chronology for these palaeoenvironmental changes have been conducted mainly in coastal settings, where organic material for 14C dating is abundant. Many of these records are, however, discontinuous due to large water level fluctuations. In the relatively deep water of the Arkona Basin (45 m deep) in the southern Baltic Sea the sediment record is expected to be more or less continuous, but lack of organic material for 14C dating has impeded previous studies.<br/><br>
<br/><br>
Here, palaeoenvironmental change in the Arkona Basin is reconstructed on the basis of geochemical, sedimentological, mineral magnetic and palaeontological investigations. Additionally, independent physically based chronological control is, for the first time, obtained using Optically Stimulated Luminescence (OSL) dating on fine quartz sand from a ~10.86 m long sediment core. Tests of luminescence characteristics confirmed the suitability of the material for OSL dating and the ages agree well with the available AMS 14C ages on shells; in contrast, bulk sediment 14C ages are generally ~1000 years too old. Stratigraphic marker horizons in this deep basin are now absolutely dated, allowing comparison and testing of existing models of post-glacial Baltic Sea regional development.<br/><br>
<br/><br>
Glacial varved clay was deposited during the Baltic Ice Lake stage and a sand layer representing the Baltic Ice Lake drainage to the North Atlantic is dated to ~11.6 ka. This event is followed by a period of low water level and enhanced influence from the Oder River. A period of very rapid sedimentation occurs between ~10.9 and ~10.4 ka and is attributed to the Ancylus Lake transgression. A first anomalous slightly brackish water inflow is recorded at ~9.8 ka, but there is no clear evidence for fully brackish conditions until ~6.5 ka. At that time, the lithologic change to clay gyttja represents a distinct shift in the circulation mode, with the onset of a high-productivity, brackish circulation system in the southern Baltic. Post-depositional diffusion of sulphur from the clay gyttja most likely explains the presence of greigite (Fe3S4) concretions in the underlying silty clay unit.<br/><br>
<br/><br>
With this new chronology an anomaly appears between the classical model of the Littorina transgressions with brackish conditions starting ~8.5 ka, supported by studies in coastal lagoons, and our first clear brackish/marine influence occurring as late as ~6.5 ka based on studies performed in the deeper basins. This implies that the circulation system of the present Baltic Sea, with fully brackish conditions and the Danish-German Straits as the dominant inflow areas, only started from ~6.5 ka onwards.},
  author       = {Kortekaas, Marloes},
  isbn         = {978-91-86746-84-1},
  issn         = {0281-3033},
  keyword      = {kartografi,klimatologi,Geofysik,fysisk oceanografi,physical oceanography,meteorology,Sedimentologi,Stratigrafi,Stratigraphy,Baltic Sea,geokemi,Petrologi,mineralogi,geochemistry,mineralogy,Petrology,greigite,mineral magnetics,sea-level changes,Holocene,Littorina transgression,geomorphology,pedology,cartography,climatology,meteorologi,Geophysics,Sedimentology,Optically Stimulated Luminescence (OSL),Fysisk geografi,geomorfologi,marklära,Physical geography},
  language     = {eng},
  pages        = {34},
  publisher    = {Department of Geology, Lund University},
  school       = {Lund University},
  series       = {LUNDQUA Thesis},
  title        = {Post-Glacial History of Sea-Level and Environmental Change in the Southern Baltic Sea},
  volume       = {57},
  year         = {2007},
}