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Holocene and Latest Glacial Paleoceanography in the North-Eastern Skagerrak
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Detailed information on past oceanographic and climatic changes is crucial for our understanding of natural climate variability and for the assessment of future climate variations. Sediments strongly influenced by the North Atlantic Current accumulate at high rates in the northeastern Skagerrak, forming a potential highresolution archive for information on past climatic and oceanographic processes and events. Through a highresolution, multi-proxy study of the 32 meter long core MD99-2286 from the north-eastern Skagerrak, and interpretation of chirp sonar profiles from the coring area, this thesis provides new and detailed insights about the paleoceanographic development of the eastern North Sea region since the deglaciation.

The chronostratigraphic control of core MD99-2286 relies on 27 radiocarbon dates. Ages are presented in calibrated thousand years before present (abbreviated “kyr”). Core MD99-2286 was correlated to chirp sonar profiles using measured physical properties. This correlation demonstrates that a strong regional acoustic reflector, previously assumed to represent the Pleistocene/Holocene boundary, was formed as a result of rapid ice retreat during the latest Pleistocene. Based on the distribution of ice rafted debris in the core, ice berg calving in the Skagerrak ended at 10.7 kyr. Detailed grain-size analyses of the core were interpreted using a novel 3D-visualization technique. Between 11.3 and 10.3 kyr, clay-rich distal glacial marine sediments were deposited in the northeastern Skagerrak, derived from Baltic melt-water outflow across south-central Sweden through the Otteid-Stenselva strait. As a result of differential isostatic uplift, the route of the major outflow and the associated sediment deposition moved southwards along the Swedish west coast. After 10.3 kyr, sediment deposition in the north-eastern Skagerrak gradually adopted to a fully interglacial normal marine sedimentation dominated by Atlantic inflow and the North Jutland Current.

The establishment of the modern circulation system in the eastern North Sea is marked by abrupt coarsening of the sediments in core MD99-2286 at 8.5 kyr. This was a result of increased Atlantic inflow, opening of the English Channel and the Danish straits, and formation of the South Jutland Current. Mineral magnetic properties of the core show a distinct relationship reflecting general sediment source variability. After 8.5 kyr, sediments in the northeastern Skagerrak were derived predominantly from the Atlantic Ocean and the North Sea, with varying contributions from the South Jutland Current, the Baltic Current, and the currents along the coasts of western Sweden and southern Norway. Between 6.3 and 3.8 kyr, the eastern North Sea was further developed towards the modern situation by an increase of the South Jutland Current flow. The Skagerrak bottom currents were probably forced by strong Atlantic water inflow between 0.9 and 0.5 kyr, and after that by increased wind stress. The influence of regional climate on the eastern North Sea circulation has increased since the middle of the Holocene.

Place, publisher, year, edition, pages
Stockholm: Institutionen för geologi och geokemi , 2005. , 30 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 322
Keyword [en]
Skagerrak, Holocene, sediment, chirp sonar, grain size, mineral magnetic properties
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-413ISBN: 91-7155-038-0 (print)OAI: oai:DiVA.org:su-413DiVA: diva2:193571
Public defence
2005-04-15, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00
Opponent
Supervisors
Available from: 2005-03-23 Created: 2005-03-23Bibliographically approved
List of papers
1. Holocene sedimentation in the Skagerrak interpreted from chirp sonar and core data
Open this publication in new window or tab >>Holocene sedimentation in the Skagerrak interpreted from chirp sonar and core data
2005 In: Journal of Quaternary Science, ISSN 0267-8179, Vol. 20, no 1, 21-32 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23627 (URN)
Note
Part of urn:nbn:se:su:diva-413Available from: 2005-03-23 Created: 2005-03-23Bibliographically approved
2. Late Glacial and Holocene paleoceanography in the Skagerrak from high-resolution grain size records
Open this publication in new window or tab >>Late Glacial and Holocene paleoceanography in the Skagerrak from high-resolution grain size records
2005 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 222, no 3-4, 344-369 p.Article in journal (Refereed) Published
Abstract [en]

High-resolution grain size analyses of the AMS 14C-dated, 32 m long core MD99-2286 from the northeastern Skagerrak were performed in order to study late Glacial and Holocene paleoceanographic and sedimentary changes. All ages in this study are given in calibrated thousand years before present (= AD 1950), abbreviated ‘kyr’, unless otherwise noted.

The distinct ending of IRD (ice rafted debris) in core MD99-2286, which was retrieved from a location down current from the final calving ice margin in the region, indicates that iceberg calving in the Skagerrak ended between 10.6 and 10.2 kyr.

A clay-rich sequence in core MD99-2286, deposited between 11.3 and 10.3 kyr, is attributed to outflow from the Baltic basin across south central Sweden. The sequence is correlated to similar units from cores along the Swedish west coast. The onset of this clay-rich deposition occurs progressively later in cores further south along the coast, supporting a previous hypothesis that differential glacio-isostatic uplift caused a southward migration of the Baltic outflow from the Otteid-Stenselva to the Göta Älv outlet.

A distinct coarsening towards younger sediments in core MD99-2286 indicates a hydrographic shift at 8.5 kyr, which is correlated to a shift previously reported in the Skagerrak, Kattegat and the Norwegian Channel. This shift reflects the establishment of the modern circulation system in the eastern North Sea, as a consequence of the opening of the English Channel and the Danish straits and increased Atlantic water inflow, and the subsequent development of the South Jutland Current. A general trend of coarsening, poorer sorting and increasing variability from 8.5 kyr until the present indicates increasing strength and influence of the variable South Jutland Current.

A series of changes from ca. 6.3 to ca. 3.8 kyr in core MD99-2286 reflects strengthening of the Jutland Current towards the present day sedimentation system in the Skagerrak–Kattegat. These changes are correlated to previously reported hydrographic shifts at 5.5 14C years BP in the Skagerrak and at 4.0 14C years BP in the Kattegat. It is suggested that these shifts were separate features of a transitional period related to strengthening of the current system. The resulting changes are differently manifested in different parts of the Skagerrak–Kattegat, due to the complex circulation system.

The last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material, reflecting a circulation system significantly modified by regional climatic conditions, especially the general wind directions and storm frequency over the southern North Sea.

Place, publisher, year, edition, pages
Elsevier B.V., 2005
Keyword
Skagerrak; Holocene; grain size; sediment; Baltic Sea; hydrographic shift
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-23628 (URN)10.1016/j.palaeo.2005.03.025 (DOI)
Note
Part of urn:nbn:se:su:diva-413Available from: 2005-03-23 Created: 2005-03-23 Last updated: 2011-01-18Bibliographically approved
3. Late Glacial and Holocene sediment sources and transport patterns in the Skagerrak interpreted from mineral magnetic properties and grain size data
Open this publication in new window or tab >>Late Glacial and Holocene sediment sources and transport patterns in the Skagerrak interpreted from mineral magnetic properties and grain size data
2006 (English)In: Quaternary Science Reviews, ISSN 0277-3791, Vol. 25, no 11-12, 1247-1263 p.Article in journal (Refereed) Published
Abstract [en]

Lateglacial and Holocene changes in circulation, sedimentation and provenance in north-eastern Skagerrak were studied using high-resolution mineral magnetic and grain size data from the 32-m-long IMAGES core MD99-2286. Ages are given in calibrated thousand years BP (‘cal. kyr’). Between 12 and 11.3 cal. kyr, a calving ice front occupied the Oslo Fjord, and sedimentation was strongly influenced by meltwater carrying re-deposited glacial sediments from southern Norway and western Sweden. Between 11.3 and 10.3 cal. kyr, sedimentation was dominated by re-deposited glacial sediments transported by meltwater outflow across south-central Sweden. After the Otteid-Stenselva outlet was closed at 10.3 cal. kyr, glacial marine sedimentation changed to normal marine sedimentation. At 8.5 cal. kyr, a hydrographic shift, marking the onset of modern circulation in the Skagerrak–Kattegat, occurred as a result of increased Atlantic inflow, transgression of former land areas, and opening of the English Channel and the Danish Straits. After 8.5 cal. kyr, sedimentation was governed by input from the Atlantic Ocean and the North Sea, with varying contributions from the South Jutland Current, Baltic Current, and currents along the coasts of western Sweden and southern Norway. From 0.9 cal. kyr until present, the sedimentation was totally dominated by southern North Sea and Atlantic Ocean sources.

Place, publisher, year, edition, pages
Elsevier Ltd, 2006
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-23629 (URN)10.1016/j.quascirev.2005.11.002 (DOI)
Note
Part of urn:nbn:se:su:diva-413Available from: 2005-03-23 Created: 2005-03-23 Last updated: 2010-09-15Bibliographically approved
4. Late Holocene coastal hydrographic and climate changes in the eastern North Sea
Open this publication in new window or tab >>Late Holocene coastal hydrographic and climate changes in the eastern North Sea
Show others...
2006 (English)In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 16, no 7, 987-1001 p.Article in journal (Refereed) Published
Abstract [en]

We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.

Keyword
*CLIMATIC changes *GEOLOGY, Stratigraphic -- Holocene *OCEAN bottom *MARINE sediments *SEDIMENTATION & deposition *SUBMARINE geology *ATMOSPHERIC circulation *OCEAN currents
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-23630 (URN)10.1177/0959683606hl989rp (DOI)
Note
Part of urn:nbn:se:su:diva-413Available from: 2005-03-23 Created: 2005-03-23 Last updated: 2010-09-10Bibliographically approved

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