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An environmental magnetic study of a marine sediment core from Disko Bugt, West Greenland : implications for ocean current variability

Persson, Jonas (2008) In Dissertations in Geology at Lund University
Department of Geology
Abstract
An 11 m long marine sediment core was collected during a June-July 2007 scientific cruise with the German research vessel R/V Maria Sibylla Merian to the area of Disko Bugt, western Greenland. The core, designated 343340-6-1, was examined using environmental magnetic methods and X-ray fluorescence. The study contributes to a larger project designed to map the variability in sediment source and transport during the Holocene and relate these to ocean circulation, the behaviour of Greenland glaciers and climate change. Measurements of magnetic susceptibility and artificially applied magnetic remanences were performed on contiguous discrete samples from the whole length of the core. Complementary element analyses were done using X-ray... (More)
An 11 m long marine sediment core was collected during a June-July 2007 scientific cruise with the German research vessel R/V Maria Sibylla Merian to the area of Disko Bugt, western Greenland. The core, designated 343340-6-1, was examined using environmental magnetic methods and X-ray fluorescence. The study contributes to a larger project designed to map the variability in sediment source and transport during the Holocene and relate these to ocean circulation, the behaviour of Greenland glaciers and climate change. Measurements of magnetic susceptibility and artificially applied magnetic remanences were performed on contiguous discrete samples from the whole length of the core. Complementary element analyses were done using X-ray fluorescence to detect shifts in major element content, which could be linked to changes in the magnetic record. The focus of the magnetic mineral identification was to distinguish between sections of elevated haematite and magnetite levels, as the relation between these two minerals is what primarily can be expected to cause any major shift in magnetic properties. An age-model was constructed for the core by means of correlation with another radiocarbon dated core from the same area, which indicates relatively ice-free conditions since approximately 8.5 kyr BP. The major mineral magnetic units comprise a relatively haematite-enriched section approximately covering the interval 1000-700 cm, followed by an area dominated by magnetite at ca. 700-400 cm. These two features comprise the main part of the core, from the bottom until around 350 cm depth, corresponding to an age of around 7.9 kyr BP. The uppermost part was not easy to interpret because the overall magnetic material content is diluted by organic content, which suggests that marine productivity increased after 7.9 kyr BP. It is argued that an increasing haematite component implies a stronger West Greenland Current (WGC). Parts that are instead dominated by magnetite, without signs of any significant amount of haematite, are thought to indicate a weaker WGC as the sediments would be influenced mainly by local, basaltic sources. These ocean current fluctuations may be connected to climate variations during the Holocene, but an improved age-model is needed to allow comparisons with other climate records. (Less)
Abstract (Swedish)
Under en vetenskaplig expedition med det tyska forskningsfartyget R/V Maria Sibylla Merian till Disko Bugt, på västra Grönland, så provtogs under sommaren 2007 ett antal marina sedimentborrkärnor. Borrkärnan med beteckningen 343340-6-1 undersöktes inom ramarna för denna studie med miljömagnetiska metoder. Syftet med undersökningen har varit att kartlägga variationer i de mineralogiska egenskaperna över tid och utifrån det bestämma hur sedimentprovenansen har skiftat. Försök har dessutom gjorts att utifrån dessa slutsatser göra kopplingar till trender och förändringar i det regionala klimatet med betoning på variationer i havsströmmarna. Mätningar har gjorts med avseende på magnetisk remanens och olika magnetiska rest-egenskaper (ARM, SIRM,... (More)
Under en vetenskaplig expedition med det tyska forskningsfartyget R/V Maria Sibylla Merian till Disko Bugt, på västra Grönland, så provtogs under sommaren 2007 ett antal marina sedimentborrkärnor. Borrkärnan med beteckningen 343340-6-1 undersöktes inom ramarna för denna studie med miljömagnetiska metoder. Syftet med undersökningen har varit att kartlägga variationer i de mineralogiska egenskaperna över tid och utifrån det bestämma hur sedimentprovenansen har skiftat. Försök har dessutom gjorts att utifrån dessa slutsatser göra kopplingar till trender och förändringar i det regionala klimatet med betoning på variationer i havsströmmarna. Mätningar har gjorts med avseende på magnetisk remanens och olika magnetiska rest-egenskaper (ARM, SIRM, IRM). Genom att bestämma dessa parametrar så är det möjligt att spåra förekomsten av vissa magnetiska mineral. Eftersom ett sedimentprov består av en stor mängd individuella mineralkorn så kommer de erhållna värdena att representera de samlade magnetiska egenskaperna för samtliga korn i provet. Svårigheterna som därmed tillkommer har gjort att det bedömts som föga meningsfullt att sträva efter en fullständig beskrivning av det mineralogiska innehållet. Arbetet har koncentrerats på att undersöka fluktuationer i förhållandet mellan magnetit- och hematitberikade sediment, samt identifiera långsiktiga trender. Ytterligare analyser gjordes med röntgenflourosensce (XRF) för att studera förändringar i mängderna av olika grundämnen har också använts. Genom korrelering med en parallell borrkärna, som daterats med ett antal 14C-analyser, har det kunnat fastsällas att den undersökta borrkärnan sannolikt inte är äldre än ca 8 500 år. Resultaten visar på ett betydande inslag av hematit i de äldre delarna, med ett skifte till mer magnetit-dominerade sediment vid en nivå av ca 750 cm, motsvarandes en ålder på omkring 8 000 år. En stadig nedgång i ett flertal magnetiska parametrar tar sin början vid ca 400 cm och övergår sedan i ett par kraftiga svängningar i de övre 200 cm. Denna nedgång har tolkats som början på Holocen, och förklaras med att det minerogena materialet spätts ut av en ökad biologisk produktion. Det argumenteras att hematitrika avsnitt av borrkärnan antyder en stark West Greenland Current (WGC), som är den norrgående ström som följer den grönländska västkusten. Delar av borrkärnan som saknar tecken på ett betydande hematitinnehåll, och som domineras av magnetit, antas signalera en försvagad WGC, då sedimenten här huvudsakligen tros vara dominerade av lokala, basaltiska källor. Dessa variationer i havsströmmarna, som indikeras av de undersökta magnetiska egenskaperna, kan eventuellt kopplas samman med klimatförändringar under Holocen. Det svaga underlaget för dateringen av borrkärnan medför att åldersbestämningen blir osäker, därmed är det i nuläget svårt att göra jämförelser med andra klimatarkiv. (Less)
Please use this url to cite or link to this publication:
author
Persson, Jonas
supervisor
organization
alternative title
En miljömagnetisk studie av en marin sedimentborrkärna från Disko Bugt, västra Grönland : följder för havsströmmarnas variabilitet
year
type
H1 - Master's Degree (One Year)
subject
keywords
Disko Bugt, mineral magnetism, environmental magnetism, magnetic susceptibility, ARM, SIRM, IRM, HIRM, miljömagnetism, magnetisk mottaglighet
publication/series
Dissertations in Geology at Lund University
report number
234
language
English
id
2303195
date added to LUP
2012-01-27 17:18:01
date last changed
2012-01-27 17:18:01
@misc{2303195,
  abstract     = {An 11 m long marine sediment core was collected during a June-July 2007 scientific cruise with the German research vessel R/V Maria Sibylla Merian to the area of Disko Bugt, western Greenland. The core, designated 343340-6-1, was examined using environmental magnetic methods and X-ray fluorescence. The study contributes to a larger project designed to map the variability in sediment source and transport during the Holocene and relate these to ocean circulation, the behaviour of Greenland glaciers and climate change. Measurements of magnetic susceptibility and artificially applied magnetic remanences were performed on contiguous discrete samples from the whole length of the core. Complementary element analyses were done using X-ray fluorescence to detect shifts in major element content, which could be linked to changes in the magnetic record. The focus of the magnetic mineral identification was to distinguish between sections of elevated haematite and magnetite levels, as the relation between these two minerals is what primarily can be expected to cause any major shift in magnetic properties. An age-model was constructed for the core by means of correlation with another radiocarbon dated core from the same area, which indicates relatively ice-free conditions since approximately 8.5 kyr BP. The major mineral magnetic units comprise a relatively haematite-enriched section approximately covering the interval 1000-700 cm, followed by an area dominated by magnetite at ca. 700-400 cm. These two features comprise the main part of the core, from the bottom until around 350 cm depth, corresponding to an age of around 7.9 kyr BP. The uppermost part was not easy to interpret because the overall magnetic material content is diluted by organic content, which suggests that marine productivity increased after 7.9 kyr BP. It is argued that an increasing haematite component implies a stronger West Greenland Current (WGC). Parts that are instead dominated by magnetite, without signs of any significant amount of haematite, are thought to indicate a weaker WGC as the sediments would be influenced mainly by local, basaltic sources. These ocean current fluctuations may be connected to climate variations during the Holocene, but an improved age-model is needed to allow comparisons with other climate records.},
  author       = {Persson, Jonas},
  keyword      = {Disko Bugt,mineral magnetism,environmental magnetism,magnetic susceptibility,ARM,SIRM,IRM,HIRM,miljömagnetism,magnetisk mottaglighet},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {An environmental magnetic study of a marine sediment core from Disko Bugt, West Greenland : implications for ocean current variability},
  year         = {2008},
}