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The paleoceanography of Kattegat during the last deglaciation from benthic foraminiferal stable isotopes

Bokhari Friberg, Yasmin LU (2015) In Dissertations in Geology at Lund University GEOR02 20152
Department of Geology
Abstract (Swedish)
En borrkärna från Anholt (Kattegatt) togs upp under IODP-expedition 347 i Östersjön. Kärnan är daterad till ~18-14 ka BP och representerar deglaciationen i slutet av Weichselistiden. Bentiska foraminiferer av arten Elphidium excavatum clavatum analyserades för stabila isotoper (δ18O och δ13C) för att rekonstruera region-ens paleoklimat och paleoceanografi, såsom salinitet, ventilation och produktivitet i bottenvattnet. Sedimentets grovkorniga fraktion (> 63μm) mättes även, samt medelvikten per foraminiferskal, för att kunna tolka andra fak-torer, såsom sedimentets ursprung och förhållanden i foraminiferernas livsmiljö. δ18O användes för att beräkna pa-leosalinitet i Kattegatts bottenvattnet genom att anta en temperatur mellan 0 och 4°C.... (More)
En borrkärna från Anholt (Kattegatt) togs upp under IODP-expedition 347 i Östersjön. Kärnan är daterad till ~18-14 ka BP och representerar deglaciationen i slutet av Weichselistiden. Bentiska foraminiferer av arten Elphidium excavatum clavatum analyserades för stabila isotoper (δ18O och δ13C) för att rekonstruera region-ens paleoklimat och paleoceanografi, såsom salinitet, ventilation och produktivitet i bottenvattnet. Sedimentets grovkorniga fraktion (> 63μm) mättes även, samt medelvikten per foraminiferskal, för att kunna tolka andra fak-torer, såsom sedimentets ursprung och förhållanden i foraminiferernas livsmiljö. δ18O användes för att beräkna pa-leosalinitet i Kattegatts bottenvattnet genom att anta en temperatur mellan 0 och 4°C. Dessa beräkningar gav salt-halter mellan 13 och 27, med en snabb minskning i början av kärnan, och sedan en långsammare minskning till 15,7 ka då saliniteten steg. Negativa δ13C-värden indikerar en stark skiktning mellan sött eller bräckt ytvatten och saltare bottenvatten, på grund av stora mängder glacialt smältvatten som släpptes ut i Kattegatt när den skandina-viska inlandsisen drog sig tillbaka. δ13C-värden ökar vid 15,7 ka, vilket tyder på en försvagad skiktning och större inflytande av havsvatten från Nordsjön. Samtidigt börjar foraminifernas skalvikt att minska, vilket tyder på sämre kalcifikationsförhållanden för Elphidium excavatum. Andelen grovt sediment visar en stor mängd sandkornigt material i början av borrkärnan, men sjunker till värden nära 0 mellan ~18 och 16 ka, vilket tyder på att Anholt var beläget nära iskanten vid 18 ka, varpå isen drog sig tillbaka under de följande ca. 3700 åren som borrkärnan repre-senterar. (Less)
Abstract
This thesis is based on a sediment record collected from the Kattegat Sea, southwestern Scandinavia (Anholt Island area) during IODP Expedition 347 in autumn 2013, and focuses on a portion of this record spanning ~18—14 thousand years ago (ka BP), representing the last deglaciation at the end of the Weichselian. Benthic foraminifera of the species Elphidium excavatum clavatum were analysed for stable isotopes (δ18O and δ13C) to reconstruct the paleoenvironment and oceanographic setting, such as bottom water salinity, temperature and venti-lation. Additionally, the sediment coarse fraction (>63μm) and mean weight per foraminifera shell were measured as a complement to the isotope analyses to interpret other factors, such as sediment origin... (More)
This thesis is based on a sediment record collected from the Kattegat Sea, southwestern Scandinavia (Anholt Island area) during IODP Expedition 347 in autumn 2013, and focuses on a portion of this record spanning ~18—14 thousand years ago (ka BP), representing the last deglaciation at the end of the Weichselian. Benthic foraminifera of the species Elphidium excavatum clavatum were analysed for stable isotopes (δ18O and δ13C) to reconstruct the paleoenvironment and oceanographic setting, such as bottom water salinity, temperature and venti-lation. Additionally, the sediment coarse fraction (>63μm) and mean weight per foraminifera shell were measured as a complement to the isotope analyses to interpret other factors, such as sediment origin and conditions at the sea-floor. δ18O was used to calculate paleosalinities in Kattegat bottom waters by assuming a temperature between 0 and 4°C. These calculations yielded salinities varying between 13 and 27, with a rapid freshening at the beginning of the record, and a subsequent slower, stepwise salinity decrease, followed by a rise in salinity after 15.7 ka. Very negative δ13C values suggest a strong stratification between fresh surface and saline bottom waters, likely due to large amounts of glacial meltwater discharging into the Kattegat as the Scandinavian Ice Sheet (SIS) melted. The δ13C values increase after 15.7 ka, suggesting a weakened stratification, perhaps due to stronger seawater influence. A simultaneous decline in average foraminifera shell weight suggests worse calcification conditions for Elphidium excavatum in Kattegat bottom waters. Percent coarse sediment data shows a high amount of sand size fraction at the very beginning of the record, but very low values between ~18 and 15.7 ka, suggesting that Anholt was situated close to the ice margin at 18 ka, but saw a retreat of the SIS during the subsequent few thousand years. (Less)
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author
Bokhari Friberg, Yasmin LU
supervisor
organization
course
GEOR02 20152
year
type
H2 - Master's Degree (Two Years)
subject
keywords
δ13C, δ18O, Kattegat, Baltic Sea, stable isotopes, foraminifera, deglaciation, paleoceanography
publication/series
Dissertations in Geology at Lund University
report number
461
language
English
id
8229269
date added to LUP
2015-11-25 10:19:50
date last changed
2016-11-23 04:10:04
@misc{8229269,
  abstract     = {This thesis is based on a sediment record collected from the Kattegat Sea, southwestern Scandinavia (Anholt Island area) during IODP Expedition 347 in autumn 2013, and focuses on a portion of this record spanning ~18—14 thousand years ago (ka BP), representing the last deglaciation at the end of the Weichselian. Benthic foraminifera of the species Elphidium excavatum clavatum were analysed for stable isotopes (δ18O and δ13C) to reconstruct the paleoenvironment and oceanographic setting, such as bottom water salinity, temperature and venti-lation. Additionally, the sediment coarse fraction (>63μm) and mean weight per foraminifera shell were measured as a complement to the isotope analyses to interpret other factors, such as sediment origin and conditions at the sea-floor. δ18O was used to calculate paleosalinities in Kattegat bottom waters by assuming a temperature between 0 and 4°C. These calculations yielded salinities varying between 13 and 27, with a rapid freshening at the beginning of the record, and a subsequent slower, stepwise salinity decrease, followed by a rise in salinity after 15.7 ka. Very negative δ13C values suggest a strong stratification between fresh surface and saline bottom waters, likely due to large amounts of glacial meltwater discharging into the Kattegat as the Scandinavian Ice Sheet (SIS) melted. The δ13C values increase after 15.7 ka, suggesting a weakened stratification, perhaps due to stronger seawater influence. A simultaneous decline in average foraminifera shell weight suggests worse calcification conditions for Elphidium excavatum in Kattegat bottom waters. Percent coarse sediment data shows a high amount of sand size fraction at the very beginning of the record, but very low values between ~18 and 15.7 ka, suggesting that Anholt was situated close to the ice margin at 18 ka, but saw a retreat of the SIS during the subsequent few thousand years.},
  author       = {Bokhari Friberg, Yasmin},
  keyword      = {δ13C,δ18O,Kattegat,Baltic Sea,stable isotopes,foraminifera,deglaciation,paleoceanography},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {The paleoceanography of Kattegat during the last deglaciation from benthic foraminiferal stable isotopes},
  year         = {2015},
}