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Sources and effects of short-term environmental changes in Gullmar Fjord, Sweden, inferred from the composition of sedimentary organic matter

Viehweger, Bernhard LU (2015) In Dissertations in Geology at Lund University GEOR02 20151
Department of Geology
Abstract
In this study I will assess sources and effects of short-term environmental changes on the sedimentary organic matter in Gullmar Fjord. To achieve this, a high resolution sediment core (sedimentation rate 0.7 cm yr -1) was retrieved from the deepest part in the fjord and analyzed with multiple geochemical methods, targeting bulk organic matter and biomarker composition. The distribution of n-alkanes did not display any major changes for the terrestrial fraction in the investigated time frame from 1954 until 2014. Marine organic matter was found to be the dominant source of sedimentary organic matter in the fjord, though it is most likely produced remotely in the Skagerrak. Sea surface temperature (SST) reconstructions based on long-chain... (More)
In this study I will assess sources and effects of short-term environmental changes on the sedimentary organic matter in Gullmar Fjord. To achieve this, a high resolution sediment core (sedimentation rate 0.7 cm yr -1) was retrieved from the deepest part in the fjord and analyzed with multiple geochemical methods, targeting bulk organic matter and biomarker composition. The distribution of n-alkanes did not display any major changes for the terrestrial fraction in the investigated time frame from 1954 until 2014. Marine organic matter was found to be the dominant source of sedimentary organic matter in the fjord, though it is most likely produced remotely in the Skagerrak. Sea surface temperature (SST) reconstructions based on long-chain alkenones do not show any general increase during the studied interval, as observed from the hydrographic data set available for Gullmar Fjord. Temperatures of 14.1 to 21.1°C (mean 16.4 ± 1.6) were reconstructed, so the haptophyte blooms producing the long-chain alkenones occurred most likely during summer to early autumn. However, they would also fit to temperatures and blooming seasons reported for the Skagerrak. Even though Gullmar Fjord is considered to be free from industrial pollution, we found indications which could be interpreted as a slight contamination of the sediments by petrogenic hydrocarbons. Lower oxygen minimum concentrations observed in the bottom water since the 1980s are thought to be caused by changes in the North Atlantic Oscillation (NAO) and were related with a possibly ongoing eutrophication in previous studies. Signs for an ongoing eutrophication in the fjord were not visible in our sedimentary organic matter record, suggesting that most marine organic matter is produced in the Skagerrak, or that there is no ongoing
eutrophication in the fjord since the 1950s. (Less)
Popular Abstract (Swedish)
Den här studien undersöker källor och effekt av kortsiktiga miljöförändringar genom studier av sedimentärt organiskt material (OM) i Gullmarsfjorden. En sedimentsekvens (sedimentationshastighet 0.7 cm år-1) från den djupaste delen av fjorden analyserades i hög upplösning med flera olika geokemiska metoder applicerat på OM med fokus på komposition av biomarkörer. Fördelningen av n-alkener uppvisade inga större förändringar i den terrestra fraktionen under den undersökta tidsperioden mellan 1954 och 2014. Marint OM visade sig vara den dominerande källan av sedimentärt OM i fjorden, dock är det troligt att att produktionen skett längre ut i Skagerrak. Rekonstruktioner av havsytans temperatur baserat på långa kedjor av alkenoner uppvisar ingen... (More)
Den här studien undersöker källor och effekt av kortsiktiga miljöförändringar genom studier av sedimentärt organiskt material (OM) i Gullmarsfjorden. En sedimentsekvens (sedimentationshastighet 0.7 cm år-1) från den djupaste delen av fjorden analyserades i hög upplösning med flera olika geokemiska metoder applicerat på OM med fokus på komposition av biomarkörer. Fördelningen av n-alkener uppvisade inga större förändringar i den terrestra fraktionen under den undersökta tidsperioden mellan 1954 och 2014. Marint OM visade sig vara den dominerande källan av sedimentärt OM i fjorden, dock är det troligt att att produktionen skett längre ut i Skagerrak. Rekonstruktioner av havsytans temperatur baserat på långa kedjor av alkenoner uppvisar ingen generell ökning av temperaturen under den undersökta tidsperioden. Samma slutsats kan dras från hydrografiska data från Gullmarsfjorden. Temperaturer mellan 14.1 till 21.1°C (medel 16.4 ± 1.6) uppmättes vilket tyder på att blomningarna av fästalger (Haptophyta) som producerar långa kedjor av alkenoner troligtvis ägde rum under sommar till tidig höst. Temperaturspannet anstår emellertid också blomningstider och temperaturer rapporterade för Skagerrak. Även om Gullmarsfjorden anses förskonad från industriella föroreningar så fanns indikationer till en ringa förorening av petrogena kolväten. Tidigare studier har föreslagit att de syre-minima som observerats sedan 1980-talet kan vara beroende av den nordatlantiska oscillationen (NAO) vilket även har kopplats till den pågående eutrofieringen av fjorden. I denna studien fanns inga tecken på en pågående eutrofiering i fjorden utifrån det sedimentära organiska materialet, antingen på grund av dominansen av organiskt material från Skagerrak över terrestert alloktont kol alternativt
bevis för avsaknaden av en pågående eutrofiering sedan 1950-talet och framåt. (Less)
Please use this url to cite or link to this publication:
author
Viehweger, Bernhard LU
supervisor
organization
course
GEOR02 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
organic matter, n-alkane, sea surface temperature, alkenone, eutrophication, deoxygenation, sources, terrestrial, marine, biomarker, Gullmar Fjord, Skagerrak
publication/series
Dissertations in Geology at Lund University
report number
460
language
English
id
8145680
date added to LUP
2015-11-04 12:12:49
date last changed
2015-11-04 12:12:49
@misc{8145680,
  abstract     = {In this study I will assess sources and effects of short-term environmental changes on the sedimentary organic matter in Gullmar Fjord. To achieve this, a high resolution sediment core (sedimentation rate 0.7 cm yr -1) was retrieved from the deepest part in the fjord and analyzed with multiple geochemical methods, targeting bulk organic matter and biomarker composition. The distribution of n-alkanes did not display any major changes for the terrestrial fraction in the investigated time frame from 1954 until 2014. Marine organic matter was found to be the dominant source of sedimentary organic matter in the fjord, though it is most likely produced remotely in the Skagerrak. Sea surface temperature (SST) reconstructions based on long-chain alkenones do not show any general increase during the studied interval, as observed from the hydrographic data set available for Gullmar Fjord. Temperatures of 14.1 to 21.1°C (mean 16.4 ± 1.6) were reconstructed, so the haptophyte blooms producing the long-chain alkenones occurred most likely during summer to early autumn. However, they would also fit to temperatures and blooming seasons reported for the Skagerrak. Even though Gullmar Fjord is considered to be free from industrial pollution, we found indications which could be interpreted as a slight contamination of the sediments by petrogenic hydrocarbons. Lower oxygen minimum concentrations observed in the bottom water since the 1980s are thought to be caused by changes in the North Atlantic Oscillation (NAO) and were related with a possibly ongoing eutrophication in previous studies. Signs for an ongoing eutrophication in the fjord were not visible in our sedimentary organic matter record, suggesting that most marine organic matter is produced in the Skagerrak, or that there is no ongoing
eutrophication in the fjord since the 1950s.},
  author       = {Viehweger, Bernhard},
  keyword      = {organic matter,n-alkane,sea surface temperature,alkenone,eutrophication,deoxygenation,sources,terrestrial,marine,biomarker,Gullmar Fjord,Skagerrak},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Sources and effects of short-term environmental changes in Gullmar Fjord, Sweden, inferred from the composition of sedimentary organic matter},
  year         = {2015},
}