Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Organic carbon dynamics in the Baltic Sea: A modelling perspective
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0001-8280-4018
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coastal seas constitute a link between land and the open ocean, and therefore play an important role in the global carbon cycle. Large amounts of carbon, of both terrestrial and marine origin, transit and are transformed in these waters, which belong to the more productive areas of the oceans. Despite much research has been done on the subject, there are still many unknown factors in the coastal sea carbon cycling. 

This doctoral thesis investigates the carbon dynamics in the Baltic Sea, with a focus on the production and fate of marine and terrestrial organic carbon and its influence on the air-sea CO2 exchange in its northernmost part, the Gulf of Bothnia. The main approach is the use of a coupled 3D physical-biogeochemical model, in combination with a long series of measurements of physical and biogeochemical parameters. 

A new coupled 3D physical-biogeochemical model, which includes the stoichiometric flexibility of plankton and organic matter, is set up for the Gulf of Bothnia. It is found that phytoplankton stoichiometric flexibility in particular, with non-Redfieldian dynamics, is key to explaining seasonal pCO2, dissolved organic carbon (DOC), and nutrient dynamics. If the Redfield ratio is instead used to predict organic carbon production, as done in most biogeochemical models currently in use, the uptake of atmospheric CO2 is reduced by half. Furthermore, it is shown that the organic carbon production needed to reproduce the summer pCO2 drawdown is larger than measured estimates of primary production. This discrepancy is attributed to a substantial production of extracellular DOC, which seems not to be captured by measurements. 

The dynamics of terrestrial dissolved organic carbon (tDOC) is studied by the use of a passive tracer released from rivers into the physical model of the Baltic Sea. It is found that 80% of the tDOC released in the Baltic Sea is removed, and the rest is exported to the North Sea. Two different parameterisations of tDOC removal are tested. In the first one a decay rate with a timescale of 1 year applied to 80% of the tDOC, and the remaining 20% is assumed to be refractory. In the second one a decay rate with a timescale of 10 years applied to 100% of the tDOC. Trying these parameterisations in a full biogeochemical model shows that only the one with the faster decay is able to reproduce observations of pCO2 in the low-salinity region. A removal rate of one year agrees well with calculated removal rates from bacterial incubation experiments, indicating that bacteria have the potential to cause this remineralisation. It is not only remineralisation of tDOC that affects the pCO2; it is also suggested that a strong tDOC induced light extinction is needed to prevent a too large pCO2 drawdown by phytoplankton in the low salinity region. 

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University , 2018. , p. 36
Keywords [en]
carbon cycle, organic carbon, primary production, remineralisation, terrestrial DOC, extracellular DOC, flexible stoichiometry, Redfield ratio, air-sea CO2 exchange, pCO2, coupled 3D physical-biogeochemical modelling, Gulf of Bothnia, Baltic Sea
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-151724ISBN: 978-91-7797-124-5 (print)ISBN: 978-91-7797-125-2 (electronic)OAI: oai:DiVA.org:su-151724DiVA, id: diva2:1175372
Public defence
2018-03-22, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Submitted.

Available from: 2018-02-07 Created: 2018-01-17 Last updated: 2018-01-31Bibliographically approved
List of papers
1. Tracing terrestrial DOC in the Baltic Sea - a 3-D model study
Open this publication in new window or tab >>Tracing terrestrial DOC in the Baltic Sea - a 3-D model study
Show others...
2016 (English)In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 30, no 2, p. 134-148Article in journal (Refereed) Published
Abstract [en]

The fate of terrestrial organic matter brought to the coastal seas by rivers, and its role in the global carbon cycle, are still not very well known. Here the degradation rate of terrestrial dissolved organic carbon (DOCter) is studied in the Baltic Sea, a subarctic semi-enclosed sea, by releasing it as a tracer in a 3-D circulation model and applying linear decay constants. A good agreement with available observational data is obtained by parameterizing the degradation in two rather different ways; one by applying a decay time on the order of 10 years to the whole pool of DOCter, and one by dividing the DOCter into one refractory pool and one pool subject to a decay time on the order of 1 year. The choice of parameterization has a significant effect on where in the Baltic Sea the removal takes place, which can be of importance when modeling the full carbon cycle and the CO2 exchange with the atmosphere. In both cases the biogeochemical decay operates on time scales less than the water residence time. Therefore only a minor fraction of the DOCter reaches the North Sea, whereas approximately 80% is removed by internal sinks within the Baltic Sea. This further implies that DOCter mineralization is an important link in land-sea-atmosphere cycling of carbon in coastal- and shelf seas that are heavily influenced by riverine DOC.

National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-124885 (URN)10.1002/2014GB005078 (DOI)000372963900004 ()
Funder
Baltic Ecosystem Adaptive Management (BEAM)
Available from: 2016-01-07 Created: 2016-01-05 Last updated: 2018-01-24Bibliographically approved
2. Non-Redfieldian Dynamics Explain Seasonal pCO2 Drawdown in the Gulf of Bothnia
Open this publication in new window or tab >>Non-Redfieldian Dynamics Explain Seasonal pCO2 Drawdown in the Gulf of Bothnia
Show others...
2018 (English)In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 123, no 1, p. 166-188Article in journal (Refereed) Published
Abstract [en]

High inputs of nutrients and organic matter make coastal seas places of intense air‐sea CO2 exchange. Due to their complexity, the role of coastal seas in the global air‐sea CO2 exchange is, however, still uncertain. Here, we investigate the role of phytoplankton stoichiometric flexibility and extracellular DOC production for the seasonal nutrient and CO2 partial pressure (pCO2) dynamics in the Gulf of Bothnia, Northern Baltic Sea. A 3‐D ocean biogeochemical‐physical model with variable phytoplankton stoichiometry is for the first time implemented in the area and validated against observations. By simulating non‐Redfieldian internal phytoplankton stoichiometry, and a relatively large production of extracellular dissolved organic carbon (DOC), the model adequately reproduces observed seasonal cycles in macronutrients and pCO2. The uptake of atmospheric CO2 is underestimated by 50% if instead using the Redfield ratio to determine the carbon assimilation, as in other Baltic Sea models currently in use. The model further suggests, based on the observed drawdown of pCO2, that observational estimates of organic carbon production in the Gulf of Bothnia, derived with the method, may be heavily underestimated. We conclude that stoichiometric variability and uncoupling of carbon and nutrient assimilation have to be considered in order to better understand the carbon cycle in coastal seas.

Keywords
pCO2 drawdown, modeling, primary production, coastal sea, DOC, stoichiometry
National Category
Oceanography, Hydrology and Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-151423 (URN)10.1002/2017JC013019 (DOI)000425589800011 ()
Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-07-26Bibliographically approved
3. Remineralization rate of terrestrial DOC as inferred from CO2 supersaturated coastal waters
Open this publication in new window or tab >>Remineralization rate of terrestrial DOC as inferred from CO2 supersaturated coastal waters
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-151718 (URN)
Available from: 2018-01-17 Created: 2018-01-17 Last updated: 2018-01-24Bibliographically approved
4. Nemo-Nordic: A NEMO based ocean model for Baltic & North Seas, research and operational applications
Open this publication in new window or tab >>Nemo-Nordic: A NEMO based ocean model for Baltic & North Seas, research and operational applications
Show others...
(English)In: Geoscientific Model Development Discussions, ISSN 1991-9611, E-ISSN 1991-962XArticle in journal (Refereed) Submitted
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-151510 (URN)
Available from: 2018-01-15 Created: 2018-01-15 Last updated: 2018-01-23Bibliographically approved

Open Access in DiVA

fulltext(812 kB)48 downloads
File information
File name FULLTEXT01.pdfFile size 812 kBChecksum SHA-512
5b94db3cfdfa7e706cc87b59b462ff46c8c5154cde85fdfc1dd7274ac2792192737f3b0ed384dc6b85566574322d35334d8e672cade22ce4f7bdb0a4cdaa7ea3
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Fransner, Filippa
By organisation
Department of Meteorology
Earth and Related Environmental Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 48 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 654 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf