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Unravelling the land source: an investigation of the processes contributing to the oceanic input of DIC and alkalinity
Stockholm University, Faculty of Science, Department of Meteorology .
2013 (English)In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, 19683- p.Article in journal (Refereed) Published
Abstract [en]

In models of the marine carbon system, it is important to correctly represent riverine and aerial inputs of dissolved inorganic carbon (DIC) and alkalinity. We have examined the different processes contributing to this exchange. In terms of DIC, we have divided the fluxes into their internal component, constituting the carbon ultimately derived from the atmosphere, and their external component originating from rocks. We find that the only process contributing to external DIC input is carbonate and fossil carbon weathering and that erosion of organic matter ultimately constitutes a DIC sink. A number of both riverine and aerial inputs affect the alkalinity. Beside carbonate and silicate weathering, we examine processes of pyrite weathering, aerial input of sulphuric acid, and riverine and aerial inputs of various nitrogen species. Using the observation that, in the ocean, the nitrate concentration follows that of phosphate, we assume a steady state in nitrate. This leads to the surprising result that the only processes affecting the alkalinity is riverine input of nitrate, constituting an alkalinity source and input of ammonia, constituting an alkalinity sink. Furthermore, we compare the flux sizes. As expected, carbonate and silicate weathering has the largest effect on alkalinity, though we note that burial of pyrite might be of importance during periods of large-scale anoxia.

Place, publisher, year, edition, pages
2013. Vol. 65, 19683- p.
Keyword [en]
dissolved inorganic carbon, alkalinity, carbon dioxide, riverine flux, weathering
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-90401DOI: 10.3402/tellusb.v65i0.19683ISI: 000318067300001OAI: oai:DiVA.org:su-90401DiVA: diva2:624876
Note

AuthorCount:2;

Available from: 2013-06-03 Created: 2013-06-03 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The global marine carbon system through time
Open this publication in new window or tab >>The global marine carbon system through time
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon dioxide is an important greenhouse gas and in order to understand its effect on the climate we need to identify its sources and sinks. This thesis focuses on different aspects of the marine carbon system and the exchange of carbon between the ocean and the atmosphere.

To understand the distribution of carbon between different reservoirs such as land, ocean and atmosphere, it is important to consider the origin of a carbon flux. If the carbon originates from rock, it comprises an external source. If, however, it originates from the atmosphere, such as a flux of organic carbon, it constitutes an internal exchange. We have re-calculated riverine fluxes that are commonly expressed in terms of ions, as fluxes of total carbon and alkalinity. Furthermore, we have separated the total carbon fluxes into their external and internal parts.

External sources and sinks, as well as internal exchange can sometimes be more easily understood if the carbon in the ocean is separated into acidic and basic carbon (AC and BC). These two state variables have opposite effect on the partial pressure of carbon dioxide in the surface ocean. We have used these new variables to describe the effect of pyrite production during periods in the geological past when large parts of the oceans have been oxygen free, so called oceanic anoxic events. Sulfate reduction that occurs in oxygen free environments leads to an increase in alkalinity. We show that the net effect of photosynthesis, sulfate reduction and pyrite production leads to a reduction of acidic carbon and thereby a decreased surface pressure of CO2. Furthermore, we demonstrate the difference between a system with and without carbonate compensation that comprises a regulatory mechanism for the carbon system.

During the anoxic events there is a shift in the composition of carbon isotopes in the system. A negative isotope shift is believed to be a result of increased supply of light carbon from volcanic activity or melting methane clathrates, while a positive shift is a result of increased burial of organic carbon. We have investigated the implications of different sources and sinks on the size of an isotope shift. This is done by comparing simple budget calculations with a more complete model. We show that carbonate compensation implies that more light carbon must be supplied to the system to obtain the same negative shift than for the simple budget calculations where sources and sinks of calcium carbonate are not considered.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2014. 32 p.
National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-103220 (URN)978-91-7447-928-7 (ISBN)
Public defence
2014-06-13, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2014-05-22 Created: 2014-05-09 Last updated: 2014-05-21Bibliographically approved

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