Assessing the sources of inorganic carbon in surface-, soil- and non-thermal groundwater in Iceland by δ13C and 14C

Árný E. Sveinbjörnsdóttir; Andri Stefánsson; Jan Heinemeier; Stefán Arnórsson; Eydís Salome Eiríksdóttir; Rósa Ólafsdóttir

doi:10.1016/j.gca.2020.03.021

Assessing the sources of inorganic carbon in surface-, soil- and non-thermal groundwater in Iceland by δ¹³C and ¹⁴C

Árný E. Sveinbjörnsdóttir^*, Andri Stefánsson, Jan Heinemeier, Stefán Arnórsson, Eydís Salome Eiríksdóttir, Rósa Ólafsdóttir

^*Corresponding author for this work

Department of Physics and Astronomy

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

Abstract

Chemical weathering and associated atmospheric CO₂ uptake by surface water and transport of dissolved inorganic carbon (DIC) by rivers to the ocean and subsequent carbonate deposition has been suggested to play a major role in long-time climate changes. However, DIC in surface-, soil- and groundwater may also be sourced from decomposition of organic matter, direct leaching of carbon from the rocks themselves and deep degassing in volcanic areas and modified by chemical reactions. Carbon isotopes (δ¹³C and ¹⁴C) of surface-, soil-, and non-thermal groundwater in Iceland were studied to assess the various sources and reactions of carbon, atmospheric CO₂ uptake upon basalt weathering, and water apparent radiocarbon age. The waters had a pH of ∼6.5–10.9, dissolved inorganic carbon (DIC) of 3.2–194 ppm, and were of meteoric origin based on the δD and δ¹⁸O content. The measured range of δ¹³C_DIC and ¹⁴C_DIC in the waters was large, −25.9 to +2.2‰ (average −8.2‰, n = 334) and 7.9–126 pMC (average 95 pMC, n = 334), respectively. Insignificant annual and seasonal variations in DIC and isotope composition were generally observed for a given location. Applying isotope modeling and comparing the results with the dataset revealed three major sources of DIC: (1) leaching of carbon from basaltic rocks, (2) atmospheric CO₂(g) through water-air exchange at the surface, and (3) decomposition of organic matter in soils. The majority of DIC originated from atmospheric CO₂(g) (15–100%, av. 64%) and decomposition of organic matter (0–85%, av. 34%) with the highest values observed for soil waters. Carbon from rock leaching was generally insignificant (av. 2%) except for some groundwater (3–100%). The atmospheric CO₂ uptake by basalt weathering for selected rivers in East Iceland was assessed to be 0.09–1.56 mol/km²/yr or ∼5–40% (av. 17%) lower than total riverine CO₂ fluxes suggest.

Original language	English
Journal	Geochimica et Cosmochimica Acta
Volume	279
Pages (from-to)	165-188
Number of pages	24
ISSN	0016-7037
DOIs	https://doi.org/10.1016/j.gca.2020.03.021
Publication status	Published - 2020

Keywords

Carbon isotopes
Dissolved inorganic carbon (DIC)
Isotope geochemical model
Soil waters
Surface waters

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10.1016/j.gca.2020.03.021

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@article{83d27768c37d4167ac633c331d698e12,

title = "Assessing the sources of inorganic carbon in surface-, soil- and non-thermal groundwater in Iceland by δ13C and 14C",

abstract = "Chemical weathering and associated atmospheric CO2 uptake by surface water and transport of dissolved inorganic carbon (DIC) by rivers to the ocean and subsequent carbonate deposition has been suggested to play a major role in long-time climate changes. However, DIC in surface-, soil- and groundwater may also be sourced from decomposition of organic matter, direct leaching of carbon from the rocks themselves and deep degassing in volcanic areas and modified by chemical reactions. Carbon isotopes (δ13C and 14C) of surface-, soil-, and non-thermal groundwater in Iceland were studied to assess the various sources and reactions of carbon, atmospheric CO2 uptake upon basalt weathering, and water apparent radiocarbon age. The waters had a pH of ∼6.5–10.9, dissolved inorganic carbon (DIC) of 3.2–194 ppm, and were of meteoric origin based on the δD and δ18O content. The measured range of δ13CDIC and 14CDIC in the waters was large, −25.9 to +2.2‰ (average −8.2‰, n = 334) and 7.9–126 pMC (average 95 pMC, n = 334), respectively. Insignificant annual and seasonal variations in DIC and isotope composition were generally observed for a given location. Applying isotope modeling and comparing the results with the dataset revealed three major sources of DIC: (1) leaching of carbon from basaltic rocks, (2) atmospheric CO2(g) through water-air exchange at the surface, and (3) decomposition of organic matter in soils. The majority of DIC originated from atmospheric CO2(g) (15–100%, av. 64%) and decomposition of organic matter (0–85%, av. 34%) with the highest values observed for soil waters. Carbon from rock leaching was generally insignificant (av. 2%) except for some groundwater (3–100%). The atmospheric CO2 uptake by basalt weathering for selected rivers in East Iceland was assessed to be 0.09–1.56 mol/km2/yr or ∼5–40% (av. 17%) lower than total riverine CO2 fluxes suggest.",

keywords = "Carbon isotopes, Dissolved inorganic carbon (DIC), Isotope geochemical model, Soil waters, Surface waters",

author = "Sveinbj{\"o}rnsd{\'o}ttir, {{\'A}rn{\'y} E.} and Andri Stef{\'a}nsson and Jan Heinemeier and Stef{\'a}n Arn{\'o}rsson and Eir{\'i}ksd{\'o}ttir, {Eyd{\'i}s Salome} and R{\'o}sa {\'O}lafsd{\'o}ttir",

year = "2020",

doi = "10.1016/j.gca.2020.03.021",

language = "English",

volume = "279",

pages = "165--188",

journal = "Geochimica et Cosmochimica Acta",

issn = "0016-7037",

publisher = "Pergamon Press",

}

Assessing the sources of inorganic carbon in surface-, soil- and non-thermal groundwater in Iceland by δ¹³C and ¹⁴C. / Sveinbjörnsdóttir, Árný E.; Stefánsson, Andri; Heinemeier, Jan et al.
In: Geochimica et Cosmochimica Acta, Vol. 279, 2020, p. 165-188.

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

TY - JOUR

T1 - Assessing the sources of inorganic carbon in surface-, soil- and non-thermal groundwater in Iceland by δ13C and 14C

AU - Sveinbjörnsdóttir, Árný E.

AU - Stefánsson, Andri

AU - Heinemeier, Jan

AU - Arnórsson, Stefán

AU - Eiríksdóttir, Eydís Salome

AU - Ólafsdóttir, Rósa

PY - 2020

Y1 - 2020

N2 - Chemical weathering and associated atmospheric CO2 uptake by surface water and transport of dissolved inorganic carbon (DIC) by rivers to the ocean and subsequent carbonate deposition has been suggested to play a major role in long-time climate changes. However, DIC in surface-, soil- and groundwater may also be sourced from decomposition of organic matter, direct leaching of carbon from the rocks themselves and deep degassing in volcanic areas and modified by chemical reactions. Carbon isotopes (δ13C and 14C) of surface-, soil-, and non-thermal groundwater in Iceland were studied to assess the various sources and reactions of carbon, atmospheric CO2 uptake upon basalt weathering, and water apparent radiocarbon age. The waters had a pH of ∼6.5–10.9, dissolved inorganic carbon (DIC) of 3.2–194 ppm, and were of meteoric origin based on the δD and δ18O content. The measured range of δ13CDIC and 14CDIC in the waters was large, −25.9 to +2.2‰ (average −8.2‰, n = 334) and 7.9–126 pMC (average 95 pMC, n = 334), respectively. Insignificant annual and seasonal variations in DIC and isotope composition were generally observed for a given location. Applying isotope modeling and comparing the results with the dataset revealed three major sources of DIC: (1) leaching of carbon from basaltic rocks, (2) atmospheric CO2(g) through water-air exchange at the surface, and (3) decomposition of organic matter in soils. The majority of DIC originated from atmospheric CO2(g) (15–100%, av. 64%) and decomposition of organic matter (0–85%, av. 34%) with the highest values observed for soil waters. Carbon from rock leaching was generally insignificant (av. 2%) except for some groundwater (3–100%). The atmospheric CO2 uptake by basalt weathering for selected rivers in East Iceland was assessed to be 0.09–1.56 mol/km2/yr or ∼5–40% (av. 17%) lower than total riverine CO2 fluxes suggest.

AB - Chemical weathering and associated atmospheric CO2 uptake by surface water and transport of dissolved inorganic carbon (DIC) by rivers to the ocean and subsequent carbonate deposition has been suggested to play a major role in long-time climate changes. However, DIC in surface-, soil- and groundwater may also be sourced from decomposition of organic matter, direct leaching of carbon from the rocks themselves and deep degassing in volcanic areas and modified by chemical reactions. Carbon isotopes (δ13C and 14C) of surface-, soil-, and non-thermal groundwater in Iceland were studied to assess the various sources and reactions of carbon, atmospheric CO2 uptake upon basalt weathering, and water apparent radiocarbon age. The waters had a pH of ∼6.5–10.9, dissolved inorganic carbon (DIC) of 3.2–194 ppm, and were of meteoric origin based on the δD and δ18O content. The measured range of δ13CDIC and 14CDIC in the waters was large, −25.9 to +2.2‰ (average −8.2‰, n = 334) and 7.9–126 pMC (average 95 pMC, n = 334), respectively. Insignificant annual and seasonal variations in DIC and isotope composition were generally observed for a given location. Applying isotope modeling and comparing the results with the dataset revealed three major sources of DIC: (1) leaching of carbon from basaltic rocks, (2) atmospheric CO2(g) through water-air exchange at the surface, and (3) decomposition of organic matter in soils. The majority of DIC originated from atmospheric CO2(g) (15–100%, av. 64%) and decomposition of organic matter (0–85%, av. 34%) with the highest values observed for soil waters. Carbon from rock leaching was generally insignificant (av. 2%) except for some groundwater (3–100%). The atmospheric CO2 uptake by basalt weathering for selected rivers in East Iceland was assessed to be 0.09–1.56 mol/km2/yr or ∼5–40% (av. 17%) lower than total riverine CO2 fluxes suggest.

KW - Carbon isotopes

KW - Dissolved inorganic carbon (DIC)

KW - Isotope geochemical model

KW - Soil waters

KW - Surface waters

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U2 - 10.1016/j.gca.2020.03.021

DO - 10.1016/j.gca.2020.03.021

M3 - Journal article

AN - SCOPUS:85083293101

SN - 0016-7037

VL - 279

SP - 165

EP - 188

JO - Geochimica et Cosmochimica Acta

JF - Geochimica et Cosmochimica Acta

ER -

Assessing the sources of inorganic carbon in surface-, soil- and non-thermal groundwater in Iceland by δ¹³C and ¹⁴C

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