ICOS Science Conference, Session 10

1. Quantifying the fluxes of
inorganic carbon and alkalinity
through UK estuaries
Ruth Matthews, Dorothee Bakker, Naomi Greenwood,
Matthew Humphreys, Silke Kroeger, Richard Sanders

2. Why do we care?
• Large uncertainty of estuarine outgassing estimate
• 0.25 ± 0.25 Pg C yr-1
• Estimates of estuarine CO2 emission and transport to coastal ocean
probably within 50%-100% of true value
• Estimates rely on extrapolation
• UK accounts for ~1/4 of NW European estuarine surface area

3. A bit of chemistry…
• Dissolved Inorganic Carbon (DIC)
• CT = [CO2*] + [HCO3
−] + [CO3
2−]
• (Total) Alkalinity
• AT = [HCO3
-] + 2[CO3
2-] + [B(OH)4
-] + [OH-] + [HPO4
2-] + 2[PO4
3-] + [SiO(OH)3
-] +
[HS-] + 2[S2-] + [NH3] - [H+] - [HSO4
-] - [HF] - [H3 PO4]
• Carbonate weathering:
• CaCO3+ CO2+ H2O ⇌Ca2++ 2HCO3
−
• Dissolved Inorganic Carbon (DIC)
• CT = [CO2*] + [HCO3
−] + [CO3
2−]
• (Total) Alkalinity
• AT = [HCO3
-] + 2[CO3
2-] + [B(OH)4
-] + [OH-] + [HPO4
2-] + 2[PO4
3-] + [SiO(OH)3
-] +
[HS-] + 2[S2-] + [NH3] - [H+] - [HSO4
-] - [HF] - [H3 PO4]
• Carbonate weathering:
• CaCO3+ CO2+ H2O ⇌Ca2++ 2HCO3
−

4. Could limestone weathering be important?
• McGrath et al., 2019:

5. Samples
• LOCATE sampling campaign
2017-18
• 16 of ~90 estuaries in UK
sampled
• 14 estuaries sampled on 5
occasions, seasonally
• We analysed samples for DIC
and alkalinity

6. Analysis
• Versatile INstrument for the
Determination of Total dissolved
inorganic carbon and Alkalinity
(VINDTA 3C)
• Adapted method for large
salinity range using different
electrode setup and adapted
alkalinity calculation

7. Results

9. Let’s focus in a bit…

12. Conclusions
• Heterogeneity in DIC and Alkalinity concentrations between estuaries
in the UK
• Some estuaries seasonally shift in gradient of DIC and Alkalinity
change with salinity
• Geology appears to affect Alkalinity concentrations at low salinity

13. Any questions?

14. References
• Regnier, P., Friedlingstein, P., Ciais, P., Mackenzie, F.T., Gruber, N.,
Janssens, I.A., Laruelle, G.G., Lauerwald, R., Luyssaert, S., Andersson,
A.J. and Arndt, S., 2013. Anthropogenic perturbation of the carbon
fluxes from land to ocean. Nature geoscience, 6(8), pp.597-607.
• Bauer, J.E., Cai, W.J., Raymond, P.A., Bianchi, T.S., Hopkinson, C.S. and
Regnier, P.A., 2013. The changing carbon cycle of the coastal ocean.
Nature, 504(7478), pp.61-70.
• https://jncc.gov.uk/
• https://nrfa.ceh.ac.uk/