Interactions of dissolved CO2 with cadmium isotopes in the Southern Ocean
De Baar, H.J.W.; van Heuven, S.M.A.C.; Abouchami, W.; Xue, Z.; Galer, S.J.G.; Rehkämper, M.; Middag, R.; van Ooijen, J. (2017). Interactions of dissolved CO2 with cadmium isotopes in the Southern Ocean. Mar. Chem. 195: 105-121. https://doi.org/10.1016/j.marchem.2017.06.010
In: Marine Chemistry. Elsevier: Amsterdam. ISSN 0304-4203; e-ISSN 1872-7581, more
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| Author keywords |
Cadmium; Carbon dioxide; Southern Ocean; Isotopes |
| Authors | | Top |
- De Baar, H.J.W., more
- van Heuven, S.M.A.C., more
- Abouchami, W.
- Xue, Z.
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- Galer, S.J.G.
- Rehkämper, M.
- Middag, R., more
- van Ooijen, J., more
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| Abstract |
Here we report the first ever observations of a strong correlation in ocean surface waters of the dissolved δ114Cdwith dissolved CO2. This is observed in the Southern Ocean along the 0°W meridian in both the AntarcticCircumpolar Current and the Weddell Gyre, as well as in the Weddell Sea proper, near the Antarctic Peninsulaand in Drake Passage. This uniform trend in several surface water masses hints at a uniform biochemical mechanismwithin the Southern Ocean. One hypothesis for the underlying mechanism would be a role of Cd in thecarbonic anhydrase function for conversion of bicarbonate ion [HCO3−] into CO2, the latter being required byRuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) that only accepts CO2. At low ambient [CO2] thealgae maintain growth by also operating a Carbon Concentrating Mechanism (CCM) for utilization of [HCO3−]and its conversion to CO2. For this the algae need more enzyme carbonic anhydrase that normally has Zn as itsco-factor, but Cd may substitute for Zn and there also are Cd-specific carbonic anhydrases known for somephytoplankton species. Indeed in incubations of the local plankton communities it is shown that the phytoplanktonhave a very strong preferential uptake of CO2, such that the uptake ratio {[CO2]/[HCO3−]} is muchhigher than the dissolved ratio {[CO2]/[HCO3−]} in ambient seawater. Therefore the here reported observationsin the Southern Ocean are also expressed for δ114Cd as function of the ratio {[CO2]/[HCO3−]} in ambientseawater. Future research of local phytoplankton in unperturbed natural waters of the Southern Ocean is recommendedto be able to verify the hypothesis of a function of Cd in carbonic anhydrase in Antarctic phytoplankton. |
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