Influence of manganese cycling on alkalinity in the redox stratified water column of Chesapeake Bay
<p>The alkalinity dynamics in coastal environments play a crucial role in controlling the global burial of carbonate minerals and the ocean's capacity to sequester anthropogenic <span class="inline-formula">CO<sub>2</sub></span>. This study presents resul...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-07-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/3053/2023/bg-20-3053-2023.pdf |
| Summary: | <p>The alkalinity dynamics in coastal environments play a crucial role in
controlling the global burial of carbonate minerals and the ocean's capacity
to sequester anthropogenic <span class="inline-formula">CO<sub>2</sub></span>. This study presents results from high
vertical resolution profiles obtained during two summers in the temperate
Chesapeake Bay estuary, enabling detailed investigation of carbonate
dynamics over salinity and redox gradients, along with measurement of the
speciation of most redox-sensitive elements. Under oxygen-rich conditions,
carbonate dissolution, primary production and aerobic respiration explain
the evolution of total alkalinity (TA) versus dissolved inorganic carbon
(DIC), once adjusted for fresh and oceanic water mixing. A significant
flooding event in 2018 promoted carbonate dissolution. In oxygen-depleted
waters, we observed a previously unreported 2.4 mol increase in DIC per 1 mol of TA production, which was consistent over the 2 years.
Stoichiometric changes suggest that <span class="inline-formula">MnO<sub>2</sub></span> reduction followed by Mn
carbonate precipitation is responsible for this characteristic carbonate
signature, likely produced in sediment pore water and then transferred to
the water column along with other by-products of anoxic respiration at the
onset of summer. Our findings highlight the critical role of Mn in
alkalinity dynamics in the Chesapeake Bay and potentially other
river-dominated environments where it can limit <span class="inline-formula">H<sub>2</sub>S</span> oxidation to
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msup><msub><mi mathvariant="normal">SO</mi><mn mathvariant="normal">4</mn></msub><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="34pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="464903d4384d88b723e5c660cbd7e466"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3053-2023-ie00001.svg" width="34pt" height="16pt" src="bg-20-3053-2023-ie00001.png"/></svg:svg></span></span> and promote sulfur burial.</p> |
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| ISSN: | 1726-4170 1726-4189 |