Ocean Alkalinity Enhancement: Implications for phytoplankton community dynamics and silicate dissolution
Ocean alkalinity enhancement (OAE) is an emerging carbon dioxide removal (CDR) strategy that leverages the natural processes of weathering and acid neutralisation to durably store atmospheric CO2 in seawater. OAE can be achieved with a variety of methods, all of which have different environmental implications. One widely considered method utilizes electrochemistry to remove strong acid from seawater, leaving sodium hydroxide (NaOH) behind. This study evaluates the impacts of OAE via NaOH (NaOH-OAE) on a coastal plankton bloom, with particular focus on how macronutrient regeneration in the aftermath of the bloom responds to the perturbation. To investigate this, we enclosed a natural coastal phytoplankton community, including coccolithophores, in nine microcosms. The microcosms were divided into three groups: control, unequilibrated (512.1 ± 2.5 µmol kg-1 alkalinity increase) and equilibrated (499.3 ±5.65 µmol kg-1 alkalinity increase). Light was provided for 11 days to stimulate a bloom (light phase) and lights were turned off thereafter to investigate alkalinity and nutrient changes for 21 days (dark phase). We found no detectable effect of equilibrated NaOH-OAE on phytoplankton community and bacteria abundances determined with flow cytometry but observed a small yet detectable restructuring of phytoplankton communities under unequilibrated conditions. NaOH-OAE had no significant effect on alkalinity, NOx- and phosphate regeneration, but increased silicate regeneration by 64% over 21 days under darkness in the unequilibrated treatments where seawater pH was highest (8.65 relative to 7.92 in the control). Additional dissolution experiments with two diatom species supported this outcome on silicate regeneration for one of the two species, thereby suggesting that the effect is species specific. Our results point towards the potential of NaOH-OAE to influence regeneration of silicate in the surface ocean and thus the growth of diatoms, at least under the very extreme NaOH-OAE conditions simulated here.
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Identification info
- Date (Publication)
- 2024-09-30T00:00:00
Identifier
- Title
- Information and documentation - Digital object identifier system
- Citation identifier
- ISO 26324:2012
- Code
- 10.25959/NNZB-2322
- Codespace
- doi.org
- Description
- Digital Object Identifier (DOI)
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Author
Author
- Credit
- This research was supported by the Australian Research Council Special Research Initiative, Australian Centre for Excellence in Antarctic Science (Project Number SR200100008). This research was also funded by a Future Fellowship (FT200100846) by the Australian Research Council awarded to LTB.
- Status
- Completed
Author
- Topic category
-
- Biota
- Oceans
Extent
))
Temporal extent
- Time period
- 2023-04-28 2023-09-04
- Maintenance and update frequency
- Not planned
- Keywords (Theme)
-
- geoengineering
- marine Carbon Dioxide Removal (mCDR)
- Keywords (Taxon)
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- Thalassiosira
- Skeletonema
- Global Change Master Directory Earth Science Keywords, Version 8.5
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- Data, products and services from IMAS are provided "as is" without any warranty as to fitness for a particular purpose.
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- This dataset is the intellectual property of the University of Tasmania (UTAS) through the Institute for Marine and Antarctic Studies (IMAS).
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https://licensebuttons.net/l/by/4.0/88x31.png
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- Title
- Creative Commons Attribution 4.0 International License
- Alternate title
- CC-BY
- Edition
- 4.0
- Website
-
https://creativecommons.org/licenses/by/4.0/
License Text
- Other constraints
- Cite data as: Butterley, A., & Bach, L. (2024). Ocean Alkalinity Enhancement: Implications for phytoplankton community dynamics and silicate dissolution [Data set]. Institute for Marine and Antarctic Studies. https://doi.org/10.25959/NNZB-2322
- Language
- English
- Character encoding
- UTF8
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- CSV
- OnLine resource
- DATA ACCESS - browse and download available data files
Resource lineage
- Statement
- This study used Kegland Fermzilla microcosms (55 L conical PET tanks; Ferderer et al., 2022) to examine the effects of alkalinity on plankton communities. Seawater was collected from the Derwent Estuary, Tasmania, in May 2023 (Salinity = 34.49), with microcosms filled by submerging them 1 m below the surface and filtering through a 2 mm mesh. Temperature and salinity were measured with a CTD probe (SonTek Castaway®), and microcosm volumes ranged from 51.72 L to 55.30 L. Microcosms were transported to a temperature-controlled room at 8.5°C. To induce convective mixing, heat belts raised the base temperature to 13-15°C, similar to the conditions at collection. Ten LED light strips provided 236 ± 3 μmol photons m⁻² s⁻¹ under a 14:10 light:dark cycle, which was turned off on day 11 to induce heterotrophic conditions. The experiment included three treatment groups: (1) Control (M1, M4, M7), (2) Unequilibrated (M2, M5, M8) with 500 μL NaOH per litre, and (3) Equilibrated (M3, M6, M9) with 423 μL NaHCO₃ and 77 μL NaOH per litre, calculated using carbonate chemistry via seacarb (Gattuso et al., 2021). Approximately 4,000 Emiliania huxleyi cells (strain CS1127) were added per litre, cultured under controlled conditions and acclimated to experimental settings. Additionally, 480 μM nitrate and 30 μM phosphate were added to induce an algal bloom. Sampling occurred daily (0900-1100), with each microcosm stirred before collection. Nutrients (NOx-, phosphate, silicic acid) were measured via spectrophotometry (Hansen and Koroleff, 1999), and carbonate chemistry (pHT, TA, DIC, Ω) was calculated using seacarb using the pH that had been taken and the total alkalinity using a Metrohm 914 pH meter and a Metrohm 862 Compact Titrosampler. respectively. Chlorophyll a (Chl-a), biogenic silica (BSi), and total particulate carbon (TPC) were filtered and analyzed. Flow cytometry was completed using a CYTEK Aurora flow cytometer and was used to distinguish phytoplankton groups and bacterial abundance based on light scatter and fluorescence. Phytoplankton biovolume was estimated following Selfe (2022), and bacterial samples were stained with SYBR Green I. An additional silicon (Si) dissolution experiment was conducted using monocultures of Skeletonema and Thalassiosira, chosen for their different aggregate-forming characteristics. Cultures were grown in filtered seawater with 480 µM nitrate, 480 µL silicic acid, and 30 µM phosphate. Alkalinity was increased by 500 μmol kg⁻¹ following seacarb calculations. Cultures were rotated to encourage aggregate formation and kept in a dark, temperature-controlled room at 15°C for 36 days. Parameters such as pHT, BSi, TPC, DSi, and TA were measured at the beginning and end of the experiment.
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- Dataset
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- Metadata identifier
- urn:uuid/918792b2-7d26-417f-b279-606d1a7868fc
- Language
- English
- Character encoding
- UTF8
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Type of resource
- Resource scope
- Dataset
- Name
- IMAS Dataset level record
- Metadata linkage
-
https://metadata.imas.utas.edu.au/geonetwork/srv/eng/catalog.search#/metadata/918792b2-7d26-417f-b279-606d1a7868fc
Point of truth URL of this metadata record
- Date info (Creation)
- 2024-09-26T00:00:00
- Date info (Revision)
- 2024-09-30T12:05:18
Metadata standard
- Title
- ISO 19115-3:2018
Overviews
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