| 05 Mar 2026
The Impact of NaOH, CaO, and HCO3–+ Ca+2 Addition on PIC and POC Formation in Los Angeles Harbor Waters
Abstract. Negative CO2 emission technologies such as ocean alkalinity enhancement (OAE), in tandem with emissions reduction are necessary to keep the climate system below a critical tipping point. While the biogeochemical consequences of OAE remain poorly constrained, field deployment is accelerating in the commercial sector, leaving questions of ecosystem impact in the wake. In this study we conduct alkalinity perturbation experiments to capture the resultant impact to the organic carbon and calcium carbonate pools. We quantify shifts in dissolved/particulate inorganic (DIC, PIC) and organic (DOC, POC) carbon after the addition of three alkalinity sources – NaOH, CaO, and NaHCO3 + CaCl2 (to simulate dissolved limestone). These experiments are conducted with coastal sea water with enhancements of +500–1000 µmol kg–1 alkalinity, and incubated in situ, to elucidate their impact over the short term, 0–4 days. Select experiments are also completely isolated from the light via bottle shading. With most treatments, there is no statistically significant CaCO3 precipitation after OAE nor changes in organic matter production or consumption, relative to the untreated controls. One exception is when CaO addition enriches the water by 1000 µmol kg–1, here we find a significant decline in POC production. 13C isotope spikes were added to trace C partitioning throughout the experiment. The seawater used in these experiments had a wide range of initial ambient PIC and POC, and within this wide range, a +500 µmol kg–1 alkalinity in the form of NaOH, CaO or NaHCO3 + CaCl2 addition did not change the production or consumption of carbon in these waters.
Competing interests: WB is the co-founder of Calcarea, Inc. The authors declare that they have no other competing interests.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
