The Effect of Ocean Acidification on Phosphorus Solubility from Wildfire Ash and its Role in Enhancing the Biological Carbon Pump

Increasing atmospheric CO₂ concentrations drives ocean acidification, potentially leading to substantial impacts on marine ecosystems and altering marine nutrient dynamics. Phosphorus (P) availability is a key limiting factor for primary productivity in the oceans. Atmospheric particles, such as wildfire ash, supply the oceans with substantial amounts of nutrients such as P. The solubility of P from aerosol particles, especially from wildfire ash, plays a critical role in oceanic nutrient cycles and may significantly impact the biological carbon pump, a key mechanism for atmospheric CO₂ regulation.

As ocean acidification continues and wildfires are projected to increase in intensity and severity with climate change, understanding how changes in seawater pH influence P release from wildfire ash is essential. This study aims to investigate the effect of past, present, and future seawater pH levels on P solubility from different wildfire ash under controlled laboratory conditions. Specifically, the study aims to examine how elevated CO₂ levels, leading to lower pH (ocean acidification), impact the availability of P in wildfire ash compared to lower CO₂ levels.

Using artificial seawater and ash samples derived from Mediterranean and agricultural vegetation, this research will analyze P release patterns under a range of CO₂ concentrations, encompassing current levels, future projections, and historical baselines.

Preliminary results demonstrated a significant dependence of P release from wildfire ash on pCO₂ concentrations and its influence on the pH. Elevated CO₂ levels of the projected future and of ancient atmosphere enhanced P solubility in both Mediterranean vegetation and agricultural vegetation treatments while reduced levels of the preindustrial and pre-Holocene periods decreased P solubility. These findings are anticipated to shed light on the role of wildfire ash in marine nutrient dynamics and its broader impact on ocean productivity and the global carbon cycle, especially in regions experiencing increasing wildfire activity.

These initial findings lay the groundwork for continued research, where I will investigate the cultivation of microalgae under controlled laboratory conditions at varying atmospheric CO2 concentrations. The research will focus on understanding how P release from wildfire ash, influenced by different CO₂ levels, impacts the growth rate of phytoplankton. The experiments will assess the role of wildfire ash as a potential P source for phytoplankton grown in P-depleted water.