Modified future diurnal variability of the global surface ocean CO₂ system

Area of Science:

• Oceanography
• Climate Science
• Biogeochemistry

Background:

• Increasing atmospheric CO2 and climate change are altering the marine CO2 system and carbonate chemistry variability.
• Seasonal variability in the ocean CO2 system has already changed, with projections indicating further amplification.
• Diurnal variability in the CO2 system, particularly in extreme events, is also expected to be affected by climate change.

Purpose of the Study:

• To modify a global ocean biogeochemical model to resolve diurnal variability in the ocean CO2 system.
• To investigate how surface ocean diurnal variability responds to historical changes and projects future changes under different emission scenarios.
• To explore the drivers of heightened CO2 diurnal variability and its impact on marine organisms.

Main Methods:

• Modification of a global ocean biogeochemical model to incorporate diurnal variability.
• Forcing the model with 3-hour atmospheric outputs from an Earth system model.
• Analysis of historical changes and projections under high-emission and high-mitigation scenarios.

Main Results:

• Global mean diurnal amplitude of pCO2 increased by 226% under a high-emission scenario and 55% under a high-mitigation scenario compared to preindustrial levels.
• The probability of extreme diurnal amplitudes of pCO2 and [H+] increased 30- to 60-fold under high 21st-century emissions.
• Enhanced sensitivity of pCO2 to temperature changes, driven by ocean CO2 absorption, is the primary cause of increased diurnal variability.

Conclusions:

• Future ocean organisms will experience enhanced diurnal variability in pCO2 and [H+].
• This increased variability is projected to lead to higher metabolic costs for marine life.
• Understanding and projecting these changes are crucial for assessing the impact of climate change on marine ecosystems.