Enhanced silica export in a future ocean triggers global diatom decline

Area of Science:

• Marine biology
• Biogeochemistry
• Oceanography

Background:

• Diatoms are crucial primary producers, accounting for up to 40% of marine production.
• They require silicic acid for growth and shell formation.
• Diatoms are often considered resistant or even beneficiaries of ocean acidification.

Purpose of the Study:

• To investigate the global-scale effects of ocean acidification on diatoms and marine biogeochemical cycles.
• To understand the impact of decreasing pH on the silicon cycle and diatom community structure.

Main Methods:

• In situ mesocosm experiments with natural plankton communities.
• Analysis of global sediment trap data.
• Earth system model simulations.

Main Results:

• Ocean acidification increased the silicon (Si) to nitrogen (N) ratio of sinking biogenic matter by 17% under projected 2100 conditions.
• This shift is attributed to slower silica dissolution at lower pH.
• Global sediment trap data confirmed the influence of pH on Si:N ratios in the water column.

Conclusions:

• Future ocean acidification is predicted to decrease silica dissolution, reducing surface silicic acid availability.
• This will lead to a projected global decline of diatoms by 13-26% by 2200.
• The findings highlight unexpected Earth system feedbacks that alter current understanding of ocean acidification impacts.