Coccolith dissolution within copepod guts affects fecal pellet density and sinking rate

Area of Science:

• Marine biology
• Biogeochemistry
• Oceanography

Background:

• Calcium carbonate, primarily calcite from coccolithophores, is the most common marine biomineral.
• Ocean surface waters are supersaturated with calcium carbonate, yet significant dissolution occurs in the upper ocean.
• Zooplankton guts are hypothesized microenvironments for this unexpected dissolution.

Purpose of the Study:

• To investigate calcite dissolution within copepod guts.
• To quantify the impact of starvation and feeding on calcite dissolution.
• To assess the effect of gut dissolution on fecal pellet characteristics and carbon export.

Main Methods:

• Utilized a novel ¹⁴C microdiffusion technique for precise measurement of calcite dissolution.
• Experimentally subjected copepods to starvation and feeding periods.
• Analyzed changes in fecal pellet density and sinking rates.

Main Results:

• Up to 38% of ingested calcite dissolved in starved copepod guts.
• Continued feeding led to a buffered gut environment, limiting further dissolution (Tums hypothesis).
• Reduced gut dissolution resulted in denser fecal pellets with doubled sinking rates.

Conclusions:

• Zooplankton guts actively facilitate calcite dissolution above the chemical lysocline.
• Zooplankton feeding history critically influences the variability of carbon export via fecal pellets.
• This process highlights a significant, previously underestimated, pathway for marine carbon cycling.