Deep Chlorophyll Maxima in the Global Ocean: Occurrences, Drivers and Characteristics

Area of Science:

• Oceanography
• Marine Ecology
• Biogeochemistry

Background:

• Stratified oceans exhibit Deep Chlorophyll a Maximums (DCMs), which are either deep biomass (DBM) or photoacclimation (DAM) maxima.
• These phenomena are not detectable by satellites, leaving knowledge gaps regarding their formation and drivers.
• Previous studies have not undertaken a global assessment of DCMs.

Purpose of the Study:

• To investigate the spatial and temporal variability of DCMs in the open ocean.
• To identify the environmental drivers responsible for DCM formation and maintenance.
• To improve the understanding and quantification of DCMs' role in oceanic carbon budgets.

Main Methods:

• Utilized a global dataset from over 500 Biogeochemical-Argo floats.
• Detected DCMs by comparing vertical distributions of chlorophyll a and particulate backscattering coefficients.
• Analyzed spatial and temporal patterns in relation to environmental factors.

Main Results:

• DCM seasonal dynamics are region-dependent.
• High-latitude regions show infrequent, summer-restricted DBMs.
• Oligotrophic regions feature permanent DAMs, sometimes replaced by DBMs in summer.
• Subequatorial waters host permanent DBMs due to favorable light and nutrient conditions.
• Light attenuation in the upper ocean is the primary driver for DCM appearance and depth.

Conclusions:

• DCM occurrence and depth are primarily influenced by light attenuation.
• Seasonal and regional differences in DCMs (DBMs vs. DAMs) are significant.
• This research provides a foundation for understanding DCMs' role in primary production and carbon export.