High-resolution observations on enrichment processes in the sea-surface microlayer

Area of Science:

• Oceanography
• Marine Chemistry
• Biogeochemistry

Background:

• The sea surface microlayer (SML) is a critical interface for air-sea exchange.
• Previous assumptions attributed dissolved organic matter (DOM) enrichment in the SML solely to concentration changes.
• The complexity of DOM enrichment processes in the SML requires further investigation.

Purpose of the Study:

• To investigate the processes controlling fluorescent dissolved organic matter (FDOM) enrichment in the SML.
• To compare FDOM dynamics in the SML with underlying waters (ULW).
• To assess the influence of environmental factors on FDOM enrichment.

Main Methods:

• High-resolution observations of FDOM were conducted at 13 stations in the Atlantic Ocean.
• Measurements were taken in both coastal and open ocean environments.
• FDOM concentrations in the SML and ULW were analyzed over time.

Main Results:

• FDOM enrichment in the SML ranged from 0.8 to 2.0 compared to ULW.
• FDOM enrichment is a common phenomenon across different distances from terrestrial sources.
• SML FDOM concentrations showed less variability than ULW, which experienced sudden changes.
• Wind speed and solar radiation had minor effects, while ULW concentration changes drove SML enrichment.
• Photochemical degradation of FDOM was observed in near-shore SML.

Conclusions:

• DOM enrichment in the SML is driven by complex processes beyond simple concentration changes.
• Environmental factors and photochemical degradation play significant roles in SML FDOM dynamics.
• Understanding SML enrichment is vital for comprehending air-sea exchange of gases and heat.