³⁹Ar dating with small samples provides new key constraints on ocean ventilation

Area of Science:

• Oceanography
• Geochemistry
• Isotope Geochronology

Background:

• Ocean ventilation is critical for regulating atmospheric CO2, ocean heat content, and oxygen distribution.
• Existing transient tracers (e.g., CFCs, 14C) have limitations in resolving centennial-scale deep ocean dynamics.
• Argon-39 (³⁹Ar) is a valuable noble gas isotope tracer with a 269-year half-life, ideal for centennial timescales, but its low abundance historically required large water samples (1000 L).

Purpose of the Study:

• To develop a more efficient method for Argon-39 (³⁹Ar) dating.
• To investigate previously unquantifiable ocean ventilation patterns in the Tropical Atlantic.
• To assess the role of advection in intermediate-depth ocean ventilation.

Main Methods:

• Utilized the atom-optical technique Atom Trap Trace Analysis (ATTA) for ³⁹Ar dating.
• Successfully dated samples using significantly reduced water volumes (5 L).
• Applied the method to analyze ventilation patterns in the Tropical Atlantic.

Main Results:

• Achieved successful ³⁹Ar dating with only 5 L of seawater, a tenfold reduction in sample size.
• Quantified ocean ventilation patterns in the Tropical Atlantic that were previously inaccessible.
• Revealed that advection plays a more significant role in ventilating the intermediate ocean depths than previously understood.

Conclusions:

• The development of ATTA for ³⁹Ar analysis dramatically lowers the required water volume, making this tracer broadly applicable.
• This advancement enables global collection of ³⁹Ar data, significantly enhancing our ability to quantify ocean ventilation.
• The findings highlight the importance of advection in deep ocean circulation and have implications for climate modeling and carbon cycle research.