Reconstructing surface ocean circulation with ¹²⁹I time series records from corals

Area of Science:

• Environmental Science
• Radiochemistry
• Oceanography

Background:

• Iodine-129 (¹²⁹I) is a long-lived radionuclide used as an environmental tracer.
• Global ¹²⁹I levels in surface water are 10-100 times higher than pre-1960 levels.
• Anthropogenic ¹²⁹I from nuclear fuel reprocessing is a major source in marine environments.

Purpose of the Study:

• To reconstruct historical ¹²⁹I levels in the Pacific Ocean using coral records.
• To differentiate the sources of ¹²⁹I in marine surface waters.
• To understand the oceanic transport and distribution of ¹²⁹I.

Main Methods:

• Analysis of ¹²⁹I concentrations in coral skeletons from four distinct Pacific locations.
• Correlation of coral ¹²⁹I records with known nuclear weapons testing and reprocessing events.
• Interpretation of ¹²⁹I distribution patterns in relation to ocean currents.

Main Results:

• Coral ¹²⁹I records show distinct temporal variations, with significant increases linked to specific events.
• Peaks in ¹²⁹I at Con Dao (1959) and Guam (1955, 1959) are attributed to nuclear weapons testing, particularly the Castle Bravo and Hardtack I tests.
• Gradual ¹²⁹I increases in Rabaul (1970s) suggest different regional influences, possibly linked to Solomon Islands records.
• Xisha Islands coral shows similar peaks to Con Dao but with lower values, potentially influenced by upwelling.

Conclusions:

• Nuclear weapons testing was the dominant source of ¹²⁹I in the Western Pacific during the latter 20th century.
• Coral ¹²⁹I time series provide valuable insights into the historical surface distribution and oceanic transport of this radionuclide.
• The study highlights the significant impact of past nuclear activities on marine environments.