Measuring actinium-227 by mass spectrometry is feasible, sensitive and reliable!

Actinium-227 (227Ac) is a radioelement (half-life = 22 y) produced in marine sediments by the decay of the protactinium 231. 227Ac remobilization in the sediment is the main source of actinium to seawater. It makes of the 227Ac a good tracer of the remobilization from sediments and of the deep vertical mixing on the decadal time scale. However, 227Ac was difficult to study until now because of its very low concentration in the environment, from 0 to 35 ag/kg (1ag = 10-18g) in seawater. Levier and co-authors (2021, see reference below) have developed a new protocol measurement of the dissolved actinium in seawater. This new is a measurement by isotope dilution, chromatographic purification, and Multi-Collection Induced Coupled Mass Plasma Spectrometry (ICPMS). The detection limit achieved with this method is around 1 ag/kg measured on samples of 10L of seawater. This new protocol was applied to archived samples from the Bonus GoodHope cruise (GIPY04) collected in 2008 in the Weddell Gyre. The resulting profile (see Figure) is consistent with previous data from the Weddell Gyre obtained by a spectrometry on 20-300 L seawater samples (Geibert and Vöge, 2008).

Figure: Seawater 227Ac profiles in Weddell Gyre, at station Super V from Bonus GoodHope cruise, measured by mass spectrometry (green diamonds) which is in good agreement with 227Ac profiles at station PS2579–2 (Geibert et al., 2002) (black dot) and PS63–121 measured by alpha-spectrometry (Geibert and Vöge, 2008) (grey dots). All uncertainties are expressed at 2σn.

The article is freely available until July 14th 2021 at:


Geibert, W., Vöge, I., 2008. Progress in the determination of 227Ac in sea water. Mar. Chem. 109, 238–249.

Levier, M., Roy-Barman, M., Colin, C., Dapoigny, A., 2021. Determination of low level of actinium 227 in seawater and freshwater by isotope dilution and mass spectrometry. Mar. Chem. 233, 103986.

Latest highlights

Science Highlights

The Arctic Ocean is a net source of micronutrients toward the North Atlantic through the gateway of Fram Strait

They present a flux budget for micronutrient exchange between the Arctic and the North Atlantic Ocean.


Science Highlights

A better insight into parameters that control particle flux in the ocean

They compiled full ocean-depth size-fractionated particle concentration and composition data from three recent U.S. GEOTRACES cruises.


Science Highlights

Confrontation of two models to constrain the hydrothermal iron contribution to the Southern Ocean export production

Tagliabue and his co-workers compare the hydrothermal dissolved iron simulated by both models.


Science Highlights

North African dust is an important (but not dominant) source of iron to the Gulf of Mexico

They have combined new GEOTRACES compliant data to estimate how important North African dust could be as a source of iron to the Gulf of Mexico.