Ever wonder how long your favourite element remains in the ocean before it’s gone again?

This timeframe, sometimes called a residence time, ranges from decades for the most reactive trace elements to millions of years for the most unreactive elements such as the major components of sea salt. The residence time is often difficult to constrain and involves estimating how much of an element is presently in the ocean (i.e., the inventory) as well as the magnitude of the total supply rate or removal rate of the element. In the study published by Hayes and co-authors in Global Biogeochemical Cycles (2018, see reference below), a replacement time (or residence time with respect to supply) can be quantified using large synthesized GEOTRACES datasets from the North Atlantic which can precisely define the inventory of trace elements as well as their supply rate using radioactive tracers. In particular, their method suggests an ocean replacement for iron that is only 6 years, meaning this micronutrient element may be cycling much more quickly than previous estimates have suggested and will provide a target for ocean models to understand how this element is removed from the ocean in terms of biological uptake or abiotic scavenging.

18 Hayes2
(Left) Replacement time of dissolved Fe across the GEOTRACES cruise section GA03. This replacement time is how long it would take to replace all of the iron in the North Atlantic Ocean with a source of iron derived from the quantifiable delivery of the crustal isotope thorium-232 to the ocean. (Right) Map showing the GEOTRACES section GA03 in the Atlantic Ocean. Click here to view the figure larger.


Hayes, C. T., Anderson, R. F., Cheng, H., Conway, T. M., Edwards, R. L., Fleisher, M. Q., Ho, P., Huang, K.-F., John, S., Landing, W.M., Little, S. H. Lu, Y., Morton, P. L., Moran, S. B., Robinson, L. F., Shelley, R. U., Shiller, A. M., Zheng, X.-Y. (2018). Replacement Times of a Spectrum of Elements in the North Atlantic Based on Thorium Supply. Global Biogeochemical Cycles, 32(9), 1294–1311. DOI: http://doi.org/10.1029/2017GB005839

 You can also read the Research Spotlight about this paper published on Eos.org: https://eos.org/research-spotlights/a-novel-approach-reveals-element-cycles-in-the-ocean

Latest highlights

Science Highlights

Loss of old Arctic sea ice increases methylmercury concentrations

Researchers from the SCRIPPS, the Stockholm Natural Museum and the Mediterranean Institute of Oceanography show the importance of sea ice composition on methylmercury budgets


Science Highlights

Estimating Atmospheric Trace Element Deposition Over the Global Ocean

A recently developed method based on the natural radionuclide Be-7 has provided a means to estimate the bulk atmospheric trace element deposition velocity

Science Highlights

Dissolved gallium unravels Pacific and Atlantic waters in the Arctic Ocean

Whitmore and co-workers demonstrate that the dissolved gallium distribution provide a better water source deconvolution than the nutrient tracers


Science Highlights

Precise estimate of the mercury export from the Arctic to the Atlantic Ocean

Using new observations acquired during GEOTRACES Arctic cruises, a refined arctic mercury budget has been established