02 Jan 2023
 | 02 Jan 2023
Status: this preprint is currently under review for the journal BG.

The Fingerprint of Climate Variability on the Surface Ocean Cycling of Iron and its Isotopes

Daniela König and Alessandro Tagliabue

Abstract. The essential micronutrient iron (Fe) limits phytoplankton growth when dissolved Fe (dFe) concentrations are too low to meet biological demands. However, many of the processes that remove, supply, or transform Fe are poorly constrained, which limits our ability to predict how ocean productivity responds to ongoing and future changes in climate. In recent years, isotopic signatures (ẟ56Fe) of Fe have increasingly been used to gain insight into the ocean Fe cycle, as distinct ẟ56Fe endmembers of external Fe sources and ẟ56Fe fractionation during processes such as Fe uptake by phytoplankton can leave a characteristic imprint on dFe signatures (ẟ56Fediss). However, given the relative novelty of these measurements, the temporal scale of ẟ56Fediss observations is limited. Thus, it is unclear how the changes in ocean physics and biogeochemistry associated with ongoing or future climate change will affect ẟ56Fediss on interannual to decadal time scales. To explore the response of ẟ56Fediss to such climate variability, we conducted a suite of experiments with a global ocean model with active ẟ56Fe cycling under two climate scenarios. The first scenario is based on an atmospheric reanalysis and includes recent climate variability (1958–2021), whereas the second comes from a historical and high emissions climate change simulation to 2100. We find that under recent climatic conditions (1975–2021), interannual ẟ56Fediss variability is highest in the tropical Pacific due to circulation and productivity changes related to the El Niño Southern Oscillation (ENSO), which alter both endmember and uptake fractionation effects on ẟ56Fediss by redistributing dFe from different external sources and shifting nutrient limitation patterns. While the tropical Pacific remains a hotspot of ẟ56Fediss variability in the future, the most substantial end of century ẟ56Fediss changes occur in the Southern hemisphere at mid to high latitudes. These arise from uptake fractionation effects due to shifts in nutrient limitation. Based on these strong responses to climate variability, ongoing measurements of ẟ56Fediss may help diagnose changes in external Fe supply and ocean nutrient limitation.

Daniela König and Alessandro Tagliabue

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-241', Anonymous Referee #1, 28 Jan 2023
    • AC1: 'Reply on RC1', Daniela König, 03 Mar 2023
  • RC2: 'Comment on bg-2022-241', Anonymous Referee #2, 08 Feb 2023
    • AC2: 'Reply on RC2', Daniela König, 03 Mar 2023

Daniela König and Alessandro Tagliabue

Data sets

The Fingerprint of Climate Variability on the Surface Ocean Cycling of Iron and its Isotopes [dataset] König, D., Tagliabue, A.

Daniela König and Alessandro Tagliabue


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Short summary
Using model simulations, we show that natural and anthropogenic changes in the global climate leave a distinct fingerprint in the isotopic signatures of iron in the surface ocean. We find that these climate effects on iron isotopes are often caused by the redistribution of iron from different external sources to the ocean, due to changes in ocean currents, and by changes in algal growth, which take up iron. Thus, isotopes may help detect climate-induced changes in iron supply and algal uptake.