Iron Fertilization Efficiency and the Number of Past and Future Regenerations of Iron in the Ocean
Abstract
Iron fertilization is explored by tracking dissolved iron (DFe) through its life cycle from injection by external sources (birth) to burial in the sediments (death). We develop new diagnostic equations that count iron and phosphate regenerations with each passage through the biological pump and partition the ocean's DFe concentration according to the number of past and future regenerations. We apply these diagnostics to a family of data-constrained estimates of the iron cycle with sources σtot in the range 1.9-41 Gmol yr-1. We find that for states with σtot > 7 Gmol yr-1, 50% of the DFe inventory has not been regenerated in the past and 85% will not be regenerated in the future. The globally averaged mean number of past and future regenerations scale like (σtot)-1 with ranges of 0.05-2.2 and 0.01-1.4, respectively. Memory of birth location fades rapidly with each regeneration, and DFe regenerated more than 5 times is found in a pattern shaped by Southern Ocean trapping. We quantify the natural fertilization efficiency at point r, anywhere in the ocean, as the global export production resulting from the DFe at r in the current state of the ocean, per DFe molecule, and show this efficiency to be equivalent to the DFe molecule's mean number of future regenerations. At the surface, this fertilization efficiency has a global mean in the range 0.7-7 mol P (mmol Fe)-1 and is largest in the central tropical Pacific, with the Southern Ocean having comparable importance only for high-source states.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGC23G1277P
- Keywords:
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- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGEDE: 1635 Oceans;
- GLOBAL CHANGEDE: 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL