Abstract
The present study investigated quantitatively the significance of HNLC (high-nutrient low-chlorophyll) regions and its grazing control with the improved iron fertilization for climate change. The limitation of iron (Fe) for phytoplankton growth in HNLC regions was confirmed by sulfur compounds (S) such as volcanic ash and hydrogen sulfide (H2S) in batch cultures, whose chemical sediment of Fe3S4 showed 4.06 wt%. The technologies developed for iron fertilization since 1993 till now were not practical to provide sufficient amounts of bioavailable iron due to sedimentary iron sulfides induced by undersea volcanic sulfur compounds. The proposed technology for iron fertilization was improved to enhance the bioavailable iron to phytoplankton by keeping minimal sulfur compounds in HNLC regions. The low productivity of phytoplankton by grazing control in HNLC regions was 6% diatoms whose 52% was grazed by copepods and 42% by krill on the basis of data analysis in 2000 EisenEx Experiment at boundary of Antarctic and African tectonic plates. All of the previous iron fertilization experiments were conducted at volcanic sulfur compounds enriched HNLC regions. The present study revealed that the enhanced phytoplankton productivity in batch culture without sedimentary iron sulfides can be possible only if sulfur compounds are minimal, as is in Shag Rocks (53°S, 42°W) of South Georgia in Scotia Sea in the Southern Ocean.
Highlights
The hypothesis of iron fertilization was speculated by English biologist Joseph Hart in 1934, raised by John Gribbin in 1988, and renewed by American oceanographer John Martin four months later
The limitation of iron (Fe) for phytoplankton growth in HNLC regions was confirmed by sulfur compounds (S) such as volcanic ash and hydrogen sulfide (H2S) in batch cultures, whose chemical sediment of Fe3S4 showed 4.06 wt%
All of the previous iron fertilization experiments were conducted at volcanic sulfur compounds enriched HNLC regions
Summary
The hypothesis of iron fertilization was speculated by English biologist Joseph Hart in 1934, raised by John Gribbin in 1988, and renewed by American oceanographer John Martin four months later. The existence of HNLC regions was attributed to constant zooplankton grazing over phytoplankton, trace metal toxicity, limitation of iron input, light limitation due to the deep mixed layer. None of these factors have been proved conclusively [1] [6]. The goal of the present study was to examine empirically the Fe limitations induced by S compounds of volcanic ash and hydrogen sulfide to improve the iron fertilization for the maximal phytoplankton productivity and estimate analytically the grazing control by copepods and krill over diatoms in HNLC regions
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