The Supply of Iron to Diatoms

Harvey, H. W.

doi:10.1017/s0025315400011954

Cited by 97 publications

(54 citation statements)

References 9 publications

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“…This ( )direct effect of Fe on the largest size class of bloom-forming diatoms would be consistent with the Ž . concept of diffusion limitation Harvey, 1937 , being most severe for larger cells with low specific surface Ž . area Hudson and Morel, 1990 .…”

Section: Limitation By Fe In the Remote Southern Oceanmentioning

confidence: 99%

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

et al. 1999

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The remote waters of the Pacific region of the Southern Ocean are the furthest away from any upstream and upwind Ž continental Fe sources. This prime area for expecting Fe limitation of the plankton ecosystem was studied March-April . 1995 along a north-south transect at ; 898W. At the end of the austral summer the upper wind-mixed layers were in the order of ; 100 m deep, thus mixing the algae down into the dimly lit part of the euphotic zone where photosynthesis is severely restricted. The dissolved Fe was found at low concentrations ranging from 0.05 nM near the surface to 0.5 nM in Ž . deeper waters. Along the transect 528S-698S , the dissolved iron was enhanced in the Polar Front, as well as near the Ž . Antarctic continental margin 0.6-1.0 nM . In between, the southern ACC branch was depleted with iron; here the concentrations in surface waters were quite uniform at about 0.21 nM. This is only somewhat lower than the 0.49 nM Ž . Ž . October 1992 and 0.31 nM November 1992 averages in early spring in the southern ACC part of Atlantic 68W sections wde Baar, H.J.W., de Jong, J.T.M., Bakker, D.C.E.. Loscher, B.M., Veth, C., Bathmann, U., Smetacek, V., 1995. Importancë of iron for phytoplankton spring blooms and CO drawdown in the Southern Ocean. Nature 373, 412-415; Loscher, B.M., 2 de Jong, J.T.M., de Baar, H.J.W., Veth, C., Dehairs, F., 1997. The distribution of iron in the Antarctic Circumpolar Current.x Deep-Sea Research II 44, 143-188. . First, the lower ; 0.21 nM in March-April 1995 may partly be due to continuation of the seasonal trend where the phytoplankton growth, albeit modest, was removing Fe from the surface waters. Secondly, the 898W Pacific stations are further downstream continental or seafloor sources than the Atlantic 68W section. In the latter case, the ACC water had passed through the Drake Passage and also over the Sandwich Plateau. Indeed for Drake Passage, intermediate Fe concentrations have been reported by others. The generally somewhat lower surface water Fe at the ACC and PF at 898W is consistent with the distance from sources and the late summer. It also would explain the very low Ž . abundance of phytoplankton Chl a in the region and the conspicuous absence of plankton blooms. In the subAntarctic waters north of the Polar Front there are no diatoms, let alone diatom blooms, due to low availability of silicate. Thus, it Baar et al.r Marine Chemistry 66 1999 1-34 2 appears the biological productivity is suppressed due to iron deficiency, in combination with the severe seasonal effects of wind mixing on the light climate, as well as regional silicate limitation for diatoms. q

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Section: Limitation By Fe In the Remote Southern Oceanmentioning

confidence: 99%

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

et al. 1999

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“…An explanation is due. In the earlier work 100 mL samples of sea water were treated with two drop~of 4 N-HCl and I mL 1% dipyridyl in 0'2 N-HCL Harvey (1937) has shown, and the writer has confirmed, that at high dilutions ferric iron will give rise tb the red ferrous-tris-dipyridyl complex.…”

Section: Ferrous Iron In the Sea And In Lakesmentioning

confidence: 93%

“…This is a development of the argument already put forward by Harvey (1945, p. 137) as to the part played by zooplankton in the upper layers of the sea. Though the minimal requirements of diatoms for iron are much less than those for phosphorus (Harvey, 1937),some iron in a usable form is essential. It would now seem likely that the planktonic plants over the continental shelf require a proper balance of animals, both planktonic and bottom dwelling, to maintain their supply of iron in such a usable form.…”

Section: Addendummentioning

confidence: 99%

“…

FORMATION AND STABILITY OF FERRIC PHOSPHATE IN SEA WATERTwo seIies of experiments in this laboratory by Harvey (1937) and by the writer (unpublished) on the precipitation of iron from sea water containing phosphate and hydroxyl ions (pH 8'1) do not agree. Sometimesmuch of the phosphate is precipitated, sometimesnone.

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Some Chemical Considerations on the Distribution of Iron in the Sea

Cooper

1948

J. Mar. Biol. Ass.

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Three purely chemical topics which have aIisen in the course of the investigation describedin the preceding paper (Cooper, 1948)will be discussed; first, a theoreticaltreatment of the formation and stabilityof ferric phosphate in sea water; secondly,an explanation as to how 2:2'-dipyIidyl may react with ferIic iron at high dilutions in natural waters to give the red ferrous complex; and thirdly, a short account of an expeIiment which showed ferrifiuoIide to be unstablein seawater.. FORMATION AND STABILITY OF FERRIC PHOSPHATE IN SEA WATERTwo seIies of experiments in this laboratory by Harvey (1937) and by the writer (unpublished) on the precipitation of iron from sea water containing phosphate and hydroxyl ions (pH 8'1) do not agree. Sometimesmuch of the phosphate is precipitated, sometimesnone. Much closer control is necessary but it has not been clear what form this should take. The followingtheoretical examination, imperfect though it is, may help in the design of such contro1.Pugh & du Toit (1936)examinedthe ionic exchange or hydrolysis of ferric phosphate and silicate in relatively concentrated systems. Solutions of ferric chloIide were titrated with solutions of phosphate or silicate containing varying amounts of sodium hydroxide. A ferIic phosphate with a higher P04/Fe203 mol-ratio than 0'71 could not be prepared since compounds richer in phosphate hydrolysed until this ratio was reached. There is an optimum value of pH above which the ferIic phosphate hydrolyses further with increasing hydroxyl-ion concentration. The same is true of ferric silicate. At pH 8'0 and above, in presence of hydroxyl, silicateand phosphate in solution, ferric hydroxide would be the stable solid phase. The isoelectric point of ferIic hydroxide prepared from its chloIide is said to be pH 7'1 so that at pH 8'1 ferric hydroxide should be regarded rather as the very sparingly soluble ferrous acid, H3Fe03, which may be expected to dissociate H3Fe03~H+ + H2FeO~. Since FeOH++ is the dominant ferric cation at the isoelectric point, for electroneutrality of the micelle, the concentration of its anion, H2FeO~, should be twice that of its cation, FeOH++. This (Cooper, 1937b, equation 12) will be about 10-}2.54 at 18°C. The solubility product of ferrous acid, (H+) (H2FeO~)will therefore be of the order

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“…This takes place in the presence of organic matterthe protein of the diatom, its surrounding slime, etc.-so a certain measure of protection may be expected. Colloidal particles of iron hydroxide adsorbed upon the plant (Harvey, 1937) are also likely to be set free in a more or less "protected" state.…”

Section: H W Harveymentioning

confidence: 99%

Note on Colloidal Ferric Hydroxide in Sea Water

Harvey

1937

J. Mar. Biol. Ass.

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If a sol of colloidal ferric hydroxide is added to sea water, or if the hydroxide is formed in sea water by adding a solution of an iron salt, the aggregated molecules of hydroxide coalesce to form flocs which fall rather rapidly as a precipitate. When several thousand mg. of iron are added per cubic metre of sea water, flocculation is immediate; on adding 300-500 mg. Fe per m.3 in sufficiently dilute solution (10-4 or 10-5 M) flocculation and sedime.ntation may be delayed for several days. Although this quantity is over twenty times as much as ordinarily occurs in the sea, it seemed rather remarkable that the waters of the open ocean could maintain any material quantity of ferric hydroxide in suspension, since it would there have many years in which to flocculate and fall.Waksman had suggested that much of the iron in sea water may be in the form of iron humates derived from the breakdown of organisms, and he had obtained evidence that such humates were compounds of lignoproteinates.Since ferric hydroxide in sea water, in spite of its great insolubility, is utilized by diatoms, some experiments concerning its nature were made, and an account of some of these may be of use to others interested in the same field. COLLOIDAL FERRIC HYDROXIDE ADSORBED ON EMULSOIDSA number of sols have been prepared by adding M/500 ferrous or ferric salts containing a small quantity of various emulsoids to an equal volume of sodium hydroxide, of such concentration that the resultant liquid was alkaline (pH 8-10).Sols prepared in this way and containing one to eight times more gum arabic by weight than iron, when added to sea water, giving a final concentration of 2000-5000 mg. per m.3, did not flocculate for several weeks. They also gave a clear solution in normal sodium hydroxide.Sols containing four to ten times more starch by weight than iron when added to sea water did not flocculate for several days. On standing or boiling, the sols darken in colour with a rise in hydrogen-ion concentration, suggesting that hydrolysis is not completed for some time even in such alkaline media. Boiled sols containing ten times more starch than iron when added to sea water did not flocculate for many weeks, and gave a clear solution in normal sodium hydroxide.Sols containing two to ten times as much albumen as iron, when added to sea water, remained in suspension for some hours or days.r-

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The Supply of Iron to Diatoms

Cited by 97 publications

References 9 publications

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

Some Chemical Considerations on the Distribution of Iron in the Sea

Note on Colloidal Ferric Hydroxide in Sea Water

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