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Submarine volcanism as a source for iron
FARTH AND PLANt.TARY SCIENCE LETTERS 9 (1970) 348-354 . NORTH-HOLLAND PUBLISHING COMPANY
SUBMARINE VOLCANISM AS A SOURCE FOR IRON Kurt BOSTROM University of Miarni, Rosenstiel School ofMarine and A tmospheric Sciences, Miami, Florida 33149, USA Received 20 May 1970 Deposition rates of iron on the East Pacific Rise are 4--30 times larger than in surrounding areas of the Pacific, suggesting local voieanisni to be the source of iron . The distributions of Co, Ni, Mn, Ti and A 1 support this conclusion .
Several recent studies indicate that some elements, particularly iron, manganese and barium, are delivered by submarine volcanism along active oceanic ridges (= ridges with ocean floor spreading ; 11 -31 . Quantitative evidence supports this conclusion [4-61 . More detailed quantitative evidence is presented here, suggesting that much iron indeed is derived from submarine volcanism . About 200 sediment samples from the East Pacific have been analyzed for several elements, including iron ( fig. l ). Iron, cobalt, nickel and titanium were uetermined by atomic absorption and emission spectrosct_py . Comparisons with G-1 and W-1 indicate accicmcies and precisions better than ± IV, which is ,,-It isfactory for the discussion below. Some of these ceàults and analyses of A 1 and Mn have been published elsewhere by Bostrdrn and co-workers [1 -21 . Additional analytical values were collated from other studies 171 . Agreement between analyses of sediments from the same general areas by different analysts is . excellent Rates of sedimentation in East Pacific have been collated by Ku et al. [81, fig . 2. Additional values derive from some other sources [91 . The absolute accumulation rate of iron can be measured by using the data figs. 1 and 2 are based on (including CdC03 determinations), assuming the in situ density of dry uncompressed surface sediment to be 0.75 g/cm3 1101 . The data points in fig. 3 represcn : location of cores used for determination of sedimentation rates while the iror, values are based on neighboring samples, exct~pt at i 3 points where sedimentation rates and iron concentrations were determined on the same samples [ I1 .
High accumulation rates for iron occur close to the continent, as is to be expected, and on the East Pacific Rise where the three highest values are 95-410 mg Fe/(cm' X 1000 yr). The corresponding values for manganese are 35-- 150 mg Mn/(cm2 X 1000 yr).On the flanks of the ridge 5-10 mg and 05-3 mg are common deposition rates per (cm? X 1000 yr) for Fe and Mn, respectively . These figures agree well with the data of Bender et al . [61 . Deeper lay,:rs ot'sotnc crest sediments were deposited more slowly than the surface layers (Blackmail 191) but even f:)r these layers the deposition rates are about 50 tng Fe per (cm 2 X 1000 yr) . Some deposition rates may be anomaiously Ingli due to ponding of sediments . However, if ponding were of prime importance, it should also influence the accumulation rates of terrigenous constituents as Ti and Al. The data (fig . 4) indicate that deposition rates for Ti vary only by a factor of 5 between the crest and the flanks of the ridge; corresponding values for iron vary by a factor of 160 . Using the deposition rates for Ti to correct for ponding effects it is found that iron is deposited at a rate that can be up to 30 times larger on the crest than on the flanks of the East Pacific Rise ; this conclusion is also suggested by the regional variation in the Fe/Ti ratio in East Pacific sediments [2[ . T1he terrigenous nature of Ti and Al in this area is indicated by the fact that the AI/Ti ratio in most sediment samples [21 is very close toy 20, which is the ratio found in average continental rock, whereas weathering products of average oceanic rock should have an Al/Ti ratio of about 5 . The total amount of terrigenous matter is very small however :
SUBMARINE VOLCANISM AS A SOURCE I-OR IRON
34 9
Fig. 1 . Distribution of iron in East Pacific sediment% on a carbonate-free basis (CFB) . The iron-minima close to the equator between 100 1600 W and at 50 60 c S are duc to dilution by opaline silica . Several recent analyses (Boström, unpublished data) 'been included but confina the patterns found here . 1q-vG
" Î~ïraï a
K .BOSTRÖM
3501
RATES OF SEDIMENTATION ON CARBONATE FREE BASIS IN mm/1000 YEARS 40' - 0 10 -10-30 - >30 RTES FOR OPALINE SILICA RICH SAMPLES ARE I%)RL NEO
OEM N MINIM No 00.6
~IMM 00.9
iwi =OEM a 0
" 0.8
'PPP '
+0.9
073
1
40`
26
*15 S ISO ,
1,60°
140°
1
120°
24
QO°
60o S
30°W
Fig . 2 . Rate of sedimentation (CFB) according to Ku et al ., etc . ( 7, 81 .
the carbonate free fraction of East Pacific Rise sediments contai~ls little besides iron hydroxides, opaline silica and some barite . Other geochemical relations in the East Pacific also suggest that the iron rich sediments on the Ridge are of local origin. Thus, stability relations for oxideshydroxides of Fe, Mn, Ni and Co 1121 suggest that in the well-oxygenated slightly alkaline bottom .vaters (if the ocean i-on should precipitate out fairly fast, followed by manganese, whereas Ni and Co should be riost mohi e and tend to be enriched in the most land-distant areas . This means that, for instance, Fe./Mn and Fe/Co should decrease with distance from the continents . Such distribution patterns are observed
in ordinary pelagic deposits and on inactive oceanic ridges fdr from land, but on active ridges reversed patterns are found as can be demonstrated with the data by Bostr6m et al. I 1 ] and in fig . 5 . The data presented in figs. 1 and 5 do not rule out the possibility that the variability in the Fe/Co ratio, for instance, is partly depth dependent . However, 70 sediment analyses distributed across the Indian Ocean from Indonesia to Madagascar do not show any depth dependency for Co or Ni . Thus close to Indonesia the ratio (Fe + Mn)/(Co + Ni) in %/ppm is close to 0 .10 but falls rapidly westward to about 0.02, a value that also is characteristic for the samples on the Ninety East Ridge. On the Mid-Indian Ocean Ridge the ratio
SUBMARINE VOLCANISM AS A SOURCE FOR IRON
351
DEPOSITION RATE OF IRON IN mg/cm2 x1000 YEARS = ®= = ®=
5-10 10-15 15 -30 >30
E00MANI'120"'1 1 rr"A' Ar /LVI IVI i
a 614,
180°
160°
140°
120°
MEN RM
60'
MU 100° SO .W
Fig. 3. Rate of deposition of iron in East Pacific . (Fe + Mn)/Co + Ni) is close to 0 .09, but half-way between the ridge and Madagascar it falls to about
0 .03, and just off Madagascar reaches values close to 0 .06 . A consequence of these findings is that pelagic sediments on the flanks of active oceanic ridges should he mixtures of ferromanganoan deposites and products A graph of the relation of continental weathering (1 Fe/Ti versus AI/(AI + Fe + Mn) (see fig . 6) supports this conclusion ; the graph also further supports the
I.
conclusion that submarine weathering of basaltic matter is a subordinate source of sediments . High deposition rates of iron have also existed in the past on active oceanic ridges . The basal layers of
the South Atlantic sediments consist of Al-poor Fe-rich sediments in which iron was accumulated at a rate of 20-50 mg/(cm 2 X 1000 yr), whereas the subsequently deposited sediments were typical pelagic sediments with the deposition rates of 5-10 mg/ (cm2 X 1000 yr) for iron 141 . The total mass of sediments delivered to the ocean from submarine volcanism can be estimated, using the areal extent of ferromanganoan and normal pelagic deposits, rate of sedimentation and rates of ocean floor spreading . It can be shown that at most 5% and probably as little as 0 .5-1% of all pelagic sediments (carbonate free matter) derive from submarine volcanism . Since the ridge deposits contain
K .BOSTRÖM
DEPOSITION RATES OF TITANIUM IN mg/cm2 x 1000 YEARS
= <035 iiili = 035 -073
"--
zum 1 q
a
d
BRUN
UNIR 11MM
200
un ~~
\1V
1,
000~ MMMMMENOW a NNEEMEN NE ilNO iin RONNE MEMOS MENNEN 160
140'
1200
1000
Fig. 4. Rate of deposition of titanium in East Pack.
O
SUBMARINE VOLCANISM AS A SOURCE FOR IRON
1906
160*
140"
120*
100*
353 709W
Co (CFB) IN ppm C. 0 - 40 40 - 100 100 - 200 200 C
0"
Fig. 5 . Distribution of Co (CFB) in East Pacific sediments. Almost identical patterns are found for Ni .
close to 30°ío iron and ordinary pelagic sediments about 5% iron this means that only about 3-6% of all iron in the pelagic sediments derive from submarine volcanism. However, since continental matter has been recycled repeatedly during the history of the Earth while the volcanic iron described here may
represent a new contribution to the surface of the Earth, and since ocean floor spreading may have been operating during most of the history of the Earth, it follows that a large fraction of the total amount of iron now at the Earth's surface may have been brought up by submarine volcanism .
K-BOSTRÖM
354
(2] K.Boström, M.N .A.Peterson, O-Joensuu and D.E.Fisher,
r
0 010 020 030 040 0.50 0.60 0.70 0.80 0.90 1 .00 14 I
Ai+Fe+Mn
Fig. 6. Co-variations between I-'--/Ti and Al/(A1 + Fe + Mn) in Felagic sediments. Curve a is generated if average oceanic basaltic matter (Al = 7.y5%, Fe = 8.33%) is mixed in various proportions with volcanic sediments, containing 22% Fe and S .8'a Nfn [ I J : curve be is generated if the same volcanic sedi= ment is mixed with average continental crustal matter (A1 proportions. The distribution of 8.4%, Fe = 5.2'f0) in various analyses (from 2) indicate that in most pelagic sediments the admixture of basaltic debris is small.
Acknowledgements This work. was supported by the NSF Grants GA-1356 and GA-15248 and ONR Contract Nonr 4(1Q8(02) . Contribution No . 1229 from the Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149, References [ 1 K .Bostr6m and h1 .N .A .Peterson, Origin of aluminum-
poor ferromanganoan sediments in areas of high heat flow on the East Pacific Rise, Marine Geology 7 (1969),' 427-477 .
Aluminum-poor ferromanganoan sediments on active oceanic ridges, J. Geophys. Res. ?4 (1969) 3261-3270. (3j K.Bostr6m and S-Valdes, Arsenic in ocean floors, Lithos 2 (1969) 351-360; K.Bostr6m and D.E .Fisher, Distribution of mercury in East Pacific sediments, Geochim. Cosmochim. Acta 33 (1969) 743-745; D.E .Fisher and K.Boström, Uranium rich sediments on East Pacific Rise, Nature 224 (1969) 64-65. (4j K.Boström, Geochemical evidence of ocean floor spreading in South Atlantic Ocean, Nature (1970) in press. [Sj K.Boström, Origin of iron-rich sediments on the East Pacific Rise. Abstract, Trans. Am . Geophys. U. 5 1 (1970) 327. [61 M.Bendcr, W-Broecker, V.Gornitz and G .M iddel, Accumulation rate of manganese and related elements in the sediments from the East Pacific Rise, Abstract, Trans. Am . Geophys. U. 51 (1970) 327 . (7j R.R .Revelle, Marine bottom samples, collected in the Pacific by the Carnegie on its 7th cruise, Camegie Inst . Wash . Publ . 556 (1944) ; E.Goldberg and G.Arrhenius, Chemistry of Pacific pelagic sediments, Geochim. Cosmochim . Acta 13 (1958) 153-212; S .K .El-Wakeel and J .P .Riley, Chemical and mineralogical studies of deep-sea sediments, Geochim. Cosmochim . Acta 25 (1961) 110-146 ; S .Landergren, On the chemistry of deep-sea sediments, Repts. Swedish Deep Sea I xped ., X, Spec . Invest . No . 5 (1964) Gothenburg . [8J T .L .Ku, W.S .Broecker and N .Opdyke, Comparison of sedimentation rates measured by palcomagnetic and the ionium methods of age determination, Earth Planet . Sci. Letters 4 (1968) 1--16 . D.B .Ericson and G.Wullin, Pleistocene climates in the Atlantic and Pacific Oceans : A comparison based on deep-sea sediments, Science 167 (1970) 1483-1485 ; A .Blackman and B .L .K .Somayajulu, Pacific Pleistocene cores: Faunal analyses and geochronology, Science 154 (1966) 886-889; A.Blackman, Pleisocene stratigraphy of cores from the Southeast Pacific Ocean, Ph . D. Dissertation, Univ . Calif. at San Diego (1966) . [101 The density of pelagic surface sediments commonly varies between 1 .40 and 1.80 g/cm 3 and the water content between 40-60í%r- by weight . (Data from A.F . Richards, Tech . Rept . TiR106, Investigations of deepsea sedimentcores, 11 . U.S. Nay Hydrographic Office, Waihington, D.C ., 1962 .) A common in situ density for dry uncompressed pelagic sediment is 0.65 - 0 .85 g/cm 3 ; the uncertainty in this figure is only of minor significance for the discussion here . [ 11 ] The accumulation rates determined in this way are looted at 0.5 ° S-8S .5 ° W, 0° S--104° W, 2.8'0 S--112 .5 ° W, 14 .2 ° S-113 .5 ° W, 14 .2° S-114 .5 ° W, 21 .5 ° J . 81 .ä ° W, 26 .5 " S-115.5" W, 27 .7 ° S- 107° W, 46 .5 ° 5--113 5° W and 46 .7 0 S--123 .5 ° W . [12] MY aurbaix, Atlas d'6quilibries électrochirniques a 2S °(' (Gauthiers-Villars and Cie, Paris, 1963) .
SUBMARINE VOLCANISM AS A SOURCE FOR IRON Kurt BOSTROM University of Miarni, Rosenstiel School ofMarine and A tmospheric Sciences, Miami, Florida 33149, USA Received 20 May 1970 Deposition rates of iron on the East Pacific Rise are 4--30 times larger than in surrounding areas of the Pacific, suggesting local voieanisni to be the source of iron . The distributions of Co, Ni, Mn, Ti and A 1 support this conclusion .
Several recent studies indicate that some elements, particularly iron, manganese and barium, are delivered by submarine volcanism along active oceanic ridges (= ridges with ocean floor spreading ; 11 -31 . Quantitative evidence supports this conclusion [4-61 . More detailed quantitative evidence is presented here, suggesting that much iron indeed is derived from submarine volcanism . About 200 sediment samples from the East Pacific have been analyzed for several elements, including iron ( fig. l ). Iron, cobalt, nickel and titanium were uetermined by atomic absorption and emission spectrosct_py . Comparisons with G-1 and W-1 indicate accicmcies and precisions better than ± IV, which is ,,-It isfactory for the discussion below. Some of these ceàults and analyses of A 1 and Mn have been published elsewhere by Bostrdrn and co-workers [1 -21 . Additional analytical values were collated from other studies 171 . Agreement between analyses of sediments from the same general areas by different analysts is . excellent Rates of sedimentation in East Pacific have been collated by Ku et al. [81, fig . 2. Additional values derive from some other sources [91 . The absolute accumulation rate of iron can be measured by using the data figs. 1 and 2 are based on (including CdC03 determinations), assuming the in situ density of dry uncompressed surface sediment to be 0.75 g/cm3 1101 . The data points in fig. 3 represcn : location of cores used for determination of sedimentation rates while the iror, values are based on neighboring samples, exct~pt at i 3 points where sedimentation rates and iron concentrations were determined on the same samples [ I1 .
High accumulation rates for iron occur close to the continent, as is to be expected, and on the East Pacific Rise where the three highest values are 95-410 mg Fe/(cm' X 1000 yr). The corresponding values for manganese are 35-- 150 mg Mn/(cm2 X 1000 yr).On the flanks of the ridge 5-10 mg and 05-3 mg are common deposition rates per (cm? X 1000 yr) for Fe and Mn, respectively . These figures agree well with the data of Bender et al . [61 . Deeper lay,:rs ot'sotnc crest sediments were deposited more slowly than the surface layers (Blackmail 191) but even f:)r these layers the deposition rates are about 50 tng Fe per (cm 2 X 1000 yr) . Some deposition rates may be anomaiously Ingli due to ponding of sediments . However, if ponding were of prime importance, it should also influence the accumulation rates of terrigenous constituents as Ti and Al. The data (fig . 4) indicate that deposition rates for Ti vary only by a factor of 5 between the crest and the flanks of the ridge; corresponding values for iron vary by a factor of 160 . Using the deposition rates for Ti to correct for ponding effects it is found that iron is deposited at a rate that can be up to 30 times larger on the crest than on the flanks of the East Pacific Rise ; this conclusion is also suggested by the regional variation in the Fe/Ti ratio in East Pacific sediments [2[ . T1he terrigenous nature of Ti and Al in this area is indicated by the fact that the AI/Ti ratio in most sediment samples [21 is very close toy 20, which is the ratio found in average continental rock, whereas weathering products of average oceanic rock should have an Al/Ti ratio of about 5 . The total amount of terrigenous matter is very small however :
SUBMARINE VOLCANISM AS A SOURCE I-OR IRON
34 9
Fig. 1 . Distribution of iron in East Pacific sediment% on a carbonate-free basis (CFB) . The iron-minima close to the equator between 100 1600 W and at 50 60 c S are duc to dilution by opaline silica . Several recent analyses (Boström, unpublished data) 'been included but confina the patterns found here . 1q-vG
" Î~ïraï a
K .BOSTRÖM
3501
RATES OF SEDIMENTATION ON CARBONATE FREE BASIS IN mm/1000 YEARS 40' - 0 10 -10-30 - >30 RTES FOR OPALINE SILICA RICH SAMPLES ARE I%)RL NEO
OEM N MINIM No 00.6
~IMM 00.9
iwi =OEM a 0
" 0.8
'PPP '
+0.9
073
1
40`
26
*15 S ISO ,
1,60°
140°
1
120°
24
QO°
60o S
30°W
Fig . 2 . Rate of sedimentation (CFB) according to Ku et al ., etc . ( 7, 81 .
the carbonate free fraction of East Pacific Rise sediments contai~ls little besides iron hydroxides, opaline silica and some barite . Other geochemical relations in the East Pacific also suggest that the iron rich sediments on the Ridge are of local origin. Thus, stability relations for oxideshydroxides of Fe, Mn, Ni and Co 1121 suggest that in the well-oxygenated slightly alkaline bottom .vaters (if the ocean i-on should precipitate out fairly fast, followed by manganese, whereas Ni and Co should be riost mohi e and tend to be enriched in the most land-distant areas . This means that, for instance, Fe./Mn and Fe/Co should decrease with distance from the continents . Such distribution patterns are observed
in ordinary pelagic deposits and on inactive oceanic ridges fdr from land, but on active ridges reversed patterns are found as can be demonstrated with the data by Bostr6m et al. I 1 ] and in fig . 5 . The data presented in figs. 1 and 5 do not rule out the possibility that the variability in the Fe/Co ratio, for instance, is partly depth dependent . However, 70 sediment analyses distributed across the Indian Ocean from Indonesia to Madagascar do not show any depth dependency for Co or Ni . Thus close to Indonesia the ratio (Fe + Mn)/(Co + Ni) in %/ppm is close to 0 .10 but falls rapidly westward to about 0.02, a value that also is characteristic for the samples on the Ninety East Ridge. On the Mid-Indian Ocean Ridge the ratio
SUBMARINE VOLCANISM AS A SOURCE FOR IRON
351
DEPOSITION RATE OF IRON IN mg/cm2 x1000 YEARS = ®= = ®=
5-10 10-15 15 -30 >30
E00MANI'120"'1 1 rr"A' Ar /LVI IVI i
a 614,
180°
160°
140°
120°
MEN RM
60'
MU 100° SO .W
Fig. 3. Rate of deposition of iron in East Pacific . (Fe + Mn)/Co + Ni) is close to 0 .09, but half-way between the ridge and Madagascar it falls to about
0 .03, and just off Madagascar reaches values close to 0 .06 . A consequence of these findings is that pelagic sediments on the flanks of active oceanic ridges should he mixtures of ferromanganoan deposites and products A graph of the relation of continental weathering (1 Fe/Ti versus AI/(AI + Fe + Mn) (see fig . 6) supports this conclusion ; the graph also further supports the
I.
conclusion that submarine weathering of basaltic matter is a subordinate source of sediments . High deposition rates of iron have also existed in the past on active oceanic ridges . The basal layers of
the South Atlantic sediments consist of Al-poor Fe-rich sediments in which iron was accumulated at a rate of 20-50 mg/(cm 2 X 1000 yr), whereas the subsequently deposited sediments were typical pelagic sediments with the deposition rates of 5-10 mg/ (cm2 X 1000 yr) for iron 141 . The total mass of sediments delivered to the ocean from submarine volcanism can be estimated, using the areal extent of ferromanganoan and normal pelagic deposits, rate of sedimentation and rates of ocean floor spreading . It can be shown that at most 5% and probably as little as 0 .5-1% of all pelagic sediments (carbonate free matter) derive from submarine volcanism . Since the ridge deposits contain
K .BOSTRÖM
DEPOSITION RATES OF TITANIUM IN mg/cm2 x 1000 YEARS
= <035 iiili = 035 -073
"--
zum 1 q
a
d
BRUN
UNIR 11MM
200
un ~~
\1V
1,
000~ MMMMMENOW a NNEEMEN NE ilNO iin RONNE MEMOS MENNEN 160
140'
1200
1000
Fig. 4. Rate of deposition of titanium in East Pack.
O
SUBMARINE VOLCANISM AS A SOURCE FOR IRON
1906
160*
140"
120*
100*
353 709W
Co (CFB) IN ppm C. 0 - 40 40 - 100 100 - 200 200 C
0"
Fig. 5 . Distribution of Co (CFB) in East Pacific sediments. Almost identical patterns are found for Ni .
close to 30°ío iron and ordinary pelagic sediments about 5% iron this means that only about 3-6% of all iron in the pelagic sediments derive from submarine volcanism. However, since continental matter has been recycled repeatedly during the history of the Earth while the volcanic iron described here may
represent a new contribution to the surface of the Earth, and since ocean floor spreading may have been operating during most of the history of the Earth, it follows that a large fraction of the total amount of iron now at the Earth's surface may have been brought up by submarine volcanism .
K-BOSTRÖM
354
(2] K.Boström, M.N .A.Peterson, O-Joensuu and D.E.Fisher,
r
0 010 020 030 040 0.50 0.60 0.70 0.80 0.90 1 .00 14 I
Ai+Fe+Mn
Fig. 6. Co-variations between I-'--/Ti and Al/(A1 + Fe + Mn) in Felagic sediments. Curve a is generated if average oceanic basaltic matter (Al = 7.y5%, Fe = 8.33%) is mixed in various proportions with volcanic sediments, containing 22% Fe and S .8'a Nfn [ I J : curve be is generated if the same volcanic sedi= ment is mixed with average continental crustal matter (A1 proportions. The distribution of 8.4%, Fe = 5.2'f0) in various analyses (from 2) indicate that in most pelagic sediments the admixture of basaltic debris is small.
Acknowledgements This work. was supported by the NSF Grants GA-1356 and GA-15248 and ONR Contract Nonr 4(1Q8(02) . Contribution No . 1229 from the Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149, References [ 1 K .Bostr6m and h1 .N .A .Peterson, Origin of aluminum-
poor ferromanganoan sediments in areas of high heat flow on the East Pacific Rise, Marine Geology 7 (1969),' 427-477 .
Aluminum-poor ferromanganoan sediments on active oceanic ridges, J. Geophys. Res. ?4 (1969) 3261-3270. (3j K.Bostr6m and S-Valdes, Arsenic in ocean floors, Lithos 2 (1969) 351-360; K.Bostr6m and D.E .Fisher, Distribution of mercury in East Pacific sediments, Geochim. Cosmochim. Acta 33 (1969) 743-745; D.E .Fisher and K.Boström, Uranium rich sediments on East Pacific Rise, Nature 224 (1969) 64-65. (4j K.Boström, Geochemical evidence of ocean floor spreading in South Atlantic Ocean, Nature (1970) in press. [Sj K.Boström, Origin of iron-rich sediments on the East Pacific Rise. Abstract, Trans. Am . Geophys. U. 5 1 (1970) 327. [61 M.Bendcr, W-Broecker, V.Gornitz and G .M iddel, Accumulation rate of manganese and related elements in the sediments from the East Pacific Rise, Abstract, Trans. Am . Geophys. U. 51 (1970) 327 . (7j R.R .Revelle, Marine bottom samples, collected in the Pacific by the Carnegie on its 7th cruise, Camegie Inst . Wash . Publ . 556 (1944) ; E.Goldberg and G.Arrhenius, Chemistry of Pacific pelagic sediments, Geochim. Cosmochim . Acta 13 (1958) 153-212; S .K .El-Wakeel and J .P .Riley, Chemical and mineralogical studies of deep-sea sediments, Geochim. Cosmochim . Acta 25 (1961) 110-146 ; S .Landergren, On the chemistry of deep-sea sediments, Repts. Swedish Deep Sea I xped ., X, Spec . Invest . No . 5 (1964) Gothenburg . [8J T .L .Ku, W.S .Broecker and N .Opdyke, Comparison of sedimentation rates measured by palcomagnetic and the ionium methods of age determination, Earth Planet . Sci. Letters 4 (1968) 1--16 . D.B .Ericson and G.Wullin, Pleistocene climates in the Atlantic and Pacific Oceans : A comparison based on deep-sea sediments, Science 167 (1970) 1483-1485 ; A .Blackman and B .L .K .Somayajulu, Pacific Pleistocene cores: Faunal analyses and geochronology, Science 154 (1966) 886-889; A.Blackman, Pleisocene stratigraphy of cores from the Southeast Pacific Ocean, Ph . D. Dissertation, Univ . Calif. at San Diego (1966) . [101 The density of pelagic surface sediments commonly varies between 1 .40 and 1.80 g/cm 3 and the water content between 40-60í%r- by weight . (Data from A.F . Richards, Tech . Rept . TiR106, Investigations of deepsea sedimentcores, 11 . U.S. Nay Hydrographic Office, Waihington, D.C ., 1962 .) A common in situ density for dry uncompressed pelagic sediment is 0.65 - 0 .85 g/cm 3 ; the uncertainty in this figure is only of minor significance for the discussion here . [ 11 ] The accumulation rates determined in this way are looted at 0.5 ° S-8S .5 ° W, 0° S--104° W, 2.8'0 S--112 .5 ° W, 14 .2 ° S-113 .5 ° W, 14 .2° S-114 .5 ° W, 21 .5 ° J . 81 .ä ° W, 26 .5 " S-115.5" W, 27 .7 ° S- 107° W, 46 .5 ° 5--113 5° W and 46 .7 0 S--123 .5 ° W . [12] MY aurbaix, Atlas d'6quilibries électrochirniques a 2S °(' (Gauthiers-Villars and Cie, Paris, 1963) .