25. MASS-ACCUMULATION RATES OF THE NON-AUTHIGENIC INORGANIC CRYSTALLINE(EOLIAN) COMPONENT OF DEEP-SEA SEDIMENTS FROM THE

WESTERN MID-PACIFIC MOUNTAINS, DEEP SEA DRILLING PROJECT SITE 4631

David K. Rea and Thomas R. Janecek, Oceanography Program, Department of Atmospheric and Oceanic Science,The University of Michigan, Ann Arbor, Michigan

ABSTRACT

Elevated regions in the central parts of ocean basins are excellent for study of accumulation of eolian material. Themass-accumulation rates of this sediment component appear to reflect changes in the influx of volcanic materialsthrough the Early Cretaceous to Recent history of Deep Sea Drilling Project Site 463, on the Mid-Pacific Mountains.Four distinct episodes of eolian accumulation occurred during the Cretaceous: two periods of moderate accumulation,averaging about 0.2 to 0.3 g/cm2/103 yr, 67 to 70.5 m.y. ago and 91 to 108 m.y. ago; a period of low accumulation, ap-proximately 0.03 g/cm2/103 yr, 70.5 to 90 m.y. ago; and a period of high accumulation, about 0.9 g/cm2/103 yr, 109 to117 m.y. ago (bottom of the hole). Much of the Cenozoic section is missing from Site 463. Upper Miocene to Recentsediments record an upward increase in accumulation rates, from less than 0.01 to about 0.044 g/cm2/103 yr. The latePliocene-Pleistocene peak may reflect the change to glacial-wind regimes, as well as an increase in volcanic sourcematerials.

INTRODUCTION

DSDP Site 463Site 463 is in 2525 meters of water on the northwest

Mid-Pacific Mountains, at 21°21.01'N, 174°40.07'E(see Site 463 report, this volume). The Mid-Pacificmountains (Fig. 1), one of the large aseismic rises in thecentral and northern Pacific Ocean, consists of severalsegments which are thought to be part of an ancientfracture-zone and ridge-crest system which separatedthe North and South Pacific plates during the EarlyCretaceous (Larson, 1976).

Four major lithologic units are recognized in the822.5 meters of sediment and rock cored at Site 463(Fig. 2). Unit I is divided into two sub-units: Sub-unitIA is 46.8 meters of highly disturbed to soupy nanno-fossil ooze (Pleistocene to late Maastrichtian); Sub-unitIB consists of foraminifer-nannofossil chalk and nanno-fossil-foraminifer chalk from 46.8 to 452 meters sub-bottom (late Maastrichtian to late Albian). Chert is acommon component of Sub-unit IB. Unit II, from 452to 587 meters, comprises multicolored limestone andsilicified limestone (middle Albian to early Aptian).Chert is also common in Unit II. Unit III is character-ized by chert layers, ash beds, tuffaceous limestone, andcarbonaceous limestone, from 587.7 to 632.5 meters(early Aptian) age. Unit IV consists of interbedded pe-lagic and clastic limestone from 632.5 to 822.5 meters atthe bottom of the hole (early Aptian to late Barremian).Within this section, there are two major hiatuses, repre-senting the middle Miocene to late Oligocene (~16m.y.) and early Eocene to late Maastrichtian ( — 17m.y.).

Initial Reports of the Deep Sea Drilling Project, Volume 62.

BACKGROUND AND OBJECTIVES

The main objective of DSDP Leg 62 was to investi-gate the late Mesozoic and Cenozoic paleoenvironmentof the north-central Pacific Ocean. The sites drilled dur-ing Leg 62 are on structural highs that have remainedabove the CCD throughout their existence, thus pre-sumably allowing preservation of calcareous sediments.In contrast, calcareous sediments have been dissolvedover wide regions of the deeper North Pacific basins.The late Mesozoic and Cenozoic calcareous sedimentscapping the Mid-Pacific Mountains could provide in-sight into changing plankton communities, biologicalproductivity, and ocean circulation during the past 118m.y. Furthermore, we hoped that the continuouslycored sediments at Site 463 would reveal information oneolian contributions to the North Pacific sediments dur-ing the late Mesozoic and Cenozoic.

Oceanographers have long known that terrigenousdusts are blown over the oceans from continents(Maury, 1855; Radczewski, 1939; Rex and Goldberg,1962; Prospero and Bonatti, 1969; Windom, 1975; Win-dom and Chamberlain, 1978). Fine-grained quartz andclays, important components of these dusts (Prosperoand Bonatti, 1969; Parkin, 1974), can be mapped inpelagic surface sediments; they reflect the major zonalwind regimes (Rex and Goldberg, 1962; Lisitzin, 1972;Molina-Cruz, 1977; Thiede, 1979).

The North Pacific aseismic rises (Hess, Shatsky, andthe plateau level of the Mid-Pacific Mountains) areamong the best locations for studying the history ofeolian deposition, for several reasons. First, theseregions probably have always been above the bottomnepheloid layer, which is generally confined to depths inexcess of 4500 meters. Second, these sites are far fromcontinental margins, and thus beyond the realm ofhemipelagic deposition. Finally, these rises lay south of

653

D. K. REA, T. R. JANECEK

10°

170° 180° 170°

Figure 1. Map of the central Pacific, showing the Leg 62 track line and DSDP drill sites.

the polar front (subpolar convergence) during both thenonglacial and glacial ages of the Pleistocene (CLIMAPProject Members, 1976), and thus were not subject todeposition by ice-rafting. Therefore, the only likelynon-authigenic, crystalline, inorganic materials are dustgrains carried by the winds. Eolian dust may come fromdistant continents or local volcanoes. The mass-ac-

cumulation rates given hereafter record changes in bothsupply rate and transport efficiency; we are unable todetermine which is the dominant control on accumula-tion rate from the rate data alone.

This paper is part of an initial attempt to establish thelate Mesozoic and Cenozoic record of eolian depositionin the central North Pacific, determined from the mass

654

MASS-ACCUMULATION RATES, SITE 463

SITE 463 accumulation rates of the non-authigenic, inorganic,crystalline material isolated from the deep-sea sedi-ments. Fluctuations in the mass-accumulation rates ofthis component should record variations of wind in-tensity and (or) periods of volcanic activity in the centralPacific.

METHODS

Mass-Accumulation-Rate Calculations. Linear sedimentation rates(LSR) and mass-accumulation rates (MAR) both give temporalmeasures of sediment accumulation on a substrate. Mass-accumula-tion rates are expressed as mass of sedimentary material accumulatingper unit area and unit time; they indicate the flux of material acrossthe sediment/water interface. The LSR, which measures only thick-ness of sediment deposited per unit time, cannot be used to determinemass flux (see discussion in van Andel et al., 1975). Furthermore, theMAR is not affected by variable compaction, which can cause asignificant change in the LSR. Thus, using MAR it is possible to com-pare sediment accumulation on both a temporal and areal basis.Calculation of the MAR requires data on the LSR and dry-bulk den-sity (DBD) for each interval of the core. MAR is then the product ofthe LSR and DBD. Furthermore, if the weight percent of any compo-nent of the sediment is known, the MAR of that component is the pro-duct of the total MAR and the weight percent of that component.

LSR's were obtained from Leg 62 revised shipboard paleon-tological information (see Site 463 report, this volume). Core intervalswere assigned ages in million-year intervals by combining sedimentages from planktonic-microfossil zonations and the appropriate timescales (Berggren and van Couvering, 1974; van Hinte, 1976; Harden-bol and Berggren, 1978) and interpolating when necessary. Core inter-vals were then assigned the appropriate LSR.

The dry-bulk density of each sediment sample was calculated bydetermining the porosity of the sediment and solving an equation ofthe form:

DBD = (1 - P/100)ρ

where

P is the porosity of the sediment in percentρ is the density of the sediment (assumed to be 2.65 g/cm3).

Porosity is defined as the ratio in percent of the volume of voids tothe total volume of the wet sediment mass and can be calculatedaccording to the following equation:

p — × 100

where

Ksw is the volume of seawaterFsed is the volume of dry sediment.

To determine the above volume terms, the water content of eachsediment sample was calculated by weighing the wet sediment, freezedrying, then reweighing the sediment. The difference between the in-itial and the final weights equals the weight of pure water lost; thefinal weight being the weight of the dry sediment plus salt. Thesevalues were substituted into the following equations:

_ (Wt. water lost) × 1.025 gsw/gwater _ Wt. water lostsw 1.025 g s w / c m 3 1.00 g/cm3

Wt. dry sediment Wt. wet sediment - 1.025 (Wt. water)

2.65 g/cm3 2.65 g/cm3

Figure 2. Stratigraphic column for Site 463 (Lithologic symbols areexplained elsewhere in this volume.)

Result of these calculations are given in Table 1.Chemical Methods. A split of 1 to 10 grams of the freeze-dried

sediment was used for the isolation of the non-authigenic, inorganic,crystalline component. The carbonate portion was removed by placingthe pre-weighed, dried sediment in an Ehrlenmeyer flask with 100 mlof 25% (vol.) acetic acid. The flask was shaken on an automatic

655

D. K. REA, T. R. JANECEK

Table 1. Data for calculation of mass-accumulation rates (MAR) for the non-authigenic,inorganic, crystalline, eolian (NICE) component of sediments recovered at DSDP Site463.

Sample(interval in cm)

463-1-1, 20-241-2, 70-721-4, 70-722-1, 20-242-2, 94-962-4, 92-942-5, 100-1012-7, 10-133-1, 10-133-2, 72-743-4, 15-193-5, 72-744-1, 10-134-2, 102-10444, 20-234-5, 102-1045-2, 58-606-2, 68-706-5, 68-707-2, 70-727-4, 46-488-3, 30-329-2, 90-9210-3, 118-12010-5, 118-12011-3, 16-1712-1, 40-4112-4, 41-4213-2, 50-5213-5, 50-5214-2, 72-7414-4, 72-7415-2, 86-8815-5, 86-8816-2, 88-9016-5, 88-9017-5, 110-11219-2, 70-7219-5, 70-7220-1, 75-7721-2, 51-5321-5, 61-6322-2, 112-11422^t, 90-9223-1,78-8024-2, 9-1124-3, 22-2425-2, 32-3426-2, 106-10826-5, 87-8927-2, 18-2029-1, 24-2630-2, 25-2731-1, 4-633-1, 123-12534-2, 30-3236-1, 1-338-1, 65-6743-2, 81-8243-5, 61-6248-2, 49-5150-1, 49-5153-1, 130-13155-1, 69-7056-1, 89-9057-2, 45-4658-1, 119-12058-3, 129-13059-3, 99-10161-1, 28-2962-1, 55-5662-3, 46-4863-1, 50-5164-2, 76-7765-1, 105-10767-1, 84-8669-2, 50-5270-2, 1-270-7, 10-1171-3, 31-3372-2, 106-10772-3, 127-12873-1, 20-2174-2, 11-1275-1, 58-5976-1, 10-1177-1, 0-178-1, 8-981-2, 50-5182-1, 60-6284-2, 45-4685-1, 128-12988-1, 6-8

Sub-bottomDepth

(m)

0.2

2.2

5.55.7

7.9

10.912.514.615.117.219.821.724.627.029.231.536.140.243.5 +45.748.556.364.976.279.284.791.495.9

102.5107.0112.0115.2119.9126.4131.4135.9145.6159.7164.2167.7178.5183.1188.6191.4196.3201.1202.7206.8217.1221.4225.7243.3254.3262.1282.3292.3309.5329.2378.3382.6426.6433.5462.8481.2490.9501.0510.2513.3522.5535.8538.1541.0547.5558.5567.1585.9606.0615.0622.6626.3635.1636.8642.2653.1661.6670.6680.0689.6712.2718.6739.0747.8775.1

Age(m.y.)

0.2

1.0

2.0

2.0

2.5

3.0

3.0

3.5

4.5

5.0

5.5

6.0

8.5

9.0

9.5

10.025.031.032.067.567.567.568.068.068.568.568.568.569.069.069.069.069.569.569.569.570.070.070.070.070.570.571.071.072.073.073.074.079.080.581.081.082.086.087.589.091.092.098.099.0

100.0101.0104.0106.0106.0107.0107.0107.0108.0109.0110.0110.0111.0112.0112.0112.0112.0112.0113.0113.0113.0113.0113.0114.0114.0114.0114.0115.0115.0115.0116.0116.0117.0

Porosity(%)

56.8459.7461.2258.3864.2268.0260.55'53.0858.3762.0158.3758.2057.5258.7762.1160.9654.7554.3749.2449.9155.2057.5157.3854.8449.5148.91*48.3250.9853.6952.0550.4154.8554.4252.7251.8847.6851.2652.1852.9051.5352.7653.9649.5751.3956.0745.7348.9055.6553.9954.2755.9654.3442.3546.0652.8949.4135.9739.24*42.5137.8843.9938.6831.8644.9032.3827.0221.0022.9817.0910.4619.3821.1319.7125.9024.4720.9024.8027.0338.5332.33*26.1232.7617.3516.4424.2026.9716.7315.9112.0817.6816.7313.7722.97

DBD(g/cm3)

1.141.071.031.100.950.851.05*1.241.101.011.101.101.131.091.001.031.201.211.341.331.191.131.131.201.341.35*1.371.301.231.27*1.311.191.211.251.271.391.291.271.251.281.251.221.341.291.161.441.351.171.221.211.171.211.531.431.251.341.701.61*1.521.641.481.621.811.461.791.932.092.042.202.372.132.092.131.962.002.101.991.931.631.79*1.951.782.192.212.011.932.202.232.332.182.212.282.04

LSR(cm/103 yr)

0.350.350.350.350.350.350.350.350.350.350.350.350.350.350.350.350.050.050.055.205.205.205.205.205.205.205.205.205.205.205.205.205.205.205.205.205.205.205.205.200.500.500.500.500.500.500.500.500.600.600.601.000.750.500.501.801.801.801.801.801.801.201.201.201.201.201.201.201.202.702.702.702.702.702.702.702.702.702.702.703.103.103.103.103.103.103.103.103.603.603.603.603.60

MAR

(g/cm2/lθ3 yr)

0.4000.3740.3600.3860.3320.2970.3680.4340.3860.3530.3840.3850.3940.3810.3500.3600.0600.0600.0676.9166.1885.8765.8766.2406.9687.0207.1246.7606.3966.6106.8126.1886.2926.5006.6047.2286.7086.6046.5006.6560.6250.6100.6700.6450.5800.7200.6750.5850.7320.7260.7021.2101.1470.7150.6252.4123.0602.9002.7362.9522.6641.9442.1721.7522.1482.3162.5082.4482.6406.3995.7516.6435.7515.2925.4005.6705.3735.2114.4014.8406.0455.5186.7896.5726.2315.9836.8206.9138.3887.8487.9568.2087.344

NICE(%)

10.2512.958.116.253.203.816.244.288.273.644.092.051.773.640.641.650.540.360.460.651.681.141.142.75

10.301.426.754.892.504.961.351.362.641.472.661.862.955.745.141.941.762.201.931.392.741.571.521.271.422.203.965.406.236.493.132.937.655.56

17.367.083.69

11.3720.1627.777.951.16

11.8112.3612.5116.5619.2511.6813.973.299.75

14.025.86

32.7356.9711.1631.9215.4011.564.98

12.8722.1614.418.437.09

18.6713.554.609.90

NICE MAR(g/cm2/lθ3 yr)

0.0410.0480.029T0.024J0.0110.011 η0.023 J0.0190.0320.0130.0160.0080.0070.0140.0020.006

—0.045 -I0.1020.067 J0.085 -i0.172 J0.717 "O.IOO0.4810.3300.160 "0.328*0.0950.0840.166 =

0.0950.1760.134 .0.198 "0.3480.3340.129-0.011 T0.013 J0.013 "I0.009 J0.0160.011 T0.010 J0.0070.0100.0160.028 T0.065 J0.0710.0450.0200.0710.2340.161*0.4750.2090.0980.2210.4380.486 "I0.171 J0.027 η0.2960.303 J0.3331.0601.107 T0.659 -10.8030.174 •0.5260.7950.3151.7052.507 "0.540*1.9300.8500.785 .0.327 "0.8021.3260.982 _0.583 "0.5951.4651.291 T0.378 J0.727

Note: Asterisks indicate samples which had dried before arrival in our laboratory; for these samples the average of the poros-ity values of overlying and underlying samples was assigned. Plus sign indicates arbitrary depth at bottom of cored inter-val for Core 6 (recorded as coring 5.5 m but recovering 8.23 m of sediment). Brackets enclose values averaged and plottedas a single point.

656

MASS-ACCUMULATION RATES, SITE 463

shaker for 2 to 4 hours; it was then removed, and the suspension wasrinsed into a centrifuge tube. The suspension was centrifuged for 10minutes at 2000 rpm, and the clear supernatant liquid was decanted.The centrifuge tube with the residual sediment was filled with candle-filtered distilled water; this was stirred into a suspension and cen-trifuged for 10 minutes at 2000 rpm. The clear supernatant liquid wasdecanted, and the procedure was repeated as necessary.

Amorphorus Fe and Mn oxides and hydroxides were removed witha sodium dithionite-sodium citrate solution buffered with sodiumbicarbonate. The procedure has been detailed elsewhere (Mehra andJackson, 1960) and is modified in part as follows: 40 ml of 0.3Msodium citrate and 5 ml of \M sodium bicarbonate were added to therinsed sediment in the centrifuge tube following the carbonateremoval. The centrifuge tube was then placed in a 75 to 80°C waterbath, and the solution was allowed to come to temperature. One gramof sodium dithionite was added, and the suspension was stirred con-tinuously for 1 minute, then occasionally for 15 minutes; 40 ml of ahot solution of equal parts water and 0.3M sodium citrate were stirredinto the suspension, and the centrifuge tube was removed from thewater bath and centrifuged for 10 minutes at 2000 rpm. The clearsupernatant liquid was then decanted, and 100 ml of full strength0.3M sodium citrate was added to the centrifuge tube, stirred, andcentrifuged as described above. The supernatant liquid was decanted,and the sediment was rinsed, as described earlier in the carbonate-removal section.

The sample was then sieved at 63 µm to remove larger diatoms andradiolarians, and the remaining opal was removed by repeatedtreatments with sodium carbonate. A 100-ml centrifuge tube contain-ing the sample was filled to three-fourths with 0.4^ sodium carbonateand placed in a boiling water bath for 20 minutes. The suspension wascooled and centrifuged at 2000 rpm for 10 minutes; the supernatantliquid was decanted, and the sediment was freeze dried and weighed todetermine the weight percent of the non-authigenic, inorganic,crystalline (eolian) component (Table 1).

Examination of the dried residue by scanning electron microscopyindicated that it contained no biogenic carbonate or opal, and noauthigenic zeolite. Any authigenic clays would presumably remain inthe residue and be included in our totals for the eolian component.The effect of not including zeolites, which have a preponderantlyvolcanic origin, and including smectites (montmorillonite), whichresult almost entirely from the diagenetic alteration of volcanic debris(Elderfield, 1976), in our totals is not clear. However, this does notappear to be a major problem in these sediments, as zeolites are muchless abundant than the clay minerals (Valuer and Jefferson, thisvolume).

The precision of these chemical techniques was determined byreplicate analyses and is commonly within 2 or 3%, a small number ofreplicate analyses being only within 10% of each other. The accuracyof our final values for the mass-accumulation rates of the eolian com-ponent is determined largely by the accuracy of the biostratigraphy.Placement of zonal boundaries, assuming a constant LSR betweenboundaries, and assignment of absolute ages to those boundariesalmost certainly result in errors larger than the few percent that are theresult of our laboratory work. We hesitate, therefore, to attachgeological significance to changes in MAR of less than a few tens ofpercent of the values.

MASS-ACCUMULATION RATESOF THE EOLIAN COMPONENT

Atmospherically transported materials include con-tinental dust and volcanic debris. The accumulation rateof the eolian component varies with distance fromsource (Parkin, 1974), among other things. Althoughvolcanic contributions are sporadic compared to therelatively steady eolian influx from continents, the prox-imity of various volcanic edifices to the study site sug-gests that the continental influx probably was maskedduring periods of volcanic activity.

In light of this and the mineralogical data on the non-biogenic sediment component at Site 463 (Valuer andJefferson, this volume), the following discussion will

focus on climatic and volcanic episodes in the inter-pretation of the fluctuating mass-accumulation ratesseen in Figure 3.

The largest average MARs (0.93 g/cm-VlO"3 yr; seeTable 1) of the inorganic, crystalline component, forsediments 109 to 117 m.y. old, are approximately higherby a factor of 3 than those of younger sediments at Site463. Initial shipboard descriptions of the cores indicateda volcanic-ash layer approximately 112 to 113 m.y. old.This ash and the other inorganic materials, which ac-cumulated rapidly from 117 to 109 m.y. ago (Fig. 3)may reflect the waning stages of the Barremian to Ap-tian volcanism that resulted in the formation of theMid-Pacific Mountains (Winterer, 1976). Basementages of the Ontong-Java Plateau (Site 289, DSDP Leg30; Andrews, Packham, et al., 1975), the ManihikiPlateau (Site 317, DSDP Leg 33; Schlanger, Jackson, etal., 1976), and the northern Hess Rise (Site 464, reportthis volume) are all Aptian to early Albian and, togetherwith the Site 463 data, provide evidence for a majormid-Cretaceous volcanic event that apparently formedseveral of the central Pacific aseismic rises.

Moderately high MARs (0.27 g/cm2/103 yr; see Table1) correspond to early Albian to early Turonian time(91-108 m.y. ago). General sediment composition andmineralogy from DSDP Sites 169, 170, and 171 (Win-terer, Ewing, et al., 1973) near the Line Islands in thecentral Pacific (Winterer, 1976) indicate moderate mid-plate volcanism 85 to 105 m.y. ago. Volcanic MARsfrom DSDP Site 462 in the Nauru Basin also are higherthan those of immediately overlying sediments for thistime (91-103 m.y. ago; Rea and Thiede, in press).

The eolian MARs from middle Turonian to upperCampanian time (70.5-89 m.y. ago) record fluctuatingbut generally low values (0.03 g/cm2/103 yr; see Table1). Shallow-water and reef fossils from guyots in theeastern Mid-Pacific Mountains area give an approxi-mate age of 90 m.y. for cessation of volcanic activity(Heezen, MacGregor, et al., 1973). The decreasingeolian MARs at Site 463 and the subsequent low valuescontinuing until 71 m.y. ago correlate well with thisregional reduction in volcanic activity about 90 m.y.ago. The MAR values during the interval 70.5 to 81m.y. ago are very low, about 0.01 g/cm2/103 yr, andmay be an accurate reflection of continental eolian in-flux to the region.

A significant increase in the eolian accumulation rateto an average of 0.21 g/cm2/103 yr (see Table 1) oc-curred during the Maastrichtian (67-70 m.y. ago) andduring the time corresponding to sediments immediatelyunderlying the lower to middle Tertiary hiatus. SeveralDSDP sites in the central Pacific record increased vol-canic activity about this same time, or perhaps some-what earlier (Sites 165, 169, 170, and 171, Leg 17, Win-terer, Ewing, et al., 1973; Sites 198 and 199, Leg 20,Heezen, MacGregor, et al., 1973; Sites 315 and 316, Leg33, Schlanger, Jackson, et al., 1976; Site 462, Leg 61,Larson, Schlanger, et al., in press). These increases inthe amount of volcanic debris during the late Campa-nian and Maastrichtian and the ages of volcanic rock atDSDP Site 171 (91-100 m.y.) (Winterer, Ewing, et al.,

657

D. K. REA, T. R. JANECEK

MAR (g/cm2/103yr)

Figure 3. Mass accumulation rates of non-authigenic inorganic crystalline, (eolian) (NICE) material at Site 463. Circled points represent averagesof two or more samples.

1973) and Site 313 (72-76 m.y.) (Larson, Moberly, etal., 1975), 150 km apart, suggest that repeated mid-platevolcanism dominated the eolian influx during thosetimes.

The late Cenozoic MARs shown in Figure 3, and atan expanded scale in Figure 4, increase by a factor of 5from late Miocene to Quaternary time. Superimposedon this general increase are significant peaks in ac-cumulation at 4.5 and 1.0 m.y. ago. Sites 464 and 466,on Hess Rise, also reveal accumulation peaks for thissame component about 4 to 6 m.y. ago (Rea andHarrsch, this volume). Regional studies of circum-Pacific (Kennett et al., 1977) and mid-plate (Rea andScheidegger, 1979) volcanism have shown a maximumin volcanic activity between 3 and 6 m.y. ago; the lowerPliocene maximum in the non-authigenic, inorganic,crystalline component MAR appears to record this sameocean-wide phenomenon.

Although increased volcanic activity may be onecause of increasing inorganic crystalline MARs duringthe Quaternary (Fig. 4), the onset of Northern Hemi-sphere glaciation and concomitant climate deteriorationmay also be an important factor. General models for at-mospheric circulation (Gates, 1976; Manabe and Hahn,1977) predict that climate changes during glacial periodswould result in significant increases in the intensity ofatmospheric circulation. The accumulation rate andgrain size of eolian sediment increase with wind inten-sity (Parkin, 1974). Data from a North Pacific long coretaken about 1000 km north of Hawaii (LL 44-GPC3; Leinen, et al., 1979) show a sharp increase in the

0.01 0.02

MAR (g/cm2/103yr)

Figure 4. Details of late Cenozoic MAR of the eolian fraction at Site463. Circled Points represent averages of two or more samples.

accumulation of quartz, Al, and Si, associated with theonset of Northern Hemisphere glaciation, when the ac-cumulation of eolian material increased significantly inthe Northern Hemisphere (Windom, 1975). Thus, the

658

MASS-ACCUMULATION RATES, SITE 463

intensification of atmospheric circulation resulting fromdeteriorating climate may account for increasing eolianMARs over the past 10 m.y., along with the periodicvolcanism discussed by Kennett et al. (1977).

ACKNOWLEDGMENTSWe would like to thank Eileen Harrsch for assistance with the

laboratory work. Margaret Leinen, Ted Moore, and Bruce Wilkinsonreviewed this manuscript, and we appreciate their comments and sug-gestions.

Portions of the work presented here were supported by NSF GrantOCE-7825341.

REFERENCESAndrews, J. E., Packham, G., et al., 1975. Init. Repts. DSDP, 30:

Washington (U.S. Govt. Printing Office).Berggren, W. A., and Van Couvering, J. A., 1974. The late Neogene

biostratigraphy, geochronology, and paleoclimatology of the last15 million years in marine and continental sequences. Palaeogeo-graphy, Palaeoclimatology, Palaeoecology, 16:1-216.

CLIMAP Project Members, 1976. The surface of the ice-age earth.Science, 191:1131-1137.

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