CONTENT AND BULK DENSITY OF LEG 138 SITE-SURVEY PISTON CORES 1

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1 Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), 1995 Proceedings of the Ocean Drilling Program, Scientific Results, Vol DATA REPORT: CONTENT AND BULK DENSITY OF LEG 138 SITE-SURVEY PISTON CORES 1 Hilde Snoeckx 2 and David K. Rea 2 ABSTRACT Nine piston cores and six triggerweight cores retrieved from the eastern equatorial Pacific Ocean during the Venture 1 expedition were analyzed for dry-bulk density () and content. Sites are located along a north-south transect at 11 W from 11 N to 3 S and along an east-west transect from 11 to 9 W, at approximately 3 S. The data reveal two - relationships and four patterns of abundance. INTRODUCTION During the late summer of 1989, the Thomas Washington surveyed and cored potential sites for Ocean Drilling Program (ODP) drilling during Leg 138 (Mayer, Pisias, Janecek, et al., 1992). During that cruise, Venture Leg 1, scientists recovered the best new suite of piston cores from the Pacific Ocean in more than 15 yr. Twenty cores were raised from two north-south profiles that cross the equatorial current systems and the Intertropical Convergence Zone at longitudes 11 and 95 W, a joining east-west transect along about 3 S, and a transect down the north side of the Cocos Ridge. To preserve the original physical properties of these cores, each section was taped, sealed with beeswax, and taped again before storing in a refrigerated van. The van with the cores was shipped back to the core laboratory at Oregon State University without interruption of the refrigeration system. Cores were kept sealed under refrigeration until their opening. Prior experience with these methods of Curation indicates that essentially all moisture loss is prevented for at least 1 yr by these precautions (L.A. Mayer, pers. comm., 199). Carbonaterich cores from the 11 W and 3 S transects were opened, described, and sampled in May 199. Those cores (Fig. 1; Table 1) form the basis of ongoing research at the University of Michigan and Oregon State University (Snoeckx and Rea, 1994). Here, we provide the carbonate and bulk density data derived from the Venture-1 cores and two older Vema-28 cores to place these in the public domain and to ensure that all pertinent paleoceanographic data from the eastern equatorial Pacific Ocean can be assembled into this volume. METHODS OF ANALYSIS Nine piston cores and six triggerweight cores were used for this study. Six of the sites, VNTR1-1, -4, -6, -7, -8, and -9, form a north-south transect along 11 Wfrom ll Nto3 S.Four, VNTR1-9, -1,-12, and -13, form an east-west transect along approximately 3 S, between 11 and 9 W (Fig. 1; Table 1). Piston cores for all sites and the corresponding triggerweight cores for Sites VNTR1-1, -4, -6, -9, -1, and -13 were sampled at approximately 5-yr intervals. Preliminary age estimates were based on carbonate stratigraphy, as revealed by magnetic susceptibility measurements conducted on board the Thomas Washington (Arason, 199). The samples span late Pleistocene to present time. Holocene Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), Proc. ODP, Sci. Results, 138: College Station, T (Ocean Drilling Program). 2 Department of Geological Sciences, University of Michigan, Ann Arbor, MI , U.S.A. sediments were recovered at the top of most piston cores. The triggerweight cores completely overlap the top of the piston cores, except for Core VNTR1-13GC, which overlaps VNTR1-13PC by approximately 4 cm and adds an extra 2.2 m to the top of the piston core record. No hiatuses were apparent. The database comprises 111 samples. Dry-bulk Density Dry-bulk density () is defined as the mass of dry sediment per unit volume of wet sample. Ideally, it is determined from fixed volumes of fresh sample by determining the grain density (mass of dry sediment per unit volume of dry sediment) and measuring the water content (or water loss) and, hence, the porosity. = (1 - P) p, (1) whereby P is porosity and p is grain density and P = (H 2 O wt/p H2θ )/(dry wt/p + H 2 O wt/p^o). Grain densities were determined on samples of known volume at intervals of approximately 25 cm for piston Cores 1, 4, 6, 9, 1, and 13 (Mayer, pers. comm., 1991) and were interpolated for the intervening samples. p = [dry wt - (%salt/(1 - %salt)] [wet wt/(vol tot - VO1H 2 O)]. (2) The salt was estimated at 3.47%. No known-volume samples were available for the triggerweight cores or for piston Cores 7, 8, and 12. However, a linear relationship between the at known grain density and the at an assumed grain density of 2.65 g/cm 3 allows for a more precise determination for Cores 7, 8, and 12 and the gravity cores, using the equation: real = (r =.998, r 2 =.9997), (3) whereby 265 is obtained by substituting 2.65 g/cm 3 for p in Equation 1. The resulting values range from.25 to.91 g/cm 3, reflecting variation in the relative proportion of, opal, and clay in the sediment. Percentage of CaCθ3 The content of the Venture samples was determined using the carbonate bomb method and a sample size of.5 g. Two control samples, consisting of a laboratory standard of homogenized, ooze were analyzed after every 15 samples. Results of these and 885

2 DATA REPORT 1 N 1 S VNTR 1-1 V V VNTR 1-4 VNTR 1-6 VNTR 1-7 S VNTR 1-8 VNTR 1-9 VNTR 1-1 VNTR Figure 1. Location of the Venture-1 and Vema-28 sites. Jm ( mm "ymm VNTR 1-13 föwmi. 8 Table 1. Location and of the VNTR1 cores and corresponding Leg 138 sites, and of two cores from cruise Vema-28. Core Trigger Corresponding Depth length Piston weight Leg 138 Core Latitude Longitude (mbsf) (cm) core core site VNTR1-1 VNTR1-4 VNTR1-6 VNTR1-7 VNTR1-8 VNTR1-9 VNTR1-1 VNTR1-12 VNTR1-13 V V TSI 5 2.9'N 'N l 1.1'N 2.3'N 3.2'S 4 3.4'S 3.9'S 3 O5.3'S 7 18'N 9 3'N 'W 'W 'W 'W 'W 'W 12.9'W 'W 'W 1 ll'w 12 4'W x 827 x 743 x 742 x 869 x 779 x 945 x 86 x 924 x 92 x 963 x replicate analyses of samples yield an analytical precision of better than 1%. DISCUSSION OF DATA Relationship of Dry-bulk Density to CaCθ3 The apparently close relationship between and content in sediments has been used in several studies to determine a quantitative relationship for estimating reliable s based upon percentages. The data disclose the existence of two - relationships in the eastern equatorial Pacific, seen in Figure 2 as two apparently parallel, crescent-shaped groupings of data points. For equal percentages of, the top group has a higher resulting from (1) different carbonate (and silica) secreting organisms having different porosities or (2) a greater relative abundance of a denser component in the noncarbonate fraction. The top, relatively more dense data cluster in Figure 2 consists of samples of Cores VNTR1-1PC, -12PC, and -13PC, the bottom group of samples of Cores VNTR1-4PC, -6PC, -7PC, -8PC, -9PC, and - 1PC but also, in the low carbonate end, of samples from a portion of Cores VNTR1-12PC, -13GC, and -13PC. No low carbonate (<4%) samples from Cores VNTR1-12PC, -13GC, and -13PC are present in the upper data cluster. The two groupings of data can be characterized by the following quantitative expressions: For the top group (N =38): = ( % )- 1. (4) The correlation coefficient (r) is and the standard error of estimate for predicting from percentage of is ±.33 g/cm 3. For the bottom group (N =73): = ( % )" 1. (5) The correlation coefficient (r) is and the standard error of estimate for predicting from percentage of is ±.39 g/cm 3. A student t-test, performed on the two groupings (t-value of 16.46), shows that the two groups are statistically different at the 99.95% confidence level (critical value = 3.29). Abundance Patterns of CaCθ3 Correlation among the cores is based on the carbonate stratigraphy and unpublished oxygen isotope data (provided by A. Mix). Stage numbers were assigned according to the Hays et al. (1969) nomenclature, with odd numbers corresponding to interglacials and even num- 1 Figure 2. Percentage of vs. dry-bulk density (). Data points form two apparently parallel, crescent-shaped groupings. For equal percentages of, the top group has higher as a result of (1) different carbonate (and silica) secreting organisms having different porosities or (2) a relatively greater abundance of a denser component in the noncarbonate fraction. The top group consists of samples from Cores VNTR1-1,-12 and -13; the bottom group of samples of Cores VNTR1-4, -6, -7, -8, -9, and -1, but also, in the low carbonate end, of samples from cores VNTR1-12 and -13. No low carbonate samples (<4%) from Cores VNTR1-12 and -13 are present in the top group. bers to glacials. Note that, except for stage 1, the numbers for carbonate stages differ by -2 from those employed in δ 18 θ stratigraphy. Four patterns of abundances can be seen in the eastern equatorial Pacific (Figs. 3 and 4). The record of Site VNTR1-4 is the only one that approximates the well-known Pacific Ocean pattern described by Hays et al. (1969). The record shows the nine carbonate peaks of the Brunhes series and reaches into the Maruyama (carbonate stage M2). The height of the peaks ( maxima) tends to decline downcore from 85% in stage B-2 to 75% in stage B-6 (at about 25, yr ago) and then returns gradually to higher values. The amplitude is large, 2% to 4%; lowest values are reached in stages B-11 and M-1. The carbonate abundance pattern of Core VNTR1-1PC is irregular, with large amplitude spikes (Fig. 3). Carbonate values range from 2% to 7%; low values near 4 cm correspond to an ash layer. Initial results suggest that the Brunhes/Matuyama (B/M) reversal boundary occurs at a shallow in this core, at about 33 cm ± 3 cm (S. Levi, pers. comm., 1992). Tentative correlation to the cores to the south is based on the B/M reversal boundary s in Cores VNTR1-1PC and 4PC (Fig. 3). Sediments at Sites VNTR1-6,7, -8, -9, and -1 are generally high in (average 74% to 82%) with low glacial/interglacial

3 DATA REPORT VNTR1-1 % VNTR1-4 % VNTR1-6 % VNTR1-7 % VNTR1-8 % VNTR1-9 Figure 3. Carbonate stratigraphy along 11 W. Cores are aligned left to right from north to south. Records are aligned at correlative carbonate values within interglacial stage B-5. Correlation is based on carbonate and isotope stratigraphy. VNTR1-9 % VNTR1-1 % VNTR1-12 % VNTR1-13 % Figure 4. Carbonate stratigraphy along 3 S. Cores are aligned left to right from west to east. Records are aligned at correlative carbonate values within interglacial stage B-5. Correlation is based on carbonate and isotope stratigraphy. The record for Core VNTR1-13 consists of data from Cores VNTR1-13GC from to 265 cm (dashed line) and VNTR1-13PC. The top of Core VNTR1-13PC is indicated by "" on the vertical axis. Cores VNTR1-13GC and VNTR1-13PC overlap approximately 4 cm. amplitude (Figs. 3 and 4). A long period trend having a minimum centered at carbonate stages B-3 to B-5 is noticeable, especially in the records of Cores VNTR1-7PC and -8PC. The combination of this long period trend and small glacial/interglacial amplitude describes an abundance pattern of associated with the South Equatorial Current. Core VNTR1-6 displays an intermediate preservation pattern between this pattern and the central equatorial Pacific pattern, as represented in Core VNTR1-4PC (Fig. 3). The records for Cores VNTR1-12PC and -13GC display a minimum/maximum pattern that is characterized by a pronounced interglacial stage B-3 with very low percentages (15%-2% in Core VNTR1-12PC and 37%-4% in Core VNTR1-13GC) and sub- 887

4 DATA REPORT' sequent increasing percentages downcore for glacial stages B-4 (55% ) to B-1 (82% and 87% for 13PC and 12PC, respectively), separated by prominent stage B-5 low and weak minima for interglacial stages B-7 and B-9 (Fig. 4). Sedimentation rates along the north-south transect increase fivefold between 11 N and the equator, from.4 to 2.2 cm/k.y. The northernmost Site VNTR1-1 is 239 to 324 m shallower than the other sites in the transect, emphasizing the deepening of the carbonate compensation (CCD) towards the equator. Along the 3 S transect (Fig. 3), observed sedimentation rates increase toward the east, from 1.1 cm/k.y. at Site VNTR1-9 at 11 W to 1.9 cm/k.y. at Site VNTR1-13 at 9 W. The span corresponding to interglacial stage B-3 and the intensity of the carbonate minimum increase toward the east. Surface samples have smaller contents in the easternmost cores, which, given the shallower of Sites VNTR1-12 and -13, indicates a shallowing of the lysocline in the eastern part of the equatorial Pacific Ocean. ACKNOWLEDGMENTS We would like to thank L. Mayer for providing grain density data, A. Mix for δ 18 θ data, and C. Erickson for assistance with the analysis. We acknowledge the support and help of the captain, the crew, and the scientific staff on board the Thomas Washington during the Venture 1 cruise. We are grateful to everyone who helped with core sampling at the Oregon State University (OSU) Core Repository in May 199 and to the staff at the OSU Core Repository, who provided additional samples later. The OSU Core Repository is supported by NSF Grants OCE and OCE This research was supported by NSF Grant ATM REFERENCES* Arason, P., 199. Whole-Core Magnetic Susceptibility Measurements During the VNTR1 Expedition, 1989: Dating Quaternary Sediments Using Climate-Susceptibility Correlations: Corvallis, OR (Oregon State University), Rept. OSU-CO , 1-. Hays, J.D., Saito, T., Opdyke, N.D., and Burckle, L.H., Pliocene-Pleistocene sediments of the equatorial Pacific: their paleomagnetic, biostratigraphic, and climatic record. Geol. Soc. Am. Bull., 8: Mayer, L.A., Pisias, N.G., Mix, A.C., Lyle, M.W., Arason, P., and Mosher, D., Site surveys. In Mayer, L.A., Pisias, N.G., Janecek, T.R., et al., Proc. ODP, Init. Repts., 138: College Station, T (Ocean Drilling Program), Snoeckx, H., and Rea, D.K., Late Quaternary stratigraphy of the eastern equatorial Pacific. Paleoceanography, 9: Abbreviations for names of organizations and publication titles in ODP reference lists follow the style given in Chemical Abstracts Service Source Index (published by American Chemical Society). Table 2., dry-bulk density, and percentage of CaCθ3 for Core VNTR1-1PC. CaCO (g/cm 3 3 CaCO ) (g/cm 3 3 ) 6 11 IS S Date of initial receipt: 1 February 1993 Date of acceptance: 8 March 1994 Ms 138SR-155

5 Table 3., dry-bulk density, and percentage of CaCθ3 for Cores VNTR1-4PC and VNTR1-4GC. (cmbsf) (g/cm- 1 ) (cmbsf) (g/cm 1 ) (g/cnv 1 ) Core VNTR1-4PC Core VNTR1-4GC I I l ' l ' l U ' l l l i l l α Table 4., dry-bulk density, and percentage of CaCθ3 for Cores VNTR1-6PC and VNTR1-6GC.1 (cmbsf) (cmbsf) Core VNTR1-6PC /7 Core VNTR1-6GC « H

6 DATA REPORT. Table 5., dry-bulk density, and percentage of CaCθ3 for Core VNTR1-7PC. Table 6., dry-bulk density, and percentage of CaCCb for Core VNTR1-8PC. ü ( / HI

7 ' DATA REPORT Table 7., dry-bulk density, and percentage of CaCθ3 for Cores VNTR1-9PC and VNTR1-9GC. Table 8., dry-bulk density, and percentage of CaCθ3 for Cores VNTR1-1PC and VNTR1-1GC. CoreVNTR1-9PC CoreVNTR CoreVNTROl-lOPC S CoreVNTROl

8 DATA REPORT. Table 9., dry-bulk density, and percentage of for Core VNTR1-12PC. Table 1., dry-bulk density, and percentage of CaCθ3 for Cores VNTR1-13PC and VNTR1-13GC. CoreVNTR1-12PC (g/cm 1 ) Core VNTRI-13PC IS SO S " I CNO (g/cm') (g/cm 1 ).78,78.8 CoreVNTRl-13GC SS I

9 i DATA REPORT Table 11., dry-bulk density, and percentage of CaCCb for Core V Table 12., dry-bulk density, and percentage of CaCθ3 for Core V Core V M.I L values are calculated fror Equation 4. Core V values are calculated fron Equation