Supplementary Material to accompany:
A 0.6-Million Year Record of Millennial-Scale Climate Variability
in the Tropics
Kelly Ann Gibson† and Larry C. Peterson, Rosenstiel School of Marine and Atmospheric
Science, University of Miami, Miami, FL 33149, USA
† Current address: Department of Earth and Ocean Sciences, University of South
Carolina, Columbia, SC, 29208, USA
Corresponding author: K.A. Gibson, Department of Earth and Ocean Sciences,
University of South Carolina, Columbia, SC, 29208, USA (kgibson@geol.sc.edu)
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Methods
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Sediment Cores
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Ocean Drilling Program Site 1002 (FS 1) (10°42.73’N, 65°10.18’W; 893 m water
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depth) was the last of a program to study Caribbean ocean history drilled during ODP
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Leg 165. The site was triple-cored to a sub bottom depth of ~170 m and recovered a
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continuous, undisturbed sequence. This study utilizes sediments from Hole 1002C except
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for a short disturbed interval in Core 1002C-9H, the result of a wireline failure during
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core recovery that resulted in the core barrel falling back down to the bottom of the hole
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[Peterson et al., 2000]. To avoid this disturbed interval, cores 9H and 10H from Hole
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1002D were also XRF scanned and analyzed for δ18O stratigraphy and the results were
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patched into the Hole 1002C record.
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MD03-2622 (10o 42.37’N, 65o 10.15’W) was recovered in 2003 during the
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IMAGES P.I.C.A.S.S.O. cruise from a location on the central basin saddle adjacent to
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Site 1002. The 48.3 m-long giant Calypso core extends into Marine Isotope Stage 6. The
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central saddle was selected as a coring location for both sites because it is less susceptible
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to deposits from turbidity flows that are known to disturb sedimentation in the two deeper
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subbasins.
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Age Models
The age model for MD03-2622 was made by correlating its lightness (L*) record
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to that of nearby Calypso core MD03-2621 on the timescale of Deplazes et al. [2013].
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The age model for MD-2621 was generated by Deplazes et al. [2013] by correlating a
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new, high-resolution (0.7μm step size) lightness (L*) record from MD03-2621 with an
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AMS 14C-dated grayscale record [Hughen et al., 2004] from the Cariaco Basin, and then
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the L* and a 1 mm resolution scanning-XRF record of Br from MD-2621 to the ice core
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δ18O record of NGRIP on the Wolff et al. [2010] timescale using the program AnalySeries
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[Paillard et al., 1996]. Parameters of sediment color in the Cariaco Basin (e.g., L*, %
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reflectance, and grayscale) are primarily controlled by concentrations of organic matter,
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which in turn appear to reflect variations in primary productivity. Independent calendar-
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age chronologies for the last deglaciation have shown that abrupt changes in Cariaco
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Basin L* values and Greenland δ18O were synchronous within dating uncertainties
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(Hughen et al., 2000), giving confidence in the use of L* for age model creation. The
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successful extension of radiocarbon calibrations into the last glacial using Site 1002
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sediments by Hughen et al. (2004, 2006) further supports this contention, as does
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recognition of century-scale “precursor” events in core MD03-2621 L* by Gaudenz et al.
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(2013) previously identified only in Greenland ice cores and in European stalagmites.
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The average sedimentation rate over the interval of study in MD03-2622 is ~30 cm/kyr.
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The planktic δ18O stratigraphy from Peterson et al. [2000] that provided the first
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age control for Hole 1002C was based on very low resolution sampling at 30 to 60- cm
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intervals from MIS 1 to 5, and 150-cm sample spacing from Termination II to the base of
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the sequence. Even with such a broad sampling interval, a recognizable δ18O stratigraphy
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was achieved because of the high sedimentation rates. A much higher resolution δ18O
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record for Hole 1002C is used in this study based on analysis of the shallow mixed-layer
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dwelling foraminifer Globigerinoides ruber at approximately 10 to 20-cm intervals down
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through MIS 12, and ~50-cm intervals for the remainder of the sequence. This new δ18O
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record from Hole 1002C covers approximately the last 600 kyr, while the scanning XRF
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data begin at ~111 ky BP and extend back through the four previous glacial-interglacial
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cycles.
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The age model for the upper ~ 123 kyr for Hole 1002C was obtained by matching
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the color record of Hole 1002C to the lightness record of MD03-2621 on its age model,
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which is described above. For the record older than ~123 kyr, the remainder of the age
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model was made by correlating the new planktic δ18O record with the Lisiecki and Raymo
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[2005] benthic δ18O stack using the program AnalySeries [Paillard et al., 1996]. Anoxic
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conditions in Cariaco Basin preclude generation of a continuous benthic record so we
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must assume that δ18O variations in the planktic Hole1002C record are in phase with the
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benthic Lisiecki-Raymo δ18O standard.
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Prior to age model tuning, gas voids larger than 5 cm were removed from the
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depth scale for Hole 1002C. A clear record of Marine Isotope Stages down through MIS
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12 is obtained, with the lower resolution δ18O sampling below that hindering confident
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identification of stages. Nonetheless, it appears that MIS 13-15 can be recognized though
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the age model in this interval should be viewed with caution. Marine isotope stage
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boundaries are after SPECMAP [Imbrie et al., 1984] applied to the Lisiecki and Raymo
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[2005] age model.
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Scanning XRF Analysis
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Core sections from MD03-2622 and Site 1002 were run on an Avaatech XRF core
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scanner for bulk elemental analysis in the Paleoclimatology Lab at RSMAS. Core MD03-
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2622 was scanned in its entirety, which extends into MIS 6. From Hole 1002C, cores
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representing sections 1002C-5H-4 through the end of 1002C-18H were scanned, which
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together cover approximately 500 kyr of deposition from ~110 ky BP to ~600 ky BP. To
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avoid scanning the disturbed interval in Hole 1002C mentioned above, cores 9H and 10H
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from Hole 1002D were also scanned and patched into the Hole 1002C record. The results
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from core MD03-2622 and Hole 1002C were spliced together at 115 ky BP, based on
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matching patterns of Mo variability during Marine Isotope Stage (MIS) 5.
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The archive sections from Hole 1002C and 1002D were photographed using a
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Geoscan II color line-scan camera mounted on a GEOTEK Multi Sensor Core Logger in
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the Paleoclimatology Lab at RSMAS. Core photographs were used to identify expansion
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gaps and shrinkage cracks in both cores that could lead to low values in the XRF data.
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Those data were subsequently removed so as to not misrepresent trends in elemental
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variation.
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Prior to analysis, cores were brought to room temperature for approximately one
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hour to reduce condensation at the sediment surface during scanning. The core surface
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was gently scraped with a glass slide to present a fresh surface for scanning, and covered
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with 0.4 m-thick Ultralene® to prevent contact between the sediment surface and the
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X-ray detector. The scanner was calibrated against a set of pressed powdered standards
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prior to each run. All core sections were scanned at a 0.5 cm resolution downcore step
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resulting in an average measurement spacing in time of ~16 yrs. Molybdenum was
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measured as part of a 30kV run with a thin Pd filter, a measurement time of 10 seconds
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and current of 1000 A.
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Scanning-XRF results are presented here as counts per second (cps), which is the
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standard output of the models that calculate the intensities of each elemental peak.
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Arguments have been made for presenting scanning XRF data as ratios of elements
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[Calvert and Pedersen, 2007] or as log ratios of elements [Weltje and Tjallingii, 2008].
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The bulk of the sedimentary Mo (97%) in the Cariaco Basin has been shown to be of
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marine origin, with comparatively little contribution from a terrigenous or biogenic
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source [Dean et al., 1999], suggesting that normalization of Mo with an element
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indicative of terrigenous input (i.e. Al or Ti) is unnecessary. Comparison of plots of Mo
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(cps) with Mo/Al and ln(Mo/Al) (FS 3) reveals very little variation between the three
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different methods of reporting downcore variability in ventilation, so for simplicity sake,
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the Mo record is presented as Mo in cps.
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Wavelet Analysis
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Wavelet analyses were performed using software provided by Grinstead et al. (available
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at http://www.pol.ac.uk/home/research/waveletcoherence/) for MATLAB. Before
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analysis, each time series was linearly interpolated at a constant 20-year timestep, with a
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95% confidence interval set assuming a red noise model. The 20-year timestep very
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closely approximates the average temporal sampling of the XRF data.
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Supplemental Material References
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Calvert, S. E., and T. F. Pedersen (2007), Elemental proxies for paleoclimatic and
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palaeoceaongraphic variability in marine sediments: interpretation and applicaition, in
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Proxies in late Cenozoic paleoceanography, edited by C. Hillaire-Marcel and A. de
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Vernal, pp. 567-644, Elsevier, Oxford.
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Dean, W. E., D. Z. Piper, and L. C. Peterson (1999), Molybdenum accumulation in
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Cariaco Basin sediment over the past 24 k.y.; a record of water-column anoxia and
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climate, Geology, 27, 507-510.
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Deplazes, G., et al. (2013), Links between tropical rainfall and North Atlantic climate
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during the last glacial period, Nature Geosci, 6(3), 213-217.
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Imbrie, J., J. D. Hays, D. G. Martinson, A. McIntyre, A. C. Mix, J. J. Morely, N. G.
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Pisias, W. L. Prell, and N. J. Shackleton (1984), The orbital theory of Pleistocene
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climate: Support from a revised chronology of the marine δ18O record, in Milankovitch
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and Climate: Understanding the Response to Astronomical Forcing, edited by A. Berger,
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D Reidel Pub Co, Higham, MA.
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Lisiecki, L. E., and M. E. Raymo (2005), A Pliocene-Pleistocene stack of 57 globally
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distributed benthic δ18O records, Paleoceanography, 20(1), 1-17.
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Paillard, D., L. Labeyrie, and P. Yiou (1996), Macintosh program performs time-series
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analysis, EOS Transations, 77(379).
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Peterson, L. C., G. H. Haug, R. W. Murray, K. M. Yarincik, J. W. King, T. J. Bralower,
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K. Kameo, S. D. Rutherford, and R. B. Pearce (2000), Late Quaternary stratigraphy and
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sedimentation at Site 1002, Cariaco Basin (Venezuela), Proceedings of the Ocean
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Drilling Program, Scientific Results, 165, 85-99.
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Weltje, G. J., and R. Tjallingii (2008), Calibration of XRF core scanners for quantitative
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geochemical logging of sediment cores: Theory and application, Earth and Planetary
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Science Letters, 274(3-4), 423-438.
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Wolff, E. W., J. Chappellaz, T. Blunier, S. O. Rasmussen, and A. Svensson (2010),
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Millennial-scale variability during the last glacial: The ice core record, Quaternary
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Science Reviews, 29(21-22), 2828-2838.
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Supplementary Figure Captions
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Fs01
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a. Position of the Cariaco Basin (indicated by the yellow star) with respect to summer
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(Sept) and winter (March) position of the ITCZ (indicated by the dashed white line). b.
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Location of Cariaco Basin and of cores utilized in this study. The lightest color on the
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bathymetric map indicates water <100 m deep. Major contributing rivers to terrigenous
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sedimentation are indicated.
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Fs02
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The age model for Hole 1002C was made by tuning the ODP Hole 1002C G. ruber δ18O
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record to the Lisiecki-Raymo [2005] stacked benthic δ18O record. Additional age control
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for the upper 125 kyr of the age model was added by matching the reflectance record
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from Hole 1002C with the well-dated L* record of MD-2621 [Deplazes et al., 2013]. The
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age model for MD-2622 was also made by correlating the MD-2622 L* record with the
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dated MD-2621 L* record. Purple triangles indicate tiepoints used in construction of the
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Hole 1002C age model. The age depth plot to the right shows that the stratigraphic
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sequence in the Cariaco Basin is continuous with no hiatuses or disturbed intervals and
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relatively constant sedimentation rates that average 30-40 cm/ky.
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Fs03
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Running averages (10 pt smooth) of Mo (cps) in blue, Mo/Al in black, and ln(Mo/Al) in
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red. Normalization of Mo with Al would provide a record of “excess Mo,” that which is
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not delivered to the sediment in the terrigenous fraction; however, 97% of the Mo in the
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Cariaco Basin is hosted in the marine fraction [Dean et al., 1999]. Therefore,
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normalization does not significantly alter the downcore appearance of Mo variability.
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Similarly, the log ratio of Mo/Al does not significantly change the downcore appearance
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of Mo variability. For simplicity sake, the results here are presented as Mo (cps).
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