U.S. Geological Survey Open-File Report OF 03-008
Gulf of Mexico Planktic Foraminifer Core-top Calibration Data Set: Raw Data
By Harry J. Dowsett[1], Charlotte A. Brunner[2], Stacey Verardo1, and Richard Z. Poore1
INTRODUCTION AND BACKGROUND
Paleoceanographers use the distribution of planktic foraminifers in sediment samples to estimate past oceanographic and paleoclimatic conditions (see Murray, 1995 for review). Analysis of climate and environmental variability on the decadal to millenial scale requires a taxonomically stable and well-dated core-top calibration data set. Databases used in global reconstructions of the last glacial maximum (Cline and Hays, 1976; CLIMAP, 1976; 1981), last interglacial (CLIMAP, 1984), and middle Pliocene (Dowsett et al., 1999) do not always meet these requirements. In this report we present planktic foraminifer faunal census data and AMS 14C data which can be be used in investigations of climate variability in the Gulf of Mexico region (eg. Poore et al., in review). More comprehensive interpretation and analysis of these data, aimed at developing a temporally and taxonomically stable data set will follow in other publications (see Dowsett et al., 2002).
Core-top samples included in this report were originally retreived during Gulf of Mexico cruises of the RV Vema and RV Robert Conrad (Lamont Doherty Earth Observatory, LDEO), RV Trident (University of Rhode Island, URI), RV Gyre (Texas A&M University, TAMU), RV Knorr (Woods Hole Oceanographic Institute, WHOI), RV Ida Green (University of Texas Marine Science Institute) and the RV Marion-Dufresne (French Polar Institute), dating as far back as 1954. Samples are from piston cores, trigger weight cores or gravity cores. Core sites selected for this study represent a range of depth and environment and are distributed througout the Gulf of Mexico (Figure 1 and Appendix 1).
The faunal data assembled here are a combination of planktic foraminifer counts from Gulf of Mexico core-top samples processed by the U.S. Geological Survey (USGS), URI, and Brown University (under the direction of Nilva Kipp). The processing technique is standard but differences between the labs are noted below. Additional information regarding methodology can be found in Imbrie & Kipp (1971), Brunner and Cooley (1976), Brunner (1979, 1982), and Dowsett & Poore (2001). Careful attention was paid to the taxonomic concepts of the various authors so that the resulting data set is internally taxonomically-consistent.
Raw samples aquired by the USGS were processed by first oven drying (<=50°C) and then soaking in dilute Calgon or H2O2 solution for several hours to disaggregate the sediment. Disaggregated sediment was washed through a 63µm mesh and oven dried at <=50°C. Dry residue was then dry-sieved at 150µm with the >150µm fraction reserved for faunal analysis. When necessary (>300 individuals in the >150µm fraction) samples were split using a CARPCO or OTTO microsplitter to obtain a representative sample of 300 specimens. Next (for samples analyzed at the USGS), individuals were fixed on a standard 60-square micropaleontological slide based upon their designation as species. Samples analyzed at URI were counted directly from a strew on a tray.
Figure 1. Distribution of samples within the Gulf of Mexico displayed on January 2001 mean sea-surface temperature (SST) map. Orange colors represent warmest SST and highlite the advection of warm water into the Gulf of Mexico from the Caribbean and the position of the Loop Current. (SST map provided by Space Oceanography Group, Johns Hopkins University Applied Physics Laboratory)
FAUNAL DATA
The taxonomies of Parker (1962, 1967), Blow (1969), Kennett and Srinivasan (1983), and informal notes of Nilva Kipp, were employed for identification. Faunal census data are reported here using the following taxonomic categories:
Orbulina universa d'Orbigny
Globigerinoides conglobatus (Brady)
Globigerinoides ruber (d'Orbigny). White and pink varieties of this species are tallied together.
Globigerinoides tenellus Parker
Globigerinoides sacculifer (Brady). We include in this category specimens assignable to Globigerinoides quadrilobatus (d'Orbigny) and Globigerinoides trilobus (Reuss).
Sphaeroidinella dehiscens (Parker & Jones)
Globigerinella aequilateralis (Brady)
Globigerinella calida (Parker)
Globigerina bulloides d'Orbigny
Globigerina falconensis Blow
Globigerina digitata Brady
Globigerina rubescens Hofker
Turborotalita quinqueloba (Natland)
Neogloboquadrina pachyderma (Ehrenberg). Right and left coiling varieties are counted separately in this report.
Neogloboquadrina dutertrei (d'Orbigny)
Globorotaloides hexagona (Natland)
Pulleniatina obliquiloculata Parker & Jones
Globorotalia inflata (d'Orbigny)
Globorotalia truncatulinoides (d'Orbigny). Right and left coiling varieties are counted separately in this report.
Globorotalia crassaformis (Galloway & Wissler)
Neogloboquadrina pachyderma - Neogloboquadrina dutertrei (P - D ) intergrade. Specimens of right-coiling Neogloboquadrina with more than four chambers in the final whorl, transitional between Neogloboquadrina pachyderma (Ehrenberg) and Neogloboquadrina dutertrei (d'Orbigny).
Globorotalia hirsuta (d'Orbigny)
Globorotalia scitula (Brady)
Globorotalia menardii (Parker, Jones, and Brady) s.l. Our Gl. menardii complex includes
Gl. menardii, Globorotalia tumida (Brady) s.l. and Globorotalia ungulata Bermudez.
Candeina nitida d'Orbigny
Globigerinita glutinata (Egger) s.l.
Hastigerina pelagica (d'Orbigny)
Other. Unidentified specimens or specimens that are rare within the Gulf of Mexico assemblages.
Raw counts of planktic foraminifers in each of 135 samples are provided in Appendix 1.
AMS 14C DATA
Archival core-top material from many of the cores shown on Figure 1 and listed in Appendix 1, is no longer available. Therefore, direct dating of core-top assemblages is for the most part, impossible. In many cases, we were able to obtain samples close to the core-top and estimate core-top ages by extrapolation. Several numerical techniques were devised to determine the probability of assemblages representing "modern" core-top conditions and will be discussed elsewhere (see also Dowsett et al., 2002).
Samples selected for Accelerator Mass Spectrometry (AMS) 14C dating were processed as indicated above. Unless indicated otherwise (Table 1), dates were obtained from mixed planktic foraminifers hand picked from the >150µm washed residue. Graphite targets for AMS dating were made at the USGS in Reston, Virginia. The carbon from these samples was captured as CO2 by acidification of the entire sample with 85% phosphoric acid (H2PO4) in a vacuum chamber. The CO2 was then dried by forcing the gas through a bath cooled (using alcohol and dry ice) to approximately -80°C. The dried CO2 was converted to pure carbon in the form of graphite by placing a measured volume (equivalent to 1mg carbon) in a chamber with iron powder, hydrogen, and zinc as a catalyst at 575°C for ten hours. The sample carbon (precipitated on the iron) was pressed into aluminum targets for AMS analysis.
Dating was done at the Lawrence Livermore Laboratory Center for Accelerator Mass Spectrometry (CAMS) in Livermore, CA (Roberts et al., 1997). Ages were reported in radiocarbon years (BP) using the Libby half-life of 5568 years. AMS 14C dates were converted to calendar years (BP) by calibration to the INTCAL98 database (Stuiver et al., 1998) and a estimated marine reservoir correction of 400 years.
Table 1 lists results of AMS 14C dating. An initial analysis of some of the data presented here can be found in Dowsett et al. (2002).
Table 1. AMS 14C results. Samples composed of mixed planktics unless otherwise noted.
Core | Interval (cm) | Age (BP)a | ±(Yrs) | CalYr (BP)b,c | Comments |
---|---|---|---|---|---|
RC09-17 | 8-10 | 1595 | 40 | 725 | |
RC09-17 | 20 | 4210 | 45 | 3736 | |
RC10-262 | 10-12 | 2930 | 40 | 2176 | |
RC10-262 | 30-32 | 7100 | 35 | 7235 | |
RC10-262TW | 0-1 | 3515 | 35 | 2870 | |
RC10-263 | 9-11 | 3500 | 30 | 2856 | |
RC10-263 | 34-36 | 6270 | 30 | 6279 | |
RC10-264 | 17-19 | 18185 | 50 | 20570 | |
RC10-264 | 38-40 | 27640 | 120 | -- | Too old to be converted |
RC10-265 | 15-17 | 1855 | 40 | 981 | |
RC10-265 | 34-36 | 4590 | 40 | 4266 | |
RC10-268 | 13-15 | 2950 | 40 | 2246 | |
RC10-268 | 34-36 | 4740 | 35 | 4443 | |
RC10-270 | 10-12 | 3295 | 40 | 2702 | |
RC10-270 | 31-33 | 3085 | 40 | 2343 | |
RC12-09 | 15-17 | 2290 | 30 | 1417 | |
RC12-09 | 36-38 | 3815 | 30 | 3306 | |
RC12-05 | 10-12 | 2435 | 40 | 1593 | |
RC12-05 | 30-32 | 3700 | 40 | 3150 | |
RC12-07 | 18-20 | 1455 | 40 | 633 | |
RC12-07 | 37-39 | 2635 | 40 | 1832 | |
RC12-07TW | 0-1 | 1680 | 35 | 824 | |
RC12-10 | 0-2 | 940 | 35 | 167 | |
RC12-10 | 16-18 | 1390 | 30 | 557 | |
RC12-10 | 50-51 | 3185 | 60 | 2489 | |
RC12-10 | 100-101 | 5325 | 60 | 5276 | |
RC12-10 | 134-136 | 6985 | 50 | 7139 | |
RC12-10 | 172-174 | 9350 | 40 | 9528 | |
RC12-10 | 210-212 | 12085 | 45 | 13153 | |
RC12-10 | 254-256 | 15710 | 45 | 17722 | |
RC12-11 | 50-51 | 5470 | 200 | 5442 | |
RC12-11 | 100-101 | 9595 | 75 | 9826 | |
RC12-11TW | 0-1 | 1280 | 35 | 500 | |
VM03-32 | 18-20 | 6255 | 40 | 6272 | |
VM03-32 | 108-110 | 9395 | 40 | 9613 | |
VM03-35 | 8-10 | 4080 | 35 | 3584 | |
VM03-42 | 10-12 | 6325 | 40 | 6311 | |
VM03-42 | 46-48 | 4835 | 30 | 4574 | |
VM03-45 | 10-12 | 6400 | 40 | 6402 | |
VM03-45 | 35-37 | 9630 | 35 | 9835 | |
VM03-49 | 39-41 | 8845 | 50 | 8932 | |
VM03-49 | 89-91 | 3875 | 40 | 3351 | |
VM03-69 | 47-48 | 3430 | 65 | 2774 | |
VM03-69 | 97-98 | 5460 | 120 | 5437 | |
VM03-96 | 15 | 1755 | 40 | 910 | |
VM03-96 | 30 | 3955 | 40 | 3438 | |
VM03-123 | 5 | 9465 | 40 | 9786 | |
VM03-123 | 23 | 26590 | 90 | -- | Too old to be converted |
VM03-146 | 8-10 | 22580 | 70 | -- | Too old to be converted |
VM03-146 | 30-32 | 32430 | 160 | -- | Too old to be converted |
VM24-22 | 9-11 | 1880 | 35 | 1030 | |
VM24-22 | 34-36 | 7385 | 120 | 7473 | |
VM24-22TW | 0-1 | 2640 | 35 | 1842 | |
VM26-142 | 0-1 | 1860 | 40 | 987 | |
VM26-142 | 30-32 | 4400 | 40 | 3985 | |
GY97-06PC20 | 11-12 | 830 | 30 | -- | |
GY97-06PC20 | 40 | 2340 | 40 | 1501 | |
GY97-06PC20 | 77-78 | 3540 | 30 | 2914 | |
GY97-06PC20 | 100 | 4900 | 40 | 4698 | |
GY97-06PC20 | 140 | 6870 | 40 | 6950 | |
GY97-06PC20 | 160 | 8300 | 40 | 8357 | |
GY97-06PC20 | 185-186 | 10050 | 35 | 10310 | |
IG19-3-35 | 20-21 | 3570 | 40 | 2946 | |
IG19-3-35 | 60-61 | 7710 | 40 | 7752 | |
TR126-10 | 118-120 | 26100 | 90 | -- | Too old to be converted |
TR126-10 | 118-120 | 29910 | 130 | -- | Globorotalia truncatulinoides (too old) |
TR126-10 | 118-120 | 34380 | 340 | -- | Neogloboquadrina dutertrei (too old) |
TR126-10 | 200-202 | 49100 | 1100 | -- | Too old to be converted |
TR126-10 | 400-402 | 49100 | 1100 | -- | Too old to be converted |
TR126-10 | 700-702 | 49300 | 1200 | -- | Too old to be converted |
TR126-11 | 100-102 | 30600 | 140 | -- | Too old to be converted |
TR126-11 | 350-352 | 46580 | 890 | -- | Too old to be converted |
TR126-23 | 0-1 | 1910 | 35 | 1053 | |
TR126-30 | 0-1 | 4865 | 35 | 4625 | |
TR126-33 | 0-1 | 4920 | 50 | 4743 | GlobigerinoidesRuber and G sacculifer |
KN159JPC6TW | 0-1 | 2210 | 40 | 1338 | |
KN159JPC6 | 0-1 | 940 | 35 | 167 | |
KN159JPC6 | 5 | 730 | 35 | -- | Too young to be converted |
KN159JPC6 | 20 | 1145 | 40 | 410 | |
KN159JPC6 | 49-50 | 1820 | 35 | 951 | |
KN159JPC6 | 100-101 | 2610 | 35 | 1813 | |
KN159JPC6 | 128-129 | 3460 | 35 | 2811 | |
KN159JPC31-1-1 | 3-4 | 1510 | 40 | 658 | |
KN159JPC31-1-3 | 0-1 | 6100 | 30 | 6111 | |
KN159JPC33 | 0-1 | 730 | 30 | -- | Too young to be converted |
KN159JPC33 | 60-61 | 2290 | 40 | 1417 | |
KN159JPC34 | 2-3 | 610 | 40 | -- | Too young to be converted |
KN159JPC34 | 81-82 | 3630 | 40 | 3039 | |
KN159JPC35 | 5 | 900 | 40 | 123 | |
KN159JPC35 | 20 | 1495 | 40 | 651 | |
GY94H2GC2 | 11-13 | 540 | 50 | -- | Too young to be converted |
GY94H2GC2 | 11-13 | 940 | 50 | 167 | Benthics |
GY94H2GC2 | 13-14.5 | 580 | 40 | -- | Too young to be converted |
GY94H2GC2 | 46-48 | 1330 | 50 | 524 | |
GY94H2GC2 | 46-48 | 1520 | 40 | 662 | Benthics |
GY94H2GC2 | 48-50 | 1320 | 30 | 518 | |
GY94H2GC2 | 48-50 | 1510 | 30 | 658 | Benthics |
GY94H8GC8 | 14-16 | 470 | 60 | -- | Too young to be converted |
GY94H8GC8 | 46-48 | 760 | 50 | -- | Too young to be converted |
GY94H17GC16 | 10-12 | 400 | 60 | -- | Too young to be converted |
GY94H17GC16 | 10-12 | 630 | 50 | -- | Benthics (too young) |
GY94H17GC16 | 12-14 | 390 | 40 | -- | Too young to be converted |
GY94H17GC16 | 12-14 | 620 | 30 | -- | Benthics (too young) |
GY94H17GC16 | 49-51 | 790 | 40 | -- | Too young to be converted |
GY94H17GC16 | 49-51 | 940 | 50 | 167 | Benthics |
GY94H17GC16 | 51-53 | 870 | 40 | 66 | |
GY94H17GC16 | 51-53 | 1160 | 40 | 421 | benthics |
GY94H23GC23 | 11-13 | 610 | 40 | -- | Too young to be converted |
GY94H23GC23 | 11-13 | 640 | 50 | -- | Benthics (too young) |
GY94H23GC23 | 48-49 | 1140 | 50 | 404 | |
GY94H23GC23 | 48-49 | 1390 | 50 | 557 | Benthics |
GY94H39GC36 | 12-14 | 1300 | 50 | 509 | Benthics |
GY94H39GC36 | 30-32 | 1860 | 50 | 987 | Benthics |
GY94H50GC43 | 10-12 | 1590 | 40 | 721 | |
GY94H50GC43 | 40-42 | 3700 | 50 | 3150 | |
GY94H50GC43 | 40-42 | 4640 | 40 | 4351 | Benthics |
GY94H114GC81 | 6-8 | 1610 | 40 | 736 | |
GY94H114GC81 | 6-8 | 2360 | 50 | 1515 | Benthics |
GY94H114GC81 | 16-18 | 1790 | 40 | 928 | |
GY94H114GC81 | 16-18 | 2800 | 40 | 2020 | Benthics |
GY94H121GC88 | 10-12 | 610 | 40 | -- | Too young to be converted |
GY94H121GC88 | 42-44 | 1300 | 40 | 509 | |
GY94H121GC88 | 42-44 | 1650 | 30 | 781 | Benthics |
MD02-2553 | 5-6 | 605 | 40 | -- | Too young to be converted |
MD02-2553 | 100-101 | 3265 | 40 | 2685 | |
MD02-2553 | 200-201 | 5155 | 40 | 4987 | |
MD02-2553 | 300-301 | 8520 | 45 | 8582 |
a radiocarbon years
b calendar years (Stuiver et al., 1998)
c samples with no entry in this column are too young/old to be calibrated
ACKNOWLEDGEMENTS
We thank Lynn Wingard and Thomas Cronin for thoughtful reviews of this work. We thank Bethany Boisvert, Kate Pavich, and Jessica Darling for help with sample procurement and processing. John McGeehin provided assistance with AMS 14C analyses. We are grateful to Nial Slowey and William Bryant (TAMU), Rusty Lotti (LDEO), Arman Silva and Steven Carey (URI) for providing material. The LDEO core lab is funded under NSF Grant OCE97-11316 and Office of Naval Research Grant N00014-96-10186. The URI core lab is funded under NSF Grant OCE-0002226. This work was supported by the USGS Earth Surface Dynamics Program.
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[1] U.S. Geological Survey, 926A National Center, Reston, Virginia, 20192
[2] Department of Marine Science, University of Southern Mississippi, Stennis Space Center, Mississippi, 39529