USGS Data Series 353
By Marci Robinson, Rocio Caballero, Emily Pohlman, Timothy Herbert, Victoria Peck, and Harry Dowsett
The U.S. Geological Survey is conducting a long-term study of mid-Pliocene climatic and oceanographic conditions. One of the key elements of the study involves the use of quantitative composition of planktic foraminifer assemblages in conjunction with other proxies to constrain estimates of sea-surface temperature (SST) and to identify major oceanographic boundaries and water masses.
Raw census data are made available as soon as possible after analysis through a series of reports that provide the basic data for future work. In this report we present raw census data (table 1) for planktic foraminifer assemblages in 14 samples from Ocean Drilling Program (ODP) Hole 677A. We also present alkenone unsaturation index (UK'37) analyses for 89 samples from ODP Hole 677A (table 2). ODP Hole 677A is located in the Panama basin, due west of Ecuador at 1°12.138'N., 83°44.220'W., in 3461.2 meters of water (fig. 1).
Figure 1. Location of Ocean Drilling Program Site 677.
Table 1. Planktic foraminifer census data, Ocean Drilling Program Hole 677A: HTML | Excel
Table 2. Alkenone unsaturation index (UK'37) data, Ocean Drilling Program Hole 677A: HTML | Excel
A variety of statistical methods have been developed to transform foraminiferal census data in Pliocene sequences into quantitative estimates of Pliocene SST. Details of statistical techniques, taxonomic groupings, and oceanographic interpretations are presented in more formal publications (Dowsett and Poore, 1990, 1991; Dowsett, 1991, 2007a,b; Dowsett and Robinson, 1998, 2007; Dowsett and others, 1996, 1999).
For micropaleontologic analyses, sediment samples were oven dried at <=50°C. The dried bulk samples were disaggregated in 250 milliliters of warm tap water with ~2 milliliters of dilute sodium hexametaphosphate (5 grams per liter water). The samples were agitated for 1 hour at room temperature and then washed over a 63 micrometer sieve using a fine spray hose. The coarse fraction was dried in an oven at <=50°C. Some samples required an additional wash cycle to obtain clean specimens. A split of 300-350 planktic foraminifer specimens was obtained from the <=150 micrometer size fraction using a CarpcoTM sample splitter. Specimens were sorted, identified, and glued to 60-square micropaleontological slides.
For alkenone analyses, sediment samples were freeze dried and homogenized. Lipid extracts were extracted in 100% dichloromethane using a Dionex automated solvent extractor (ASE 200). The ASE 200 exposes each sample to a small volume of solvent (~25 milliliters) at elevated pressure (1500 pounds per square inch) and temperature (150ºC). After evaporation under a N2 stream and dilution with a small volume of toluene (~0.2 milliliters), the extracts were analyzed using a Hewlett-Packard 6890 gas chromatograph equipped with a flame ionization detector and a DB-1 column (60 meter x 0.32 meter x 0.10 micrometer file thickness). The temperature program used to quantify alkenones starts at 90ºC holding for 2 minutes, then ramps to 250ºC at 40ºC per minute, followed by a slow ramp of 1ºC per minute to 300ºC, and finishes with an isothermal holding step at 320ºC for 11 minutes. Peak areas of C37:2 and C37:3 alkenones were determined using Hewlett-Packard ChemStation software and were used to calculate the alkenone unsaturation (UK'37) index.
In general, our taxonomic concepts follow Parker (1962; 1967) and Blow (1969); exceptions to their practices are documented in Dowsett and Robinson (2007). ODP sample designations are abbreviated in table 1 as core section, depth within section in centimeters (for example, 10-5, 34-35 cm = core 10, section 5, 34-35 centimeters below the top of section 5). The depth columns list depth of sample below the sea floor in meters and a composite depth scale. Figure 2 presents the faunal abundance in percent for each sample.
Figure 2. Planktic foraminifer relative abundances, Ocean Drilling Program Hole 677A. Abbreviation: mcd, meters composite depth.
We thank Kevin Foley and Ben DeJong for reviewing this manuscript. We thank the Ocean Drilling Program for access to the samples. This report is a product of the U.S. Geological Survey Earth Surface Dynamics Program.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
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Robinson, Marci, Caballero, Rocio, Pohlman, Emily, Herbert, Timothy, Peck, Victoria, and Dowsett, Harry, 2008, Mid-Pliocene planktic foraminifer census data and alkenone unsaturation indices from Ocean Drilling Program Hole 677A: U.S. Geological Survey Data Series 353, available only online at https://pubs.usgs.gov/ds/353.