Statement_of_Work_Sample_Analysis.docx

STATEMENT OF WORK

Stable isotope analysis of carbonate microfossils

Section I. General Information

A. Introduction

The USGS Florence Bascom Geoscience Center requires the analysis of 12C/13C and 18O/16O isotope ratios on samples of carbonate microfossils (predominantly benthic foraminifera and ostracodes) from marine sediment samples collected from various locations. Samples will support scientific work on the Paleo-perspectives on hazards and ecosystem change project. The purposes of this work are to: 1) apply stable isotope proxy records to reconstruct changes in global ice volume (i.e., sea level), ocean temperature, ocean circulation, and/or salinity; and 2) quantify the offsets between diagenetically unaltered foraminiferal tests relative to those that have been moderately- to heavily altered by diagenesis. Of the maximum number analyses (2,000) to be conducted prior to the end of FY27 (i.e., before September 30, 2027), it is estimated that 15-20% of the individual shells/tests to be analyzed will be as small as 5-9µg. Therefore, the stable isotope mass spectrometer of the chosen contractor must be able to generate reliable data within this size range, while maintaining acceptable analytical precision (see below).

B. Background

Stable isotopes of carbon and oxygen recorded in the tests of foraminifera (and other microfossil groups) preserved in the geologic record provide the most common long-term archives of past environmental changes. From deep-sea benthic foraminifera, these stable isotope records are interpreted to track changes in global ice volume (i.e., sea level), as well as in ocean temperature and circulation. These records also provide orbitally tuned age control. From shallow marine settings, such records can also elucidate changes in salinity and other environmental parameters. Analyses for this study will be conducted on samples derived from sediment cores recovered from a variety of locations and settings, and the results from which will be used in several different peer-reviewed research manuscripts. As such, all data shall be reported relative to Carrara Marble standards, on instruments with documented analytical precision for carbonate samples in the 5-150µg size range of better than 0.060% for δ13C and 0.080‰ for δ18O. This contract will require up to 2,000 stable isotope measurements to be conducted through the end of FY27 (i.e., prior to September 30, 2027), with the potential for additional measurements to be conducted in subsequent years.

Section II. Work Requirements

Task 1 – Sample Preparation:

Provided with pre-picked and pre-imaged individual carbonate shells/tests, the contractor shall prepare the sample for isotopic analysis. This will involve at minimum, but not limited to, 1) weighing each individual shell/test on a microbalance, 2) sorting into vials by mass, 3) rinsing each sample in methanol to remove any residual organic material, 4) drying each vial in a laboratory oven at 50-60oC for at least 24 hours, and 5) capping each vial prior to analysis. The USGS employee responsible for the order may dictate to the lab the exact methodology required for a given set of samples, as exact preparation procedures may differ between sample types. The contractor must provide the USGS with written, detailed sample preparation and analytical methodology at the end of each call order.

Task 2 – Standards:

Once sorting all samples by mass, Carrara marble standards of appropriate mass (i.e., matching the sample mass range for a given run) will be picked and sorted, to be positioned throughout each analytical run.

Task 3 – Analysis:

All samples analyzed by the contractor must be accomplished with appropriate mass-groupings of samples and standards, using appropriate tuning parameters on an isotope ratio mass spectrometer with documented analytical precision for carbonate samples in the 5-250µg size range of better than 0.060‰ for δ13C and 0.080‰ for δ18O.

Time Standard(s): Sample preparation and analysis must take place within six months of receiving samples, barring unforeseen circumstances such as equipment malfunction and associated repair time. In the event of such circumstances, the principal investigator and the contractor may mutually agree on a time frame in which samples must be prepared and analyzed, or funds will be deobligated from the order Deliverable: The contractor shall deliver corrected δ13C and δ18O values for each sample in per mil VPDB, as well as the corresponding 12C/13C and 18O/16O isotope ratios, analytical uncertainties, error correlations, and mass spectrometer signal intensity data.

Quality Assurance: Analyses and reports that are less than the quality standard shall be redone by the contractor at no additional cost to the government.

Acceptance: The U.S. Geological Survey’s Technical Liaison (TL) will accept the work if all δ13C and δ18O results are reported following corrections to the Carrara Marble standard in per mil (‰) VPDB, and the analytical precision for each run is reported and better than 0.060‰ for δ13C and 0.080‰ for δ18O.

Section III. Supporting Information

A. Place of performance

External lab; location to be determined.