Statement of Work Sample Analysis

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.