Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

Samples were collected using a McLane Parflux 78H sediment trap deployed at depths >400 meters (m) in the central Santa Barbara Basin (34.2450389, -120.0592917). The sampling interval was 10 to 14 days, and samples were preserved in borate-buffered formalin solution. A 1/16th split of the sediment trap sample was used. Samples were rinsed with tap water over a 125-micron sieve, and foraminifera tests were removed from other trap material using a fine paintbrush. Foraminifera tests were dried on a micropaleontology slide, then species were identified by test morphology and sorted. Tests of the three most abundant species were removed to separate micropaleontology slides. These tests were inspected under a dissecting microscope to ensure no organic particles were adhered to the exterior or interior of tests. Any organic particles were gently removed with a wet brush. The removed tests were counted and weighed on a microbalance. Tests from multiple sediment trap samples were combined to achieve a sample of 5-10 milligrams (mg). This combined sample was gently rinsed with methanol three times, then dried.

Compound-specific stable isotopes were measured at the UC Santa Cruz Stable Isotope Lab. Tests were demineralized by adding ~1 milliliter (mL) 1N HCl to dissolve carbonate, then stored at 4 degrees Celsius (°C) overnight to complete the demineralization reaction. The HCl was then evaporated under N₂. The remaining organic matter was then hydrolyzed with ~ 1mL 6N HCl at 110°C for 20 hours after the vial was purged with N₂ to remove oxygen. Samples were purified by cation-exchange chromatography with DOWEX 50WX8-400 resin. Amino acids were measured as trifluoroacetyl isopropyl ester derivatives following Silfer et al. (1991). After drying under N₂, samples were esterified with a 1:5 mixture of acetyl chloride:isopropanol at 110 °C for 60 minutes. Samples were dried again under N₂, then trifluoroacetylation was completed using a 1:3 mixture of trifluoroacetic anhydride (TFAA) and dichloromethane (DCM) at 110 °C for 15 minutes. Inorganic salts were removed from samples by liquid-liquid extraction of derivatized amino acids in chloroform and an aqueous phosphate buffer. Trifluoroacetylation was completed again after liquid-liquid extraction. Samples were dried and dissolved in ethyl acetate for gas chromatography-isotope ratio mass spectrometry (GC-IRMS).

Amino acid stable isotopes were measured on a Thermo Trace gas chromatograph coupled to a Finnegan Delta-Plus IRMS and GCC III (isoLink). Samples were analyzed alongside a set of amino acid standards of known δ¹³C and δ¹⁵N values. Amino acids included in analysis were: alanine (Ala), glycine (Gly), threonine (Thr), serine (Ser), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), aspartic acid/asparagine (Asx), glutamic acid/glutamine (Glx), phenylalanine (Phe), and lysine (Lys).

The δ¹³C of amino acids was corrected for carbon added during derivatization using standards and following the methods of Silfer et al. (1991). Reproducibility was estimated by the standard deviation of triplicate injections of each sample. Accuracy was checked by analyzing an in-house long-term lab reference material (cyanobacteria) with every sample set.

- Imported original file "BCO-DMO_SBB_foram_CSI-AA_N.csv" into the BCO-DMO system.
- Added the following columns and populated with values provided in the metadata: Start_date, End_date, Lat, Lon.
- Saved the final file as "989777_v1_csi-aa_sbb_nitrogen.csv".

NSF Award Abstract:
Current climate change is unique in human history. To understand how the Earth and life on it responds to comparable change it is necessary to look millions of years in the past. A huge amount of what we know about past climate comes from the fossils of marine plankton. Specifically, a group of single-celled organisms called foraminifera. Foraminifera make tiny fossil shells which capture the chemistry of the water they grew in. As a result, they can be used to reconstruct ancient ocean waters and climate. To use the fossil shells of foraminifera to their greatest effect, the ecology of the living creature must be understood. Variables like what the foraminifera ate, what depth it lived at, and whether it had symbionts will all impact how shell chemistry is interpreted. Compound-specific nitrogen and carbon isotopes of specific amino acids (CSI-AA) represent a unique approach to study these variables in living plankton. This proposal would test how well this approach can be applied to fossil shells. If successful, this would provide powerful ways to describe the ecology of long extinct planktic foraminifera. In doing so, one may better understand the records they hold of Earth’s past. The project broader impacts include support for a postdoctoral researcher, development of a career-opportunities workshop to introduce students from Primarily Undergraduate Institutions to geoscience research, and content contributions to a summer program for at-risk STEM transfer students at UC Santa Cruz.

Specifically, this project will investigate and develop multiple aspects of CSI-AA to better understand the species-level ecology of planktic foraminifera. This is key to generating paleoclimate and paleoceanographic records that can contextualize the Ocean’s future climate and trajectory. The proposed project will use CSI-AA to constrain three key aspects of planktic foraminiferal ecology: depth habitat, diet, and symbiosis. CSI-AA from shell-bound organics will be used in foraminifera for the first time to refine species-level inferences about these ecological traits. First CSI-AA applications in extant species will be ground-truthed using plankton tows, sediment traps, and recent sedimentary samples from the Santa Barbara Basin. Lessons learned will then be applied deeper into the fossil record to elucidate the trophic ecology of extinct foraminifera. Finally, amino acid molar ratios and racemization (the diagnostic shift between amino acid forms which occurs with fossil age) will be used to assess amino acid preservation in fossils and ultimately test the limits of this approach by targeting a suite of abundant species from the Miocene, Eocene, and Cretaceous.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.