Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • BCO-DMO Curation Notes
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Cruises and sample Collection:
Study locations were selected based on the positions of New Zealand's National Institute for Water and Atmospheric Research (NIWA) long‑term biophysical moorings, deployed along 178°30'E in two major surface‑water masses. The Subtropical Mooring (STM) was situated in subtropical waters at 41°47'S with an annual SST range of 14 to 18 degrees Celsius (°C), whereas the Subantarctic Mooring (SAM), located at 46°40'S, lay within subantarctic waters where annual SSTs range from 10 to 14 °C. A third site was located on the crest of the Chatham Rise (CR), positioned just north of the Subtropical Front (STF).

Water‑column particle samples for this study were collected aboard the NIWA vessel Tangaroa during three cruises: TAN0804 in April 2008 (autumn), TAN0902 in February 2009 (summer), and TAN0909 in October 2009 (spring). Additional casts were conducted on the crest of the Chatham Rise during the autumn (43.43°S, 178.5°E) and spring (43.40°S, 178.5°E).

Methods & Sampling:
A Seabird 911plus CTD rosette was used to collect 60 to 100 liters (L) of seawater throughout the surface mixed layer and thermocline by closing multiple Niskin bottles at targeted depths. Water samples for alkenone analysis were filtered onto 142-millimeter (mm) GF/F filters and stored frozen until processing.

Frozen, filtered samples were extracted using an Accelerated Solvent Extractor (Dionex ASE 200) with a 4:1 dichloromethane:methanol solvent mixture, following procedures modified from Sikes et al. (1997) and (Sikes et al., 2009). Alkenone recovery using this approach is estimated at ~95% (Shin et al., 2002).

Extracts were saponified in 5% KOH in methanol, and the neutral fraction containing the alkenones was isolated by partitioning into a hexane-chloroform mixture. Saponification removes fatty acids that elute in the sterol region, which simplifies compound identification and eliminates the co‑elution of the C37 tri‑unsaturated fatty acid methyl ester, thereby improving quantification (Sikes and Volkman, 1993; Sikes et al., 1997). The purified neutral fraction was analyzed by capillary gas chromatography (GC) on a Shimadzu GC‑17 equipped with an autosampler, cooled on‑column injector, and flame‑ionization detector.

This section documents curation actions performed prior to publication review with the submitter, and additional information relevant to understanding and reusing this dataset. It distinguishes changes made to the submitted (meta)data from unresolved issues and/or enhancements that improve future reuse and interoperability.

CURATION ACTIONS PERFORMED ON DATA

- Imported original file "NZ alkenone data 2026 4BCO-DMO.xlsx" (sheet 1) into the BCO-DMO data processing system.
- Treated "NaN" and "NaNN" as missing data values (missing data are empty/blank in the final CSV file).
- Renamed columns to comply with BCO-DMO naming conventions.
- Added column "longitude", setting value "178°30'E" for all rows.
- Converted latitude from degrees-decimal_minutes format to decimal degrees South.
- Converted longitude from degrees-decimal_minutes format to decimal degrees East.
- Rounded latitude and longitude to 2 decimal digits (maximum precision).
- Converted Date column to format %Y-%m-%d.
- Saved the final file as "1008819_v1_nz_alkenones.csv".

CURATION ACTIONS PERFORMED ON METADATA

- BCO-DMO's standard metadata entry and text formatting steps were performed. See: https://www.bco-dmo.org/how-to/standard-curation-edits

ISSUES POTENTIALLY IMPACTING REUSE

- N/A

NSF Award Abstract:

The subtropical front (STF) is the northern boundary of the Southern Ocean, separating oligotrophic, warm subtropical surface waters north of the STF from cooler, nutrient-rich, subpolar waters to the south. East of New Zealand, the STF is bathymetrically anchored to the Chatham Rise, a 1000 km long submerged continental plateau. The National Institute of Water and Atmospheric Research (NIWA), New Zealand, maintains two sediment trap arrays only 200 km apart on the Chatham Rise. The traps, although closely spaced, sit just out of the axis of the STF and thus allow comparison of subtropical and subpolar waters under similar environmental conditions such as weather and light levels over the annual cycle without the complication of frontal migrations.

In this project, researchers at Rutgers University and the University of Hawaii will examine at these sites the processes involved in the formation of the proxies on which paleo-sea surface temperatures (SST) records are based and resolve the issue of differential seasonality between the organisms which are arguably two of the most important paleotemperature estimators now in use (e.g. U37 K ' accuracy, foraminiferal ä18O values). The principle hypotheses to be tested are:

1. Episodic delivery of alkenones and foraminifera exported from the surface mixed layer are the underlying cause of differences between alkenone and foraminiferal temperature reconstructions.

2. Nutrient depletion in subtropical waters during summer months and subsurface production during prolonged winter darkness in subpolar waters are important environmental influences controlling the accuracy of U 37 K ' SST reconstructions.

Efforts in this work primarily and actively address the broader impact criteria of enhancing infrastructure for research. Collaborations among United States, New Zealand, and European scientists represent a significant investment in outreach with international colleagues by the US PI?s. The combined results will enhance the research of all members by disseminating shared data widely and serve to stimulate future partnerships. Additionally, training of students who will take central roles in this research addresses advancing training and learning. Better quantification of SST records will benefit paleoclimatic reconstructions and thus have societal benefits.