Dataset: Alkenones and nutrients from water column samples collected at the Chatham Rise, east of New Zealand, on R/V Tangaroa cruises TAN0804, TAN0902, and TAN0909 from 2008-2009

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.