Planktonic foraminiferal assemblages and geochemistry (i.e. Mg/Ca and delta 18O) are among the most widely-utilized climate proxies in paleoceanographic studies. Foraminifera-based sea surface temperature (SST) reconstructions are interpreted as representative of mean annual conditions. However, foraminifera fluxes vary seasonally, temperature reconstructed from this material will harbor a strong seasonal imprint. Additionally, recent studies have suggested that Mg/Ca is affected by salinity, which is not accounted for in most existing calibrations and has varied significantly over glacial-to-interglacial timescales.

Well-preserved, bi-weekly sediment trap samples and accompanying high-resolution water column measurements from the Hawaii Ocean Time-Series (HOT) at Station ALOHA (A Long Term Oligotrophic Habitat Assessment) provide ideal conditions to evaluate temporal variability in foraminiferal flux and calibrate Mg/Ca to precisely-measured environmental parameters. A 2.5 year faunal record at HOT shows total planktonic foraminifera fluxes are highest (>100 shells/m 2/day) from May-October, coincident with warmest SSTs and high primary productivity. Annual peaks occur in July and late September; unique 5-day sampling reveals that these maxima occur in response to summer blooms of N 2-fixing bacteria.

Low salinity and pH variability at ALOHA (0.7 psu and 0.11 units, respectively) allows the temperature influence on Mg/Ca to be isolated and quantified. Globigerinoides ruber (sensu lato) temperature sensitivity ranges from 6.3 +/- 1.6% to 7.7 +/- 2.4% Mg/Ca per degrees Celsius, with higher values arising from the assumption of deeper habitat depth. T. sacculifer exhibits a similar temperature sensitivity range, up to 7.7 +/- 2.4% for a subsurface habitat. Our results highlight the sensitivity of Mg/Ca-temperature regressions to parameter choices used in calibration.