Considerations for Globigerinoides ruber (White and Pink) Paleoceanography: Comprehensive Insights From a Long‐Running Sediment Trap

Abstract We present a detailed analysis of the seasonal distribution, size, morphological variability, and geochemistry of co‐occurring pink and white chromotypes of Globigerinoides ruber from a high‐resolution (1–2 weeks) and long‐running sediment trap time series in the northern Gulf of Mexico. We find no difference in the seasonal flux of the two chromotypes. Although flux of G. ruber is consistently lowest in winter, the flux‐weighted signal exported to marine sediments represents mean annual conditions in the surface mixed layer. We observe the same morphological diversity among pink specimens of G. ruber as white. Comparison of the oxygen and carbon isotopic composition (δ 18 O and δ 13 C) of two morphotypes ( sensu stricto and sensu lato ) of pink G. ruber reveals the isotopes to be indistinguishable. The test size distribution within the population varies seasonally, with the abundance of large individuals increasing (decreasing) with increasing (decreasing) sea surface temperature. We find no systematic offsets in the Mg/Ca and δ 18 O of co‐occurring pink and white G. ruber . The sediment trap data set shows that the Mg/Ca‐temperature sensitivity for both chromotypes is much lower than the canonical 9%/°C, which can likely be attributed to the secondary influence of both salinity and pH on foraminiferal Mg/Ca. Using paired Mg/Ca and δ 18 O, we evaluate the performance of a suite of published equations for calculating sea surface temperature, sea surface salinity, and isotopic composition of seawater (δ 18 O sw ), including a new salinity‐δ 18 O sw relationship for the northern Gulf of Mexico from water column observations.