Modern observations of planktic foraminifera from sediment trap studies help to constrain the regional ecology of paleoceanographically valuable species. Results from a weekly-resolved sediment trap time series (2008–2014) in the northern Gulf of Mexico demonstrate that 92% of Globorotalia truncatulinoides flux occurs in winter (January, February, and March), and that encrusted and non-encrusted individuals represent calcification in distinct depth habitats. Individual foraminiferal analysis (IFA) of G. truncatulinoides tests were used to investigate differences in the elemental Magnesium/Calcium (Mg/Ca) and isotopic composition (δ18O and δ13C) of the encrusted and non-encrusted ontogenetic forms of G. truncatulinoides, and to estimate their calcification depth in the northern Gulf of Mexico. Estimates show that non-encrusted and encrusted G. truncatulinoides have mean calcification depths of 66 ± 9 meters and 393 ± 83 meters, respectively. The Mg/Ca-calcification temperature relationship was validated for G. truncatulinoides and demonstrated that the δ18O and Mg/Ca of the non-encrusted form is a suitable proxy for winter surface mixed layer conditions in the Gulf of Mexico. Care should be taken not to combine encrusted and non-encrusted individuals of G. truncatulinoides for down core paleoceanographic studies. For further information regarding data collection and/or processing methods as well as the associated published manuscript refer to Reynolds and others (2018b).