STEMSeas (STEM Student Experiences Aboard Ships) III is an NSF-funded project designed to address the persistent under-representation of minoritized demographic groups in STEM, specifically, in the geosciences by designing 5-10 day learning experiences at sea aboard ships for undergraduate students. Informed by an ecosystem model, key program components include: experiential learning; mentored experiences during ship transits; student participation in data collection; geoscience inquiry; career discussions; and reflection. Analogous to the braided river, the project engages undergraduate students in geoscience learning at critical transitions in their academic pathways, for example, prior to selecting a major, prior to choosing graduate school, and/or transitioning from a 2-year to a 4-year institution. STEMSeas III builds on 6 years of implementation and expands the program scope to include a project team of 4 Principal investigators with additional expertise in science communication and geoscience education research. The STEMSeas III project aims to: improve self efficacy with respect to geoscience knowledge; increase student understanding of pathways to geoscience professions; support transformative experiences (positive shifts in perspective of the geosciences); and broaden representation in STEM fields.