Date of Award


Degree Type


Degree Name

Master of Science in Oceanography


Marine Geology and Geophysics



First Advisor

Rebecca Robinson


>The Subtropical front (STF) is an area of intense mixing between the cold Southern Ocean and the warm subtropical South Indian Ocean. On interglacial-glacial timescales the STF migrates, altering surface chemical and biological conditions as it moves. A recent study interpreted this migration through changes in the isotopic composition of nitrogen in the surface ocean during the Last Glacial Period by measuring the isotopic composition of nitrogen of foraminifera-bound nitrogen in a single species of foraminifera. Relying on a single species interpretation in this dynamic mixing zone may bias toward species-related ecological preferences. Here we explore the possibility that measuring additional species of foraminifera and/or a bulk mixed assemblage may change or even improve understanding of the surface dynamics in this mixing zone. We demonstrated that the species-specific nitrogen isotope values and their distributions were distinct and that they appeared to reflect their ecological preferences. We also found that the bulk assemblage nitrogen isotope values looked most similar to the most abundant species in the assemblage. These results suggest that ecological preferences of foraminifera species need to be considered when selecting a group for paleoceanographic reconstructions in mixing zones. The data also show that the cost of isolating species that are relatively poorly represented may outweigh the benefit to the analysis.

Available for download on Thursday, September 05, 2024