Award: OCE-2123623

From December 2022 to January 2023, the U.S. GEOTRACES GP17-OCE cruise sailed from Papeete, Tahiti, to Punta Arenas, Chile, aboard the research vessel Roger Revelle (Fig. 1). The aim of this research expedition was to collect samples from the ocean water column and surface waters to document the distribution of a broad suite of trace elements and isotopes in the Southeast Pacific Ocean and Southeast Pacific sector of the Southern Ocean.  As part of the GP17-OCE science program, our NSF-funded project focused on at-sea and post-cruise measurements of three dissolved trace elements, iron, manganese and aluminum, in water samples that were collected during the expedition.

Dissolved iron and manganese are important because they are essential micronutrients that are thought to regulate primary production in surface waters of the Southern Ocean, which holds importance for the ocean-atmosphere exchange of the greenhouse gas carbon dioxide, as well as comprising the foundation of the marine ecosystem in this vast region of the polar ocean. In particular, our measurements of these metals aimed to understand how dissolved iron and manganese that is introduced to deep ocean waters by submarine hot springs along the volcanically-active mid-ocean ridges may eventually be upwelled into surface waters of the Southern Ocean, and thereby support phytoplankton growth in that region.  Our project results suggest that two mid-ocean ridges are important in this regard, (1) the Southern East Pacific Rise, from which hot-spring-derived dissolved iron, but not manganese, appears able to upwell into Southern Ocean surface waters near 80°W (Fig. 2), and (2) the Pacific-Antarctic Ridge, from which hot springs discharge iron- and manganese-rich waters that can upwell to surface waters over the ridge axis near 60°S (Fig. 2).

In addition, we are using our measurements of the concentrations of dissolved aluminum and manganese in surface waters of the Southeast Pacific to estimate the rate of deposition of continental soil dust to the ocean in this ocean region. Dust deposition provides an important source of numerous chemical constituents to the ocean, including micronutrients such as iron and manganese and potentially toxic elements such as lead and copper. The rate of dust deposition to is difficult to constrain over remote open-ocean regions, with aluminum and manganese serving as chemical tracers that we are using to estimate dust deposition, in combination with other measurements made by researchers involved in the GP17-OCE program.

Broader impacts of our project have included the training of graduate students and early-career researchers. In addition, the improved understanding of the oceanic cycling of iron and manganese, and estimates of dust deposition, will advance our ability to predict how ocean biology and chemistry will respond to future environmental changes, such as a warming climate and changes in the supply of dust to the surface ocean.

Last Modified: 11/26/2025
Modified by: Peter N Sedwick