Award: OCE-2122886

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 following the cruise track shown in Figure 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. The sources of these elements along the transect, include hydrothermal vents, dust, and the Chilean oceanic shelf.

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. Our measurements of these metals provides understanding of the mechanisms by which dissolved iron and manganese are introduced to deep ocean waters by submarine hot springs along the volcanically active mid-ocean ridges and how these metals may eventually be transported upward (upwelled) into surface waters of the Southern Ocean, where they fuel phytoplankton growth. Our project results suggest that two mid-ocean ridges are important in this regard, the Southern East Pacific Rise, from which hot-spring-derived dissolved iron and manganese are present on the deep ocean near 80W (Figure 2), and the Pacific-Antarctic Ridge, from which hot springs discharge iron- and manganese-rich waters that appear to be rising towards the surface ocean near the ridge axis at 60S (Figure 2).

In addition, we are using our measurements of the concentrations of dissolved manganese (and aluminum) in surface waters of the Southeast Pacific to estimate the rate of deposition of continental soil dust to the ocean in this ocean region (due to the very low concentrations and technical issues, the aluminum data may not be of sufficient quality to make this estimate).  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 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 that may change the supply of dust to the surface ocean and the magnitude of the coastal sources of these metals to the ocean.

Figure 1. Map showing the track of the U.S. GEOTRACES GP17-OCE cruise, including the meridional section (north to south, in green) and zonal section (west to east, in red).

Figure 2.  Water column concentrations (indicated by color scales) of dissolved iron (upper panels) and manganese (lower panels) along the N-S meridional (left panels) and W-E zonal (right panels) sections of the GP17-OCE cruise track. The elevated Mn concentrations in the surface ocean between 20S and 50S allow us to estimate the input of dust to this part of the ocean. The higher concentrations near 60 S are from submarine volcanic hot-springs. The higher Mn concentrations in the shallow ocean near the coast of Chile are likely sourced from the ocean shelf.  The higher Fe and Mn in the deep ocean near Chile are likely from distal hydrothermal sources, however the shelf may also contribute to the observed enrichments.

Last Modified: 03/13/2026
Modified by: Joseph A Resing