Award: OCE-1736906

This project constructed a map of the dissolved trace elements aluminum (Al), iron (Fe), and manganese (Mn) at 41 locations in the Pacific Ocean during a 62-day research cruise from Alaska to Tahiti (from September 18^th to November 24^th, 2018) as part of the US GEOTRACES Pacific Meridional Transect (PMT). The PMT research cruise is part of the international GEOTRACES program which is designed to improve understanding of global ocean biogeochemical cycles by mapping the distribution of a variety of reactive trace elements. For example, the growth of microscopic oceanic plants in surface waters depends critically on the availability of, amongst other things, dissolved Fe. In addition, the distribution of Fe and other trace elements records current and past chemical and biological processes in the ocean. The PMT cruise track was designed to include multiple unique oceanic hydrographic conditions and thus the results of this work provide important insights into diverse global ocean processes. By using a shipboard flow injection analysis system to provide near real-time measurements of these trace elements, it allows shipboard personnel to modify sampling strategies thus allowing unexpected discoveries to be further investigated resulting in maximum scientific return. The shipboard results also help identify any sampling contamination problems that are a constant risk when collecting these low-level trace elements.

The dissolved Al distribution which is not a required element by oceanic plants serves as an effective oceanographic tracer. Its distribution in the ocean records the chemical signature of mineral dust that has been blown over the oceans from the continents and then deposited by rain or gravitational settling into the surface ocean. Since this acts as a tracer for lithogenic material inputs, it also records where dissolved Fe coming from mineral dust is also added to the ocean.  The dissolved Al can also be used to examine the dispersion of mining effluent as well as sediment resuspension processes that can occur along the edges of the ocean.

Intellectual Merit: The basin-wide data set of dissolved trace elements during the GEOTRACES project will significantly improve our understanding of how global ocean biogeochemical cycles operate.  The dataset will be used to improve and constrain coupled ocean/atmosphere nutrient and carbon cycling models and permit more accurate prediction of the role played by atmospheric dust deposition in providing biogeochemically important trace elements to the surface ocean and the mechanisms by which they are transferred to the interior of the ocean.

Broader Impacts: A graduate student benefited from participation in the GEOTRACES project that brought technologies and scientists from different institutions together creating a collaborative cohort that will outlast the specific project.  Additionally, using our local contacts we developed a collaboration with several faculty members from the University of Hawaii at Hilo and arranged a visit and tour of the ship during its port call in Hilo for their students.  The GEOTRACES project also provided an initial survey of background chemical conditions in the water column of the Clarion-Clipperton Fracture Zone between 15ºN to 5 ºN, which is a region scheduled for the seabed mining of manganese deposits.  The United Nations law of the sea requires a baseline assessment (physical, geochemical, biological) of this area before mining commences, as it will likely produce large-scale sediment resuspension during mining and will produce detritus from shipboard processing of nodules.

 

Last Modified: 01/27/2024
Modified by: Mariko Hatta