CHARACTERIZING THE STABLE OXYGEN ISOTOPIC COMPOSITION OF THE SOUTHEAST PACIFIC OCEAN AND SOUTHERN OCEAN

Stable oxygen isotopes are useful tools for understanding hydrological processes. Processes such as precipitation, glacial melt, and sea ice formation/melt create a water mass with a specific oxygen isotope value of the seawater, δ¹⁸O_SW, making δ¹⁸O_SW an effective tracer of water masses and water mass origination. There has been an increasing scientific demand for δ¹⁸O_SW data in general circulation models, as understanding the spatial distribution and variation of δ¹⁸O_SW throughout the global ocean is fundamental in modeling paleoclimate and paleoceanography; however, many areas of the modern oceans have little to no δ¹⁸O_SW data. The Southeast Pacific and Southern Oceans are particularly data deficient, especially in the deep ocean. Additionally, understanding deep-water mass origination in the Amundsen Sea region of the Southern Ocean is becoming progressively important as increasing glacial meltwater input has been observed to decrease bottom water formation and affect stratification in the upper ocean.

The principal goal of this research is to fill a δ¹⁸O_SW data gap and evaluate the controls on the spatial distribution of δ¹⁸O_SW regarding the water masses of the Southeast Pacific and Southern Oceans. The U.S. GEOTRACES GP17-OCE and GP17-ANT scientific cruises collected seawater samples along transects that extended from Tahiti to Chile and from the Antarctic continental shelf in the Amundsen Sea, respectively. Samples for stable oxygen isotope analysis were collected from 31 stations from the GEOTRACES GP17-OCE expedition, including samples from the South Pacific subtropical gyre crossing multiple oceanic fronts and the Antarctic Circumpolar Current. Samples for stable oxygen isotope analysis were collected from 27 stations from the GP17-ANT expedition and included stations across the Amundsen Sea continental shelf. Water masses of the Southeast Pacific and Southern Ocean will be characterized through stable oxygen isotopes to trace them through their circulation in the South Pacific and Southern Oceans. Preliminary analysis suggests that the deep water masses throughout the South Pacific show different isotope signatures. The distribution and transport of glacial meltwater into the Amundsen Sea will also be investigated through δ¹⁸O_SW analyses.