Award: OCE-1756138

This project was part of a larger national program, US GEOTRACES, that collected water samples from throughout the deep Pacific Ocean along a due N-S oriented line extending from the Aleutian Islands in the North Pacific, via Hawaii to Tahiti in the South Pacific along Longitude~150W.The larger GEOTRACES program sought to understand the chemical behavior of a wide range of trace elements and isotopes that can vary as a result of biological and mineralogical processes in the oceans.But our study focused on the so-called noble gases which make up the far, right-hand column of the Periodic Table of the Elements.These elements are known for the level to which they are chemically inert they dont undergo any chemical reactions which makes them particularly useful (especially when analyzed as a group) to learn more about physical mixing processes that happen in the ocean.For the US GEOTRACES program, a particular value that we brought to the program was that we could provide a physical framework of how deep and shallow waters were circulating in the Central North Pacific Ocean which, in turn, provided context for all the other measurements made in other laboratories participating in the same endeavor.There were a series of highlights to what we discovered, just from this study alone.First, one of the elements studied, Helium, showed enrichment in Deep Pacific Waters in the lighter isotope of this element compared to the heavier isotope which provides an unambiguous tracer of input from hot-springs at the deep ocean floor that can be transported thousands of miles across ocean basins.These signals were strongest in the tropical south Pacific and in the tropical north Pacific but decreased closer to the Aleutian islands where release of the heavier isotope (from alpha decay of other radioactive elements) from sediments masked the hydrothermal signals.In the upper ocean, one of the most insightful results from our work were to reveal that we could use measurements of the heavier elements in the noble gas series to investigate seasonal changes in heating of the upper 200m of the Pacific Ocean from sunlight whereas the lighter elements could be used to trace how air bubbles are trapped by and dissolved into that seawater.Two particularly unexpected results from the work were as follows.Close to Hawaii, we found that there was a very strong and shallow input of hydrothermal fluids from the Kamaehuakanaloa Seamount and, combining our analyses with theoretical models, we were able to predict that these shallow, hydrothermally enriched waters might travel across the Pacific to offshore Washington State, Vancouver Island in Canada and perhaps as far as Alaska and the Aleutian Islands where they could deliver important nutrient chemicals to stimulate and enhance biological activity.Separately, using the heaviest noble gas measurements from the deep north Pacific ocean, coupled with ocean circulation models, we were able to derive information from the oldest deep waters on Earth, which carried information about the atmosphere near Antarctica, and how air pressure in that region has varied (with implications for how stormy the weather there must have been), dating back as far as the time of the Roman Civilization, more than 2000 years ago. Last Modified: 01/23/2025 Submitted by: ChrisGerman