On the Cooling and Freshening of Antarctic Intermediate Water in the South Pacific Ocean Between 1970 and 2018

• Main Author: Racioppi, Alexis
• Other Authors: College of Arts and Sciences, Environment, Ecology, and Energy Program - Environmental Science, Cable, Jaye
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: Antarctic; Lyttelton; Pacific; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://doi.org/10.17615/zr2e-k427; https://cdr.lib.unc.edu/downloads/vx021m571?file=thumbnail; https://cdr.lib.unc.edu/downloads/vx021m571

Global warming is a driver of sometimes subtle shifts in climate patterns. One such area where subtle changes occur is deep ocean water formation, where alterations in processes regulating water density may impact surface conditions that determine water mass density (e.g., precipitation/evaporation, warming/cooling). The Antarctic Intermediate Water mass (AAIW) forms as an amalgamation of multiple water masses at the Antarctic Polar Front and spreads northward into all ocean basins. This feature of the AAIW makes it especially interesting for identifying how climate change impacts deep water formation, as the presence of the AAIW in all of the southern ocean basins allows scientists to use it as an early warning sign of climate change. Modern climatic processes, such as increased precipitation and rising surface ocean temperatures, influence the conservative temperature and salinity characteristics of the waters contributing to the volume of the AAIW, thus influence the characteristics of the AAIW itself. The AAIW should retain the signatures of temperature and salinity change at the time of its formation as it sinks and travels throughout the South Pacific Ocean during thermohaline circulation. In March and April of 2018, the expectation of preserved temperature and salinity change was tested aboard the Sea Education Association vessel SSV Robert C. Seamans. This senior honors thesis research sought to calculate rates of temperature and salinity change in the South Pacific AAIW from 1970 to 2018 on multiple time scales at both the upper boundary (700-800 m) and core (950-1050 m) of the water mass. CTD data collected during the six-week SEA cruise from Lyttelton, NZ, to Pape’ete, French Polynesia, were compared to historical cast data from the 2018 version of NOAA’s World Ocean Database to derive these temperature and salinity trends. For the sampled region of the South Pacific in my study, the AAIW was found to be experiencing freshening at both upper boundary and core depth zones, with increased freshening in ...