ASSESSING SAN PEDRO BASIN BOTTOM WATER DYNAMICS: MIT GENERAL CIRCULATION MODEL OUTPUT VERSUS USC SPOT IN-SITU MEASUREMENTS

Dichlorodiphenyltrichloroethane (DDT) is a persistent organic pollutant that poses long-term ecological risks through bioaccumulation in marine organisms. It was extensively dumped along the Southern California coast, including the San Pedro Basin, where DDT has now accumulated in the bottom basin. Understanding the movement of bottom water masses—driven by oceanographic processes like flushing events from sill overflows, and changes in temperature and salinity—is crucial for assessing the distribution and potential re-exposure of DDT. This project evaluates how well the MIT General Circulation Model (MITgcm) reproduces bottom water characteristics by comparing model output with in-situ observations from the University of Southern California San Pedro Ocean Time-series (SPOT) collected between 2016 and 2017. We focus on the model’s representation of temperature and salinity profiles, and emphasize the deepest sill at 740 meters in driving bottom water exchanges. Initially, the MITgcm indicated warmer, saltier bottom water and increasing temperatures with depth, contrasting with SPOT observations. After May 2017, model predictions improved, aligning more closely with the observed inverse relationship between temperature and salinity at 800 meters depth. Despite these improvements, the model exhibits a freshwater bias, especially in the last three months of each year, and shows evidence of excessive vertical diffusion. Accurately modeling these dynamics is vital for understanding how DDT disperses in the San Pedro Basin and assessing risks of pollutant exposure in the ocean.

Presentation Preference: Poster

Primary Presenter: Katie Chan, University of California Los Angeles (chanks7550@gmail.com)

Authors:

Katie Chan, University of California Los Angeles  (chanks7550@g.ucla.edu)

Dr. Sarah Gille, University of California San Diego  (sgille@ucsd.edu)

Dr. Saulo Soares, University of California San Diego  (saulo@ucsd.edu)