Understanding Regional Sea Level Variations and Budget Closures of Seismically Active Oceans

Author:

Y. Tony Song (Jet Propulsion Laboratory)

Co-Investigator(s):

Benjamin Hamlington (Jet Propulsion Laboratory)

Collaborator(s):

Jae-Hong Moon (Jeju National University, South Korea)

Hyeonsoo Cha (Jeju National University, South Korea)

Project Summary:

Understanding the physical processes behind 30 years of altimetry sea-level variations has significant societal benefits, particularly for low-lying coastal communities. However, achieving accurate regional sea-level budget closure in areas with strong submarine seismic activities has been challenging.

Recent assessments of regional sea-level variations and budget closure for the northwestern Pacific marginal seas during the satellite altimetry era have shown that seismicity plays a significant role (Cha et al., 2023). Submarine earthquakes, such as the 2004 Sumatra Mw9.1 earthquake and the 2011 Tohoku Mw9.0 earthquake, have permanently altered local bathymetry and ocean mass redistribution. The post-seismic effects, which can last for years, are among the largest contributors to the regional sea level rise (SLR) budget. Similarly, a study on relative sea-level rise by Oelsmann et al. (2024) demonstrates that vertical land motions, particularly in those seismic active regions, play an equally significant role in its projection as climate-driven processes. These findings lead us to hypothesize that seafloor deformations can significantly redistribute ocean mass and alter regional SLR trends, particularly in seismically active oceans.

This project aims to understand the physical processes behind regional sea level variations and budget closures of seismically active oceans. Building on our previous work, we will utilize gravimetry (GRACE/GRACE-FO) measurements to derive seafloor deformations caused by large earthquakes. Our research objectives are as follows:

1. Assessment of Regional Sea Level Variations and Budget: We will focus on four seismically active regions: the northwestern pacific, Indo-Pacific seas, Oceania Nations and Territories, and the South American West Coast, each with a distinct geophysical setting.
2. Quantification of Ocean Mass Redistribution (OMR): We will derive the regional mass changes from GRACE/GRACE-FO and employ a global non-Boussinesq regional ocean modeling system (NB-ROMS) allowing seafloor motions to analyze the underlying dynamic processes.
3. Understanding Seismic-induced bottom pressure torque: We will use both data-driven and model-based approaches to investigate the dynamic impact of seismic-induced seafloor deformation on ocean bottom pressure torque and OMR, including changes in Kuroshio transport.
4. Data Products: This project will produce a global seismic-corrected OMR and ocean bottom pressure dataset, which will be instrumental in ocean data assimilation efforts to reduce uncertainties in global and regional sea-level rise (SLR) budgets.

This project is expected to significantly advance our understanding of the full-length altimetry data on the aspects of regional sea-level variations and budget closures for a precise climate record from reference altimetry missions. Our multidisciplinary team, which includes experts in altimetry oceanography, seismology, and ocean modeling, will focus on ocean circulations, mass redistribution, and regional sea-level changes with direct societal implications. By utilizing various data and models, this project directly supports OSTST priorities, particularly in "2.1 Large-scale Ocean physics: studies that improve our understanding of large-scale physical processes, such as ... global mean and regional sea level variations and budget of satellite altimetry records."