Quantifying solute fluxes through Submarine Groundwater Discharge (SGD) into the ocean is challenging due to the complex groundwater flow mechanisms in coastal aquifers and subterranean estuaries. These mechanisms operate across diverse temporal and spatial scales, from wave- and tide-driven circulation to seasonal variations, and density-driven circulation that spans thousands of years. This study, based on a comprehensive dataset from coastal aquifers and new analyses of major elements (Ca, Mg, Na, K, and Sr) in subterranean estuaries, demonstrates that these elements are predominantly influenced by longer-term seawater circulation. Using a multi-element Monte Carlo ocean budget, we quantified the long-term seawater circulation flux at approximately 1,000 km³/year. Additionally, we developed a method to quantify local long-term circulating seawater fluxes in the field, employing an array of piezometers and seepage meters. A case study from Indian River Bay, Delaware, identified the long-term seawater component as contributing about 10% of the total circulating seawater discharge, based on major element concentrations.