batch_auto_20260713 202607131256465730 BOEM ESP geoESPIS ESPIS@boem.gov Bureau of Ocean Energy Management Exploring radium isotopes as tracers of groundwater inputs, flushing rates, and produced water in Cook Inlet University of Alaska Fairbanks University of Alaska Fairbanks This project tested novel methods for tracing the flow of seawater and its dissolved constituents into, through, and out of Kachemak Bay, Alaska. Oceanographic surveys in Kachemak Bay collected radium isotope samples to assess the feasibility of creating radium budgets to characterize groundwater inputs, a potentially dominant source of freshwater, carbon, and nutrients to the Gulf of Alaska. The low concentration of 223Ra in seawater led to challenges in the collection and analysis of this isotope. Instead, we analyzed a select group of samples for longer-lived Ra. Results indicated that offshore waters that enter Kachemak Bay from the Northern Gulf of Alaska are relatively enriched in long-lived radium, violating a key assumption needed to perform residence time calculations.\n Radium (Ra) has been used to trace the flux of produced water in the coastal system, but in a river-dominated system, the naturally occurring Ra from rivers may obstruct the signal of Ra from other sources. We sampled six major rivers flowing into Kachemak Bay to determine the relationship between the concentration of Ra in rivers and watershed characteristics. We found that Ra from sources other than rivers, such as groundwater, could only be detected in areas with minimal river discharge or further offshore. 396926 U.S. Department of the Interior, Bureau of Ocean Energy Management, Environmental Studies Program https://doi.org/10.13039/100012475 M20AC10016 10.67297/9A1E5A https://boem.gov/awardpages/100314