Marine Reservoir Effect

The Marine Reservoir Effect is a phenomenon that complicates radiocarbon dating. Organisms in the ocean consume carbon that is often significantly older than the atmospheric carbon absorbed by land-based plants and animals. As a result, samples from marine life, or from humans and animals that ate large amounts of seafood, can produce radiocarbon dates that appear much older than their true age.

Correcting for this effect requires detailed accounting of oceanic carbon dynamics, which vary over time. The impact differs substantially by location, depending on factors such as water depth, upwelling currents, and inputs of freshwater.

Typically, affected radiocarbon dates appear about 400 ¹⁴C years older than they would otherwise. However, the offset is highly variable in space and time and can reach 800 to 1,200 ¹⁴C years in Arctic regions.

In 2013, archaeologists at the Gottorp Castle Museum conducted an experiment to test how fish preparation in pottery influences carbon-14 measurements. They prepared fish in a newly made clay vessel over a fire, ensuring some residue stuck to the pot. When they tested the pot and the burnt crust, the sample returned a ¹⁴C age of about 700 years old. At the time, researcher Felix Riede suggested that such dietary or preparatory factors could cause the carbon-14 method to be off by as much as 2,000 years in certain contexts.

Richard III
An example of the Marine Reservoir Effect was the discovery in 2012 beneath a parking lot in Leicester of the remains of the English king Richard III (1452-1485). Historical records confirm he died in 1485 at the Battle of Bosworth Field. However, initial radiocarbon dating produced results that were too early[1].

Tests, done at the Scottish Universities Environmental Research Centre (SUERC) dated the bones to around AD 1430–1460 (95% probability), while tests at the University of Oxford dated them to around AD 1412–1449 (95% confidence).

These dates predated Richard’s known death by decades, initially raising questions about whether the skeleton belonged even to him. Stable isotope analysis (particularly of nitrogen-15) revealed the discrepancy: Richard had a high-protein diet rich in seafood, especially in his later years as a high-status noble. Medieval religious fasting rules often required fish consumption, and his royal lifestyle included luxury items like fish.

Because of the marine reservoir effect, the 'old' carbon from his seafood-heavy diet made his bones appear older in radiocarbon testing. After correcting for this dietary input using stable isotope ratios and applying Bayesian statistical modelling (while also constraining the date to before the 1538 Dissolution of the Monasteries), the calibrated range shifted to approximately AD 1475–1530 (69% confidence) or broader estimates like AD 1450–1540 (95.4%). This range comfortably includes 1485, resolving the apparent contradiction and supporting the identification of the remains.

The Richard III case highlights why marine reservoir corrections, and dietary reconstructions via isotopes, are essential for accurate radiocarbon dating of human remains. Without them, high-seafood diets can introduce offsets of hundreds of years. Similar issues arise in coastal or marine-influenced archaeological sites.

Egyptian Pharaohs
But what happens if you apply the Marine Reservoir Effect to, say, Egyptian pharaohs of the Old Kingdom? That was a period spanning from circa 2,700 BC to circa 2,200 BC. The Old Kingdom could be younger by hundreds of years, maybe even thousands of years. Which means the whole timeline of ancient Egypt could be in disarray. And, if that's true, writers like Immanuel Velikovsky (1895-1979) and Alfred de Grazia (1919-2014) would be vindicated after all these years. They always claimed that the Egyptian timeline was far younger that historians claimed.

[1] Jack Wilkin: Isotopes and Richard III in Historic UK - 2020. See here.