Geologists have identified rocks that originated in the deep sea during the early Jurassic era, around 180 million years ago, indicating a deficiency of oxygen in the ocean. These rocks were enriched with carbon atoms, specifically Carbon 12 compared to heavier carbon atoms, known as Carbon-13. Carbon-13 is denser than Carbon-12 due to having an additional neutron. Atoms belonging to the same element but with varying neutron counts are referred to as Isotopes, and the decrease in the ratio of carbon-13 to carbon-12 in rock samples is termed Negative carbon isotope distal.

Previous studies have demonstrated that during the early Jurassic, the release of photocarbon 12 into the atmosphere led to a doubling of carbon dioxide levels and an increase in ocean temperatures by 5°C, equivalent to about 9°F. This warming event is known as the Toarcian Marine Anoxia Event.

Sadly, the specific triggers for this carbon 12 release remain unclear, as there is no defined timeline for the Toarcian events. Previous estimates suggested that rock sections exhibiting low carbon isotopic ratios spanned between 300,000 to 1.5 million years. This uncertainty complicates comparisons between Toarcian warming events and more contemporary warming occurrences. Consequently, an international research team recently employed a high-precision dating technique to ascertain the exact duration of these events.

The team analyzed the Sakuradani tick section in the Tab Basin, Japan. During the early Jurassic, this region was accumulating sediment, including mud, sand, and organic matter near the coastline. The section, approximately 90 meters thick (or about 300 feet), contained layers with negative carbonate isotopic distals. Within the slope, these layers extend from around 33 meters deep to 45 meters deep.

Researchers also identified three layers of rock formed from volcanic ash both above and below the layer containing distal carbon isotopes. The upper ash layer is located about 16 meters within the rock section, while the lower ash layer can be found at approximately 49 and 51 meters. The researchers utilized volcanic ash minerals to accurately date the crystallization age of the layers. They reported that the volcanic ash layers are approximately 182.3 million, 182.5 million, and 182.9 million years old, from youngest to oldest.

These observations indicate that 62 meters (approximately 200 feet) of rock between the ash layers accumulated over a span of 400,000 years. Considering the sediment volume deposited during this time, the researchers concluded that the rock sections with distal carbon isotopes required more than 300,000 years to develop. They estimated that the duration of the Toarcian marine anoxic events was significantly shorter than earlier assumptions, lasting less than 417,000 years, with a minimum duration of 169,000 years.

With this information, the team sought to connect the Toarcian warming event and the associated carbon isotope distal to its source. They hypothesized that the event was at least partially related to volcanic activity during the early Jurassic period, which altered the composition of the surface rocks. This surge of magma to the surface could have caused the rocks to emit carbon dioxide and methane, leading to a rise in global temperatures and releasing 12 photocarbons.

The researchers concluded that volcanic activity was likely responsible for the marine anoxia events during the Toarcian period. They noted that earlier scientists had proposed volcanic mechanisms for other warming events of a similar nature. They recommend that future studies explore the direct impacts of the marine anaerobic events during the Toarcian and quantify the extent of carbon release that occurred.

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