World’s largest logjam in the Arctic stores 3.4 million tons of carbon

“To put that in perspective, that’s about two and a half million car emissions for a year. That’s a sizeable amount of carbon. We have great knowledge about carbon in other forms, like dissolved or particulate organic carbon, but not what we call ‘large carbon’ — large wood. That’s starting to change,” said Alicia Sendrowski, a research engineer who led the study while at Colorado State University, in a statement. 

Mapping the delta

The team used satellite imagery to conduct a detailed examination of wood deposits found in the Mackenzie River. They scanned nearly 5,000 square miles (13,000 square kilometers) of delta using high-resolution imagery to map the logjam. During the fieldwork, they also took measurements and sampled the wood using radiocarbon dating. Some logs date from 1950, while others date from around 700 CE.

According to the investigation, there could be many such logs buried in the soil or submerged underwater that were not visible through aerial imagery. If these are added together, the total amount of carbon stored in the delta's wood could be double the amount present. This particular river delta was chosen for the study because it has been identified as a "hotspot" of carbon storage due to the presence of carbon-rich soils. 

The study also sheds light on wood preservation and its significance in times of climate change. It adds to our understanding of the woody deposits found throughout the Arctic. 

“There’s been a lot of work on fluxes of carbon from water and sediment, but we simply didn’t pay attention to the wood until very recently. This is a very young field of research that is developing quite fast. And it’s important to study this wood not only for the carbon cycle, but in general for our understanding of how these natural fluvial systems work, how the rivers mobilize and distribute the wood,” said Virginia Ruiz-Villanueva, a fluvial geomorphologist at the University of Lausanne who was not involved in the study.

The study was published in Geophysical Research Letters.

Study abstract:

The Mackenzie River Delta (MRD) has been recognized as an important host of river-derived wood deposits, and Mackenzie River wood has been found across the Arctic Ocean. Nevertheless, we lack estimates of the amount of carbon stored as wood and its age in the delta, representing a gap in carbon cycle estimates. Here, we use very high-resolution satellite imagery and deep learning to map wood deposits in the MRD, combining this with field data to measure the stock and age of wood-based carbon. We find >400,000 individual large wood deposits, collectively storing 3.1 × 1012 g-C, equating to 2 × 106 g-C ha−1 across the delta. Sampled wood pieces date from 690 AD to 2015 AD but are mostly young with ∼40% of the wood samples formed after 1955 AD. These estimates represent a minimum bound on an important surficial, potentially reactive, carbon pool compared to other deeper carbon stocks in permafrost zones.