Plants and animals living along the coast of the Mackenzie Delta in the Canadian Arctic have been devastated by a salt-water flood, made more severe by climate change. After local Inuvialuit natives told them that where they could hunt had changed, Canadian scientists showed the damage was unrivalled during the period they could document by studying tree rings and lake sediments. “The impacts of this storm were truly unique in the last millennium,” commented biologist John Smol of Queen’s University in Kingston, Ontario.
“The Inuvialuit brought to our attention the occurrence of a large storm surge that happened in late September 1999,” said Joshua Thienpont, a postgraduate student at Queen’s. “The region was frequented by members of the local communities to hunt waterfowl that would nest near the delta front. The Inuvialuit hunters noted that, after the storm, birds no longer nested there.” At that point, however, it wasn’t clear how common such events were, so Smol, Thienpont, and their colleagues exploited the nearby “natural archives” to try and find out. One such record of previous surges came because they thought that plants not used to being covered in saltwater would grow less quickly when under the flood waters. “With this in mind, we sampled alder shrubs and measured their growth rings using a microscope and specialized measuring system,” said Michael Pisaric, a geographer at Ottawa’s Carleton University.
Surging far inland
Sediments taken from a lake six kilometres away from the coast offered a perspective further into the past, as they contain the remains of tiny organisms that have lived in the lake through history. “Among these fossils are the remains of different groups of algae, the microscopic plant-like organisms at the bottom of the aquatic food web,” Thienpont said. “One particular algal group, called diatoms, are an excellent indicator of changing salinity levels in the lake. Some diatom species live only in low-salinity waters, while others live only in salty conditions.” Taken together the analysis of vegetation and diatoms, published in a Proceedings of the National Academy of Sciences of the USA paper online ahead of print last Monday, showed just how unusual the 1999 surge was.
The research team collected 107 tree-ring samples from live, stressed and dead specimens at 10 sites across the study area in 2006 and 2007. “The storm led to a prolonged growth decline that was longer than any of the previous events and more importantly caused a massive death of almost all the vegetation across the impacted area,” Pisaric said. “More than 50% of the dead shrub samples collected and dated died in 1999 or 2000. The remaining samples died in the several years following. There was no evidence that previous storm surges led to mass mortality similar to the 1999 storm.”
Invasion by sea
Thienpont and Queen’s colleague Holly Nesbitt studied the lake sediment in Smol’s lab, and discovered an increase in the amount of salt-loving diatoms immediately following the 1999 storm. This demonstrated that the lake had become saltier. “Over a decade later, these species are still dominant, which leads us to conclude the lake has not recovered from the impacts of the storm,” Thienpont explained. “At no other point in the history of the lake during the last 1,000 years did we find any evidence of saltwater algae having lived in the lake.” That evidence, says Smol, showed that no similar surge had occurred in the past millennium.
The team emphasises that while the storm surge itself may “just” be an isolated severe weather event, changing conditions in the Arctic link its uniqueness to climate change. “Because of the dramatic declines in sea ice cover and duration during recent decades, combined with rising sea levels, this large storm resulted in a massive amount of saltwater moving into the Mackenzie Delta,” Thienpont said. “Had this storm occurred a month later when the ocean was capped by ice, for example, there probably would not have been an impact on the ecosystem.” As such, they feel that discovering the significance of this one event – which has left much of the landscape lifeless – can be used to help understand impacts climate change may have in other parts of the world. “As we look to the future, where even greater decreases in sea ice, further sea-level rise and changing patterns of stormsare predicted,” Thienpont said, “we are very worried that other low-lying ecosystems are at risk of similar events.”