Secchi disk project reaches the Arctic Circle

Fewer people have sailed through the Northwest Passage between Canada and Greenland than have reached the summit of Mount Everest – but that’s exactly where Dr Richard Kirby’s Secchi disk will be heading to thanks to the crew of the Aventura.

Part of the Blue Planet Odyssey, devised by veteran sailor and author Jimmy Cornell, the Aventura will make the 900-mile journey in eight weeks and collect data on weather conditions, wildlife, phytoplankton levels and microplastics.  

Until relatively recently, the Northwest Passage was inaccessible for most vessels because it was blocked with sea ice.

"The Northwest Passage has only been occasionally ice-free since 1999 so before this time we have very little data," Dr Kirby told the BBC, in an interview with Environmental Reporter Mark Kinver.
"Of course, there is data from the western and eastern sides of the Passage. For example, we do know that one of the first consequences of ice-free water in the Arctic was when plankton scientists noticed the appearance of a Pacific diatom (Neodenticula seminae) in the Atlantic." 

The eight-strong crew, which includes 14-year-old Nera Cornell, who is believed to be the youngest Briton to sail the route in the Arctic Circle, will be taking measurements using a device known as a Secchi disk, a white disk measuring 30cm in diameter. It is lowered into the water on the end of a tape measure, and when it is no longer visible from the surface, the reading - known as the Secchi depth - is recorded.

"It is a very robust method and not prone to error and it is a good measure of phytoplankton abundance," Dr Kirby said."This expedition will give us the first Secchi-disk data from the Northwest Passage, which will establish a baseline for future studies. When we go back in future years, we will be able to look at when it changes because we are there at the beginning (of an ice-free era). Will we, on this trip beat the Secchi-disk record, which stands at 79.5m in the Atlantic?"

The Secchi disk, invented in 1865 by Angelo Secchi - the Pope's astronomer - is a circular disk that is used to measure water transparency in oceans and lakes.

The concept had long been used as a navigational tool by sailors. By lowering a dinner plate beneath the waves and measuring the depth it disappeared, it provided the crew with an indication of what ocean current they were currently sailing through.

As well as a partnership with Unesco's Intergovernmental Oceanographic Commission (IOC), the crew will also be collecting data for US researchers and plastic pollution reduction organisation 5 Gyres.