The trough is about 3.5 km (about 2 miles) below sea level but there is no ocean water there. Instead, it is filled with ice flowing from the interior of the ice sheet towards the coast. The trough measures about 100 km in length and is 20 km wide, according to the study.
Think about how long 100 km is. The District of Columbia is 16 km on a side. According to Wikipedia, 100 km is 9/10 as long as the English Channel and not quite as wide as the narrowest point. And it is on land! Think about that with your morning coffee.