The oldest evidence of human impact on the marine environment?

John Smol of Queen's University in Ontario & Marianne Douglas from the University of Toronto have found that lakes near abandoned Thule whaling sites are often loaded with nutrients and contain many types of diatoms that are different from those found in other lakes.
Take for example the Thule people who abandoned Somerset Island about 400 years ago, probably due to a decline in bowhead whales. James Savelle of McGill University, the archaeologist on the team, estimated that the Thule people used up to 60 percent of each whale carcass."They used bones (for rafters and wall supports), blubber for heat and the meat as food," Smol said. "They were an ecologically efficient people."
Efficient certainly, but they still made an impact on their environment by the waste products they left behind. This must though be put into context: we are talking about microscopic evidence of their impact here, not the destruction of forests and waterways. If modern man can say that they have as little effect on the environment as the Thule people we can truly say we have walked softly.