Paleolimnological data from three high-arctic ponds on Cape Herschel,
Ellesmere Island, Canada, show that diatom assemblages were relatively
stable over the last few millennia but then experienced unparalleled
changes beginning in the 19th century. The environmental factors causi
ng these assemblage shifts may be related to recent climatic warming.
Regardless of the cause, the biota of these isolated and seemingly pri
stine ponds have changed dramatically in the recent past and any hopes
of cataloging natural assemblages may already be fruitless.