Marine chemistry of a fiord:
Doubtful Sound, New Zealand

Barrie M. Peake, Ph.D.
University of Otago, New Zealand

Wednesday, July 26, 2000
3:00 p.m.—Pacific Forum

Fiords are drowned lower reaches of valleys formed by glacial action which gives them characteristic features of deep basins separated from the open ocean by submarine sills. They also have steep sides which can shade their waters for much of the day, and they often have significant fresh water input from rivers, waterfalls and glaciers. This outgoing surface layer mixes with the underlying seawater to give an up-fiord estuarine-type circulation pattern.

Doubtful Sound is one of fourteen main fiords formed 15,000 years ago in the South-West corner of New Zealand. It has additional features of significant anthropogenic input of freshwater from the discharge of an 800 MW hydroelectric power plant as well as very high annual rainfall (around 20 ft). It also has experienced an increase over recent years in the intensity of UV-B radiation arising from the ozone depletion over the Antarctic in springtime.

All these features make for some unique chemistry. This talk will present the results of initial studies of the spatial and seasonal variability in salinity, temperature, and the levels of nutrients, chlorophyll and dissolved oxygen within Doubtful Sound. The variation in light intensity through the freshwater and saltwater layers will also be discussed in relation to the photochemical production of H₂O_2.

Next: Issues for science and management of the Great Barrier Reef Marine Park