Polycom availability with Darling Marine Center, Gulf of Maine Research Institute, and Bigelow Laboratories.
David W. Townsend
Professor of Oceanography
UMaine School of Marine Sciences
Host: Emmanuel Boss
This talk will begin as a general overview of how the Gulf of Maine works in an oceanographic sense. But at the outset, I will show examples of some observations and ideas that have popped up in recent years which suggest the oceanography of the Gulf may be changing, and/or undergoing highly variable shifts in its properties ─ changes that are forcing us to rethink some of our most basic ideas about the workings of the Gulf. First described by Henry Bryant Bigelow a century ago, we all are generally aware, or have been told, that the Gulf is biologically productive ─ and it is, owing to the combined effects of features and processes that are fairly unique to the Gulf of Maine. In the simplest sense, the Gulf can be viewed as a shallow (average depth ca. 150m) semi-enclosed, continental shelf sea, which forms a cul-de-sac along the coastline of eastern North America. More importantly, the Gulf is situated adjacent to a confluence of major ocean currents just offshore: where cold waters from the north meet warm waters from the south. The Gulf’s interior waters, however, are partially isolated from free exchanges with those offshore waters by shallow banks along the Gulf’s shelf edge. Nonetheless, the Gulf of Maine is a dynamic flow-through system driven by variable influxes oft hose different water masses from outside the Gulf ─ water masses that provide both salt and fresh water, nutrients, and which influence the Gulf’s heat budget. Once in the Gulf, those imported water masses are diluted some by rivers (although the main supply of fresh water is from outside the Gulf), and are vertically mixed: They are mixed year round by the Gulf’s large tides (in some areas), and everywhere by winter convection, which bring nutrient-rich waters into sunlit surface layers, this stimulating biological production. It is principally the resulting density contrasts of its different water masses that drive the Gulf’s complex residual circulation. Woven into this rough sketch of the Gulf of Maine will be ideas based on some of my own research interests, including: Ideas about the causes of redtides; Why they and other oceanographic features may be changing, and/or varying significantly among years; Some ideas about why the Gulf may be warming at such an alarming rate, and; Why we need to pay closer attention to ocean acidification.