Melting Arctic Ice = New Fishing Bonanza As Fleets . . . Oh, No, Wait . . . Oops.

[hatrack]

EDIT

The upshot is more plankton, farther north. That attracts more fish. In 2000 Atlantic cod were caught throughout the Barents Sea. By 2012 their distribution was skewed towards the northern part of that sea. Stocks of capelin (a small fish eaten by cod) used to be concentrated south of Svalbard, at latitude 75°N. In 2012 this had moved to 78°N. Some found their way as far up as 80°N.

Which all sounds most promising. But many researchers think it will not continue. First, the central Arctic is too deep for some important species, such as the polar cod (which belongs to a different genus from the Atlantic cod, and can live farther north). Young polar cod (those less than a year old) are pelagic, meaning they live at or near the surface. Those one or more years old are benthic, meaning they live near the bottom. In the Beaufort that bottom is 200 metres down. In the central Arctic it descends to about 4,000 metres, which is too deep for polar cod to survive.

A second reason why there may be no bonanza is acidification of the ocean. When water absorbs carbon dioxide, it produces carbonic acid. More CO₂ means oceans everywhere are becoming more acidic, but the phenomenon is particularly marked at high latitudes because cold water absorbs CO₂ more readily than warm water does. The retreat of the ice also exposes ever more sea to do the absorbing. Cruises by the United States Geological Survey and the University of South Florida over the past three years have found rising carbonic-acid levels north of Alaska. They have also discovered that the shells of many organisms in the area are short of aragonite, a form of calcium carbonate that gives them strength, but whose formation acid discourages. Weaker shells means fewer shelled organisms and less food for fish.

The most important reason, though, for thinking that global warming will not produce an Arctic feeding frenzy is that it may increase ocean stratification. This is the tendency of seawater to separate into layers, because fresh water is lighter than salt and cold water heavier than warm. The more stratified water is, the less nutrients in it move around. Most free-swimming sea creatures are pelagic. Algae need light, so must live near the surface—as must the zooplankton and other animals that need the phytoplankton. When they die, all these organisms sink to the bottom, where they become food for benthic creatures. Once they have been consumed their component molecules, including nutrients such as nitrates, phosphates and iron, are stuck in Davy Jones’s locker. For the surface to be productive, the locker must be opened and the nutrients lifted back up, so that they can feed the growth of phytoplankton.

EDIT

http://www.economist.com/news/science-and-technology/21571386-global-warming-may-make-northernmost-ocean-less-productive-not-more

[geckosfeet]

1. A teaching moment - one lesson being that biology/ecology are much more complex than

we like to think. Just because we think something makes sense (warmer water --> less ice --> more plankton --> more fish!) and has some kind of disconnected logic, does not mean nature will agree with us.