Marine Ecology of Alaska
The Waters of Southeast Alaska, much like the waters of the Gulf of Maine, are extremely high in biological productivity. The reasons for this are, or course, quite complicated, but we can summarize the various factors that make these waters so productive quite easily. In order to have a highly productive marine environment you need two basic ingredients... cold, oxygen rich water, and a lot of nutrients mixed into the surface layers of the ocean. Southeast Alaska has both of these. The waters of Southeast Alaska are derived from the "Japanese Current" that flows eastward across the North Pacific and passes just beneath the Aleutian chain of islands of western Alaska before tuning south and filling the bays and fjords of "Southeast". This cold current is rich in oxygen that comes from the photosynthetic activities of billions of tiny plants called "phytoplankton". These tiny plants are like the "grass of the sea"... they begin the food chain that feeds everything else in the ocean. These tiny plankton are fed upon by tiny animals (zooplankton), which are, in turn, fed upon by small fish, larger fish, seals, sea lions, seabirds, and whales. All the while the phytoplankton is photosynthesizing (producing their own foods, in this case sugar, by combining sunlight and carbon dioxide) and one of the byproducts of this photosynthesis is oxygen. Some of the oxygen produced by these little plants escapes into the atmosphere and enriches it with the oxygen that we breath. Thus much of the oxygen that birds, bears, and even humans need to breath comes from the sea (not just trees and plants on land). We owe a great debt of gratitude to these tiny plants as they are an essential part of transforming our seas and atmosphere into one suitable to life as we know it. But not all of the oxygen the plankton produces escapes into the atmosphere. Because the waters of the Japanese Current (and therefore Southeast Alaska) are quite cold, the ocean retains much of its dissolved oxygen Warm seawater has a much reduced ability to hold onto dissolved gasses, and is thus much lower in oxygen content. I know this seem a little counterintuitive, so let me give you an example. Imagine you pour for yourself two glasses of soda. Then you leave one glass uncovered on the kitchen counter overnight, and one glass (also uncovered) in the refrigerator overnight. Which would you rather drink in the morning? Probably neither... most of us don't drink soda in the morning! But if you had to I bet you'd drink the one from the fridge. The soda that was left in the refridgerator stayed cold all night, and thus retained the ability to hold onto dissolved gas (in this case carbon dioxide) and stayed somewhat "crisp". The glass left on the kitchen counter warmed and lost its ability to hold onto dissolved gasses and went "flat". The same principle is at work in the ocean as well. Thus cold seawater is more oxygen rich that warm seawater!
An Orca Passing in front of the Mendenhall Glacier near Juneau, Alaska
So
now we have cold water with plenty of oxygen in it, but how about
nutrients? The fjords of Southeast Alaska are very deep... over
10,000 feet in places... and much of the organic nutrients from decaying
plant and animal matter settles in the deep, dark depths of these fjords
far below the reach of sunlight and completely inaccessible to fish and
other animals. In order for these nutrients to be utilized by most
living things, some mechanism must bring these nutrients to the surface.
In most cases this mechanism is "upwelling". Upwelling is a process
that occurs in the Gulf of Maine when currents and tides collide with the
steep sides of Stellwagen Bank and get forced upwards. In southeast
Alaska a very similar phenomena takes place when currents and tides, which
flow very rapidly through the narrow fjords, collide with submerged hills
and crash into submerged mountainsides. When this happens, nutrients
are swept up to the surface where they can mix with the sunlight that
filters down through the clouds and this mixture of nutrients and sunlight
causes an explosion of photosynthetic phytoplankton. The plankton,
remember, is the base of the food pyramid in the sea. Thus when you
have a huge abundance of plankton (a wide base to the food pyramid) you
can support a lot of life (you can have a tall pyramid)! These are
the basics of why the waters of Southeast Alaska are so productive and why
one can find such an abundance of salmon, herring, sand lance, seals, sea
lions, and whales in the region
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