 A
picture from the Gulf of Alaska that has been making the rounds on the
Internet for the last few years -- though particularly in recent weeks
-- shows a strange natural phenomenon that occurs when heavy,
sediment-laden water from glacial valleys and rivers pours into the open
ocean. There in the gulf, the two types of water run into each other, a
light, almost electric blue me
Informally
dubbed “the place where two oceans meet,” the explanation for the photo
is a simple one, though there are many misconceptions about it,
including that catchy title. In particular on popular link-sharing
website Reddit, where users have on multiple occasions erroneously
attributed the photo’s location as “Where the Baltic and North Sea meet”
and the two types of water as being completely incapable of ever
mixing, instead perpetually butting against each other like a boundary
on a map.
You also may have seen a variation on the photo
featuring the same phenomenon, taken by photographer Kent Smith while on
a July 2010 cruise in the Gulf of Alaska. That photo too has been
circulating the web for some time, though the misconceptions about it
seem to be less thanks to Smith's explanation of the photo on his Flickr
page. That one has also been making the rounds on Reddit and social
media for years, and had racked up more than 860,000 views by early 2013
on that one page alone, Smith said.
That original photo,
however, originates from a 2007 research cruise of oceanographers
studying the role that iron plays in the Gulf of Alaska, and how that
iron reaches certain areas in the northern Pacific.
Ken Bruland,
professor of ocean sciences at University of California-Santa Cruz, was
on that cruise. In fact, he was the one who snapped the pic. He said the
purpose of the cruise was to examine how huge eddies -- slow moving
currents -- ranging into the hundreds of kilometers in diameter, swirl
out from the Alaska coast into the Gulf of Alaska.
Those eddies
often carry with them huge quantities of glacial sediment thanks to
rivers like Alaska’s 286-mile-long Copper River, prized for its salmon
and originating from the Copper Glacier far inland. It empties out east
of Prince William Sound, carrying with it all that heavy clay and
sediment. And with that sediment comes iron.
“Glacier rivers in
the summertime are like buzzsaws eroding away the mountains there,”
Bruland said. “In the process, they lift up all this material -- they
call it glacial flour -- that can be carried out.”
Once these
glacial rivers pour out into the larger body of water, they’re picked up
by ocean currents, moving east to west, and begin to circulate there.
This is one of the primary methods that iron -- found in the clay and
sediment of the glacial runoff -- is transported to iron-deprived
regions in the middle of the Gulf of Alaska.
As for that specific
photo, Bruland said that it shows the plume of water pouring out from
one of these sediment-rich rivers and meeting with the general ocean
water. It’s also a falsehood that these two types of water don’t mix at
all, he said.
“They do eventually mix, but you do come across
these really strong gradients at these specific moments in time,” he
said. Such borders are never static, he added, as they move around and
disappear altogether, depending on the level of sediment and the whims
of the water.
There is much study being conducted on how this
iron influences marine productivity, in particular its effects on the
growth of plankton, which Bruland referred to as “the base of the food
chain.”
But rivers aren’t the only way that glacier sediment
finds its way into the Gulf of Alaska -- occasionally strong winds can
whip up enough silt to create a cloud of dust that’s visible even from
space as its being carried out to sea.
So next time somebody
shares a “really cool photo” of “the place where two oceans meet,” feel
free to let them know the science behind the phenomenon. After all, in
this Internet age,
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