Springtime in the Maritimes, and Ghosts of the Past
SeaWiFS Level 1A image of the Canadian Maritime
provinces and northeastern United States, acquired May 18, 2003.
SeaWiFS composite Level 1A (land) and Level 2
(ocean) image of the Canadian Maritime Provinces and northeastern
United States, acquired May 18, 2003
Full-size Level 1A JPEG image (1.8 MB)
Full-size Level 1A JPEG image (1.9 MB) (with labeled features of interest)
Full-size composite Level 1A and Level 2 JPEG image (3.3 MB)
These two SeaWiFS images, processed from data acquired on May 18, 2003,
provide a remarkable view of the Canadian Maritime provinces, as well as
part of the northeastern United States. Although the primary concern
of ocean color remote sensing observations is what is happening in the
present -- the day-to-day fluctuations of phytoplankton concentrations
in the global ocean -- this particular SeaWiFS image also provides a
remarkable window on past events. These ghostly reminders of past hours,
days, seasons, or geological eras demonstrate the linkage between the
climate and environment of the present day and the multitude of events
which shaped the Earth in the past.
Spring phytoplankton blooms (refer to large composite
image or labeled Level 1A image)
In May, the North Atlantic and the eastern coast of North America
host explosions of phytoplankton productivity that mark the annual
North Atlantic spring bloom. The SeaWiFS composite image vividly
shows the swirling patterns of bloom activity along the Gulf Stream, and
also displays eruptions of phytoplankton chlorophyll in the Gulf of Maine
and the Gulf of St. Lawrence. This spring abundance of phytoplankton
relies on the increasing amount of sunlight and the "ghosts" of past
generations of phytoplankton and zooplankton, now in the form of
nutrients. After these organisms die, bacteria convert the dead organic
matter that once formed their cells and bodies back into their
primary constituents, notably carbon, nitrogen, and phosphorus. Over
the winter, the concentrations of the vital nutrients nitrate and
phosphate increase, and they fuel the phytoplankton in the spring as
they responding to longer days and more intense light from the Sun. Though
it may be slightly macabre to contemplate how life in the ocean is linked to
the death of previous inhabitants, the annual renewal of the North Atlantic
spring bloom is one of the ocean's most powerful biological events.
The North Atlantic Bloom
Coastal swirls (ice and fog) on the Labrador Coast
Image of
larger coastal area
The effects of winter linger on the frigid shores of the Labrador
coast. Snow still covers the ground, while winds, waves, and coastal
currents shape the coastal ice (and possibly overlying fog) into
swirling vortices. In the large SeaWiFS Level 2 image, these vortices
can also be seen in the offshore chlorophyll concentrations.
Pack ice and icebergs that float in the Labrador Current move
southward, into the northwestern Atlantic Ocean. In 1912, the great
cruise ship Titanic struck an iceberg southeast of Newfoundland,
an iceberg that likely came from the Labrador Sea. For this reason,
the U.S. Coast Guard and Canadian Ice Service continually map ice
distributions using remote sensing.
Reservoir Manicouagan
From space, one of the easiest features to recognize on the east coast
of North America is the circular Reservoir Manicouagan in Quebec. In this
image, snow still covers the ice on the lake surface, while the snow has
melted in the surrounding region, making it particularly easy to see.
The reservoir lake outlines the boundaries of an ancient asteroid impact
crater, dated to 212-214 million years ago. The reservoir is approximately
100 kilometers wide and is an important part of Quebec's hydroelectricity
generation capacity.
Researchers in England reported the discovery of an ejecta layer 214
years old, which might have been associated with the Manicouagan impact.
Subsequent research discovered that there are actually five ancient craters,
all formed during the Triassic period, that would have formed a linear
pattern on the continents of the Earth at that time. It has been
hypothesized that this impact event may have been responsible for the
Carnian-Norian extinction event, an extinction event within the Triassic
period that may have wiped out up to 80% of the species living on Earth at
that time. Though the geologic dates of the Manicouagan impact and the
Carnian-Norian boundary are not simultaneous, they are close enough to
allow this scenario as a possibility.
Bay of Fundy
Is this image boring? Well, this image, which shows Nova Scotia's famous
Bay of Fundy, doesn't capture the dynamic changes in sea level that occur
here daily, the site of the world's highest tides. And it doesn't show
the tidal bore (a tidally-driven wave) that surges up several of the rivers
that enter the bay, particularly near the northern terminus. For many
years, the tidal bore that moved up the Petitcodiac River to Moncton was
the most famous bore in the region, but a causeway has diminished its
power, and the strongest bores are now generally in the Minas Basin on
the eastern side of the bay. The bores, and the 10-12 meter changes in
sea level that occur every day, are remarkable reminders of the invisible
tug of the Moon's gravity on the ocean's surface.
In this image, Moncton is the starlike light area closest to the top
of the image; the Petitcodiac River extends southeastward to the Bay
of Fundy. The Minas Basin is the bay's northeastern extension. Sediments
stirred by the incessant tidal cycle can be easily seen in the upper
reaches of the bay and along the coast.
Sable Island
The bright crescent seen in the image above is one of the most unusual
islands in the world, the isolated Sable Island. For centuries, Sable
Island has been feared because of its noteworthy number of shipwrecks.
Sable Island is near the Grand Banks fishing area and the Gulf Stream,
and numerous fishing and trade vessels came to an end on its sandy
beaches. In addition, many Atlantic storms moving up the East Coast would
push disabled ships toward Sable Island. The decaying skeletons of these
ships still lurk in the shallows today. Sable Island is a nature reserve
and is not inhabited by humans, but scientists come there
every year to perform a variety of experiments. The only "large"
year-round residents are the Sable Island horses, descendants of horses
once owned by Acadians and procured by a Boston merchant when the
Acadians were deported from Nova Scotia.
Sable Island itself is also a specter from the Ice Ages, the last
glacial period in Earth's geologic history. It appears to mark
the edge of the last large ice sheet that covered Nova Scotia, and may be
a glacial moraine where the sediments moved by the ice sheets were
deposited (due to the presence of the ice sheets, sea level was much
lower than today). The sand that keeps Sable Island above water is derived
from an immense sand bank on the continental shelf.
Newfoundland (refer to large Level 1A images)
When discussing Earth's geological history and the Canadian Maritime
provinces, the island of Newfoundland should certainly not be overlooked.
Newfoundland hosts an amazing variety of geological features, ranging
in age from the Cambrian (with fossil thrombolites, similar to stromatolites)
to land-locked freshwater fjords formed during the last glacial period.
Of particular interest is Gros Morne National Park on the island's northern peninsula, which is a UNESCO (United Nations Educational, Scientific,
and Cultural Organization) World Heritage Site. Among the many
geological features of Gros Morne National Park is an ophiolite, a
section of the ocean bottom that has been lifted above the ocean surface
by tectonic forces.
Aircraft contrails
Much more modern ghosts than the ancient geology of Newfoundland are
seen in this large area of aircraft contrails indicating planes flying
the busy trans-Atlantic routes originating or terminating in New York City.
The large island at bottom right is Prince Edward Island, and the large
elongated island at top center is Anticosti island, a provincial park.
Southeast of Anticosti Island is the Gaspe Peninsula, a haven for nature
and wildlife in northern Quebec.
In the days following the tragic attacks on the World Trade Center
in New York City, the absence of aircraft contrails allowed atmospheric
scientists to investigate the climate influence of these high altitude
clouds.
Upstate New York
This tour of the northeast coast of North America and the Canadian
Maritimes ends in the bottom right corner of the image, which is slightly
blurry at the edge of the SeaWiFS scanning swath. Question:
What is the largest freshwater lake in the United States that is not one of
the Great Lakes? Answer: Lake Champlain, which lies along the New York-
Vermont border and has a small segment in Quebec. Lake Champlain, and the
St. Lawrence River to the north, are also reminders of a dramatic period
which took place at the end of the last glacial period. The glacial
ice first deepened the valley that currently holds Lake Champlain. Then,
as Earth's temperature warmed and the ice sheets retreated, a giant
lake of meltwater (Lake Vermont) formed in this area, behind dams of ice.
When the ice dams broke (a larger lake, Lake Agassiz in central Canada,
drained into Hudson Bay) an immense volume of fresh water flowed into the
north Atlantic Ocean, causing an abrupt shutdown of the ocean's thermohaline
circulation pattern and a sudden interruption in the warming trend that
lasted about 1,000 years. This period of time in geological history is
called the "Younger Dryas" period. At about the same time, the retreat
of the ice sheet allowed the ocean to flow into the Champlain Valley
due to the depression of the Earth's surface caused by the weight of the ice. The combination of the Atlantic Ocean and Lake Vermont formed the
"Champlain Sea". Over time, the Earth's surface rose again (a process
called glacial rebound), and fresh water replaced the salt water from the
ocean in Lake Champlain.
The glaciers of the Pleistocene Ice Age were also responsible for the
formation of the Finger Lakes, seen in the lower left part of the image
excerpt. The largest Finger Lakes and Lake Champlain are both very
deep, in some places exceeding a depth of 400 feet.
Another important geological feature in this region is the Adirondack
Mountains. The Adirondacks are visible in this image because their higher
altitude means that winter still lingers on them, and the "spring greening"
of their vegetation cover has not quite taken place. The Adirondacks are
also notable for their geology, which consists of a granitic bedrock that
was formed about 1.3 billion years ago, and uplifted as a "dome" about
15 million years ago, during the Miocene period. The uplift may have been
due to a volcanic process similar to the formation of the Hawaiian Islands,
a "hot spot", though in this case the molten rock only lifted the overlying
rocks and did not break through to the surface.
The granitic bedrock of the Adirondacks makes the Adirondack lakes
particularly susceptible to acidification due to acid rain. These lakes
have very little buffering capacity to neutralize the acidity of rainfall
created primarily by coal-burning electrical power plants in the Midwest.
Due to the implementation of the Clean Air Act, power plant emissions have
decreased and the acidity of the Adirondack Lakes is gradually being
reduced. However, it may take several more decades before the lakes
are fully recovered and fish return to their former haunts.
Acknowledgements
This Science Focus! article acknowledges the information provided
by the authors of the Web sites linked above and thanks them for their
assistance in the creation of this article.
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