Mark Van Arsdale: Estuaries, September 19, 2018

NOAA Teacher at Sea

Mark Van Arsdale

Aboard R/V Tiglax

September 11 – 26, 2018


Mission: Long Term Ecological Monitoring

Geographic Area of Cruise: North Gulf of Alaska

Date: September 19, 2018


Weather Data from the Bridge

Clear skies, calm seas

 60.25N, 145.5 W (Middleton Island Line)


Science Log


Water chemistry for the Middleton Transect Line
Water chemistry for the Middleton Transect Line

Estuaries are semi-enclosed bodies of water where fresh and saltwater mix.  By this morning, we had moved into the Copper River Estuary and the salinity reading at the surface showed nearly fresh water.  Estuaries can be sites of incredible biological productivity, but in Alaskan high rates of water flushing due to rain and glacial melt along with low rates of plant decay (and almost zero use of agricultural fertilizers) mean that may not be the case.  Close to the Copper River, light may also become a limiting factor as the glacial sediments increase turbidity and decrease water clarity.  Along this line, we did see a narrow band of higher productivity (seen as Fluorescence on the graph above) about fifty kilometers out where water clarity had improved.

Estuaries tend to be shallow with lots of tidal movement.  This creates ideal conditions for plankton growth, and our nightly plankton tows did see more algae than we had in previous tows.  We also started to see juvenile pink shrimp and salmon smolt.  Much to our surprise, we were still catching jellies well into the freshwater area. For most oceanic species, fresh water is a stressor. Dealing with the constantly changing salinity is a challenge for any estuarine species.  An inflowing tide brings in denser saltwater, which moves along the bottom.  Freshwater flows in from rivers at the surface.   Depending on the conditions of the estuary, that can create either well mixed brackish water or distinct salt and freshwater wedges.

Bird biologist Dan Cushing entering data along the Middleton Line.
Bird biologist Dan Cushing entering data along the Middleton Line.

Estuaries across the world have historically been centers of intensive human development. In the U.S., New York, San Francisco, Baltimore, and Seattle are just a few examples of large urban areas sitting along large and important estuaries.  For historically developing cities, estuaries meant easy to access food and oceanic transportation, as well as the benefits of fresh water for drinking and the outflow of sewage waste.  Sixty percent of North America’s estuaries are considered to have significantly degraded habitat. However, the Copper River Estuary remains a largely undisturbed gem.  There are no dams on the Copper River and very little development along its watershed.   

Personal Log

Human Connections

When the sun came up in the morning we could see the heavy glacial silt of the Copper River.  There were sightings of ducks and other water fowl.  The water was grey and murky, but the peaks surrounding the Copper River water shed were sensational, and I found myself wishing I could stay awake.  As we get further east and into areas that I am completely unfamiliar with, there is so much to see, and I find myself wishing I did not have to sleep through the mornings.

Sunrise over the Copper River Estuary
Sunrise over the Copper River Estuary

At this point we were just a few miles away from the town of Cordova.  Although I did not, many people on board had cell service this morning.  When I woke up after five hours of sleep it was impossible to walk around the boat without seeing someone looking down at their phone.  Scientists at sea are very work focused, but even hard core scientists miss their human connections.  People wanted to talk to spouses or kids, and get updates on their friend’s social media.  There were also murmured discussions about what news we had missed over the last eight days, much of it ominous.  Our human connections are life sustaining points of encouragement, our twenty-four-hour news cycle maybe not so much.  By afternoon we were headed far back out to sea working on the Middleton line.  Because of the zig-zag nature of our day-night work, we have had a clear view of Middleton Island several times now.  Those who were here last year recall such torrential rains that they never saw the island once.  Our weather continues to be remarkably good.  We hope to complete the Middleton Line tomorrow and head further east to Cape Suckling after that.  Ironically, the good weather seems to be leaving the captain and crew slightly ill at ease.  It can’t last forever, and they seem to be wondering when the other shoe will drop.  I just hope that if and when the weather goes bad, it’s during the last leg of our trip when we have moved into the protected waters of Prince William Sound.

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