Mark Van Arsdale: Modeling the Ocean, September 24, 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 24, 2018


Weather Data from the Bridge

30 knot easterly winds, rain, waves to eight feet

60.20 N, 147.57 W (Prince William Sound)


Science Log 

Modeling the Ocean

During the last two weeks, scientists aboard the Tiglax will have done over 60 CTD casts, 60 zooplankton tows, measured over one thousand jellies caught Methot Net tows, and collected hundreds of water and chlorophyll samples. What happens with all of this data when we get back?   The short answer is a lot more work. Samples have to be analyzed, plankton have to be counted and measured, DNA analysis work has to be done, and cohesive images of temperature, salinity, and nutrients have to be stitched together from the five different transects.

Preparing for another CTD cast. More than 60 CTD casts were made during our cruise.
Preparing for another CTD cast. More than 60 CTD casts were made during our cruise.

Much of this data will eventually be entered into a computer model.  I’ve spent a great deal of time talking with one of the scientists on aboard about how models can be used to answer essential scientific questions about how the Gulf of Alaska works.  Take Neocalanus, the copepods we collected yesterday, for example.  A scientist could ask the question, what factors determine a good versus bad year for Neocalanus?  Or what are the downstream effects on a copepod species of an anomalous warming event like “the blob” of 2014-2015? A model allows you to make predictions based on certain parameters. You can run numerous scenarios, all with different possible variables, in very short periods of time. A model won’t ever predict the future, but it can help a scientist understand the “rules” that govern how the system works.  But a model is only as good as its baseline assumptions, and those assumptions require the collection of real world data.  A computer doesn’t know how fast Neocalanus grows under optimal or sub-optimal conditions unless you tell it, and to tell it, a scientist has to first measure it.

The fishing industry is a billion-dollar piece of the Alaskan economy.  The ocean is getting warmer and more acidic.  Food webs are shifting, and the abundance and distribution of the species we depend upon are changing as a result.  Using models may allow us to better predict what sustainable levels of fish catches will be as conditions in the Gulf of Alaska change.

I also asked the scientists on board about the future of oceanography in light of the advancements in autonomous unmanned vehicles.  Do you still need to send people out to sea when sending a Slocum Glider or Saildrone can collect data much cheaper than a ship filled with twenty scientists?  The answer I got was, “No, at best these technologies will enhance but not replace what we do at sea.  There will always be a place for direct scientific observations.”  We still need oceanographers at sea.

In twenty-one years of teaching I have had lots students go on to be doctors, PA’s, nurses, micro-biologists, geneticists, and a variety of other scientific occupations, but no oceanographers.  I guess I still have some work to do.

Personal Log

The Weather Finally Gets Us

We have had a few showers, bits of wind and waves, but the weather has been remarkably good for a cruise through the North Gulf of Alaska in late September.  This morning, during the night shift the winds started to blow, it started to rain, and the waves came up. When I went to bed around six AM, the wind was blowing thirty knots, and when I woke up at eleven, it was pushing up some pretty rough seas.  Things got really crazy after lunch.  The winds were being channeled right down Night Island Passage and all work was put to a stop.  I retired to my bunk to read, unable to even go outside and take look.  They eventually battened down the hatches; and we changed course to go hide in a bay sheltered from the wind. (Yes, they really do say batten down the hatches.)

By dinner time decisions were made to not work for the night.  It looked better where we were, but the stations we needed to sample were exposed to winds that were still blowing.  No zooplankton sampling for the night meant that it was time to start washing, disassembling, and drying nets.  We used seventeen different nets to sample zooplankton during the course of this trip and all of them needed to be washed and cared for before they got packed up.

Plankton nets hanging to dry (oceanographer laundry.)
Plankton nets hanging to dry (oceanographer laundry.)

Tomorrow we will begin the journey home with two stations un-sampled.  The storm kept us from getting to the last stations, and another storm is just a few days away. Once the decision was made, I think we were all relieved to be heading in.  Doing oceanography is hard work, and being away from lives, work, and family for such extended periods of time is tough.  Some of the scientists on board have spent as much as six or eight weeks at sea this year.  Having been out here for two weeks, I now understand what commitment that takes.

Unless something really interesting happens tomorrow, this will be my last blog.  This trip has been personally challenging, but a rich experience, and I believe it will be formative to my teaching.  I have learned a great deal about oceanography in general, and the Gulf of Alaska in particular.  The Gulf of Alaska is a magical place.  There is life almost everywhere you look.  More than anything I will leave with a deep impression of the dedication that scientists give to the accuracy and integrity of their work.

[Postscript:  Zooplankton and jelly work was done, so I was able to spend the entire last day on the flying bridge.  There was a good amount of swell from the previous day’s storm, but the sun and scenery made it an enjoyable trip back to Seward.  As we left Prince William Sound we were greeted by an abundance of seabirds that had been blown into the Sound by the weather.  On that day, we documented almost as many species as the rest of the trip combined.  We also got to watch a large group of orcas patrolling the area around Danger Island at the entrance to the Sound.  We made our way back to GAK1.  If the weather allows, GAK1 is always sampled at the beginning and ending of any trip.  The weather was beautiful, Bear Glacier and the entrance to Resurrection Bay was alive with color, and I was going home.  It was a great day.]

Views of the southern coast of the Kenai Peninsula as we traveled from Prince William Sound back to Seward.
Views of the southern coast of the Kenai Peninsula as we traveled from Prince William Sound back to Seward.

Animals seen today

  • Sea otters
  • Fewer birds today, bald eagles, kittiwakes, gulls

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