Results tagged “LOPC”

Week 3 since the cruise, and the pieces of the puzzle are beginning to come into focus.  Cameron's incubation experiments indicate a presence we've not sensed since last year--the presence of diapausing copepods deep in the abyss.  As I typed earlier, I'm getting a similar signal in the laser data: an anomalously large aggregation of particles at just the size and depth we would expect to find C. finmarchicus.  Here is another view:

While it is possible that this deep aggregation of particles is some mysterious, and as yet undiscovered presence in the gulf, the evidence points to one plausibility: if it quacks like a copepod, it's probably a copepod.

I returned to my personal microcomputer to plot up quasi-silhouettes from the lasers, showing these particles.  Here are the preliminary results:


A glance at this image is far from conclusive, and it remains to demonstrate that the blobules we see are actually diapausing copepods.  I conjecture that they are indeed that, and I am presently taking steps to convince myself that I'm correct.

Nick Record, signing off.

With the thrill of the lobster molt wearing off, the time has come to crunch some numbers.  A few weeks ago--the 22nd of July, 2010 to be more precise--we spent a full day on our deep station in Wilkinson Basin.  For six relentless hours, we sampled profile after profile at the same station.  What began as a routine and sunny carefree day slowly morphed into grueling repetition, and as twilight descended upon us, so did the madness of tedium.  (I won't speak here of what that madness led to.)



The driving motivation behind this long series of profiles was to capture the twilight transition in Wilkinson Basin.  Every night, an unfathomable host of plankton emerges from the depths of the world's ocean to feed at the surface under the cloak of darkness.  This transition occurs, for the most part, during the twilight hours--hence the name of this sampling series.  Our objective is to sort out some of the major players in this massive migration, and to pinpoint as well as we can their preferred depths.

Naturally, we are in the early stages of unraveling this depth-stratified tapestry of plankton, but some curious signals are already appearing.  The plot shown below is taken from a night sample, well after the sun has set.  On the left is a plot from our laser optical plankton counter.  It shows the depth concentration of each size class of plankton--divided by equivalent spherical diameter (ESD).  You can see that most of the critters we observed are near the surface, with the concentration tapering off around a depth of 20-40 meters.  What stands out is the strong signal at the size range 1000-2000 microns (1-2 mm) at depths below 120 meters.  I have labeled this "Diapausing finmarks"-- what I believe to be the copepod Calanus finmarchicus, gathered in large numbers in its deep hibernation.  This is something that we hope to confirm with the net tows.

It is interesting to note that, while we think of this species as a cold-water animal at the southern edge of its range here in the Gulf of Maine, it appears to be actively avoiding the coldest depths at this station.  The right-hand plot shows a temperature profile, with a classic Maine-intermediate-water signal. I've labeled that.  It's a cold layer that forms between two warmer layers in the ocean, due to a combination of processes.

The other curiosity to this temperature plot is the blip of warmer water around 50 meters depth.  This I've labeled with a question mark.  It appears in nearly all of our profiles, at the same depth, and I've since noticed it in other temperature profiles from the Gulf of Maine.  I have yet to find an explanation.  Thus, another mystery has bubbled up to the surface.




PS in response to Pete's comment, I've posted some of the LOPC shapes on the LOPC blog: www.seascapemodeling.org/lopc/

We live in a digital age.  Grocery stores use automatic scanning to read prices.  Factories use machines to build machines.  Robots can vacuum carpets and land on Mars.  Even our trusted local RoboCop struggles with his dual cyborg identity.

But what does this have to do with plankton?

Digital instruments are changing the way we view the ocean as well.  While nets are still the most common plankton sampling device, other instruments are starting to catch on.  In our lab, we use the laser optical plankton counter, or LOPC, which I've written about before.  Instead of hauling up a net and counting every critter by eye, we lower this instrument into the ocean, it scans the nearby water with a laser, and records what it sees.  Very futuristic.

The advantage to this technology is that we can now collect large amounts of detailed data at a much faster rate, and sometimes in rougher weather conditions.  Also, we don't have to mess with chemicals and look through a microscope for long hours to identify each critter one at a time.

Still, as we march relentlessly toward a dystopian future ruled by hyper-intelligent robots, it's important to bear in mind the value of a human--in this case, a taxonomist human.  To illustrate the point, I've invented a game called "Where's Sheldon?  The plankton-or-detritus game."  When we lower the LOPC into the water, it records every particle that is sees.  Some of those particles are planktonic, and others are not.  It can often be difficult to distinguish the two.

Can you tell the difference?  I did a lab test, and passed these items through the LOPC:

I want to quickly share a couple of snapshots from my trip to Halifax last week.

The main purpose of the trip was a day with Brooke Ocean / Odim / Rolls-Royce -- the maker of our LOPC (that's LASER optical plankton counter; see previous posts).  Our instrument was under repair/upgrading.  I had a very nice visit, and a productive day.  They greeted me with Timbits and showed me around the facility.  Then we went to work on the LOPC.  Here is a picture of the guts of one:



Ours was opened up like a surgery patient.  By the end of the day, we got everything smoothly working.  Let's hope we have the same luck when we're bobbing at sea.  Hijinks to follow later this summer.

While I was in Halifax, I stopped by the Bedford Institute of Oceanography.  I had a very productive day there as well--some great jam sessions with other scientists.  It's good to get out of my bubble and add some new sparks to ideas that are starting to go into dormancy.  One of the best parts of visiting a DFO building is touring the labs.  Here are a couple of snapshots.

Our biological oceanography lab has a biweekly zooplankton time-series study collected from the Darling Marine Center in Walpole, Maine.  The study samples the zooplankton at two stations: one well within the Damariscotta estuary, and the other a few miles out.  At the nearshore station, we see an estuarine community, with a diverse collection of copepods and other zooplankton.  At the offshore station, depending on the time of year, the community is dominated by the large copepod, Calanus finmarchicus.  

These two communities are characteristic of two different marine ecosystems.  The big copepods in the oceanic system provide essential prey for pelagic species ranging from herring to right whales.  The smaller, more diverse estuarine system can serve as a nursery for larval fish.  The seascape modeling lab is interested in the processes that maintain the boundary between the two types of system.

In order to characterize the nearshore-offshore gradient, we ran a cruise on Thursday, taking profiles with the LOPC at fixed intervals of roughly 1 km (see map).  We're still feeding out and reeling the LOPC cable by hand, until we get the data logger fixed.  This can be tiresome, but thanks to ongoing splicing efforts (including some last-minute work before leaving the dock), it's effective.  We have a nice transect showing the shift in size distribution from the nearshore out towards the offshore.

Additionally, it was nice to be on the water on a brisk October day.  We got an early start, catching the sunrise ferry from Peaks Island, and we saw some fair wildlife, which, hopefully, Pete will share some pictures of in a later entry.

Pete again:

It's 12:40 AM. We just finished our last station of the day. Pictured is us geting the LOPC ready. We also put the Tucker in. During which a minke whale came to play. Literally. Phoebe and I got distracted putting the net in as a minke whale surfaced not 5 feet off the starboard stern. It was glowing as it agitated the bioluminescence. Alex, the captain, quickly got us back on task with a quick shout. It's important to stay focused when putting things over the stern when you're miles from shore. Way too easy to get pulled in. The whale hung around while we were towing the Tucker and as we put it away. Wicked cool. Quite a day. Up at 6 for the next station. Night.

From Nick:

Here's our first LOPC cast, by the side of the dock.  Splice held.  Phoebe is here safely, after rowing this morning from Witch Island.  Plan is to test the weather tomorrow at 6 am, and hopefully begin sampling, though it could be rough.  If things go as planned, I won't be in internet contact after tomorrow morning.  Maybe next time we dock, I can get a signal and do another post.

The figure is the output from the LOPC test cast.  Each bar on the left indicates the number of particles passing through the unit that had a particular "equivalent spherical diameter".  As you can see, not a lot of big stuff. 

From Peter:

After a nice sleep on the boat we woke up to clouds and drizzel, ate a nice breakfast and got to work setting things up. Here's a picture of me setting up the Tucker trawl. We got it together much faster this year since our winch, big Bertha, is working. Also Nick says "things look promising for the LOPC",  (laser optical plankton counter) but our intern missed the bus in Portland and will be late.
Time for a quick trip to town to get sunscreen, butt connectors (electrical supplies, thank you), and some diesel for Bertha. This afternoon we'll head out and test the gear, perhaps get the first station in.