The spring-summer transition in the Chesapeake Bay

Our beloved and temperamental Scanfish did not cooperate on our first day, so we don’t have the nice images of conditions that I usually make on the cruise. Instead we did CTD casts every 4 miles or so. A Scanfish is pretty much just a CTD that swims up and down behind the ship and can be towed at 5-6 knots, whereas a CTD is simply lowered from the ship to near the bottom and retrieved. The CTD can collect water though, so each instrument has its advantages. But I digress. The reason I’m describing the differences is because I finally was able to plot up some of the data from this cruise and I think it tells an interesting story. Instead of focusing on the CTD casts from our transect that took the place of the Scanfish survey I plotted up all the casts from our southern station – the one that is supposed to be more oxic. That data is shown in the plot below. The four panels with contour plots show temperature, salinity, dissolved oxygen, and chlorophyll fluorescence. Time is on the x-axis and depth is on the y-axis. The colors for all plots range from low values in blue to high values in red. On the right is a map with the station location of these samples clearly marked.

DZZ 1101 South CTD data

CTD contour plots from the south station in May 2011 (DeZoZoo cruise 1101), including temperature (upper left), salinity (upper middle), dissolved oxygen (lower left), fluorescence (lower middle), and a station map (right).

What I see in these graphs is that during the two days at our station the surface water warmed considerably – from about 20C to nearly 24C – while the dissolved oxygen in the deep water decreased. Salinity did not seem to change too much, though the depth of the interface between low and high salinity water shoaled (or became shallower). Fluorescence was patchy, with evidence of a rather large bloom at one point.

The really good news is that things are going pretty well so far, and we’ve got about 24 hours left out here, and we’re a little ahead of schedule. That means we’ll actually put the Scanfish back in the water for a 20 mile run of the mid-Bay tomorrow night. We’ve missed quite a large swatch of what we hoped to get because of Scanfish problems, but this way we will get some of it back, and we might even gain some insight onto the changes we’ve seen the last few days out here. Once back on land I’ll be doing some comparisons between the CTDs from the first survey and the up coming Scanfish survey. But now, it’s almost time to put the MOCNESS in the water, after I swing by the ice cream freezer…

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About planktoneer

I'm a zooplankton ecologist who studies how individual behaviors and variability affect populations of copepods in marine and estuarine systems.
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