# Mixed or Layers

The availability of “ingredients” that phytoplankton need to grow — carbon, nutrients, light — is directly tied to the ocean’s physical environment.

Determine whether marine waters are layered or mixed AND if these conditions are tied to phytoplankton diversity.

#1) Discover whether stations had layered or mixed conditions when sampled.

STEP A: Look at each season’s temperature profiles (background) for: Station 3 | Station 4 | Station 5 | Station 6 | Station 7 | Station 8 | Station 9 | Station 10 | Station 11 | Station 12

Keep track of the following:

• Is the station layered (i.e., large temperature contrast between shallow and deep water)?
• OR is the station well-mixed (i.e., temperature is relatively consistent)?

STEP B: Now examine their salinity profiles (background): Station 3 | Station 4 | Station 5 | Station 6 | Station 7 | Station 8 | Station 9 | Station 10 | Station 11 | Station 12

• At these stations, is the salinity profile consistent with the temperature profile for that season? In other words, do stations with layered temperature profiles also have layered salinity profiles? And do stations with “well-mixed” temperature profiles also have “well-mixed” salinity profiles?

#2) Compare the top of the thermocline with the depth of fluorescence.

STEP A: For stations with layered conditions (see “Data Tracking Sheet” from Activity #1), find the depth where there is adistinct decrease in the temperature(example at right, >>): Station 3 | Station 4 | Station 5 | Station 6 | Station 7 | Station 8 | Station 9 | Station 10 | Station 11 | Station 12

• Note this depth on your “Data Tracking Sheet” under “Top of Thermocline.”

STEP B: Find the corresponding graph of fluorescence for these stations. Note the depth where the fluorescence (background) drops below the value of 1: Station 3 | Station 4 | Station 5 | Station 6 | Station 7 | Station 8 | Station 9 | Station 10 | Station 11 | Station 12

• Compare the depths you found in Step A (the top of the thermocline) with those you found in Step B (where fluorescence has dramatically diminished).
• Is the top of the thermocline at the depth where fluorescence declines sharply? Can you guess why or why not?
• Quickly examine a few (6 or so) fluorescence profiles for mixedconditions (based on Activity #1 results): are their traces different from those of layered stations? Why or why not?

#3) Examine whether phytoplankton species diversity is tied to layered versus mixed ocean conditions.

STEP A: Look at the plankton net samples and descriptions for every station during each season: Station 1 | Station 2 | Station 3 | Station 4 | Station 5 | Station 6 | Station 7 | Station 8 | Station 9 | Station 10 | Station 11 | Station 12

• For each station / season, determine whether the plankton (background)assemblage is:

1. MOSTLY DIATOMS (note with a “C” if there are many chain diatoms);
2. MOSTLY DINOFLAGELLATES;
3. ABOUT EQUAL AMOUNTS OF DIATOMS and DINOFLAGELLATES; or
4. OTHER (including Phaeocystis)
• Note results on your “Data Tracking Sheet” under “Biology.”

STEP B: When possible, compare these findings with whether each station is “layered” or “mixed” during that season (analyzed during Activity #1).

One view of the relationship between physical conditions and phytoplankton is shown (below). According to your Gulf of Maine research, are certain types of phytoplankton thrive better under layered conditions? How about mixed conditions?

Does the diversity of “successful species” change from season to season? Why or why not?