Lab 7.2 – IMPORTANCE OF WATER MASSES ALONG THE COAST: HOW DO GULF STREAM INFLUENCES IMPACT FISH POPULATIONS ON THE EAST COAST?

Fundamental concept: TBD
Estimated time to complete: 45 minutes
Data skills preparation: TBD
Materials needed: None

 

picture of a yellow cowfish

Photo by Chris Paparo. https://onthewater.com/gulf-stream-riders

This cowfish was photographed offshore of Long Island, New York.  Cowfish are tropical species, found in warm waters near coral reefs.  So, what is this fish doing up near New York?  How did it get here?

It likely hitched a ride on the Gulf Stream!

In this lab, you will learn about the Gulf Stream, what type of data is used to detect its influence and the impact it has on fish populations.

 

Look at this animation of the currents at the surface of the ocean:

As the video zooms in on the east coast of the United States, you will notice an obvious current in the surface of the ocean shown by the concentration of moving white arrows that looks like a river meandering along the southeast coast and then heading toward the northern Atlantic Ocean. This is the Gulf Stream, and it is the most powerful surface current in the north Atlantic.

Unlike the thermohaline circulation discussed in Lab 7.1, which is density driven, surface currents like the Gulf Stream are wind driven.  The water at the ocean surface moves as energy is transferred from the winds blowing along the surface of the ocean to the surface water. The surface currents are further modified due to the Coriolis Effect, the size and shape of ocean basins, and locations of the continents.

 

Let’s review some concepts before we dive into the Gulf Stream:

Quick Check Questions

 

As you have learned, the Gulf Stream is a powerful surface current that moves warm water along the western Atlantic northward and tends to move offshore beginning near North Carolina.  Coastal waters over the continental shelf tend to remain cooler and less salty due to estuarine influences.  Therefore, water in the Gulf Stream has a distinct temperature and salinity that allows us to distinguish it from other water masses such as water above the continental shelf.  The water of the Gulf Stream flowing past Florida has a salinity of around 36.5 parts per thousand (ppt) and a typical temperature of about 28⁰ C. The temperature typically decreases as the Gulf Stream heads north into higher latitudes and the salinity also tends to decrease due to inputs of freshwater from estuaries (Environmental_Geology_(Earle)).  Oceanographers can therefore detect the presence of the Gulf Stream water mass by looking at data of temperature and salinity.

Gawarkiewicz et al. (2018) did just that using data from the OOI Pioneer Array located over the New England shelf.   The data suggested that onshore intrusions of warm, salty water (from the Gulf Stream) are becoming more prevalent.  One consequence of this warm intrusion was the appearance of warm-water fish species that were presumably carried onto the continental shelf in January 2017 as part of one of these events. Let’s take a closer look at the example of a saltwater intrusion event that took place in January of 2017 described in this paper.

The following graphs show data that points to this Gulf Stream intrusion event.  The top graph shows salinity profiles over time.  Each day is shown as a vertical bar that is color coded to show the salinity of the water from near the surface at 25m to the bottom at about 120m. The lower graph shows a time series of the salinity and temperature near the surface at 7m depth.  Notice the change in salinity during the event from January 8th through January 25, 2017.

[open in new window]

 

 

Now let’s see if you can spot another example of a saltwater intrusion event due to the Gulf Stream coming close to shore.  In 2022-2024, the Pioneer Array of instruments was moved from its initial location on the New England Shelf to its new location in the southern part of the Mid-Atlantic Bight off the coast of North Carolina near Cape Hatteras.  Below, data from this new location are shown in interactive graphs for you to explore.

The top graph shows salinity profiles over time and the middle graph shows temperature profiles over time.  In these two graphs, each day is shown as a vertical bar that is color coded to show the salinity or temperature of the water from near the surface at 28m to the bottom at about 80m. The lower graph shows a time series of the salinity, temperature, and density near the surface at 7 m depth.  Observe the data, zoom in and out, and see if you can find evidence of another event where Gulf Stream water was detected by these sensors, which are located on continental shelf. Answer the questions that follow the graphs.

[open in new window]

 

Orientation Questions

          1. Focus on the top graph:
            1. What variable is shown on the y-axis of the first graph? What are the units?
            2. What variable is shown on the y-axis of the first graph? What are the units?
          2. Focus on the second graph:
            1. What variable is shown on the y-axis of the second graph? What are the units?
            2. What do the colors indicate on the second graph? What are the units?
          3. Focus on the third graph:
            1. What variable is shown on the left y-axis of the third graph? What are the units?
            2. What variable is shown on the right y-axis of the third graph? What are the units?
          4. Focus on the fourth graph:
            1. What variable is shown on the y-axis of the fourth graph? What are the units?
            2. What variable is shown on the x-axis for all four graphs?
          5. What time period do the graphs cover?
            1. What is the starting date?
            2. What is the ending date?
          6. Think about the location where this dataset was collected:
            1. In which hemisphere is the Coastal Pioneer array located?
            2. What season is shown on these graphs?
            3. Which coast of the United States is this data from?
            4. Which side of the Atlantic Ocean is this data from?
          7. What graph type are the top two graphs (hint: Look back at Labs 2-3)? Choose from below
            1. Time series
            2. Vertical profile
            3. Bathymetric chart
          8. What graph type are the bottom two graphs (hint: Look back at Labs 2-3)? Choose from below
            1. Time series
            2. Vertical profile
            3. Bathymetric chart

        Interpretation Questions

        Focus on the bottom two graphs showing a time series of temperature, salinity and density at the surface in this location.

        1. Compare temperature to the density: What happens to the water density as the temperatures cool?
        2. Compare salinity to the density: What happens to the water density as the salinity increases?
        3. Gulf Stream water is warmer and has a higher salinity; describe how these characteristics would combine to affect density.
        4. What dates show evidence that the Gulf Stream water intruded onto the continental shelf where this data was collected? Provide evidence to support your answer

    Application Questions

    1. What impact do you think this Gulf Stream intrusion event would have on local fish populations?

     

  2.  

    ⇐ Previous LAB 7.1
    Next LAB 7.3 ⇒

    Table of contents