August 3rd, 2017 by Stephanie Uz
Note that these examples are intended for curious people looking for hands-on Earth data exploration. Primary scientific research will require additional analyses through other methods. For the basics on how to use the NEO tool, see ‘Analysis tool in 10 easy steps’.
Here we explore phytoplankton blooms and their relationship to sea surface temperatures, with background information featured in ClimateBits: Phytoplankton.
Recent studies link warmer waters off the U.S. west coast to more frequent toxic algae blooms, negatively impacting the marine food web and the economy. In 2014-16, the waters off the west coast were unusually warm and were famously dubbed the ‘warm blob’ by the press. The warmer ocean impacted weather on the west coast and was linked to lower fish catches and stressed sea life.
A toxic algae bloom in 2015 extended from California to Alaska resulting in the closure of the Dungeness crab fishery and an economic decline of $100 million, according to the Fisheries of the U.S. Report, 2015. Sea lion strandings increased, including a starving baby sea lion that seated itself at a San Diego restaurant in early 2016, weighing half of what it should for its age according to the Sea World rescue team.
Following the strong El Niño of 2015-16, ocean temperatures off the west coast returned to ‘normal’. Here we use NEO to explore these reports. How do the satellite sea surface temperature records compare before, during, and after the warm anomaly?
A NEO comparison of ocean surface temperatures for the month of February before the warm anomaly in 2013 (red), during the warm anomaly in 2015 (green), and after the warm anomaly in 2017 (blue). Along the entire west coast – from Alaska to the Baja Peninsula – temperatures during the warm blob (February 2015) were roughly 3 degrees C (or 5 degrees F) warmer compared to before (February 2013) and after (February 2017).
Temperatures off of Alaska (Distance ~ 0km along the transect) were around 7C in February 2013 and 2017, but around 10C in 2015. Off of southern California (Distance ~ 2000km), temperatures were around 13C in February 2013 but 16C during the warm blob in 2015. West of the Baja Peninsula (Distance ~ 3500km), temperatures were around 21C in 2013 and 2017, but 25C in 2015.
How do the temperature changes relate to ocean biology measured by satellites?
Chlorophyll concentrations indicate the amount of phytoplankton blooming. More phytoplankton means more food for fish and the rest of the marine food web. In the chlorophyll histogram in Figure 2, chlorophyll during the warm blob in February 2015 (green) had lower values (around 0.1 mg/m3) more frequently than the other two years. The waters were almost 10 times more productive (approaching 0.9 mg/m3) in February 2013 (red) compared to the other two years. Recall that February 2013 had the coolest water.
Usually, cooler surface water means that the water has recently been at depth — below the sunlit surface. Deep water containing unused nutrients can support new phytoplankton blooms. Thus, cooler water is generally associated with higher chlorophyll concentrations. How do the two data sets compare along the west coast before, during, and after the warm blob?
Here we compare sea surface temperature and chlorophyll along a transect from NW to SE off the coast of California for February 2013, 2015, 2017.
In all of the plots in Figures 3, sea surface temperature and chlorophyll demonstrate their inverse relationship. Cooler, more productive water to the north is contrasted with warmer, less productive water toward the south. The peaks in the chlorophyll (green line) correspond to phytoplankton filaments typically associated with nutrient entrainment along the boundaries of circulation features, such as in the California Current system. Note that over the 2000km transect from northwest to southeast, temperatures changed about 10C and chlorophyll concentrations changed more than an order of magnitude (10x). Also notice that February 2013 (Figure 3, left) had chlorophyll peaks reaching concentrations around 5 mg/m3. During the warm anomaly in 2015, chlorophyll concentrations were never above 0.9 mg/m3. After the demise of the warm blob, sea surface temperatures cooled in 2017 (Figure 3, right) compared to 2015 (Figure 3, middle), chlorophyll concentrations remained low (< 0.9 mg/m3) and were certainly much lower than in 2013.
Diving into the 2017 data a bit more through scatter plots, we can highlight the geographical distributions of different data combinations.
Where are the highest chlorophyll concentrations?
Where are the warmest waters within the area outlined in white?
Where are the coolest waters within the area outlined in white?
Not surprisingly, the coolest waters are in the north; the warmest waters are in the south and the most productive waters with the highest chlorophyll values are next to the coast where nutrients were plentiful. Recall that January and February 2017 was a time of plentiful rain and snow on the west coast (a.k.a. atmospheric rivers that led to much run-off from land).
Note: This blog was written in response to a request for an analysis comparing sea surface temperature and chlorophyll. If there is an analysis you would like to see in this blog, please let us know!
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