Northern summer
Northern winterThe two images below show variations in primary productivity (that is, plant growth) based on satellite measurements of chlorophyll pigment. Red colors indicate high values and purple colors indicate low values (see color bar scale below). Black areas are parts of the ocean where insufficient data were collected.
Two factors affect the amount of primary productivity in the ocean: light and nutrients. Light changes seasonally, particularly at high latitudes. High nutrient levels are often associated with areas of upwelling currents and low levels are often associated with downwelling currents. In the displayed images, notice how the productivity values correlate to the surface ocean currents that are explored in the ocean currents exercise at this site.
The images below are composites of July through September data (northern hemisphere summer months / southern hemisphere winter months) and January through March data (northern hemisphere winter months / southern hemisphere summer months).
NOTE: To obtain larger-sized images (312K and 351K in size), double-click
on the displayed images.
Northern summer
Northern winter
(a.) Describe the locations in the ocean that have high productivity
values (that is, high pigment concentrations) and explain why values are
high at these locations.
(b.) Describe the locations in the ocean that have low productivity
values and explain why values are low at these locations.
(c.) Compare the winter (northern hemisphere) and summer (northern hemisphere)
images in terms of high and low productivity regions.
Some aspects of the images to look for when considering your answers: (1) when equatorial upwelling is strongest and why; (2) compare specific coastal locations and speculate about reasons for observed variations; (3) explain seasonal variations in the high latitude regions (near the poles). Remember that productivity depends on both nutrients (often from upwelling currents) and from light (variations particularly important in temperate to high latitudes).