Density and Ocean Circulation
Understanding salinity helps us understand global patterns, including the circulation of water in the deep ocean. Together, salinity and temperature control density at the ocean surface. Thus, satellite salinity measurements are complementary to existing programs that monitor sea surface temperature. The resources on this page illuminate the connection between density and the ocean's motion, and the consequences to our climate.
Scientists have observed freshwater outflow from the Amazon River traveling a great deal farther into the Atlantic Ocean than had previously been documented, at times reaching almost to the African Continent. Do fresh water pockets created by rainfall over the ocean's surface hold together (over time and space) in a similar way to those of freshwater outflows from large rivers such as the Amazon?
I think with the information we're obtaining from Aquarius, we're learning to go back and re-assess - re-evaluate - the role of vertical mixing and horizontal advection in ocean dynamics. So, even for a region we think is dominated by evaporation, or for some reason, dominated by precipitation, now the general picture is we can only grasp these as hypotheses. Horizontal advection, vertical mixing, evaporation, precipitation, all these play an important role at different times, at different scales and resolutions.
For example, another very interesting science phenomena discovered by Aquarius is what we call a tropical instability wave in the Atlantic and Pacific Oceans. (Tropical instability waves are north-south deflections of the "tongue" of upwelled cold water that extends westward from African and South American continental margins and along the Equator. These waves propagate with an average period of about 30 days, and a wavelength of about 1100 kilometers.) This is a new discovery by Aquarius. While it has been seen in ocean surface temperature images from locations a few degrees north of the equator, Aquarius now shows us that these kinds of waves also exist near the equator - but can only be seen in the salinity dataset.
The other example is the river outflow. Standard thinking has been that fresh river outflow from the Mississippi River would only affect coastal regions near Texas, Mississippi and Louisiana. The Aquarius data now shows that the fresh water on the surface can reach all the way to the southern end of the Gulf of Mexico. In the winter, when there's not much precipitation in the region, then in the summer when there is precipitation, we can see that salinity cycle in the upper ocean through the Aquarius data.
Another example I'd like to tell you is pretty interesting, it's something that we've just started to understand. It's a combination of how useful it is to combine the whole motion image salinity together. One of the interesting regions for the oceanographer or the climate scientist is the ocean surrounding the Indian Subcontinent. Why is that region so important? They have a monsoon season, right? In September, they get a lot of rain. Then, in the Indian sub-continent, around Tibet, they also get lots of snow. So the heavy precipitation and river run-off dump vast quantities of fresh water in the Bay of Bengal. We also have heavy precipitation over the open ocean in the same region. When we start to look at the soil moisture changes over the continent, and the salinity changes in the ocean, we can see their time correlation. Then, we can see when the fresh water will actually reach the southern point in the Bay of Bengal. But there's something else, more than just the fresh water coming into the Bay of Bengal. There's also a current in the Bay of Bengal, and that current can change direction in winter and summer. So, we can see how everything plays together, with fresh water coming out of the Bay of Bengal, and then the ocean current actually moving the fresh water around.