What Remains to be Learned?
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There are many questions still to be answered about the open-ocean time-series at BATS. Here are just a few of those questions:
The time-series at BATS gives us an excellent idea of the changes that occur through time at one particular spot in the ocean. What remains to be clarified is how the open ocean near BATS varies from place to place, and how this may affect the seasonal and annual cycles observed at BATS. The BATS satellite data show that the Sargasso Sea is not uniform but instead varies substantially in temperature and abundance of phytoplankton.
Some of this variability is due to ocean eddies that move through the BATS area. Ocean eddies can be similar to the swirling patches you may have seen in a stream (only much bigger!). Other eddies are more like an underwater wave. Some eddies form when meanders in the Gulf Stream are pinched off and wander into the Sargasso Sea. The properties of ocean eddies (their temperature, salinity, nutrient concentrations, and organisms) can differ significantly from the properties of the ocean at BATS. Thus the passage of an eddy past the BATS site can dramatically alter its chemical, physical, and biological characteristics. We understand little about how the biological community at BATS might respond to the different conditions brought on by the eddies.
While scientists take measurements once a month at the BATS site, some episodic events occur that monthly sampling does not always capture. These events can change the ocean near BATS. One example is hurricanes. These often move through the Sargasso Sea in the late summer and early fall. We know from BATS satellite data that hurricanes leave a track of cooler water behind them and thus increase the amount of carbon dioxide that the ocean can absorb from the atmosphere. But we still know little about how hurricanes might affect other ocean properties.
Another unknown at BATS is the role that migrating zooplankton play in transporting carbon and nutrients to the deep sea. Each evening as the sun sets over the Sargasso Sea, millions of zooplankton migrate up from the depths to feast on microscopic plants growing in sunlit surface waters. At dawn, these animals reverse course, sinking or swimming down to spend another day in the darkness. The zooplankton feed in surface waters at night to avoid being seen and eaten by their predators. By eating plant material in the surface waters at night and swimming downward each day, the migrating animals potentially move a tremendous amount of carbon from the surface to the ocean depths. The animals recycle the carbon into different forms at depth by egesting it as feces, respiring it as carbon dioxide, or excreting it as dissolved organic carbon. The amount of plant material they eat each night can be significant, and makes up an important part in the global carbon cycle. However, much remains to be discovered about how much the migrators remove, how deeply they move it, and how much they recycle.
Yet another mystery at the BATS site relates to the abundance and types of bacteria in the water. BATS scientists are very interested in the types of bacteria at BATS because bacteria are important in nutrient cycling, and different species are involved in the cycling of different elements. Bacteria are so small (in the sea most are around 1/1000 of a millimeter in diameter) that it is very difficult to tell the difference between kinds of bacteria even with a high-magnification microscope. New molecular techniques that identify bacteria by looking at their genetic material (RNA and DNA) appear to be a promising way of telling them apart and determining how they affect cycling of elements.
