Tracers in the Sea

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Exotic mysteries that flow underneath a seemingly familiar surface teem with opportunities for the inquisitive mind.  A most literal and timely example is the topic of ocean circulation.  As the erudite listeners of Science… sort of may already know; not only is the earth quite a bit rounder than once thought, the oceans that dance on its surface are not mere mixing bowls of uniformly salty fluids churned by a flick of King Neptune’s trident.  Ocean water is stratified into layers that separate because of differential densities controlled by temperature and salinity.  As water moves, it travels along planes of constant density (isopycnals); which means that on average, water is more likely to flow laterally rather than vertically.


Sure, you can model most earth processes with a few basic equations of state and the watery bits are no exception.  Our minds can readily adapt the example of a continuous conveyor belt, so that now we can visualize water sinking at high latitudes (N. Atlantic, Antarctica) and upwelling in areas such as the N. Pacific.  Unfortunately, thermohaline circulation is not so simple and the conveyor belt often fails when the basic schema is tested on different levels of detail.   Physical oceanographers devise complicated calculations day in and day out to understand the mess of currents.  But, if you ask an average scientist what they want for Christmas, data is at the top of the list; cold, hard data.   How do you measure something you can’t see under sometimes miles of water?  The answer is, you measure a tracer.  You introduce something into the system with the same properties of water, something that will travel with the water, something that can be detected.

The tragic loss of human life and impending ecological conflagration notwithstanding, the injection of a readily identified chemical tracer into the deep waters of the Gulf of Mexico creates an interesting opportunity to study flow at extreme depths.  It wouldn’t be the first time an accidental spill has been used for ocean current research.

The work of Curtis Ebbesmeyer, sometimes referred to as “flotsametrics”, studies the movements of surface currents by the appearance of sea “junk” washed ashore.  Just as one man’s trash is another’s treasure, one man’s bathtime buddy is another’s powerful scientific instrument.  One such haul of cargo lost at sea contained over 29,000 rubber duckies.  Since freed in the central Pacific in 1992, the movements of the so called “friendly floatees” have been tracked by Ebbesmeyer and others to refine global circulation models such as OSCURS (Ocean Surface CURent Simulator).  Just 14 years after their trip began, floatees started to appear on the balmy coasts of Iceland and N. Europe.

The chemical tracer released in the Gulf of Mexico, a cocktail of emulsified gas, water, oil, and dispersants, is clearly less benevolent, and the time window for observation is narrow as the material starts to spread.   A group of researchers from USF lead by David Hollander set sail aboard the RV Weatherbird II to sample water at various depths throughout the water column.  Their goal is to determine the limits of a deep sea plume of dissolved hydrocarbons in the water surrounding the ruptured Macondo well head and track the effects on plankton.  Initial results suggest this plume covers 6 miles in aerial extent, at depths greater than 2 miles.  Many important and interesting things can come from this data, such as an estimate of the magnitude of the leak and information to help mitigate damage, but also the advancement of basic science and general understanding of physical and chemical oceanography.

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One Response to Tracers in the Sea

  1. PatrickNo Gravatar 8 June, 2010 at 8:58 am #

    I knew there was a good reason to spew a bunch of oil into the Gulf.

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