Oceanopox

A more recent feature of our enthralling journey are these unusual, small-scale depressions on the ocean floor:

They're easy to miss, as they're typically no more than 100 meters deep...a small feature compared to many other structural features on the sea floor (fault scarps, seamounts, and even abyssal hills).  In typical geological parlance, these are called "pock marks," and they record geologic events that are somewhat independent of their structural surroundings.  Silicious (made of silica) tests, that is, the shells laid down by small or microscopic organisms (think clams or scallops, but silica instead of calcium carbonate, floating in the water column instead of rock or bottom-dwelling, and much, much smaller), fall to the sea floor after the organisms die.  They form distinct layers of silicious material, typically containing an abundance of water incorporated into the chemical structure of the mineral. 

Over time, as material newly deposited over the silicious layer begins to exert force on the silicious material, and, in some cases, as heat from surrounding structural activity (volcanism, dykes, et cetera) surrounds the silicious material, the water is squeezed or heated out of the chemical structure.  As a result, the silica mineral greatly decreases in volume, and its mineral structure may also be changed.  The result is not only a more widely recognizable mineral, opal, but also a depression in the Earth above the original material.  As water is squeezed out and volume decreases, overlying material begins to sink down, creating these typically round pock marks.  Their shape can vary, however, depending on how easily water can escape and via what conduits...for example, existing fracture and pore spaces (which occur especially in volcanic regions) can transport water away more effectively than other places around the silicious material, and therefore the resulting depression may show a shape bias towards those fractures and pore spaces.  But even the strangest shapes are variants on the original circle -- crescents, ovals, and the like.

Over the next couple of days, we're all excited to start our intensive survey south of Panama and prepare data for analysis once it arrives back at Scripps.


Brad