During the last few days we have been exploring the deepest depths of our Hudson cruise. ROPOS descended to nearly 3,000 m in the Northeast Fan on Sunday and to 2,500 m on Monday. At these deep depths life (and the ROPOS!) are subject to 300x the pressure experienced at the surface of the Earth, and the temperature is around 4C. The ROPOS team expertly collected rocks and sea urchin specimens for later analyses, carried out a video transect, did a plankton tow, a multibeam survey, and collected mud core samples. The multicorer was also used to collect mud samples at depth, and several CTD casts were carried out.
So what lives at those depths? We saw long stretches of mud with an abundance of brittlestars; bright yellow and purple sea cucumbers; large sea urchins; stalked crinoids, fish called grenadiers, bright red shrimp, and a silvery chimaera that looked like something out of the imagination of Dr.Seuss. The mud had evidence of bioturbation and was often covered in tracks of epifauna (such as brittlestars and sea cucumbers). Boulders were few, but when we did come across them they were commonly covered in dense epifaunal communities - the basketstars were particularly stunning - like a large flower at the bottom of the sea.
We could also see a continuous shower of large concentrations of 'marine snow' in the water column - marine snow is a term for the organic detritus (i.e. dead plankton, diatoms, sand, fecal matter, sand) falling from the productive sunlit surface layer (upper 200 m) down to the depths where light is absent (and so photosynthesis can not occur). As such, deep sea organisms are dependent upon this fall of marine snow as an energy source.