The mighty R/V Pelican entered the final sampling location early Friday evening. The location? The Orca Basin (and no, it’s not the Okra Basin, as I first heard it) is the most westward and the deepest of our 6 sampling sites. The basin, located about 300 km southwest of the mouth of the Mississippi River, is famous for what lurks in its depths: anoxic brine!
After watching the dramatic shift in the halocline on the CTD readings at around 2100 m, we launched our final multi-core sampler to retrieve sediment and water at the brine-sediment interface. The multi-core arrived on deck in the wee hours of the morning, but Shelby and I eagerly hopped to it. This core turned out to be the most exciting one of the trip!
Unlike previous cores, which typically were an elephant-gray (the anoxic layer), capped with 10-20 cm of rich brown-gray sediment on top (the oxic layer), there was a distinct third layer, from 10-25 cm, of a rusty-red hue.
Due to the anoxic brine (which one of the graduate students accidentally tasted when removing the brine prior to extrusion), there were no visible forms of life at the surface, unlike previous sediments, which were populated with tubeworms, foraminifera, and even a sea cucumber at one site.
As Shelby and I extruded the core, there was one more surprise at the interface of the brown and red layer:
We wondered, “Peach-fuzz? Glass wool?…Traces of alien life?”
We took a subsample and Jo Muller, a geologist and professor from Florida Gulf Coast University, suggested these were spiculae, or hair-thin fibers of silica formed by foraminfera in the sediment. But Jo was quick to admit that these spiculae were longer than anything she had encountered before.
We could barely contain our curiosity and excitement, and after sampling from the 10-15 cm range, we sieved through the remaining sediment of that layer to get a better sense of the spiculae and happily packed it away in a separate jar. At around 25 cm in depth, the color of the core changed from red to gray, and the spiculae all but disappeared. The concurrence of the red sediment and the spiculae? That’s a mystery for another day…
Your faithful maritime mystery seekers,
Shelby and Sarah
(*definitely not “Redrum” on the high seas, nor any other Shining moments!)