Day 4 of Sampling: Holy Beach!

Today we finished sampling all of the gravity core samples and opened the one intact vibracore we collected from Pos482 CADISED on the cute vessel POSEIDON.  A gravity core can mainly sample only mud.  This device has of 1.5 tons of weight attached to a cable with the core pipe and core sample sleeve inside.  As a gravity core is slowly lowered through the seafloor, it collects material as far into the strata as the material will allow it to penetrate.  The core catcher keeps the sample within the core sleeve as the device is brought back up to the ship.  A vibracore is much more complicated since it is meant to sample sands and more consolidated sediments. This device is lowered to the seafloor where it sits as it cores. A vibrating motor is located on top of the coring rod with a core sleeve inside.  The vibration from the motor pushes the core into the sediment.

The left photo shows the gravity core.  The right photo shows the vibracore.  Credit: Pos482 CADISED.

Most of the gravity core samples were from mud depocenters.  The material inside of these cores mainly consisted of pretty homogeneous mud, surprise, surprise.  The one intact virbacore came from a location that was only in 40 meters of water, close to shore.  About halfway through this 5m core we found very rounded pebbles within sand that indicate a high energy environment.  The only type of environment with high enough energy to round pebbles is a beach where the waves constantly move them.  For beach pebbles to be within the middle of a core 40m below the surface of the Gulf of Cadiz, sea level had to of been much lower, bringing us to the early Holocene. Below the beach horizon, a solid reddish soil horizon exists suggesting an even older history of sea level changes.  Exciting Science!! 

A view of the area within the core with rounded pebbles. Credit: Mary Lee King.

German word of the day: Fire Extinguisher = Feuerlöscher

Prost from across the pond,

Mary Lee