January 11, 2013 - Sampling day!
So, in order for me to explain where and how we take sediment samples, I need to explain a bit about what we're doing when we stay up all night on watch.
Those CHIRP lines from an earlier post are cross-sections of the ocean subsurface, which we see on the computer as soon as the CHIRP receives them.
We're looking for divots, mounds, or channels that have been filled in or for scours -- really any sign of erosion or deposition. Because we're focusing on the upper ~ 2 meters (~6 feet), any of these features could have been made by Hurricane Sandy.
We have pre-Sandy maps and cross-sections of the seafloor. Now we're making new maps and getting cross-sections of post-Sandy in order to compare and see the effects of a superstorm on the coastal system.
However, mapping these features with geophysical techniques isn't enough. We need to know what they are made of, which is where the geology comes in. This is where we get dirty! We need to grab a piece of the seafloor to see what kind of sediment it contains.
It could be mud (black, green, etc...) or sand (coarse, medium, or fine) or full of broken shells, all of which mean different things. So we send down a conveniently named "grab sampler," which is kind of like a bear trap.
It's open when we lower it off the ship, and when it hits the seafloor, it snaps shut, grabbing a part of the surface and roughly 5 cm below. Then we pull it up and see what we've gotten.
We got everything from green mud to coarse sand and sometimes, mixtures of both! The sample's contents are important and can provide information about what happened during the storm. For example, if we see a thin layer mud on top of sand, indicating that the sand was there originally, and the mud was "draped" over it in the storm.
That means the energy of the water pushing out after the storm was great enough to carry mud all the way from the bays between Long Island and the barrier islands (like Fire Island) to where we grabbed it, about 2.25 nautical miles (~ 2.5 miles) offshore.
These data on the storm are important because we, as a scientific community, do not understand how large storms affect things such as coastal resources or beaches or plant and animal habitats offshore and in marsh area. We know that storms take sand off the beaches, so we replace the sand.
Then another storm hits and we do it again. But where does Long Island's sand go? Can it come back? Will it show up somewhere in Delaware, or maybe Maine? Can Long Island get sand from Rhode Island beaches if a storm hits there?
In order to protect and preserve our beautiful beaches for future generations, we must study how storms change them and figure out how to work with Mother Nature instead of against her.
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