hello my name is Emmet Bush and I'm a
senior in oceanography at the University
of Washington my project for the
undergraduate research symposium is
titled "Lignin phenol based evidence of a
rapid 8 centimeter sediment deposition
from a flooding event in the continental
margin San Blas Basin of Mexico" My
advisers were Dr. Rick Keil and Jaqui Neibauer. And that's like a lot of words for
a title so a better title -- pretty
comprehensive -- "Sticks in the Ocean Mud"
a lot of this work was done on Duwamish
and Coast Salish peoples land and we as
a school and Emmet as himself recognized
these people as the current and
ancestral stewards of this land and I
thank them for me being able to work on
their land so in the spring of 2018, I went
on a research vessel for a really long
time called the R/V Roger Revelle and about
day 35 at sea we arrived at this
location in the world (yellow star) off the Pacific
coast of Mexico on the Continental
margin and from a more flat earth
perspective this region of the world
looks like that it sticks out on the hip
of Mexico and there's a river nearby
called the Santiago River
it delivers sediment and water
and on an even more zoomed in map, this is from Geomap App. Our sampling location is
about 50 kilometers off of the coast and
it's that Red Dot down in the middle right there
that's where we took a sample. How we
got the sediment was we sent down a
multi core which is a really cool
instrument because it takes eight
samples that are pretty well-preserved
from the top sediment and our sediment
core got about 45 centimeters which is a
REALLY good yield
and we Chuck this thing off the side,
pretty carefully, and it gets lowered
down with the seafloor, and it drops, and it
scoops up the sediment and keeps the
strata intact and it is brought onto the
deck and that top photo is the top
fluffy layer of the sediment and is
pretty cool because it's like 80% water
20 percent sediment and as you go down
the core, there is compaction it gets more and more
thicker. The bottom photo is a you
can see kind of laminations of where the
bottom water had more oxygen or less
oxygen depending on the year and where
there's like black it shows like a an
event of what that microbial community
looked like at that time and after it's
brought up we spend HOURS slicing the
sediment into very fine slices sometimes
people will want to slice at 3
millimeters but for my sediment core we
sliced it every 2 centimeters so it
didn't take that long and as we were
slicing it in the middle of it at about
18 centimeters into the into the depth
the sediment core there is was a STICK
and then there's like a BIG seed pot and
there were just sticks EVERYWHERE and
that's weird
because we're like... Okay. First of all,
sticks -- they float -- what are they doing at
the bottom of the ocean? Two, um why are
there so many? like what's going on? like
we're so far away from the coast there
must have been some crazy geologic event
that happened so um the person named
Loïc Barbara who's that person right
there in the blue bandana was like
"Emmet you like lignin take one of the
octuplets from the multicore and go
study lignin" that's the cool thing about the
multi core you can give many
identical sediment cores to your
friends and they can do many experiments
all in one so you get like a lot of cool
data from one station. So there's sticks
everywhere what's going on? in the dry
bulk density analysis,
Loïc found out that there was a big
increase in density where there were
plant debris and on a previous research cruise
from the winter of 2016-2017,
that sediment core (left figure) was taken a little
bit south of the sediment core from the
2018 cruise (right figure). The winter 2016-2017 cruise (left figure) didn't have these
plant debris so we're like okay there's
some weird geologic big event that
happened it delivered these sticks to
the sediment and so we looked at the
terrestrial organic carbon through
lignin and lignin is a molecule that is
found in trees. It's highly abundant and
it helps trees stand up and oppose the
force of gravity. Lignin is in the
secondary cell wall of plants and it
binds the cellulose together.
Cellulose is that blue crystal-
crystalline structure and the lignin is
that reddish orange-y plaster kind of
spiderman molecule that's like grabbing
onto it in weird ways. it's a very like
complex structure to model yeah but
lignin is a big molecule it's made out
of teeny tiny little monomers called
lignin phenols and all these different
types of ligand phenols grouped together
to form the crazy complex spiderweb
structure and these are some pretty
common lignin phenols there's many more
but these ones are like pretty highly
abundant and are used in lignin analysis
for like environmental studies and we
eat some of these ligand phenols like
every day like you know: cinnamon, vanilla
like you've probably eaten --
I've eaten Lignin, it's pretty tasty
like cinnamon is like like you know how
people say cinnamon is from bark or
whatever cuz it's like from the trees
anyway that's a tangent so in the lab we
put a bunch of chemicals and the sediment
into a microwave and the microwave like
shakes all the lignin apart and it
breaks it up into lignin monomers and
then we can measure the relative of
abundance of the lignin monomers on a
mass spec or a gas chromatography
instrument and what we found was there
was a huge concentration of lignin
phenols in the sediment in that one area
where we found a bunch of sticks by like
an order of magnitude. notice the
logarithmic scale on the graph. so okay
cool we weren't just finding big sticks
we were finding teeny tiny microscopic
small plant fragments as well. This is a
zoomed up photo off the internet-- I don't
know who did this --my bad for not citing you. but it's like a
thin section of a ... of a plant and this is
woody tissue that has been exposed to fungal
degradation where fungus had consumed
and broken it up and fungus is kind of
cool cuz it can consume lignin. On the
left is an image of Red Rock fungus for
fungus degrades the cellulose the leaves
behind the red lignin. and on the right
is a example of fungus that degrades
lignin that leaves behind the white
cellulose. so there is a degradation
proxy we can use with the lignin phenols
based on their ratios (Vanilic Acid/Vanilin) to see how fresh
or degraded a sample is and in the
flooding event area in the sediment core
all that lignin had the same freshness
and it was the freshest ... the freshest in the whole sediment core sample. we can also find
out the approximate taxonomic origin of
where the plants in the sediment core
kind of came from and in this big plot
there's like four areas there's like an
angiosperm wood in the top left, there's
grasses and leaves in that big kind of
pale pink box, there's gymnosperm wood
down at the origin, and there's genus
firm needles farther out on the x-axis
and all of the lignin in the sediment
core from every single depth had a
strong presence of
angiosperm -- yeah either leaves or the
wood and that makes sense cuz we're in
México there's not like pine trees
around. there's like plants that have
leaves and like grasses like tropical
plants. we can also tell that the
degradation of the angiosperm in our samples meant that
this plot all of the these points should
have been more elevated on the y-axis
and like when there would have been a
fresh sample the lignin would have
presented more angiosperm endmembered
yeah by the way
Loic Barbera down in university of baja
california in Ensenada did a study on
the lead-210 for the age of when this
flooding event took place and he found
that it was in approximately 1750 and
there's a really cool paper by Núñez-Cornú at al 2008 called The Great 1787
Mexican Tsunami in this region is on a
subduction zone so a tsunami could have
caused this big floating event. (Rushing because I am out of time <3)
thank you so much to Rick and Jackie my
advisers Loic, Christina, Edgar and José
Carriquiry and my lab partner Garrett and
Khadijah, Jamee, Anna, and Megan and the
National Science Foundation for giving
us funding! (clap clap you rock!) Thank you so much! any
questions?
