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McKee: We‘re on a mangrove island off the coast of Belize, and we’ve come here to collect some cores
through the entire profile of the island down to the Pleistocene limestone. Beneath me is eleven meters
of peat. That’s the equivalent of a three- story building.
What we are doing is we are collecting cores in segments that we’re bringing up and collecting and
preserving and later we’re going to be looking at the botanical fossils that are contained in those cores.
We’ll also be radiocarbon dating some of these cores to tell us how old each segment of the core is.
Previous cores suggest that this island has always been a mangrove system and it has built vertically
over a period of about 8,000 years…as sea level has risen over that time period. It has built vertically
many, many meters and has accumulated this peat very gradually. And this allows the island to keep up
with changes in sea level.
Vervaeke: Got it?
McKee: Yep. OK.
McKee: OK, so this is one of our peat cores. It’s a half-meter section. This is from four point five to five
meters in depth, and this is probably between forty-five hundred and five thousand years old. And what
we’ll be doing is we’ll be collecting this and taking it back to the lab where we will log in all the
characteristics of it…anything…any strata..sections that we see in this…any changes in the consistency of
the core. Then we’ll be taking subsamples to identify any botanical fragments that we find in this core.
And we’ll also be taking samples for looking at the chemistry of the core as well as some other features
that will tell us something about the past environment that this peat was formed under. So now we’re
gonna package up this core and take the next section.
McKee: OK. So, we’re at ten meters..here. Still in mangrove peat. Pretty solid. I can see a lot of root
material and some leaf material.
Vervaeke: Count us down, Karen.
McKee: OK. One. Two. Three. Holy smokes!
Vervaeke: There it is!
Vervaeke: Ha, ha..good call.
McKee/Vervaeke: (gasp) Ooohh. Look at that.
Vervaeke: Keep going?
McKee: (gasp) Look at that. (Gasp)
Vervaeke: What do you want me to do?
McKee: Just hold it.
McKee: Uh. Wow.
Vervaeke: What is it?
McKee: It’s, ah, sediment. Clay…it looks clay-like.
Vervaeke: That’s new.
Vervaeke: Got it?
McKee: Yep .
McKee: I’m here in the Smithsonian’s Carrie Bow Cay field laboratory, and what I’m doing is examining
under magnification the peat samples that we collected yesterday. By identifying fragments within the
peat, this will tell us something about the plants and plant communities that existed in the past in this
mangrove ecosystem. We take photographs of these fragments, and compare them to modern material
and this allows us to identify the species of plants that were present in the past.
McKee: With dating of the peat, we can use those dates to reconstruct the sea level history of this
region along with cores taken in other locations around the Caribbean.
McKee (animation narration): By radiocarbon dating peat at different depths, we can determine how
many years ago that peat was formed. This core covered a time span of almost 8,000 years…based on
the oldest date measured at the bottom of the core. This time period is referred to as the Holocene.
Beneath the Holocene peat is limestone that was formed during the Pleistocene, an earlier time period.
By comparing the peat dates with a sea-level curve for the region, we can see if this mangrove island has
kept pace. The four peat dates measured in this core all fall on the sea-level curve, which shows that
these mangroves have kept up with sea-level rise for the past eight thousand years.
These mangrove islands accomplish this feat by slowly accumulating roots in layers at the soil surface.
Over time, the roots die and contribute to peat formation.
Because oxygen is lacking in the saturated soil, the roots are preserved, creating a strong matrix that is
not easily eroded. These fossil roots were dated and found to be over 7500 years old.
McKee: What this work tells us is that intact and healthy mangroves are essential to vertical building of
these islands as sea level increases. The information from this project will also help us understand how
mangroves may respond to future sea level rise.
IMAGES AND ANIMATIONS
“Mangrove Peat Island”, “Peat Chronology”, and “Peat Formation” animations; videography; and still
photography: Karen L. McKee
MUSIC AND SOUND EFFECTS
“Jaracanda”, “Island Long”, “Pendulum” (Apple iMovie Royalty-Free Music Clips)
McKee, K.L. 2004. Belowground dynamics in mangrove ecosystems. USGS Fact Sheet 2004-3126.
McKee, K.L. 2004. Global change impacts on mangrove ecosystems. USGS Fact Sheet 2004-3125.
McKee, K.L. 2011. Biophysical controls on vertical accretion and elevation change in Caribbean
mangrove ecosystems. Estuarine, Coastal and Shelf Science 91: 475-483.
McKee, K.L., D.R. Cahoon, and I.C. Feller. 2007. Caribbean mangroves adjust to rising sea-level through
biotic controls on change in soil elevation. Global Ecology and Biogeography 16: 545-556.
McKee, K.L. and P.L. Faulkner. 2000. Mangrove peat analysis and reconstruction of vegetation history at
the Pelican Cays, Belize. Atoll Research Bulletin 468: 46-58.
Middleton, B.A. and K.L. McKee. 2001. Degradation of mangrove tissues and implications for peat
formation in Belizean island forests. J. Ecology 89(5): 818-828.
Toscano, M.A., & Macintyre, I.G. 2003. Corrected western Atlantic sea-level curve for the last 11,000
years based on calibrated C-14 dates from Acropora palmata framework and intertidal mangrove peat.
Coral Reefs 22: 257-270.
Rutzler, K., & Feller, I.C. 1996. Caribbean mangrove swamps. Scientific American 274: 94-99.
Filmed on location in Belize.
Thanks to the Smithsonian Institution’s Carrie Bow Cay Laboratory for logistical support.
Title: What Lies Beneath: Using Mangrove Peat to Study Ancient Coastal Environments and Sea-Level Rise
This video describes how scientists study past changes in sea-level and coastal environments by analyzing mangrove peat. Mangrove islands located off the coast of Belize are underlain by deep deposits of peat (organic soil), which retain a record of past sea level, vegetation, and climate. By studying past changes in sea level and how intertidal ecosystems, such as mangroves, have responded to these changes, we can better predict what will happen in the future as sea levels increase. The information generated by such research is critical to geophysical modeling efforts as well as to management and conservation of coastal ecosystems.
Location: , Belize, Central America
Date Taken: 5/1/2008
Video Producer: Karen McKee , U.S. Geological Survey
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Read USGS fact sheet: “Belowground Dynamics in Mangrove Ecosystems”
and “ Global Change Impacts on Mangrove Ecosystems” for more information.
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