201
sea level was some 400 ft. (120 m) lower than today. The land mass of the Florida
peninsula was about double the current size, with the western side extending far out
into the Gulf of Mexico (Fig. 12.9b). As the ice sheets melted, waters rose, and
coastlines migrated laterally to give us the geographic shape of the Florida we know
today. So, what would future changes in sea level and climate mean for the
Everglades, the mangrove coastline and the urban areas of south Florida?
I had been contemplating where the best places would be to collect cores that
could answer these questions when fate intervened in the form of Hurricane Wilma,
which struck south Florida as a category 3 storm in 2005. Wilma was the first significant hurricane to hit south Florida since we began our work there in 1994. Two
months after Wilma, we went out to do field work in Florida Bay and as we pulled
up to one of our sites near an island, we saw large piles of seagrass on the open
mudflats inside of the mangroves that form the edge of the island. I had looked at
the open flats on the interior of these islands for years, but that was my “Aha!”
moment. I realized that these mud flats were acting like large bowls – storm surges
were depositing material on the flats, but the surrounding mangroves were the rim
of the bowl, protecting the deposits from subsequent erosion. What was deposited
on the island, probably stayed on the island. This would be the ideal place to look
for evidence of changes in sea level, past storm events and the role of mangroves in
forming the islands and coastal margins. Now I just had a couple of problems. First,
finding the time and funding for the plan that was unfolding in my mind; and second, the bigger hurdle of convincing the Park Service to give me permission to go
on the islands (protected wilderness) with a field crew and take a bunch of cores!
Finally, in 2014 everything fell into place and we launched our expedition. In
addition to myself and the project’s irreplaceable lab manager and field assistant
who joined us in 2009, the team of eight included experts in pollen, diatoms (microscopic algae), storm deposition, carbon storage, and sediment geochemistry. We
needed two boats to carry all the people, gear, core tubes, and enough food and
water to last for at least 2 days in case something went wrong. Once we got to the
island, the boats had to be off-loaded. This was especially tricky on one island
where we needed to anchor the boat over a hundred yards off-shore and make our
way through the soft mud and seagrasses carrying the equipment. This required
what we refer to as “the duck walk” or “knee-walking.” The idea is to move forward
on your knees with your lower legs splayed out behind you acting like snow-shoes
to prevent you from sinking in. Definitely a good workout!
We had planned to core on five islands, but at the last minute we had to eliminate
one island because we couldn’t disturb a family of nesting bald eagles. On each of
the four islands we were coring, our goal was to collect a transect of cores from near
the edge, just inside the perimeter of the mangroves, and toward the center of the
mudflats. Comparing the sediments on the edges of the island to those in the center
would hopefully show us how the islands formed. However, once we set foot on the
islands, we realized that wasn’t going to be possible in every case. The mudflats
consist of very fine-grained carbonate mud, and on some of the islands this mud
turns to the consistency of pudding when wet (Fig. 12.10). It is impossible to set up
12 Climate, Sea Level, and People – Changing South Florida’s Mangrove Coast
sea level was some 400 ft. (120 m) lower than today. The land mass of the Florida
peninsula was about double the current size, with the western side extending far out
into the Gulf of Mexico (Fig. 12.9b). As the ice sheets melted, waters rose, and
coastlines migrated laterally to give us the geographic shape of the Florida we know
today. So, what would future changes in sea level and climate mean for the
Everglades, the mangrove coastline and the urban areas of south Florida?
I had been contemplating where the best places would be to collect cores that
could answer these questions when fate intervened in the form of Hurricane Wilma,
which struck south Florida as a category 3 storm in 2005. Wilma was the first significant hurricane to hit south Florida since we began our work there in 1994. Two
months after Wilma, we went out to do field work in Florida Bay and as we pulled
up to one of our sites near an island, we saw large piles of seagrass on the open
mudflats inside of the mangroves that form the edge of the island. I had looked at
the open flats on the interior of these islands for years, but that was my “Aha!”
moment. I realized that these mud flats were acting like large bowls – storm surges
were depositing material on the flats, but the surrounding mangroves were the rim
of the bowl, protecting the deposits from subsequent erosion. What was deposited
on the island, probably stayed on the island. This would be the ideal place to look
for evidence of changes in sea level, past storm events and the role of mangroves in
forming the islands and coastal margins. Now I just had a couple of problems. First,
finding the time and funding for the plan that was unfolding in my mind; and second, the bigger hurdle of convincing the Park Service to give me permission to go
on the islands (protected wilderness) with a field crew and take a bunch of cores!
Finally, in 2014 everything fell into place and we launched our expedition. In
addition to myself and the project’s irreplaceable lab manager and field assistant
who joined us in 2009, the team of eight included experts in pollen, diatoms (microscopic algae), storm deposition, carbon storage, and sediment geochemistry. We
needed two boats to carry all the people, gear, core tubes, and enough food and
water to last for at least 2 days in case something went wrong. Once we got to the
island, the boats had to be off-loaded. This was especially tricky on one island
where we needed to anchor the boat over a hundred yards off-shore and make our
way through the soft mud and seagrasses carrying the equipment. This required
what we refer to as “the duck walk” or “knee-walking.” The idea is to move forward
on your knees with your lower legs splayed out behind you acting like snow-shoes
to prevent you from sinking in. Definitely a good workout!
We had planned to core on five islands, but at the last minute we had to eliminate
one island because we couldn’t disturb a family of nesting bald eagles. On each of
the four islands we were coring, our goal was to collect a transect of cores from near
the edge, just inside the perimeter of the mangroves, and toward the center of the
mudflats. Comparing the sediments on the edges of the island to those in the center
would hopefully show us how the islands formed. However, once we set foot on the
islands, we realized that wasn’t going to be possible in every case. The mudflats
consist of very fine-grained carbonate mud, and on some of the islands this mud
turns to the consistency of pudding when wet (Fig. 12.10). It is impossible to set up
12 Climate, Sea Level, and People – Changing South Florida’s Mangrove Coast