[Coral-List] hurricanes, muddy water and coral reefs

[Eugene Shinn]

Recent Hurricane Ian and the suspended lime mud and ground water issue 
observed in the Western side of the Florida Keys have reminded me of 
some useful earlier observations. I once wrote all these observations up 
but unfortunately I cannot locate them. From memory here are what I 
consider the significant geological observations regarding suspended 
calcium carbonate mud now being observed in post Ian satellite images.

Following our monitoring well installations at Dry Tortugas in August 
2004, where we used my personal trawler, Papa-San as a dormitory, we 
were interrupted by the approach of hurricane Charley. It was about to 
cross Western Cuba as did Ian. After storing our equipment at Ft 
Jefferson I transported the crew (Dr.Dale Griffin, Donald Hickey, and 
Ann Tihansky) back to Key West where they boarded our USGS vehicle and 
drove home to St. Petersburg.

My wife Patricia, flew to Key West and we piloted the boat to Miami and 
moored it at Crandon Marina. We then flew home to prepare our home for 
Charley which was coming ashore near Ft. Meyers. Ironically the storm 
was following a course similar to storm Ian moving northward and east of 
St. Petersburg. Afterwards we flew back to Miami and piloted Papa-San, 
to Stuart, Fl. As we departed Miami’s Government Cut to begin the 
offshore transit to Stuart I noticed that when we reached the area 
seaward of the reef tract the bottom suddenly disappeared on our 
fathometer. I switched to my second fathometer and again observed that 
the bottom was not being recorded. Surface water was crystal clear blue 
as is typical seaward of the outer reef line. I knew the depth in that 
region was between 100 and 150 ft and there was nothing wrong with the 
fathometers. As we continued northward at between 7 and 8 knots we never 
saw bottom until we turned westward to enter the Stuart Inlet. It was 
clear something was absorbing the seismic signals and preventing any 
returns. All the while I was remembering observations relayed to me many 
years earlier by Underwater Photographer Ed Fisher.

Back then, (1957) I was a marine Tec for Sigmund Miller at the 
University of Miami Marine Lab on Virginia Key. Ed Fisher, who also 
worked there had asked me to help him with a Navy project off Ft, 
Lauderdale, Florida. The Navy had been testing experimental air-drop 
mines in 125 ft of water a few miles south of the Port Everglades ship 
channel. The mines were anchored by a specially shaped concrete anchor 
attached by a long cable to the torpedo shaped mine positioned about 35 
ft below the surface. The navy had two tall towers on shore equipped 
with telescopes that by cross triangulation allowed them to pin-point 
the mines exact locations. (this was long before GPS). Using radios, 
operators on the towers guided our Navy utility boat to the mine’s exact 
location. Using SCUBA, Ed Fisher and I jumped into the water directly 
over the mine. Ed, was shooting a 35mm UW still camera while I filmed 
with a 16mm Bolex underwater film camera. We took photos because the 
mines were painted with an experimental copper based antifouling pant 
invented by my supervisor sig Miller at the University of Miami Marine 
Lab. I would then follow the cable down to the bottom and film the 
cement anchor focusing especially on the cable connections. What was 
surprising to me were evenly spaced half meter high sand ripples 
(mega-ripples) oriented east west. It was clear that fairly strong 
currents moving northward had periodically created the ripples. It 
seemed unusual to me that these ripples had formed at a depth of 125 ft. 
(later as described in my Memoir "Bootstrap Geologist” We photographed 
and filmed a destroyer with secrete devises on the bottom passing 
overhead at full speed. That was a thrill.)

Now jump forward to a few days after Hurricane Donna smashed through the 
coral reefs off the Florida Keys on Sept 10, 1960. I was then working 
for Robert N. Ginsburg at a small lab in Coral Gables funded by Shell 
Development co. (the research arm of Shell Oil). In the mean time I 
remained a good friend of Ed Fisher who was still doing some contract 
work with the Naval Facility at Ft. Lauderdale. Around a week after the 
storm Ed described diving down to inspect the mine anchor but was 
stopped 15 or 20 ft above the bottom by a wall of extremely muddy opaque 
water moving northward. It was clearly a product of Hurricane Donna the 
effects of which we were studying in the Florida Keys. In the Keys I 
worked with Mahlon Ball who was observing the geologic effects of the 
storm on offshore coral reefs (see Ball et al 1967). We observed that 
the reef tract turned extremely muddy for at least a month every time 
the wind increased to about 15 mph and aerial photos showed the milky 
water sinking below the surface seaward of the reef tract. It became 
apparent that the northward moving layer of muddy water Ed had observed 
off Ft Lauderdale had been created by the hurricane. Ed collected a jar 
of the muddy water but no one at the Marine Lab was interested. That 
surprised us because creation of “turbidites” as they are called was a 
hot ticket in geology at the time. On later dives Ed reported the mud 
had settled in swales between the sand ripples at the mine anchor 
location. This memory was on my mind when my two fathometers could not 
see the bottom as we cruised northward following Hurricane Charley.

I remembered all of this again when Ken Banks and others were observing 
the die off of corals off Ft. Lauderdale in the mid 1980s. They reported 
finding layers of stiff lime mud around the corals offshore of Ft. 
Lauderdale. At the time I was serving on an active committee with these 
researchers during the 1980s and 1990s. All of this came to light again 
after the passage of Hurricane Katrina, West of Dry Tortugas in 2005. 
Deep water corals west of Tortugas bank experienced vast amounts of lime 
mud around the corals and again muddy water again was reported flooding 
along the bottom off Ft. Lauderdale. I suspect this is a common 
phenomenon after hurricanes stir up the bottom off the west coast of 
Florida. The layers of stiff lime mud are probably like the stiff mud 
layers that were formed when Andrew passed over the Bahama Bank as we 
documented in our 1993 publication. This should be remembered when coral 
researcher find unexpected mud layers in areas where there are also 
coral reefs. Gene

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Ball, M.M., Shinn, E.A., and Stockman, K.W., 1967, The geologic effects 
of Hurricane Donna in south Florida: Journal of Geology, v. 75, no. 5, 
p. 556-591.

Banks, K.W. Reigl, B. M. Shinn, E. A. Piller, W. E. Dodge, E. R. 
,(2007), Geomorphology of the Southeast Florida continental reef tract 
(Miami-Dade, Broward, and Palm Beach Counties, USA) Coral Reefs, 26: 617-633

Shinn, E.A., Steinen, R.P., Dill, R.F., and Major, R., 1993, Lime-mud 
layers in high-energy tidal channels: A record of hurricane deposition: 
Geology, v. 21, p. 603-606.