Pk. Swart et al., The use of proxy chemical records in coral skeletons to ascertain past environmental conditions in Florida Bay, ESTUARIES, 22(2B), 1999, pp. 384-397
This paper wilt discuss the use of chemical proxies in coral skeletons to r
econstruct the history of salinity (from the delta(18)O of the skeleton) an
d nutrients in the water (from the delta(13)C) in Florida Bay between 1824
and 1994. Monthly salinity and water temperature data collected since 1989
were used to establish a correlation between salinity, temperature, and the
delta(18)O Of the skeleton of the coral Solenastrea bournoni from Lignumvi
tae Basin in Florida Bay. This relationship explains over 50% of the varian
ce in the delta(18)O Of the skeleton. Assuming that interannual variations
in the temperature of the water are small, we have applied this relationshi
p to the delta(18)O measured in the coral skeleton collected from Lignumvit
ae Basin which has a record between 1824 and 1993. These data provide a rev
ised estimate of salinity variation in Lignumvitae Basin for the period whe
n historical records for salinity were not available, and show that the hig
hest salinity events occurred in the past 30 yr. Using the relationships be
tween the salinity in Lignumvitae Basin and other basins, obtained using a
modern dataset, we are able to estimate ranges in salinity for other portio
ns of Florida Bay. Skeletons of specimens of the coral species Siderastrea
radians collected from other areas of Florida Bay show similar patterns in
the delta(18)O over the past 10 yr, indicating that corals in most portions
of Florida Bay are recording salinity variations in their skeletons and th
erefore support the idea that salinity variations in different portions of
Florida Bay can be related. Fluorescence analysis of the coral from Lignumv
itae Basin shows a large change in the magnitude of the 10-yr signal coinci
dent with the construction of the railway, confirming that this event had a
significant impact upon Florida Bay. The delta(13)C of the coral skeletons
reveals a long-term history of the oxidation of organic material, fixation
of carbon by photosynthesis (algal blooms), and the intrusion of marine wa
ter into the bay. Since the construction of the railway from Miami to Key W
est there has been a long-term decrease in the delta(13)C of the coral skel
eton from Lignumvitae Basin, suggesting the increased oxidation of organic
material in this area. This decrease in delta(13)C appears to have reached
a minimum value around 1984 and has increased since this time in the wester
n portions of Florida Bay. The increase may be related to the algal blooms
prevalent in the area or alternatively could result from intrusion of more
marine water. In the eastern areas, a small increase in the delta(13)C betw
een 1984 and 1988 was followed by further decline suggesting more oxidation
of organic material. We have also attempted to use the concentration of ba
rium in the coral skeleton as a proxy indicator of the nutrient status in F
lorida Bay.