Geology Reference
In-Depth Information
(a)
Station 2: East Cape Canal North
40
3
35
2.5
30
2
25
400
Spring tide
300
200
100
0
20 Feb 05
21 Feb 05
22 Feb 05
23 Feb 05
24 Feb 05
25 Feb 05
Date
(b)
Station 5: Lake Ingraham
40
2.5
35
2
30
1.5
Fig. 12.
Time series of water level
(dashed) and salinity on top and
suspended sediment concentration on
bottom, measured with a CTD (conduc-
tivity-temperature-depth) and turbid-
ity meter: (a) Station 2 in East Cape
Canal (February 2005) and (b) Station 5
in Lake Ingraham (March 2005).
The drop in salinity on February 24
measured at Station 2 was caused by
extensive rainfall that day.
25
1
20
600
Spring tide
400
200
0
09 March 05
10 March 05
11 March 05
12 March 05
13 March 05
Date
Synthesis and interpretation
plumes are still fl owing out of HSC South and
ESC (Fig. 14b), where they meet the incoming
fl ood waters (Fig. 14c) and mix in the bend of ECC
(Fig. 14d). Vortices of organic-rich sediment
plumes are carried by the incoming tide towards
Lake Ingraham (Fig. 14e), building a rapidly
accreting delta (Fig. 14f).
The large amounts of suspended sediment
during the last phase of the ebb tide contain an
important component of carbonate and particu-
late organic matter, interpreted to originate from
the collapsed and decaying marsh behind the
marl ridge. A typical sediment sample in the col-
lapsed freshwater marsh contains >80% TOM
(decaying peat) at the sediment-water interface.
This widespread subtidal surface of loosely com-
pacted, low-density material can easily erode with
the slightest fl ow. Saline water that fl ows over the
marl ridge is trapped behind the marl ridge and
can escape only through the canals and natural
creeks that cut across this slightly higher, imper-
meable ridge. Large volumes of trapped tidal and
rain water fl ush out from this subtidal back-barrier
basin through HSC West and South and ESC, and
into Lake Ingraham and ECC (Fig. 14a). As these
waters 'fl ush' the collapsed freshwater marsh,
they carry large quantities of decayed, organic-
rich sediment. Every time the water level in the
collapsed marsh is higher than the water level in
ECC, and this situation happens basically with
every ebbing tide, large volumes of water drain
through the narrow canals. As the tide reverses
and Florida Bay waters come in, heavy sediment
DISCUSSION
Sea-level and coastal dynamics
Recent global stratigraphic and radiometric
studies indicate the existence of metre-scale
(0.5-2 m) high-frequency sea-level oscillations
after the mid-Holocene climatic optimum around
6000 years ago (DePratter & Howard, 1981;
Goodbred
et al
., 1998; Angulo
et al
., 1999; Islam &
Tooley, 1999; Martin
et al
., 2003). As a result,
the late Holocene sea-level trend is suggested
(Dominguez & Wanless, 1991; Stapor
et al
., 1991;
Baker & Haworth, 2000; Banerjee, 2000; Morton
et al
., 2000) to have been stepwise or with
embedded oscillations, instead of asymptotically
reaching its present position.
A sea-level oscillation recognized throughout
the Atlantic between 3200 and 2400 yr
BP
