feature of Halimeda bioherms in the Great Barrier Reef at
least, that is, they produce 3 kg CaCO 3 m
2 year
À1 compared to 3–4 kg for the reefs; however, the bioherms
occupy a larger area. They may, therefore, lock up
a greater proportion of CaCO 3 than do the reefs. Since
the correlation between carbon dioxide (CO 2 ) levels and
global temperatures was established in the ice core
records, this conclusion assumes an even greater significance because it indicates not only the relevance of calcareous algae as important additional CO 2 sinks but when
estimated on a global basis it also doubles the contribution
of shallow water carbonate sediments (in conjunction with
reefs) as CO 2 reservoirs (Rees et al., 2007).
Summary
Halimeda bioherms have been described from three parts
of the Great Barrier Reef: from the Sahul Shelf, from the
Makassar Straits, and from the Nicaraguan Bank. They
form mounds that are up to 20 m height and are comprised
of the skeletal remains of various species of Halimeda
A
C
D
E
G
F
B
Top
1.42
2.42
a
430 cm
500 cm
470 cm
3.40
4.4
5.42
Base
b
c
d
e
f
h
g
400 cm
5 cm
150 cm
150 cm
300 cm
Halimeda Bioherms, Figure 6 Cores from the Halimeda banks on the Cooktown shelf. The positions of detailed photographs are
shown on the cores.
HALIMEDA BIOHERMS
547