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bioerosion data that are scant at best. While none
of the values are inconsistent with those found
in the literature, this cartoon is neither a quan-
titative treatment nor a proof that the proposed
relationship actually exists. This must await more
careful measurement of depth-related bioerosion
and sediment-export patterns. It nevertheless
highlights the potential importance of bioero-
sion as something more than a secondary control
of reef accretion and architecture. It may ulti-
mately prove to be as important as calcifi cation
by corals in determining the rates at which reefs
are built.
This study has shown that in the Caribbean and
western Atlantic these relationships have not
been as strong over the past 10-12,000 years,
as has been assumed. It is not clear whether
this pattern holds for other oceans or other time
periods. Dullo (2005) has provided an excellent
synthesis of coral growth and reef accretion in the
Caribbean versus the Indo-Pacifi c, and has pro-
posed that the early plateau in sea level c . 6000
years ago restricted reef-building and resulted
in slower rates of reef accretion in the latter.
A more-detailed look at shorter-term accretion
within individual reefs (and cores) would pro-
vide an excellent comparison to this study and
could serve to broaden our understanding of the
role of sea-level rise and accommodation space in
a pattern that seems considerably different than
has been taught.
Whether or not something akin to the scenario
depicted in Fig. 11 ultimately emerges as the
correct explanation, the lack of a substantial
decrease in reef accretion according to either
depth or species cannot be ignored, and may have
profound implications for models of coral-reef
accretion over the past 10,000 years, and perhaps
longer. At the very least, these fi ndings reinforce
the idea that reefs do not grow in the organic
sense, rather they build or accrete as largely
physical structures in which biological processes
make varying contributions. Thus, although
impossible, it would be fortuitous indeed if it
were possible to simply strike the phrase 'reef
growth' from the literature. While 'growth' in the
strictest sense is not incorrect, the phrase 'reef
growth' makes a strong inference of biological
primacy that would not be of concern when
discussing, for example, 'delta growth' or 'fault
growth'.
In the absence of oceanographic stresses that
limit calcifi cation as a supplier of raw material
for reef building, the rate of sea-level rise emerges
as the primary determinant of whether or not a
reef will “keep up” or “give up” ( sensu Neumann
& Macintyre, 1985). Prior to 7000 cal. yr BP, sea-
level rose at a rate exceeding 5 m kyr 1 , faster than
accretion in most of the core intervals measured in
this study. After 6000 cal. yr BP, this rate dropped
below 1 m kyr 1 , and virtually every reef shallower
than 25 m was capable of keeping pace or exceed-
ing on rising sea level. In some instances, accretion
in reefs closer to sea level was probably con-
strained by a lack of accommodation space. While
this undoubtedly skewed the pattern of shallow-
water accretion rates reported in this study, its
The 'drowning paradox'?
Based on an assumption that 'many Holocene
reefs can be shown to have outpaced even the
fastest sea-level rise', Schlager (1981) proposed
that reef drowning presents a paradox that can be
resolved only by extreme events such as sudden
and rapid sea-level rise or degraded oceanic
conditions that severely compromise the accre-
tionary capacity of a reef or platform. Based on
the results of this study, reefs that accrete at rates
in excess of 7 m kyr 1 are in fact rare. Only one
out of 151 intervals exceeded that threshold and
was not part of a slower, long-term aggradational
history. Given this, the drowning of a reef or plat-
form seems much less surprising. Parts of reefs
are capable of extraordinary 'sprints', but reef
accretion is generally slower and sea level
largely exerts the dominant control. At the
average rate of reef accretion proposed by this
study (3-4 m kyr 1 ; blue band in Fig. 10b),
reefs would have lagged behind rising sea
level prior to 7000-6000 years ago when the
rate of sea-level rise slowed below this value.
After this time, most Caribbean reefs were
able to catch up in the absence of some envir-
onmental stress that severely compromised the
ability of reef biota to make carbonate.
Signifi cance to existing models
Two fundamental principles that underlie our
existing Holocene coral-reef models are:
(1)
reefs in shallow water (i.e. <5 m) build an
order of magnitude faster than their deeper-
water counterparts (i.e. >10-15 m);
reefs dominated by branching corals accrete
(2)
much faster than those primarily inhabited by
slower-growing, massive species.
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