Ja. Kleypas, MODELED ESTIMATES OF GLOBAL REEF HABITAT AND CARBONATE PRODUCTION SINCE THE LAST GLACIAL MAXIMUM, Paleoceanography, 12(4), 1997, pp. 533-545
Estimated changes in reef area and CaCO3 production since the last gla
cial maximum (LGM) are presented for the first time, based on a model
(ReefHab) which uses measured environmental data to predict global dis
tribution of reef habitat. Suitable reef habitat is defined by tempera
ture, salinity, nutrients, and the depth-attenuated level of photosynt
hetically available radiation (PAR). CaCO3 production is calculated as
a function, of PAR. When minimum PAR levels were chosen to restrict r
eef growth to 30 m depth and less, modern reef area totaled 584-746 x
10(3) km(2). Global carbonate production, which takes into account; to
pographic relief as a control on carbonate accumulation, was 1.00 Gt y
r(-1). These values are close to the most widely accepted estimates of
reef area and carbonate production and demonstrate that basic environ
mental data can be used to define reef habitat and calcification. To s
imulate reef habitat changes since the LGM, the model was run at 1-kyr
intervals, using appropriate sea level and temperature values. These
runs show that at the LGM, reef area was restricted to 20% of that tod
ay and carbonate production to 27%, due primarily to a reduction in av
ailable space at the lower sea level and secondarily to lower sea surf
ace temperatures. Nonetheless, these values suggest that reef growth p
rior to shelf flooding was more extensive than previously thought. A c
rude estimate of reef-released CO2 to the atmosphere since the LGM is
of the same order of magnitude as the atmospheric CO2 change recorded
in the Vostok ice core, which emphasizes the role of neritic carbonate
s within the global carbon cycle. This model currently addresses only
the major physical and chemical controls on reef carbonate production,
but it provides a template for estimating shallow tropical carbonate
production both in the present and in the past. As such, the model hig
hlights several long-standing issues regarding reef carbonates, partic
ularly in terms of better defining the roles of light, temperature, ar
agonite saturation state, and topography on reef calcification.