Reef Science: Development Highlights
Watanabe, Atsushi, Kayanne, Hata, Kudo, Nozaki, Kato,
Negishi, Ikeda, and Yamano. Analysis of the seawater CO2
system in the barrier reef-lagoon system of Palau using total
alkalinity-dissolved inorganic carbon diagrams. Limnol. Oceanogr.,
51(4), 2006, 1614-1628.
We studied the seawater carbon dioxide (CO2) system
in the Palau coral reef by measuring total alkalinity (TA)
and total dissolved inorganic carbon (DIC). Variation in the
CO2 system on the reef flat and in the lagoon was
analyzed by TA-DIC diagrams, taking into accounts the differing
residence times of seawater. CO2 in the offshore
water was relatively stable in space and time, but on the
reef flat it was subject to rapid (about 3 hours) and substantial
changes due to photosynthesis and calcification during the
day and due to respiration and calcification at night. Water
flowed into the lagoon where decomposition of organic matter
and continuing calcification occurred over relatively long
residence times (~30 days). Despite the spatial and temporal
variations, the center of the lagoon had relatively constant
TA and DIC values similar to the mean values for the entire
lagoon. A long-term 30-40% decrease in reef productivity and
calcification has occurred over the last decade, primarily
a result of degradation of the reef environment following
a major coral reef bleaching event in 1998. This is reflected
in decreases in the differences in TA and DIC between offshore
lagoon waters and those in center of the lagoon.
The CO2 concentration in water varies with photosynthesis,
respiration and water exchange rates. The authors noted that
offshore water's CO2 concentration was reasonably
stable over time. On the reef flat, however, it changed rapidly
within several hours and substantially between day and night
due to differences in calcification rates, and a change from
photosynthesis to respiration modes.
In recent years the differences in CO2 concentration
between different waters have decreased dramatically due to
a coral bleaching event in 1998, which degraded the reef environment.
Hence, even in a natural flourishing reef environment, where
there is plenty of water exchange and movement, the CO2
concentration (and also it's pH value) can change significantly
during the day.