11th ICRS Abstract book - Nova Southeastern University

1-9
Coral Community Change Over A Cyclone Disturbance Gradient During The
Quaternary in The Solomon Islands
Brian BECK* 1 , Sean CONNOLLY 2 , John PANDOLFI 1
1 ARC Centre of Excellence for Coral Reef Studies, University of Queensland, Brisbane,
Australia, 2 ARC Centre of Excellence for Coral Reef Studies, James Cook Univeristy,
Townsville, Australia
Cyclones have a demonstrable impact on the short-term (100,000 years). It has been
proposed that higher sea surface temperatures associated with projected changes in global
climate might generate higher intensity storms with greater frequencies than in the recent
past, and that these changes might adversely affect coral reefs. During the Pleistocene of
the South Pacific, sea surface temperatures were higher than current temperatures. In this
study, we investigated the effects of cyclones on coral communities over long time scales
in the Solomon Islands. The Solomons have extensive raised reefs from the Pleistocene to
the recent, and there has been a marked spatial gradient in cyclone frequency during this
period; these characteristics allow an in depth look at how long-term community change
is influenced by cyclone frequency. Taxonomic composition and diversity of coral
communities were surveyed at several sites across a cyclone gradient, incorporating
multiple levels of cyclone frequency and multiple stratigraphic ages, using a hierarchical
sampling design. Coral diversity and growth form was examined over varying cyclone
frequencies from the warm Pleistocene seas to the comparatively cooler seas of the
Holocene. We found differences in the coral communities across cyclone gradients
attributable to varying cyclone frequencies. These differences not only illustrate
variation in community structure across a cyclone gradient within the same stratigraphic
age, but also show how communities in similar cyclone frequency change with sea
surface temperature change over time. These results are relevant in understanding how
coral communities can change as sea surface temperatures and cyclone intensity varies.
1-10
Reef slope failure in the northeastern corner of Male`, Maldives
Mahmood RIYAZ* 1 , Kyung-Ho PARK 1
1 School of Engineering Technology, Asian Institute of Technology, Pathum Thani,
Thailand
This study deals with the investigation of the reef slope failure occurred in the
northeastern corner of Male`, Maldives on the 6th of February 2002. Malé is the capital
of the Maldives with an area of 1.5m2 and a population of 130,000. Failed slope area was
mapped and systematically investigated. Radiocarbon dates of rock samples from various
depths were obtained. Aerial photograph and satellite image of Male reef 1969-2007
were compared to observe changes in the reef edge . The investigation shows that the
reef-flat, cap-rock, consists of 2~3m thick slightly cemented coral rock and rubble, and
beneath the cap-rock lays a 4~6m thick weakly cemented, highly erodible mixture of
coral sand and coral rubble. Further down 10~30m deep the slope of 30o steep is built up
by loose gravel and sand. The failure movement might have occurred during one single
event and the rock mass was sliding ‘en-block’ which finally disintegrated into individual
blocks in the block field. Radiocarbon dating of rock samples shows that the oldest is
8200 years at 20m depth, while the youngest is 6510 years at top reef, which indicates
that with the rapid vertical reef growth the horizontal progression of reef played a more
vital role in reef formation than the vertical growth. Aerial photographs and satellite
images show four more reef failure areas on the northern side and concentrated in the
areas of heavy weight and continuous vibration generation works. Due to the reef failure,
the capping rock layer was removed and subsequently the weakly cemented highly
erodible layer is exposed to further erosion. The eroded parts are expected to fall into
atoll lagoon and cause further retreat of the reef edge. Proper remedial actions must be
suggested for the overall stability and ground bearing capacity of the island.
Oral Mini-Symposium 1: Lessons From the Past
1-11
A 1500 Year Holocene Caribbean Climate Archive From The Blue Hole, Lighthouse Reef,
Belize
Eberhard GISCHLER* 1 , Eugene SHINN 2 , Wolfgang OSCHMANN 1 , Jens FIEBIG 1 , Noreen
BUSTER 3
1 Geosciences/Geography, Johann Wolfgang Goethe University, Frankfurt am Main, Germany,
2 College of Marine Science, University of South Florida, St. Petersburg, FL, 3 Florida Integrated
Science Center, ETI Professionals Inc., St. Petersburg, FL
Aspects of historical climate change are becoming increasingly important in reef research.
Common reefal climate archives include skeletons of corals and shells of mollusks among
others. Pleistocene sinkholes in reefal limestone also have great potential as archives of climate
data because they may act as sediment traps. Sediment cores (up to 6 m in length) from the
bottom of the Blue Hole, a 125 m deep Pleistocene sinkhole located in the Lighthouse Reef
Atoll, Belize, consist of undisturbed, annually layered biogenic carbonate muds and silts with
intercalated coarser grained storm beds. Sedimentation-rate is 2.5 mm/yr on average, and the
cores span the past 1500 yrs. Oxygen isotopes provide a late Holocene climate proxy: a highresolution
δ 18 O time series traces the Medieval Warm Period, the Little Ice Age, and the
subsequent temperature rise. Carbon isotopes (δ 13 C) decrease upcore and show the impacts of
the decline of the Maya culture and the Suess Effect. Time series analyses of δ 18 O and δ 13 C
reveal 88, 60, 52, and 32 year cyclicities, and suggest solar forcing. Storm event beds are most
common during AD 650-850, AD 1000, AD 1200-1300, and AD 1450-1550. Major storm beds
are rare during the past 500 years BP.
Holocene thickness in the Blue Hole is estimated to >20 m of annually layered sediment, given
the average sedimentation rate of 2.5 mm/yr and the early Holocene marine inundation of the
Lighthouse Reef lagoon. Because the Blue Hole probably formed not only during the previous
but during several Pleistocene sea-level lowstands, we expect that similar, laminated sediments
of previous Pleistocene highstands are present below the Holocene package. We plan to
investigate this late Quaternary climate archive in a future larger scale core study.
1-12
Environmental Factors Controlling Community Structure, Morphology And Linear
Extension Of Mid-Holocene Reef Corals From Cañada Honda, Southwestern, Dominican
Republic
David CUEVAS* 1 , Clark SHERMAN 1 , Wilson RAMIREZ 2 , Dennis HUBBARD 3
1 Marine Sciences, University of Puerto Rico at Mayaguez, Lajas, Puerto Rico, 2 Geology,
University of Puerto Rico at Mayaguez, Mayaguez, Puerto Rico, 3 Geology, Oberlin College,
Oberlin, OH
The Mid-Holocene Cañada Honda (CH) fossil reef, located in southwestern Dominican
Republic, provides a unique opportunity to examine a well-preserved fossil coral reef that
thrived in a high-sedimentation environment between 9.0 to 5.0 ky ago. Growth rates of fossil
Montastraea faveolata and Siderastrea siderea were determined in order to make comparisons
with growth rate data of these same species from modern coral reefs. Also, assessments of coral
species abundance and distribution, morphology, age, as well as reef sediment composition
were completed in order to determine the paleoenvironment of reef accretion.
The CH reef is characterized by the high abundance of sediment-tolerant coral species and their
tendency to form almost monospecific stands. Individual colonies have a propensity to grow as
encrusting, dome-shaped, platy-like forms and colonies of Montastraea faveolata commonly
contain bands of sediment incorporated within their skeletons. Calibrated radiocarbon ages of
fossil corals range from 9,256±137 to 6,737±94.5 BP. Correlation of radiocarbon ages with
well-established Holocene sea-level curves indicates that most corals on this reef developed at
depths greater than 15m. Growth rates in CH varied from 0.09-0.44 cm/yr and are relatively low
compared with growth rates from modern reef sites, suggesting reduced light penetration caused
by either coral growth at great depths and/or under conditions of high turbidity. Reef sediment
is characterized by more than 85% carbonate material. A significant portion of the carbonate is
allochtonous and was derived from nearby Neogene limestones.
Our investigations indicate that the CH reef persisted for at least 3,000 years under conditions
of high sedimentation. The reef was able to survive under these conditions because of the high
carbonate content of incoming terrigenous sediment that would have allowed better light
penetration and that storms probably occurred sporadically providing intervening lowsedimentation
periods during which reef corals could respond and grow back, “keeping-up”
with sedimentation.
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