11th ICRS Abstract book - Nova Southeastern University

1.24
Enigmatic Coral Rock Pillars -Another Look Into Reef Dynamics
Helmut SCHUHMACHER* 1 , Roland KRONE 2 , Peter VAN TREECK 1
1 Dept of Hydrobiology, Universitaet Duisburg-Essen, Essen, Germany, 2 Marine animal
ecology, Alfred-Wegener-Institute for polar and marine research, Bremerhaven, Germany
Stone capped calcareous pillars, rising 10-70 cm above the surrounding reef surface are
to be found at Aqaba (Jordan) and on several other fringing reefs of the Northern Red Sea
from intertidal down to 3 m depth. Terrigenous (non-calcareous) cobbles and boulders
are fixed on top of coral limestone. It is assumed that the stones were once introduced by
fishermen or by exceptional floods and came to rest in depressions of the reef.
Afterwards the surrounding reef limestone was eroded so that only the substrate
underlying the granite stones has been left as singular towers. 14C-dating of a column
sample from Aqaba provided an age of 560-345 years. Several interpretations are
possible: the respective reef part did not grow since then, or younger layers were
removed by bioerosion – during which time? Some suggestions are provided based on
erosion data of sea urchins (Diadema setosum) and fish, gathered at that site. More
(subtidal and intertidal) examples of partial reef decline are presented to stir discussion
about circumstances and modes of bioerosional reef shaping.
1.25
Ancient Reefs And The "Legacy Cycle": A New Pedagogical Approach To Teaching
Earth Science, With Emphasis On Climate Change And Sea Level Rise Awareness
Katherine ELLINS* 1 , Lida TENEVA 2
1 Institute for Geophysics, University of Texas - Austin, Austin, TX, 2 Earth and
Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University,
Palisades, NY
Effective communication of recent findings to the public, especially on issues pertaining
to global climate change, is vitally important in order to prepare citizens to make
informed decisions that affect human well-being and the future of our planet. We have
designed a new pedagogical approach, Legacy Cycle,that uses computer technology to
formulate a series of inquiry activities around a set of three driving questions. Students
mimic the work of scientists by generating ideas around a given challenge, listening to
multiple perspectives from experts on the topic, researching a set of sub-questions and
revising their original ideas, testing their mettle with labs and quizzes, and finally
composing a project or paper that answers the original challenge. Each challenge builds
on the previous challenge(s); students start with more concrete, basic knowledge and
eventually apply it to novel situations. In our Legacy Cycle, the first challenge asks
students to identify what the presence of certain corals (Montastrea annularis, Acropora
palmata, and Acropora cervicornis) in coral cores indicates about the marine
environment of the coral at the time of growth and sea level. Sub-questions involve
learning about modern coral reef environments and investigating the ancient El Capitan
reef complex (Permian) in the Guadeloupe Mountains of Texas to understand how this
typical rimmed carbonate platform formed, at a time of great biodiversity, and just prior
to the Permo-Triassic extinction. The second challenge asks students to examine and
evaluate the quality of paleosealevel data from Barbados, Tahiti, Papua New Guinea and
other records. The third challenge requires that students gain a better understanding of
current climate change and present and future influences causing sea level to rise and fall,
in particular.
Poster Mini-Symposium 1: Lessons from the Past
1.26
Coral Morphology as an Indicator of Sedimentation Rate in Two Exposed Holocene
Reefs: Western Dominican Republic
Allicia DAVIS* 1 , Dennis HUBBARD 2 , Alexandra STEIN 3
1 Geological Sciences, Indiana University, Bloomington, IN, 2 Geology, Oberlin College,
Oberlin, OH, 3 Monterey Bay Aquarium, Monterey, CA
Coral-community structure was examined in two subaerially exposed Holocene reefs in the
western Dominican Republic. Four coral facies (branching, mixed, massive, platy) were
identified based on species abundance and diversity. At both sites, coral-growth rates were
slower (1-3 mm/yr) than for similar species at the same water depths on modern reefs. Corals
were also classified by shape along over 20 vertical transects. Colony shape is controlled by a)
the intensity of sediment stress and b) coral species. Within a single species, colonies change
from hemispherical to conical to columnar as increasing sedimentation progressively
discourages lateral colony extension. In the Cañada Honda reef, colonies of Montastaea
faveolata are predominantly columnar, compared to a more conical shape for nearby colonies of
Siderastrea spp. The reef at Las Clevellinas was closer to shore and is characterized by
interfingering alluvial sediments and nearshore reefs under greater sediment stress.
Accordingly, colonies of more-tolerant Siderastrea shifted to a columnar morphology, and lessresistant
Montastaea spp. all but disappeared. These patterns collectively support the
presumption of high levels of sediment stress in these outcrops, despite the occurrence of over
25 species of coral and an overall abundance rivaling or exceeding what has been reported for
unstressed modern Caribbean reefs. On both reefs, fluctuating sedimentation results in fluted
colony margins, as the colony base is overcome by rapid sediment and later grows outward in
times of lower sedimentation (termed "pancakes", owing to their stacked morphology). Within
colonies exhibiting this morphology, patterns appear to be rhythmic on a scale of 8-15 years,
and may reflect cyclic rainfall under the influence of larger climate patterns (e.g., ENSO).
Equally important, because these corals appear to be growing at or near their ability to avoid
burial, they provide a unique opportunity to quantitatively characterize sedimentation on these
reefs, both spatially and temporally.
1.27
120 Years Record Of Delta-18ow Deconvolving From Porites Coral Delta-18o And Sr/ca
At San Benedicto Island in The Mexican Transition Zone in The Northeastern Pacific.
Julio VILLAESCUSA* 1 , Jose CARRIQUIRY 1
1 IIO-Environmental Geochemistry, Universidad Autonoma de Baja California, Ensenada,
Mexico
The oxygen isotopic composition of seawater (delta-18Ow) was reconstructed from delta18O
and Sr/Ca records from a coral Porites sp. from Island San Benedicto, Revillagigedo
Archipelago in the Tropical - Subtropical Transitional zone in the Mexican Pacific (PTM), for
the last 120 years. This region is located in the north edge of the eastern Pacific warm pool and
is one of the areas less studied of the major coastal currents of the world, despite the tropical
Mexican Pacific is recognized as a key region that modulates the climate of an important part of
Mexico and North America. The delta-18Ow variation reconstructed responds directly to the
changes in the regional sea surface salinity (SSS) and consequent with the hydrologic balance
(Evaporation – Precipitation or E-P). The delta-18Ow shows a freshening trend during the last
four decades, coherent with the trend analyses of salinity or precipitation (e.g., Boyer et al.
2005, GRL 32, L01604, doi:10.1029/2004GL021791). The delta-18Ow from the San Benedicto
coral varies with the long term changes in the average position of the Intertropical Convergence
Zone (ITCZ) in the northeastern Pacific. The negative correlation between both signs implies
that the northern displacement of ITCZ (~14ºN) produces an enhancement of rainfall in San
Benedicto region (19Nº). The correlation between delta-18Ow and the changes in the ITZC
position, as well as the long term changes in delta-18Ow show low frequency variability, are in
phase with the interdecadal changes in the intensity of the ENSO events. The periods from 1878
to 1906 and from 1932 to 1967, a more positive delta-18Ow signal suggests a lower rainfall
than average and is consistent with periods of low variability in the ENSO activity. In contrast,
a more negative delta-18Ow, that implicate periods of rainfall higher than average that occurs
from 1906 to 1932 and of 1967 until the end of record, and are coincident with periods of strong
ENSO activity.
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