11th ICRS Abstract book - Nova Southeastern University

1-17
Holocene Reef Development At The Flower Garden Banks: Recent Surprises
William PRECHT* 1 , Ken DESLARZES 2 , Emma HICKERSON 3 , G.P. SCHMAHL 3 ,
James SINCLAIR 4 , Richard ARONSON 5
1 Applied Coastal and Environmental Services, Battelle Memorial Institute, Miami Lakes,
FL, 2 Marine Sciences, Geo-Marine Inc., Plano, TX, 3 Flower Garden Banks National
Marine Sanctuary, NOAA, Galveston, TX, 4 Gulf of Mexico Region, Minerals
Management Service, New Orleans, LA, 5 Marine Sciences, Dauphin Island Sea Lab,
Dauphin Island, AL
The first living colonies of Acropora palmata were discovered on the Flower Garden
Banks (FGB) in 2003 and 2005. Those discoveries, coupled with a known history of bank
flooding since the last glacial maximum, led us to predict that Acropora-dominated
reefs underlie and form the structural foundation of the living reef community at the
FGB. In June 2006, while scuba diving on the southeast corner of the East FGB, we
examined an open cave at 21 m depth, which exposed a 3-m vertical section of the reef
subsurface just below the living community. Within that exposure we discovered large
branches and trunks of A. palmata (>1 m in height) in growth position. Radiocarbon
dating of a branch from a colony at the top of the section yielded a date of 6330 ± 60
14Cyr (radiocarbon years before 1950), corresponding to a calibrated age of 6780 calbp.
Follow-up surveys in June 2007 revealed an A. palmata dominated under story dating
between 10-6 ky on both banks. The discovery of fossil A. palmata has profound
implications for understanding the history of reef development at the FGB. The banks
supported a shallow, warm-water, reef-coral assemblage up until ~6000 years ago. This
community lagged behind rapidly rising sea level in the middle Holocene. As sea
temperatures cooled in the late Holocene the reef was capped by a eurythermal deeperwater
assemblage dominated by massive corals, which persists to this day. During our
2007 surveys we also found the first fossils of Acropora cervicornis on the East FGB.
This species appears to have persisted (and flourished) until the Little Ice Age in deeper
water on the flanks of the Bank. Follow-up studies are proposed to document and explain
the turn-on and turn-off mechanisms for Acropora reef development on these isolated
reef complexes.
1-18
Response Of acropora To Warm Climates; Lessons From The Geological Past
Clare WHITE* 1,2 , Brian ROSEN 3 , Dan BOSENCE 1
1 Earth Sciences, Royal Holloway University of London, Egham, Surrey, United
Kingdom, 2 Palaeontology, Natural History Museum, London, United Kingdom,
3 Zoology, Natural History Museum, London, United Kingdom
Predictions about the future responses of modern coral reefs to global climatic change
lack data from the deeper past. The geological record offers a storehouse of information
which documents how reef coral palaeodistributions have been highly sensitive to climate
change, modulated by the availability of suitable habitats. The geological record of one
individual taxon, Acropora, illustrates how an important reef coral genus has responded
to climate change, and additionally tectonics, through its Cenozoic history.
We have reconstructed Acropora’s changing spatio-temporal distribution using museum
specimens, literature reviews and databases, and plotted the data on a time-series of
palaeogeographic maps and on ‘Boucotgrams’. Unlike Acropora’s widespread lowlatitude
distribution today, with its centre of diversity in the Indo-West Pacific, this coral
was absent from this region in the Paleogene to early Neogene, but was common in
Europe. Here we highlight (1) latitudinal changes in distribution in response to major
climatic trends, and (2) the relatively late arrival of Acropora in the Indo-West Pacific,
apparently in response to tectonically-driven rearrangement of Tethyan and Indo-Pacific
seaways and land-masses around the end of the Paleogene. Focusing on a particular
section of this record, the high palaeolatitude (48˚N) occurrences in the Middle-Late
Eocene (~48-33Ma) of southern England and northern France, we use taphonomic and
geochemical analyses to reconstruct the palaeoenvironmental setting. This confirms that
Acropora existed in tropical-like climatic conditions in Northwest Europe during the
Eocene. This individual coral genus’s latitudinal expansion, compared with modern
distributions, illustrates “coral creep” as a response to the hot greenhouse setting of the
early Cenozoic, and periods of extreme climatic warming of the Eocene, with sea-surface
temperatures and ρCO2 higher than present. Hence this work shows how the geological
record can provide information to complement predictions on the fate of modern coral
reef genera with respect to climate change.
Oral Mini-Symposium 1: Lessons From the Past
1-19
Abrupt Drowning And Cooling 8.2-8.4 Ka Observed In A 0.8-M Diameter And 24-M
Long Core Through A Hawaiian Coral Reef, Oahu, USA
Eric GROSSMAN* 1 , Jody WEBSTER 2 , Christina RAVELO 3 , Jim BARRY 4 , Stewart
FALLON 5 , Yael SAGY 1 , Bruce RICHMOND 1 , Mike TORRESAN 6 , David CLAGUE 7
1 Coastal and Marine Geology Program, US Geological Survey, Santa Cruz, CA, 2 School of
Earth and Environmental Sciences, James Cook University, Townsville, Australia, 3 Ocean
Sciences Department, University of California, Santa Cruz, Santa Cruz, CA, 4 Sea Engineering,
Inc., Honolulu, HI, 5 Research School of Earth Sciences, Australian National University,
Canberra, Australia, 6 Coastal and Marine Geology Program, US Geological Survey, Menlo
Park, CA, 7 Monterey Bay Aquarium Research Institute, Moss Landing, CA
Sediment collected in a 0.8 m diameter, 24 m long core at 18 m depth offshore of Pearl Harbor
provide a geologic archive of reef response to the Holocene sea-level transgression on the island
of Oahu, Hawaii. CHIRP seismic reflection data reveal a 5-15 m thick reef complex buried
below the seafloor within a paleostream valley. An olivine-rich, black sand and rounded basalt
cobble unit, inferred as an early Holocene delta occurs at the base of the core overlying a soilstained,
caliche-encrusted limestone dated to 124 ka. 14-C ages indicate a shallow-water coral
reef assemblage comprised of encrusting P. lobata and branching coralline algae P. gardineri
accreted until 8.4 ka, then was abruptly replaced by a mono-specific P. compressa reef between
8.4 and 8.2 ka and added 10 m to the reef by about 4.9 ka. Approximately, 4.5 m of carbonaterich
sand buried this reef complex and comprises the modern seafloor substrate at the site. The
abrupt transition from shallow-water to deeper-water coral assemblages at 8.4-8.2 ka is
coincident with rapid climate change observed in other reefs, lakes, and sedimentary records
throughout the tropics. Reconstruction of paleowater depths at this transition indicates a rapid
rise in sea level of at least 3 m, helping to explain preservation of a drowned erosional notch
surrounding many shorelines of Hawaii at -24 m like a bath-tub ring. High-resolution
measurements of δ18O and Sr/Ca ratios from three P. compressa corals 8.7-8.3 ka, indicate
cooler surface water temperatures than today and a slight cooling during this event. Abrupt sealevel
rise of several meters could explain the transition in coral community structure, the
dominance of mono-specific P. compressa, and colder sea surface temperatures.
1-20
Evidence of rapid sea-level rise from reef backstepping during the Last Interglacial
highstand.
Paul BLANCHON* 1
1 Inst. of Marine Sciences & Limnology, National University of Mexico, Cancun, Mexico
Investigation of reef development during the Last Interglaciation has focussed on flights of
exhumed terraces in neotectonic terranes. But the timing of climatic cycles has taken
precedence over reef response to sea-level change. As a result, we have no clear picture of
highstand reef development nor sea-level changes that controlled it.
Here I report the facies architecture of a highstand reef from the NE Yucatan Peninsula that
affords significant insight into reef development and sea-level behaviour during the Last
Interglaciation. Excavations for a theme park (Xcaret) have exposed two coeval reef-tracts that
are offset and at different elevations. The lower-tract crops-out along the coast and the crest
facies reaches an elevation of +3.0 m amsl. One hundred metres in-land, the crest of the uppertract
reaches +5.7 m amsl. Crests in both tracts were true breakwaters, each consisting of large
colonies of A. palmata and boulder-sized fragments with a suite of surf-zone encrusters. Lowertract
frameworks are occluded by crustose corallines, but those in the upper-tract remained open
and were infiltrated by abraded sand during forced shoreface regression. This infiltration is
clear evidence that the upper-tract was younger than the lower, and that reef backstepping
occurred.
Backstepping was not related to shelf flooding to the north, because that had occurred during
lower-tract development. But backstepping was accompanied by increased sediment flux that
shifted lagoonal biofacies to a sediment-tolerant assemblage. Similar changes occurred in the
strand-plain sequence to the north, but here it involved a switch from low- to high-energy
coastal sedimentation. This energy switch and reef backstepping are both consistent with a +3
m sea-level jump at the end of the Last-Interglacial highstand.
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