11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 3: Calcification and Coral Reefs - Past and Future
3.49
Style Of Reef Accretion At Poleward Front in The Late Holocene, in The Northern
Ryukyu Islands, Japan
Hironobu KAN* 1 , Yosuke NAKASHIMA 2 , Nobuyuki HORI 3 , Tatsuo NAKAI 4 , Yusuke
YOKOYAMA 5 , Nozomu HAMANAKA 6 , Takehiro OKAMOTO 1 , Tomoya OHASHI 1
1 Faculty of Education, Okayama University, Okayama, Japan, 2 Ariake National College
of Technology, Omuta, Japan, 3 Department of Geography, Nara University, Nara, Japan,
4 Geography and Environmental Studies, Kokushikan University, Tokyo, Japan,
5 Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan,
6 Department of Earth System Science, Okayama University, Okayama, Japan
Typical acroporid reefs with distinct wave-resistant structure gradually disappear around
30 degrees north latitude in the northwestern Pacific. The Holocene development of two
high-latitude reefs in the northern Ryukyu Islands was studied by core drilling and
exposure of a cutting excavated across a modern reef.
Misaki Reef at northwestern Mage Island (30°45'40"N) developed from 6,650 to 4,500
cal yBP with an accumulation rate between 1.2 and 2.3 m/ka to form a 2.5 to 4.0 m-thick
reef structure. Shojiura Reef at northeastern Tane Island (30°42'N) developed from 3,500
to 2,300 cal yBP with an accumulation rate between 1.2 and 2.3 m/ka to form a 2.8 mthick
reef structure.
Major reef development at these sites ceased within less than 2,000 years. The timing of
reef development at Misaki Reef is coincidental with the Holocene maximum, whereas
Shojiura Reef developed after Misaki Reef formation stopped. This phase shift shows
that reef growth at high latitude is a site-specific phenomenon; similar reef development
did not occur at nearby areas at the same timing, resulting in patchy distribution of reefs
around the two islands.
The characteristic features of high-latitude reef development is delayed onset of growth
after sea level rise, slow accumulation rate and short duration of reef formation, forming
thin reef structures. The site-specific reef development indicates the uncertainty of reef
response to environmental factors that have increased at the poleward front in the
northern Ryukyu Islands during the late Holocene.
3.50
In Situ Measurements Of Calcification Rates And Calcification/dissolution
Thresholds in Coral Reef Communities Of South Florida And The U.s. Virgin
Islands
Kimberly YATES* 1 , Chris DUFORE 1 , Nathan SMILEY 1
1 U.S. Geological Survey, St. Petersburg, FL
Rates of community calcification were measured, in situ, in representative habitat types
of coral reef ecosystems in Florida Bay, Biscayne National Park, and the U.S. Virgin
Islands using a large benthic incubation chamber called the Submersible Habitat for
Analyzing Reef Quality (SHARQ). Carbonate system parameters including total
alkalinity, pH, and total carbon dioxide were measured every four hours during 24-hour
incubation periods, and calcification rates were calculated using the alkalinity anomaly
method. Habitat types included patch reef, seagrass, hard bottom, and mud substrate.
Diurnal trends in calcification rates were observed for all substrate types with
calcification occurring primarily during day-light hours and dissolution of carbonate
sediments observed during dark hours. Average rates of calcification during 24-hour
incubation periods were 0.47 and 1.18 g CaCO3 m -2 for patch reefs and hard bottom
communities, respectively. Seagrass and mud bottom communities showed equivalent
rates of net carbonate sediment dissolution of -0.22 g CaCO3 m -2 . Linear correlations
were calculated for each substrate type. Carbonate ion and pCO2 thresholds were
estimated as the concentration of CO3 2- and pCO2 at which rates of calcification and
dissolution were equivalent. The average pCO2 threshold for all substrate types was 585
µatm, and the average CO3 2- threshold was 203 µmol kg -1 . Threshold values vary
considerably among substrate types, and on similar substrate types during different time
periods. Atmospheric pCO2 is predicted to reach 700 µatm by the year 2100, surpassing
the average pCO2 threshold for these substrate types, and indicating that a significant
amount of sediment in coral reef ecosystems may be lost due to carbonate sediment
dissolution.
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