11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 3: Calcification and Coral Reef - Past and Future
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A Tropical Surface Water Calcium Carbonate Saturation History For The Late
Pleistocene
Bradley OPDYKE* 1 , Stephen EGGINS 2
1 Research School of Earth Science, Australian National University, Canberra ACT,
Australia, 2 Research School of Earth Science, The Australian National University,
Canberra ACT, Australia
Knowing the history of the surface water calcium carbonate saturation in tropical waters
is critical to understanding the dangers posed to Coral Reefs by declining saturation states
in the future due to increased CO2 inputs from anthropogenic sources. We present here
the first paleo- saturation record from the Indo-Pacific Warm pool region, specifically the
Timor Sea, south of the Island of Timor. Near surface dwelling (0-50m) planktonic
foraminifera Globigerinoides ruber were measured for the time intervals spanning 6-
63Ka and 130 to 110Ka. Mg and Sr were measured employing a novel approach; laser
ablation inductively coupled mass spectrometer (LA-ICP-MS). This method allows for
precise determination of the chemistry of foraminifera tests in depth profiles of their trace
element content. A stratigraphy was constructed from the MD 982167 core.
From each layer sampled, fifteen to twenty G. ruber per were analysed and the average
value determined. In was discovered that Sr/Ca increases in Globigerinoides ruber at
higher surface water saturation state and Sr/Ca peaks at 1.6 (mmol/mol) in the Early
Holocene (8ka) and dips to 1.5 (mmol/mol) during colder time intervals back to Stage 5e
(128ka) where the ratios return to Holocene values. Coral Reefs, also respond strongly to
changes in temperature and calcium carbonate saturation state. Combining these data
with paleotemperature data will allow us to predict where and how vigorously coral reef
communities would have thrived going back in time. These paleo-saturaturation data not
only allow us to put future changes of the chemistry of the surface sea water in context
but will allow more accurate modeling of coral growth histories around the globe.
3-2
The Darwin Point: a Conceptual and Historical Review
Richard GRIGG* 1
1 Oceanography, University of Hawaii, Honolulu, HI
The term “Darwin Point” is defined as the geographic or depth limit (threshold) beyond
which vertical growth or net accretion of reef building corals is zero or negative.
Consequently, coral reefs and/or atolls that exist at, below or beyond a Darwin Point
threshold would be expected to undergo drowning under conditions of constant sea level.
If present ecological conditions were to change, for example, due to a rise or fall in sealevel,
or geophysical uplift or subsidence, or due to Global Climate Change, the
geographic location or depth limit of a Darwin Point would correspondedly change. In
this paper, the history of the Darwin Point concept is reviewed and several examples are
given of reefs and atolls that have drowned having exceeded a Darwin Point threshold.
Such appears to be the case for: 1) guyots beyond the northwestern end of the Hawaiian
Archipelago, 2) atolls that crossed equatorial latitudes due to plate movement in the
Pacific during Cretaceous Time, and 3) many drowned reefs extant at the present time; a
result of sea-level rise since the last Glacial Maximum 21,000 years ago.
3-3
Declining Coral Calcification in Massive Porites in Two Nearshore Regions Of The
Northern Great Barrier Reef
Timothy F COOPER* 1,2 , Glenn DE'ATH 1 , Katharina E FABRICIUS 1 , Janice M LOUGH 1
1 Australian Institute of Marine Science, Townsville, Australia, 2 School of Marine and Tropical
Biology, James Cook University, Townsvile, Australia
Temporal and spatial variation in skeletal density, linear extension and calcification rate in
massive Porites from two nearshore regions of the northern Great Barrier Reef (GBR) were
examined over a 16 year study period. Calcification rates declined by approximately 21% in the
two regions, which are ~450 km apart. This is a function primarily of a decrease in linear
extension (~16%) with a smaller decline in skeletal density (~6%). These changes were linear
over time. Averaged across colonies, skeletal density declined over time from 1.32 g cm -3 (SE =
0.017) in 1988 to 1.25 g cm -3 (0.013) in 2003, equivalent to 0.36% yr -1 (0.13). Annual extension
declined from 1.52 cm yr -1 (0.035) to 1.28 cm yr -1 (0.026), equivalent to 1.02% yr -1 (0.39).
Calcification rates (the product of skeletal density and annual extension) declined from 1.96 g cm -2
yr -1 (0.049) to 1.59 g cm -2 yr -1 (0.041), equivalent to 1.29% yr -1 (0.30). Mean annual seawater
temperatures had no effect on skeletal density but a modal effect on annual extension and
calcification with maxima at ~26.7ºC. There were minor differences in the growth parameters
between regions. A decline in coral calcification of this magnitude with increasing seawater
temperatures is unprecedented in recent centuries based on analysis of growth records from long
cores of massive Porites. This talk will discuss the decline in calcification within the context of
known environmental controls on coral growth. Although these findings are consistent with
studies of the synergistic effect of elevated seawater temperatures and pCO2 on coral
calcification, further data on seawater chemistry of the GBR are required to better understand
the links between environmental change and effects on coral growth.
3-4
Declining Calcification Rates Of Bermudan Brain Corals Over The Past 50 Years
Anne COHEN* 1 , Nicholas JACHOWKSI 2 , Ross JONES 3 , Struan SMITH 4
1 Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, 2 Stanford
University, Palo Alto, CA, 3 Bermuda Institute of Ocean Sciences, St Georges, Bermuda,
4 Georgia State University, Atlanta, GA
We used ScionImage (freeware) to quantify greyscale variability in CT-scan images of twenty
colonies of the brain coral Diploria labyrinthiformis, collected live from four sites on Bermuda.
The average colony age, determined from counts of annual high/low density couplets, was 45
years, spanning the time period 1959-2004 AD. A 233 yr-old colony, collected live, was also
included in the analysis. 6cm-wide slabs, cut from the center of each colony were scanned
alongside a series of Ca-hydroxyapatite standards of known density. The CT images (*.dicom)
were manipulated to expose the appropriate (upward) orientation and slice thickness, in our
case, 7.5 mm. Using ScionImage, greyscale variability (x-ray intensity) was quantified along a
minimum of 10 tracks down the length of each colony, averaged and converted to density
(g/cm3) using the standard calibration. Skeletal extension rates were determined from the
distance (in mm) between successive high-density bands, and calcification rates as the product
of extension and density.
Our data indicate that skeletal extension and calcification rates of D. labyrinthiformis across the
reef declined significantly between 1959 and 2004. On average, annual skeletal extension rates
decreased by more than 25%, from 4.2 (±0.2) mm/yr to 3.1 (±0.1) mm/yr, while annual
calcification rates decreased by 25%, from ~4 g/cm2/yr to 3 g/cm2/yr. The last 45 years of
growth of the 233-yr old coral reproduced these trends, indicating that ontogenetic processes
were not a factor in the trends observed in the younger colonies. That documented changes in
oceanographic conditions in the subtropical North Atlantic over the past 50 years - including
rising SST, changes in circulation patterns linked to NAO and decreased saturation state of the
surface ocean - may have individually or collectively influenced the skeletal growth of
Bermuda’s corals, will be discussed.
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