11th ICRS Abstract book - Nova Southeastern University
11th ICRS Abstract book - Nova Southeastern University
11th ICRS Abstract book - Nova Southeastern University
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Oral Mini-Symposium 4: Coral Reef Organisms as Recorders of Local and Global Environmental Change<br />
4-13<br />
Coral Records Of Late 20th Century Warming And Freshening in The Central<br />
Tropical Pacific<br />
Intan NURHATI* 1 , Kim COBB 1 , Chris CHARLES 2<br />
1 Georgia Tech, Atlanta, GA, 2 Scripps Inst. of Oceanography, UCSD, La Jolla, CA<br />
Corals have been widely used to reconstruct past climate due to high fidelity in capturing<br />
climate variability. Modern corals from the central tropical Pacific (CTP) have provided<br />
monthly climate records that show trends toward depleted coral d18O values in the late<br />
20th century. These trends might infer warming and/or seawater freshening in the region.<br />
It is important to understand the mechanism behind these trends, to better predict lowfrequency<br />
changes in tropical Pacific climate that may be associated with anthropogenic<br />
warming. One mechanism involves weakened tropical Pacific zonal SST gradient that<br />
would warm the CTP by reducing upwelling and enhance precipitation. Alternatively,<br />
warming might have occurred without changes in upwelling, and the lower salinities may<br />
signal changes in the location and/or strength of the ITCZ. Here we reconstruct late 20th<br />
century SST and salinity using coral d18O and Sr/Ca from Palmyra, Fanning and<br />
Christmas Islands (2-6ºN,157-162ºW). Palmyra at the northern end, is heavily influenced<br />
by the North Equatorial Counter Current (NECC) and the ITCZ; while Christmas at the<br />
southern end, is heavily influenced by the South Equatorial Current and equatorial<br />
upwelling. We measure Sr/Ca (SST proxy) and coral d18O values with analytical errors<br />
of ±0.3% or ±0.4ºC(1s), and ±0.05‰(1s), respectively. We derive d18O of seawater<br />
(salinity proxy) by removing the Sr/Ca-derived SST contribution from coral d18O values.<br />
Sr/Ca-based SST reconstructions show warming of 0.22, 0.25 and 0.5ºC/decade from<br />
Palmyra to Christmas, which may suggest a decrease in equatorial upwelling. d18Oswbased<br />
salinity reconstructions show seawater freshening of 0.31, 0.1 and 0.12psu/decade<br />
from Palmyra to Christmas, which may suggest an enhanced and/or southward migration<br />
of the ITCZ as well as changes in the salinity of waters advected by the NECC.<br />
Simultaneous warming and freshening in CTP corals may indicate a weakening of the<br />
tropical Pacific zonal SST gradient in the late 20th century.<br />
4-14<br />
Reconstructing Sea Surface Temperature Variability in The Southwest Pacific: A<br />
Replication Study Using Multiple Coral Sr/ca Records From New Caledonia<br />
Kristine DELONG* 1 , Terrence QUINN 2,3 , Frederick TAYLOR 2<br />
1 College of Marine Science, <strong>University</strong> of South Florida, St. Petersburg, FL, 2 Institute for<br />
Geophysics, Jackson School of Geosciences, <strong>University</strong> of Texas at Austin, Austin, TX,<br />
3 Dept. of Geological Sciences, Jackson School of Geosciences, <strong>University</strong> of Texas at<br />
Austin, Austin<br />
Coral Sr/Ca reproducibility was investigated using three intracolony and three<br />
intercolony coral records from the reefs offshore of Amédée Island, New Caledonia. By<br />
convention, coral colonies are sampled along the vertical growth axis. This convention<br />
was tested by comparing vertical and horizontal paths on a small Porites colony from<br />
Vanuatu and a larger colony from New Caledonia. No significant difference in Sr/Ca<br />
variations was observed when the corallite growth direction was parallel to the sampling<br />
path and the sampling path followed the top of the lobe. Different sampling resolutions<br />
were examined in coral Sr/Ca (fortnightly and monthly) and δ18O (fortnightly, monthly,<br />
and seasonally) as well as similar scale subsampling of the daily in situ sea surface<br />
temperature (SST) record. The mean coral Sr/Ca, δ18O, and SST values do not change as<br />
a function of sampling resolution. The coral Sr/Ca signal is highly reproducible; the<br />
average absolute offset between coeval monthly Sr/Ca determinations between any two<br />
coral time series is 0.035 ± 0.026 mmol/mol (1σ) (~0.65ºC), which is less than twice the<br />
analytical precision of the coral Sr/Ca measurements. The stack average of the monthly<br />
coral Sr/Ca variations and monthly anomalies are significantly correlated with monthly in<br />
situ SST (1967–1992; r = –0.96 and –0.64, respectively; p < 0.05; and n = 302) and 1º<br />
grid monthly SST data product (1900–1999; r = –0.95, and –0.56, respectively; p < 0.05,<br />
n = 1198). The coral Sr/Ca–SST reconstruction exhibits interannual and decadal-scale<br />
fluctuations that exceed those observed in the gridded SST record, which may reflect true<br />
differences between SST at a shallow reef site and those averaged over a 1º grid box or<br />
inadequacies in the methodology used to create the gridded SST product when few<br />
observations are available.<br />
4-15<br />
Stable Isotope Records From Western Pacific Shallow-Water Soft Coral And Black Coral<br />
Branwen WILLIAMS* 1 , Andrea GROTTOLI 2<br />
1 School of Earth Sciences, Ohio State <strong>University</strong>, Columbus, 2 School of Earth Sciences, Ohio<br />
State <strong>University</strong>, columbus, OH<br />
In some genera of soft corals and black corals, the δ 13 C and δ 15 N composition of the<br />
concentrically banded organic skeleton is controlled by the δ 13 C and δ 15 N composition of the<br />
particulate organic matter (POM) consumed by the coral colony. To test if these organisms<br />
record differences in the geochemistry of POM across depth, a sub-surface black coral (5m) and<br />
a deeper soft coral (85m) were collected live in 2006 from Palau (western tropical Pacific).<br />
High resolution (100 micron increments) δ 13 C and δ 15 N values were measured across a radial<br />
transect of the base of the organic skeleton in both colonies. The sub-surface black coral record<br />
showed an overall depletion of organic skeletal δ 13 C values at a rate comparable to that<br />
measured over the past few decades in atmospheric CO2-δ 13 C (i.e., Suess effect). The 85m soft<br />
coral record showed a depletion of δ 13 C values consistent with the past century of the Suess<br />
effect suggesting that this specimen was over one hundred years old. Overall, these initial data<br />
suggest the 85m colony had a slower growth rate typical of deep-water taxa, and that POM is<br />
the main source of carbon for skeletogenesis in these organisms. The ages of the two colonies<br />
will be more accurately constrained using radiocarbon measurements. A statistical comparison<br />
of the skeletal records with a seven year in-situ temperature record will be run to test for<br />
correlations between temperature (i.e., a proxy for water mass such that colder temperatures<br />
represents water below the mixed layer), and stable isotopes in the skeletal records. Together,<br />
soft corals and black corals in the western Pacific may provide paleoceanographic information<br />
on decadal to centennial timescales across the entire ocean depth range.<br />
4-16<br />
523 Years Of Interannual (Enso-Like) To Multidecadal (Pdo-Like) Climatic Signals<br />
Continuously Recorded in New Caledonia By Sr/ca And δ 18 o in A Giant Massive Porites<br />
Tim OURBAK* 1,2 , Thierry CORRÈGE 2 , Bruno MALAIZÉ 2 , Florence LE CORNEC 3 , Boris<br />
DEWITTE 4<br />
1 College of Marine Science, St Peterbsurg, FL, 2 UMR 5805 EPOC, Universite Bordeaux 1,<br />
Talence cedex, France, 3 Institut de Recherche pour le Developpement, Bondy, France,<br />
4 Observatoire Midi Pyrénées., Toulouse, France<br />
The southwest Pacific is a critical region concerning interannual to interdecadal climatic<br />
phenomena, such as El Niño Southern Oscillation (ENSO) or the Pacific Decadal Oscillation<br />
(PDO). Unfortunately, the length of meteorological data critically limits the understanding and<br />
analyses of such climatic variability. Trace elements and stable isotopes have been investigated<br />
in a 7m long coral core which records more than 500 years of environmental variability from Ile<br />
des Pins, south of New Caledonia (22°S, 167°E). This multiproxy approach allows<br />
reconstruction of sea surface temperature (SST) and sea surface salinity (SSS). SST variations,<br />
estimated from Sr/Ca, reveal a long-term warming over the period 1475 to 1998, modulated by<br />
interdecadal cycles. By removing SST component from the δ 18 O signal, we have estimated the<br />
paleosalinity variability. The SSS reconstruction presents mean saltier conditions at the<br />
beginning of the record, and a slow decrease in SSS throughout the whole record punctuated<br />
with freshening events, such as the one coinciding with a strong warming trend observed since<br />
~1890. We argue that changes in wind intensity (via evaporation/precipitation), together with<br />
advection processes, have changed over the last centuries in New Caledonia. Moreover, this<br />
very long core has recorded very intense ENSO phenomena during the end of the 16th century<br />
and the beginning of the 17th century consistent with numerous proxies circum-Pacific.<br />
21