Rarotonga Coral Based Radiocarbon Data: Readme file

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                   NOAA Paleoclimatology Program
                               and
              World Data Center A - for Paleoclimatology
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NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!!

NAME OF DATA SET: Rarotonga Coral Radiocarbon
LAST UPDATE: 10/2000 (Original Receipt by WDC Paleo)

CONTRIBUTORS: T. Guilderson (1,2), D. Schrag (2), E. Goddard (2)
M. Kashgarian (1), G. Wellington (3), and B. Linsley (4)


1.	Center for Accelerator Mass Spectrometry
	LLNL, L-397
	Livermore CA  94551

2.	Dept. of Earth and Planetary Sciences
	Harvard University
	Cambridge MA  02138

3.	Dept. of Biology and Biochemistry
	University of Houston
	Houston TX 77204

4.	Dept. of Earth and Atmospheric Sciences
	University at Albany, SUNY
	Albany NY 12222
	
IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2000-062

SUGGESTED DATA CITATION: Guilderson, T.P., et al., 2000,
Rarotonga Coral Based Radiocarbon Data, IGBP PAGES/
World Data Center A-Paleoclimatology 
Data Contribution Series #2000-062. 
NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. 


ORIGINAL REFERENCE: Guilderson, T.P., D.P. Schrag, E. Goddard,
M. Kashgarian, G.M., Wellington, and B.K. Linsley, 2000, 
Southwest subtropical Pacific surface water radiocarbon 
in a high-resolution coral record.
Radiocarbon, 42 (2), 249-256, 2000.


Additional References:
 
Stuiver, M., and H. A. Polach, Discussion and reporting of
14C data,  Radiocarbon, 19, 355-363, 1977.

Vogel, J. S., J. R. Southon, and D. E. Nelson, Catalyst and binder
effects in the use of filamentous graphite for AMS, Nucl. Instrum. 
Methods Phys. Res., Sect.B, 29, 50-56, 1987.

Davis, J. C., et al..,  LLNL/UC AMS facility and research program,
Nucl. Instrum. Methods Phys. Res., Sect. B, 52, 269-272, 1990.

Schrag, D.P., Rapid analysis of high-precision Sr/Ca ratios in 
corals and other marine carbonates, Paleoceanography 14, 97-102,1999.

 
GEOGRAPHIC REGION: subtropical South Pacific

PERIOD OF RECORD: 1950-1997 AD

FUNDING SOURCES: (US) NSF, Lawrence Livermore National Laboratory

LIST OF FILES: Readme.Rarotonga.txt (this file),
Rarotonga_14c.txt.
 
Variable names  CAMS#/DATE/Delta-14C  (integer/time/per mil)
missing data (NaN)

LONGITUDE: 159° 49'W
LATITUDE:  21° 14'S
WATER DEPTH:  Top of coral water depth 18m
CORAL SPECIES: Porites lutea
CORE LENGTH: 3.7m
DATE OF COLLECTION: 03/97 (J. Wellington et al.)


DESCRIPTION: 
Rarotonga coral radiocarbon (14C) timeseries.

Coral radiocarbon (Delta-14C) on untreated, low-speed drilled 
samples. Precision is ±4 per mil as documented by an in-house 
homogenized coral standard, and presented as AGE CORRECTED DELTA-14C 
[see Stuiver & Polach, 1977].


The sample cores were made on a Porites lutea coral located in open
marine conditions off Rarotonga. Cores were split and cleaned with distilled 
water.   After identifying the major vertical growth axis, the coral was 
sequentially sampled at 1 mm increments with a low-speed drill. 
Splits (~1 mg) were reacted in vacuo in a modified autocarbonate 
device at 90°C and the purified  CO2 analyzed on a gas source stable 
isotope ratio mass spectrometer.   Additional splits were analyzed
by ICP-AES for Sr, and Ca.  The delta-18O and [Sr/Ca] results were
individually mapped to the Kaplan OI and IGOSS sea surface temperature
time-series for the grid box containing Rarotonga.  The resulting age model
indicates an average linear extension rate on the order of 16mm/yr with
an estimated age-model error of ±1 month.  For the interval 1959-1997,
approximately every other sample was analyzed for 14C (~8samples/yr), and
for the interval 1950-1959 every sample was analyzed.

Splits (~10mg) were placed in individual reaction chambers, evacuated, 
heated, and then acidified with orthophosphoric acid at 90°C.  The 
evolved CO2 was  purified, trapped, and converted to graphite in the 
presence of cobalt catalyst in individual reactors [Vogel et al., 1987].
Graphite targets were measured at the Center for Accelerator Mass 
Spectrometry, Lawrence Livermore National Laboratory [Davis et al., 
1990].  Radiocarbon results are reported as Delta-14C (”) as defined 
by Stuiver and Polach [1977] and include the d13C correction obtained 
from the stable isotope results and are "age corrected".  
Analytical precision and accuracy  of the radiocarbon measurements is 
±4” (1s) based on repeated analyses of an in-house homogenized near-modern 
coral and accepted secondary and tertiary radiocarbon standards. 


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In keeping with the definition of "high-precision radiocarbon" 
(<3 per mil, 1-sigma) data have been rounded to zero significant 
figures.