Parent record: Datasets relating to core GC-12, located in the Capricorn Channel at a depth of 990.5 mbsl

Researchers: Bostock, Helen (principalInvestigator) ,  Bostock, Helen, Dr (principalInvestigator) ,  Opdyke, Bradley, Dr (collaborator)

Brief description Core GC12 (23o34' 37S 153o49' 94E) was collected from the Capricorn Channel at a depth of 990.5 mbsl (metres below sea level). By investigating the properties and components of this core we are able to reveal some information about this hemi-pelagic sedimentary environment over the last glacial / interglacial cycle. Information obtained or inferred from the core include the isotopic composition of oxygen and carbon through time, an age vs. depth profile, the percentage of grainsize fractions throughout the core and the percentage of carbonate material in each sample. X-Ray Diffraction (XRD) analyses were also run on several samples from each core to determine changes in the carbonate mineralogy and terrestrial influx, which provided further palaeoclimatic information.

Lineage Maintenance and Update Frequency: notPlanned

Lineage Statement: ISOTOPES AND GRAINSIZE - Foraminifera dried in oven at 60oC before re-soaking in distilled water. Samples wet sieved through a series of 4 mesh sizes (400µm, 300µm, 200µm and 100µm) before size fractions transferred to drying trays. Size fractions then weighed to determine % of each grainsize from the overall collected dry sample. 10-15 large foraminifera (>300 µm and >400µm) were hand-picked picked under microscope before being washed in methanol and ultrasonicated for 30 secs. Samples analysed at Research School of Earth Science, Australian National University, using automated individual carbonate reaction (Kiel) device coupled with a Finnigan MAT-251 mass spectrometer. RADIOCARBON DATING - Radiocarbon dating undertaken on ~300 individuals of Globigerinoides sacculifer of >300µm size. Samples were rinsed, ultrasonically cleaned, and then dried. Samples then dissolved in 103% orthophosphoric acid and the CO2 collected under vacuum. The CO2 was converted to graphite by reacting with hydrogen over iron catalyst at 600oC. Graphite transferred to small cathodes and run on the AMS. CaCO3 - Sample from each depth was dried and ground into fine powder (~100mm) using a mortar & pestle. ~1g of each sample was weighed accurately. 20ml of ~1mol/l HCl was added to the sample, heated & stirred until all the carbonate had reacted. Resulting solution was titrated with 0.5mol/l NaOH using the Metrohm Ion analysis 716 DMS Titrino series 6.0 to determine the CaCO3 %. Error range of 2%. XRD - Samples were ground in an agate mortar with acetone or ethanol, then dried, and filled into side-packed sample holders. Powder diffraction data was collected at room temp with a Siemens D501 diffractometer at the Department of Earth and Marine Science, Australian National University. The diffractometer was equipped with a curved graphite monochromator, a scintillation detector, and CuK alpha radiation was used. Scans recorded in one pass from 2 to 70 degrees 2-theta, using a step-width of 0.02 degrees and a scan speed of 1 degree per minute. Results Interpreted using the SIEMENS software package Diffracplus Eva (2000), and quantitative estimates performed using Siroquant 2.5.

Lineage Statement: STABLE ISTOPES AND GRAINSIZE - Values are provided for 5cm, 10cm, 15cm, 20cm and then every 10cm down the core to depth of 510cm. Mass spectrometer was run concurrently with international standards NBS-19 and NBS-18, and has a very small analytical error. The percentage values for grainsize at each sample depth is not accurate. This is due to wastage during washing and sieving and occasional spills. RADIOCARBON DATING/AGE-MODEL - Radiocarbon dating was undertaken on samples at 20cm, 30cm, 80cm, 90cm, 150cm, 190cm, 250cm, 300cm and 350cm.These values are provided, before being corrected and calibrated with the age curve. The age vs. depth profile were made primarily by correlating 18O values with the SPECMAP age-model. CaCO3 -Values for CaCO3 % are recorded at 5cm, 10cm, 15cm, 20cm and then for every 10cm down the core until reaching a depth of 510cm. Percentage values for CaCO3 have an error range of ± 2%. XRD - XRD analysis was undertaken for four samples within core GC12. Two samples, at the sediment surface and at 30cm, represents interglacial sediment, while the deeper two samples, at 210cm and 330cm, represent glacial sediments. Clay data must be treated with caution since it has been suggested that clay minerals, transported to the coast by river suspended loads, undergo significant diagenesis within environments like mangroves. The percentages of sample components are not exact and the dataset also displays the % error of each component. Errors range from 0.07 - 1.7%. Stable isotope parameters: Depth in core (cm), oxygen-18 G. ruber (parts per thousand), carbon-13 G. ruber (parts per thousand). Age-model parameters: Depth through core (cm), carbon-14 age (yr BP), error (yr), calibrated age (yr BP), sedimentation rate (cm/kyr). Grainsize parameters: Depth through core (cm), grainsize (µm), percentage of total dry mass at each sample depth (%). Calcium carbonate parameters: Depth through core (cm), percentage of calcium carbonate (%). XRD parameters: XRD run number, percentage of sample components (%), total percentage (%). Oxygen-18 values for foraminiferal species parameters: Depth through core (cm), age (yrs BP), foraminiferal species, oxygen-18 values down the core for different species. Carbon-13 values for foraminiferal species parameters: Depth through core (cm), age (yrs BP), foraminiferal species, carbon-13 values down the core for different species.

Notes Credit
Funded by The Australian Research Council (ARC)

Notes Credit
Funded by The Australian National University (ANU) Faculties Research Grant Scheme

Notes Purpose
The data from the stable isotopes of Globigerinoides ruber, grainsize, CaCO3 % and x-ray diffraction of samples for their mineralogy, allows a preliminary understanding of this hemipelagic sedimentary environment over the last glacial / interglacial cycle. Very little work has been previously undertaken within this area.

Data time period: 1997 to 1997

153.83198,-23.57259 153.8327,-23.57258 153.83264,-23.57319 153.83192,-23.57316 153.83198,-23.57259

153.83231,-23.572885

153,-23 153,-24.5 151.5,-24.5 151.5,-23 153,-23

152.25,-23.75

text: westlimit=151.5; southlimit=-24.5; eastlimit=153; northlimit=-23

text: uplimit=990.5; downlimit=990.5