CEAMARC marine sediment samples - collected on voyage 3 of the Aurora Australis, 2007-2008

Brief description

Marine sediment samples were obtained from box corer, Smith-MacIntyre and Van Veen grabs.

Samples were named by:
1. CEAMARC site (e.g. 16)
2. Instrument (e.g. box corer = BC; Smith-MacIntyre = GRSM; Van Veen = GRVV) 3. Sequence of sample at each site (e.g. first sample = 01; second sample = 02) So 16BC02 is the second sample at CEAMARC site 16, using the box corer.

From each successful sample, a sub-sample was obtained:
1. 200 g surface scrape (labelled A)
2. short (20 cm) push core (labelled B)
3. bulk (labelled Bulk)
4. rocks-only (labelled Rocks)
e.g. 16BC02A is a 200 g surface scrape subsample from 16BC02.
16BC02B is a push core subsample from 16BC02
16BC02Bulk is a bulk sediment subsample from 16BC02.
16BC02Rocks is a rocks-only subsample from 16BC02.

Post-cruise analyses:
1. Grain size
2. Total organic carbon
3. Total organic nitrogen
4. Carbon and nitrogen isotopes
5. Biogenic silica and carbonate
6. Physical properties of cores
7. Zircon dating
8. X-rays for infauna and sedimentary structures

Added by Alix Post - March 2010:

Seabed samples were collected from 52 sites across the George V Shelf. Most samples were collected with a box corer (BC), though more gravelly sediments required a Smith-McIntyre (GRSM) or Van-Veen grab (GRVV) as indicated by the station name in the spreadsheet. A small volume of sediment was frozen following collection and later analysed for organic carbon and nitrogen content, in addition to carbon and nitrogen isotopes. Organic carbon and nitrogen values are express as percent of the total sediment, and have been corrected back to the total sediment volume. Isotopic values are expressed as values per mil.

Where sufficient volume of sediment was collected, a mini-core was pushed into the sediment to provide a depth profile of the sample, and a bulk surface sample was also taken. Surface sediment samples analysed for sieve grainsize, calcium carbonate and biogenic silica content. All values are expressed as percentage values. The naming convention of the samples describes the type of gear used and the nature of the sediment analysed: e.g. 01BC01Bulk is a bulk sediment sample collected with a box core; 38GRVV02B/0-1 is a slice taken from 0 to 1 cm at the top of a van veen grab.

Lineage

Progress Code: completed

Statement: Data quality is good for all sediment records.

Tin-wrapped samples are loaded into carousels with 49 samples in each tray and 3 trays making up a full run of 147 samples. The carousels are placed on an AS200 autosampler that drops a sample in response to a pulse of compressed air. Gases are swept through the columns and GC by an approximately 100 ml min-1 flow of high purity helium. The sample dropper uses a sliding port that maintains the approximately 1 atmosphere pressure of the helium required to force the gases through the columns and GC.

The autosampler sits on top of a Carlo Erba CE1110 CHN-S analyser containing the two furnaces, the scrubber and the GC (Gas Chromatograph). After the GC in the gas stream sits a TCD (Thermal Conductivity Detector) which is used to measure peak area when the machine is used as an elemental analyser. The samples are dropped into the left-hand furnace which is the oxidising furnace and is maintained at 1050 degrees C. It consists of a silica glass tube filled with chromium oxide to the midpoint, with cobaltous silver oxide under it. A tube takes the carrier gas from the bottom of this reactor to the second, reducing furnace tube which the mixed gases flow up through. The second silica glass tube is filled with metallic copper pellets and is kept at 660 degrees C. The gases flow out of the top of this tube and through a scrubber filled with magnesium perchlorate to absorb all water vapour. The dried gases then pass through a packed GC consisting of a 1/4" stainless steel tube with Porapak QS 50-80 mesh. This is held at about 25 degrees C. Nitrogen gas exits from the GC, followed by carbon dioxide after about one minute. These flow to an open split where they are sucked into the mass spectrometer through a 75 micro silica capillary.
The gas pulses, still mixed with the helium carrier, flow into the Fisons Isochrom CF-IRMS (Continuous-flow Isotope Ratio Mass Spectrometer) where their isotopic compositions are determined.

Surface sediment samples were analysed to determine the gravel, sand and mud content by washing through 2 mm and 63 micron sieves. The less than 2 mm fraction was also analysed for laser particle size. Carbonate content was determined on the bulk material as well as the mud and sand fractions using the carbonate bomb method (Muller and Gastner, 1971). The carbonate content of the gravel fraction was determined by visual analysis. The biogenic silica content of the bulk sediment was measured based on the method of Mortlock and Froelich (1989). Muller, G., Gastner, M., 1971. The "Karbonat-Bombe," a simple device for the determination of the carbonate content in sediments, soils and other materials. Neues Jahrbuch fur Mineralogie, Monatshefte 10, 466-469. Mortlock, R.A., Froelich, P.N., 1989. A simple method for the rapid determination of biogenic opal in pelagic marine sediments. Deep Sea Research 36, 1415-1426.