Although oceanic crust covers about 60% of the Earth, relatively little is known of its geology and the processes that have created it. Macquarie Island represents a unique subaerial exposure of the seafloor, and an exceptional environment for active study and research into the ocean crust. We plan to utilise geological and geophysical techniques to help us better understand the lithological complexity and evolution of the oceanic crust. Project objectives: Our primary objective is to conduct coordinated ground- and air-based magnetic and electromagnetic surveys of the oceanic crust that comprises Macquarie Island and the surrounding seafloor for ~ 5 km from the island. We will integrate these geophysical data with the results of our recent studies of the Island and additional follow-up geological investigations. Together these data will improve our understanding of the tectonic and hydrothermal evolution of Macquarie Island ocean crust and through it, the evolution of oceanic crust in a more general sense. We believe the acquisition of these data will allow us to: (1) better resolve the complex geologic structure of the island; (2) determine the three-dimensional extent of the hydrothermal alteration of this example of oceanic crust; (3) map active fault zones across the island; and (4) correlate the geology of the Island with the offshore geology, linking it to regional data sets and the nearby active plate boundary. The dataset has two forms. The main dataset is magnetic field data recorded in the Bauer Bay to Boot Hill area of Macquarie Island, on 200 m line spacings (csv file). The subsidiary dataset are sample locations for the same area for a small set of rock samples obtained to check on magnetic character (word file). Data were collected using a GEM Systems GSM-19 Overhauser Magnetometer. The fields in this dataset are: Easting Northing Sample Rock Type Magnetic Intensity (nT) Taken from the 2008-2009 Progress Report: Progress against objectives: This project was in abeyance for the 2007-8 season due to our scientific field program being postponed as a necessity of the rabbit eradication program on Macquarie Island. A detailed study of the formation of specific magnetic lows from our regional ground magnetic survey, with the aim of determining their cause, and gaining insight into interpretation of magnetic lows in ocean crust in general. Hydrothermal alteration in ocean crust typically results in magnetic lows because it involves magnetite destruction. However, it is apparent that on Macquarie Island this is not the only cause of magnetic lows. There are 5 principal study sites: (1) Prion Lake to Brothers Point, and including the Mt Tulloch summit and slopes; (2) Waterfall Lake and surrounds; (3) Hurd Point to the coast immediately east of Mt Jefferies; (4) East Ainsworth area, east of the Caroline Cove protection zone; (5) Whisky Creek area, cutting through the eastern escarpment ~ 5 km north of Hurd Point. The 2008-9 season has involved (1) compiling of geological mapping from each site and rectification with the available topographic base and most recent satellite imagery; (2) processing of magnetic data from each of the detailed surveys; (3) extraction of field observations into a digital database that can be accessed within his GIS platform; (4) petrographic description of ~100 polished thin sections to evaluate magnetite behaviour; and (5) a brief return to Macquarie Island to attempt to infill areas of geological data/sample deficiency. In terms of the objective of correlating the geology of the island with the offshore geology, this has been in process within the USGS under the supervision of Dr Carol Finn. This part of the project is employing heli-magnetics obtained with the cooperation of AAD during resupply, using a USGS instrument The data was partly processed at Utas by Dr Michael Roach, and then transferred on for more detailed processing at the USGS.

This project exploited the unique exposures of the uppermost oceanic crust found on Macquarie Island as a window into the internal structure of the oceanic crust. The form of rock units and the way in which they are arranged on the Island provided a means of understanding how they were assembled. This assembly occurred beneath a mid-ocean ridge spreading center, an area that can probably never be directly investigated. The general process by which this crust has formed is responsible for the creation of about 60% of the bedrock geology of the Earth. The Macquarie Island ophiolite is an uplifted block of oceanic crust formed at the Australia-Pacific spreading centre between 12 and 9 Ma. The sense of motion and geological processes across this plate boundary reflect an evolution from orthogonal spreading through progressively more oblique spreading to the present-day transpressional regime. The crust that makes up the island was formed during an interval of oblique spreading along east-trending spreading segments punctuated by a series of northwest-trending discontinuities. The discontinuities are accommodation zones marked by oblique-slip dextral-normal faults, localised dikes and lava flows, and extensive hydrothermal alteration, indicating that these zones were active near the spreading axis. These features provide a window into the internal structure of oceanic crust generated by oblique spreading. The download file contains: I. Publication folder (PDF files): 1. Alt, J.C., G. Davidson, D.A.H. Teagle and J.A. Karson, The isotopic composition of gypsum in the Macquarie Island Ophiolite: Implications for sulfur cycle and the subsurface biosphere in oceanic crust, Geology, 31, 549-552, 2003. 2. Rivizzigno, P.A. and J.A. Karson, Mid-ocean ridge fault zones preserved on Macquarie Island: Faulting, hydrothermal processes and magmatism in an oblique-spreading environment, Geology 32, 125-128, 2004. 3. Rivizzigno, P. A., The Major Lake Fault Zone: An Oblique Spreading Structure Exposed in the Macquarie Island Ophiolite, Southern Ocean, MS Thesis, Duke University, Durham, NC USA, 2002, 59 pp. II. Macca Maps folder (TIFF files): 1. Helicopter Video: Macca map showing the path and view direction from a video made during a helicopter trip over the island in 2000 during an unusually clear day. Copies of the video were left with ANARE and with various people at UTas (R. Varne, G. Davidson and others). 2. JAK2000Samples: Macca map with locations of samples collected by J.A. Karson during the 2000 field season. Samples are numbered MAC00-XX. Samples are under study at Duke University. 3. JAKMK2000Samples: Macca map with locations of samples of dike rocks collected for geochemicial studies by J.A. Karson during the 2000 dield season. Samples are numbered MK-XX. They were left with Dr. R. Varne (UTas) in 2000. 4. PAR2000Samples: Macca map with locations of samples collected by P.A. Rivizzigno during the 2000 field season. Samples are under study at Duke University and reported in Rivizzigno (2002) and Rivizzigno and Karson (2004). 5. PARMK2000: Macca map with locations of samples of dike rocks collected for geochemicial studies by J.A. Karson during the 2000 dield season. Samples are numbered MK-XX. They were sent to Dr. R. Varne (UTas) in 2000. 6. Geological map from Rivizzigno (2002) in vector art (Canvas 8.0) and bitmap (jpeg) formats. New data are plotted on a base map by Goscombe and Everard (1998). III. Other Information folder (WORD files): 1. References: citations of journal articles, theses, abstracts from this project. 2. JAK Sample Log: List of samples, locations, etc. for Karson samples from 2000.

Production of the arsenic species total inorganic arsenic [As(V+III)],arsenite [As(III)], monomethyl arsenic (MMA) and dimethyl arsenic (DMA) was studied in the Subantarctic Zone (SAZ) of the Southern Ocean, south of Australia, during the austral autumn (March 1998). Surface samples were collected approximately every degree of latitude along the meridional transect 14130' E from 42 to 55 S. In addition, representative vertical profiles were collected at: 4206' S, 14153' E (Subtropical Convergence Zone - STCZ), 4643' S, 14159' E (Subantarctic Zone - SAZ), 5104' S, 14336' E (Subantarctic Front - SAF) and 5344' S, 14142' E (northern branch of the Polar Frontal Zone - PFZ). As(V) was the dominant arsenic species in both vertical profiles and surface waters along the transect. It was also the only species observed at depths greater than 600 m. Production of the reduced arsenic species (As(III), MMA, DMA) was low in these waters compared with other oceanic sites with similar concentrations of chlorophyll a. As(III) concentrations could not be reliably quantified at any sites (less than 0.04 nM). Greatest conversion of arsenic to 'biological' species was found at the surface in the Subtropical Convergence Zone (2.5%) and decreased heading southward to 1% in the Polar Front (PF). While the decline in methyl arsenic production was broadly associated with water temperature and measures of biological production, slightly different trends in methyl arsenic production were found in the SAZ and PF. North of the Subantarctic Front (SAF) methyl arsenic production was well correlated with water temperature, while south of the front no such relation existed. In addition, the ratio of DMA/MMA increased south of the SAF, associated with a change in the microalgal community composition. Low water temperature, phosphate-replete conditions and low biological productivity in the SAZ all contribute to the concentrations of biologically produced arsenic species in this region being amongst the lowest reported for oceanic waters. The data are stored in an excel spreadsheet, and a readme text file.

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.

Amery Ice Shelf AM05 borehole drilled mid-December 2009. Sub-shelf water profiling measurements conducted over a period of a few days. Partial video recording of borehole walls and sea floor benthos. Collection of targeted ice core samples. Sediment sample collected from sea floor. Long term monitoring instruments installed (thermistors in ice, 3 x CTD in ocean cavity). This is a parent record - see the child records for further information. Some general readme documents are available for download from the provided URL.

This project used computer-based modelling and existing field data to analyse the production and cycling of dimethylsulphide (DMS) and predicted its role in climate regulation in the Antarctic Southern Ocean. From the Final Report: Aims (i) To calibrate an existing dimethylsulphide (DMS) production model in a section of the Antarctic Southern Ocean. (ii) To use the calibrated model to investigate the effect of GCM-predicted climate change on the production and sea-to-air flux of DMS under current and enhanced greenhouse climatic conditions. (iii) To provide regional assessments of the sign and strength of the DMS-climate feedback in the Southern Ocean. Characteristics of Study Region: Our study region extends from 60-65 degrees S, 123-145 degrees E in the Antarctic Southern Ocean, and was the site of a major biological study in the austral summer of 1996 (Wright and van den Enden, 2000). Field observations show that a short-lived spring-summer bloom event is typical of these waters (El-Sayed, 1988, Skerratt et al. 1995); however there can be high interannual variability in the timing and magnitude of the bloom (Marchant and Murphy, 1994). The phytoplankton community structure has been described by Wright and van den Enden (2000), who report maximum chlorophyll (Chl) concentrations during January-March in the range (1.0-3.4) microgL-1. During this survey, macronutrients did not limit phytoplankton growth. Thermal stratification of the mixed layer was strongly correlated with high algal densities, with strong subsurface Chl maxima (at the pycnocline) observed. The mixed layer depth determined both phytoplankton community composition and maximum algal biomass. Coccolithophorids (noted DMS producers) were favoured by deep mixed layers, with diatoms dominating the more strongly stratified waters. Pycnocline depth varied from 20-50 m in open water. Algal abundance appeared to be controlled by salp and krill grazing. Field data support the existence of seasonal DMS production in the Antarctic region. However, a large range in DMS concentrations has been reported in the open ocean , reflecting both seasonal and spatial variability (Gibson et al., 1990, Berresheim, 1987; Fogelqvist, 1991). Blooms of the coccolithophores, and prymnesiophytes such as Phaeocystis, form a significant fraction (~23%) of the algal biomass (Waters et al 2000). Concentrations of DMS in sea ice are reported to be very high (Turner et al. 1995) and may be responsible for elevated water concentrations during release from melt water (Inomata et al. 1997). Field measurements of dissolved DMS made in the study region have been summarised by Curran et al. (1998). DMS concentrations were variable in the open ocean during spring and summer (range: 0-22 nM), with the higher values recorded in the seasonal ice zone and close to the Antarctic continent. Zonal average monthly mean DMS in the study region have been estimated by Kettle et al. (1999). (See downloadable full report for reference list). A copy of the referenced publication is also available for download by AAD staff. It contains the modelling information.

40Ar/39Ar geochronology data of basalt samples from the Kerguelen Plateau and Broken Ridge The samples include basalts from ODP drilling cores and dredge sites. The drilling core samples were stored in the Kochi Core Centre, Japan and the dredged samples were stored in the National Museum of Natural History, France. Analytical methods of the 40Ar/39Ar geochronology data: Samples were crushed and minerals/groundmass were separated using a Frantz magnetic separator. Plagioclase, pyroxene, amphibole, sericite, and basaltic glass crystals and groundmass were separated from either the 125–212 μm or the 212–355 μm size fractions using a Frantz isodynamic magnetic separator. Minerals and groundmass were subsequently hand-picked grain-by-grain under a binocular stereomicroscope. Plagioclase and groundmass were further leached using diluted HF (2N) for 5 minutes and thoroughly rinsed in distilled water. Samples were loaded into several large wells of 1.9cm diameter and 0.3 cm depth aluminium discs. The discs were Cd-shielded to minimise undesirable nuclear interference re-actions and irradiated for 40 hours in the Oregon State University nuclear reactor (USA) in the central position. The samples were irradiated alongside FCs and GA1550 standards, for which ages of 28.294 ± 0.037 Ma and 99.738 ± 0.100 Ma were used, respectively. The 40Ar/39Ar analyses were performed at the Western Australian Argon Isotope Facility at Curtin University. The samples were step-heated using a continuous 100 W PhotonMachine© CO2 (IR, 10.4 µm) laser fired on the crystals during 60 seconds. Each of the standard crystals was fused in a single step. The gas was purified in an extra low-volume stainless steel extraction line of 240cc and using one SAES AP10 and one GP50 getter. Ar isotopes were measured in static mode using a low volume (600 cc) ARGUS VI mass spectrometer from Thermofisher© set with a permanent resolution of ~200. Measurements were carried out in multi-collection mode using four faradays to measure mass 40 to 37 and a 0-background compact discrete dynode ion counter to measure mass 36. We measured the relative abundance of each mass simultaneously using 10 cycles of peak-hopping and 33 seconds of integration time for each mass. Detectors were calibrated to each other electronically and using air shot beam signals. The raw data were processed using the ArArCALC software. The criteria for the determination of plateau are as follows: plateaus must include at least 70% of 39Ar released. The plateau should be distributed over a minimum of 3 consecutive steps agreeing at 95% confidence level and satisfying a probability of fit (P) of at least 0.05. Plateau ages are given at the 2σ level and are calculated using the mean of all the plateau steps, each weighted by the inverse variance of their individual analytical error. Uncertainties include analytical and J-value errors.

Marine sediments often represent an important reservoir of carbonate minerals that will react rapidly to changing seawater chemistry as a result of ocean acidification. Ocean acidification (the reaction of CO2 with seawater) lowers the saturation state with respect to carbonate minerals and may lead to dissolution of these minerals if undersaturation occurs. There are three main carbonate minerals found in marine sediments: 1. aragonite 2. calcite (also referred to as low-magnesium calcite, containing less than 4mol% MgCO3) 3. high-magnesium calcite (greater than 4 mol% MgCO3) Due to the different structure of these minerals, they have different solubilities with high-Mg calcite the most soluble, followed by aragonite and then calcite. As seawater CO2 increases and the saturation state with respect to carbonate minerals decreases, high-Mg calcite will be the first mineral subject to undersaturation and dissolution. By measuring the carbonate mineral composition of sediments, we can determine which areas are most at risk from dissolution. This information forms an important baseline with which we can assess future climate change. The effect of ocean acidification on carbonates in marine sediments will occur around the world, but due to the lower seawater temperatures in Antarctica, solubility is much lower so the impacts will occur here first. This dataset is a compilation of carbonate mineralogy data from surface sediments collected from the East Antarctic margin. The dataset includes sample metadata, bulk carbonate content, %calcite, % aragonite and mol% MgCO3 (i.e. the magnesium content of high-Mg calcite). This dataset was compiled from new (up to 2020) and archived sediment samples that contacted sufficient carbonates (typically greater than 3% CaCO3)/