Sediment samples were collected with an Eckamn grab from four locations within the Windmill Islands (Herring Island, O'Connor Island, Shannon Bay and Brown Bay). A weekly sampling program was performed over a 10 week period, however not all locations could be accessed each time due to sea-ice conditions. All samples were collected at an 8 m water depth. Preliminary analysis of fortnightly ... samples are presented here. Diatom data are given as relative abundances of benthic diatom species. The abbreviations used to identify species are explained in the accompanying file sp_list.
This work was completed as part of ASAC project 1130 (ASAC_1130) and project 2201 (ASAC_2201).
Public summary from project 1130:
Algal mats grow on sea floor in most shallow marine environments. They are thought to contribute more than half of the total primary production in many of these areas, making them a critical food source for invertebrates and some fish. We will establish how important they are in Antarctic marine environments and determine the effects of local sewerage and tip site pollution. We will also investigate the impact on the algal mats of the additional UV radiation which results from the ozone hole.
Public summary from project 2201:
As a signatory to the Protocol on Environmental Protection to the Antarctic Treaty Australia is committed to comprehensive protection of the Antarctic environment. This protocol requires that activities in the Antarctic shall be planned and conducted on the basis of information sufficient to make prior assessments of, and informed judgements about, their possible impacts on the Antarctic environment. Most of our activities in the Antarctic occur along the narrow fringe of ice-free rock adjacent to the sea and many of our activities have the potential to cause environmental harm to marine life. The Antarctic seas support the most complex and biologically diverse plant and animal communities of the region. However, very little is known about them and there is certainly not sufficient known to make informed judgements about possible environmental impacts.
The animals and plants of the sea-bed are widely accepted as being the most appropriate part of the marine ecosystem for indicating disturbance caused by local sources. Attached sea-bed organisms have a fixed spatial relationship with a given place so they must either endure conditions or die. Once lost from a site recolonisation takes some time, as a consequence the structure of sea-bed communities reflect not only present conditions but they can also integrate conditions in the past. In contrast, fish and planktonic organisms can move freely so their site of capture does not indicate a long residence time at that location. Because sea-bed communities are particularly diverse they contain species with widely differing life strategies, as a result different species can have very different levels of tolerance to stress; this leads to a range of subtle changes in community structure as a response to gradually increasing disturbance, rather than an all or nothing response.
This project will examine sea-bed communities near our stations to determine how seriously they are affected by human activities. This information will be used to set priorities for improving operational procedures to reduce the risk of further environmental damage.
Various methods were applied to improve the accuracy of elevation estimates over the Greenland ice sheet, including waveform tracking, slope correction, data filtering (tests for return-echo waveform shape, backscatter coefficient, and retracking correction values for each altimeter height estimate), and removal of anomalous orbits. Errors in the estimate of derived ice thickness measurements ... were determined by comparing the radar-based measurements with those from the Greenland Ice Sheet Project (GISP) and Greenland Ice Core Project (GRIP) ice cores. Results showed that radar-based measurements were within 10 m of ice core measurements. No corrections were made for firn effect. Since elevation and ice thickness data from the 1970s were much less accurate than the 1990s data, errors in the merged grid were most significant where 1970s and 1990s tracks were in close proximity. Errors in the 1970s data did not cause anomalously high ice thickness gradients at a distance of three grid points (15 km) away from the 1990s data, so gridded data points closer than three grid cells to the 1990s data were removed (Bamber, Layberry, and Gogenini 2000). See guide document for a more complete description.
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Province or State:
Bamber, J.L., S. Ekholm, W.B. Krabill. 2000. A new, high-resolution digital elevation model of Greenland fully validated with airborne laser altimeter data. Journal of Geophysical Research. In press. Bamber, J.L., R.L. Layberry, S.P. Gogenini. 2000. A new ice thickness and bedrock dataset for the Greenland ice sheet: part I. Journal of Geophysical Research. In press. Bamber, J.L., Ekholm, ... S., and Krabill, W. B. 1998. The accuracy of satellite radar altimeter data over the Greenland ice sheet determined from airborne laser data, Geophysical Research Letters. 25(16): 3177-3180. Bamber, J.L. and R.A. Bindschadler. 1997. An improved elevation dataset for climate and ice-sheet modelling: validation with satellite imagery. Annals of Glaciology 25:438-444. Bamber, J.L. and P. Huybrechts. 1996. Geometric boundary conditions for modelling the velocity field of the Antarctic ice sheet. Annals of Glaciology 23:364-373. Bamber, J. and C. Bentley. 1994. A comp arison of satellite-altimetry and ice thickness measurements of the Ross Ice Shelf, Antarctica. Annals of Glaciology 20:357-364. Bamber, J. 1994. A digital elevation model of the Antarctic ice sheet derived from ERS-1 altimeter data and comparison with terrestrial measurements. Annals of Glaciology 20:48-54. Bamber, J. 1994. Ice sheet altimeter processing scheme. International Journal of Remote Sensing 15:925-938. Bogorodskiy, V.V., C.R. Bentley, P.E. Gudmandsen. 1985. Radioglaciology. Dordrecht: D. Reidel Publishing Company. Brenner, A.C., R.A. Bindschadler, R.H. Thomas, H.J. Zwally. 1983. Slope-induced errors in radar altimetry over continental ice sheets. Journal of Geophysical Research 88:1617-1623. Davis C.H., H.J. Zwally. 1993. Geographic and seasonal variations in the surface properties of the ice sheets by satellite radar altimetry. Journal of Glaciology 39:687-697. Gogineni, S., D. Tammana, D. Braaten, C. Leuschen, T. Atkins, J. Legarsky, P. Kanagaratnam, J. Stiles, C. Allen, and K. Jezek. 2000. Coherent radar ice thicknes s measurements over the Greenland Ice Sheet. Journal of Geophysical Research. In press. Hodge, S.M., D.L. Wright, J.A. Bradley, R. W. Jacobel, N. Skou, and B. Vaughn. 1990. Determination of the surface and bed topography in central Greenland. Journal of Glaciology 36(122):17-30. Weng, W.L. 1995. Untitled. Arctic 48(2):206. Zwally, H.J., R.A. Bindschadler, A.C. Brenner, T.V. Martin, R.H. Thomas. 1983. Surface elevation contours of Greenland and Antarctic ice sheets. Journal of Geophysical Research 88(C3):1589-1596.