(Table 3) Age-related trends of desert pavement properties in the Transantarctic Mountains

Compared to mid-latitude deserts, the properties, formation and evolution of desert pavements and the underlying vesicular layer in Antarctica are poorly understood. This study examines the desert pavements and the vesicular layer from seven soil chronosequences in the Transantarctic Mountains that have developed on two contrasting parent materials: sandstone-dolerite and granite-gneiss. The pavement density commonly ranges from 63 to 92% with a median value of 80% and does not vary significantly with time of exposure or parent material composition. The dominant size range of clasts decreases with time of exposure, ranging from 16-64 mm on Holocene and late Quaternary surfaces to 8-16 mm on surfaces of middle Quaternary and older age. The proportion of clasts with ventifaction increases progressively through time from 20% on drifts of Holocene and late Quaternary age to 35% on Miocene-aged drifts. Desert varnish forms rapidly, especially on dolerite clasts, with nearly 100% cover on surfaces of early Quaternary and older age. Macropitting occurs only on clasts that have been exposed since the Miocene. A pavement development index, based on predominant clast-size class, pavement density, and the proportion of clasts with ventifaction, varnish, and pits, readily differentiated pavements according to relative age. From these findings we judge that desert pavements initially form from a surficial concentration of boulders during till deposition followed by a short period of deflation and a longer period of progressive chemical and physical weathering of surface clasts. The vesicular layer that underlies the desert pavement averages 4 cm in thickness and is enriched in silt, which is contributed primarily by weathering rather than eolian deposition. A comparison is made between desert pavement properties in mid-latitude deserts and Antarctic deserts.

(Table 1, page 641) Hf isotope time series for the uppermost part of a ferromanganese crust from the San Pablo ferro-manganese pavement

The Hf isotope composition of seawater does not match that expected from dissolution of bulk continental crust. This mismatch is generally considered to be due to retention of unradiogenic Hf in resistant zircons during incomplete weathering of continental crust. During periods of intense glacial weathering, zircons should break down more efficiently, resulting in the release of highly unradiogenic Hf to the oceans. We test this hypothesis by comparing Nd and Hf isotope time series obtained from NW Atlantic ferromanganese crusts. Both isotope systems show a decrease associated with the onset of northern hemisphere glaciation. The observed changes display distinct trajectories in epsilon Nd- epsilon Hf space, which differ from previously reported arrays of bulk terrestrial material and seawater. Such patterns are consistent with the release of highly unradiogenic Hf from very old zircons, facilitated by enhanced mechanical weathering.

Chemical composition of oxide-phosphorite pavement from the Blake Plateau under various preparation treatment

Sample preparation technique is critical for valid chemical analyses. A main source of error comes from the fact that the great specific surface area of crusts or nodules enhances their tendency to retain or attract hygroscopic moisture. Variable treatment of this moisture can in extreme cases lead to analytical value differences as great as 40-50 %. In order to quantify these influences, samples of ferromanganese oxide-phosphorite pavement from the Blake Plateau have been subjected to various drying techniques before analysis using X-ray fluorescence.

(Table 2, page 10) Bulk spectroscopic, X-ray fluorescence and colorimetric analyses of samples from the San Pablo ferro-manganese pavement

The Bedford Institute of Oceanography provided ship time on the C.S.S. Hudson during the B.I.0. 1967 Metrology and IODAL Cruise for surveying two separate bottom features in the North Atlantic; the Flemish Cap and the San Pablo Seamount one of the Kelvin Seamounts (also known as the New England Seamounts) about 400 miles SSE of Halifax, Nova Scotia. Underwater photography, dredging, and drilling showed San Pablo seamount to have a very considerable covering of manganese deposit, which may be recoverable by mining. San Pablo Seamount was surveyed and sampled; good hauls were made both on the top and on the slopes, at various depths from 500-1000 fathoms; in all cases samples of an unusual stratified manganese-iron ore were recovered. In the hope of gaining additional information in the immediate sample area, one of the dredges had been previously modified to accommodate underwater photographic equipment. X-ray chemical analyses indicate that the ore contains 20 to 25 per cent MnO2, with similar amounts of Fe2O3. Since bottom photographs indicate that these deposits form a continuous cover 1 foot to 3 feet thick over most of the seamount, it is estimated that there are ore reserves in the order of 10 to 30 M tons above 1,000 fathoms.