Physical oceanography and current velocity during Nathaniel B. Palmer cruise NBP97-05

An extensive set of conductivity-temperature-depth (CTD)/lowered acoustic Doppler current profiler (LADCP) data obtained within the northwestern Weddell Sea in August 1997 characterizes the dense water outflow from the Weddell Sea and overflow into the Scotia Sea. Along the outer rim of the Weddell Gyre, there is a stream of relatively low salinity, high oxygen Weddell Sea Deep Water (defined as water between 0° and ?0.7°C), constituting a more ventilated form of this water mass than that found farther within the gyre. Its enhanced ventilation is due to injection of relatively low salinity shelf water found near the northern extreme of Antarctic Peninsula's Weddell Sea shelf, shelf water too buoyant to descend to the deep-sea floor. The more ventilated form of Weddell Sea Deep Water flows northward along the eastern side of the South Orkney Plateau, passing into the Scotia Sea rather than continuing along an eastward path in the northern Weddell Sea. Weddell Sea Bottom Water also exhibits two forms: a low-salinity, better oxygenated component confined to the outer rim of the Weddell Gyre, and a more saline, less oxygenated component observed farther into the gyre. The more saline Weddell Sea Bottom Water is derived from the southwestern Weddell Sea, where high-salinity shelf water is abundant. The less saline Weddell Sea Bottom Water, like the more ventilated Weddell Sea Deep Water, is derived from lower-salinity shelf water at a point farther north along the Antarctic Peninsula. Transports of Weddell Sea Deep and Bottom Water masses crossing 44°W estimated from one LADCP survey are 25 ? 10**6 and 5 ? 10**6 m**3/s, respectively. The low-salinity, better ventilated forms of Weddell Sea Deep and Bottom Water flowing along the outer rim of the Weddell Gyre have the position and depth range that would lead to overflow of the topographic confines of the Weddell Basin, whereas the more saline forms may be forced to recirculate within the Weddell Gyre.

Sporomorphs and dinoflagellate cysts of ODP Leg 113 holes

Palynological studies were carried out on Paleogene sections from Sites 693 and 696 of Ocean Drilling Project Leg 113 in the Weddell Sea region. Dinoflagellate cysts and sporomorphs were recovered at Site 696 (61°S, 42°W) indicating a middle Eocene to late Eocene/earliest Oligocene age for a glauconitic silt/sandstone. At Site 693 (70°S, 14°W) early Oligocene siliciclastic mud contains a low diversity palynoflora. In an upper Oligocene section (Site 693) only rare, reworked Mesozoic palynomorphs were encountered. Palynological data from Kerogen analyses, dinocysts, and sporomorphs are used to reconstruct the climatic change on the South Orkney microcontinent from the middle Eocene to the late Eocene/earliest Oligocene at Site 696 and the late early Oligocene/early late Oligocene time interval at Site 693 near the continental margin. The middle Eocene was a warm period in the Orkney region with good growing conditions for a warm temperate Nothofagus/conifer forest with an admixture of Proteaceae. Temperate surface water masses, which allowed the growth of a reasonably diverse dinocyst assemblage (ca. 15-20 species), persisted until the end of the Eocene at Site 696. Late early Oligocene sediments of Site 693 (Antarctic continental margin) contain only a low diversity dinocyst flora (two species). The major Cenozoic cooling event in the Weddell Sea region probably occurred at the Eocene/Oligocene boundary. A second dramatic climatic deterioration seems to have taken place during the late early/early late Oligocene, when dinocysts disappeared at the Dronning Maud Land margin area.

Middle Eocene to Pleistocene calcareous nannofossils of ODP Leg 113 holes

Long sequences of Upper Cretaceous through Quaternary sediments rich in calcareous and siliceous microfossils were recovered at Ocean Drilling Program Sites 689 and 690 on Maud Rise off East Antarctica. These sites have become the southernmost anchor in the Atlantic Basin for bio-, magneto-, chemostratigraphic, and paleobiogeographic studies. ODP Sites 692 and 693 on the Weddell Sea margin of East Antarctica and Site 696 on the South Orkney microcontinent of West Antarctica yielded calcareous nannofossils within some stratigraphic intervals. Sites 691, 692, 694, 695, and 697 did not recover Cenozoic calcareous nannofossils. Calcareous nannofossil biostratigraphy suggests a major hiatus across the Paleogene/Neogene boundary at Sites 689 and 690, and two additional hiatuses in the middle Eocene-lower Oligocene section at Site 690. Correlation with magnetostratigraphy reveals: the last occurrence (LO) of Reticulofenestra umbilica at Maud Rise is over 1 m.y. younger than that at the middle-latitude sites; the LO of Isthmolithus recurvus is synchronous in the middle-latitude and high-latitude areas (about 34.8 Ma); Reticulofenestra oamaruensis ranges from 38.0 to 36.0 Ma at Maud Rise; Reticulofenestra reticulata has a shorter range at Maud Rise (42.1 to 38.9 Ma) than at the middle-latitude DSDP Site 516; the range of Chiasmolithus oamaruensis is diachronous over different latitudes; and the LO of Chiasmolithus solitus is a good datum at 41.3 Ma from 30°S to 65°S in the South Atlantic Ocean. Comparison of calcareous nannofossil abundances in a latitudinal transect shows: Reticulofenestra bisecta is a temperate-water species and its LO, which crosses below that of Chiasmolithus altus at Maud Rise, is not applicable for the Paleogene/Neogene boundary in high southern latitude areas; Clausicoccus fenestratus is rare or absent at Maud Rise and can not be used as a marker; Coccolithus formosus is a warm-water species which disappeared earlier toward higher latitudes. Calcareous nannofossil assemblages indicate that by at least the middle Eocene, surface water temperatures became considerably lower in the high southern latitudes than in the middle-latitude areas and that there have been more extreme cold events in the high latitudes during the Neogene. Bicolumnus ovatus n. gen., n. sp. is proposed in this paper.

Ascidiofauna in the Southern Ocean

Three Spanish Antarctic research cruises (Ant-8611, Bentart-94 and Bentart-95) were carried out in the South Shetland Archipelago (Antarctic Peninsula) and Scotia Arc (South Orkney, South Sandwich and South Georgia archipelagos) on the continental shelf and upper slope (10-600 m depth). They have contributed to our knowledge about ascidian distribution and the zoogeographical relationships with the neighbouring areas and the other Subantarctic islands. The distribution of ascidian species suggests that the Scotia Arc is divided into two sectors, the South Orkney Archipelago, related to the Antarctic Province, and the South Georgia Archipelago (probably including the South Sandwich Archipelago), which is intermediate between the Antarctic Province and the Magellan region.

Peak areas and heights for minerals of ODP Leg 113-696B (Table 1)

Seismic data acquired over the eastern shelf and margin of the South Orkney microcontinent, Antarctica, have shown a high-amplitude reflection lying at a sub-bottom two-way traveltime (TWT) of 0.5-0.8 s. There appear to be two causes for the reflection which apply in different parts of the shelf. The more widespread cause of the reflection is a break-up unconformity associated with the opening of Jane Basin to the east. This is clearly seen where reflections in the underlying sequence are discordant. In contrast, in Eotvos Basin and the southeastern part of Bouguer Basin, the high-amplitude reflection in places cuts across bedding and is interpreted to be caused by silica diagenesis. A post-cruise analysis of core samples from Site 696 in Eotvos Basin by X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the presence of a silica diagenetic front at 520-530 mbsf. The position of the unconformity at this site is uncertain, but probably coincides with a change of detrital input near 548 mbsf. Fluctuations of physical properties related to the depth of the diagenetic front are difficult to separate from those related to the variation of detrital composition over the same depth interval. Correlation of the drilling record with the seismic record is difficult but with a synthetic seismogram it is demonstrated that diagenesis is the probable cause of the high-amplitude reflection. In Bouguer Basin at Site 695 the depth of the high-amplitude reflection was not reached by drilling; however, the reflection is probably also caused by silica diagenesis because of the biogenic silica-rich composition of the sediments cored. The estimated temperatures and ages of the sediments at the depths of the high-amplitude reflections at Sites 695 and 696 compare favorably with similar data from other diagenetic fronts of the world. The high-amplitude reflection in Bouguer Basin is commonly of inverse polarity, possibly caused either by interference between reflections from several closely-spaced reflecting layers, such as chert horizons, or by free gas trapped near the diagenetic front.

Table 2: Evaporation from individual shoots of antarctic mosses

Experimental observations on pathways of water movement are discussed in relation to anatomical and micromorphological features of five moss species from Signy Island, South Orkney Islands. Significant internal uptake of water was recorded only in the mesic species Polytrichum alpinum (internal=>60% of total) and Bartramia patens (internal=c.30% of total), in experiments in which uptake by cut shoots was compared in individuals with the external pathway blocked, and others with both external and internal pathways open. Internal uptake maintained shoot water content close to full turgor in P. alpinun and at 30% of full tugor in B. patens, whereas water content fell to 12-15% dry wt. in the lithophytes Andreaea gainii and Schistidium antarctici and in the mesic/hydric species Drepanocladus uncinatus, with the external pathway blocked. Where both pathways were open water uptake from below maintained water content at or above full turgor in shoots of all five species. External water uptake by capillarity occurred most rapidly in the lithophytes, and was slower in initially air-dry than in hydrated shoots of the other species. The spreading limbs of leaves in B. patens and P. alpinum are water-repellent, as are the bright green leaves in the apical 1-2 mm of dry shoots of the lithophytes. A central strand of hydroids is well-developed only in B. patens and P. alpinum. These two species have deposits of surface wax on parts of the leaves, and surface wax also occurs on the green apical leaves in some specimens of S. antarcticum and other lithophytes from Signy Island.

Tab.1: Tabulation of pinguin population within the Antarctic Peninsula region

Six species of penguins breed on the Antarctic continent, the Antarctic Peninsula, the South Shetland and South Orkney Islands. Their breeding populations within the Antarctic Peninsula, and the South Orkney and South Shetland Is., and estimates of global populations are given. Typical breeding seasons are also presented, but it must be noted that these will vary inter-annually and intra-annually under the influence of factors such as sea-ice extent and ENSO (interannual) and the location of each breeding colony (southerly localities will be later than northerly localities, as their breeding season is "compressed" within the shorter summer). Their foraging strategies (categorized as near-shore or offshore) and typical durations of foraging trips are also tabulated. As with breeding season events, foraging behaviour will vary intra-seasonally and inter-seasonally (in terms of dive duration, dive depth, foraging location, etc). The distribution of known penguin breeding colonies is circum-continental, with Emperor and Adelie penguins predominant on approximately 75 % of the coast, with two major concentrations in the Ross Sea and in Prydz Bay. The third concentration is in the Antarctic Peninsula region, where some of the largest penguin colonies are present. All six species breed within the area (predominantly Chinstrap Penguins), and the Peninsula region has a greater diversity than the remainder ofthe Antarctic with respect to penguins. The distribution at sea of nonbreeding penguins is less cIear. Non-breeding individuals of all six species move throughout the Southern Ocean, and in many cases, to areas well north of the winter pack-ice zone. However, it is not possible to estimate densities of penguins at sea as there are no estimates of non-breeding penguin populations the extent of their travels.

Consolidation tests of ODP Leg 113 samples

Examination of the geotechnical characteristics of Weddell Sea, Maud Rise, and South Orkney microcontinental margin sediments recovered during ODP Leg 113 reveals that the reduction in porosity (consolidation) of the siliciclastic, calcareous, and diatomaceous sediments is primarily a process governed by vertical stresses created by overburden. The initial porosity of the sediments in these areas is governed by the amount of diatoms present. The more diatoms, the higher the porosity. Surficial diatom-rich sediments are everywhere overconsolidated. This is attributed to the strong microfabric created by the diatoms, calcareous and clay particles. The deeper diatom-free sediments of Maud Rise range from slightly underconsolidated to normally consolidated. The silty clays and clays of the Weddell Sea and South Orkney margin are underconsolidated. The degree of underconsolidation of these sediments is similar to that determined in a number of different locations throughout the world's oceans. The very low permeability of the Weddell Sea and South Orkney margin sediments appears to account for this underconsolidation.

Amino acids in the interstitial waters from ODP Hole 113-695A

Site 695 lies on the southeast margin of the South Orkney microcontinent on the northern margin of the Weddell Sea, at 62°23.48'S, 43°27.10'W in 1305 m water depth. The inorganic properties of interstitial waters at this site, including sulfate reduction, biogenic methane production, and high concentrations of ammonia and phosphate, imply high microbial activity. However, no clear relationship between amino acid composition and concentration and the type of microbial activity (e.g., sulfate reduction or methane production) can be identified. The THAA (total hydrolyzable amino acids) values range between 2.45 and 17.31 µmol/L, averaging 7.14 µmol/L. The mean concentrations and relative abundance values of acidic, basic, neutral, aromatic, and sulfur-containing amino acids are 1.34 (18%), 1.09 (15%), 3.93 (54%), 0.50 (8%), and 0.02 (0%) µmol/L, respectively. Glycine is the most abundant amino acid residue, with serine, glutamic acid, and ornithine next. The DFAA (dissolved free amino acids) values range from 0.10 to 12.73 µmol/L, averaging 4.07 µmol/L. The acidic, basic, neutral, aromatic, and sulfurcontaining amino acids are on average 0.21, 0.79, 2.56, 0.41, and 0.01 µmol/L, respectively. The relative abundances of acidic, basic, neutral, and aromatic amino acids average 4%, 18%, 58%, and 15%, respectively. Predominance of DFAA over DCAA (dissolved combined amino acids) in interstitial waters of Lithologic Units I and II is contrary to the predominance of DCAA over DFAA in other interstitial waters and seawater. The comparison of amino acid compositions between DCAA and siliceous plankton suggests that the DCAA in interstitial waters originally comes from amino acids derived from siliceous plankton. However, other sources which are much enriched in glutamic acid contribute to the DCAA composition.

Grain shape of sediment from the Weddell Sea

Very fine quartz sand was examined from Paleogene and Neogene sediments of ODP Sites 693, 694, 695, 696, and 697 to determine their grain roundness using Fourier analysis and SEM surface texture characteristics. The objective of this study was to identify grain roundness and surface texture characteristics unique to East (Site 693) and West (Sites 695, 696, and 697) Antarctica and to glacial regimes. Once identified, these distinguishing features could then be used to determine changes in source area and glacial conditions in the central Weddell Sea Basin (Site 694). Three end members of very fine quartz sand are recognized in the Oligocene to Pleistocene sediments of the Weddell Sea: angular, rounded, and intermediate. End member 1 (angular) consists of extremely angular grains with numerous fracture textures. Previous investigations suggested that these sands are derived from crystalline rocks that fractured during formation or deformation and/or were exposed to weathering by ice. In this study, however, the correlation of angularity with ice activity is problematical as the most angular sands were recovered in the lower Oligocene sediments of the South Orkney Microcontinent, a period of temperate climatic conditions. End member 3 (rounded) consists of rounded grains with chemically and mechanically produced surface textures. These sands are presumed to be derived from the Beacon-type rocks in East Antarctica and the sedimentary deposits of the Northern Antarctic Peninsula. End member 2 (intermediate) grains display crystalline nodes and grain embayments. They are thought to be derived from felsic intrusives, East Antarctic quartzites, basement metamorphics of the South Orkney Microcontinent, and/or the Andean intrusive series of West Antarctica. Unfortunately, no features unique to either the East or West Antarctic sediment sources or to glacial conditions could be isolated. Therefore, the objective of determining provenance changes and sediment erosion and transport mechanisms could not be achieved using this approach.

Sedimentology on two core from the Bransfield Strait area

The raw material for these investigations are samples from marine (sub)surface sediments around the northern part of the Antarctic Peninsula. They had been sampled in the years 1981 to 1986 during several expeditions of the research vessels Meteor, Polarstern and Walther Herwig. 83 box core, gravity core and dredge samples from the area of the Bransfield Strait, the Powell Basin and the northern Weddell Sea have been examined for their grain-size distribution, their mineralogical and petrographical composition. Silt prevails and its clay proportions exceed 25% wt. in water depths greater than 2000 m. The granulometrical results reveal some typical sedimentation processes within the area of investigation. While turbiditic processes together with sediment input from melting icebergs control the sedimentation in the Weddell Sea, the South Orkney Island Plateau and the Powell Basin, the fine grained material from Bransfield Strait mainly relies on marine currents in the shelf area. In addition, the direct sediment input of coarse shelf sediments from the Bransfield Strait into the Powell Basin through submarine canyons could be proven. Variations in the grain-size composition with sediment depth are smalI. The mineral composition of the clay and fine silt fractions is quite uniform in all samples. There are (in decreasing order): illite, montmorillonite, chlorite, smectite, mixed-Iayers, as well as detrital quartz and feldspars. A petrographically based sediment stratigraphy can be established in using the considerable changes in the chlorite- and Ca-plagioclase portions in samples from Core 224. For this sedimentation area a mean sedimentation rate of 7 cm/1000 a is assumed. Remarkable changes in the portions of amorphous silica components - diatom skeletons and volcanic glass shards - appear all over the area of investigation. They contribute between 4-83 % to the clay and fine silt fraction. Several provinces according to the heavy mineral assemblages in the fine sand fraction can be distinguished: (i) a province remarkably influenced by minerals of volcanic origin south and north of the South Shetland Islands; (ii) a small strip with sediment dominated by plutonic material along the western coast of the Antarctic Peninsula and (iii) a sediment controlled by metamorphic minerals and rock fragments in the area of the Weddell Sea and Elephant Island. While taking the whole grain-size spectrum into account a more comprehensive interpretation can be given: the accessoric but distinct appearance of tourmaline, rutile and zircon in the heavy mineral assembly along the northwestern coast of the Antarctic Peninsula is in agreement with the occurrence of acid volcanic rock pieces in the coarse fraction of the ice load detritus in this region. In the vicinity of the South Shetland Islands chlorite appears in remarkable portions in the clay fraction in combination with leucoxene, sphene and olivine, and pumice as well as pyroclastic rocks in the medium and coarse grain fractions, respectively. Amphiboles and amphibole-schists are dominant on the South Orkney Island Plateau. In the sediments of the northwestern Weddell Sea the heavy mineral phases of red spinel, garnet, kyanite and sillimanite in connection with medium to highgrade metamorphic rocks especially granulitic gneisses, are more abundant. A good conformity between the ice rafted rock sampIes and the rocks in the island outcrops could be proven, especially in the vicinity of offshore islands nearby. On the continent enrichments of rock societies and groups appear in spacious outlines: acid effusive rocks in the west of the ice divide on the Antarctic Peninsula, clastic sedimentites at the tip of the Antarctic Peninsula and granoblastic gneisses in central and eastern Antarctica. Coarse grain detritus with more than 1 cm of diameter must have been rafted by icebergs. These rock fragments are classified as rock types, groups and societies. The spacial distribution of their statistically determined weight relations evidently shows the paths of the iceberg drift and in nexus with already known iceberg routes also point to the possible areas of provenance, provided that the density of sample locations and the number of rock pieces are sufficient.