ALBERT

Description: A multiproxy study of palaeoceanographic and climatic changes in northernmost Baffin Bay shows that major environmental changes have occurred since the deglaciation of the area at about 12 500 cal. yr BP. The interpretation is based on sedimentology, benthic and planktonic foraminifera and their isotopic composition, as well as diatom assemblages in the sedimentary records at two core sites, one located in the deeper central part of northernmost Baffin Bay and one in a separate trough closer to the Greenland coast. A revised chronology for the two records is established on the basis of 15 previously published AMS 14C age determinations. A basal diamicton is overlain by laminated, fossil-free sediments. Our data from the early part of the fossiliferous record (12 300–11 300 cal. yr BP), which is also initially laminated, indicate extensive seasonal sea-ice cover and brine release. There is indication of a cooling event between 11 300 and 10 900 cal. yr BP, and maximum Atlantic Water influence occurred between 10 900 and 8200 cal. yr BP (no sediment recovery between 8200 and 7300 cal. yr BP). A gradual, but fluctuating, increase in sea-ice cover is seen after 7300 cal. yr BP. Sea-ice diatoms were particularly abundant in the central part of northernmost Baffin Bay, presumably due to the inflow of Polar waters from the Arctic Ocean, and less sea ice occurred at the near-coastal site, which was under continuous influence of the West Greenland Current. Our data from the deep, central part show a fluctuating degree of upwelling after c. 7300 cal. yr BP, culminating between 4000 and 3050 cal. yr BP. There was a gradual increase in the influence of cold bottom waters from the Arctic Ocean after about 3050 cal. yr BP, when agglutinated foraminifera became abundant. A superimposed short-term change in the sea-surface proxies is correlated with the Little Ice Age cooling.

Description: The diet composition of Emperor Penguin Aptenodytes forsteri chicks was examined at Auster and Taylor Glacier colonies, near Australia's Mawson station, Antarctica, between hatching in mid-winter and fledging in mid-summer by “water-offloading” adults. Chicks at both colonies were fed a similar suite of prey species. Crustaceans occurred in 82% of stomach samples at Auster and 87% of stomachs at Taylor Glacier and were heavily digested: their contribution to food mass could not be quantified. Fish, primarily bentho-pelagic species, accounted for 52% by number and 55% by mass of chick diet at Auster, and squid formed the remainder. At Taylor Glacier the corresponding values were 27% by number and 31% by mass of fish and 73% by number and 69% by mass of squid. Of the 33 species or taxa identified, the fish Trematomus eulepidotus and the squid Psychroteuthis glacialis and Allu-roteuthis antarcticus accounted for 64% and 74% of the diets by mass at Auster and Taylor Glacier, respectively. The sizes of fish varied temporally but not in a linear manner from winter to summer. Adult penguins captured fish ranging in length from 60 mm (Pfeura-gramma antarcticum) to 250 mm (T. eulepidotus) and squid (P. glacialis) from 19 to 280 mm in mantle length. The length-frequency distribution of P. glacialis showed seasonal variation, with the size of squid increasing from winter to summer. The energy density of chick diet mix increased significantly prior to “fledging”.

Description: The Denmark Strait Overflow (DSO) today compensates for the northward flowing Norwegian and Irminger branches of the North Atlantic Current that drive the Nordic heat pump. During the Last Glacial Maximum (LGM), ice sheets constricted the Denmark Strait aperture in addition to ice eustatic/isostatic effects which reduced its depth (today ∼630 m) by ∼130 m. These factors, combined with a reduced north-south density gradient of the water-masses, are expected to have restricted or even reversed the LGM DSO intensity. To better constrain these boundary conditions, we present a first reconstruction of the glacial DSO, using four new and four published epibenthic and planktic stable-isotope records from sites to the north and south of the Denmark Strait. The spatial and temporal distribution of epibenthic δ18O and δ13C maxima reveals a north-south density gradient at intermediate water depths from σ0∼28.7 to 28.4/28.1 and suggests that dense and highly ventilated water was convected in the Nordic Seas during the LGM. However, extremely high epibenthic δ13C values on top of the Mid-Atlantic Ridge document a further convection cell of Glacial North Atlantic Intermediate Water to the south of Iceland, which, however, was marked by much lower density (σ0∼28.1) The north-south gradient of water density possibly implied that the glacial DSO was directed to the south like today and fed Glacial North Atlantic Deep Water that has underthrusted the Glacial North Atlantic Intermediate Water in the Irminger Basin.

Description: Quantitation of nucleic acids is a fundamental tool in molecular biology that requires accuracy, reliability, and the use of increasingly smaller sample volumes. This unit describes the traditional absorbance measurement at 260 nm and three more sensitive fluorescence techniques, as well as three microvolume methods that use fiber optic technology in specialized cells or instrumentation. These procedures allow quantitation of DNA solutions ranging from 1 pg/µl to 50 mg/ml.

Description: Studies of laboratory cultures of Chordaria linearis (Hooker et Harvey) Cotton from southernmost South America revealed that this species has an obligate sexual life history in which a macroscopic sporophyte alternates with a monoecious microscopic gametophyte. Sexual reproduction is isogamous and under photoperiodic control. Gametes are produced only in short days, whereas in long days, asexual zoospores are formed that recycle the gametophyte generation. Unfused gametes develop into gametophytes, and sporophytes originate only from zygotes. Unlike other sexual members of the Chordariales, gametes of C. linearis have a reduced stigma and do not show phototaxis. They are released at the beginning of the night, not in the morning. In nature, C. linearis seems to be regularly infected by a dictyosiphonalean epiphyte resembling the rare arctic species Trachynema groenlandicum (Lund) Pedersen. The epiphyte is responsible for previous contradictory results obtained in laboratory cultures of C. linearis. This is the first record of Trachynema in the southern hemisphere.

Description: The constancy of postmoult/premoult ratios of measures of linear size during ontogeny in insect and other arthropods is widely known as Dyar's rule. We tested this rule in nine species of the waterstrider genera Gerris and Aquarius (Heteroptera: Gerridae), using two size variables: head width and a multivariate measure derived from the pattern of multivariate allometry common to the species considered. Allometric patterns were similar in two independent datasets of laboratory-reared and field-caught specimens. Although our data strictly followed Dyar's rule injust a few instances, all growth ratios varied within a limited range only. Growth ratios for head width differed more between moults than those for multivariate size. The relationship between growth ratios for the two size measures conformed to the predictions based on allometry. We discuss hypotheses of the possible adaptive significance of growth ratios, such as their relation to mobility and systematic differences between hemimetabolous and holometabolous insects, and emphasize the importance of allometry. Since Dyar's rule is consistent with available evidence of physiological mechanisms underlying growth and moulting control of insects and crustaceans, it can be used as a general frame of reference to test alternative growth models.

Description: In contrast to continuum systems where localization or shear banding arises through a bifurcation in a predefined system of differential equations, shear bands emerge in numerical simulations of deforming granular systems with no prescribed mathematical relations other than simple contact forces between particles. Shear bands emerge from the self‐organization of large numbers of particles with long‐range geometrical interactions playing a dominant role; both translation and rotation of particles are important. Granular media therefore deform more like materials with non‐local constitutive relations than materials where only first‐order interactions are relevant. In this paper we adopt a thermo‐mechanical approach and explore the fluxes of energy in the evolving granular system (that has cohesion as well as friction between the particles) as it is loaded through the unstable localization regime, and track the evolution of energy dissipation. As in continua, the sign of the second‐order work defines the emergence of instability in the system. Initially, these instabilities decay into stable configurations of particles but with continued loading, force chains collapse locally to generate geometrically necessary fractures. These zones then propagate to generate localization zones. When these fractures form a continuous network, the system is at the percolation thresh‐hold for broken bonds. However, long before this stage, the second‐order work fluctuates in bursts weakly correlated with bursts in kinetic energy as damage accumulates. This behaviour suggests that any continuum constitutive description of granular media must be (i) non‐local in an anisotropic manner, (ii) micro‐polar, and (iii) involve damage evolution.

Description: The ultimate cause of the onset of glaciations remains elusive, but in the case of northem hemisphere glaciation it is probable that several factors acted in combination. General global cooling resulted from reduction of atmospheric C02 by weathering of silicate rocks exposed by erosion of late Cenozoic uplifts. Uplifts in south Asia, southwestern North America and Scandinavia occurred at distances appropriate for the generation of quasi-permanent Rossby waves in the atmosphere. The resulting winds, given suitable moisture sources, were favourable for causing large-scale precipitation at mid-latitudes on the northern continents. Moisture sources were provided by the closure of the Central American isthmus. Gulf Stream flow increased, carrying warm subtropical waters to high latitudes. The Denmark Strait deepened permitting greater outflow of deep water from the Norwegian-Greenland Sea. The relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies.

Description: King Penguins are the second largest of all diving birds and share with their congener, Emperor Penguins, breeding habits strikingly different from other penguins. Our purpose was to determine the feeding behavior, energetics of foraging and the prey species, and compare these to other sympatric species of subantarctic divers. We determined: (1) general features of foraging behavior using time—depth recorders, velocity meters, and radio transmitters, (2) energetics by doubly labeled water, (3) food habits and energy content from stomach lavage samples, and (4) resting and swimming metabolic rate by oxygen consumption measurements. The average foraging cycle was ≈6 d, during which the mass gain of 30 birds was ≈2 kg. When at sea, the birds exhibit a marked pattern of shallow dives during the night, whereas deep dives of 〉100 m only occurred during the day. Maximum depth measured from 34 birds and 18 537 dives was 304 m, and maximum dive duration from 23 birds and 11 874 dives was 7.7 min. The frequency distribution of dive depth was bimodal, with few dives between 40 and 100 m. Overall, swim velocities when a bird was at sea averaged 2.1 m/s (N = 5), while descent and ascent rates of change in depth averaged 0.6 m/s for dives 〈60 m (N = 74) and 1.4 m/s for dives 〉150 m (N = 90). Night feeding dives occurred at a rate of ≈20 dives/h, and deep dives occurred at a rate of ≈5 dives/h. The energy consumption rate while resting ashore was 3.3 W/kg (N = 3) or 1.6 times the predicted standard metabolic rate (SMR). The average energy consumption rate while away from the colony was 10 W/kg (N = 8) or 4.6 x SMR, compared to 4.3 x SMR estimated from a time—energy budget. The latter value is based on an average metabolic rate of 4.2 W/kg for three birds while resting in 5°C water and 9.6 W/kg while swimming at 2 m/s, which was extrapolated from the average of three birds swimming at 1 m/s. The average energy intake based on 9 stomach content samples was nearly 24.6 kJ/g dry mass. The main prey by number are myctophid fish of the species Krefftichthys anderssoni and Electrona carlsbergi. It was concluded that: (1) feeding begins ≈28 km from the colony, (2) prey is pursued night and day through its vertical movements, (3) vertical distribution of the prey is reflected closely by diving habits of the birds, (4) deep—diving, for unknown reasons, is an important component of foraging success, (5) diving capacities of King Penguins are remarkable compared to other birds and many pinnipeds, and (6) calculated foraging energetics can be closely estimated from time—energy budgets.