Factors influencing the distribution of Subantarctic deep-sea benthic foraminifera,Campbell and Bounty Plateaux,New Zealand

We investigate the combination of environmental factors that influence the distribution patterns of benthic foraminiferal tests (> 63 μm) in a topographically varied region crossed by both the Subtropical and Subantarctic Fronts, south-east of New Zealand. Seafloor sample sites, extending from outer shelf (50 m) to abyssal (5000 m) depths, are bathed by five different water masses, and receive phytodetritus from Subtropical, Subantarctic and Circumpolar surface water masses. Eight mappable associations are recognised by Q-mode cluster analysis of the benthic foraminiferal census data. Similar associations are identified using cluster analysis based solely on the presence or absence of species. Canonical correspondence analysis and a correlation coefficient matrix were used to relate the faunal data to a set of environmental proxies. These show that factors related to water depth (especially decreasing food supply with increasing depth) are the most significant in determining the overall foraminiferal distribution. Other contributing factors include surface water productivity and its seasonality; bottom water ventilation; energetic state of the benthic boundary layer and resulting substrate texture; and bottom water carbonate corrosiveness. Three shallow-water associations (50–700 m), dominated by Cassidulina carinata, Trifarina angulosa, Globocassidulina canalisuturata, Gavelinopsis praegeri, and Bolivina robusta, occur in coarse substrates on the continental shelf, and on the crests and upper slopes of four seamounts under well-oxygenated, high energy regimes, and high food input. Three mid bathyal to upper abyssal associations (500–3300 m), dominated by Alabaminella weddellensis, C. carinata, and Epistominella exigua, occur in biopelagic sandy mud, beneath a region of strongly seasonal food supply, with their composition influenced by total food flux, ventilation (Oxygen Minimum Zone), and bottom current strength. An unusual lower bathyal association (1200–2100 m), dominated by T. angulosa and Ehrenbergina glabra, occurs in a belt of coarser sandy substrate that runs along the crest of the submarine plateaux slopes beneath the strongly-flowing Subantarctic Front-related currents. A deep abyssal association (3500–5000 m), dominated by Nuttallides umbonifer and Globocassidulina subglobosa, occurs on the abyssal plain beneath oligotrophic lower Circumpolar Water south-east of the Subantarctic Front and is strongly influenced by the cold, carbonate-corrosive conditions.     

New latest Coniacian to middle Campanian foraminiferal data from the lower Zongshan Formation in the Chaqiela section,Gamba, southern Tibet

A first and detailed foraminiferal biostratigraphic work on the lower part of the Zongshan Formation (Limestone I and Calcareous Marl I sequence) in the Chaqiela section, Gamba, southern Tibet, allows the recognition of three latest Coniacian to middle Campanian planktic foraminiferal biozones: Dicarinella asymetrica Total Range Zone, Globotruncanita elevata Partial-Range Zone, and Contusotruncana plummerae Interval Zone. The base and top of the Santonian Stage in the Chaqiela section were placed at the lowest occurrence (LO) of Globotruncana linneiana and the highest occurrence (HO) of Dicarinella asymetrica, respectively. The deposition of the latest Coniacian to middle Campanian sediments of the lower Zongshan Formation in the Chaqiela section seems to have been continuous or at least without any major gap based on the planktic foraminiferal biozones and events.     

Pilot trophic model for subantarctic water over the Southern Plateau, New Zealand: a low biomass, high transfer efficiency system

The Southern Plateau subantarctic region, southeast of New Zealand, is an important feeding area for birds, seals and fish, and a fishing ground for commercially significant species. The Southern Plateau is a major morphometric feature, covering approximately 433,620 km² with average depth of 615 m. The region is noted for its relatively low levels of phytoplankton biomass and primary production that is iron-limited. In order to evaluate the implications of these attributes for the functioning of this ecosystem a steady-state, 19-compartment model was constructed using Ecopath with Ecosim software of Christensen et al. [www.ecopath.org]. The system is driven by primary production that is primarily governed by the supply of iron and light. The total system biomass of 6.28 g C m⁻² is very low compared with systems so far modelled with a total system throughput of 1136 g C m⁻² year⁻¹. In the model, the Southern Plateau retains 69% of the biomass in the pelagic system and 99% of total production. Although fish are caught demersally, most of their food is part of production in the pelagic system. Top predators represent about 0.3% of total biomass and account for about 0.24 g C m⁻² year⁻¹ of food consumed made up of birds 0.058 g C m⁻² year⁻¹, seals 0.041 g C m⁻² year⁻¹, and toothed 0.094 g C m⁻² year⁻¹ and baleen whales 0.051 g C m⁻² year⁻¹. This amounts to 105,803 tonnes carbon over the whole of the Southern Plateau and is about 17% of the total amount of food eaten by non-mesopelagic fish. Mean transfer efficiencies between trophic levels II and IV of 23% are at the high end of the range reported in the literature. In the model, adult fish production is almost completely accounted for by the fisheries take (32%), consumption by seals (7%), toothed whales (21%), other adult fish (13%), and squid (20%). Fish and squid catches are at the trophic levels of 4.8 and 5.0, respectively. The gross efficiency of the fishery is 0.018% (catch/primary production). Although not all data come from direct knowledge of this system, the model reflects its general characteristics, namely a low primary production system dominated by the microbial loop, low sedimentation to the seafloor, high transfer efficiencies, a long food web and supporting high-level predators.     

The second investigation of Lake Puma Yum Co located in the Southern Tibetan Plateau,China

Limnological features of Lake Puma Yum Co, a typical alpine lake located at the altitude of 5030 m in the Tibetan Plateau, China, are described based on the findings of the second expedition in September 2004. The lake surface is about 280km² and maximal depth is 65 m. Total inflow just after the rainy season was estimated to be about 860 000m³ day⁻¹, and the lake water was drained from a newly excavated channel at a rate of 960 000m³ day⁻¹. We may have to expect undesirable lowering of the water level by this new drainage, especially in the dry season. Thermocline developed from 20 to 30 m depth, and the euphotic zone reached the 50 m depth. Dissolved oxygen in surface water was supersaturated as in productive lakes, although there were no large point and nonpoint sources of nutrient in the catchment. Vertical distribution of phytoplankton biomass and primary production suggested the presence of photoinhibition. What should be noted about the flora and fauna is that a Chara zone and a shell zone were distributed at about 30 or 40 m of depth.     

Prasionema heeschiae sp. nov. (Prasiolales,Chlorophyta) from Campbell Island,New Zealand: first record of Prasionema in the southern hemisphere

A new species in the genus Prasionema (Prasiolales, Trebouxiophyceae) is described from Campbell Island, in the New Zealand subantarctic region, the first record of this genus in the southern hemisphere. Prasionema heeschiae sp. nov. is filamentous, uni- to predominantly biseriate, with disc-shaped cells, and an axial plastid with a central pyrenoid. It is anchored by an enlarged pigmented basal cell. There is evidence of reproduction by both spores and fragmentation. This species was found growing on a timber wharf above the high tide level. The only other species in the genus, P. payeri Heesch, M.Pazoutová & Rindi, was described from Spitzbergen growing on soil in a high nutrient environment. The bipolar distribution of Prasionema is discussed. Based on phylogenetic analyses that included sequence data from holotype material of southern filamentous Prasiolales, we reduce Rosenvingiella australis to synonymy with R. tasmanica.