Plankton of lake Ototoa,a sand‐dune lake in Northern New Zealand

The seasonal cycles of abundance of the phytoplankton and zooplankton in Lake Ototoa, Northland, at 36° 31 S, 174° 14 E, are described. Concentrations of chlorophyll a were low (range 0.04–4.61 mg.m^‐3; mean 0.97 mg.m^‐3), and highest values were in winter. Phytoplankton densities were also low; an oligo‐trophic diatom‐desmid assemblage associated with Botryococcus, Dinobryon, and Svhaerocyslis was found.

The zooplankton was dominated by the calanoid copepod Calamoecia lucasi whose numbers remained fairly constant throughout the year, and the only other copepod found was the cyclopoid Mesocyclops leuckarti which was present in very low numbers. Bosmina meridionalis was the only limnetic cladoceran and was most abundant during autumn and spring. A number of rotifer species were also common.     

Mass stranding of molluscs at Te Waewae bay,southland, New Zealand (note)

A stranding of shellfish on the beach at Te Waewae Bay, Southland, occurred during a period of very cold, stormy weather in September 1970. More than 20 million shellfish were stranded, the majority being Mactra discors Gray. It is suggested that the cause was a combination of Strong inshore winds and low air temperatures, coupled with an increased flow of fresh, cold water across the beach.     

Structure of a mudflat diatom community in the Avon‐Heathcote Estuary,New Zealand

Parameters of community structure (species composition and relative abundance, number of taxa, diversity, evenness, and cell density) were measured for a mudflat diatom community in the Avon‐Heathcote estuary, New Zealand. Fifty three diatom species were identified: 25 taxa (species and varieties) are new New Zealand records. The Shannon‐Wiener information index (H') was 3.46, indicating high diversity. Evenness (J') ranged from 0.57–0.67. The association between the biomass of the pulmonate gastropod, Amphibola crenata, and benthic diatom community structure was studied using large open enclosures (4.0 m²) to manipulate snail biomass. Community structure was compared at 0, 5 (natural biomass), and 10 g A. crenata dry weight per m. A similarity index (SIMI=0.88–0.95), as well as H’ and J’ indicated close similarity between the diatom assemblages within all enclosures, but number of taxa increased from 33 to 49 with increasing snail biomass. Cell densities were significantly lower at high snail biomass (6088 valves per mm²) compared to enclosures with no snails (10 110 valves per mm ). A. crenata had a higher ratio of diatom fragments to whole diatom valves in its faeces (2.42) than in its crop (0.55), indicating that it is capable of fragmenting diatoms.     

The hydrodynamic and sedimentary setting of nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a case study

The Great Barrier Reef (GBR) shelf contains a range of coral reefs on the highly turbid shallow inner shelf, where interaction occurs with terrigenous sediments. The modern hydrodynamic and sedimentation regimes at Paluma Shoals, a shore‐attached ‘turbid‐zone’ coral reef, and at Phillips Reef, a fringing reef located 20 km offshore, have been studied to document the mechanisms controlling turbidity. At each reef, waves, currents and near‐bed turbidity were measured for a period of ≈1 month. Bed sediments were sampled at 135 sites. On the inner shelf, muddy sands are widespread, with admixed terrigenous and carbonate gravel components close to the reefs and islands, except on their relatively sheltered SW side, where sandy silty clays occur. At Paluma Shoals, the coral assemblage is characteristic of inner‐shelf or sheltered habitats on the GBR shelf (dominated by Galaxea fascicularis, up to >50% coral cover) and is broadly similar to that at Phillips Reef, further offshore and in deeper water. The sediments of the Paluma Shoals reef flats consist of mixed terrigenous and calcareous gravels and sands, with intermixed silts and clays, whereas the reef slope is dominated by gravelly quartz sands. The main turbidity‐generating process is wave‐driven resuspension, and turbidity ranges up to 175 nephelometric turbidity units (NTU). In contrast, at Phillips Reef, turbidity is <15 NTU and varies little. At Paluma Shoals, turbidity of >40 NTU probably occurs for a total of >40 days each year, and relatively little time is spent at intermediate turbidities (15–50 NTU). The extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning (autotrophy and heterotrophy) in response to different levels of turbidity. Sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux (BTF) of sediment to the sea floor, i.e. 10 000 BTF, over three orders of magnitude greater than the Holocene average for Halifax Bay of <3 BTF. As elsewhere along the nearshore zone of the central GBR, dry‐season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments. The location of modern nearshore coral reefs is controlled by the presence of suitable substrates, which in Halifax Bay are Pleistocene and early Holocene coarse‐grained (and relatively stable) alluvial deposits.     

泌阳断陷下第三系核三上亚段层序地层学研究

根据陆相层序在地震剖面及电测曲线上的识别标志和在岩石矿物学方面的旋回性特征,采用沉积旋回分析技术及Ｆｉｓｃｈｅｒ图解法,将泌阳断陷双河—赵凹地区下第三系核三段上亚段划分为３个陆相层序,其沉积体系呈现冲积扇—扇三角洲—湖相空间配置关系。在这３个陆相层序中共发育小层序组１３个,其中可识别的小层序达５０余个。针对研究区目的层段所划３个陆相层序发育的共同特点,在连井剖面层序地层对比的基础上,编制了研究区目的层段的陆相层序地层等时框架模式。     

The flux of floating macrodetritus in the North inlet estuarine ecosystem

An estimate of floating macrodetritus flux in a salt marsh-dominated estuarine ecosystem indicates that this material is exported regularly. However, the amount of macrodetrital material exported is small, less than 1% of the net marsh primary productivity. The export of floating macrodetritus is seasonal with maximum values in summer.     

Geochemistry of Peruvian near-surface sediments

Sixteen short sediment cores were recovered from the upper edge (UEO), within (WO) and below (BO) the oxygen minimum zone (OMZ) off Peru during cruise 147 of R/V Sonne. Solids were analyzed for major/trace elements, total organic carbon, total inorganic carbon, total sulfur, the stable sulfur isotope composition (δ³⁴S) of pyrite, and sulfate reduction rates (SRR). Pore waters were analyzed for dissolved sulfate/sulfide and δ³⁴S of sulfate. In all cores highest SRR were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and/or diffusion of sulfate from bottom water. δ³⁴S of dissolved sulfate showed only minor downcore increases. Strong ³²S enrichments in sedimentary pyrite (to −48‰ vs. V-CDT) are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction. Manganese and Co are significantly depleted in Peruvian upwelling sediments most likely due to mobilization from particles settling through the OMZ, whereas release of both elements from reducing sediments only seems to occur in near-coastal sites. Cadmium, Mo and Re are exceptionally enriched in WO sediments (<600 m water depth). High Re and moderate Cd and Mo enrichments are seen in BO sediments (>600 m water depth). Re/Mo ratios indicate anoxic and suboxic conditions for WO and BO sediments, respectively. Cadmium and Mo downcore profiles suggest considerable contribution to UEO/WO sediments by a biodetrital phase, whereas Re presumably accumulates via diffusion across the sediment-water interface to precipitation depth. Uranium is distinctly enriched in WO sediments (due to sulfidic conditions) and in some BO sediments (due to phosphorites). Silver transfer to suboxic BO sediments is likely governed by diatomaceous matter input, whereas in anoxic WO sediments Ag is presumably trapped due to sulfide precipitation. Cadmium, Cu, Zn, Ni, Cr, Ag, and T1 predominantly accumulate via biogenic pre-concentration in plankton remains. Rhenium, Sb, As, V, U and Mo are enriched in accordance with seawater TE availability. Lead and Bi enrichment in UEO surface sediments is likely contributed by anthropogenic activity (mining). Accumulation rates of TOC, Cd, Mo, U, and V from Peruvian and Namibian sediments exceed those from the Oman Margin and Gulf of California due to enhanced preservation off Peru and Namibia.     

Marine and terrigenous lipids in coastal sediments from the Peru upwelling region at 15°S: Sterols and triterpene alcohols

The distributions of free 4-desmethyl sterols in sediments from the Peru coastal zone at 15°S have been determined. Major free sterols in the surface sediments include cholesterol, which is mainly derived from zooplankton, and two C₂₈ sterols: 24-methylcholesta-5,24(28)-dien-3β-ol and 24-methylcholesta-5,22E-dien-3β-ol both of which are derived fro diatoms. Their concentrations decrease by almost an order of magnitude in the top 20 cm of sediment depth, indicating that free sterols are rapidly degraded in this sedimentary environment. Lipids from higher plants were also detected: long chain fatty acids and alcohols and various triterpenoid alcohols, including taraxerol, lupeol and α- and β-amyrin. The concentrations of most terrigenous lipids varied by less than a factor of 3 over the same depth, and these changes were not correlated with changes in the concentrations of total organic carbon. Below 3 cm, lipids from higher plants predominated in the extractable lipid distributions due to the more rapid degradation of marine lipids. We postulate that there are significant marine sources of the higher plant sterols 24-ethylcholesterol, 24-ethylcholesta-5,22E-dien-3β-ol and 24-methylcholesterol in these sediments. A high proportion of many of the terrigenous lipids in these sediments are probably transported into the coastal zone by rivers, rather than from the atmosphere, and then redistributed by bottom currents.     

Seagrass development in terrigenous-influenced inner ramp settings during the middle Eocene (Urbasa–Andia Plateau,Western Pyrenees,North Spain)

Since their first occurrence in the late Cretaceous, seagrasses have played a major role in carbonate production and sedimentation across shallow-water and nearshore environments, sustaining a prolific carbonate factory and contributing to sediment accumulation through the combination of baffling and trapping effects. Most reported Palaeogene seagrass occurrences developed in oligo?mesotrophic shallow warm-water habitats and are characterized by distinct associations of small and larger benthic foraminifers adapted to low terrigenous influence. This study describes a number of seagrass episodes interbedded in the Bartonian (middle Eocene) of San Fausto–Lazkua area (Navarra region, North Spain), within a nearshore to inner-ramp succession that, in spite of being deposited under general transgressive conditions, was highly influenced by terrigenous supply from the adjacent land. Up to twelve different seagrass bed intervals occur interbedded in a cyclical manner with high-energy nearshore siliciclastics and inner ramp bioclastic carbonates rich in mesophotic?oligophotic foraminifers and heterozoan biota (red algae, echinoderms, bryozoans). Seagrass deposits exhibit typical unsorted textures, abundant bioturbation and moderate to high terrigenous content, and comprise a characteristic skeletal association of epiphytic foraminifers, red algae and, most particularly, of abundant encrusting acervulinids, commonly with distinct hooked and tubular growth forms. This abundance of suspension-feeders relative to autotrophs and mixotrophs may be indicative of temperate waters, although the taxonomic diversity of the foraminiferal assemblages in both seagrass and non-seagrass embedding deposits supports the interpretation of shallow, warm-water conditions. The studied seagrass deposits provide evidence that high siliciclastic supply and associated nutrient input may determine the occurrence of temperate-like seagrass deposits in warm-water settings, analogous to extensive heterozoan carbonate production in modern shallow-tropical environments. Thus, the identification and correct interpretation of past seagrass-vegetated environments are crucial for reconstructing palaeoecological conditions in ancient shallow-marine environments. Therefore, in comparison with carbonate-dominated environments, the mixed terrigenous?carbonate seagrass deposits are volumetrically less important, presenting a more irregular, patchy distribution, and a skeletal assemblage dominated by heterotrophs, regardless of the water temperature.     

Desert detritivory: Nutritional ecology of a dung beetle (Pachysoma glentoni) subsisting on plant litter in arid South African sand dunes

Dry conditions limit microbial decomposition of plant litter in deserts, which leaves a primary role to detritivorous macroarthropods. In the sandy arid strip along the west coast of South Africa, such detritivores include the large scarabaeid dung beetle Pachysoma glentoni. Highly unusual among dung beetles, this species collects surface litter and drags it into an underground storage and feeding chamber which is abandoned after 6–7 days. Fresh stores for single beetles and for breeding pairs (mean depths: 30 and 39 cm) contained about 1.1 and 2.9 g organic matter, respectively. Using ergosterol as a biomarker for fungal biomass, we tested the hypotheses that (1) the dry detritus takes up water underground; (2) this promotes fungal growth on the detritus, and (3) fungi are the main food of the beetles. These hypotheses were disproved, but the stored litter, including floral remains, was shown to have relatively high quality (mean atomic C:N ratio: 35) and the beetles assimilated about 60% of it. Estimated weekly water gain per beetle, supplied entirely by the food, was about 0.6 g. Our results highlight unique nutritional adaptations to survival in deserts without the usual dung beetle food: wet dung of large herbivores.