Zealand Landmass Research Articles

Moving Earth (not heaven): A novel approach to tropical cyclone impact modelling, demonstrated for New Zealand

Some of the historically highest-impact weather events to affect New Zealand have been caused by ex-tropical cyclones (ex-TCs) which have had significant direct and indirect adverse effects. The weather theme of a New Zealand government funded research programme known as the Resilience to Nature’s Challenges (RNC2) aims to create physical datasets of high-impact, yet credible, extreme weather events not previously available to researchers and end-users. This paper focusses on the potential scenarios of a major ex-TC impacting Auckland and surrounding areas in the north of New Zealand. Highly-detailed, meteorologically consistent data of such events are produced by relocating the New Zealand land mass into the path of historical ex-TC cases, using convection permitting simulations of the Met Office Unified Model. We illustrate the applicability of this method over simpler (non-consistent) methods, and show for ex-TC Cook (April 2017) what wind strength and precipitation totals would have been for a track just slightly to the west of reality. Finally, we illustrate how sub-kilometre simulations nested within the main simulation can add significant additional detail at the city scale, and show how simple modifications, for example raising the sea-surface temperature, can illustrate how events may change in future. Such scenarios may prove invaluable in designing future infrastructure and planning for such an event.

An endemic dung beetle species feeding on kauri snail carrion in Northland, New Zealand

AbstractWorldwide, Scarabaeidae are coprophages, feeding on mammalian dung. In New Zealand, endemic Scarabaeidae are restricted to forested habitats, where they have evolved a more generalised diet of carrion and dung from a variety of fauna. The scarab beetle Saphobius sp. A is an undescribed flightless dung beetle endemic to New Zealand. The diet of Saphobius is of interest as these Scarabaeidae have evolved on the isolated New Zealand landmass, in the absence of large forest‐dwelling land mammals. Here, I observe Saphobius sp. A feeding on a non‐dung food source, kauri snail Paryphanta busbyi, Gray, carrion.

Multiple lineages of hyper‐diverse Zopheridae beetles survived the New Zealand Oligocene Drowning

AbstractAimDuring the late Oligocene (23 mya) the New Zealand landmass was reduced to approximately 18% of its current area. It has been hypothesized that this event, known as the Oligocene Drowning, caused population bottlenecking and mass extinction. Using phylogenetic methods, we examine the effect of this and other environmental events on the hyper‐diverse Zopheridae beetles (162 morphospecies), which largely inhabit leaf litter and dead wood.LocationNew Zealand.TaxonZopheridae, Coleoptera.MethodsHere we use a fossil‐calibrated phylogenetic tree estimated from mitochondrial cytochrome c oxidase subunit I and nuclear large subunit rRNA genes to identify monophyletic New Zealand zopherid lineages and date the age of these lineages. We used Bayesian diversification models (compound Poisson process on mass extinction times) to test the hypothesis that the New Zealand zopherids underwent a mass extinction in the late Oligocene followed by an increase in speciation rate in the Miocene. We also used these data to estimate the age of these lineages in New Zealand.ResultsWe demonstrate that 15–20 zopherid lineages survived the Oligocene Drowning depending on the calibration scheme. Of these lineages from 3 to 11 have posterior intervals that encompass the rifting of New Zealand from Gondwana in the late Cretaceous, again depending on the calibration scheme. The diversification model shows no evidence of an increase in extinction rate during the Oligocene Drowning or during any other period since the Cretaceous. Furthermore, rather than recovering an increase in speciation rate during the Miocene and Pliocene, due to environmental changes, we instead recovered a large drop in the speciation rate during this time.Main conclusionsThe New Zealand zopherid fauna is a combination of lineages, some of which may have existed on New Zealand since the rifting from Gondwana and other more recent arrivals. The late Oligocene reduction in land area was insufficient to cause a mass extinction in the Zopheridae. This suggests the amount of emergent land was great enough to support a diverse invertebrate fauna. Our study demonstrates the different biogeographic patterns evident in cryptic, hyper‐diverse, and poorly dispersing invertebrate species relative to more mobile plants and animals.

Earth history and the passerine superradiation

Avian diversification has been influenced by global climate change, plate tectonic movements, and mass extinction events. However, the impact of these factors on the diversification of the hyperdiverse perching birds (passerines) is unclear because family level relationships are unresolved and the timing of splitting events among lineages is uncertain. We analyzed DNA data from 4,060 nuclear loci and 137 passerine families using concatenation and coalescent approaches to infer a comprehensive phylogenetic hypothesis that clarifies relationships among all passerine families. Then, we calibrated this phylogeny using 13 fossils to examine the effects of different events in Earth history on the timing and rate of passerine diversification. Our analyses reconcile passerine diversification with the fossil and geological records; suggest that passerines originated on the Australian landmass ∼47 Ma; and show that subsequent dispersal and diversification of passerines was affected by a number of climatological and geological events, such as Oligocene glaciation and inundation of the New Zealand landmass. Although passerine diversification rates fluctuated throughout the Cenozoic, we find no link between the rate of passerine diversification and Cenozoic global temperature, and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents. Taken together, these results suggest more complex mechanisms than temperature change or ecological opportunity have controlled macroscale patterns of passerine speciation.

Nutrient‐enriched soils and native N‐fixing plants in New Zealand

AbstractApproximately 40% of New Zealand's land mass is fertilized grassland with entirely non‐native plants, but currently there is substantially increased interest in restoration of native plants into contemporary agricultural matrices. Native vegetation is adapted to more acid and less fertile soils and their establishment and growth may be constrained by nutrient spillover from agricultural land. We investigated plant–soil interactions of native N‐fixing and early successional non N‐fixing plants in soils with variable fertility. The effects of soil amendments of urea (100 and 300 kg N ha−1), lime (6000 kg CaCO3 ha−1), and superphosphate (470 kg ha−1) and combinations of these treatments were evaluated in a glasshouse pot trial. Plant growth, soil pH, soil mineral N, Olsen P and nodule nitrogenase activity in N‐fixing plants were measured. Urea amendments to soil were not inhibitory to the growth of native N‐fixing plants at lower N application rates; two species responded positively to combinations of N, P and lime. Phosphate enrichment enhanced nodulation in N‐fixers, but nitrogen inhibited nodulation, reduced soil pH and provided higher nitrate concentrations in soil. The contribution of mineral N to soil from the 1‐year old N‐fixing plants was small, in amounts extrapolated to be 10–14 kg ha−1 y−1. Urea, applied both alone and in conjunction with other amendments, enhanced the growth of the non N‐fixing species, which exploited mineral N more efficiently; without N, application of lime and P had little effect or was detrimental. The results showed native N‐fixing plants can be embedded in agroecology systems without significant risk of further increasing soil fertility or enhancing nitrate leaching.

Terrestrial climate evolution in the Southwest Pacific over the past 30 million years

A reconstruction of terrestrial temperature and precipitation for the New Zealand landmass over the past ∼30 million years is produced using pollen data from >2000 samples lodged in the New Zealand Fossil Record Electronic Database and modern climate data of nearest living relatives. The reconstruction reveals a warming trend through the late Oligocene to early Miocene, peak warmth in the middle Miocene, and stepwise cooling through the late Neogene. Whereas the regional signal in our reconstruction includes a ∼5–10° northward tectonic drift, as well as an increase in high altitude biomes due to late Neogene and Pliocene uplift of the Southern Alps, the pattern mimics inferred changes in global ice extent, which suggests that global drivers played a major role in shaping local vegetation. Importantly, seasonal temperature estimates indicate low seasonality during the middle Miocene, and that subsequent Neogene cooling was largely due to cooler winters. We suggest that this may reflect increased Subantarctic influence on New Zealand vegetation as the climate cooled.

Annual cycles of deep‐ocean biogeochemical export fluxes in subtropical and subantarctic waters, southwest Pacific Ocean

AbstractThe annual cycles of particle fluxes derived from moored sediment trap data collected during 2000–2012 in subtropical (STW) and subantarctic waters (SAW) east of New Zealand are presented. These observations are the most comprehensive export flux time series from temperate Southern Hemisphere latitudes to date. With high levels of variability, fluxes in SAW were markedly lower than in STW, reflecting the picophytoplankton‐dominated communities in the iron‐limited, high nutrient‐low chlorophyll SAW. Austral spring chlorophyll blooms in surface STW were near synchronous with elevated fluxes of bio‐siliceous, carbonate, and organic carbon‐rich materials to the deep ocean, probably facilitated by diatom and/or coccolithophorid sedimentation. Lithogenic fluxes were also high in STW, compared to SAW, reflecting proximity to the New Zealand landmass. In contrast, the highest biogenic fluxes in SAW occurred in spring when surface chlorophyll concentrations were low, while highest annual chlorophyll concentrations were in summer with no associated flux increase. We hypothesize that the high spring export in SAW results from subsurface chlorophyll accumulation that is not evident from remote‐sensing satellites. This material was also rich in biogenic silica, perhaps related to the preferential export of diatoms and other silica‐producing organisms, such as silicoflagellates and radiolarians. Organic carbon fluxes in STW are similar to that of other mesotrophic to oligotrophic waters (∼6–7 mg C m−2 d−1), whereas export from SAW is below the global average (∼3 mg C m−2 d−1). Regional differences in flux across the SW Pacific and Tasman region reflect variations in physical processes and ecosystem structure and function.

New Zealand’s deepwater frontier

New Zealand’s deepwater frontier

The effect of submerged plateaux on Pleistocene gyral circulation and sea-surface temperatures in the Southwest Pacific

Uniquely in the Southern Hemisphere the New Zealand micro-continent spans the interface between a subtropical gyre and the Subantarctic Circumpolar Current. Its 20° latitudinal extent includes a complex of submerged plateaux, ridges, saddles and basins which, in the present interglacial, are partial barriers to circulation and steer the Subtropical (STF) and Subantarctic (SAF) fronts. This configuration offers a singular opportunity to assess the influence of bottom topography on oceanic circulation through Pleistocene glacial – interglacial (G/I) cycles, its effect on the location and strength of the fronts, and its ability to generate significant differences in mixed layer thermal history over short distances. For this study we use new planktic foraminiferal based sea-surface temperature (SST) estimates spanning the past 1 million years from a latitudinal transect of four deep ocean drilling sites. We conclude that: 1. the effect of the New Zealand landmass was to deflect the water masses south around the bathymetric impediments; 2. the effect of a shallow submerged ridge on the down-current side (Chatham Rise), was to dynamically trap the STF along its crest, in stark contrast to the usual glacial–interglacial (G–I) meridional migration that occurs in the open ocean; 3. the effect of more deeply submerged, downstream plateaux (Campbell, Bounty) was to dynamically trap the SAF along its steep southeastern margin; 4. the effects of saddles across the submarine plateaux was to facilitate the development of jets of subtropical and subantarctic surface water through the fronts, forming localized downstream gyres or eddies during different phases in the G–I climate cycles; 5. the deep Pukaki Saddle across the Campbell-Bounty Plateaux guided a branch of the SAF to flow northwards during each glacial, to form a strong gyre of circumpolar surface water in the Bounty Trough, especially during the mid-Pleistocene Climate Transition (MIS 22-16) when exceptionally high SST gradients existed across the STF; 6. the shallower Mernoo Saddle, at the western end of the Chatham Rise, provided a conduit for subtropical water to jet southwards across the STF in the warmest interglacial peaks (MIS 11, 5.5) and for subantarctic water to flow northwards during glacials; 7. although subtropical or subantarctic drivers can prevail at a particular phase of a G–I cycles, it appears that the Antarctic Circumpolar Current is the main influence on the regional hydrography. Thus complex submarine topography can affect distinct differences in the climate records over short distances with implications for using such records in interpreting global or regional trends. Conversely, the local topography can amplify the paleoclimate record in different ways in different places, thus enhancing its value for the study of more minor paleoceanographic influences that elsewhere are more difficult to detect. Such sites include DSDP 594, which like some other Southern Ocean sites, has the typical late Pleistocene asymmetrical saw-tooth G–I climate pattern transformed to a gap-tooth pattern of quasi-symmetrical interglacial spikes that interrupt extended periods of minimum glacial temperatures.

The discovery of a new sedimentary basin: offshore Raukumara, East Coast, North Island, New Zealand

The East Coast of North Island, New Zealand, is the site of subduction of the Pacific below the Australian plate, and, consequently, much of the basin is highly deformed. An exception is the Raukumara Sub-basin, which forms the northern end of the East Coast Basin and is relatively undeformed. It occupies a marine plain that extends to the north-northeast from the northern coast of the Raukumara Peninsula, reaching water depths of about 3,000 m, although much of the sub-basin lies within the 2,000 m isobath. The sub-basin is about 100 km across and has a roughly triangular plan, bounded by an east-west fault system in the south. It extends about 300 km to the northeast and is bounded to the east by the East Cape subduction ridge and to the west by the volcanic Kermadec Ridge. The northern seismic lines reveal a thickness of around 8 km increasing to 12–13 km in the south. Its stratigraphy consists of a fairly uniformly bedded basal section and an upper, more variable unit separated by a wedge of chaotically bedded material. In the absence of direct evidence from wells and samples, analogies are drawn with onshore geology, where older marine Cretaceous and Paleogene units are separated from a Neogene succession by an allochthonous series of thrust slices emplaced around the time of initiation of the modern plate boundary. The Raukumara Sub-basin is not easily classified. Its location is apparently that of a fore-arc basin along an ocean-to-ocean collision zone, although its sedimentary fill must have been derived chiefly from erosion of the New Zealand land mass. Its relative lack of deformation introduces questions about basin formation and petroleum potential. Although no commercial discoveries have been made in the East Coast Basin, known source rocks are of marine origin and are commonly oil prone, so there is good potential for oil as well as gas in the basin. New seismic data confirm the extent of the sub-basin and its considerable sedimentary thickness. The presence of potential trapping structures and direct hydrocarbon indicators suggest that the Raukumara Sub-basin may contain large volumes of oil and gas.

Comparative phylogeography of coastal limpets across a marine disjunction in New Zealand

Cook Strait, which separates the North and South Island of New Zealand, has been a transient, but re-occurring feature of the New Zealand land mass throughout the Pleistocene, maintaining its current width and depth for the past 5000 years. Historic land fragmentation coupled with the complex hydrography of the Greater Cook Strait region has created both biogeographic and phylogeographic disjunctions between the North and South Island in several marine species. Here we use mitochondrial cytochrome b DNA sequences of three endemic intertidal limpets, Cellana ornata, Cellana radians and Cellana flava to assess intraspecific phylogeographic patterns across Cook Strait and to look for interspecific concordance of ecological and evolutionary processes among closely related taxa. We sequenced 328-359 bp in 85-321 individuals from 8-31 populations spanning the biogeographic range of the three species. Intraspecific phylogeographic analyses show moderate to strong genetic discontinuity among North and South Island populations due to allopatric fragmentation. This pattern was broadly concordant across the three species and the observed divergence among this group of intertidal limpets (0.3-2.0%) is similar to that of previously studied subtidal organisms. For each species, divergence time calculations suggest contemporary North and South Island lineages diverged from their respective most recent common ancestor approximately 200 000 to 300 000 years before present (bp), significantly earlier than previous estimates in other coastal marine taxa that arose from a miscalculation of divergence time.

Decadal temperature changes in the Tasman Sea

Ocean temperature changes between 1991 and 2005 in the eastern Tasman Sea were analysed. This area was chosen because of a combination of data availability, low mesoscale variability and because of its importance in determining the climate of the downwind New Zealand landmass. A large warming extending to the full depth of the water column (c. 800 m) was found to have occurred between 1996 and 2002. This warming was seen in measurements by expendable bathythermographs and also in satellite sea surface temperature and sea surface height products, and has a clear impact on New Zealand's terrestrial temperature. The nature of the warming is discussed, together with likely forcing mechanisms. No local forcing mechanisms are consistent with the observed warming, leading to the conclusion that the signal seen in the Tasman Sea is part of a larger South Pacific‐wide phenomenon.

MESOZOIC EVOLUTION OF THE GREATER TARANAKI BASIN AND IMPLICATIONS FOR PETROLEUM PROSPECTIVITY

A paradigm of New Zealand petroleum geology was that the oldest source rocks known in the region were of Cretaceous age, so any older sedimentary rocks were considered to be economic basement. Two major projects have revealed that this is not universally the case and that a Jurassic petroleum system should now be considered.Firstly, the Astrolabe 2D speculative survey, acquired by TGS-NOPEC in 2001, has revealed that a significant section underlies the traditional Cretaceous petroleum systems. Secondly, the Wakanui–1 well, drilled by Conoco, Inpex and Todd in 1999, which has recently become open-file, penetrated a Mid-Jurassic coal measure sequence.Jurassic rocks, including coal measure units, are known onshore in New Zealand, They are part of the Murihiku Supergroup, one of the basement terranes comprising the Permian to Cretaceous volcanic arc that forms the basement rocks of the present New Zealand landmass. Wherever they have been seen in outcrop, these rocks generally record low grade metamorphism and have been discounted as petroleum source rocks. Where rocks of the same age were deposited distal to the volcanic arc (and the effects of heat and pressure), however, they may form components of an effective petroleum system.The New Caledonia Basin, extending more than 2,000 km from Taranaki to New Caledonia, may have been the site of a Mesozoic back-arc basin. Jurassic coal measure successions and their equivalent marine units may be locally, or regionally important as source rocks. Implications of a Jurassic petroleum system for prospectivity of the region are investigated.

Low genetic divergence obscures phylogeny among populations of Sphenodon, remnant of an ancient reptile lineage

Tuatara (two species of Sphenodon) are the last representatives of a branch of an ancient reptilian lineage, Sphenodontia, that have been isolated on the New Zealand landmass for 82 million years. We present analyses of geographic variation in allozymes, mitochondrial DNA, nuclear DNA sequences, and one-way albumin immunological comparisons. These all confirm a surprisingly low level of genetic diversity within Sphenodon for such an ancient lineage. We hypothesise a recent extended population bottleneck, probably during the Pliocene/Pleistocene glaciation cycles, to explain the current paucity of variation. All data sets reveal clear genetic differentiation between the northern populations and those in Cook Strait, but offer conflicting views of the history and taxonomic relationships of the Cook Strait population on North Brother Island, currently recognised as Sphenodon guntheri. Allozymes show this population to be the most divergent of all tuatara populations, but preliminary mitochondrial DNA data indicate few differences between S. guntheri and Cook Strait Sphenodon punctatus. Interpretation of the trees is confounded by the lack of a suitable outgroup. As in other cases of conflicting nuclear and mitochondrial data sets, the different data sets likely reveal different aspects of the animals’ evolutionary history, and introgression is not uncommon between species pairs.

Detailed structure of the Subtropical Front over Chatham Rise, east of New Zealand

A detailed description of the Subtropical Front (STF) over Chatham Rise is presented. Information is provided by conductivity‐temperature‐depth (CTD) profiler temperature and salinity transects, high‐resolution (3–4 km spacing), near‐synoptic expendable bathythermograph surveys, shipboard acoustic Doppler current profiler measurements, a 160 km constant depth undulator tow, and satellite SST measurements in austral autumn and spring (April and October) near 178°30′E. Detailed sections across the front reveal that the STF can be divided into northern and southern fronts (NSTF and SSTF) separated by a frontal zone, consistent with observations of the STF elsewhere. Comparison with a western CTD section along 176°E reveals that this structure breaks down close to the New Zealand landmass. The dominant impact of seasonally is the formation and decay of a seasonal thermocline of fairly constant depth over the entire region. Velocity measurements indicate eastward zonal flows on the northern and southern flanks of Chatham Rise. The flow over Chatham Rise is complicated by stirring processes but has a mean southward trend consistent with the less dense, warm, salty subtropical water (STW) overriding the more dense, cold, fresh subantarctic water (SAW) to the south. Horizontal‐length‐scale analyses of the temperature field for a constant depth tow at 21 m indicate a k−2.4 spectral falloff with no proof of preferential length scales. The temperature salinity gradients are largely density compensated in this mixed layer tow. The horizontal temperature standard deviation shows subsurface maxima concentrated at the locations of the NSTF and SSTF. Vertical length scales vary across the front, with large scales (80–100 m) in the STW north of the STF and smaller scales (20–40 m) in the subtropical frontal zone and SAW to the south. The surface vertical length scales are dominated by the presence of a seasonal thermocline.

Ocean Surface Winds off the West Coast of New Zealand: A Comparison of Ocean Buoy, ECMWF Model, and Land-Based Data

Abstract Wind data for the period July–October 1994 from an ocean buoy moored off the west coast of New Zealand have been compared with model wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and data from the nearest land-based station. The buoy and ECMWF winds were highly coherent and strongly polarized in the alongshore direction, suggesting that the ECMWF model correctly accounts for the orographic effect of the mountainous New Zealand landmass on the prevailing synoptic weather systems. At low frequencies, the ECMWF data can be used as a substitute for in situ wind data in oceanographic applications in the New Zealand region. This is a similar result to that reported in some Northern Hemisphere studies. In contrast, winds at the land-based site were much weaker and less strongly aligned alongshore than winds recorded offshore.

Seismic stratigraphy and structural history of the Reinga Basin and its margins, southern Norfolk Ridge system

The Reinga Basin northwest of the North Island of New Zealand was initially formed by crustal extension in Cretaceous time. Gravity models suggest up to 35—40% crustal thinning. The seismic stratigraphy of the basin is continuous with that of the offshore western North Island, where reflectors are well constrained by oil exploration data. In the Reinga Basin, there are two Cretaceous sequences above an older Mesozoic basement. The lower sequence is apparently terrestrial and may include both pre‐rift and syn‐rift subsequences; the upper is a rift‐filling marine sequence. These are overlain by Paleocene and Eocene blanket sequences that were laid down during a period of relative tectonic quiescence consistent with cooling subsidence, continued submergence, a northeast‐facing continental shelf, and absence of a significant active plate boundary. A strong regional reflector, caused by a combined unconformity and Oligocene condensed sequence, separates the Paleogene and Neogene sequences. The Neogene sequences record sedimentary infill from several source directions, not only from the New Zealand landmass, but from the north and west as well. Near the Northland coast, sediment accumulated in clastic wedges and ponded sub‐basins from the Miocene to the present day. Along the flanking ridges to the northwest, similar deposition occurred in the Early and Middle Miocene but changed in the Late Miocene to sedimentation in drifts flanked by scours. This change reflects the end of tectonism, a diminishing clastic sediment supply, and the establishment of a throughgoing oceanic current regime as the marginal ridges submerged. This pattern of sedimentation persists today. Post‐Cretaceous volcanism occurred in two parts of the basin. In the central southeastern part, volcanic bodies in the ?Oligocene to Early Miocene sequences could be a northwestern extension of the Northland volcanic arc. In the western part, small intrusive and extrusive bodies appear to be of Pliocene intraplate origin. Compression (or transpression) had an important role in developing the basin's present form. Miocene compressional structures—asymmetric anticlines, reverse faults, everted basins, and pop‐ups—are present everywhere but at the southeastern end. The present marginal ridges have structurally complex origins. The Reinga Ridge which forms the northeastern margin is a transform boundary with the Norfolk backarc basin. Deformation thought to be caused by the action of the transform is recorded in folded and faulted Cretaceous‐Paleogene sequences and syntectonic Early and Middle Miocene sequences along its length. The southwestern margin of the basin is a double ridge comprising the Wanganella Ridge, an early Middle to early Late Miocene, compressional uplift, and the older, eroded West Norfolk Ridge, which contains Cretaceous half‐grabens. The northern half of the Wanganella Ridge is an everted ?Oligocene to Early Miocene aulacogen in which slivers of basement rock were thrust up along with the sedimentary fill, whereas the southern half is an uplifted block of folded sedimentary rocks of probable Cretaceous or older age. Paleogeographic reconstructions show that Oligocene uplift of the Norfolk Ridge and Miocene uplift of the Reinga Ridge could have provided a means for terrestrial biota of New Caledonian affinities to spread into New Zealand. The total sediment thickness in the Reinga Basin is estimated to be 3.5–5.5 km. Potential source, seal and reservoir rocks are present, and there is an abundance of suitable structures. The potential for petroleum occurrences in the basin is good.

Provenance of the detrital component of deep-sea sediments from the SW Pacific Ocean based on mineralogy, geochemistry and Sr isotopic composition

Clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep-sea sediments from the SW Pacific Ocean. Continental detritus derived mainly from the New Zealand landmass is characterised by high illite and chlorite contents, and 87Sr/ 86Sr ratios close to 0.7110. This material, eroded from the eastern margin of both islands, is transported into deeper water by turbidity currents and hemipelagic processes, and is carried northwards by the strong Western Boundary Current as far north as the Samoan Basin. Due to the great distance from source and unfavourable prevailing winds, the contribution of aeolian dust from the Australian deserts to the sediment appears to be relatively small, particularly in the northernmost part of the region. In the vicinity of the oceanic volcanic islands of Tonga, Samoa and the Cook Islands, volcaniclastic material including heavy minerals (pyroxene and magnetite), pumice, glass shards (proximally) and smectite clays (distally) is dispersed into the sediments by turbidity currents and airfall. In areas of very low sedimentation distant from landmasses, the sediments contain significant amounts of authigenic material (RSOs) characterised by high concentrations of transition metals and rare earth elements. Strontium isotopes, together with trace element compositions, have proved particularly useful in determining the relative proportions of the detrital types. The contrasting 87Sr/ 86Sr ratios and Sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the Cook Islands contain 80% volcanic detritus, and those more than 1200 km away contain up to 20% volcanic detritus.

The nature of the lower North Island floristic gap

Abstract Patterns of regional endemism and disjunction of higher plants in the lower North Island are reviewed in relation to the plants' habitats. A redefinition of the lower North Island floristic gap emerges. A northern boundary in the southern central North Island uplands replaces the previous one at 39°S latitude. Southern boundaries occur either in Cook Strait or in southern Wellington-southern Wairarapa. Most endemic and disjunct species defining the gap occur in non-forest habitats. Previous explanations for these distribution patterns centre either on the disruptive effects of glacial ice and harsh climates of the Last Glaciation or on the tectonic modification of the New Zealand land mass since the Oligocene. It is suggested that regional discontinuities in the availability of non-forest habitats account for many disjunctions. Furthermore, patterns of endemism and disjunction most closely equate with the tectonic alteration of lower North Island. In particular, fault displacement of large land m...

Magnetic field fluctuations at the Eyrewell Observatory, Christchurch, New Zealand

Abstract Four months of magnetic records from the Eyrewell Observatory near Christchurch, New Zealand, have been digitised, and analysed to produce Parkinson response arrows. The magnitudes and azimuths of both the real and quadrature arrows are smooth functions of period. Real arrows at three particular periods are similar to arrows published previously for the earlier observatory at Amberley, some 43 km northeast of Eyrewell. Differences between the Eyrewell and Amberley arrows are consistent with effects due to the closer proximity of Amberley to the ocean, the different analysis techniques employed in the various studies, and possibly with some local geological effects. The magnitude of the real arrow at Eyrewell has a narrow peak at a period of about 1000s. At longer periods, the Eyrewell real response decreases sharply, a characteristic which is interpreted as being due to the limited width of the New Zealand landmass, and the balancing effect of the Tasman Sea on its western side. At intermediate p...