South Tasman Sea Research Articles

Observed Interhemispheric Meridional Heat Transports and the Role of the Indonesian Throughflow in the Pacific Ocean

Abstract The net surface energy flux is computed as a residual of the energy budget using top-of-atmosphere radiation combined with the divergence of the column-integrated atmospheric energy transports, and then used with the vertically integrated ocean heat content tendencies to compute the ocean meridional heat transports (MHTs). The mean annual cycles and 12-month running mean MHTs as a function of latitude are presented for 2000–16. Effects of the Indonesian Throughflow (ITF), associated with a net volume flow around Australia accompanied by a heat transport, are fully included. Because the ITF-related flow necessitates a return current northward in the Tasman Sea that relaxes during El Niño, the reduced ITF during El Niño may contribute to warming in the south Tasman Sea by allowing the East Australian Current to push farther south even as it gains volume from the tropical waters not flowing through the ITF. Although evident in 2015/16, when a major marine heat wave occurred, these effects can be overwhelmed by changes in the atmospheric circulation. Large interannual MHT variability in the Pacific is 4 times that of the Atlantic. Strong relationships reveal influences from the southern subtropics on ENSO for this period. At the equator, northward ocean MHT arises mainly in the Atlantic (0.75 PW), offset by the Pacific (−0.33 PW) and Indian Oceans (−0.20 PW) while the atmosphere transports energy southward (−0.35 PW). The net equatorial MHT southward (−0.18 PW) is enhanced by −0.1 PW that contributes to the greater warming of the southern (vs northern) oceans.

Attribution of Exceptional Mean Sea Level Pressure Anomalies South of Australia in August 2014

August 2014 saw very strong monthly positive mean sea level pressure (MSLP) anomalies and intense daily to multiday MSLP events south of Australia and in the Tasman Sea (Fig. 32.1a). To the west of Tasmania there were monthly anomalies of over 10 hPa (2.4 standard deviations from the mean), the highest on record since 1979 using ERA-Interim reanalysis (ERAint; Dee et al. 2011), or from 1850 using the Hadley Centre Sea Level Pressure analysis (HadSLP2r; Allan and Ansell 2006). Atmospheric blocking west of Tasmania on 10–15 August (Figs. 32.1b,c) featured the highest daily August MSLP anomaly in either record in that location. Blocking was seen in the south Tasman Sea later in the month, including the highest daily MSLP anomaly on record at that location. The spatial distribution of the monthly MSLP anomalies resembles a wave-3 pattern (Fig. 32.1a).

Reviewing the circulation and mixing of Antarctic Intermediate Water in the South Pacific using evidence from geochemical tracers and Argo float trajectories

Evidence from physical and geochemical tracers measured during the World Ocean Circulation Experiment (WOCE) shows that there are four sub-types of Antarctic Intermediate Water (AAIW) in the South Pacific. The main formation region of AAIW is the southeast Pacific, where fresh, cold, high oxygen, low nutrient, intermediate waters are created. This AAIW is transported north and mixes with Equatorial Pacific Intermediate Waters (EqPIW), themselves a combination of AAIW and nutrient rich, old North Pacific deep waters. ‘Tasman’ AAIW found in the Coral and Tasman Seas is more saline and warmer than the main subtropical gyre, and appears to have formed from mixing of AAIW with thermocline waters in the Tasman Gyre. Tasman AAIW leaks out of the Tasman basin to the north of New Zealand and along Chatham Rise, and also in the South Tasman Sea via the Tasman Leakage. Another source of relatively fresh, high oxygen, low nutrient, young AAIW comes directly from the Southern Ocean, flowing into the southwest and central South Pacific Basin, west of the East Pacific Rise. This ‘Southern Ocean’ (SO) AAIW is most likely a mixture of AAIW formed locally at the Subantarctic Front (SAF), and AAIW formed along the SAF in the southeast Pacific or Indian oceans and transported by the Antarctic Circumpolar Current (ACC). Interpreting physical and geochemical tracers, combined with velocity estimates from Argo floats, and previous research, has allowed us to refine the detailed circulation pattern of AAIW in the South Pacific, especially in the topographically complex southwest Pacific.

Sea surface temperature and subtropical front movement in the South Tasman Sea during the last 800 ka

Hemisphere mid-latitude westerlies contribute to the ventilation of the deep Southern Ocean (SO), and drive changes in atmospheric carbon dioxide (CO2) and the global climate. As the westerlies control directly oceanic fronts, the movement of the subtropical front (STF) reflects the westerlies migration. Thus it is important to understand the relationships between STF movement and the weaterlies, ventilation of the deep SO, ice volume and atmospheric CO2. To this end, we use two new high-resolution records from early Marine Isotope Stage (MIS) 20 (∼800 ka) of sea surface temperature (SST) based on U37k’ paleo-thermometer and benthic oxygen isotope (δ18OB) at Ocean Drilling Program (ODP) Site 1170B in the southern Tasman Sea (STS), to construct linkages between the marine records and atmospheric proxies from Antarctic ice-cores. During the last 800 ka, the average SST (10.2°C) at Site 1170B is 1.8°C lower than today (annual average 12°C). The highest average SST of 11.6°C occurred during MIS 1, and the lowest average SST of 7.8°C occurred during MIS 2. The warmest and coldest records of 14.7°C and 6.2°C occurred in the MIS 5 and MIS 2, respectively. In the glacial-interglacial cycles of the last 800 ka, variability of reconstructed SST shows that the STF moved northward or southward more than 3° of latitude compared with its present location. In the warmest stage MIS 5, the STF shifted to its southernmost location of ∼49°S. In contrast, in the coldest stage MIS 2, the STF moved to its northernmost location of ∼43°S. In response to orbital cycles, the westerlies movement led ice volume and atmospheric CO2 changes, but it was in phase with change in Antarctic atmospheric temperature. Ice volume only preceded atmospheric CO2 only a little at the 23-ka precession band, lagged the atmospheric CO2 at the 100-ka eccentricity band, and was in phase with atmospheric CO2 at the 40-ka obliquity band.

Foraging ecology of the Cook’s petrel Pterodroma cookii during the austral breeding season: a comparison of its two populations

This study examined divergence in the foraging distribution, at-sea behaviour and pro- visioning strategies of a small procellarid, the Cook's petrel Pterodroma cookii, during chick-rearing at 2 islands off New Zealand, separated latitudinally by ~1000 km. There was little overlap in forag- ing distribution between adults from Little Barrier Island (LBI), which ranged to the west into the Northern Tasman Sea and east into the Pacific Ocean, and conspecifics from Codfish Island (CDF), which foraged west of the South Island in the south Tasman Sea in association with the subtropical convergence zone. Although birds from CDF ranged further than those from LBI, there was no differ- ence in mean foraging trip duration. Cook's petrels from CDF foraged over deeper, cooler water, with higher primary productivity, than conspecifics from LBI. At-sea behaviour also differed: adults from LBI spent less time in flight, and showed less variation in total flight time per day. Overall, Cook's petrels spend much more time in flight than albatrosses, and approximately the same amounts of time on the water during the night as during the day, suggesting a high portion of nocturnal foraging. Dive depths did not differ between colonies but were greater than expected for a gadfly petrel. Stable isotope signatures of blood indicated population-specific diets, and suggested that birds from LBI primarily consume cephalopods and fish, whereas those from CDF eat more crustaceans. Chicks at CDF received more food. These results suggest a broad divergence in foraging strategies between geographically well-separated colonies in response to regional differences in oceanography.

Strong-wind events and their impact on the near-surface climate at Kohnen Station on the Antarctic Plateau

AbstractStrong-wind events occur 10–20 times per year at Kohnen Station, East Antarctica (75°00′S, 0°04′E, 2892 m above sea level), and are often caused by warm-core cyclones in the north-eastern Weddell Sea. An uncommon event occurred in January 2002, when blocking both in the south Atlantic Ocean and in the south Tasman Sea caused a split-up of the circumpolar vortex, and large amounts of heat and moisture were transported onto the Antarctic Plateau. During strong-wind events over the plateau the near-surface temperature can increase by tens of degrees, which is partly caused by the advection of heat, but for an important part by the destruction of the stable temperature-deficit layer by enhanced vertical mixing. The temperature rise is larger during the winter/night than during the summer/day, due to a better-developed temperature deficit. Snowdrift during the January 2002 event linearly increased surface roughness for momentum with friction velocity, for values over about 0.18 m s-1. The cloud cover during the event reduced down-welling solar radiation by 32%, and increased the albedo from about 0.86 to 0.92. Changes in longwave radiation largely cancelled the daytime changes in shortwave radiation, thus net radiation was most affected at night.

South Tasman Sea alkenone palaeothermometry over the last four glacial/interglacial cycles

Alkenone palaeothermometry has demonstrated a wide spatial and temporal applicability for the reconstruction of sea-surface temperatures (SST). Some oceanic realms, however, remain poorly studied. We document U 37 K' index data for two sediment cores retrieved from the South Tasman Sea, one west of New Zealand (SO136-GC3) and the other southeast of Tasmania (FR1/94-GC3), extending back 280 kyr BP for the former and 460 kyr BP for the latter. High climatic sensitivity on orbital time scales is observed at both locations, particularly west of New Zealand, where typical glacial/interglacial SST amplitudes always span more than 7 °C. Southeast of Tasmania, SST amplitudes are lower in amplitude (4.3 to 6.9 °C) with the exception of Termination IV, which involved a SST change over 8 °C. The evolution of maximum glacial cooling through time is different at each location. Offshore New Zealand, maximum cooling during glacial stages increases with time, whereas south of Tasmania maximum cooling decreases with time. In addition, our data suggest heterogeneity in the spatial expression of SST during the penultimate and last glacial stages. These glacial periods are recorded differently in both areas, with Marine Isotopic Stage 6 being warmer than Marine Isotopic Stage 2 west of New Zealand, but slightly colder southeast of Tasmania. The area southwest of New Zealand appears susceptible to expansions and contractions of the Western Pacific Warm Pool and/or meridional migrations and changes in intensity of currents associated with the Tasman Front. The region southeast of Tasmania seems more sensitive to thermal changes as seen at high southern latitudes.

Precipitation over the Interior East Antarctic Ice Sheet Related to Midlatitude Blocking-High Activity

Intermittent atmospheric blocking-high activity in the South Tasman Sea is shown to play a key role in delivering substantial snowfall as far south as at least 75°S on the central East Antarctic Ice Sheet plateau. Typically, cyclones fail to penetrate this far (>1000 km) inland, and accumulation was thought to be dominated by clear-sky precipitation. In East Antarctica, the meridional cloud bands delivering the moisture originate from as far north as 35°–40°S, and appear to preferentially pass over the East Antarctic coast in a corridor from ∼120° to 160°E. Comparison of surface observations, model, and satellite data suggests that a few such episodes contribute a significant proportion of the (low) mean annual accumulation of the central East Antarctic Ice Sheet (e.g., an estimated 44% at Dome C over 18 days in December 2001–January 2002). Blocking-high-related incursions also cause abrupt increases in the surface wind speed (snow redistribution) and air temperature; this has implications for the interpretation of ice core data. Blocking-high-related precipitation episodes can generally be detected over the ice sheet interior, via abrupt changes (of ∼0.02–0.04) in polarization in 37- and 85-GHz SSM/I data, due to the relative stability of the surface and its “background” microwave signature and the relative lack of cloud cover overall. This is not the case in high-accumulation near-coastal regions such as Law Dome, where additional information is required. Ambiguities remain due to blowing snow and hoarfrost formation. Further research is necessary to examine the frequency of occurrence and variability of midlatitude blocking-high systems, their effect on precipitation in the Antarctic Ice Sheet interior, and the potential effect of global change.

Pacific-Antarctic-Australia motion and the formation of the Macquarie Plate

Magnetic anomaly and fracture zone data on the Southeast Indian Ridge (SEIR) are analysed in order to constrain the kinematic history of the Macquarie Plate, the region of the Australian Plate roughly east of 145°E and south of 52°S. Finite rotations for Australia–Antarctic motion are determined for nine chrons (2Ay, 3Ay, 5o, 6o, 8o, 10o, 12o, 13o and 17o) using data limited to the region between 88°E and 139°E. These rotations are used to generate synthetic flowlines which are compared with the observed trends of the easternmost fracture zones on the SEIR. An analysis of the synthetic flowlines shows that the Macquarie Plate region has behaved as an independent rigid plate for roughly the last 6 Myr. Finite rotations for Macquarie–Antarctic motion are determined for chrons 2Ay and 3Ay. These rotations are summed with Australia–Antarctic rotations to determine Macquarie–Australia rotations. We find that the best-fit Macquarie–Australia rotation poles lie within the zone of diffuse intraplate seismicity in the South Tasman Sea separating the Macquarie Plate from the main part of the Australian Plate. Motion of the Macquarie Plate relative to the Pacific Plate for chrons 2Ay and 3Ay is determined by summing Macquarie–Antarctic and Antarctic–Pacific rotations. The Pacific–Macquarie rotations predict a smaller rate of convergence perpendicular to the Hjort Trench than the Pacific–Australia rotations. The onset of the deformation of the South Tasman Sea and the development of the Macquarie Plate appears to have been triggered by the subduction of young, buoyant oceanic crust near the Hjort Trench and coincided with a clockwise change in Pacific–Australia motion around 6 Ma. The revised Pacific–Australia rotations also have implications for the tectonics of the Alpine Fault Zone of New Zealand. We find that changes in relative displacement along the Alpine Fault have been small over the last 20 Myr. The average rate of convergence over the last 6 Myr is about 40 per cent smaller than in previous models.

Phonolitic Diatremes within the Dunedin Volcano, South Island, New Zealand

The Port Chalmers Breccia is a vent-filling, clastic volcanic unit exposed within the Miocene Dunedin Volcano of South Island, New Zealand. Clasts (up to in excess of 1 m but generally <20 cm) are supported in ash and fine lapilli of phonolitic (ne-benmoreite or tephro-phonolite) composition and the dominant clast type (55 to almost 100%) is also phonolitic. Less abundant lithologies include ne-normative basalt (basanite), hawaiite, mugearite and trachyandesite, syenites and microsyenites, coarse-grained mafic (gabbros) and ultramafic rocks (pyroxenites, hornblendites), schists and sediments. The breccias were emplaced as diatremes associated with localized, but highly explosive, eruptive events in which mantle-derived CO2 was an important component. The syenitic and ultramafic clasts could represent intrusive suites produced by crystal fractionation acting on parental ne-benmoreite magmas that may themselves have been derived by crystal fractionation from basanitic precursors. An alternative variation on this model is that the parental ne-benmoreites were generated through partial melting of an alkalic igneous underplate. Sr, Nd and Pb isotopic compositions are strikingly similar to those of intraplate igneous rocks, ranging in age from 100 to less than 10 Ma, from elsewhere in the South Island, and New Zealand's sub-Antarctic islands, the south Tasman Sea and the Ross Sea region. This regional, HIMU-influenced, isotopic signature is believed to be derived from within the lithospheric mantle.

Cenozoic motion between East and West Antarctica

The West Antarctic rift system is the result of late Mesozoic and Cenozoic extension between East and West Antarctica, and represents one of the largest active continental rift systems on Earth. But the timing and magnitude of the plate motions leading to the development of this rift system remain poorly known, because of a lack of magnetic anomaly and fracture zone constraints on seafloor spreading. Here we report on magnetic data, gravity data and swath bathymetry collected in several areas of the south Tasman Sea and northern Ross Sea. These results enable us to calculate mid-Cenozoic rotation parameters for East and West Antarctica. These rotations show that there was roughly 180 km of separation in the western Ross Sea embayment in Eocene and Oligocene time. This episode of extension provides a tectonic setting for several significant Cenozoic tectonic events in the Ross Sea embayment including the uplift of the Transantarctic Mountains and the deposition of large thicknesses of Oligocene sediments. Inclusion of this East-West Antarctic motion in the plate circuit linking the Australia, Antarctic and Pacific plates removes a puzzling gap between the Lord Howe rise and Campbell plateau found in previous early Tertiary reconstructions of the New Zealand region. Determination of this East-West Antarctic motion also resolves a long standing controversy regarding the contribution of deformation in this region to the global plate circuit linking the Pacific to the rest of the world.

Distribution of Jasus spp. (Decapoda:Palinuridae) phyllosomas in southern waters:implications for larval recruitment

We sampled the distribution of mid- and late-stage (= advanced) Jasus group 'lalandii' rock lobster phyllosomas at 28 approximately equidistant stations across similar to 16 000 km of ocean between the west coast of Africa and the west coast of New Zealand to determine whether the larvae were mostly associated with the patchy allopatric distribution of the adults or were widespread. The Jasus phyllosomas (n = 210) occurred in greatest abundance in the general vicinity of adults. Nucleotide-sequencing and restriction-fragment length polymorphism (RFLP) techniques were used to identify 93 of these larvae from 18 stations to species level. Most of the larvae caught were J. lalandii and J, edwardsii, and a few were probably J. paulensis. Most of these larvae were taken near (within a few hundred kilometres) their respective adult habitat off southern Africa, Australia and New Zealand, and Amsterdam Island. The exceptions were small numbers of J. lalandii larvae in the southwest Indian Ocean as far east as Amsterdam Island, adjacent to the J. paulensis habitat, and J. edwardsii larvae across the south Tasman Sea. A single larva off southwest Africa could not be identified to any known Jasus species and may indicate the presence in the genus of an as yet undiscovered species or subspecies. No J. caveorum, J. frontalis, or J. verreauxi (and probably no J. tristani) were found. Our results suggest that Jasus spp. larvae which subsequently recruit to benthic populations use behavioural strategies and/or physical mechanisms to avoid being carried too far away from their parental ground. However, a proportion of larvae, small yet possibly not insignificant, occurs great distances from where adults of the species are known. These larvae are unlikely to recruit to benthic populations, but their occurrence invites further consideration of how Jasus spp. maintain allopatric populations.

Carbon monoxide measurements from 76° N to 59° S and over the South Tasman Sea

In November and December of 1995, carbon monoxide (CO) measurements were made in a Pacific transect and over the South Tasman Sea as part of the First Aerosol Characterization Experiment (ACE 1) program. Airborne CO measurements were made from 76° N to 59° S. A clear latitudinal gradient in CO concentrations was measured, with the southern hemisphere average about 80 parts per billion by volume (ppbv), and increasing to 120–130 ppbv at the most northern latitudes. Plumes of CO with a 30–40 ppbv concentration increase over the general background concentrations could be seen at several latitudes. The National Oceanic and Atmospheric Administration R/V Discoverer made CO measurements over the South Tasman Sea from November 15 to December 9, 1995. A systematic decrease of 0.31 ppbv/d CO was observed. Vertical profile measurements of CO from near the ocean surface to 2500 m altitude during the Lagrangian B intensive of ACE 1 suggested the mixing of stratospheric air with reduced CO concentrations.

LATE PLEISTOCENE MARINE CHRONOLOGY OF THE GIPPSLAND LAKES REGION, AUSTRALIA

Thermoluminescence dating is used to define the chronology of the coastal barriers of the Gippsland Lakes region, Australia. The area evidences a long history of marine deposition extending back to the Middle Pleistocene. However, the majority of Pleistocene barriers have formed since the Last Interglacial during two phases at 59 to 72 ka and 40 to 48 ka corresponding to interstadials. A third phase, with dates around the Last Glacial, appears to represent rapid shoreward movement of Late Pleistocene sediment from the shelf during the Holocene. Barriers have developed in an en echelon fashion seaward as the region has been uplifted tectonically. Some Late Pleistocene marine deposits reach elevations of 40 m above present sea level. These elevations imply rates of tectonic uplift exceeding 80 mm per thousand years, rates that may have increased toward the present. Deposits are preserved as isolated remnants because of subsequent fluvial and marine erosion. Both erosion and rebuilding may have occurred under the influence of tsunami originating from the south Tasman Sea. The unique distribution and preservation of recurrent interstadial barriers in the Gippsland Lakes region reflect rapid uplift, abundant sand supplies, and the proximity of this coast to sources for tsunami. [Key words: Gippsland Lakes, coastal barriers, chronology, thermoluminescence dating, Late Pleistocene, tsunami.]

Catastrophic wave (tsunami?) transport of boulders in southern New South Wales, Australia

Deposits of large boulders above modern limits of storm waves along the coast of southern New South Wales record catastrophic wave action. The largest boulders that were moved weigh 80-90 tonnes, and the maximum height of wave action was 32 m. Hydraulic reconstruction indicates flow depths of 3.4 and perhaps > 4 m and velocities of 5.5 m/s to 10.3 m/s. Cavitation features on some rock surfaces support the estimates of maximum velocities. A remarkably limited range in the orientation of imbricated boulders along 150 km indicates that the deposits record a single event that approached from the SE. to SSE. The fabric and size of the deposits point to a tsunami wave train rather than to exceptional storm waves. The most probable source of the wave train is the Macquarie Ridge in the south Tasman Sea. An earliest Holocene age for the event is indicated by a thermoluminescence determination of 9.5ka from sand associated with one boulder deposit, and by the transport of some boulders from below present sea level.

An analysis of Australian seasonal rainfall anomalies: 1950–1987. II: Temporal variability and teleconnection patterns

AbstractA detailed examination of the variability of Australian district rainfall of seasonal time‐scales over the period 1950–1987 is described. In Part I, S‐ and T‐mode rotated principal component analysis (RPCA) was used to obtain a compressed representation of Australian district rainfall anomalies on seasonal time‐scales.In this paper, the temporal variability of these spatial patterns is examined, and their relationship to some large‐scale circulation indices, such as the Southern Oscillation (SO) and Pittock's L index. The S‐mode components show large intercomponent correlations as a result of the rotation of the principal components, although much of this is due to a common relationship to the SO. The T‐mode components are less strongly interrelated and only the first two show large correlations with the SO. The relationship with the SO and the L index are consistent with previous studies. Spectral analysis shows that most components do not have any dominant periodicity. Two distinct biennial tendencies are identified; in the north‐east associated with the SO, and in the south‐east associated with the L index.The large‐scale circulation anomalies associated with both the S‐ and T‐mode patterns are examined using the Comprehensive Ocean Atmosphere Data Set (COADS) and a network of rawindsonde stations over Australia and the South‐west Pacific. Three dominant teleconnection patterns are identified; the well‐known Southern Oscillation anomalies associated with the dominant T1 pattern of continental‐scale rainfall anomalies, a predominantly winter season Indonesian‐Indian Ocean pattern previously documented by Nicholls, and a spring/summer south Tasman Sea pattern. The evolution of these patterns is examined through composites, and the physical mechanisms for the initiation and maintenance of the anomaly patterns are discussed. In the latter two cases both the rainfall and SST anomalies appear to be driven by anomalies in the large‐scale mid‐latitude circulation.

Systematic status of the rock lobstersJasus edwardsiifrom New Zealand andJ. novaehollandiaefrom Australia

Abstract Rock lobsters of Jasus subgroup lalandif in New Zealand (Jasus edwardsii (Hutton, 1875)) and south‐eastern Australia (J. novaehollandiae Holthuis, 1963) are biologically similar and gene flow is possible. The variation between Australian populations, and overlap with the New Zealand population, in morphology, colour, and biochemical genetics, and the agreement in life‐history characters, make it impossible to distinguish animals from the two countries. The New Zealand and Australian populations of rock lobster should therefore be referred to as a single species, which by priority is J. edwardsii. The long‐lived phyllosoma larval stage is widespread in the central and south Tasman Sea. Rates of any larval recruitment in New Zealand from animals spawned in Australia are likely to be variable because of variability in flow in the Tasman Sea, and because of the distance involved.

Geographical distribution of living planktonic foraminifera (Protozoa) off the east coast of Australia.

Major water masses found off eastern Australia can be identified by their planktonic foraminiferal faunas. A total of 83 surface and oblique plankton samples from two cruises, in spring (October) and summer (January), between Hobart at 44� S. and Townsville at 18� S. yielded 27 species belonging to four distinct faunas: 'tropical', 'warm subtropical', 'cool subtropical' and 'transitional'. The tropical fauna is characterized by Globigerinoides sacculifer at an abundance greater than 42% and the co- dominance of Globigerinoides conglobatus, and is associated with Coral Sea water of equatorial origin. The subtropical fauna can be subdivided into warm and cool elements. The warm-subtropical fauna, with G. sacculifer more abundant than Globigerinoides ruber, inhabits Coral and Tasman Sea waters. The cool-subtropical fauna is a mixture of the warm subtropical and the transitional faunas. The transitional fauna is dominated by Globorotalia inflata and Globigerina bulloides in the south Tasman Sea subantarctic waters. It characterizes the South West Tasman water as defined by Rochford (1957). These water masses can be clearly separated, and the extent of mixing determined by their foraminiferal fauna. The shifts in the boundaries between the faunal zones was evident between spring and summer. The boundary between the tropical and subtropical water corresponds to the tropical convergence and the subtropical/transitional boundary is the Tasman Front. During the spring cruise, a warm core eddy was identified by its warm subtropical foraminiferal fauna surrounded by a transitional fauna to the south and cool subtropical fauna to the north. This water body was near 32� S., which is consistent with the reported positions of eddies shed by the East Australian Current. The distribution patterns of individual species are discussed.

Late Cretaceous-Cenozoic tectonic development of the southwest pacific region

A new model of the plate tectonic development of the southwest Pacific integrates the continental geology of New Zealand with the age structure of the surrounding oceanic crust revealed previously from magnetic anomaly lineations. The model differs from previous ones in that the onland geology of New Zealand is used to constrain the tectonic development in two important ways: (1) the modern Australia-Pacific plate boundary did not transect the New Zealand sector until 23 million years ago; (2) there has been a total of only c.500 km of dextral displacement on the plate boundary through New Zealand. The model is described with reference to a series of paleotectonic maps drawn to represent the setting at the times of anomalies 32, 24, 7 and 5. Novel interpretations based on these reconstructions include the following. During the late Cretaceous the Campbell Fault was a continental transform fault between the Tasman Sea spreading centre and the Bounty Rift, its 330 km of dextral displacement accompanying 25° of counterclockwise rotation of a Campbell Plateau block. When the eastward-propagating Southeast Indian Ridge broke into the south Tasman Sea 57 million years ago, it continued to propagate directly into southern South Island, and generated late Eocene-Oligocene continental rifting through western New Zealand. At the same time, back-arc spreading in the Norfolk Basin caused continental rifting along a similar trend in western North Island. The Australia-Pacific plate boundary originated as a transform fault between the Southeast Indian Ridge and the pre-existing Kermadec Trench. It developed in response to the sudden cessation of spreading on the segment of the Southeast Indian Ridge east of a fracture zone here named Fracture Zone Z. Two implications arise from this model regarding the integrity of Antarctica: 1. (1) during the Cretaceous, Marie Byrd Land was probably no more than 200 km northwest of its present position; 2. (2) the proposition made in some earlier plate tectonic reconstructions, that if the Alpine Fault did not form until after the late Eocene there must be a late Cretaceous-early Tertiary plate boundary within Antarctica, is most probably valid.

Arachnodinium, anew dinoflagellate genus from the lower tertiary of Antarctica

Abstract Arachnodinium antarcticum gen. et sp. nov., a distinctive trabeculate dinoflagellate cyst, is described from erratics of probable Eocene Age in the McMurdo Sound area. Additional records of the taxon are provided from Lower Tertiary localities in South America, from DSDP sites in the south Tasman Sea, and from other Antarctic localities.