Tasman Sea Research Articles

Possible windborne transmission of giant willow aphid Tuberolachnus salignus (Gmelin) (Hemiptera: Aphididae: Lachninae) westward from New Zealand to Australia

ABSTRACTThe first records of Tuberolachnus salignus (Gmelin), the giant willow aphid, were reported from New Zealand and Australia in December 2013 and March 2014 respectively. The host plants are various members of Salix and Populus. The pathway used by the aphid to enter Australasia remains unknown, but natural aerial dispersal across the Tasman Sea is proposed to explain its first appearance within 3 months in Australia and New Zealand. Previous examples of aphids crossing the Tasman Sea are summarised. Windborne transmission due to the predominantly westerly winds from Australia to New Zealand is more likely based on past experience. However, we demonstrate using the HYSPLIT air trajectory model that it is possible that the aphid was carried on a reverse trajectory from New Zealand to southern Tasmania. Without more regular and systematic surveillance of New Zealand and Australian insect biota, it will continue to be difficult to ascertain the timing, origin and dispersal pathways of introduced insects.

Genetic variation and phylogeography of the Australian and New Zealand fern Asplenium flabellifolium (Aspleniaceae)

Asplenium flabellifolium Cav. is a cytologically variable Australian and New Zealand fern. Here, we sequence chloroplast trnL-trnF and rps4-trnS from samples throughout its range to provide the first phylogeographic investigation of a fern common in both countries. Twenty-three haplotypes were detected, which formed six haplogroups in a network. Australian specimens were placed in all haplogroups. The placement of New Zealand haplotypes in five of the haplogroups suggests that this species has dispersed across the Tasman Sea at least five times. Sexually reproducing plants of lower ploidy, detected only in south-eastern Australia, contained haplotypes from the two haplogroups that are successive sisters to the remaining diversity in the phylogeny. This likely suggests that A. flabellifolium was originally a sexually reproducing species in south-eastern Australia and spread to the rest of its distribution where apomictic plants dominate. More than one haplogroup was detected in several areas across its distribution, suggesting that these areas were colonised several times. Other areas harboured several haplotypes from a single haplogroup or haplogroups not recovered elsewhere, indicating possible long-term persistence in these areas. Haplotypes and morphological features were not found to be exclusive to either breeding system or ploidy and no taxonomic revision is proposed.

Comparison of Wind Speed and Wave Height Trends from Twentieth-Century Models and Satellite Altimeters

AbstractThe trends in marine 10-m wind speed U10 and significant wave height Hs found in two century-long reanalyses are compared against a model-only integration. Reanalyses show spurious trends due to the assimilation of an increasing number of observations over time. The comparisons between model and reanalyses show that the areas where the discrepancies in U10 and Hs trends are greatest are also the areas where there is a marked increase in assimilated observations. Large differences in the yearly averages call into question the quality of the observations assimilated by the reanalyses, resulting in unreliable U10 and Hs trends before the 1950s. Four main regions of the world’s oceans are identified where the trends between model and reanalyses deviate strongly. These are the North Atlantic, the North Pacific, the Tasman Sea, and the western South Atlantic. The trends at +24-h lead time are markedly weaker and less correlated with the observation count. A 1985–2010 comparison with an extensive dataset of calibrated satellite altimeters shows contrasting results in Hs trends but similar U10 spatial trend distributions, with general agreement between model, reanalyses, and satellite altimeters on a broad increase in wind speed over the Southern Hemisphere.

Observational Insight Into the Subsurface Anomalies of Marine Heatwaves

Marine heatwaves (MHWs) are extreme ocean warming events that can have devastating impacts, from biological mortalities to irreversible redistributions within the ocean ecosystem. MHWs are an added concern because they are expected to increase in frequency and duration. To date, our understanding of these extreme ocean temperature events is mainly limited to the surface layers, despite some of the consequences they are known to have on the deep marine environment. In this paper, using data from sea surface temperature (SST) and in situ observations from Argo floats, we investigate the anomalous water characteristics during MHWs down to 2000 m in the western Tasman Sea which is located off the east coast of Australia. Focusing on their vertical extensions, characteristics and potential drivers, we break MHWs down into three categories (1) shallow [0 – 150 m], (2) intermediate [150 – 800 m], and (3) deep events [> 800 m]. Only shallow events show a relationship between surface temperature anomalies and depth extent, in agreement with a likely surface origin in response to anomalous air-sea fluxes. By contrast, deep events have greater and deeper maximum temperature anomalies than their surface signal (mean of almost 3.4oC at 165 m depth) and are more frequent than expected (>45%), dominating MHWs in winter. They predominantly occur within warm core eddies, which are deep mesoscale anticyclonic structures carrying warm water-mass from the East Australian Current. This study highlights the importance of MHWs down to 2000 m and the influence of oceanographic circulation on their characteristics. Consequently, we recommend a complementary analysis of sea level anomalies and SST be conducted to improve the prediction of MHW characteristics and impacts, both physical and biological.

Post Gondwana breakup evolution of the SE Australia rifted margin revisited

AbstractLow‐temperature thermochronology (LTT) is commonly used to investigate onshore records of continental rifting and geomorphic evolution of passive continental margins. The SE Australian passive margin, like many others, has an elevated plateau separated from the coastal plain by an erosional escarpment, presumed to originate through Cretaceous rifting prior to Tasman Sea seafloor spreading. Previous LTT studies have focused on reconciling thermal histories with development of the present‐day topography. New apatite LTT data along an escarpment‐to‐coast transect define a classic “boomerang” (mean track length vs. fission‐track age), indicating variable overprinting of late‐Palaeozoic cooling ages by a younger, mid‐Cretaceous cooling event. Regionally, however, the boomerang trend diverges NNW away from the coast and crosses the escarpment, implying the underlying thermal history pre‐dates escarpment formation and is largely independent from post‐breakup landscape evolution. We suggest that Cretaceous cooling might relate to erosion of Permo‐Triassic sedimentary cover from a formerly more extensive Sydney Basin.

Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave

The waters east of Tasmania, Australia, are warming at a rate 3–4 times the global average, largely as a result of the increasing duration and frequency of the southward penetration of the East Australia Current (EAC). In 2015/16, the southward movement of this sub-tropical current caused a severe marine heatwave (MHW) event. The effects of this event on the abundance and structure of the zooplankton community of south-east Tasmania are examined between November 2015 and January 2018. Generalized additive models indicated temperature to be significantly correlated with total zooplankton abundance (R2 = 0.6, p < 0.001). When modelled separately, species groups that are highly associated with the EAC, including bryozoan larvae (R2 = 0.2), echinoderm larvae (R2 = 0.6) and gelatinous zooplankton such as thaliaceans (R2 = 0.3), exhibited significant positive relationship with temperature (p < 0.001). The most abundant groups in samples; copepods (R2 = 0.6), appendicularians (R2 = 0.5) and cladocerans (R2 = 0.2), all exhibited negative relationships (p < 0.001; p < 0.001; p < 0.01, respectively). The abundances of cold-water and warm-water species of copepods were also analysed in relation to temperature. Sub-tropical species which are indicative of the East Australia Current, such as copepods from the Family Corycaeidae, and the calanoids Temora turbinata and Acartia danae, were present when temperatures exceeded ~17 °C, with a concurrent drop in the abundance of cold-water species. The east-coast of Tasmania is a region of rapid oceanographic change, and we have linked these changes with shifts in zooplankton population structure. Long-term studies from other regions that have also experienced marine heatwaves indicate these changes may have cascading implications for higher trophic levels. Gelatinous zooplankton and other zooplankton taxa not previously observed have now been documented in local predator diets. During warm periods, these species may represent an important alternative energy pathway.

Dissolved inorganic Radiocarbon content of the Western Coral sea: Implications for Intermediate and Deep Water Circulation

ABSTRACTThe South Pacific Ocean contributes to the global carbon cycle by exchanging CO2 between the atmosphere and intermediate to deep water masses. The path of the Antarctic Intermediate Water (AAIW) in the South Pacific gyre has been inferred from salinity, oxygen, and nutrient measurements, but radiocarbon (14C) measurements—a direct tracer of the carbon cycle—remain sparse. Here, we present the first radiocarbon profiles in the western Coral Sea and compare our measurements with South Pacific stations from GLODAPv2, a database of ocean hydrochemistry. Surface and subsurface waters in the Coral Sea cannot be attributed to a single source based on their Δ14C signatures, and we observe a penetration of bomb-produced 14C. AAIW in the western Coral Sea shows Δ14C values comparable to those in the South Pacific gyre, consistent with circulation of AAIW in the lower part of the southern equatorial current. The deep waters of the western Coral Sea have significantly higher 14C than the South Pacific at the same isopycnal, consistent with a northward intrusion of Circumpolar Deep Water from the Tasman Sea, along with a westward influx of deep waters from the Central Pacific. In accordance with silicate concentrations published previously, this shows the dual origin of deep waters in the Coral Sea.

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.

Dynamic variability of the phytoplankton electron requirement for carbon fixation in eastern Australian waters

Fast Repetition Rate fluorometry (FRRf) generates high-resolution measures of phytoplankton primary productivity as electron transport rates (ETRs). How ETRs scale to corresponding inorganic carbon (C) uptake rates (the so-called electron requirement for carbon fixation, e,C), inherently describes the extent and effectiveness with which absorbed light energy drives C-fixation. However, it remains unclear whether and how e,C follows predictable patterns for oceanographic datasets spanning physically dynamic, and complex, environmental gradients. We utilise a unique high-throughput approach, coupling ETRs and 14C-incubations to produce a semi-continuous dataset of e,C (n = 80), predominantly from surface waters, along the Australian coast (Brisbane to the Tasman Sea), including the East Australian Current (EAC). Environmental conditions along this transect could be generally grouped into cooler, more nutrient-rich waters dominated by larger size-fractionated Chl-a (>10 um) versus warmer nutrient-poorer waters dominated by smaller size-fractionated Chl-a (< 2 um). Whilst e,C was higher for warmer water samples, environmental conditions alone explained less than 20% variance of e,C, and changes in predominant size-fraction(s) distributions of Chl-a (biomass) failed to explain variance of e,C. Instead, NPQNSV was a better predictor of e,C, explaining 55% of observed variability. NPQNSV is a physiological descriptor that accounts for changes in both long-term driven acclimation in non-radiative decay, and quasi-instantaneous PSII downregulation, and thus may prove a useful predictor of e,C across physically-dynamic regimes, provided the slope describing their relationship is predictable.

Evidence of a common source component for east Australian Cenozoic mafic magmatism

Eastern Australia includes Cenozoic mafic volcanic provinces that are commonly divided into age-progressive and non-age-progressive groups. The former group is typically ascribed to the Cenozoic northward motion of Australia over fixed thermal anomalies in the mantle (i.e., “hotspots”), while the latter group is traditionally attributed to the opening of the Tasman and Coral Seas, though more recent interpretations have linked its formation to edge-driven convection or other processes. However, the initial criteria used to define the groups based on morphological and lithological features are neither robust nor consistently able to be applied to individual provinces. Despite their importance in the Cenozoic tectonic history of eastern Australia and, more broadly, the SW Pacific, geochemical distinctions between the two groups have been underexplored. Based on examination of an extensive database of new and previous major element, trace element, and radiogenic isotope data and principal component analysisfrom key volcanic exposures in Queensland and New South Wales, we find no systematic geochemical differences between the two groups. Both age-progressive and non-age-progressive Cenozoic mafic volcanic rocks in eastern Australia have an EM1-like source signature that could have originated in the asthenosphere and interacted with SCLM upon ascent. Our work underpins the necessity of understanding the magma generation mechanisms and the geodynamic context of individual volcanoes across eastern Australia.

Dust Storm Event of February 2019 in Central and East Coast of Australia and Evidence of Long-Range Transport to New Zealand and Antarctica

Between 11 and 15 February 2019, a dust storm originating in Central Australia with persistent westerly and south westerly winds caused high particle concentrations at many sites in the state of New South Wales (NSW); both inland and along the coast. The dust continued to be transported to New Zealand and to Antarctica in the south east. This study uses observed data and the WRF-Chem Weather Research Forecast model based on GOCART-AFWA (Goddard Chemistry Aerosol Radiation and Transport–Air Force and Weather Agency) dust scheme and GOCART aerosol and gas-phase MOZART (Model for Ozone And Related chemical Tracers) chemistry model to study the long-range transport of aerosols for the period 11 to 15 February 2019 across eastern Australia and onto New Zealand and Antarctica. Wildfires also happened in northern NSW at the same time, and their emissions are taken into account in the WRF-Chem model by using the Fire Inventory from NCAR (FINN) as the emission input. Modelling results using the WRF-Chem model show that for the Canterbury region of the South Island of New Zealand, peak concentration of PM10 (and PM2.5) as measured on 14 February 2019 at 05:00 UTC at the monitoring stations of Geraldine, Ashburton, Timaru and Woolston (Christchurch), and about 2 h later at Rangiora and Kaiapoi, correspond to the prediction of high PM10 due to the intrusion of dust to ground level from the transported dust layer above. The Aerosol Optical Depth (AOD) observation data from MODIS 3 km Terra/Aqua and CALIOP LiDAR measurements on board CALIPSO (Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations) satellite also indicate that high-altitude dust ranging from 2 km to 6 km, originating from this dust storm event in Australia, was located above Antarctica. This study suggests that the present dust storms in Australia can transport dust from sources in Central Australia to the Tasman sea, New Zealand and Antarctica.

The squat lobster genus Phylladiorhynchus Baba, 1969 in New Zealand and eastern Australia, with description of six new species.

The small galatheid squat lobster genus Phylladiorhynchus currently contains five species, three of which supposedly have wide Indo-Pacific distributions. To date, two putatively widespread species, P. pusillus and P. integrirostris have been recorded from New Zealand and Australian waters. Here, we review the New Zealand and eastern Australian species of Phylladiorhynchus based on extensive collections from the region using morphological and molecular data. The type species, P. pusillus (Henderson, 1885) (type locality: Twofold Bay, Australia) is redescribed and shown to occur on both sides of the Tasman Sea. Phylladiorhynchus integrirostris, for which the original Hawaiian type material has been lost, is redescribed based on a neotype and shown not to occur in New Zealand or Australian waters, previous records being referable to other species. Six new species of Phylladiorhynchus are described. Seven species of Phylladiorhynchus are now known from New Zealand and eastern Australia. A key to all species of the genus is provided. Results of the present study show that the regional diversity of Phylladiorhynchus is significantly higher than previously reported and demonstrates the utility of a number of subtle morphological characters as diagnostic of species.

Navigating the southern seas with small fins: Genetic connectivity of seahorses (Hippocampus abdominalis) across the Tasman Sea

AbstractAimHistorical patterns of ocean circulation in the Southern Hemisphere have been well‐studied, but the effects of coastal oceanography on marine biogeography in this region remain poorly understood relative to northern latitudes. Our study investigates historical and contemporary patterns of migration and dispersal across the Tasman Sea.LocationCoastal regions of the Tasman Sea including southeastern Australia, Tasmania and New Zealand.TaxonHippocampus abdominalis, the pot‐bellied seahorse, one of the most broadly distributed seahorse species, and the only seahorse to have successfully colonized New Zealand from Australia across 2,000 km of open ocean.MethodsWe used a multilocus genetic dataset to measure population diversity and differentiation from seahorses across the full species range to investigate contemporary and historical demography, and to reconstruct colonization routes across the Tasman Sea.ResultsGenetic data indicate that seahorses colonized New Zealand from Australia during the previous interglacial‐glacial cycle (12,000–120,000 ybp), and have evolved in relative isolation since the initial establishment event. Contemporary effective population sizes in the newly colonized range are substantially larger than those inferred in Australia, and both appear to be reduced relative to ancestral levels. Australian seahorses are genetically diverse and show high levels of population connectivity, while the distribution of genetic variation in New Zealand suggests an initial colonization of the South Island following by northward migration. Importantly, despite clear evidence that New Zealand seahorses are descendent from Australian ancestors, patterns of contemporary genetic diversity are consistent with trans‐Tasman migration from New Zealand to Australia, suggesting that genetic variation accumulated in the newly colonized range may be contributing to the genetic diversity of Australian seahorses.Main conclusionsDespite a largely independent evolutionary trajectory of seahorses separated by the Tasman Sea, haplotype sharing between populations in Australia and New Zealand suggests that secondary genetic exchange is contributing to the contemporary phylogeography of the species. Patterns of genetic structure in H. abdominalis mirror those found in other rafting species, suggesting that adult dispersal via rafting has been an important vector of marine dispersal in this species.

Airborne dust traffic from Australia in modern and Late Quaternary times

Abstract A review is provided of first-documented occurrences of dust transport within Australia for the last century, but which later on were considerably improved as a result of access to satellite observations and extensive ground observations. This was followed by the use of the HYSPLIT tracking models that enabled people to determine the major sources of dust in Australia. As a result of several important studies, the Lake Eyre Basin in central Australia is now considered to be the main source of dust entrainment, although other regions do contribute to dust production. This is followed by examination of the occurrence over the last few decades of dust transport and deposition within Australia and across the Tasman Sea, with dust being deposited even as far as New Zealand. After that, consideration is given to the deposition of dust not only at sea around Australia but also in New Zealand during the Holocene and Late Quaternary. As a consequence of these observations, a shift in the direction of dust plumes exiting Australia is noted. For example, during the Last Glacial Maximum (LGM), a substantial northerly shift of the Trans-Tasman dust plume is recorded and this coincides with stronger westerlies and an equatorward shift of oceanic fronts such as the Intertropical Convergence and Subpolar and Antarctic Fronts that were located closer to Australia compared to today. Strengthening of the winds during the LGM may have prevented dust plumes from travelling over the southern part of the Tasman Sea, even perhaps reaching Antarctica. Examination of the dust components in cores in the western Pacific Ocean would address this question. The second part of the paper examines the geochemical fingerprints of dusts from Australia, South America and those recovered from Antarctic ice cores. Examination of atmospheric conditions that prevailed in the Southern Ocean around Antarctica during a major dust storm event that occurred in Australia in October 2002 helps identify how dust can be entrained around cold fronts and eventually reach the Antarctic mainland. Once again, it appears that Australian dust did travel as far as Antarctica more frequently during the Holocene, than prior to that time. New Zealand as a dust source to some Antarctic sites is also discussed. Examination of the isotopic fingerprints in Antarctic ice cores point to South America being the main source of dust during the Last Glacial Maximum and previous glacial periods, with intermittent occurrences likely to have come from Australia and New Zealand as well. It is postulated that Australian dust plumes did travel mostly over the Tasman Sea, and eventually over the western Pacific Ocean during the LGM, and frequently less so towards Tasmania and the Southern Ocean as a result of the strengthening of the westerlies and their northward shift. It transpires that the dust flux from Australia was much higher during the glacial periods. It appears also that the dust plumes that traverse the eastern Indian Ocean remained unchanged during the LGM. Finally, this paper concludes by identifying that there is a need to either obtain larger dust samples from ice cores, or use more elaborate analytical techniques to combine more than two isotopes to fingerprint the origin of dusts recovered in ice cores. Perhaps a combination of not only isotopes, but also rare earth elements and major elements would eventually provide a better definition of atmospheric circulation in the Southern Hemisphere for comparison between glacial and interglacial periods.

Tandem host‐parasite dispersal inferred from similarities in phylogeographical patterns among Little Penguins and their ‘terrestrial’ ectoparasites

AbstractAimOrganisms with poor intrinsic dispersal capacity, such as parasites, often rely entirely on transport with host species that have a greater dispersal capacity. Penguins, for example, are exploited by terrestrial ectoparasites when they come ashore to breed. Recent research indicates that Little Penguin (Eudyptula minor and E. novaehollandiae) hard ticks (Ixodes eudyptidis and I. kohlsi) may be capable of surviving short periods (days) at sea with their hosts, but their capacity to survive longer voyages (weeks) is not known. We here aimed to assess whether phylogeographical patterns in Little Penguins and their ticks indicate that the terrestrial ectoparasites are able to disperse long distances at sea with their swimming hosts.LocationSouthern Australia and New Zealand.TaxonIxodes eudyptidis and I. kohlsi ticks.MethodsWe conducted a broad‐scale genomic assessment of Little Penguin ticks from across their hosts’ ranges in Australia and New Zealand. Using genotyping by sequencing, we generated SNP data sets from ticks from 14 penguin colonies, and analysed phylogeographical structure. We included ticks from some sympatric flighted seabirds to verify host specificity.ResultsWe resolved two distinct lineages of Ixodes from Little Penguins, with one restricted to Australia, and the other found throughout New Zealand and in low numbers at some eastern Australian sites. Both lineages exhibited phylogeographical structure consistent with patterns observed in their hosts, with some evidence of occasional oceanic dispersal, including across the Tasman Sea between Australia and New Zealand. Ticks from sympatric short‐tailed shearwaters (Ardenna tenuirostris), which disperse aerially, were genetically distinct from those collected from Little Penguins, supporting prior evidence of host specificity in seabird ticks.Main conclusionsThe most parsimonious explanation for our results is that ticks can travel at sea with Little Penguins. We infer that some terrestrial ectoparasites associated with aquatically dispersing hosts have evolved the capacity to survive oceanic voyages.

Forecasting the extreme rainfall, low temperatures, and strong winds associated with the northern Queensland floods of February 2019

From late January to early February 2019, a quasi-stationary monsoon depression situated over northeast Australia caused devastating floods, killing an estimated 625,000 head of cattle in northwest Queensland, and inundating over 3 000 homes in the coastal city of Townsville. The monsoon depression lasted ~10 days, driving daily rainfall accumulations exceeding 200 mm/day, maximum temperatures 8–10 °C below normal, and wind gusts above 70 km/h. In this study, the atmospheric conditions during the event and its predictability on the weekly to subseasonal range are investigated. Results show that during the event, the tropical convective signal of the Madden-Julian Oscillation was over the western Pacific, and likely contributed to the heavy rainfall, however the El Niño-Southern Oscillation was not in the usual phase for increased rainfall over Queensland. Over the northern Tasman Sea, an anticyclone helped maintain a positive phase of the Southern Annular Mode and promote onshore easterly flow. Somewhat consistent with these climate drivers, the monthly rainfall outlook for February issued by the Australian Bureau of Meteorology on 31 January provided no indication of the event, yet forecasts, not available to the public, of weekly-averaged conditions by the Bureau's dynamical subseasonal-to-seasonal (S2S) prediction system were more successful. For the week of 31 January to 6 February the prediction system forecast a more than doubling of the probability of extreme (highest quintile) weekly rainfall a week prior to the event, along with increased probabilities of extremely low (lowest quintile) maximum temperatures and extreme (highest quintile) wind speeds. Ensemble-mean weekly rainfall amounts, however, were considerably underestimated by the prediction system, even in forecasts initialised at the start of the peak flooding week, consistent with other state-of-the-art dynamical S2S prediction systems. Despite this, one of the individual ensemble members of the Bureau's prediction system did manage to forecast close to 85% of the magnitude of the rainfall across the most heavily impacted region of northwest Queensland a week before the event. Predicting this exceptional event beyond two weeks appears beyond our current capability despite the dynamical system forecasts showing good skill in forecasting the broad-scale atmospheric conditions north of Australia a week prior.

Mapping the global prey-field: Combining acoustics, optics and net samples to reduce uncertainty in estimates of mesopelagic biomass

Mesopelagic (200–1000 m depth zone) biomass largely comprises zooplankton, jellyfish, squid and fish. Part of this biomass actively migrates between the surface and the mesopelagic zone on a daily basis, playing an important role in global biogeochemical cycling. When observed using echosounders, aggregated components of this community (largely made up of fish and siphonophores) are known as Deep Scattering Layers (DSLs). DSLs have been used to partition the Global Ocean into biogeographically distinct regions, based on DSL vertical distribution and echo energy, and estimates of mesopelagic biomass have stemmed from this work. These estimates are typically derived using a combination of biological sampling, optics, and active-acoustics, but are often biased (e.g., through trawl-based escapement and avoidance) and uncertain. We have developed a new method that combines multiple strands of observations, both from vessels and ocean probes, to minimise sampling bias and produce accurate estimates of mesopelagic biomass. We apply the method to the specific case of estimating mesopelagic fish biomass in the Tasman Sea, combining observations made from a vessel and a Profiling Lagrangian Acoustic Optical System. We compare our new biomass estimates to previous estimates and ecosystem model predictions. Our new method provides a robust framework for future ocean biomass estimates.

The Sealing Industry and the Architecture of the Tasman World

ABSTRACTThis paper forms part of a collaborative project that aims to reframe the architectural histories of Australia and New Zealand by producing the first connected history of early colonial architecture in the Tasman World, a concept defined connectively as a working region of traffic across the Tasman Sea. In the early nineteenth century the Tasman World denoted a sub-set of imperial ventures between the south-eastern Australian colonies and pre(proto)-colonial New Zealand that were also linked commercially to British India and to imperial encroachments in China. Avoiding nationalist frameworks, the project expects to show how the earliest colonial architecture in “our” region was an outcome of the industries that brought into being and shaped the colonial world. Seal hunting was foremost among these early European industries, providing the first export profits for the British colony of New South Wales. Yet the legacy of the sealing entrepreneurs based in New South Wales (here termed “sealer dealers”) and their frontier gangs of seal hunters remains unexamined in architectural history. Using historical methods, this paper argues that the sealing industry, while ephemeral in time, was foundational in place-making by establishing the Tasman World’s early-colonial built environment from the 1790s to about 1830.

Shallow water masses and their connectivity along the southern Australian continental margin

Four water masses are identified and described using hydrographic, nutrient and stable isotope data for the top 1000 m water depth of the southern Australian continental margin, from Cape Leeuwin to Tasmania. Three are identified from previous literature on the southeast Indian Ocean: Subtropical Surface Water (STSW), Tasmanian Subantarctic Mode Water (TSAMW) and Tasmanian Intermediate Water (TIW), and one is newly identified and named: South Australian Basin Central Water (SABCW). STSW (0–250 m) is transported east by the Leeuwin Current System and is modified by heating and evaporation along the subtropical continental shelf. SABCW (250–400 m) and TSAMW (400–650 m) form southwest of Tasmania from deep winter mixing in the region: SABCW at the Subtropical Front and TSAMW north of the Subantarctic Front. TIW (>650 m) forms southwest of Tasmania from mixing of warm, saline Antarctic Intermediate Water from the Tasman Sea and cool, fresh Antarctic Intermediate Water from the Antarctic Circumpolar Current. SABCW, TSAMW and TIW are transported west along the slope by the Flinders Current System, here defined as the western slope-trapped Flinders Current, Tasman Outflow and equatorward Sverdrup transport. Water mass distributions on the slope identify the interface between subantarctic water from the Southern Ocean and subtropical water transported by the Leeuwin Current System. This interface is ~300 m during winter and ~250 m during summer, but can be 150 m during summer in upwelling regions and off western Tasmania. Furthermore, stable isotope data of the water masses south and west of Australia show connectivity between the Subantarctic Zone, the southern Australian margin and the western Australian margin.

Year-round distribution, activity patterns and habitat use of a poorly studied pelagic seabird, the fluttering shearwater Puffinus gavia.

We present the first study to examine the year-round distribution, activity patterns, and habitat use of one of New Zealand’s most common seabirds, the fluttering shearwater (Puffinus gavia). Seven adults from Burgess Island, in the Hauraki Gulf, and one individual from Long Island, in the Marlborough Sounds, were successfully tracked with combined light-saltwater immersion loggers for one to three years. Our tracking data confirms that fluttering shearwaters employ different overwintering dispersal strategies, where three out of eight individuals, for at least one of the three years when they were being tracked, crossed the Tasman Sea to forage over coastal waters along eastern Tasmania and southeastern Australia. Resident birds stayed confined to waters of northern and central New Zealand year-round. Although birds frequently foraged over pelagic shelf waters, the majority of tracking locations were found over shallow waters close to the coast. All birds foraged predominantly in daylight and frequently visited the colony at night throughout the year. We found no significant inter-seasonal differences in the activity patterns, or between migratory and resident individuals. Although further studies of inter-colony variation in different age groups will be necessary, this study presents novel insights into year-round distribution, activity patterns and habitat use of the fluttering shearwater, which provide valuable baseline information for conservation as well as for further ecological studies.