Campbell Plateau Research Articles

Calcareous nannofossils from the Paleogene Southern Ocean (IODP Site U1553, Campbell Plateau)

Calcareous nannofossils from the Paleogene Southern Ocean (IODP Site U1553, Campbell Plateau)

Unlocking the geochemical features of the Paleocene southern Pacific Ocean using carbon isotopes and biolipids

Little is known about the Paleocene in the southern Pacific Ocean due to scarce marine records. Here, we present a systematic geochemical investigation using biomarkers, carbonate content, and carbon isotopes of a set of early Paleocene deep-sea cores from International Ocean Discovery Program Expedition 378 Site U1553. The results provide a new Paleocene biomarker profile for the Campbell Plateau, New Zealand. The occurrence and distribution of a series of hopenes, ββ hopanes, sterenes and biomarker-based maturity parameters indicate that these organically-lean sediments are in an early diagenetic stage, with an equivalent vitrinite reflectance of approximately 0.4%. Biomarker data (e.g., gammacerane index and homohopane index), carbonate carbon isotopes (−27.9 ‰ to +2.0 ‰) combined with onboard data (sulphur and methane contents) indicate that the redox properties of the Paleocene southern Pacific Ocean changed from an oxidising-anoxic transition zone to a more reducing marine environment (water depth > 1000 m). The sources of the organic matter are diverse, including algae, bacteria, diatoms, dinoflagellates, and higher plants, but are dominated by aquatic organisms. Our new biomarker record bridges a Paleocene biosphere knowledge gap in the high latitude South Pacific.

Apparent Diachroneity of Calcareous Nannofossil Datums During the Early Eocene in the High‐Latitude South Pacific Ocean

AbstractThe late Paleocene to early Eocene interval is characterized by a series of carbon perturbations that caused transient warming (hyperthermal) events, of which the Paleocene‐Eocene Thermal Maximum (PETM) was the largest. These hyperthermals can be recognized in the pelagic sedimentary record as paired negative δ13C and δ18O excursions, in addition to decreased calcium carbonate and increased iron content caused by carbonate dissolution. However, current data are predominantly sourced from the equatorial‐to subequatorial regions. Here we present a new high‐latitude late Paleocene—early Eocene record, recovered during International Ocean Discovery Program (IODP) Expedition 378 on the Campbell Plateau off New Zealand, in the southwest Pacific Ocean. To construct an age model, we correlated our chemostratigraphic and biostratigraphic data to existing astronomically‐tuned age models from Walvis Ridge (South Atlantic Ocean) and Demerara Rise (equatorial Atlantic Ocean). Our results indicate that the Site U1553 composite section spans ∼7 million years of the latest Paleocene to early Eocene (50.5–57.5 Ma), and preserves many of the early Eocene hyperthermals; including a PETM interval that is more expanded than elsewhere in this region. However, construction of the age model also revealed discrepancies between the chemostratigraphic and biostratigraphic tie points used for correlation. This is likely due to latitudinal diachroneity in the calcareous nannofossil biostratigraphic datums, which are primarily based on low‐to mid‐latitude assemblages. Therefore, our study highlights the need to establish a revised calcareous nannofossil biozonation that is more appropriate for high‐latitude age models.

Characteristics and Trends of the Campbell Plateau Meander in the Southern Ocean: 1993–2020

AbstractMeanders are significant features of the Antarctic Circumpolar Current in the Southern Ocean and sites of enhanced upwelling, cross‐frontal tracer fluxes, and exchanges between the surface and deep ocean. They often overlap the locations of fronts and are linked to topographic features. While much is known about Southern Ocean fronts and how they are changing, the response of meanders to climate change is largely unexplored. In this study, we investigate the Campbell Plateau meander south of New Zealand. We apply a local gradient maxima method to satellite altimetry data to identify the position of the meander and estimate its width, geostrophic current speed, and associated trends from 1993 to 2020. We find that the position of the meander has been relatively fixed, except for a section downstream of the Plateau, which has shifted northward by about 0.4° latitude per decade. The meander has become flatter at the western edge of the Plateau, but steeper at the eastern edge of the Plateau. Overall, the meander has widened by 2 km per decade and accelerated by 0.01 m s−1 per decade, particularly downstream of the Plateau. These findings are consistent with other work on standing meanders in the Southern Ocean. Increases in eddy kinetic energy and of the South Pacific Gyre index support our hypotheses that changes in the downstream jet stability and the South Pacific Gyre contribute to these observed trends. The impacts of these trends on cross‐frontal transport remain to be evaluated.

Decoupled growth and grazing rates of diatoms and green algae drive increased phytoplankton productivity on HNLC sub‐Antarctic plateaux

AbstractThe combination of iron limitation and microzooplankton grazing controls phytoplankton productivity and taxonomic composition in high‐nutrient low‐chlorophyll (HNLC) regions. While increased productivity and diatom contribution triggered by iron enrichment support this view, direct measurements of underpinning group‐specific growth and grazing rates are scarce for the Southern Ocean. To assess these rates, we conducted dilution experiments coupled to high‐performance liquid chromatography and flow‐cytometry in sub‐Antarctic waters on and off Campbell Plateau, southeast of Aotearoa‐New Zealand. Off the plateau, growth and grazing were closely balanced for all groups despite a two‐fold difference between slow‐ and fast‐growing groups. On Campbell Plateau, where HNLC conditions were alleviated, the balance was disrupted, mainly by the preferential growth of diatoms and green algae, which was stimulated beyond grazing. Our results expand the recognized ability of diatoms to escape grazing control to picoplanktonic green algae that also avoid grazing and contribute significantly to phytoplankton productivity and biomass accumulation.

Changing Sub‐Surface Chemistry Resulting From a 26‐Million‐Year Unconformity: Porewater Chemistry From IODP Site U1553 in the South Pacific

AbstractWhereas changes in pore water chemistry are known to impact carbonate sediment geochemistry, little is known about the impact of long unconformities on carbonate alteration. IODP Site 378‐U1553 on the southern Campbell Plateau, with a 26‐million‐year, erosional unconformity, provides a key location for examining the impact of long‐term unconformities on sub‐surface chemistry and carbonate archives. This study examined 76 interstitial water samples for sulfate sulfur and oxygen isotopes, as well as 28 bulk carbonate samples for carbonate associated sulfate (CAS) sulfur isotopes, to quantify the effects of this unconformity on the sub‐surface redox chemistry of the Site. The current state of the system suggests limited influence of redox processes on the CAS archive. Manganese reduction reaches 30 mbsf, with a decrease in manganese reduction between 20 and 30 mbsf. Below 30 mbsf, the system transitions to iron reduction to a depth of approximately 140 mbsf where sulfate reduction begins. Dissolved sulfate sulfur and oxygen isotope values suggest repeated oxygenation of sulfides. The CAS record from the Site deviates from previously published seawater values. However, the lack of a relationship between the dissolved sulfate and CAS records suggests most of the alteration of the CAS record likely occurred before the unconformity when the carbonate sediments were more reactive. This further supports the CAS record as a relatively robust archive, withstanding most post‐depositional mechanisms of carbonate alteration.

Morphological diversity and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from the Western Pacific (Singapore and New Zealand), with implications for a re-evaluation of rhabdopleurid species diversity

The recent discovery of Rhabdopleura in Singapore and the chance collecting of fresh material from northern New Zealand (Three Kings Shelf) provided an opportunity to sequence the specimens with an aim to determine their species identity. Phylogeny reconstructions of two new Rhabdopleura taxa based on ribosomal and mitochondrial genes suggest a different identity from known samples, including putative Rhabdopleura annulata, first described from the Three Kings Shelf but sequenced from the Great Barrier Reef. Pairwise distances between rhabdopleurids for the 16S rRNA locus were several magnitudes larger than that of 18S rRNA, and might potentially be a suitable barcoding gene once sufficient samples of conspecifics are collected to determine the barcoding gaps. Type material of R. annulata was re-examined, as well as Rhabdopleura material from eight other New Zealand localities from north of subtropical Raoul Island (Kermadec Ridge) at ~29° S to the subantarctic Campbell Plateau at ~49° S. Six morphological characters, four of them new, were applied to all samples. The findings from morphology suggest (1) the holotype and cotype of R. annulata might not be conspecific; (2) there are 3–4 variants (species?) on the Three Kings Shelf; and (3) there are 2–3 additional variants (species?) elsewhere in the New Zealand region.

Eocene-Oligocene southwest Pacific Ocean paleoceanography new insights from foraminifera chemistry (DSDP site 277, Campbell Plateau)

Despite its major role in the Earth’s climate regulation, the evolution of high-latitude ocean dynamics through geological time remains unclear. Around Antarctica, changes in the Southern Ocean (SO) circulation are inferred to be responsible for cooling from the late Eocene and glaciation in the early Oligocene. Here, we present a geochemical study of foraminifera from DSDP Site 277 (Campbell Plateau), to better constrain thermal and redox evolution of the high latitude southwest Pacific Ocean during this time interval. From 56 to 48 Ma, Mg/Ca- and δ18O-paleothermometers indicate high surface and bottom water temperatures (24–26°C and 12–14°C, respectively), while weak negative Ce anomalies indicate poorly oxygenated bottom waters. This is followed by a cooling of ∼4° between 48 and 42 Ma, possibly resulting from a weakening of a proto-EAC (East Australian Current) and concomitant strengthening of a proto-Ross gyre. This paleoceanographic change is associated with better ventilation at Site 277, recorded by an increasing negative Ce anomaly. Once this proto-Ross gyre was fully active, increasing biogenic sedimentation rates and decreasing Subbotina sp. δ13C values indicate enhanced productivity. This resulted in a shoaling of the oxygen penetration in the sediment pile recorded by increasing the foraminiferal U/Ca ratio. The negative Ce anomaly sharply increased two times at ∼35 and ∼31 Ma, indicating enhanced seawater ventilation synchronously with the opening of the Tasmanian and Drake Passage gateways, respectively. The Oligocene glaciation is recorded by a major increase of bottom seawater δ18O during the EOT (Eocene-Oligocene Transition) while Mg/Ca-temperatures remain rather constant. This indicates a significant ice control on the δ18O record.

The Impact of Southern Ocean Topographic Barriers on the Ocean Circulation and the Overlying Atmosphere

Abstract Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean–atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the wind and buoyancy forcing of the ACC transport, which increases by between 4% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea. When the barriers are removed, zonal flattening of the currents leads to sea surface temperature (SST) anomalies that strongly correlate to precipitation anomalies, with correlation coefficients ranging between r = 0.92 and r = 0.97 in the four experiments. The SST anomalies correlate to the surface winds too in some locations. However, they also generate circumpolar waves of sea level pressure (SLP) anomalies, which induce remote wind speed changes that are unconnected to the underlying SST field. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau, and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on surface winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern. Significance Statement Several studies in the past have pointed to the controlling effect of bathymetry on currents in the Southern Ocean circulation, but a clear idea of the importance of the major topographic barriers in the Southern Ocean is lacking. By removing these barriers systematically in a coupled climate model, we can evaluate their impact on several important components of the climate system, such as the Antarctic Circumpolar Current (ACC) pathways and strength, Antarctic Bottom Water formation, sea surface temperature, overlying winds, air–sea fluxes, and even precipitation. This helps in our understanding of what controls the pathways of the ACC and how much it matters for climate.

Archean and Paleoproterozoic zircons in Paleozoic sandstones in southern New Zealand: evidence for remnant Nuna supercontinent and Ur continent rocks within Zealandia

Detrital zircon age patterns are reported from quartz sandstones and metaquartzites in the Russet and Wangapeka formations (Western Province, Takaka Terrane) in Fiordland and northwest Nelson, and the Pegasus Group on Stewart Island. The latter indicate a possible maximum early Carboniferous depositional age with a significant Lower Devonian zircon component that suggests a source on the Campbell Plateau or Marie Byrd Land, West Antarctica. In contrast, Russet Formation ages indicate a correlation with Upper Ordovician, Wangapeka Formation quartz sandstones in northwest Nelson. These zircon age patterns have two major groups: late Mesoproterozoic (1200–1000 Ma) of Rodinia origin and Cambrian–late Neoproterozoic (700–500 Ma) of early Gondwana derivation. Both groups have local Zealandia provenances. In addition, there are unusually high proportions (to 20%) of early Paleoproterozoic and Archean zircons, 3500–2000 Ma, with significant age components, 2550–2450 Ma and ca 2800 and 2650 Ma, which are characteristic of an Expanded-Ur continent. Their high proportions of euhedral grains indicate a local source within a postulated Archean basement block at or near the eastern margin of the Takaka Terrane. A proposed Rodinia supercontinent reconstruction locates this Precambrian basement as a Zealandia component placed between Gawler and North Australia cratons of Australia and Yangtze Block of the South China Craton. KEY POINTS Pegasus Group, metaquartzites, Stewart Island are not correlated with the Russet Formation, Fiordland but are an Upper Devonian or lower Carboniferous sedimentary unit. Russet Formation high-grade metasandstones in Fiordland are correlated with the lower-grade and fossiliferous Upper Ordovician Wangapeka Formation in Nelson. Upper Ordovician sandstones in Western Province, New Zealand contain unusually high proportions of Neoarchean euhedral detrital zircons that suggest a local Zealandia source. An Archean block is proposed within the Rodinia supercontinent, between the Gawler and North Australia cratons of Australia and Yangtze Block of the South China Craton.

Observations on Late Cretaceous Micrampulla (Corethrales, Bacillariophyceae) from the Campbell Plateau (Zealandia), southwest Pacific Ocean

Late Cretaceous (late Campanian) diatom assemblages from the Campbell Plateau (Zealandia), southwest Pacific Ocean, obtained from Deep Sea Drilling Project (DSDP) Leg 29 Site 275, contain well-preserved specimens of two enigmatic diatom species currently assigned to the genus Ktenodiscus; Micrampulla parvula originally described from the Maastrichtian-age Moreno Shale, California, and Pterotheca cretacea from DSDP Site 275. In general, the two species share a number of common features with modern Corethron (domed valves, probable heterovalvate frustules, T-shaped serrated articulated spines, marginal sockets), but differ in the location of the sockets (i.e. vertically at the base of the valve dome and not on the rim), the design of the spines and sockets, and the hollow structure extending from the valve centre. Although hooked spines are absent, equivalent 1-spine and 2-spine valves can be recognized in these two species. The recently described genus Praecorethron from the same late Campanian sediments shares many features with Micrampulla, but lacks the inflated central valve structure. As a result of our studies, the relevant subclass, order and family definitions are emended, as well as those of Micrampulla, M. parvula and M. cretacea comb. nov., and a new family, Micrampullaceae fam. nov., is erected to distinguish the ancient genera (Micrampulla and Praecorethron) from modern Corethron.

Regional-scale genetic differentiation of the stony coral Desmophyllum dianthus in the southwest Pacific Ocean is consistent with regional-scale physico-chemical oceanography

Deep-sea corals are diverse and abundant in New Zealand’s EEZ and the southwest Pacific Ocean. We assessed genetic diversity and gene flow of the deep-sea scleractinian (stony cup coral) Desmophyllum dianthus in five areas (Kermadec Ridge, Louisville Seamount Chain, Chatham Rise, Campbell Plateau, Macquarie Ridge), and applied dispersal kernels estimated from drifters observations and seascape genetics to compare with observed connectivity patterns and regional physico-chemical data. We observed pronounced between-region genetic differentiation, high levels of self-recruitment, but also high connectivity between distant sites (e.g., at the Kermadec Ridge inside the New Zealand EEZ, and the Louisville Seamount Chain outside the New Zealand EEZ). Genetic diversity was marginally highest at the Kermadec Ridge, whilst populations on the Chatham Rise showed evidence of unique genetic diversity that may be driven by converging ocean currents. Overall, patterns of genetic connectivity were consistent with oceanographic predictions of dispersal routes. Seascape genetic analyses indicated that environmental variables most often related to physical seafloor habitat characteristics were important predictors of regional-scale genetic differentiation of D. dianthus. Our research shows that current spatial closures within the New Zealand EEZ and surrounding high seas areas do not encompass the extent of genetic diversity and connectivity for D. dianthus, which parallels research for other deep-sea taxa in the region. Future measures implemented to protect deep-sea coral biodiversity require consideration of complex connectivity patterns and migration routes amongst taxa, at various spatial scales. This study demonstrates that a combined gene flow, seascape genetics and dispersal kernel modelling approach can provide a robust evaluation of connectivity in deep-sea environments to inform management decision making at the scale of the southwest Pacific Ocean.

The year‐round distribution and habitat preferences of Campbell albatross (Thalassarche impavida)

Abstract The use of miniaturized electronic tracking devices has illuminated our understanding of seabird distributions and habitat use, and how anthropogenic threats interact with seabirds in both space and time. To determine the year‐round distribution of adult Campbell albatross (Thalassarche impavida), a single‐island endemic, breeding only at Campbell Island in New Zealand's subantarctic, a total of 68 year‐long location data sets were acquired from light‐based geolocation data‐logging tags deployed on breeding birds in 2009 and 2010. During the incubation and chick‐guard phases of the breeding season, birds used cool (<10°C) waters over the Campbell Plateau, but also ranged over deeper, shelf‐break and oceanic waters (4,000–5,500 m) beyond the Plateau. Later in the breeding season, during post‐guard chick‐rearing, Campbell albatrosses exploited generally deep waters (4,000–5,000 m) beyond the Campbell Plateau. During the non‐breeding period, adults tended to move northwards into warmer (approximately 15°C) waters and occupied areas beyond western Australia in the west to offshore from Chile in the east. Overall, about 30% of adults spent some of their non‐breeding period in the central and eastern Pacific Ocean, substantially expanding the previously reported range for this species. One bird, that failed in its breeding attempt in October 2009, departed Campbell Island and circumnavigated the southern oceans before being recaptured back at Campbell Island in October 2010. This is the first example of an annually‐breeding albatross species completing a circumnavigation between breeding attempts. Overlap with fishing effort, using data from the Global Fishing Watch database, was assessed on a monthly and seasonal basis. Generally, levels of overlap between Campbell albatross and fishing effort were relatively low during the breeding season but were approximately 60% higher during the non‐breeding period, underlining the need for international initiatives to safeguard this species.

Using correlative and mechanistic niche models to assess the sensitivity of the Antarctic echinoid Sterechinus neumayeri to climate change

The Southern Ocean is undergoing rapid environmental changes that are likely to have a profound impact on marine life, as organisms are adapted to sub-zero temperatures and display specific adaptations to polar conditions. However, species ecological and physiological responses to environmental changes remain poorly understood at large spatial scale owing to sparse observation data. In this context, correlative ecological niche modeling (ENMc) can prove useful. This approach is based on the correlation between species occurrences and environmental parameters to predict the potential species occupied space. However, this approach suffers from a series of limitations amongst which extrapolation and poor transferability performances in space and time. Mechanistic ecological niche modeling (ENMm) is a process-based approach that describes species functional traits in a dynamic environmental context and can therefore represent a complementary tool to understand processes that shape species distribution in a changing environment. In this study, we used both ENMc and ENMm projections to model the distribution of the Antarctic echinoid Sterechinus neumayeri. Both models were projected according to present (2005–2012) and future IPCC scenarios RCP 4.5 and 8.5 for (2050–2099). ENMc and ENMm projections are congruent and predict suitable current conditions for the species on the Antarctic shelf, in the Ross Sea and Prydz Bay areas. Unsuitable conditions are predicted in the northern Kerguelen Plateau and South Campbell Plateau due to observed lower food availability and higher sea water temperatures compared to other areas. In contrast, the two models diverge under future RCP 4.5 and 8.5 scenarios. According to ENMm projections, the species would not be able to grow nor reach sexual maturity over the entire ocean, whereas the Antarctic shelf is still projected as suitable by the ENMc. This study highlights the complementarity and relevance of EMN approaches to model large scale distribution patterns and assess species sensitivity and potential response to future environmental conditions.

Regional Trends in Southern Ocean Eddy Kinetic Energy

AbstractPrevious model‐based studies and observation‐based studies suggest that increasing wind energy input into the Southern Ocean will primarily cause increases in eddy kinetic energy (EKE) with no significant change in the mean circulation, a result that has been named the “eddy‐saturation” hypothesis. However, due to the sparsity of the available observations, quantifying and understanding regional EKE changes in the Southern Ocean is challenging. In this study, we examine regional trends in the Southern Ocean EKE using altimetry crossover measurements and an ocean reanalysis product to quantify if undersampling by altimetry will bias EKE trend estimates and to test if previously observed EKE trends are homogenous throughout the Southern Ocean or concentrated in a few regions. To verify that the EKE computed from altimetry crossovers accurately represents yearly averaged EKE over the Southern Ocean, we first conduct a sampling experiment with the HYCOM Global Ocean Forecasting System 3.1 ocean reanalysis. We find that the crossover sampling is sufficient to represent the yearly averaged EKE when averaged over sectors of at least 30° of longitude. We find no coherent increase in EKE over the entire Southern Ocean from altimetry crossover measurements, but instead find significant EKE increase over only one region, primarily south of New Zealand and downstream of the Campbell Plateau. We conclude that the EKE change in the Southern Ocean is not as homogenous as implied by previous studies and more work is needed to understand if this is consistent with the “eddy‐saturation” hypothesis or related more to local dynamics.

Calcareous nannoplankton response to early Eocene warmth, Southwest Pacific Ocean

Episodes of pronounced climatic warming in the early Eocene (56–48 Ma) provide insights into how biological systems might respond to future climate changes. Eocene climate reconstructions for the Southwest (SW) Pacific have proved challenging due to some disparities between geochemical proxy-based estimates for sea temperatures and estimates derived from climate models. Changes in marine phytoplankton populations through the early Eocene provide a means to evaluate model and proxy-based approaches and also reveal how climatic changes affected the ocean ecosystem. This study documents early to middle Eocene calcareous nannofossil assemblages from legacy Deep Sea Drilling Project (DSDP) sites in the SW Pacific. We integrate nannofossil assemblage changes with foraminiferal-based stable isotopes and other microfossil data to provide updated age models for DSDP Sites 207 (Lord Howe Rise) and 277 (Campbell Plateau), and to infer past environmental change through the early to mid-Eocene in the SW Pacific. Although these sites record a short hiatus in the earliest Eocene, deposition resumed by ~54 Ma, prior to the onset of the Early Eocene Climate Optimum (EECO). Both sites show an increase in warm-water taxa from the onset of the EECO until approximately 50.5 Ma. Abundance of warm-water taxa was higher (~23%) at the EECO onset at the more northerly Site 207 and increased only slightly to ~27%, whereas at Site 277 warm-water taxa comprised only ~3% at the EECO onset but increased to ~31% by 50.5 Ma. Cool-water taxa at both sites were present in very sparse numbers (<3%) through much of the EECO and only began to increase in abundance after 50 Ma, concomitant with a decrease in warm-water taxa. These results are similar to other mid-latitude sites in the SW Pacific and Indian Ocean, including mid-Waipara River (Canterbury Basin, New Zealand) and ODP Site 762 (Exmouth Plateau), and indicate assemblages during the EECO are best described as warm temperate. Benthic δ18O records from both sites show good agreement with nannofossil trends and, despite the possibility of recrystallization at Site 277, sea surface temperatures (SSTs) indicated by planktic foraminifera also imply warm temperate conditions. This suggests that a warm proto-East Australian Current extended to at least 55°S during the EECO, displacing the proto-Tasman Front southward, which migrated northward after termination of the EECO possibly due to expansion of a proto-Ross Sea Gyre.

Apprehending novel biodiversity redux – thirteen new genera and three new families of Zealandian Bryozoa, with the first living species of the Eocene‒Miocene genus Vincularia (Vinculariidae)

AbstractThirteen new genera and three new families of cheilostome Bryozoa are described from the New Zealand biogeographic region, centred on Zealandia, between 26.42° (northern Norfolk Ridge) and 54.02°S latitude (south-east Campbell Plateau) from coastal waters to bathyal depths (46‒1676 m). The new genera, comprising 15 new and one previously described Zealandian species, are: Elementella (Elementellidae n. fam.), Niwapora, Quasicallopora, Quitocallopora, Judyella (Calloporidae), Ellisantropora (Antroporidae), Rhizellisina (Ellisinidae), Radixenia (Calloporoidea incertae sedis), Granomurus (Granomuridae n. fam.), Carolanna (Bugulidae), Borioplebs (Borioplebidae n. fam.), Seabournea (Cribrilinidae) and Waeschenbachia (Romancheinidae). A new Recent species of the otherwise Eocene‒Miocene genus Vincularia is also described from deep water on the Three Kings Ridge. Two new combinations are created – Judyella precocialis (Gordon, 1984) and Ellisantropora aggregata (Gordon, 1984). Ellisantropora tilbrooki sp. nov. is also introduced for a species from Torres Strait. Four of the deep-sea genera (three from one station on the northern Norfolk Ridge, one from a station on the Three Kings Ridge) have species with plesiomorphies or distinctive skeletal characters that suggest they are relict. Almost half of the new species form spot-like colonies on hard substrata.

Frontal dynamics and water mass variability on the Campbell Plateau

ABSTRACT The Campbell Plateau is a dominating bathymetric feature of New Zealand’s subantarctic region, strongly influencing the dynamics of both the Subtropical Front (STF) to the north and the Subantarctic Front (SAF) to the south. We present a consistent survey across New Zealand’s subantarctic of the relationships between front positions, bathymetry and water masses. The northwest side of the Campbell Plateau is comparatively warm due to a southward extension of the STF over the plateau. The SAF is steered south and east by the combined effect of the plateau and Macquarie Ridge, with waters originating in the SAF also found north of the plateau. Formation of Subantarctic Mode Water (SAMW) is confirmed, with a deep reservoir of SAMW persisting nearly a year after formation. Antarctic Intermediate Water (AAIW) is observed around the edges of the plateau, but not present on the plateau, confirming that the waters on the plateau are isolated from deeper Southern Ocean.

Decoupling Between Phytoplankton Growth and Microzooplankton Grazing Enhances Productivity in Subantarctic Waters on Campbell Plateau, Southeast of New Zealand

AbstractThe Subantarctic zone is one of the largest High‐Nutrient Low‐Chlorophyll zones of the Southern Ocean. Despite widespread iron limitation, phytoplankton accumulation (chlorophyll a (chla) &gt; 0.3 mg m−3) often occurs near islands and bathymetric features such as on the Campbell Plateau, southeast of New Zealand. To investigate the processes responsible for localized increases in chla commonly observed by satellites, we characterized phytoplankton biomass structure, production, and microzooplankton grazing on Campbell Plateau and surrounding waters in austral autumn (March 2017). Chla on the plateau tended to be higher, more variable (0.52 ± 0.38 mg chla m−3, mean ± standard deviation), and characterized by larger phytoplankton forms (22 ± 27%chla &gt; 20 μm) than surrounding waters (0.29 ± 0.12 mg chla m−3, 5 ± 2%). The increased contribution of diatoms, together with higher photosystem II maximum photochemical efficiency (Fv/Fm = 0.45 ± 0.05) and lower effective absorption cross‐section (σPSII = 774 ± 90 Å RCII−1) on the plateau, suggests an alleviation of iron stress relative to surrounding waters (Fv/Fm = 0.37 ± 0.04, σPSII = 974 ± 89 Å RCII−1). Phytoplankton growth (μ0 = 0.42 ± 0.20 day−1) and production rates (6.1 ± 3.2 mg C m−3 day−1) were also higher compared to surrounding waters (0.27 ± 0.04 day−1, 3.5 ± 1.9 mg C m−3 day−1). While microzooplankton grazing (g = 0.28 ± 0.18 day−1) balanced phytoplankton growth off the plateau (g:μ0 = 1.13 ± 0.18), the imbalance observed on Campbell Plateau (g = 0.25 ± 0.25 day−1) allowed a substantial proportion of primary production to escape microzooplankton grazing control (g:μ0 = 0.48 ± 0.31). Overall, the degree of coupling tended to decrease with the depth of the mixed layer (R2 &gt; 0.6, p &lt; 0.001). We hypothesize that the entrainment of deeper water into the mixed layer regulates the onset and fate of the autumn bloom by altering nutrient supply and microzooplankton grazing pressure.

Unnamed for over 30 years: Gigartina falshawiae sp. nov. (Gigartinaceae, Rhodophyta) and its confusion with Iridaea tuberculosa in New Zealand

ABSTRACTGigartina species are very common and abundant on intertidal rocky shores in New Zealand but members of this genus and the family Gigartinaceae are still not fully documented. A well-known species, distributed as No. 164 of the Lindauer Nova-Zelandicae Exsiccatae, were labelled by Lindauer as Gigartina tuberculosa from material collected in Stewart Island. However, Gigartina tuberculosa (as Chondrus tuberculosus) was described based on specimens collected from the New Zealand subantarctic Auckland Island. Later, material from the Strait of Magellan was referred to this species. In 1993, Gigartina tuberculosa was transferred to Iridaea tuberculosa with its distribution considered to be Chile, Cape Horn, Antarctica, Falklands Islands, Tristan da Cunha, Gough Island and the Campbell Plateau. The species distributed by Lindauer is here described as Gigartina falshawiae sp. nov. These species can be differentiated morphologically: G. falshawiae has thalli that are forked, somewhat irregular and form bushy clumps, with proliferations at the margins and on the blades, and with cystocarps surrounded by lobes, whereas thalli of Iridaea tuberculosa are fan-shaped, lack proliferations, and have globose cystocarps. The distributional ranges of these species also differ: G. falshawiae is found on Stewart Island and I. tuberculosa on the New Zealand subantarctic islands (recorded from the Antipodes, Auckland and Campbell Islands), while the species co-occur on the Snares Islands.