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The South Pacific Oscillation (SPO), characterized by a north–south dipole-like pattern of sea level pressure anomalies, is one of the key factors in understanding tropical–extratropical interactions in the South Pacific. We show that in boreal summer (June–August), the center of the northern lobe sea level pressure anomalies in the SPO is shifted to the east gradually after the 1960–70s. This study focuses on the relationship between the boreal summer SPO and following winter El Niño–Southern Oscillation (ENSO) diversity before and after the eastward shift of the SPO's subtropical lobe. The eastward shift of the SPO's subtropical lobe altered both the seasonal footprint mechanism and the trade wind charging mechanism associated with the SPO and thus profoundly influenced the ENSO diversity. It is revealed that when the northern lobe of the SPO shifts to the west of its average location, it tends to strengthen the eastern Pacific (EP) El Niño mainly via the seasonal footprint mechanism. But after the SPO's northern lobe shifts to the east of its average location, it tends to promote the development of central Pacific (CP) El Niño mainly via the trade wind charging mechanism. The changes in the spatial structure of convection over the tropical Pacific and Indian Oceans may be one of the possible causes for the eastward shift in the SPO's northern lobe. The findings in the present study have implications for a better understanding of ENSO diversity. Significance Statement: Previous studies have demonstrated that the South Pacific Oscillation (SPO), as an important El Niño–Southern Oscillation (ENSO) precursor in the South Pacific, has the potential to provide an enhancement of the prediction of specific ENSO flavor. However, the historical variation in the SPO's spatial structure and related changes in the relationship with the diversity of ENSO are still unclear. In this paper, we show that the subtropical lobe of the boreal summer (June–August) SPO is shifted to the east gradually after the 1960–70s. The changes in the spatial structure have also altered both the seasonal footprint mechanism and the trade wind charging mechanism which play important roles in the developmental processes of different types of ENSO. Our work highlights the importance of the interdecadal changes in the spatial structure of the SPO in understanding the relationship between the SPO and ENSO diversity. [ABSTRACT FROM AUTHOR]

Contrasting with their current ranges in the Antarctic and subantarctic zones, the fossil record reveals that phocids (true and elephant seals) inhabited widespread subtropical regions across the Southern Hemisphere in the geologic past. At least four extinct phocid taxa have been described from Miocene and Pliocene fossiliferous levels in Chile and Peru, constituting two of the taxonomically richest phocid assemblages known. Still, some Chilean remains morphologically differ from those recovered from Peru, suggesting an unprecedented phocid diversity. We examined phocid mandibular remains from the Bahía Inglesa Formation in northern Chile. We identified the occurrence of the long-snouted seal Acrophoca longirostris, a morphologically distinguishable and undescribed form of Acrophoca, and Hadrokirus martini, an extinct phocid with a robust feeding morphology, constituting the first record of this taxon outside Peru. We also recognised four other indeterminate phocids with considerable morphological differences from contemporaneous taxa. Moreover, one of these specimens uniquely combines morphological attributes distinct from all known extant and extinct phocids, likely corresponding to a new taxon. These reports significantly increase the taxonomic and morphological diversities of fossil seals from the eastern South Pacific and emphasise the substantial transformations of phocid assemblages over geologic time. [ABSTRACT FROM AUTHOR]

Sea level variabilities in the southwest Pacific contribute to the variations of equatorial current bifurcation and the Indonesian Throughflow transport. These processes are closely related to the recharge/discharge of equatorial heat content and dynamic distribution of anthropogenic ocean heating over the Indo-Pacific basin, thus being of profound significance for climate variability and change. Here we identify the major features of seasonal and interannual sea level variabilities in this region, confirming the dominance of the first baroclinic mode in the tropics (contributing 60%–80% of the variances) and higher baroclinic modes in the extratropics (40%–60% of the seasonal variance). Seasonally, except in the western Coral Sea where the Ekman pumping is significant, the wind-driven first-mode baroclinic Rossby waves originating to the east of the date line control the sea level variations over most tropical Pacific regions. In the domain where the 1.5-layer reduced gravity model becomes deficient, the surface heat fluxes dominate, explaining ∼40%–80% of sea level variance. For interannual variability, ∼40%–60% of the variance are El Niño–Southern Oscillation (ENSO) related. The wind-driven Rossby and Kelvin waves east of the date line explain ∼40%–78% of the interannual variance in the tropical Pacific. Outside the tropics, small-scale diffusive processes are presumed critical for interannual variability according to a thermodynamic analysis using an eddy-permitting ocean model simulation. Further process and predictive understandings can be achieved with the coupled climate models properly parameterizing the subgrid-scale processes. [ABSTRACT FROM AUTHOR]

Thermohaline structure and time evolution in the subsurface ocean play a critical role in climate variability and predictability. They are still poorly represented in ocean and climate models. Here, the characteristics of subsurface thermohaline biases in the southern tropical Pacific and their causes are investigated through CMIP-based analyses and model-based experiments. There exists a pronounced subsurface cold bias at 200-m depth over the southern tropical Pacific in CMIP6 simulations with an ensemble mean of about −4°C and an extreme close to −10°C. This cold bias is accompanied by a fresh subsurface bias of about −0.9 psu in the ensemble mean (−1.9 psu minimum). Similar subsurface thermohaline biases also exist in CMIP5 outputs, indicating that reduction of these biases remains a long-standing challenge for model developments. To understand the causes of these biases, attribution analyses and POP2-based sensitivity experiments are performed. It is found that the subsurface thermohaline biases are attributed to the model deficiencies in simulating wind stress curl and precipitation in the southern tropical Pacific. By conducting CESM2-based coupled experiments, a warm SST bias in the southeastern tropical Pacific is found to be responsible for the poor simulations in wind stress curl and precipitation. The consequences of these biases are also analyzed. The subsurface thermohaline biases cause the density field to increase substantially along 10°S, flattening the zonal isopycnal surface and reducing equatorward interior transport. In addition, the anomalously cold and fresh subsurface signals in the southern tropical Pacific are seen to propagate to the equator, leading to an overall spurious cooling in the equatorial subsurface. Significance Statement: Subsurface biases severely degrade the credibility of climate models in their predictions and projections; hence, it is important to understand the causes of these subsurface biases. Our study analyzes the characteristics of subsurface thermohaline biases in the southern tropical Pacific and investigates their causes. A pronounced subsurface cold bias is found over the southern tropical Pacific, accompanied by an obvious subsurface fresh bias. By performing attribution analyses and numerical experiments, it is found that the subsurface thermohaline biases are attributed to the model deficiencies in simulating wind stress and precipitation, which are further attributed to the warm SST bias in the southeastern tropical Pacific. These results provide a guide for improving climate model performances. [ABSTRACT FROM AUTHOR]

This study investigates the influence of the Southern Annular Mode (SAM) on chlorophyll- a (Chl- a ) concentrations and the underlying mechanisms governing their associated environmental variations in the mid-latitude (35–50° S) ocean from 1998 to 2021. The intensification of westerly winds during positive SAM phases influences meridional water transport and mixed layer depth (MLD), which are both critical factors that affect surface nutrient availability. A marked contrast in the relationship between the meridional current anomaly and the SAM was observed, with reduced northward transport of nutrient-rich water in regions north of 50° S during positive SAM phases. This reduction could be attributed to the poleward migration of the westerly winds, which impeded the meridional current from reaching the mid-latitudes. The relationship between SAM and MLD south of 50° S was positive whereas that in the mid-latitude eastern (60–110° E) South Indian Ocean and eastern (90–140° W) South Pacific Ocean was negative or weak. The immediate effect of a more positive SAM on Chl- a in the mid-latitude ocean was reduced productivity caused by enhanced nutrient depletion. However, in the mid-latitude eastern South Pacific Ocean, the northward migration of the zonal mean meridional current anomaly closely aligned with the lagged correlation pattern between SAM variability and Chl- a over time, suggesting that the delayed northward transport of nutrient-rich waters may partially counterbalance the immediate effects of the SAM on ocean productivity. This mechanism was not present in the mid-latitude eastern South Indian Ocean, implying that future climate change may variably affect these regions. Our findings emphasize the importance of considering regional differences and temporal lags when evaluating the influence of SAM variability on ocean productivity and nutrient dynamics in the context of climate change.

The South Pacific convergence zone (SPCZ) exhibits well-known spatial displacements in response to anomalous sea surface temperatures (SSTs) associated with the El Niño-Southern Oscillation (ENSO). Although dynamic and thermodynamic changes during ENSO events are consistent with observed SPCZ shifts, explanations for these displacements have been largely qualitative. This study applies a theoretical framework based on generalizing arguments about the relationship between the zonal-mean intertropical convergence zone (ITCZ) and atmospheric energy transport (AET) to 2D, permitting quantification of SPCZ displacements during ENSO. Using either resolved atmospheric energy fluxes or estimates of column-integrated moist energy sources, this framework predicts well the observed SPCZ shifts during ENSO, at least when anomalous ENSO-region SSTs are relatively small. In large-amplitude ENSO events, such as the 1997/98 El Niño, the framework breaks down because of the large change in SPCZ precipitation intensity. The AET framework permits decomposition of the ENSO forcing into various components, such as column radiative heating versus surface turbulent fluxes, and local versus remote contributions. Column energy source anomalies in the equatorial central and eastern Pacific dominate the SPCZ shift. Furthermore, although the radiative flux anomaly is larger than the surface turbulent flux anomaly in the SPCZ region, the radiative flux anomaly, which can be viewed as a feedback on the ENSO forcing, accounts for slightly less than half of SPCZ precipitation anomalies during ENSO. This study also introduces an idealized analytical model used to illustrate AET anomalies during ENSO and to obtain a scaling for the SPCZ response to an anomalous equatorial energy source.

Over the past few decades, the global mean sea level rise and superimposed regional fluctuations of sea level have exerted considerable stress on coastal communities, especially in low-elevation regions such as the Pacific Islands in the western South Pacific Ocean. This made it necessary to have the most comprehensive understanding of the forcing mechanisms that are responsible for the increasing rates of extreme sea level events. In this study, we explore the causes of the observed sea level variability in the midlatitude South Pacific on interannual time scales using observations and atmospheric reanalyses combined with a 1.5 layer reduced-gravity model. We focus on the 2004–2020 period, during which the Argo's global array allowed us to assess year-to-year changes in steric sea level caused by thermohaline changes in different depth ranges (from the surface down to 2000 m). We find that during the 2015–2016 El Niño and the following 2017–2018 La Niña, large variations in thermosteric sea level occurred due to temperature changes within the 100–500 dbar layer in the midlatitude southwest Pacific. In the western boundary region (from 30°S to 40°S), the variations in halosteric sea level between 100 and 500 dbar were significant and could have partially balanced the corresponding changes in thermosteric sea level. We show that around 35°S, baroclinic Rossby waves forced by the open-ocean wind-stress forcing account for 40 to 75% of the interannual sea level variance between 100°W and 180°, while the influence of remote sea level signals generated near the Chilean coast is limited to the region east of 100°W. The contribution of surface heat fluxes on interannual time scales is also considered and shown to be negligible. [ABSTRACT FROM AUTHOR]

The South Pacific Ocean is emerging as an arena of U.S.-China strategic competition while the practices of the two countries in some areas suggest that the model of cooperation could benefit the regional States. It is hard to foresee whether competition or cooperation will drive the future development of the South Pacific or whether the two phenomena may co-exist. It is determined not only by policies taken by the two States themselves and their perspective engagements with both external stakeholders and regional States. Also, it is critical to understand how the regional states view the United States and China and how they are responding to U.S.-China competition. [ABSTRACT FROM AUTHOR]

We report for the first time the presence of local populations of the starfish Odontaster penicillatus in the regions of Atacama and Antofagasta, Chile. This finding indicates an extension of the distribution limit of 500 km with respect to the last observation made in 2007 in Isla Grande de Atacama. A total of 121 specimens of O. penicillatus were recorded at depths of between 8 m and 24 m. They were associated with rocky substrate and with different species of barnacles, sponges and bryozoans. The presence of O. penicillatus expands the knowledge of the benthic biodiversity of the region, and the development of studies on its ecological importance will be promoted. [ABSTRACT FROM AUTHOR]

Hydrothermal vents are a source of many trace metals to the oceans. Compared to mid-ocean ridges, hydrothermal vent systems at arcs occur in shallower water depth and are much more diverse in fluid composition, resulting in highly variable water column trace metal concentrations. However, only few studies have focused on trace metal dynamics in hydrothermal plumes at volcanic arcs. During R/V Sonne cruise SO253 in 2016/2017, hydrothermal plumes from two hydrothermally active submarine volcanoes along the Kermadec arc in the Southwest Pacific Ocean were sampled: (1) Macauley, a magmatic dominated vent site located in water depths between 300 and 680 m, and (2) Brothers, located between 1,200 and 1,600 m water depth, where hydrothermalism influenced by water rock interactions and magmatically influenced vent sites occur near each other. Surface currents estimated from satellite-altimeter derived currents and direct measurements at the sites using lowered acoustic Doppler current profilers indicate the oceanic regime is dominated by mesoscale eddies. At both volcanoes, results indicated strong plumes of dissolved trace metals, notably Mn, Fe, Co, Ni, Cu, Zn, Cd, La, and Pb, some of which are essential micronutrients. Dissolved metal concentrations commonly decreased with distance from the vents, as to be expected, however, certain element/Fe ratios increased, suggesting a higher solubility of these elements and/or their stronger stabilization (e.g., for Zn compared to Fe). Our data indicate that at the magmatically influenced Macauley and Brothers cone sites, the transport of trace metals is strongly controlled by sulfide nanoparticles, while at the Brothers NW caldera wall site iron oxyhydroxides seem to dominate the trace metal transport over sulfides. Solution stabilization of trace metals by organic complexation appears to compete with particle adsorption processes. As well as extending the generally sparse data set for hydrothermal plumes at volcanic arc systems, our study presents the first data on several dissolved trace metals in the Macauley system, and extends the existing plume dataset of Brothers volcano. Our data further indicate that chemical signatures and processes at arc volcanoes are highly diverse, even on small scales.

Over the past few decades, the global mean sea level rise and superimposed regional fluctuations of sea level have exerted considerable stress on coastal communities, especially in low-elevation regions such as the Pacific Islands in the western South Pacific Ocean. This made it necessary to have the most comprehensive understanding of the forcing mechanisms that are responsible for the increasing rates of extreme sea level events. In this study, we explore the causes of the observed sea level variability in the midlatitude South Pacific on interannual time scales using observations and atmospheric reanalyses combined with a 1.5 layer reduced-gravity model. We focus on the 2004–2020 period, during which the Argo’s global array allowed us to assess year-to-year changes in steric sea level caused by thermohaline changes in different depth ranges (from the surface down to 2000 m). We find that during the 2015–2016 El Niño and the following 2017–2018 La Niña, large variations in thermosteric sea level occurred due to temperature changes within the 100–500 dbar layer in the midlatitude southwest Pacific. In the western boundary region (from 30°S to 40°S), the variations in halosteric sea level between 100 and 500 dbar were significant and could have partially balanced the corresponding changes in thermosteric sea level. We show that around 35°S, baroclinic Rossby waves forced by the open-ocean wind-stress forcing account for 40 to 75% of the interannual sea level variance between 100°W and 180°, while the influence of remote sea level signals generated near the Chilean coast is limited to the region east of 100°W. The contribution of surface heat fluxes on interannual time scales is also considered and shown to be negligible.

Purpose: The nematode Ascarophis distorta Fusco et Overstreet, 1978 (Cystidicolidae), originally described from the butterflyfish Chaetodon paucifasciatus Ahl (Perciformes, Chaetodontidae) in the Red Sea, was established based solely on the light microscopical (LM) examination of specimens. However, the present taxonomy of cystidicolid nematodes is mostly based on details of the cephalic structures properly visible only with the use of scanning electron microscopy (SEM). Methods: Helminthological examinations of some marine fishes from coral reefs off New Caledonia, South Pacific, carried out in the years 2003–2007, revealed the presence of A. distorta in two Chaetodon spp. and thus enabled its redescription. The nematode specimens were studied with the use of both LM and SEM. Results: The specimens of A. distorta were obtained from the stomach of the threadfin butterflyfish Chaetodon auriga Forsskål and the vagabond butterflyfish Chaetodon vagabundus Linnaeus. This is just the second record of this parasite since its description 43 years ago. SEM, used in this species for the first time, revealed some taxonomically important, previously unreported or insufficiently described morphological features, such as details in the cephalic structure, the shape of deirids, structure of the distal tip of the left spicule, or the exact number and distribution of male caudal papillae. The finding of A. distorta in C. auriga and C. vagabundus off New Caledonia represents new host and geographical records. The examination of 39 specimens of butterflyfishes from off New Caledonia, belonging to 14 Chaetodon spp. and 3 Heniochus spp., revealed that the nematode was only present in the 2 fish species listed above. Conclusions: This parasite seems to be host-specific to only certain species of butterflyfishes (Chaetodon spp.), and is probably widespread in the Indo-Pacific region, as well as its hosts. [ABSTRACT FROM AUTHOR]

During late 2019 and early 2020, Australia experienced one of the most active bushfire seasons that advected large emissions over the adjacent ocean. Herein, we present a comprehensive research on mixed atmospheric aerosol particulate pollution emitted by wildfires in the atmosphere and the ocean. Based on a wide range of physical and biochemical data, including the Aerosol Robotic Network, multi-satellite observations, and Argo floats, we investigated the spatio-temporal variations and mixed compositions of aerosol particles, deposition in the coastal waters of eastern Australia and the South Pacific Ocean, and biogeochemical responses in the water column. Four types of wildfire-derived mixed particles were classified by using the optical properties of aerosols into four types, including the background aerosols, mineral dust, wildfire smoke particles, and residual smoke. The coarse particles accounted for more than 60% of the mineral dust on 22 November 2019 in the Tasman Sea; afterwards, during the wildfire smoke episode from December 2019 to January 2020, the particles affected large areas of the atmosphere such as eastern Australia, the South Pacific Ocean, and South America. The maximum value of the aerosol optical depth reached 2.74, and the proportion of fine particles accounted for 98.9% in the smoke episode. Mineral dust and smoke particles from the fire emissions changed the particle composition in the surface ocean. Particle deposition accounted for increases in chlorophyll-a concentration (Chla) standardized anomaly up to maximum of 23.3 with a lag time of less than 8 days. In the vertical direction, float observations showed the impact of exogenous particles on the water column could up to 64.7 m deep, resulting in Chla of 1.85 mg/m3. The high Chla lasted for a minimum period of two months until it returned to normal level. [ABSTRACT FROM AUTHOR]

Abstract The occurrence of extreme precipitation events in New Zealand regularly results in devastating impacts to the local society and environment. An automated atmospheric river (AR) detection technique (ARDT) is applied to construct a climatology (1979–2019) of extreme midlatitude moisture fluxes conducive to extreme precipitation. A distinct seasonality exists in AR occurrence aligning with seasonal variations in the midlatitude jet streams. The formation of the Southern Hemisphere winter split jet enables AR occurrence to persist through all seasons in northern regions of New Zealand, while southern regions of the country exhibit a substantial (50%) reduction in AR occurrence as the polar jet shifts southward during the cold season. ARs making landfall on the western coast of New Zealand (90% of all events) are characterized by a dominant northwesterly moisture flux associated with a distinct dipole pressure anomaly, with low pressure to the southwest and high pressure to the northeast of New Zealand. Precipitation totals during AR events increase with AR rank (five-point scale) throughout the country, with the most substantial increase on the windward side of the Southern Alps (South Island). The largest events (rank 5 ARs) produce 3-day precipitation totals exceeding 1000 mm. ARs account for up to 78% of total precipitation and up to 94% of extreme precipitation on the west coast of the South Island. Assessment of the multiscale atmospheric processes associated with AR events governing extreme precipitation in the Southern Alps of New Zealand should remain a priority given their hydrological significance and impact on people and infrastructure. [ABSTRACT FROM AUTHOR]

The sea surface temperature (SST) and upper-ocean heat content (OHC) have been explored along the track of two tropical cyclones (TCs): TC Pam (2015) and TC Winston (2016). These TCs severely affected the islands of Vanuatu and Fiji, in the South Pacific region (8°–30°S, 140°E−170°W). The SST decreased by as much as 5.4°C along the tracks of the TCs with most cooling occurring to the left of the TCs tracks relative to TC motion. SST cooling of 1°–5°C has generally been observed during both the forced and relaxation stages of TC passage. Argo profiles near the TCs revealed observable temperature-based mixed layer deepening. Subsurface warming was also observed post-TC passage from the temperature profile of one of the floats after the passage of both TCs. The OHC and heat fluxes are seen to play an important part in TC intensification as both these TCs intensified after passing over regions of high OHC and enhanced heat fluxes. Apart from the traditionally used OHC obtained up to the depth of the 26°C isotherm (QH), the OHC was also determined up to the depth of the 20°C isotherm (QH,20). The QH and QH,20 values decreased in the majority of cases post TC passage while QH,20 increased in one instance post-TC passage for both the TCs. QH,20 was also used to identify heat energy changes at deeper levels and it correlated well with the traditionally used OHC during the weaker stages of the TCs. [ABSTRACT FROM AUTHOR]

Synoptic-scale moisture transport during large snowfall events in the New Zealand Southern Alps is largely unknown due to a lack of long-term snow observations. In this study, records from three recently developed automatic weather stations (Mahanga, Mueller Hut, and Mt Larkins) near the Main Divide of the Southern Alps were used to identify large snowfall events between 2010 and 2018. The large snowfall events are defined as those events with daily snow depth increase by greater than the 90th percentile at each site. ERA-Interim reanalysis data were used to characterize the hydrometeorological features of the selected events. Our findings show that large snowfall events in the Southern Alps generally coincide with strong fields of integrated vapor transport (IVT) within a northwesterly airflow and concomitant deepening low pressure systems. Considering the frequency of large snowfall events, approximately 61% of such events at Mahanga were associated with narrow corridors of strong water vapor flux, known as atmospheric rivers (ARs). The contributions of ARs to the large snowfall events at Mueller Hut and Mt Larkins were 70% and 71%, respectively. Analysis of the vertical profiles of moisture transport dynamics during the passage of a landfalling AR during 11–12 October 2016 revealed the key characteristics of a snow-generating AR in the Southern Alps. An enhanced presence of low- and midlevel moisture between 700 and 850 hPa and pronounced increases of wind velocities (more than 30 m s−1) with high values of the meridional component between 750 and 850 hPa were identified over the Southern Alps during the event. [ABSTRACT FROM AUTHOR]

The destructive nature of tropical cyclones poses a risk to the regions where they occur during and after landfall. Southern hemisphere countries are usually more vulnerable to these risks and impacts due to their lower adaptive capacity. Research for the northern hemisphere has comprehensively explored the nature of tropical cyclones. This information has since been applied to long‐term adaptation plans and short‐term evacuation plans. This study interrogates the characteristics and nature of Southern Hemisphere tropical cyclones and critically explores their differences to Northern Hemisphere storm characteristics. The differences found between the hemispheric storm activities include seasonality, number of storms and the latitudinal position at which these storms undergo genesis and intensification. Similarities were found in storm intensity, which was observed to increase with the time taken to reach maximum lifetime intensity. Higher sea surface temperatures were similarly found to be a major factor associated with increased intensity and lifetime of Southern Hemisphere tropical cyclones. Tropical cyclone seasonality is also centred around the warmer months within each hemisphere. Compared to the Northern Hemisphere the tropical cyclone seasonal length indicates no increase. The magnitude of sea surface temperature increase is also lower in the Northern Hemisphere. These fundamental links observed with temperature in both hemispheres implicates climate warming and its impact on tropical cyclones in both hemispheres, regardless of their seasonality and frequency. [ABSTRACT FROM AUTHOR]

As climate change accelerates, effective adaptation is an urgent and unavoidable priority. Bottom-up approaches such as community-based adaptation have been portrayed as the panacea. Recent studies are, however, highlighting the ongoing and inherent issues with normative "community" conceptualizations that assume a geographically bound, temporally fixed, and harmonious unit. Despite documentation on the negative impact these problematic assumptions can have on adaptation outcomes, adaptation at the community scale remains the preferred option for project delivery in highly exposed places such as the Pacific Islands region. More creative entry points that are less charged with problematic assumptions are needed at the local scale. This paper draws from three examples in Vanuatu to offer compelling alternative entry points for adaptation: 1) a rural technical college embedded within an Anglican mission village, 2) a whole-of-island approach, and 3) the "collective of vendors" at marketplaces. We offer hope by identifying ways to expand on and complement existing, restricted notions of community and, through this, to improve adaptation outcomes. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential element for life and controls the magnitude of primary productivity in the ocean. In order to describe the microorganisms that catalyze N transformations in surface waters in the South Pacific Ocean, we collected high-resolution biotic and abiotic data along a 7000 km transect, from the Antarctic ice edge to the equator. The transect, conducted between late Austral autumn and early winter 2016, covered major oceanographic features such as the polar front (PF), the subtropical front (STF) and the Pacific equatorial divergence (PED). We measured N2 fixation and nitrification rates and quantified the relative abundances of diazotrophs and nitrifiers in a region where few to no rate measurements are available. Even though N2 fixation rates are usually below detection limits in cold environments, we were able to measure this N pathway at 7/10 stations in the cold and nutrient rich waters near the PF. This result highlights that N2 fixation rates continue to be measured outside the well-known subtropical regions. The majority of the mid to high N2 fixation rates (>∼20 nmol L–1 d–1), however, still occurred in the expected tropical and subtropical regions. High throughput sequence analyses of the dinitrogenase reductase gene (nifH) revealed that the nifH Cluster I dominated the diazotroph diversity throughout the transect. nifH gene richness did not show a latitudinal trend, nor was it significantly correlated with N2 fixation rates. Nitrification rates above the mixed layer in the Southern Ocean ranged between 56 and 1440 nmol L–1 d–1. Our data showed a decoupling between carbon and N assimilation (NO3– and NH4+ assimilation rates) in winter in the South Pacific Ocean. Phytoplankton community structure showed clear changes across the PF, the STF and the PED, defining clear biomes. Overall, these findings provide a better understanding of the ecosystem functionality in the South Pacific Ocean across key oceanographic biomes.

Climate change, malnutrition, and noncommunicable diseases (NCDs) are three of the most significant health challenges of this century, and they share fundamental underlying drivers. Pacific Island countries (PICs) are at the forefront of the impacts of climate change, which is likely to affect food and nutrition security (FNS) directly and indirectly, and many countries have existing high NCD burdens. This paper surveys the climate change adaptation (CCA) landscape in one PIC, Vanuatu. It explores the extent to which FNS and diet-related NCDs are considered and addressed within CCA initiatives. A comprehensive review of the literature related to CCA, FNS, and NCDs in Vanuatu was combined with 32 semistructured interviews with key experts and stakeholders. This study found that some promising groundwork has been laid for tackling the effects of climate change on FNS in policy and governance, agriculture, coastal management, and nutrition. However, several opportunities for strengthening CCA were identified: targeting urban populations; complementary integration of disaster risk reduction and CCA; incorporating local knowledge; applying a systems-based framing of NCDs as climate-sensitive health risks; and emphasizing humancentered, community-led CCA. Vanuatu will continue to be affected by accelerating climate change. A strong foundation for CCA presents clear opportunities for further development. As food and nutrition insecurity and diet-related NCD risk factors are increasingly exacerbated by climate change, alongside other socioeconomic drivers, it is crucial to find new and innovative ways to increase transformational resilience and adaptive capacity that also improve nutrition and health outcomes. [ABSTRACT FROM AUTHOR]

Understanding multiscale rainfall variability in the South Pacific convergence zone (SPCZ), a southeastward-oriented band of precipitating deep convection in the South Pacific, is critical for both the human and natural systems dependent on its rainfall, and for interpreting similar off-equatorial diagonal convection zones around the globe. A k-means clustering method is applied to daily austral summer (December–February) Tropical Rainfall Measuring Mission (TRMM) satellite rainfall to extract representative spatial patterns of rainfall over the SPCZ region for the period 1998–2013. For a k = 4 clustering, pairs of clusters differ predominantly via spatial translation of the SPCZ diagonal, reflecting either warm or cool phases of El Niño–Southern Oscillation (ENSO). Within each of these ENSO phase pairs, one cluster exhibits intense precipitation along the SPCZ while the other features weakened rainfall. Cluster temporal behavior is analyzed to investigate higher-frequency forcings (e.g., the Madden–Julian oscillation and synoptic-scale disturbances) that trigger deep convection where SSTs are sufficiently warm. Pressure-level winds and specific humidity from the Climate Forecast System Reanalysis are composited with respect to daily cluster assignment to investigate differences between active and quiescent SPCZ conditions to reveal the conditions supporting enhanced or suppressed SPCZ precipitation, such as low-level poleward moisture transport from the equator. Empirical orthogonal functions (EOFs) of TRMM precipitation are computed to relate the "modal view" of SPCZ variability associated with the EOFs to the "state view" associated with the clusters. Finally, the cluster number is increased to illustrate the change in TRMM rainfall patterns as additional degrees of freedom are permitted. [ABSTRACT FROM AUTHOR]

Albacore tuna (Thunnus alalunga) exhibit patchy concentrations associated with biological process at a wide range of spatial scales, resulting in variations in their catchability by fishing gears. Here, we investigated the association of catch variation for pelagic longlines in the South Pacific Ocean with oceanographic mesoscale structures (in horizontal dimension) and ambient conditions (in vertical dimension). The distribution of albacore tuna as indicated by catch per unit effort (CPUE) of longlines was significantly related to the presence of mesoscale structures, with higher CPUE found at locations closer to thermal fronts and with greater gradient magnitudes, as well as areas marked by peripheral contour line of the anticyclone indicated by Sea Surface Height Anomalies ~0.05 m. Surface mesoscale current velocity had the negative effect on the catch, probably as a result of decreased catchability by shoaling the hook depth. Vertical distribution of albacore in the survey region of South Pacific Ocean was hardly restricted by ambient temperature and oxygen concentration, though effect of ambient temperature was relevant and showed a negatively linear correlation with CPUE at the range of 20–24°C. On the contrary, albacore distribution was evidently dominated by the water depth and showed strong preference on water depth of 200 m, which was likely a representative feeding layer. The presence of prey resources and their accessibility by albacore revealed by mesoscale structures in the biological and physical processes, and catchability determined by the location of the baited hooks comprehensively contribute to the variability of catch. [ABSTRACT FROM AUTHOR]

In the present study, we profiled bacterial and archaeal communities from 13 phylogenetically diverse deep-sea sponge species (Demospongiae and Hexactinellida) from the South Pacific by 16S rRNA-gene amplicon sequencing. Additionally, the associated bacteria and archaea were quantified by real-time qPCR. Our results show that bacterial communities from the deep-sea sponges are mostly host-species specific similar to what has been observed for shallow-water demosponges. The archaeal deep-sea sponge community structures are different from the bacterial community structures in that they are almost completely dominated by a single family, which are the ammonia-oxidizing genera within the Nitrosopumilaceae. Remarkably, the archaeal communities are mostly specific to individual sponges (rather than sponge-species), and this observation applies to both hexactinellids and demosponges. Finally, archaeal 16s gene numbers, as detected by quantitative real-time PCR, were up to three orders of magnitude higher than in shallow-water sponges, highlighting the importance of the archaea for deep-sea sponges in general. [ABSTRACT FROM AUTHOR]

The Southern Ocean features ventilation pathways that transport surface waters into the subsurface thermocline on time scales from decades to centuries, sequestering anomalies of heat and carbon away from the atmosphere and thereby regulating the rate of surface warming. Despite its importance for climate sensitivity, the factors that control the distribution of heat along these pathways are not well understood. In this study, we use an observationally constrained, physically consistent global ocean model to examine the sensitivity of heat distribution in the recently ventilated subsurface Pacific (RVP) sector of the Southern Ocean to changes in ocean temperature and salinity. First, we define the RVP using numerical passive tracer release experiments that highlight the ventilation pathways. Next, we use an ensemble of adjoint sensitivity experiments to quantify the sensitivity of the RVP heat content to changes in ocean temperature and salinity. In terms of sensitivities to surface ocean properties, we find that RVP heat content is most sensitive to anomalies along the Antarctic Circumpolar Current (ACC), upstream of the subduction hotspots. In terms of sensitivities to subsurface ocean properties, we find that RVP heat content is most sensitive to basin-scale changes in the subtropical Pacific Ocean, around the same latitudes as the RVP. Despite the localized nature of mode water subduction hotspots, changes in basin-scale density gradients are an important controlling factor on heat distribution in the southeast Pacific. [ABSTRACT FROM AUTHOR]

Atlantid heteropods are a family of holoplanktonic marine gastropods that occur primarily in tropical and subtropical latitudes. Atlantids bear a delicate aragonitic shell (<14 mm) and live in the upper ocean, where ocean acidification and ocean warming have a pronounced effect. Therefore, atlantids are likely to be sensitive to these ocean changes. However, we lack sufficiently detailed information on atlantid taxonomy and biogeography, which is needed to gain a deeper understanding of the consequences of a changing ocean. To date, atlantid taxonomy has mainly relied on morphometrics and shell ornamentation, but recent molecular work has highlighted hidden diversity. This study uses an integrated approach in a global analysis of biogeography, variation in shell morphology and molecular phylogenies based on three genes (CO1, 28S and 18S) to resolve the species boundaries within the Atlanta brunnea group. Results identify a new species, Atlanta vanderspoeli, from the Equatorial and South Pacific Ocean, and suggest that individuals of A. brunnea living in the Atlantic Ocean are an incipient species. Our results provide an important advance in atlantid taxonomy and will enable identification of these species in future studies of living and fossil plankton. [ABSTRACT FROM AUTHOR]

Diet and morphospace of larval stages of two sympatric lanternfish Diogenichthys atlanticus and D. laternatus from the south‐east Pacific Ocean were compared and the covariance between both variables was assessed for each species. Diogenichthys atlanticus stomach contents consisted mainly of copepod nauplii and digested remains and this species had a broader niche than D. laternatus, in which stomach contents were highly digested. No dietary overlap was found between both species. The covariance between skull shape and diet for D. atlanticus was given by a wider mouth gape related to the presence of copepod nauplii, whilst for D. laternatus, a shorter snout and posteriorly displaced eye were related to the presence of highly digested stomach contents. Interspecific differences between diets and skull shapes suggest that both species may have undergone morphological or niche divergence to avoid competition, such as feeding at different hours or depth stratification. [ABSTRACT FROM AUTHOR]

High-throughput sequencing is revolutionizing our ability to comprehensively characterize free-living and symbiotic Symbiodiniaceae, a diverse dinoflagellate group that plays a critical role in coral reef ecosystems. Most studies however, focus on a single marker for metabarcoding Symbiodiniaceae, potentially missing important ecological traits that a combination of markers may capture. In this proof-of-concept study, we used a small set of symbiotic giant clam (Tridacna maxima) samples obtained from nine French Polynesian locations and tested a dual-index sequence library preparation method that pools and simultaneously sequences multiple Symbiodiniaceae gene amplicons per sample for in-depth biodiversity assessments. The rationale for this approach was to allow the metabarcoding of multiple genes without extra costs associated with additional single amplicon dual indexing and library preparations. Our results showed that the technique effectively recovered very similar proportions of sequence reads and dominant Symbiodiniaceae clades among the three pooled gene amplicons investigated per sample, and captured varying levels of phylogenetic resolution enabling a more comprehensive assessment of the diversity present. The pooled Symbiodiniaceae multi-gene metabarcoding approach described here is readily scalable, offering considerable analytical cost savings while providing sufficient phylogenetic information and sequence coverage.

• Nine years of glider transects measure the transport across the Solomon Sea. • Seasonal and ENSO fluctuations are 25–50% of the mean. • A linear wind-driven model identifies distinct wind forcing driving the anomalies. • Interannual temperature advection through the sea influences the equatorial Pacific. The Solomon Sea carries the equatorward western boundary current of the South Pacific, a principal element of subtropical-equatorial communication. Eighty-seven glider transects across the mouth of the Sea over nine years describe the velocity structure and variability of this system. The time series spans two El Niños and two La Niñas, which produced large transport anomalies, up to 50% of the mean. While transport increased during El Niños and decreased during La Niñas, their signatures were inconsistent among the events. Separated glider tracks show the merging of two inflows, one from the tropics east of the Solomon Island chain, the other entering as a western boundary current generated by winds over the full subtropical gyre. A model of linear wind-driven dynamics, including western boundary currents, had skill in describing the variability of the two inflows, identifying the distinct wind forcing driving each. The model suggests that both the mean and low-frequency variability of flow entering the Solomon Sea are driven remotely by wind over the South Pacific, acting through long Rossby waves. The ultimate significance of in situ observations in this small sea will be to describe its role in subtropical-tropical heat exchange that is crucial to ENSO and longer-timescale climate variations along the equator. We take an initial step here, suggesting that temperature advection through the Solomon Sea is a first-order contribution to interannual temperature changes of the equatorial strip as a whole. [ABSTRACT FROM AUTHOR]

This paper describes how a combination of high-resolution numerical modeling, a robust homogenization algorithm, and local pressure observations have been used to understand and reconcile time series of daily, seasonal, and annual peak wind gusts recorded at observing sites in the Cook Strait region of New Zealand. The homogenization algorithm consists of corrections for the relocation of masts, changes in instrumentations, data acquisition and signal processing, surrounding surface roughness, and measurement heights. In addition, a statistical method, penalized maximal F test (PMFT), was used to assess the homogeneity of the wind speed time series and detect and eliminate all remaining, undocumented, artificial (i.e., nonclimatic) breakpoints. A three-dimensional time-dependent computational fluid dynamics (CFD) simulation was carried out using the Gerris model to characterize the turbulence environment at the mast sites and to estimate topographic speedup effects. Trends in magnitudes and frequencies of the homogenized seasonal and annual peak wind gusts are evaluated and presented for the Cook Strait region. The pressure gradients between pairs of stations were used to study the correlation between the gust wind speeds and the pressure field. A high-resolution convection-resolving numerical weather prediction model [the New Zealand Convective-Scale Model (NZCSM)] was employed to aid the interpretation of results and analyze wind trends. The trend in gust speeds is also shown to be consistent with larger-scale NCEP–NCAR reanalysis pressure trends. The homogenization algorithm showed promising results in eliminating the artificial breakpoints and trends. Overall, strong correlations were found between the homogenized gust speeds, the pressure field across the region, and NZCSM predictions. [ABSTRACT FROM AUTHOR]

Abstract The Cd isotopic analysis of waters from an increasing number of oceanic regions has provided a wealth of new information on the oceanic cycling of Cd, revealing the complex interplay of a multitude of different biogeochemical processes. In this study, paired Cd concentration and Cd isotopic measurements were made on samples collected during the GEOTRACES GP-13 zonal section in the South West Pacific Ocean. The South Pacific subtropical gyre is the most oligotrophic gyre in the global ocean and a unique area to study the Cd isotope systematics associated with phytoplankton productivity under ultra-low nutrient concentrations. The dissolved Cd and PO 4 concentrations of the study area are well correlated and can be expressed by two different linear relationships, as observed in other oceanic regions. The near quantitative biological uptake of Cd in the upper water column and the mixing of different water masses with different pre-formed Cd/PO 4 ratios likely produces the 'kink' in the Cd–PO 4 relationship. Across the GP-13 zonal section, the Cd isotopic composition of deep waters is relatively constant, as observed in other regions, and is centred around a δ 114 Cd value of 0.26 ± 0.11‰ (2 SD, n = 40). In contrast, across the thermocline depth range, extending from 150 to 1500 m depth, the Cd concentration and δ 114 Cd values are negatively correlated and best described by Cd isotope fractionation under open-system conditions with continuous replenishment of the Cd source/s and a fractionation factor of 1.0006 ± 0.0002. This contrasts with the closed-system conditions without Cd replenishment that have been used to describe some other open ocean settings. Below 500 m depth, the Cd isotope systematics can largely be explained by three component mixing between key water masses with different pre-formed Cd isotope signatures. However, above 500 m, the Cd isotope systematics appear to be influenced by both water mass mixing and the biological uptake of isotopically light Cd in local and remote surface waters and the regeneration of Cd from sinking organic material deeper in the water column. Additionally, an unusual positive correlation was observed between Cd concentration and Cd isotopic composition in the upper water column of the South Pacific Ocean, from 15 to 150–200 m depth. These systematics can potentially be explained by one, or a combination, of the following processes: (i) a dominant role of supply-limited conditions during Cd uptake, (ii) partitioning of Cd into ligand phases, and/or (iii) atmospheric sources of Cd in these oligotrophic waters. Although subject to uncertainty, flux calculations suggest that atmospheric input could contribute 10–83% of the total Cd input to the surface waters of the subtropical South Pacific gyre. Highlights • Mixing of water masses with different Cd/PO 4 control the Cd–PO 4 relationship. • Open-system Cd uptake in thermocline waters of the oligotrophic South Pacific Ocean. • Mixing of water masses controls Cd isotope signatures below 500 m depth. • Biological uptake dominates Cd isotope systematics above 500 m depth. • Atmospheric Cd is likely an important source to the oligotrophic upper mixed layer. [ABSTRACT FROM AUTHOR]

High-throughput sequencing is revolutionizing our ability to comprehensively characterize free-living and symbiotic Symbiodiniaceae, a diverse dinoflagellate group that plays a critical role in coral reef ecosystems. Most studies however, focus on a single marker for metabarcoding Symbiodiniaceae, potentially missing important ecological traits that a combination of markers may capture. In this proofof-concept study, we used a small set of symbiotic giant clam (Tridacna maxima) samples obtained from nine French Polynesian locations and tested a dual-index sequence library preparation method that pools and simultaneously sequences multiple Symbiodiniaceae gene amplicons per sample for in-depth biodiversity assessments. The rationale for this approach was to allow the metabarcoding of multiple genes without extra costs associated with additional single amplicon dual indexing and library preparations. Our results showed that the technique effectively recovered very similar proportions of sequence reads and dominant Symbiodiniaceae clades among the three pooled gene amplicons investigated per sample, and captured varying levels of phylogenetic resolution enabling a more comprehensive assessment of the diversity present. The pooled Symbiodiniaceae multi-gene metabarcoding approach described here is readily scalable, offering considerable analytical cost savings while providing sufficient phylogenetic information and sequence coverage. [ABSTRACT FROM AUTHOR]

Abstract To date, simulation-optimization (S/O) based groundwater management models have delivered optimal saltwater intrusion management strategies for coastal aquifer systems. At times, however, uncertainties in the numerical simulation model due to uncertain aquifer parameters are not incorporated into the management model. The present study explicitly incorporated aquifer parameter uncertainty into a multi-objective management model for the optimal design of groundwater pumping strategies from the unconfined Bonriki aquifer situated in a small Pacific island country. The objective of the multi-objective management model was to maximise pumping from production wells and minimize pumping from the barrier wells (hydraulic barriers) to ensure that the water quality at different monitoring locations (MLs) were within pre-specified sustainable limits. To achieve the targeted management goal, a coupled flow and transport numerical simulation model of the Bonriki aquifer was developed using the FEMWATER numerical code. The developed three-dimensional numerical model was calibrated and validated using limited available hydrological data. To achieve computational efficiency and feasibility of the management model, the numerical simulation model in the S/O model was replaced with ensembles of Support Vector Machine Regression (SVMR) surrogate models. Each SVMR standalone surrogate model in the ensemble was constructed using datasets from different numerical simulation models with different hydraulic conductivity and porosity values. These ensemble SVMR models were coupled to the multi-objective genetic algorithm optimization model to solve the Bonriki aquifer management problem. The executed optimization model presented a Pareto-front with 600 non-dominated optimal trade-off pumping solutions. The reliability of the management model established after validation of the optimal solution results suggests that the implemented constraints of the optimization problem were satisfied, i.e., the salinity concentrations at respective MLs were within the pre-specified limits. Overall, the results from this study indicated that the developed management model has the potential to address groundwater salinity problems in small island countries. Graphical abstract Image 1 Highlights • A groundwater numerical simulation model is developed for the Bonriki aquifer system. • Ensemble models are developed to incorporate aquifer parameter uncertainty. • The ensemble models are linked to the multi-objective genetic algorithm optimization model. • Optimal groundwater pumping patterns are presented based on the optimal Pareto-front. [ABSTRACT FROM AUTHOR]

Highlights • Fragile deep-sea sessile fauna can be impacted by bottom trawl fisheries. • Habitat suitability was modeled for vulnerable marine ecosystem indicator taxa. • Ensemble models performed better than individual models. • Models can help assess current and historical extent of bottom trawling impacts. • Habitat suitability modeling can support improved spatial management of fisheries. Abstract Resolutions of the United Nations General Assembly (UNGA) require states and competent authorities to protect vulnerable marine ecosystems (VMEs), ecologically important habitats in the deep sea that are considered to be especially at risk from anthropogenic disturbances such as fishing. The lack of data concerning the location and extent of VMEs poses a significant obstacle to their protection. Habitat suitability modeling is increasingly used in spatial management planning due to its ability to predict the distribution and niche of marine organisms based on limited input data. We generated broad-scale, medium-resolution (1 km2) ensemble models for ten VME indicator taxa within the New Zealand Exclusive Economic Zone and a portion of the South Pacific Regional Fishery Management Organisation (SPRFMO) convention area. Ensemble models were constructed using a weighted average of three habitat suitability model types: Boosted Regression Trees, Maximum Entropy, and Random Forest. All models performed well, with area under the curve scores above 0.9, and ensemble models marginally outperformed any of the individual modeling approaches. Highly suitable habitat for each VME indicator taxa was predicted to occur in relatively small areas throughout the region, typically associated with elevated seafloor features with steep slopes. Determining the spatial distribution of VME indicator taxa is critical for assessing the current and historical extent of bottom trawling impacts on benthic communities, and for supporting the improved spatial management of fisheries in the South Pacific Ocean. Given the additional threats of climate change and ocean acidification to VME indicator taxa throughout the deep sea, habitat suitability modeling is likely to play an increasing role in designing effective, long-term protection measures for cumulative impacts on VMEs. [ABSTRACT FROM AUTHOR]

The Pacific meridional mode, a thermodynamically coupled mode of variability, links extratropical Pacific oceanic and atmospheric anomalies to the tropical Pacific and may give rise to El Niño–Southern Oscillation (ENSO) events. While mechanistic studies on the impacts of the North Pacific meridional mode (NPMM) are prevalent in the literature, the South Pacific meridional mode (SPMM) has only recently been examined. Reanalysis and models from the archive of phase 5 of the Coupled Model Intercomparison Project (CMIP5) are used in this study to investigate further the SPMM and its role in ENSO predictability. Akin to the NPMM, the SPMM features anomalous subtropical South Pacific sea surface temperature (SST) warming in response to a weakened South Pacific subtropical high and relaxed trade winds. However, as opposed to the NPMM, the seasonality of the SPMM SST and wind components vary out of phase, in part because of the seasonal cycle of local mixed layer depth. Thus, the SPMM and the associated wind–evaporation–SST feedback are most energetic during austral summer, facilitating interaction with the concurrent NPMM conditions to regulate the occurrence, evolution, amplitude, and diversity of ENSO events. Parallel analyses with the CMIP5 models indicate that the models reasonably capture the temporal statistics and physical processes of the observed SPMM. Nonetheless, ENSO predictability within the models relies more on the slowly evolving equatorial ocean heat content than on the meridional modes. These findings reveal how the SPMM energizes components of ENSO variability, providing an additional benchmark for model evaluation of Pacific climate variability across multiple time scales. [ABSTRACT FROM AUTHOR]

The Oligotrophy to UlTra-oligotrophy PACific Experiment (OUTPACE) cruise took place in the western tropical South Pacific (WTSP) during the austral summer (March-April 2015). The aim of the OUTPACE project was to investigate a longitudinal gradient of biological and biogeochemical features in the WTSP, and especially the role of N2 fixation in the C, N, and P cycles. Two contrasted regions were considered in this study: the Western Melanesian Archipelago (WMA), characterized by high N2 fixation rates, significant surface production and low dissolved inorganic phosphorus (DIP) concentrations, and the South Pacific Gyre (WGY), characterized by very low N2 fixation rates, surface production and high DIP concentrations. Since physical forcings and mixed layer dynamics in both regions were similar, it was considered that the gradient of oligotrophy observed in situ between the WMA and WGY was not explained by differences in physical processes, but rather by differences in biogeochemical processes. A one-dimensional physical-biogeochemical coupled model was used to investigate the role of N2 fixation in the WTSP by running two identical simulations, only differing by the presence (simWMA) or absence (simWGY) of diazotrophs. We showed that the nitracline and the phosphacline had to be, respectively, deeper and shallower than the mixed layer depth (MLD) to bring Ndepleted and P-repleted waters to the surface during winter mixing, thereby creating favorable conditions for the development of diazotrophs. We also concluded that a preferential regeneration of the detrital phosphorus (P) matter was necessary to obtain this gap between the nitracline and phosphacline depths, as the nutricline depths significantly depend on the regeneration of organic matter in the water column. Moreover, the model enabled us to highlight the presence of seasonal variations in primary production and P availability in the upper surface waters in simWMA, where diazotrophs provided a new source of nitrogen (N) to the ecosystem, whereas no seasonal variations were obtained in simWGY, in the absence of diazotrophs. These main results emphasized the fact that surface production dynamics in the WTSP is based on a complex and sensitive system which depends on the one hand on physical processes (vertical mixing, sinking of detrital particles), and on the other hand on biogeochemical processes (N2 fixation, remineralization). [ABSTRACT FROM AUTHOR]

Helminthological examinations of three species of sharks, Galeocerdo cuvier, Triaenodon obesus (both Carcharhinidae, Carcharhiniformes) and Stegostoma fasciatum (Stegostomatidae, Orectolobiformes) from New Caledonian waters, carried out during 2003–2005, revealed the presence of three species of adult anisakid nematodes referable to Terranova Leiper et Atkinson, 1914. However, this genus can no longer be considered valid, because its type species has been designated a species inquirenda. Therefore, the present nematodes are assigned to two newly established genera, Euterranova n. gen. [type species E. dentiduplicata n. sp.] and Neoterranova n. gen. [type species N. scoliodontis (Baylis, 1931) n. comb.], based mainly on different labial structures. Euterranova dentiduplicata n. sp. from the stomach of S. fasciatum is mainly characterized by the presence of lips with two rows of denticles. Innominate specimens of Euterranova (a female and a third-stage larva) were collected from the digestive tract of T. obesus. Specimens of N. scoliodontis were recorded from G. cuvier. The two named species are described based on light and scanning electron microscopical examinations. Neoterranova scoliodontis has previously been recorded in New Caledonian waters from the same host species. Species previously attributed to Terranova are transferred to Euterranova (5 species), Neoterranova (4 species) or considered species inquirendae (10 species). Since Pseudoterranova Mozgovoy, 1950 was found to be a nomen nudum according to the International Code of Zoological Nomenclature (ICZN), the available name of this genus is Pseudoterranova Mozgovoy, 1953. A key to Porrocaecum-like nematode genera (Porrocaecum, Pseudoterranova, Pulchrascaris, Euterranova, and Neoterranova) is provided.