Southeast Indian Ocean Research Articles

The life history characteristics of Neosebastes pandus and the relationship between sexually dimorphic growth and reproductive strategy among Scorpaeniformes.

Scorpaeniformes are an important component of commercial and recreational fisheries world-wide. The Neosebastes species, found in the western Pacific and south-east Indian Ocean, have received little attention from a research perspective. Samples of the bighead gurnard perch, Neosebastes pandus, collected from the lower west and south coasts of Western Australia, were used to undertake the first comprehensive investigation of the biological characteristics of a Neosebastes species. Opaque zones in sectioned sagittal otoliths were validated as forming annually. Female N. pandus grow to a significantly larger size, on average, than males and dominate the largest size classes, while males, growing to a smaller size, accumulate in the intermediate size classes. Although males were far less numerous than females in those age classes in which both sexes were found, males and females attain similar maximum ages >25 years. Neosebastes pandus spawns over a brief period between May (austral late autumn) and July (austral mid-autumn) when water temperature and day length are declining. The mean monthly gonadosomatic indices (GSI, IGS ) values of females during the spawning period are 37-50 times higher than those of males, which mature at an earlier age and smaller length compared to females. Histological examination of the ovaries of females indicate that their structure is consistent with "general" teleost ovarian anatomy and thus differs from Scorpaena, Helicolenus and Sebastes species whose ovaries are adapted for specialized reproductive modes. The reproductive strategy of N. pandus of maximizing the reproductive output of females, by this sex attaining a larger size than males and pair spawning (i.e., large disparity in IGS values) demonstrates the close lineage between the Neosebastes and other Scorpaeniformes, such as the Scorpaena, Helicolenus and Sebastes.

Anatomy of the Indian Summer Monsoon and ENSO relationships in state-of-the-art CGCMs: role of the tropical Indian Ocean

Indian Summer Monsoon (ISM) rainfall and El Nino-Southern Oscillation (ENSO) exhibit an inverse relationship during boreal summer, which is one of the roots of ISM interannual variability and its seasonal predictability. Here we document how current climate and seasonal prediction models simulate the timing and amplitude of this ISM-ENSO teleconnection. Many Coupled General Circulation Models (CGCMs) do simulate a simultaneous inverse relationship between ENSO and ISM, though with a large spread. However, most of them show significant negative correlations before ISM, which are at odd with observations. Consistent with this systematic error, simulated Nino-3.4 Sea Surface Temperature (SST) variability has erroneous high amplitude during boreal spring and ISM rainfall variability is also too strong during the first part of ISM. The role of the Indian Ocean (IO) in modulating the ISM-ENSO relationships is further investigated using dedicated experiments with the SINTEX-F2 CGCM. Decoupled tropical Pacific and IO experiments are conducted to assess the direct relationship between ISM and IO SSTs on one hand, and the specific role of IO feedback on ENSO on the other hand. The direct effect of IO SSTs on ISM is weak and insignificant at the interannual time scale in the Pacific decoupled experiment. On the other hand, IO decoupled experiments demonstrate that El Nino shifts rapidly to La Nina when ocean–atmosphere coupling is active in the whole IO or only in its western part. This IO negative feedback is mostly active during the decaying phase of El Nino, which is accompanied by a basin-wide warming in the IO, and significantly modulates the length of ENSO events in our simulations. This IO feedback operates through a modulation of the Walker circulation over the IO, which strengthens and shifts eastward an anomalous anticyclone centered on the Philippine Sea and associated easterly wind anomalies in the equatorial western Pacific during boreal winter. In turn, these atmospheric anomalies lead to a fast ENSO turnabout via oceanic adjustement processes mediated by eastward propagating upwelling Kelvin waves. An experiment in which only the SouthEast Indian Ocean (SEIO) is decoupled, demonstrates that the equatorial SST gradient in the IO during boreal winter plays a fundamental role in the efficiency of IO feedback. In this experiment, simulated ISM-ENSO lead-lag correlations match closely the observations. This success is associated with removal of erroneous SEIO SST variability during boreal winter in the SEIO decoupled experiment. Finally, it is illustrated that most CMIP5 CGCMs exhibit similar SST errors in the SEIO during boreal winter in addition to an exagerated SEIO SST variability during boreal fall.

Large-scale asymmetry in thickness of crustal accretion at the Southeast Indian Ridge due to deep mantle anomalies

Abstract Hot mantle plumes and ancient cold slabs have been observed beneath modern mid-ocean ridges, but their specific and detailed effects on mid-ocean ridge crustal accretion are poorly understood. The oceanic lithosphere beneath the Southeast Indian Ocean displays unique morphological, geophysical, and geochemical characteristics, which may reflect the influence of both mantle anomalies and upwelling plumes on seafloor spreading. In this study, we combined gravity-derived oceanic crustal thickness with plate tectonic reconstructions to investigate patterns of asymmetry in thickness of crust accreted at the Southeast Indian Ridge over the last 50 m.y. Our results reveal several distinct features: (1) small-scale, short-lived asymmetries in the thickness of crustal accretion of up to 0.75 km are alternatively distributed on the southern and northern flanks of the 90°–120°E Southeast Indian Ridge segment. These can be explained by variations in mantle depletion or mantle temperature. (2) Two large-scale, long-lived (duration of ∼50 m.y.) asymmetries in crustal accretion of >2.5 km are observed around the Kerguelen Plateau and Balleny Islands, which we attribute to excess crust from the off-axis Kerguelen and Balleny mantle plumes. (3) Two large-scale, long-lived (duration of ∼50 m.y.) asymmetries in crustal accretion of 0.75–2.5 km are observed on the northern flank of the westernmost (70°–80°E) Southeast Indian Ridge and the southern flank of the eastern (120°–140°E) Southeast Indian Ridge segment, respectively. We attribute these to asymmetry in mantle temperature of up to 20–53 °C. We suggest these asymmetric temperatures across the Southeast Indian Ridge are associated with the foundered lithospheric fragments of the Indian Craton triggered by the African Large Low-Shear-Velocity Province during the breakup of Gondwanaland and an intraplate subducted slab of the Paleo-Tethys Ocean, respectively. The remnant craton fragments and subducted oceanic slab may have moved north in concert with the northward-migrating Southeast Indian Ridge beginning at 50 m.y. ago.

Planktonic Foraminiferal Endemism at Southern High Latitudes Following the Terminal Cretaceous Extinction

AbstractAustral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/Pg) boundary at Ocean Drilling Program Hole 690C (Maud Rise, Weddell Sea) and International Ocean Drilling Program Hole U1514C (southeast Indian Ocean) show a much different record of post-extinction recovery than anywhere outside the circum-Antarctic region. Species of Woodringina and Parvularugoglobigerina, genera with well-documented evolutionary successions within the early Danian P0 and Pα biozones at tropical/subtropical and mid-latitude localities, are absent from southern high latitude sequences. This study proposes new criteria for biostratigraphic correlation of the lowermost Danian Antarctic Paleocene AP0 and AP1 Zones using stratophenetic observations from Scanning Electron Microscope images of lower Danian planktonic foraminifera at deep-sea sites in the southern South Atlantic and southern Indian Ocean. The small but distinctive species Turborotalita nikolasi (Koutsoukos) is a highly reliable index species for the lowermost Danian as it consistently occurs immediately above the K/Pg boundary at multiple southern high latitude sites, which is consistent with its distribution at middle and low latitudes. Also useful for cross-latitude correlation is Parasubbotina neanika n. sp., which first appears within the lowermost Danian worldwide. The geographic distribution of the New Zealand species Antarcticella pauciloculata (Jenkins) and Zeauvigerina waiparaensis (Jenkins), as well as Eoglobigerina maudrisensis n. sp. from just above the K/Pg in the southern South Atlantic and southern Indian Ocean, helps define the extent of the Austral Biogeographic Province and provides evidence for marine communication via marine seaways across Antarctica. While An. pauciloculata was previously considered a benthic species, new stable isotope evidence demonstrates that it lived a planktonic mode of life. It is possible this species evolved from a benthic ancestor and that the benthic to planktonic transition occurred through an intermediate tychopelagic lifestyle at a time when calcareous plankton were less abundant as a result of the terminal Cretaceous mass extinction.

Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

Abstract. Balloon-borne measurements of cryogenic frost-point hygrometer (CFH) water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory on Réunion Island in the southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on tropical tropopause layer (TTL) composition. The balloon launches were specifically planned using a Lagrangian model and Meteosat-7 infrared images to sample the convective outflow from tropical storm (TS) Corentin on 25 January 2016 and tropical cyclone (TC) Enawo on 3 March 2017. Comparing the CFH profile to Aura's Microwave Limb Sounder's (MLS) monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa), originated from convectively active regions of TS Corentin and TC Enawo 1 d before the planned balloon launches according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin's active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the southeast Indian Ocean where a monthly water vapor anomaly of 0.5 ppmv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the SWIO. It also demonstrates the need for accurate balloon-borne measurements of water vapor, ozone and aerosols in regions where TTL in situ observations are sparse.

Seasonal acoustic presence of blue, fin, and minke whales off the Juan Fernández Archipelago, Chile (2007–2016)

The southeast Pacific (SEP) contains the home ranges of several migratory large whale species, determined largely based on research in coastal waters. These whales’ pelagic seasonal residency is unknown. The Juan Fernandez Archipelago (JFA) is an offshore island in the SEP where passive acoustic monitoring (PAM) data collection is ongoing at the HA03 hydroacoustic station (sample rate of 250 Hz) maintained by the Preparatory Comprehensive Nuclear-Test-Ban Treaty Organization. Six years (2007–2009 and 2014–2016) of PAM data from HA03 were examined for the acoustic presence of Antarctic, Chilean (southeast Pacific 1, southeast Pacific 2), and southeast Indian Ocean blue whale song types; the fin whale 20-Hz song; and minke whale vocalizations. The weekly presence or absence of these six vocalization types was annotated manually by an expert analyst and then averaged across all years. For each vocalization type, the number of weeks per month with presence was averaged over all years. Consistently, we found austral wintertime presence of Antarctic blue, fin, and minke whales; and the year-round presence of Chilean blue whales. Southeast Indian Ocean blue whales were also detected, but very rarely. We discuss the possible seasonal movements of each species or acoustic group in the offshore SEP. This is the first year-round multispecies study of baleen whale in the offshore SEP and provides valuable information for understanding the migrations of endangered baleen whales in this region, highlighting the importance of offshore areas as hotspots for baleen whale biodiversity.

Vertical Structure of the Upper–Indian Ocean Thermal Variability

AbstractMulti-time-scale variabilities of the Indian Ocean (IO) temperature over 0–700 m are revisited from the perspective of vertical structure. Analysis of historical data for 1955–2018 identifies two dominant types of vertical structures that account for respectively 70.5% and 21.2% of the total variance on interannual-to-interdecadal time scales with the linear trend and seasonal cycle removed. The leading type manifests as vertically coherent warming/cooling with the maximal amplitude at ~100 m and exhibits evident interdecadal variations. The second type shows a vertical dipole structure between the surface (0–60 m) and subsurface (60–400 m) layers and interannual-to-decadal fluctuations. Ocean model experiments were performed to gain insights into underlying processes. The vertically coherent, basinwide warming/cooling of the IO on an interdecadal time scale is caused by changes of the Indonesian Throughflow (ITF) controlled by Pacific climate and anomalous surface heat fluxes partly originating from external forcing. Enhanced changes in the subtropical southern IO arise from positive air–sea feedback among sea surface temperature, winds, turbulent heat flux, cloud cover, and shortwave radiation. Regarding dipole-type variability, the basinwide surface warming is induced by surface heat flux forcing, and the subsurface cooling occurs only in the eastern IO. The cooling in the southeast IO is generated by the weakened ITF, whereas that in the northeast IO is caused by equatorial easterly winds through upwelling oceanic waves. Both El Niño–Southern Oscillation (ENSO) and IO dipole (IOD) events are favorable for the generation of such vertical dipole anomalies.

Impacts of the upper-ocean salinity variations on the decadal sea level change in the Southeast Indian Ocean during the Argo era

In the past nearly two decades, the Argo Program has created an unprecedented global observing array with continuous in situ salinity observations, providing opportunities to extend our knowledge on the variability and effects of ocean salinity. In this study, we utilize the Argo data during 2004–2017, together with the satellite observations and a newly released version of ECCO ocean reanalysis, to explore the decadal salinity variability in the Southeast Indian Ocean (SEIO) and its impacts on the regional sea level changes. Both the observations and ECCO reanalysis show that during the Argo era, sea level in the SEIO and the tropical western Pacific experienced a rapid rise in 2005–2013 and a subsequent decline in 2013–2017. Such a decadal phase reversal in sea level could be explained, to a large extent, by the steric sea level variability in the upper 300 m. Argo data further show that, in the SEIO, both the temperature and salinity changes have significant positive contributions to the decadal sea level variations. This is different from much of the Indo-Pacific region, where the halosteric component often has minor or negative contributions to the regional sea level pattern on decadal timescale. The salinity budget analyses based on the ECCO reanalysis indicate that the decadal salinity change in the upper 300 m of SEIO is mainly caused by the horizontal ocean advection. More detailed decomposition reveals that in the SEIO, there exists a strong meridional salinity front between the tropical low-salinity and subtropical high salinity waters. The meridional component of decadal circulation changes will induce strong cross-front salinity exchange and thus the significant regional salinity variations.

Processes Controlling Sea Surface Temperature Variability of Ningaloo Niño

AbstractA high-resolution (3–8 km) regional oceanic general circulation model is utilized to understand the sea surface temperature (SST) variability of Ningaloo Niño in the southeast Indian Ocean (SEIO). The model reproduces eight Ningaloo Niño events with good fidelity and reveals complicated spatial structures. Mesoscale noises are seen in the warming signature and confirmed by satellite microwave SST data. Model experiments are carried out to quantitatively evaluate the effects of key processes. The results reveal that the surface turbulent heat flux (primarily latent heat flux) is the most important process (contribution > 68%) in driving and damping the SST warming for most events, while the roles of the Indonesian Throughflow (~15%) and local wind forcing are secondary. A suitable air temperature warming is essential to reproducing the reduced surface latent heat loss during the growth of SST warming (~66%), whereas the effect of the increased air humidity is negligibly small (1%). The established SST warming in the mature phase causes increased latent heat loss that initiates the decay of warming. A 20-member ensemble simulation is performed for the 2010/11 super Ningaloo Niño, which confirms the strong influence of ocean internal processes in the redistribution of SST warming signatures. Oceanic eddies can dramatically modulate the magnitudes of local SST warming, particularly in offshore areas where the “signal-to-noise” ratio is low, raising a caution for evaluating the predictability of Ningaloo Niño and its environmental consequences.

Influence of atmospheric rivers on the Leeuwin Current system

Previous work has demonstrated the strong ocean response to atmospheric rivers (ARs) in the northeast Pacific including coastal currents along the west coast of North America, because of strong surface winds associated with ARs. A recent study on the global distribution of ARs also suggests that the southeast Indian Ocean is one of the areas of relatively strong AR activity. This study investigates the influence of ARs on the Leeuwin Current system, which is one of the major boundary currents in the Indian Ocean. It is demonstrated that winds associated with typical ARs in the southeast Indian Ocean can generate strong poleward coastal currents and sea level rise along the west coast of Australia using a high-resolution ocean reanalysis (0.08° HYCOM). The composite of upper ocean currents and sea surface height (SSH) associated with landfalling ARs along the west coast of Australia is constructed using the HYCOM reanalysis, long-term AR data set, and tide gauge data. The enhancement of the poleward currents generated by ARs is found in the composite, and the magnitude of the enhancement is comparable to the strength of the Leeuwin Current itself. The results also indicate that the fluctuation of SSH and coastal currents along the west coast propagates along the southern coast all the way to the southeast coast (Pacific side) of Australia. The SSH propagation along the coasts is also detected in the tide gauge data in the west and southern coasts of Australia.

Mooring Observations of Air–Sea Heat Fluxes in Two Subantarctic Mode Water Formation Regions

AbstractWintertime surface ocean heat loss is the key process driving the formation of Subantarctic Mode Water (SAMW), but there are few direct observations of heat fluxes, particularly during winter. The Ocean Observatories Initiative (OOI) Southern Ocean mooring in the southeast Pacific Ocean and the Southern Ocean Flux Station (SOFS) in the southeast Indian Ocean provide the first concurrent, multiyear time series of air–sea fluxes in the Southern Ocean from two key SAMW formation regions. In this work we compare drivers of wintertime heat loss and SAMW formation by comparing air–sea fluxes and mixed layers at these two mooring locations. A gridded Argo product and the ERA5 reanalysis product provide temporal and spatial context for the mooring observations. Turbulent ocean heat loss is on average 1.5 times larger in the southeast Indian (SOFS) than in the southeast Pacific (OOI), with stronger extreme heat flux events in the southeast Indian leading to larger cumulative winter ocean heat loss. Turbulent heat loss events in the southeast Indian (SOFS) occur in two atmospheric regimes (cold air from the south or dry air circulating via the north), while heat loss events in the southeast Pacific (OOI) occur in a single atmospheric regime (cold air from the south). On interannual time scales, wintertime anomalies in net heat flux and mixed layer depth (MLD) are often correlated at the two sites, particularly when wintertime MLDs are anomalously deep. This relationship is part of a larger basin-scale zonal dipole in heat flux and MLD anomalies present in both the Indian and Pacific basins, associated with anomalous meridional atmospheric circulation.

Influence of the subtropical ridge on directional wave power in the southeast Indian Ocean

AbstractChanges in the intensity and position of subtropical anticyclones are major drivers of wave climate around Australia. The quasi‐stationary ridge of high atmospheric pressure in the mid‐latitudes is known as the Subtropical Ridge (STR). In this study, we decompose the directional wave climate along the Western Australian Shelf (WAS) into three primary modes of variability using a statistical‐synoptic typing approach, and relate the wave power signatures of each to movements in the STR. We find a significant reduction in wave power along the WAS over the past 35 years. This is synonymous with an intensification of the STR resulting in blocking of powerful Southern Ocean Low wave conditions, a small increase in weaker anticyclonic waves, and a reduction in total wave power. A persistent intensification and/or poleward shift in the STR, associated with anthropogenic warming, may result in a continued decrease and anticlockwise rotation in wave power along the WAS. The approach taken in this article relates empirical changes in wave climate to movements in large‐scale climate drivers which can be used to complement the understanding of climate‐model based scenarios of wave climate change.

Atmospheric microplastic over the South China Sea and East Indian Ocean: abundance, distribution and source

At present, microplastic (MP) is pervasive globally and has a regional difference. Recent studies have identified MP in the terrestrial atmospheric environment. However, the connection between terrigenous atmospheric MP emissions and impacts over the ocean is not well known. Here, we present the distribution of atmospheric MP abundance over the ocean based on a transoceanic survey conducted across 21 sampling transects from the Pearl River Estuary (PRE) to the South China Sea (SCS) and then to the East Indian Ocean (EIO). The abundance of atmospheric MP over the PRE (4.2 ± 2.5 items/100 m3) was significantly higher than that over the EIO (0.4 ± 0.6 items/100 m3). However, the abundance of atmospheric MP in the SCS (0.8 ± 1.3 items/100 m3) was not significantly different from the EIO and PRE. This result revealed that MP undergoes long-range transport, more than 1000 km away, through the atmosphere, but atmospheric MP transmission as the main source of oceanic MP based on transoceanic studies is not a plausible assumption. Furthermore, backward trajectory model analysis of 21 sampling transects preliminary showed the potential sources of atmospheric MP over the PRE, SCS, and EIO.

Decadal SST Variability in the Southeast Indian Ocean and Its Impact on Regional Climate

Abstract The southeast Indian Ocean (SEIO) exhibits decadal variability in sea surface temperature (SST) with amplitudes of ~0.2–0.3 K and covaries with the central Pacific (r = −0.63 with Niño-4 index for 1975–2010). In this study, the generation mechanisms of decadal SST variability are explored using an ocean general circulation model (OGCM), and its impact on atmosphere is evaluated using an atmospheric general circulation model (AGCM). OGCM experiments reveal that Pacific forcing through the Indonesian Throughflow explains <20% of the total SST variability, and the contribution of local wind stress is also small. These wind-forced anomalies mainly occur near the Western Australian coast. The majority of SST variability is attributed to surface heat fluxes. The reduced upward turbulent heat flux (QT; latent plus sensible heat flux), owing to decreased wind speed and anomalous warm, moist air advection, is essential for the growth of warm SST anomalies (SSTAs). The warming causes reduction of low cloud cover that increases surface shortwave radiation (SWR) and further promotes the warming. However, the resultant high SST, along with the increased wind speed in the offshore area, enhances the upward QT and begins to cool the ocean. Warm SSTAs co-occur with cyclonic low-level wind anomalies in the SEIO and enhanced rainfall over Indonesia and northwest Australia. AGCM experiments suggest that although the tropical Pacific SST has strong effects on the SEIO region through atmospheric teleconnection, the cyclonic winds and increased rainfall are mainly caused by the SEIO warming through local air–sea interactions.

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

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

Analisis Temporal Suhu Permukaan Laut di Perairan Indonesia Selama 32 Tahun (Era AVHRR)

One of the important factor that influences global climate dynamics is sea surface temperature (SST). Indonesian waters are semi-closed and located between the Pacific and Indian Oceans so that they have different characteristics of SPL in each region. The purpose of this research is to know the trend and local characteristics of Indonesian SST and adjacent areas in response to 6-monthly and seasonal variability with moving average method and correlation. The data used are SST data from AVHRR satellite with domain 15°N-15°S, 90°-145° E. The results showed of increase trend 0.34°C in Indonesian sea for 32 years (1981-2012). The characteristics of SST in Indonesian territory are closely related to the Mosoon cycle where in the East period in the northern region the Natuna Sea is warmer in contrast to the West monsoon period, in the southern part of the Arafura Sea to the warmer Sawu Sea and around the equator experiencing the warmest in the transitional period. The moving-average analysis shows that 6-monthly variability appears to be dominated in equatorial waters including the Java Sea and Banda Sea whereas seasonal variability occurs in the northern and southern regions of Indonesia's waters including the Pacific Ocean Oceans, the northwest Pacific Ocean and the southeast Indian Ocean. Based on correlation analysis, ENSO has a strong (negative) relationship in eastern Indonesia waters including the Sea in the northern part of Papua and the northwest Pacific Ocean while IOD has a strong (negative) relationship in the western Sumatra Sea, Banda Sea and Arafura Sea.

Revisiting the predictors for the long‐range forecasting of southwest monsoon rainfall over South Asia with a focus on Pakistan

The predictors of the south Asian summer monsoon used in statistical long‐range forecasting by the Indian and Pakistan Meteorological Departments have, in recent decades, had their validity reassessed. The results of such studies, including this one, show that the relationships between numerous predictors and the monsoon rainfall have changed over time, and many predictors have lost or gained significance. Tropical Atlantic sea surface temperature (SST) has been identified as a robust new predictor, having been found to exhibit a significant correlation with monsoon rainfall in northern Pakistan as well as with Indian summer monsoon rainfall. Empirical orthogonal function (EOF) analysis is performed on the Pakistan monsoon rainfall data in order to identify the dominant coupled modes of variability, on interannual timescales, for the classification of two sub‐regions of Pakistan. Overall, few predictors showed significant correlations with the monsoon rainfall across Pakistan. However, with respect to rainfall over northern Pakistan, significant correlations were found for the tropical Atlantic SST anomaly, equatorial southeast Indian Ocean SST anomaly and quasi‐biennial oscillation anomaly. With respect to rainfall over southern Pakistan, warm water volume anomaly, North Asia sea level pressure tendency and Nino3.4 SST tendency showed significant correlations. Although the predictability of Pakistan summer monsoon rainfall is low, a simple multiple linear regression model has nevertheless been developed for its prediction. The model has shown good predictive skill for the primary monsoon region of Pakistan

Air-Sea Heat Flux Variability in the Southeast Indian Ocean and Its Relation With Ningaloo Niño

Previous studies suggest that both air-sea heat flux anomalies and heat advection caused by an anomalous Leeuwin Current play an important role in modulating the sea surface temperature (SST) variability associated with the Ningaloo Niño. However, the estimates of surface heat fluxes vary substantially with the datasets, and the uncertainties largely depend on the time scale and locations. This study investigates air-sea flux variability associated with the Ningaloo Niño using multiple datasets of surface fluxes. The climatological net surface heat flux off the west coast of Australia from six major air-sea flux products shows large uncertainties, which exceeds 80 W m-2, especially in the austral summer when the Ningaloo Niño develops. These uncertainties stem mainly from those in shortwave radiation and latent heat flux. The use of different bulk flux algorithms and uncertainties of bulk atmospheric variables (wind speed and air specific humidity) are mostly responsible for the difference in latent heat flux climatology between the datasets. The composite evolution of air-sea heat fluxes over the life cycle of Ningaloo Niño indicates that the anomalous latent heat flux is dominant for the net surface heat flux variations, and that the uncertainties in latent heat flux anomaly largely depend on the phase of the Ningaloo Niño. During the recovery period of Ningaloo Niño, large negative latent heat flux anomalies (cooling the ocean) are evident in all datasets and thus significantly contribute to the SST cooling. Because the recovery of winds occurs earlier than SST, high SST and strong winds favor large evaporative cooling during the recovery phase. In contrast, the role of latent heat flux during the developing phase is not clear, because the sign of the anomalies depends on the datasets in this period. The use of high-resolution SST data, which can adequately represent SST variations produced by the anomalous Leeuwin Current, could largely reduce the errors in latent heat flux anomalies during the onset and peak phases.

First ROV Exploration of the Perth Canyon: Canyon Setting, Faunal Observations, and Anthropogenic Impacts

This study represents the first ROV-based exploration of the Perth Canyon, a prominent submarine valley system in the southeast Indian Ocean offshore Fremantle (Perth), Western Australia. This multi-disciplinary study characterises the canyon topography, hydrography, anthropogenic impacts, and provides a general overview of the fauna and habitats encountered during the cruise. ROV surveys and sample collections, with a specific focus on deep-sea coral, were conducted at six sites extending from the head to the mouth of the canyon. Multi-beam maps of the canyon topography show near vertical cliff walls, scarps, and broad terraces. Biostratigraphic analyses of the canyon lithologies indicate Late Paleocene to Late Oligocene depositional ages within upper bathyal depths (200-700 m). The video footage has revealed a quiescent ‘fossil canyon’ system with sporadic, localised concentrations of mega- and macro-benthos (~680-1800 m), which include corals, sponges, molluscs, echinoderms, crustaceans, brachiopods, and worms, as well as plankton and nekton (fish species). Solitary (Desmophyllum dianthus, Caryophyllia sp., Vaughanella sp., and Polymyces sp.) and colonial (Solenosmilia variabilis) scleractinians were sporadically distributed along the walls and under overhangs within the canyon valleys and along its rim. Gorgonian, bamboo, and proteinaceous corals were present, with live Corallium often hosting a diverse community of organisms. Extensive coral graveyards, discovered at two disparate sites between ~690-720 m and 1560-1790 m, comprise colonial (S. variabilis) and solitary (D. dianthus) scleractinians that flourished during the last ice age (~18 ka to 33 ka BP). ROV sampling (674-1815 m) spanned intermediate (Antarctic Intermediate Water) and deep waters (Upper Circumpolar Deep Water) with temperatures from ~2.5-6°C. Seawater CTD profiles of these waters show consistent physical and chemical conditions at equivalent depths between dive sites. Their carbonate chemistry indicate supersaturation (Ωcalcite ~1.3-2.2) with respect to calcite, but mild saturation to undersaturation (Ωaragonite ~0.8-1.4) of aragonite; notably some scleractinians were found living below the aragonite saturation horizon (~1000 m). Seawater δ13C and nuclear bomb produced Δ14C compositions decrease in the upper canyon waters by up to ~0.8‰ (< 800 m) and 95‰ (< 500 m) respectively, relative to measurements taken nearby in 1978, reflecting the ingress of anthropogenic carbon into upper intermediate waters.

Inter-annual variability of March to May rainfall over Tanzania and its association with atmospheric circulation anomalies

This study used Empirical Orthogonal Function (EOF), student t test, composite and correlation analysis techniques to investigate the inter-annual variability of March to May rainy season over Tanzania and its association atmospheric circulation anomalies. The EOF results showed that the rainfall over Tanzania during MAM season does not vary too much with the first dominant mode (EOF1) showing the variance of 22.4% of the total rainfall and that much of the rainfall being concentrated over the coast, northeastern and southern regions. It was found that during wet years, the study area was dominated by convergence at lower level which is associated with enough moisture advected by south easterlies from Indian Ocean due to the relaxation of Mascarene high (MH) over the region and westerlies from Congo basin. The rising motion at lower level was enhanced with the presence of ascending limb of Walker circulation cell over the western Indian Ocean (WIO) and the coast region. Central Pacific and east coast of Atlantic Oceans are relatively warm during wet years. Furthermore, significantly negative correlation observed between southeast Indian Ocean (SEIO) region and MAM rainfall over Tanzania at the 95% confidence level portrays that much of the regions receive high sufficient amount of rainfall when the western Indian Ocean (WIO) is relatively warmer than the SEIO. The results show that Nino 3.4 and Tropical North Atlantic (TNA) indices are strongly positively correlated with MAM rainfall over the east coast region. This study will help to improve seasonal forecasts over Tanzania.