Arafura Sea Research Articles

Impacts of the Madden‐Julian Oscillation on Marginal Sea Heatwaves of the Southeastern Tropical Indian Ocean

AbstractMarginal seas of the southeastern tropical Indian Ocean (SETIO), including the South Java coasts and the Timor and Arafura Seas, are hotspots of large‐scale marine heatwaves (MHWs) in austral summer with notable impacts on local ecosystems. Yet, the prediction of these MHWs remains challenging. By analyzing 39 MHWs and 45 marine cold‐spells (MCSs) observed in the summers of 1982–2021, this study reveals a robust modulation effect of the Madden‐Julian Oscillation (MJO) on these events. The results show that 56% of MHWs and 51% of MCSs overlapped with MJO events, and their duration is systematically longer than others. Moreover, MHWs in phases 3–4 and MCSs in phases 6–7 of the real‐time multivariate MJO (RMM) index were nearly 2–3 times stronger in intensity than the others. The passage of MJOs drives prominent intraseasonal sea surface temperature (SST) variability in the SETIO through perturbing surface heat fluxes, which in turn modulates the occurrence of MHWs and MCSs. During RMM phases 1–2 (convective center over of the east of Africa or the central‐western Indian Ocean), the SETIO is controlled by a dry condition, with increased surface insolation and suppressed latent heat release. These anomalous fluxes drive a persistent SST increase, facilitating the emergence of strong and prolonged MHWs in the subsequent RMM phases 3–4. Further analysis suggests an 18% probability for MHWs in the SETIO 12 ± 10 days after Phase 1. Therefore, the MJO contributes to the predictability of MHWs/MCSs of the SETIO, with implications for predicting climate extremes and hazards.

An integrated approach for the decision of wave energy converter deployment based on forty-five-years high-resolution wave climate modeling

Climate change is driving the urgent need for sustainable and renewable energy sources to mitigate its impacts and reduce greenhouse gas emissions. Ocean wave energy, as one of the promising alternatives to fossil fuels, plays a critical role in providing renewable energy in coastal areas. To fully exploit regional wave energy potential, various performance metrics of wave energy converters (WECs) need to be considered to optimize location decisions and WEC categories. This study introduces an integrated approach by incorporating a novel factor, the maximum consecutive cut-off duration of WECs due to extreme weather conditions. It aims to enhance the efficiency of WEC selection and deployment location optimization in the southern and eastern Asian seas. Through 45 years of high-resolution (up to 250 m) ocean wave simulations, conducted using WaveWatch III ®(WW3) on unstructured mesh, Wave Dragon was identified as providing the highest index. This study suggests that placing WECs along the coastlines of the South China Sea, the eastern and northern Bay of Bengal, the western sector of the Malay Archipelago, and parts of the Arafura Sea may result in the most efficient conversion of wave energy in the southern and eastern Asian seas. While the proposed approach alone may not dictate deployment decisions, this study provides an applicable index to potentially rank WEC deployment options in the eastern and southern Asian seas, by considering both exploitable wave energy production, and long-term stability.

Toward Sustainable Fishing Practices in Indonesia: Defining a Catch Quota Allocation for Saddletail Snapper (Lutjanus Malabaricus) in the Arafura Sea

The Arafura Sea hosts the commercially significant fish species, Lutjanus malabaricus, commonly known as the saddletail snapper. We devised a quota allocation approach for sustainably capturing this species. This approach involved estimating the species’ life history parameters through calculations of the size at 50% maturity, as well as life history ratios (M/K and Lm/L∞) to figure out the Total Allowable Catch (TAC). We based our calculations on the Maximum Sustainable Yield (MSY) that came from the catch and landing data from Probolinggo Port. This helped us set a fishing quota that fits the situation in Indonesia. Our analysis revealed that the size at 50% maturity was 52 cm, slightly lower compared to the neighborhood waters. Using the Length Based-Spawning Potential Ratio (LB-SPR) model, we determined the stock’s SPR to be approximately 17%, which falls below the targeted healthy fish stock SPR reference of 40%. The estimated MSY stood at 2,307 tons, and the TAC calculation slightly exceeded the approach based on time series fitting. Given the notably low SPR estimate, we suggest a cautious approach, recommending an MSY of 2,307 tons per year for Probolinggo Port, emphasizing the importance of maintaining the fishing mortality rate within the sustainable threshold.

Analysis of The Effect of mooring Depth & Fatigue Damage on Mooring Line FPSO Ship Azurite In The Masela Block

Oil & gas drilling in the open sea cannot be avoided with the use of FPSO. Floating Production Storage and Offloading (FPSO) is a facility in the form of a floating production storage and unloading vessel in the form of crude oil and natural gas originating from the seabed. The selected type of floater that will be operated in the Abadi field, Masela Block, Arafura Sea is the Azurite FPSO ship. In its operation, the FPSO will not be separated from the influence of dynamic loads such as sea waves, ocean currents and wind on the mooring rope structure periodically. This may cause damage to the structure mooring line which influences the performance of the structure. The aim of this research is to analyze motion trajectory (surge and sway), mooring line stress, and fatigue damage on the mooring system catenary by making comparisons using variations in mooring depth. Dimensions mooring line type chain on fairlead with six (6) variations in mooring depth, namely 1000, 900, 800, 700, 600 and 500 meters which will then be analyzed fatigue damage from mooring line the. Observation result Motion Trajectory It was found that the shallower the mooring depth mooring line then value ∆Offset or movement surge & sway will get bigger. Meanwhile in observations Mooring Line Stress and Fatigue Damage obtained both are directly proportional where the greater the tension mooring line then the ratio of damage that occurs due to fatigue in the structure will also be greater. This is because the mass of the rope used is not proportional to displacement boat. And in this numerical analysis simulation it only reaches the initial movement, namely at 100 seconds, where the ship's condition has not yet reached the stable condition it should be.

Mooring Design and Fatigue Damage on Variant Fairlead Positions During FPSO Operation – Case Study

This comprehensive case study delves into the intricate dynamics of deepwater mooring systems, specifically focusing on Floating Production Storage and Offloading (FPSO) operations. Our investigation centers on the Anoa Natuna FPSO, situated in the Arafura Sea. We examine how varying fairlead positions, employing a 4x3 chain configuration, influence structural integrity, operational stability, and fatigue damage. The research meticulously analyzes the response of the FPSO to environmental forces, providing a detailed understanding of the vessel's behavior under different fairlead positions. The results showcase the vessel's stability, elucidate variations in its motion response, and highlight the effects of fairlead positioning on structural fatigue, offering valuable insights for safe and efficient deepwater FPSO operations.

Satellite observations of coastal upwelling in the northern Arafura Sea

Satellite observations of coastal upwelling in the northern Arafura Sea

Estimation of The Potential of Large Pelagic Fish Fisheries Using Satellite Data in The Banda and Arafura Seas

The Banda and Arafura Sea possesses significant potential for the fisheries and fishing industry in the country. The large pelagic fish production data studied were derived from satellite imagery data in the Banda and Arafura Seas (2002-2022). The data of chlorophyll-a content, sea surface temperature and Photosynthetically Available Radiation (PAR) derived from AQUA MODIS satellite images were used to estimate the value of primary productivity with the Vertically Generalised Production Model (VGPM). The results showed that the biomass of large pelagic fish fluctuated seasonally, with the Banda Sea and Arafura Sea having high average fish biomass values in the eastern season. With the highest fish biomass peak in August and the lowest in December. The high value of fish biomass in the Banda Sea and Arafura Sea is caused by upwelling events where sea surface temperatures are low but chlorophyll is high. in the Arafura Sea the value of fish biomass is higher than the Banda Sea, this is due to the large amount of nutrient input from large rivers in the area.

New records, one new genus and 21 new species of Callianassidae (Crustacea, Axiidea) from the Indo-West Pacific

Poore, G.C.B. 2023. New records, one new genus and 21 new species of Callianassidae (Crustacea, Axiidea) from the Indo-West Pacific. Memoirs of Museum Victoria 82: 167–255. The collections of ghost shrimps from the Indo-West Pacific that contributed to recent molecular phylogeny and resulting reclassification of Callianassidae (Poore et al., 2019; Robles et al., 2020) provide opportunities to review 11 genera and describe one new genus, redescribe existing species and describe 21 new species. Aqaballianassa aqabaensis (Dworschak, 2003), A. brevirostris (Sakai, 2002), A. lewtonae (Ngoc-Ho, 1994) are rediagnosed and Aqaballianassa papua sp. nov. from Papua New Guinea and Aqaballianassa seychellensis sp. nov. from the Seychelles are described as new. Three new species of Caviallianassa Poore, Dworschak, Robles, Mantelatto and Felder, 2019 are compared in a key with Caviallianassa cavifrons (Komai and Fujiwara, 2012): Caviallianassa arafura sp. nov. from the Arafura Sea, Caviallianassa riwo sp. nov. from Papua New Guinea and Caviallianassa moorea sp. nov. from French Polynesia. Callianassa thailandica Sakai, 2005 is treated as species inquirenda. No species of Cheramus Bate, 1888 occurs in the Indo-West Pacific despite the genus name having been widely used. Five species of Coriollianassa Poore, Dworschak, Robles, Mantelatto and Felder, 2019 are recognised and figured: C. sibogae (De Man, 1905), C. coriolisae (Ngoc-Ho, 2014) and new species, Coriollianassa mainbazae sp. nov. and Coriollianassa maputo sp. nov. from the Mozambique Channel, and Coriollianassa nyinggulu sp. nov. from the North West Australian slope. Darryllianassa felderi gen. et sp. nov. is described from Papua New Guinea. Necallianassa nosybeensis sp. nov. is described as a new species from Madagascar. Praedatrypaea Poore, Dworschak, Robles, Mantelatto and Felder, 2019 is rediagnosed. Thirteen species are recognised and most diagnosed; four species are described as new: Praedatrypaea jangamo sp. nov. and Praedatrypaea mozambiquensis sp. nov. from Mozambique, and Praedatrypaea mandu sp. nov. and Praedatrypaea ningaloo sp. nov. from the North West Shelf of Australia. Callianassa malaccaensis Sakai, 2002 is treated as a junior synonym of P. orientalis (Bate, 1888). A key to separate ten species of Praedatrypaea is presented. Pugnatrypaea Poore, Dworschak, Robles, Mantelatto and Felder, 2019 is rediagnosed and confined to three species. Rayllianassa Komai and Tachikawa, 2008 is rediagnosed and its species discussed. Rayllianassa amboinensis (De Man, 1888), a variable species, is rediagnosed; Callianassa ngochoae Sakai, 1999 and Callianassa sahul Poore, 2008 are treated as synonyms. Rayllianassa aurora sp. nov., Rayllianassa bifida sp. nov. and Rayllianassa huonensis sp. nov. are described as new species; the first two are associated with submerged wood at depths greater than 100 m. Rudisullianassa Poore, Dworschak, Robles, Mantelatto and Felder, 2019 is rediagnosed. Rudisullianassa rudisulcus Komai, Fujita and Maenosono, 2014 is discussed and partially illustrated; Rudisullianassa pandan sp. nov. is described as a new species from submerged wood. Spinicallianassa Poore, Dworschak, Robles, Mantelatto and Felder, 2019 is reviewed and a key is provided to five species; three species are described as new: Spinicallianassa bilbili sp. nov. from Papua New Guinea; Spinicallianassa papetoai sp. nov. from French Polynesia; and Spinicallianassa westralia sp. nov. from Western Australia. Callianassa parvula Sakai, 1988 is treated as a possible synonym of S. spinicauda (Komai, Maenosono and Fujita, 2014). Trypaea Dana, 1852 contains only T. australiensis Dana, 1852 and does not occur in the Indo-West Pacific as sometimes reported.

Notes on Two Rare Species of Brachyuran Crabs (Families Matutidae and Parthenopidae) From Indonesian Waters with New Distribution Records.

Several species of brachyuran crabs in Indonesian waters have not been reported since almost 100 years ago. This research reports a brachyuran crab that is rarely found and one new record in Indonesian waters. This study was conducted in the waters of southern Aru Island and the Malacca Strait using trawls during a cruise held by the Research Institute for Marine Fisheries, Ministry of Marine Affairs and Fisheries, Indonesia.. Our findings were Izanami reticulata, a new record (family Matutidae) from southern Aru Island, and Cryptopadia fornicata (family Parthenopidae) from the Malacca Strait. The two locations are close to where the species were found in previous studies: the Arafura Sea, which is adjacent to the Aru Islands, and the Malacca Strait, which is adjacent to Borneo. It is suspected that the presence of these two species in Indonesia is due to their distribution through sea currents during the pelagic larval stage. This article also provides the specific habitat for both species in Indonesia, which was previously unknown. In addition, this article contributes to strengthening Indonesia as a mega-biodiversity country with an initial compilation of a database of Brachyura in its waters.

Density distribution of Penaeus merguensis De Man, 1888 based on habitat in the waters of Merauke District, South Papua Province, Indonesia

Abstract. Lantang B, Najamuddin, Nelwan AFP, Samawi MF. 2023. Density distribution of Penaeus merguensis De Man, 1888 based on habitat in the waters of Merauke District, South Papua Province, Indonesia. Biodiversitas 24: 4427-4437. The waters of Merauke District, located in the Arafura Sea area, have relatively hight penaeid resource, but prawn fishing productivity is the lowest of 11th other Indonesian fisheries management areas.. The optimization of the fishery resource utilization remains poor after the moratorium on fishing vessel licensing in 2014, which is only 11%. Hence, a study is needed to determine the resources’ distribution, abundance, and sustainability. This research aims to analyze the density distribution of banana prawn (Penaeus merguensis De Man, 1888) based on the habitat type, each location separated by ~4-5 kilometers within the coastal ecosystem waters of Merauke District. The research was carried out from March to August 2022. Data were collected within each habitat: the catch, prawn fishing equipment, and oceanographic parameters, and then analyses were undertaken using statistical tests. The results showed that the highest density of banana prawn was obtained in shallow waters adjacent to the mangrove habitat at Bokem (32.68 kg/km2) and Yobar (20.27 kg/km2). In waters adjacent to the sandy beach at Payum (17.98 kg/km2), the density was higher than within the estuarine habitat of Maro River (14.60 kg/km2) and adjacent to the sandy beach at Lampu Satu (14.39 kg/km2). This is due to the influx of fresh water in estuarial habitat, sandy beaches in Lampu Satu and Payum, and mangroves in Yobar, resulting in prawn emigration to areas with higher salinity in Bokem mangroves. It is also thought to be associated with increasing turbidity with a similar pattern in salinity and affecting the density of banana prawns.

Life history (length-weight relationship, conditional factors, reproductive aspects), stomach contents and nursery ground of stingray in the Arafura Sea

Stingrays are a resource that is vulnerable to overfishing and habitat degradation. The research was conducted to obtain data and information that is still lacking and much needed for the utilization and protection of stingrays, including; life history, stomach contents, and nursery ground. The study was conducted in October - November 2018 by exploratory, including taking stingrays by trawling and measuring habitat conditions with Conductivity, Temperature, and Depth. The results showed a total stingrays are 744 individuals, weighing 2,986.6 kg and 24 species. Individual stingrays have a width disc range of 9-134 cm and a weight of 20-67000 g. The growth pattern of stingrays is generally allometric, except for Gymnura zonura. The average value of the relative condition factors is generally >1, except for Aetomylaeus maculatus and Brevitrygon walga. Stingrays have an unbalanced sex ratio, gonads consist of 43% adolescent and 57% mature, and the number of neonates is 1-6 /parent. The correlation between clasper length and disc width is generally positive, except for Hemitrygon longicauda. Of the stomach contents of all stingray species, 64 % is shrimp, Himantura leoparda which have various prey. The area east of Aru and west of Papua are the locations used as nursery grounds by most various stingrays. Nursery grounds of Stingray is generally shallow coastal areas with low oxygen, eutrophic and high turbidity. The results of this study are expected to be used as a basis for managing stingray resources in the Arafura Sea and further research is recommended to be carried out in four different seasons.

Stock assessment and management strategies for shark fisheries in the Arafura Sea: A length-based analysis of Carcharhinus sealei

Increased demand for the production of sharks in the Arafura Sea can lead to the overfishing condition, which resulted in the depletion of fish stocks. Effective management measures are crucial to ensure the sustainability of shark fisheries. The objectives of this study were to investigate the stock status and to recommend some management strategies for shark fisheries in the Arafura Sea. Length frequency data and some life history parameters were used to perform a length-based stock assessment of Carcharhinus sealei in the Arafura Sea. C. sealei has an asymptotic length of 102.25 cm with a growth constant of 0.36 year−1. C. sealei has been exploited heavily, which was indicated by the current fishing mortality (Fcur = 1.2 year−1), which was much higher than its natural mortality (M = 0.29 year−1) and the optimal fishing mortality (F40%=0.49 year−1). This study revealed that the high fishing pressure of sharks has resulted in the stock overfished condition for C. sealei in the Arafura Sea, with the current spawning potential ratio (SPRcur = 0.23) less than the reference point 40% SPR. The low selectivity of drift gillnet (current Lc50 = 66 cm) caused the low spawning stock biomass of C. sealei. The stock rebuilding strategy would be required to increase the spawning stock biomass of C. sealei. A minimum legal size of 77 cm, a marine protected area, and effort controls were some management strategies that can be adopted for the sustainability of shark fisheries in the Arafura Sea.

Seasonal variation of some oceanographic parameters in the Arafura Sea – Gulf of Carpentaria

The shallow continental shelf of Arafura Sea-Gulf of Carpentaria borders the Torres Strait in the east and the deep Banda Sea in the west, where the monsoonal winds system controls shelf circulation. This study aims to investigate spatial and temporal variation of shelf circulation, surface temperature (SST), seas surface height (SSH), using the multi-datasets of validated model output and satellite-derived data. The model reproduced well the satellite derived SST and SSH (corr.> 0.98). The northwesterly monsoonal winds are fully developed between December and February (NWM period), but the southeasterly winds are intensified during the southeast monsoon (SEM). During the monsoon breaks, the southeasterly-easterly winds are still dominant. The shelf circulation is coincident with the wind direction. During the NMW period the eastward flows from Banda basin and Timor Sea are dominant, creating a clockwise circulation within the Gulf. In contrast, the westward flow dominates during the SEM period, creating an anti-clockwise circulation in the Gulf. Exchange of water via the Torres Strait is also seen. Spatial pattern of temperature and SSH reveal a dissimilarity between the Gulf and the Arafura Sea (99.9% of explained variance) with dominant periodicity of annual and semi-annual scales.

A northward range extension of Thysanophrys papillaris (Actinopterygii: Scorpaeniformes: Platycephalidae) to Taiwan

The smallknob flathead, Thysanophrys papillaris Imamura et Knapp, 1999, is redescribed based on six specimens collected from southern Taiwan, which constitutes a northward range extension of the species [previously recorded from the Andaman, Timor, and Arafura seas (eastern Indian Ocean), and Nha Trang, Vietnam (western Pacific Ocean)]. Thysanophrys papillaris is distinguished from all congeneric species in having a combination of 11 second dorsal-fin rays, 12 anal-fin rays, 58–75 scale rows below the lateral line (slanting downward and forward), a longer snout (snout length / orbital diameter ratio 1.1–1.3), 1 or 2 small papillae on the eye, the upper iris lappet with short branches, a single preorbital spine and 3–5 suborbital spines. Previously suggested intraspecific variation in the number of eye papillae is confirmed.

Shrimps distribution and their relationship to the environmental variables in Arafura Sea

Arafura Sea is well-known as the important area for commercial shrimp fisheries in Indonesia. The density of shrimps was highly influenced by their fishing pressure and environmental condition. The objective of this research was to study the distribution of shrimps based on its stock density and their relationship with the environmental variables. Trawling swept area method was used in 16 sampling sites of Arafura Sea during the transition monsoon in 2016. Some environmental variables in bottom layers as shrimp habitat were measured, including chlorophyll-a, dissolved oxygen, depth, salinity, temperature and pH. The results showed that the largest density of shrimps was found in the southern coast of Aru where it has the largest concentration of chlorophyll-a and dissolved oxygen. Among all the environmental variables, Chlorophyll-a was the main variable affected the density of shrimps. Three most dominant species were Penaeus semisulcatus, Metapenaeus endeavouri and Metapenaeus ensis. There was indication of the decreasing shrimp stock in Arafura Sea. The ecosystem-based fisheries management should be developed to rebuild the stock density and to enhance the environmental quality of Arafura Sea.

Mangroves in Southeast Aru Marine Protected Area

Southeast Aru Marine Protected Area (MPA) is a 114,000 hectares reserve-type national conservation area in Arafura Sea, Maluku Province, Indonesia where the Ministry of Marine Affairs and Fisheries managed since 2009. Its mangrove is the largest coastal ecosystem which is important for sustainable fisheries and coastal disaster mitigation. The main objective of this study is to understand the condition of mangrove community, its impact on fisheries and threats to its continuity. Stratified random sampling on three plots of 10 m x 10 m and hemispherical photography are employed on 13 observation sites across four zones. Local fishermen are interviewed about their activities related to mangroves. From 13 observation sites, 19 species from 8 families and 10 genera are identified. The average of mangrove density and its canopy coverage were respectively 2,997 stand/ha and 74.66%. These values can be interpreted as in good condition and moderate coverage (KepmenLH 201/2004). Rhizophora mucronate and Sonneratia alba are the two most dominant species in all observation sites. Local fishermen’s activities in the mangrove area are catching crabs, trap-fishing, and cutting mangrove woods for firewood and/or simple non-permanent housing. Bruguiera gymnorrhiza, Phemphis acidula, Rhizophora mucronate and Ceriops tagal are their favourites.

A new species of the ghost shrimp genus Andamancalliax Sakai, 2011 from Iran (Crustacea: Decapoda: Axiidea: Eucalliacidae)

A new species of eucalliacid ghost shrimp is described from the Gulf of Oman, Iran. Andamancalliax poorei sp. nov. is the first species of the genus described from Iranian subtidal waters and the third species worldwide. Andamancalliax poorei sp. nov. most resembles A. arafura Poore, 2021 from the Arafura Sea but can be differentiated by characters of the minor cheliped, maxilliped 3 and uropodal endopod.

VARIABILITAS MUSIMAN SUHU PERMUKAAN LAUT DAN ANGIN DI LAUT ARAFURA

Research on sea surface temperature (SST) and wind in the Arafura Sea is very important to answer various processes and phenomena that occur in the water column, for example upwelling and downwelling phenomena, the influence of monsoon winds, ENSO and LaNina phenomena, mixing of water masses, forecasting fishing areas, determination of marine cultivation areas, and so on. This study aims to examine the spatial distribution and variability of sea surface temperature (SST) and wind and to examine the correlation of SST with wind speed and direction in the Arafura Sea. SST data is obtained from the AQUA MODIS satellite which is downloaded on the website http://oceancolor.gsfc.nasa.gov. Wind data obtained from the site: ftp://ftp.ifremer.fr/ifremer/cersat. The results of the analysis show that the SST in the Arafura Sea varies seasonally with a range of 23–34oC and a variation of 3.01-4.60%. The wind speed ranges from 0.02-10 m/s with a variation of 40.07-47.76%. There is a strong correlation between SST and wind speed and direction based on latitude and longitude. The correlation between wind speed and SST ranges from -0.01 to -0.87, while the correlation between wind direction and SST ranges from 0.52 and -0.71. In certain waters there is a positive linear correlation of SST with wind direction of 0.18-0.78

Investigating ocean deoxygenation and the oxygen minimum zone in the Central Indo Pacific region based on the hindcast datasets.

Deoxygenation is increasingly recognized as a significant environmental threat to the ocean following sea temperature rises due to global warming and climate change. Considering the cruciality of the deoxygenation impacts, it is important to assess the current status and predict the future possibility of ocean deoxygenation, for instance, within the Central Indo Pacific (CIP) regions represent climate-regulated marine areas. This study divided CIP into five regions then investigated the deoxygenation parameters (dissolved oxygen, temperature, salinity, and pH) collected from 1993 to 2021 sourced from in situ measurement and long-term hindcast data. The overall error statistics indicate a good accuracy of hindcast data and are comparable to the in situ values. The surface waters were identified to have the most fluctuated seasonal pattern of dissolved oxygen (DO) concentration compared to other water columns. However, DO fluctuation occurred in a different pattern in each region. The study shows ocean deoxygenation is accelerated in all five regions over decades. The strongest oxygen minimum zone (OMZ) is identified in the Bay of Bengal and the Arafura Sea with the lowest oxygen concentration less than 0.5mmol/m3, while the weakest OMZ is located in the South China Sea with 60mmol/m3 of DO concentration. The deoxygenation rates in CIP regions are varied by 0.09-2.75mmol/m3/year depending on the different controlling factors that work in the five regions. Our results indicate that deoxygenation is attributed to ocean warming, seawater salinity increases, and ocean acidification and possibly continue in the future with continued global changes.

Atmospheric concentrations and sources of black carbon over tropical Australian waters

Black carbon (BC) aerosols significantly contribute to radiative budgets globally, however their actual contributions remain poorly constrained in many under-sampled ocean regions. The tropical waters north of Australia are a part of the Indo-Pacific warm pool, regarded as a heat engine of global climate, and are in proximity to large terrestrial sources of BC aerosols such as fossil fuel emissions, and biomass burning emissions from northern Australia. Despite this, measurements of marine aerosols, especially BC remain elusive, leading to large uncertainties and discrepancies in current chemistry-climate models for this region. Here, we report the first comprehensive measurements of aerosol properties collected over the tropical warm pool in Australian waters during a voyage in late 2019. The non-marine related aerosol emissions observed in the Arafura Sea region were more intense than in the Timor Sea marine region, as the Arafura Sea was subject to greater continental outflows. The median equivalent BC (eBC) concentration in the Arafura Sea (0.66 μg m−3) was slightly higher than that in the Timor Sea (0.49 μg m−3). Source apportionment modelling and back trajectory analysis and tracer studies consistently suggest fossil fuel combustion eBC (eBCff) was the dominant contributor to eBC across the entire voyage region, with biomass burning eBC (eBCbb) making significant additional contributions to eBC in the Arafura Sea. eBCff (possibly from ship emissions or oil and gas rigs and their associated activities) and cloud condensation nuclei (CCN) were robustly correlated in the Timor Sea data, whereas eBCbb positively correlated to CCN in the Arafura Sea, suggesting different sources and atmospheric processing pathways occurred in these two regions. This work demonstrates the substantial impact that fossil fuel and biomass burning emissions can have on the composition of aerosols and cloud processes in the remote tropical marine atmosphere, and their potentially significant contribution to the radiative balance of the rapidly warming Indo-Pacific warm pool.