Pub Date : 2025-12-01Epub Date: 2025-11-11DOI: 10.1016/j.dsr2.2025.105565
Homira Agah , Zahra Eslami , Maryam Ghaemi
Mangrove ecosystems function as natural biogeochemical filters and can retain substantial amounts of heavy metals from terrestrial and marine sources. Given increasing global concern over metal contamination in coastal sediments, assessing heavy-metal levels in mangrove habitats is essential for evaluating ecosystem health. Mangrove forests in Bushehr Province, Iran, are located near industrial and coastal development zones, raising concern about potential ecological risks.
This study assessed concentrations and ecological risks of heavy metals in 78 surface sediment samples collected from three mangrove areas (Bardestan, Mel Ganzeh, and Nayband). Metal concentrations were determined using ICP-MS following acid digestion. The abundance of elements followed the order Al > Fe > Mn > V > Cr > Ni > Cu > Zn > As > Se > Mo > Co > Pb > Cd > Bi. Significant positive correlations among most metals (Mn, Cr, V, Zn, Cu, Ni, As, Cd, P < 0.05) indicated predominantly natural sources, except for Se. Ni concentrations in Mel Ganzeh and deeper Bardestan stations exceeded the Threshold Effect Level (19.7 mg kg−1), while other metals remained below guideline values. Contamination and enrichment indices confirmed generally natural origin (except for Se) and low enrichment. According to the results, the pattern of elements accumulation in sediments of the studied areas was as the following order: Mel Ganzeh > Bardestan > Nayband > Coastal parts of Nayband. Overall, ecological risk indices indicated low risk, suggesting that current heavy-metal inputs do not pose a significant threat to mangrove sediments in Bushehr Province.
{"title":"Ecological risk assessment and distribution pattern of heavy metal contamination in mangrove sediments at Bushehr Province, West-northern Persian Gulf, Iran","authors":"Homira Agah , Zahra Eslami , Maryam Ghaemi","doi":"10.1016/j.dsr2.2025.105565","DOIUrl":"10.1016/j.dsr2.2025.105565","url":null,"abstract":"<div><div>Mangrove ecosystems function as natural biogeochemical filters and can retain substantial amounts of heavy metals from terrestrial and marine sources. Given increasing global concern over metal contamination in coastal sediments, assessing heavy-metal levels in mangrove habitats is essential for evaluating ecosystem health. Mangrove forests in Bushehr Province, Iran, are located near industrial and coastal development zones, raising concern about potential ecological risks.</div><div>This study assessed concentrations and ecological risks of heavy metals in 78 surface sediment samples collected from three mangrove areas (Bardestan, Mel Ganzeh, and Nayband). Metal concentrations were determined using ICP-MS following acid digestion. The abundance of elements followed the order Al > Fe > Mn > V > Cr > Ni > Cu > Zn > As > Se > Mo > Co > Pb > Cd > Bi. Significant positive correlations among most metals (Mn, Cr, V, Zn, Cu, Ni, As, Cd, P < 0.05) indicated predominantly natural sources, except for Se. Ni concentrations in Mel Ganzeh and deeper Bardestan stations exceeded the Threshold Effect Level (19.7 mg kg<sup>−1</sup>), while other metals remained below guideline values. Contamination and enrichment indices confirmed generally natural origin (except for Se) and low enrichment. According to the results, the pattern of elements accumulation in sediments of the studied areas was as the following order: Mel Ganzeh > Bardestan > Nayband > Coastal parts of Nayband. Overall, ecological risk indices indicated low risk, suggesting that current heavy-metal inputs do not pose a significant threat to mangrove sediments in Bushehr Province.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105565"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145525778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-11-02DOI: 10.1016/j.dsr2.2025.105559
Sonia Yáñez , Pamela Hidalgo , Nicole Trefault , Kam W. Tang , Rodrigo De la Iglesia
Mesozooplankton can suffer a high degree of non-predatory mortality within the Oxygen Minimum Zone (OMZ), resulting in a high abundance of carcasses. Copepod carcasses are subject to bacterial decomposition with unclear consequences for nitrogen cycling, microbial biodiversity, and ecosystem functioning. We investigated the bacterial decomposition of carcasses of the copepod Acartia tonsa from Mejillones Bay within the Humboldt Current System under different dissolved oxygen concentrations. Using molecular methods, we followed the dynamics of bacterial composition and functional marker genes for nitrogen cycling. Decomposition of carcass tissues was observed earlier under oxic conditions than under Microxic/Suboxic conditions. Aerobic bacteria colonized the carcasses, and the associated functional gene for ammonia oxidation (amoA) was detected. Under Microxic/Suboxic conditions, decomposition was dominated by anaerobic bacteria and the related denitrification functional genes, specifically nitrite reductases (nirK) and of nitrous oxide reduction (nosZ), consistent with an estimated high denitrification rate. Based on these microscale observations, our study suggested that copepod carcasses were anaerobic microenvironments that potentially supported denitrification activity in the upper and lower oxyclines. Carcass driven denitrification may be an important loss of fixed N in the OMZ.
{"title":"Decomposition of marine copepod carcasses potentially contributes to the presence of denitrification genes in oxygen-depleted waters","authors":"Sonia Yáñez , Pamela Hidalgo , Nicole Trefault , Kam W. Tang , Rodrigo De la Iglesia","doi":"10.1016/j.dsr2.2025.105559","DOIUrl":"10.1016/j.dsr2.2025.105559","url":null,"abstract":"<div><div>Mesozooplankton can suffer a high degree of non-predatory mortality within the Oxygen Minimum Zone (OMZ), resulting in a high abundance of carcasses. Copepod carcasses are subject to bacterial decomposition with unclear consequences for nitrogen cycling, microbial biodiversity, and ecosystem functioning. We investigated the bacterial decomposition of carcasses of the copepod <em>Acartia tonsa</em> from Mejillones Bay within the Humboldt Current System under different dissolved oxygen concentrations. Using molecular methods, we followed the dynamics of bacterial composition and functional marker genes for nitrogen cycling. Decomposition of carcass tissues was observed earlier under oxic conditions than under Microxic/Suboxic conditions. Aerobic bacteria colonized the carcasses, and the associated functional gene for ammonia oxidation (<em>amoA</em>) was detected. Under Microxic/Suboxic conditions, decomposition was dominated by anaerobic bacteria and the related denitrification functional genes, specifically nitrite reductases (<em>nirK)</em> and of nitrous oxide reduction (<em>nosZ</em>), consistent with an estimated high denitrification rate. Based on these microscale observations, our study suggested that copepod carcasses were anaerobic microenvironments that potentially supported denitrification activity in the upper and lower oxyclines. Carcass driven denitrification may be an important loss of fixed N in the OMZ.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105559"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145525884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-11-01DOI: 10.1016/j.dsr2.2025.105560
Devin S. Vlach , Olívia S. Pereira , Francis Nguyen , Angelica Bradley , Kira Mizell , Lisa A. Levin
The Southern California Borderland (SCB) is a topographically complex region on the active continental margin that hosts varied hardground habitats, including ferromanganese (FeMn) crusts and phosphorites, marine minerals being considered for resource extraction. The SCB is influenced by seasonal upwelling and terrestrial inputs, and has a well-defined oxygen-minimum zone (OMZ). We analyzed megafaunal community composition, density, and diversity across 41 ROV video transects at 10 SCB hard substrate sites spanning depth (378–2765 m), temperature (1.79–7.96 °C), and oxygen (3.91–105.67 μM) gradients, with varying rock types (FeMn crusts, phosphorites, other rocks). We counted 32,426 individuals representing 146 unique taxa over a total area of 21,935 m2. Echinodermata contributed 48 % of the total abundance; Cnidaria 24 %; Porifera 13 %; Annelida 6 %; Arthropoda 6 %; Chordata 2 %; Mollusca, Foraminifera, and Hemichordata <1 %. Megafauna communities showed clear heterogeneity, with density, diversity, and community composition varying among transects within sites and across sites. Rock type recorded no influence on megafaunal density, but habitats that included FeMn crusts had higher diversity and distinct taxonomic composition. Location, depth, and oxygen were the most important variables explaining variance among megafaunal communities, with distinct communities formed at deeper depths and within the OMZ. This study provides baseline information about the megafauna inhabiting SCB hardgrounds, particularly those associated with minerals considered for their resource potential. It extends existing documentation of such communities to greater depths, reveals increased representation of sponges and corals below 1000 m, and highlights the variability within and among deep-sea megafaunal communities, offering context for informed policy decisions.
{"title":"Megafaunal community structure on ferromanganese and phosphorite hardgrounds in the Southern California Borderland","authors":"Devin S. Vlach , Olívia S. Pereira , Francis Nguyen , Angelica Bradley , Kira Mizell , Lisa A. Levin","doi":"10.1016/j.dsr2.2025.105560","DOIUrl":"10.1016/j.dsr2.2025.105560","url":null,"abstract":"<div><div>The Southern California Borderland (SCB) is a topographically complex region on the active continental margin that hosts varied hardground habitats, including ferromanganese (FeMn) crusts and phosphorites, marine minerals being considered for resource extraction. The SCB is influenced by seasonal upwelling and terrestrial inputs, and has a well-defined oxygen-minimum zone (OMZ). We analyzed megafaunal community composition, density, and diversity across 41 ROV video transects at 10 SCB hard substrate sites spanning depth (378–2765 m), temperature (1.79–7.96 °C), and oxygen (3.91–105.67 μM) gradients, with varying rock types (FeMn crusts, phosphorites, other rocks). We counted 32,426 individuals representing 146 unique taxa over a total area of 21,935 m<sup>2</sup>. Echinodermata contributed 48 % of the total abundance; Cnidaria 24 %; Porifera 13 %; Annelida 6 %; Arthropoda 6 %; Chordata 2 %; Mollusca, Foraminifera, and Hemichordata <1 %. Megafauna communities showed clear heterogeneity, with density, diversity, and community composition varying among transects within sites and across sites. Rock type recorded no influence on megafaunal density, but habitats that included FeMn crusts had higher diversity and distinct taxonomic composition. Location, depth, and oxygen were the most important variables explaining variance among megafaunal communities, with distinct communities formed at deeper depths and within the OMZ. This study provides baseline information about the megafauna inhabiting SCB hardgrounds, particularly those associated with minerals considered for their resource potential. It extends existing documentation of such communities to greater depths, reveals increased representation of sponges and corals below 1000 m, and highlights the variability within and among deep-sea megafaunal communities, offering context for informed policy decisions.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105560"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145462848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-09-03DOI: 10.1016/j.dsr2.2025.105537
Ullas M. Pillai , Ajith Joseph K , Roshin P. Raj , Ola M. Johannessen
Eddy kinetic energy (EKE) in the southeastern Arabian Sea (SEAS) during the relatively least explored winter season spanning 28 years (1993–2020) was studied using satellite observational and reanalysis data from the Copernicus Marine Service Data Center. The generation and enhancement of EKE resulting from current instabilities are discussed, and the significant role of barotropic energy conversion in the SEAS, is further examined, considering the roles of surface currents and wind forcing obtained from ERA5 reanalysis dataset. The strong EKE observed during winter within the Laccadive Sea in the SEAS is partly attributed to dominant barotropic instability arising from horizontal shear in surface currents driven by strong negative wind stress curl. Furthermore, EKE shows a significant positive correlation with chlorophyll-a (Chl-a) concentration during winter in the SEAS, highlighting the influence of physical-biological coupling associated with eddies and the zonal advection of Bay of Bengal waters by the northeast monsoon current.
{"title":"Enhanced eddy kinetic energy in the southeastern Arabian Sea during winter: the influence of surface currents and wind force","authors":"Ullas M. Pillai , Ajith Joseph K , Roshin P. Raj , Ola M. Johannessen","doi":"10.1016/j.dsr2.2025.105537","DOIUrl":"10.1016/j.dsr2.2025.105537","url":null,"abstract":"<div><div>Eddy kinetic energy (EKE) in the southeastern Arabian Sea (SEAS) during the relatively least explored winter season spanning 28 years (1993–2020) was studied using satellite observational and reanalysis data from the Copernicus Marine Service Data Center. The generation and enhancement of EKE resulting from current instabilities are discussed, and the significant role of barotropic energy conversion in the SEAS, is further examined, considering the roles of surface currents and wind forcing obtained from ERA5 reanalysis dataset. The strong EKE observed during winter within the Laccadive Sea in the SEAS is partly attributed to dominant barotropic instability arising from horizontal shear in surface currents driven by strong negative wind stress curl. Furthermore, EKE shows a significant positive correlation with chlorophyll-<em>a</em> (Chl-<em>a</em>) concentration during winter in the SEAS, highlighting the influence of physical-biological coupling associated with eddies and the zonal advection of Bay of Bengal waters by the northeast monsoon current.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105537"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-10-17DOI: 10.1016/j.dsr2.2025.105555
Asmi M. Napitu, Arnold L. Gordon, Shannon M. Bohman
Indonesian throughflow (ITF) spreads along two major pathways within the Indian Ocean: the westward route within the South Equatorial Current (SEC) and the southward route within the Leeuwin Current (LC) along western Australia. The LC pathway is favored over the SEC pathway when northward winds off the west coast of Australia are weak, such as during Ningaloo Niño in 2010–2014. In this study, we track the ITF spreading into the relatively saline southern Indian Ocean subtropics using the Argo data-derived Relative Fresh Water Content (RFWC) as a marker of ITF water. We contrast the spreading pattern during a strong LC period in 2010–2014 to that during a weak period in 2015–2019. The highest RFWC occurs in the upper 300 m, above the 25.5 kg/m3 density surface, and migrates westward from the LC as anticyclonic eddies at approximately 4 cm/s. Interannual variability in the RFWC is evident with advective lag times from the LC. The eddies mix their low-salinity ITF water into the salty subtropical water laterally along the density surfaces with an estimated diffusivity rate of 2.4 × 102 m2/s, affecting the overall freshwater budget of the subtropical gyre. Eddy shedding from the LC system represents an alternative pathway for ITF spreading into the Indian Ocean.
{"title":"Indonesian Throughflow into the Leeuwin Current and subtropical Indian Ocean","authors":"Asmi M. Napitu, Arnold L. Gordon, Shannon M. Bohman","doi":"10.1016/j.dsr2.2025.105555","DOIUrl":"10.1016/j.dsr2.2025.105555","url":null,"abstract":"<div><div>Indonesian throughflow (ITF) spreads along two major pathways within the Indian Ocean: the westward route within the South Equatorial Current (SEC) and the southward route within the Leeuwin Current (LC) along western Australia. The LC pathway is favored over the SEC pathway when northward winds off the west coast of Australia are weak, such as during Ningaloo Niño in 2010–2014. In this study, we track the ITF spreading into the relatively saline southern Indian Ocean subtropics using the Argo data-derived Relative Fresh Water Content (RFWC) as a marker of ITF water. We contrast the spreading pattern during a strong LC period in 2010–2014 to that during a weak period in 2015–2019. The highest RFWC occurs in the upper 300 m, above the 25.5 kg/m<sup>3</sup> density surface, and migrates westward from the LC as anticyclonic eddies at approximately 4 cm/s. Interannual variability in the RFWC is evident with advective lag times from the LC. The eddies mix their low-salinity ITF water into the salty subtropical water laterally along the density surfaces with an estimated diffusivity rate of 2.4 × 10<sup>2</sup> m<sup>2</sup>/s, affecting the overall freshwater budget of the subtropical gyre. Eddy shedding from the LC system represents an alternative pathway for ITF spreading into the Indian Ocean.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105555"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145412761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-10-01DOI: 10.1016/j.dsr2.2025.105549
Tanya A. Marshall , Eesaa Harris , Sarah E. Fawcett
The western South Indian Ocean is a highly dynamic region where tropical and subtropical waters converge. As in other ocean areas, the nutrient conditions of its thermocline play a critical role in setting regional productivity, yet they remain largely unstudied. Here, we investigate local biogeochemical processes that alter thermocline nutrient ratios in the western South Indian Ocean by applying a regional optimum multiparameter analysis to WOCE data collected across the northern and southern entrances to the Mozambique Channel, the Southeast Madagascar Current, and the Agulhas Current. We first quantify the relative contributions of three proximate source waters (Equatorial, Tropical, Subtropical) to the regional thermocline (∼100–900 m), along with the nutrient (i.e., nitrate and phosphate) inventories expected from isopycnal mixing of these source waters. We then use the difference between the expected and observed nutrient concentrations and ratios to diagnose the occurrence of local biogeochemical processes such as organic matter remineralization and N2 fixation. We find that distinct regimes characterize the two entrances to the Mozambique Channel, with nutrient-rich Tropical source waters dominating the northern entrance (>55%) while nutrient-poor Subtropical source waters dominate the south (>80%). At the northern entrance, overlapping nutrient addition and removal processes drive only minor changes to the thermocline nutrient inventory relative to the nutrients supplied by the proximate source waters, with no evidence of local N2 fixation. By contrast, south of the Mozambique Channel (>25°S), including across the Southeast Madagascar Current and Agulhas Current, a strong local remineralization signal indicates nutrient addition to the Subtropical thermocline. These nutrients have a high nitrate-to-phosphate ratio relative to those supplied by the proximate and underlying source waters, which we interpret as evidence of local N2 fixation. Our analysis shows that N2 fixation occurs locally in the subtropical southwest Indian Ocean where it will fuel regional productivity and carbon export.
{"title":"Remineralisation signals in the western South Indian Ocean thermocline: diagnosing local biogeochemical processes from nutrient stoichiometry","authors":"Tanya A. Marshall , Eesaa Harris , Sarah E. Fawcett","doi":"10.1016/j.dsr2.2025.105549","DOIUrl":"10.1016/j.dsr2.2025.105549","url":null,"abstract":"<div><div>The western South Indian Ocean is a highly dynamic region where tropical and subtropical waters converge. As in other ocean areas, the nutrient conditions of its thermocline play a critical role in setting regional productivity, yet they remain largely unstudied. Here, we investigate local biogeochemical processes that alter thermocline nutrient ratios in the western South Indian Ocean by applying a regional optimum multiparameter analysis to WOCE data collected across the northern and southern entrances to the Mozambique Channel, the Southeast Madagascar Current, and the Agulhas Current. We first quantify the relative contributions of three proximate source waters (Equatorial, Tropical, Subtropical) to the regional thermocline (∼100–900 m), along with the nutrient (i.e., nitrate and phosphate) inventories expected from isopycnal mixing of these source waters. We then use the difference between the expected and observed nutrient concentrations and ratios to diagnose the occurrence of local biogeochemical processes such as organic matter remineralization and N<sub>2</sub> fixation. We find that distinct regimes characterize the two entrances to the Mozambique Channel, with nutrient-rich Tropical source waters dominating the northern entrance (>55%) while nutrient-poor Subtropical source waters dominate the south (>80%). At the northern entrance, overlapping nutrient addition and removal processes drive only minor changes to the thermocline nutrient inventory relative to the nutrients supplied by the proximate source waters, with no evidence of local N<sub>2</sub> fixation. By contrast, south of the Mozambique Channel (>25°S), including across the Southeast Madagascar Current and Agulhas Current, a strong local remineralization signal indicates nutrient addition to the Subtropical thermocline. These nutrients have a high nitrate-to-phosphate ratio relative to those supplied by the proximate and underlying source waters, which we interpret as evidence of local N<sub>2</sub> fixation. Our analysis shows that N<sub>2</sub> fixation occurs locally in the subtropical southwest Indian Ocean where it will fuel regional productivity and carbon export.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105549"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-11-09DOI: 10.1016/j.dsr2.2025.105564
Michael R. Landry , Raúl Laiz-Carrión , Sven A. Kranz , Karen E. Selph , Michael R. Stukel , Estrella Malca , David Die , Lynnath E. Beckley , Moira Décima , Rasmus Swalethorp , José M. Quintanilla , Natalia Yingling , Claire H. Davies , Claudia Traboni , Ricardo Borrego-Santos , Joaquim I. Goes , Ariana de Souza , Patricia Romero-Fernández , M. Grazia Pennino , Lindsey E. Kim , Luke Matisons
Southern Bluefin Tuna (SBT, Thunnus maccoyii) range broadly in rich feeding grounds of the Southern Hemisphere but spawn only in a small tropical region off northwestern Australia directly downstream of the Indonesian Throughflow. Here, we describe goals, physical context, design and major findings of an end-to-end process study conducted during the peak SBT spawning season (January–March 2022) to understand nutrient sources, productivity, pelagic food web structure and their relationships to larval SBT feeding, growth and survival. Mesoscale variability was investigated by continuous underway measurements of surface waters and station sampling along the cruise track. Biogeochemical and community relationships, process rates, and trophic interactions were determined in four multi-day Lagrangian experiments in the southern Argo Basin. The study revealed strong system balances among nitrogen fluxes, phytoplankton production, grazing processes, and export. Highly selective feeding on appendicularians allows efficient trophic transfer from picophytoplankton-dominated production to SBT larvae. Plankton productivity, phytoplankton carbon and zooplankton biomass were proportionately elevated compared to similar measurements from the Atlantic bluefin larval habitat in the Gulf of Mexico, but with less advective input from the coastal margins. Individual-based otolith and stable isotope analyses identify larvae of low trophic position, narrow diet, and narrow maternal diet as the fastest growers most likely to contribute to stock recruitment. Our study highlights the importance of system-level studies to document and understand the subtleties of how food webs of oligotrophic regions respond to climate change, which may not be predictable from the acquired knowledge of historical studies.
{"title":"Overview of BLOOFINZ/INDITUN investigations of the southern bluefin spawning region off northwest Australia, January–March 2022","authors":"Michael R. Landry , Raúl Laiz-Carrión , Sven A. Kranz , Karen E. Selph , Michael R. Stukel , Estrella Malca , David Die , Lynnath E. Beckley , Moira Décima , Rasmus Swalethorp , José M. Quintanilla , Natalia Yingling , Claire H. Davies , Claudia Traboni , Ricardo Borrego-Santos , Joaquim I. Goes , Ariana de Souza , Patricia Romero-Fernández , M. Grazia Pennino , Lindsey E. Kim , Luke Matisons","doi":"10.1016/j.dsr2.2025.105564","DOIUrl":"10.1016/j.dsr2.2025.105564","url":null,"abstract":"<div><div>Southern Bluefin Tuna (SBT, <em>Thunnus maccoyii</em>) range broadly in rich feeding grounds of the Southern Hemisphere but spawn only in a small tropical region off northwestern Australia directly downstream of the Indonesian Throughflow. Here, we describe goals, physical context, design and major findings of an end-to-end process study conducted during the peak SBT spawning season (January–March 2022) to understand nutrient sources, productivity, pelagic food web structure and their relationships to larval SBT feeding, growth and survival. Mesoscale variability was investigated by continuous underway measurements of surface waters and station sampling along the cruise track. Biogeochemical and community relationships, process rates, and trophic interactions were determined in four multi-day Lagrangian experiments in the southern Argo Basin. The study revealed strong system balances among nitrogen fluxes, phytoplankton production, grazing processes, and export. Highly selective feeding on appendicularians allows efficient trophic transfer from picophytoplankton-dominated production to SBT larvae. Plankton productivity, phytoplankton carbon and zooplankton biomass were proportionately elevated compared to similar measurements from the Atlantic bluefin larval habitat in the Gulf of Mexico, but with less advective input from the coastal margins. Individual-based otolith and stable isotope analyses identify larvae of low trophic position, narrow diet, and narrow maternal diet as the fastest growers most likely to contribute to stock recruitment. Our study highlights the importance of system-level studies to document and understand the subtleties of how food webs of oligotrophic regions respond to climate change, which may not be predictable from the acquired knowledge of historical studies.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105564"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145525780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-09-16DOI: 10.1016/j.dsr2.2025.105548
Andrew R. Majewski , Krystal Woodard , Andrea Niemi , Sheila Atchison , Jane Eert , Shannon MacPhee , James D. Reist
Marine fishes occupy a range of trophic positions, all of which play integral roles in energy pathways within and amongst habitats. Understanding marine fish community structure and habitat associations is prerequisite to understanding ecosystem structure and function in the western Canadian Arctic, and the lack of regional-scale information impedes effective regulation of emerging industrial activities and climate adaptation strategies. Our study documented 46 demersal fish species from 29 genera, recording eight new species occurrences for Amundsen Gulf. The demersal fish community of Amundsen Gulf is largely structured by the depth-mediated water masses of the region where they interface with seafloor habitats. The fish assemblages appeared stable over the seven-year span of the study, while interannual fluctuations in abundance reflected species-level variability. Species richness was higher in Amundsen Gulf relative to the adjacent Canadian Beaufort Shelf and slope, but indexes for evenness and species dominance in Amundsen Gulf were skewed by the pervasiveness of Boreogadus saida. The average abundance of B. saida was 4.7 times higher at stations where fishing occurred within Atlantic waters relative to Pacific waters, with peak average abundance documented in Minto Inlet. The deep Atlantic water and large embayments of Amundsen Gulf support high abundances of B. saida across life-history stages and warrant special consideration for industrial planning and conservation initiatives. Our results provide contemporary baselines on marine fish community structure and diversity for the Amundsen Gulf region and provide a basis for evaluating future change and comparisons with neighboring regions.
{"title":"Offshore demersal fish community structure and habitat associations in Amundsen Gulf, Canadian Arctic","authors":"Andrew R. Majewski , Krystal Woodard , Andrea Niemi , Sheila Atchison , Jane Eert , Shannon MacPhee , James D. Reist","doi":"10.1016/j.dsr2.2025.105548","DOIUrl":"10.1016/j.dsr2.2025.105548","url":null,"abstract":"<div><div>Marine fishes occupy a range of trophic positions, all of which play integral roles in energy pathways within and amongst habitats. Understanding marine fish community structure and habitat associations is prerequisite to understanding ecosystem structure and function in the western Canadian Arctic, and the lack of regional-scale information impedes effective regulation of emerging industrial activities and climate adaptation strategies. Our study documented 46 demersal fish species from 29 genera, recording eight new species occurrences for Amundsen Gulf. The demersal fish community of Amundsen Gulf is largely structured by the depth-mediated water masses of the region where they interface with seafloor habitats. The fish assemblages appeared stable over the seven-year span of the study, while interannual fluctuations in abundance reflected species-level variability. Species richness was higher in Amundsen Gulf relative to the adjacent Canadian Beaufort Shelf and slope, but indexes for evenness and species dominance in Amundsen Gulf were skewed by the pervasiveness of <em>Boreogadus saida</em>. The average abundance of <em>B. saida</em> was 4.7 times higher at stations where fishing occurred within Atlantic waters relative to Pacific waters, with peak average abundance documented in Minto Inlet. The deep <span>Atlantic</span> water and large embayments of Amundsen Gulf support high abundances of <em>B. saida</em> across life-history stages and warrant special consideration for industrial planning and conservation initiatives. Our results provide contemporary baselines on marine fish community structure and diversity for the Amundsen Gulf region and provide a basis for evaluating future change and comparisons with neighboring regions.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105548"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120043","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-11-17DOI: 10.1016/j.dsr2.2025.105563
Karen E. Selph , Natalia Yingling , Claudia Traboni , Michael R. Landry
The Argo Basin of the eastern Indian Ocean in austral summer (February 2022) was characterized by warm (28.5–30.6 °C), oligotrophic surface waters (nitrate and phosphate ≤0.1 μM), with relatively shallow mixed layers and deep chlorophyll biomass maxima. From euphotic zone depth-resolved samples analyzed by for DNA and acid vacuole staining (Hoechst and LysoTracker Green) by ship-board flow cytometry, we found that autotrophic populations were dominated by Prochlorococcus, followed by mixotrophs (58 and 28 % of autotrophic community biomass, respectively), with only 14 % obligate phototrophic phytoplankton (i.e., plastidic cells without acid vacuole fluorescence). Acid vacuole-containing microbes (mixotrophs and heterotrophs) were 34 % of the microbial community, and 80 % of the eukaryotic biomass. In shallow waters, the eukaryotic chlorophyll-containing community was comprised of pico-sized obligate phototrophs and mixotrophs (233–325 cells mL−1), nano-sized obligate phototrophs and mixotrophs (72 and 374 cells mL−1, respectively), with all groups increasing several-fold in the deep chlorophyll maxima. Mixotrophs were a higher proportion of the chlorophyll-containing community in the shallow nutrient-poor mixed layer, consistent with a nutrient-acquisition argument for their prevalence. Heterotrophic eukaryotes averaged 524 ± 36 cells mL−1 in the euphotic zone, changing little with depth and showing a significant positive relationship with Prochlorococcus, but not any other group. In contrast, mixotrophs were positively correlated with heterotrophic bacteria, but not with Prochlorococcus. Overall, the high proportion of mixotrophs in the microbial community may channel more productivity to higher trophic levels than expected given the region's nutrient-poor status.
{"title":"Acidic vacuole-containing organisms are a majority of the eukaryotic microbial community in oligotrophic Argo Basin waters (eastern Indian ocean)","authors":"Karen E. Selph , Natalia Yingling , Claudia Traboni , Michael R. Landry","doi":"10.1016/j.dsr2.2025.105563","DOIUrl":"10.1016/j.dsr2.2025.105563","url":null,"abstract":"<div><div>The Argo Basin of the eastern Indian Ocean in austral summer (February 2022) was characterized by warm (28.5–30.6 °C), oligotrophic surface waters (nitrate and phosphate ≤0.1 μM), with relatively shallow mixed layers and deep chlorophyll biomass maxima. From euphotic zone depth-resolved samples analyzed by for DNA and acid vacuole staining (Hoechst and LysoTracker Green) by ship-board flow cytometry, we found that autotrophic populations were dominated by <em>Prochlorococcus</em>, followed by mixotrophs (58 and 28 % of autotrophic community biomass, respectively), with only 14 % obligate phototrophic phytoplankton (i.e., plastidic cells without acid vacuole fluorescence). Acid vacuole-containing microbes (mixotrophs and heterotrophs) were 34 % of the microbial community, and 80 % of the eukaryotic biomass. In shallow waters, the eukaryotic chlorophyll-containing community was comprised of pico-sized obligate phototrophs and mixotrophs (233–325 cells mL<sup>−1</sup>), nano-sized obligate phototrophs and mixotrophs (72 and 374 cells mL<sup>−1</sup>, respectively), with all groups increasing several-fold in the deep chlorophyll maxima. Mixotrophs were a higher proportion of the chlorophyll-containing community in the shallow nutrient-poor mixed layer, consistent with a nutrient-acquisition argument for their prevalence. Heterotrophic eukaryotes averaged 524 ± 36 cells mL<sup>−1</sup> in the euphotic zone, changing little with depth and showing a significant positive relationship with <em>Prochlorococcus</em>, but not any other group. In contrast, mixotrophs were positively correlated with heterotrophic bacteria, but not with <em>Prochlorococcus</em>. Overall, the high proportion of mixotrophs in the microbial community may channel more productivity to higher trophic levels than expected given the region's nutrient-poor status.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105563"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01Epub Date: 2025-10-18DOI: 10.1016/j.dsr2.2025.105554
Jordan Toullec , Millat Blanc , Pierrick Penven , Alexandre Epinoux , Natasha Buckiewicz , Emmanuelle Jaouen , Valentine Szrama , Margaux Noyon , Jean-François Ternon , Luis Felipe Artigas
Fine-scale oceanographic structures such as eddies, fronts, and filaments strongly influence biogeochemical and ecological processes. So far, the characterization of phytoplankton communities of the Mozambique Channel (MZC) was limited to in-situ sampling and satellite monitoring of chlorophyll-a biomass estimation. Few studies have looked at phytoplankton community composition. During the RESILIENCE cruise in 2022, three structures were sampled; an anticyclonic eddy, a frontal area and a cyclonic eddy. Phytoplankton functional groups (PFGs) were studied at small-scale (1 km) in subsurface (about 5m depth) waters using automated underway measurements. A multispectral fluorometer (FLP) and an automated pulse shape-recording flow cytometer (AFCM). The oceanographic mesoscale features clearly structured the phytoplankton groups with distinct patterns observed in each of the three areas studied. A relatively high concentration of brown pigmentary group (groups containing xanthophyll and carotenoids-like pigments) was observed in the cyclonic eddy. High abundance of nano-microeukaryotes and of prokaryotic phytoplankton (Synechococcus spp. and Prochlorococcus spp.) were identified in the cyclonic eddy. These differences could potentially affect higher trophic levels such as zooplankton, micronekton, large pelagic fish, mammals, and seabirds. Finally, this phytoplankton community differentiation could also impact biogeochemical processes such as carbon sequestration and nutrient dynamics in the MZC.
{"title":"Response of phytoplankton to eddy dipole structure in the Mozambican channel: An automated underway evaluation","authors":"Jordan Toullec , Millat Blanc , Pierrick Penven , Alexandre Epinoux , Natasha Buckiewicz , Emmanuelle Jaouen , Valentine Szrama , Margaux Noyon , Jean-François Ternon , Luis Felipe Artigas","doi":"10.1016/j.dsr2.2025.105554","DOIUrl":"10.1016/j.dsr2.2025.105554","url":null,"abstract":"<div><div>Fine-scale oceanographic structures such as eddies, fronts, and filaments strongly influence biogeochemical and ecological processes. So far, the characterization of phytoplankton communities of the Mozambique Channel (MZC) was limited to <em>in-situ</em> sampling and satellite monitoring of chlorophyll-<em>a</em> biomass estimation. Few studies have looked at phytoplankton community composition. During the RESILIENCE cruise in 2022, three structures were sampled; an anticyclonic eddy, a frontal area and a cyclonic eddy. Phytoplankton functional groups (PFGs) were studied at small-scale (1 km) in subsurface (about 5m depth) waters using automated underway measurements. A multispectral fluorometer (FLP) and an automated pulse shape-recording flow cytometer (AFCM). The oceanographic mesoscale features clearly structured the phytoplankton groups with distinct patterns observed in each of the three areas studied. A relatively high concentration of brown pigmentary group (groups containing xanthophyll and carotenoids-like pigments) was observed in the cyclonic eddy. High abundance of nano-microeukaryotes and of prokaryotic phytoplankton (<em>Synechococcus</em> spp. and <em>Prochlorococcus</em> spp.) were identified in the cyclonic eddy. These differences could potentially affect higher trophic levels such as zooplankton, micronekton, large pelagic fish, mammals, and seabirds. Finally, this phytoplankton community differentiation could also impact biogeochemical processes such as carbon sequestration and nutrient dynamics in the MZC.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105554"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145358149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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