Pub 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":"2025-11-02","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 : 2025-11-01DOI: 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":"2025-11-01","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 : 2025-10-30DOI: 10.1016/j.dsr2.2025.105557
Criado Léa , Barboni Alexandre , Carton Xavier
The PHYSINDIEN 2019 campaign occurred in the Northwestern Arabian Sea, during the spring intermonsoon, between 16 and 25 °N. Along its 3000 km transect, it sampled 5 anticyclones, 3 cyclones and 2 cyclonic submesoscale coherent vortices (SCV) with continuous hydrological and velocity measurements. Remarkably, the two cyclonic SCV were located beneath surface mesoscale anticyclones. Also, a water mass analysis shows that small anticyclones with Persian Gulf Water (PGW) are found in the Gulf of Oman, while anticyclones further south are shallower vortices containing Arabian Sea High Salinity Water (ASHSW). Comparison of in situ data with the META atlas, a state-of-the-art eddy detection and tracking atlas based on altimetry, reveals that eddy radii are often underestimated by remote sensing. In this atlas, eddy tracks are often discontinuous due to missing detections. Both hydrological measurements and remote-sensing tracking are however consistent in indicating that along the southern Omani coast anticyclones are formed offshore during the spring intermonsoon, near the center of the Arabian Sea. These results underline the diversity of surface and subsurface eddies in the sparsely explored Arabian Sea, and provide insight on the potential bias of their remote detections.
{"title":"Mesoscale processes in the northern Arabian Sea: Linking in situ observations to remote-sensing","authors":"Criado Léa , Barboni Alexandre , Carton Xavier","doi":"10.1016/j.dsr2.2025.105557","DOIUrl":"10.1016/j.dsr2.2025.105557","url":null,"abstract":"<div><div>The PHYSINDIEN 2019 campaign occurred in the Northwestern Arabian Sea, during the spring intermonsoon, between 16 and 25 °N. Along its 3000 km transect, it sampled 5 anticyclones, 3 cyclones and 2 cyclonic submesoscale coherent vortices (SCV) with continuous hydrological and velocity measurements. Remarkably, the two cyclonic SCV were located beneath surface mesoscale anticyclones. Also, a water mass analysis shows that small anticyclones with Persian Gulf Water (PGW) are found in the Gulf of Oman, while anticyclones further south are shallower vortices containing Arabian Sea High Salinity Water (ASHSW). Comparison of in situ data with the META atlas, a state-of-the-art eddy detection and tracking atlas based on altimetry, reveals that eddy radii are often underestimated by remote sensing. In this atlas, eddy tracks are often discontinuous due to missing detections. Both hydrological measurements and remote-sensing tracking are however consistent in indicating that along the southern Omani coast anticyclones are formed offshore during the spring intermonsoon, near the center of the Arabian Sea. These results underline the diversity of surface and subsurface eddies in the sparsely explored Arabian Sea, and provide insight on the potential bias of their remote detections.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105557"},"PeriodicalIF":3.0,"publicationDate":"2025-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145462846","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}
In marine environments, plastic debris serves as a vector for pathogenic bacteria that can negatively impact marine fauna, including corals. The Saya de Malha and Nazareth Banks, located in the Indian Ocean, harbor an extensive area of coral reefs that may be susceptible to diseases associated with plastic pollution. In this context, we aimed to determine whether plastic debris in this region can act as a vector for coral-associated pathogenic bacteria. During the "Indian Ocean mission 2022," floating plastic debris (>500 μm) was collected from the Saya de Malha region using manta trawling. The collected debris were quantified, classified by type, size, and weighed. The associated microbiome, along with the viable bacterial communities attached to the plastic, were analyzed using 16S rDNA high-throughput sequencing and traditional molecular and microbiological techniques. A high concentration of plastic debris was recorded both on Saya de Malha and Nazareth Bank, with 105 items.km−2. The mean viable bacterial count was 15,519 ± 9340 CFU/g of plastic debris. Nine bacterial phyla were identified, with Firmicutes (58 % of the total) and Proteobacteria (42 %) being the dominant groups. The bacterial diversity on the plastic was measured at 0.92, including coral pathogens, such as Acinetobacter (27 %), Psychrobacter (2 %), and Pseudomonas (2 %). In addition, probiotic bacteria such as Exiguobacterium (58 %), Rheinheimera (1 %), and Idiomarina (1 %) were also detected. This preliminary study states the presence of both pathogenic and probiotic coral-associated fixed to plastic. Further research is needed to confirm their direct effect on coral reef disease. Nevertheless, these findings add to the growing evidence of the widespread presence of plastic debris floating in the region.
在海洋环境中，塑料碎片是致病菌的载体，会对包括珊瑚在内的海洋动物产生负面影响。位于印度洋的Saya de Malha和拿撒勒浅滩拥有大面积的珊瑚礁，可能容易受到与塑料污染有关的疾病的影响。在这种情况下，我们的目的是确定该地区的塑料碎片是否可以作为珊瑚相关致病菌的载体。在“印度洋任务2022”期间，使用蝠鲼拖网在Saya de Malha地区收集了漂浮的塑料碎片（>500 μm）。收集到的碎片按类型、大小和重量进行了量化、分类。使用16S rDNA高通量测序和传统的分子和微生物学技术分析了相关的微生物组，以及附着在塑料上的活菌群落。在Saya de Malha和拿撒勒银行都记录到了高浓度的塑料碎片，有105件。平均活菌数为15519±9340 CFU/g。共鉴定出9个细菌门，其中厚壁菌门（占总数的58%）和变形菌门（42%）是优势类群。塑料上的细菌多样性测量为0.92，包括珊瑚病原体，如不动杆菌（27%），冻干杆菌（2%）和假单胞菌（2%）。此外，还检出了Exiguobacterium（58%）、Rheinheimera（1%）和Idiomarina（1%）等益生菌。本初步研究表明，与珊瑚相关的致病性和益生菌均固定在塑料上。需要进一步的研究来证实它们对珊瑚礁疾病的直接影响。然而，这些发现进一步证明，该地区漂浮着广泛存在的塑料碎片。
{"title":"Plastic pollution: A potential vector of both pathogens and probiotics for corals on the Mascarene Ridge, Indian Ocean","authors":"Vyctoria Marillac , Philippe Jourand , Pierre-Louis Stenger , Gwennais Fustemberg , Julie Gindrey , Margot Thibault","doi":"10.1016/j.dsr2.2025.105556","DOIUrl":"10.1016/j.dsr2.2025.105556","url":null,"abstract":"<div><div>In marine environments, plastic debris serves as a vector for pathogenic bacteria that can negatively impact marine fauna, including corals. The Saya de Malha and Nazareth Banks, located in the Indian Ocean, harbor an extensive area of coral reefs that may be susceptible to diseases associated with plastic pollution. In this context, we aimed to determine whether plastic debris in this region can act as a vector for coral-associated pathogenic bacteria. During the \"Indian Ocean mission 2022,\" floating plastic debris (>500 μm) was collected from the Saya de Malha region using manta trawling. The collected debris were quantified, classified by type, size, and weighed. The associated microbiome, along with the viable bacterial communities attached to the plastic, were analyzed using 16S rDNA high-throughput sequencing and traditional molecular and microbiological techniques. A high concentration of plastic debris was recorded both on Saya de Malha and Nazareth Bank, with 10<sup>5</sup> items.km<sup>−2</sup>. The mean viable bacterial count was 15,519 ± 9340 CFU/g of plastic debris. Nine bacterial phyla were identified, with Firmicutes (58 % of the total) and Proteobacteria (42 %) being the dominant groups. The bacterial diversity on the plastic was measured at 0.92, including coral pathogens, such as <em>Acinetobacter</em> (27 %), <em>Psychrobacter</em> (2 %), and <em>Pseudomonas</em> (2 %). In addition, probiotic bacteria such as <em>Exiguobacterium</em> (58 %), <em>Rheinheimera</em> (1 %), and <em>Idiomarina</em> (1 %) were also detected. This preliminary study states the presence of both pathogenic and probiotic coral-associated fixed to plastic. Further research is needed to confirm their direct effect on coral reef disease. Nevertheless, these findings add to the growing evidence of the widespread presence of plastic debris floating in the region.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105556"},"PeriodicalIF":3.0,"publicationDate":"2025-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145412760","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 : 2025-10-18DOI: 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":"2025-10-18","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}
Pub 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":"2025-10-17","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 : 2025-10-16DOI: 10.1016/j.dsr2.2025.105552
Saskia Brix , Thea Sophie Elsig , Patricia Esquete , Áki Jarl Láruson , Katrin Linse , Elisabeth Schaal , Lydia Anastasia Schmidt , Carolin Uhlir , Johanna N.J. Weston , Anne-Nina Lörz
Amathillopsis spinigera Heller, 1875, is an enigmatic peracarid crustacean species found in the Arctic Ocean. During the summer of 2024, it was recorded in the HAUSGARTEN observatory for the first time, following 25 years of regular sampling as part of the Fram Strait Long-Term Ecological Research observatory. This study significantly broadens the known geographic and bathymetric range of A. spinigera, with a total of 46 specimens collected from HAUSGARTEN (HG) and cold seeps at Svyatogor Ridge, during two expeditions conducted in 2024. Further, our review of all publicly available database (historical) records for A. spinigera leads to an expansion of its depth range from 186 – 1972 m to 11 – 3182 m. Recent observations using remotely operated vehicles (ROVs) have confirmed their clinging behavior on organic structures such as worm tubes, likely elevating the species within the water column to facilitate food capture. Females at various life stages, including egg-bearing individuals, were observed alongside juveniles and males of different sizes, enabling a redescription of the species based on an integrative taxonomy approach that incorporates both molecular and morphological data. The study also highlights biogeographic patterns, with a notable preference for eastern occurrences along the Arctic continental slope. While gaps in data from Greenland and Canadian regions, coupled with minimal sampling in the Central Arctic Ocean, suggest potential sampling bias, circumarctic connectivity appears plausible. This inference is supported by high genetic similarity in barcode data from individuals found across distant geographic locations.
{"title":"Clinging onto Arctic Benthos: Biogeography of Amathillopsis spinigera Heller, 1875 (Crustacea: Amphipoda), including its redescription","authors":"Saskia Brix , Thea Sophie Elsig , Patricia Esquete , Áki Jarl Láruson , Katrin Linse , Elisabeth Schaal , Lydia Anastasia Schmidt , Carolin Uhlir , Johanna N.J. Weston , Anne-Nina Lörz","doi":"10.1016/j.dsr2.2025.105552","DOIUrl":"10.1016/j.dsr2.2025.105552","url":null,"abstract":"<div><div><em>Amathillopsis spinigera</em> Heller, 1875, is an enigmatic peracarid crustacean species found in the Arctic Ocean. During the summer of 2024, it was recorded in the HAUSGARTEN observatory for the first time, following 25 years of regular sampling as part of the Fram Strait Long-Term Ecological Research observatory. This study significantly broadens the known geographic and bathymetric range of <em>A. spinigera</em>, with a total of 46 specimens collected from HAUSGARTEN (HG) and cold seeps at Svyatogor Ridge, during two expeditions conducted in 2024. Further, our review of all publicly available database (historical) records for <em>A. spinigera</em> leads to an expansion of its depth range from 186 – 1972 m to 11 – 3182 m. Recent observations using remotely operated vehicles (ROVs) have confirmed their clinging behavior on organic structures such as worm tubes, likely elevating the species within the water column to facilitate food capture. Females at various life stages, including egg-bearing individuals, were observed alongside juveniles and males of different sizes, enabling a redescription of the species based on an integrative taxonomy approach that incorporates both molecular and morphological data. The study also highlights biogeographic patterns, with a notable preference for eastern occurrences along the Arctic continental slope. While gaps in data from Greenland and Canadian regions, coupled with minimal sampling in the Central Arctic Ocean, suggest potential sampling bias, circumarctic connectivity appears plausible. This inference is supported by high genetic similarity in barcode data from individuals found across distant geographic locations.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105552"},"PeriodicalIF":3.0,"publicationDate":"2025-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145525779","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 : 2025-10-14DOI: 10.1016/j.dsr2.2025.105553
Paola Galloso , Giancarlo M. Correa , Pierre Legendre
The northern Humboldt Current System (HCS) is a highly productive eastern boundary upwelling system off Peru. El Niño Southern Oscillation (ENSO) is one of the main drivers of short-term climate variability, whose warm (El Niño) and cold (La Niña) phases can trigger changes in the physical, chemical, biological, and socioeconomic conditions of the northern HCS. We explored the impacts of ENSO phases and magnitude in the region over the structure of the pelagic fish community in the northern HCS through the study of spatial and temporal beta diversity changes. To achieve this goal, we used 25-year taxonomic composition data from pelagic scientific surveys and statistical multivariate methods. We found that, depending on the magnitudes, most of the El Niño (EN) categories substantially increased the diversity index values in this system with respect to the neutral phase. In contrast, La Niña (LN) decreased it. The community spatial structure principally showed three ecological regions, which varied in extension, indicator species, and composition across ENSO phases. The local contribution to beta diversity (LCBD) showed that the shelf break is essential in shaping the community structure among ENSO phases. The changes in temporal beta diversity suggest that the spatial structure or change of the community abundance is influenced by the magnitude of the EN phase. We conclude that the oceanographic changes caused by the ENSO phases may significantly impact the fish community structure in the northern HCS. Our results are relevant to implementing climate-ready management measures in this ecosystem.
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The 2022 Indian Ocean Expedition organised by Monaco Explorations rolled out an ambitious outreach and communication strategy to raise awareness among a wide range of audiences about critical ocean issues and share the expedition outcomes with various target groups: the media, the general public, decision-makers and civil society stakeholders, teachers, the young generation, etc. This article provides an in-depth critical analysis of the objectives, design, and implementation of outreach mechanisms and the results achieved, using quantitative and qualitative indicators to highlight successes, limitations, and challenges, particularly in terms of assessing the results and the ownership of issues. In conclusion, a number of avenues are proposed to amplify and optimise the impact of such outreach and communication activities and their contribution to the Ocean Literacy approach, particularly in the context of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030).
{"title":"Awareness-raising, communication methods and objectives for an ocean expedition: the example of the Monaco explorations Indian Ocean expedition 2022","authors":"Didier Théron , Océane Gasquy , François Simard , Dominique Benzaken , Elise Rigot , Amwar Bhai Rumjaun , Stéphane Dugast , Rémi Leroy , Carolyn Scheurle","doi":"10.1016/j.dsr2.2025.105551","DOIUrl":"10.1016/j.dsr2.2025.105551","url":null,"abstract":"<div><div>The 2022 Indian Ocean Expedition organised by Monaco Explorations rolled out an ambitious outreach and communication strategy to raise awareness among a wide range of audiences about critical ocean issues and share the expedition outcomes with various target groups: the media, the general public, decision-makers and civil society stakeholders, teachers, the young generation, etc. This article provides an in-depth critical analysis of the objectives, design, and implementation of outreach mechanisms and the results achieved, using quantitative and qualitative indicators to highlight successes, limitations, and challenges, particularly in terms of assessing the results and the ownership of issues. In conclusion, a number of avenues are proposed to amplify and optimise the impact of such outreach and communication activities and their contribution to the Ocean Literacy approach, particularly in the context of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030).</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105551"},"PeriodicalIF":3.0,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145412759","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 : 2025-10-01DOI: 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":"2025-10-01","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}
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