Pub Date : 2026-01-14DOI: 10.1016/j.dsr.2026.104653
Hugh W. Ducklow , Oscar M. Schofield , Sharon E. Stammerjohn , David L. Kirchman
Marine pelagic ecosystems around the world are changing in response to climate change. The marine pelagic ecosystem extending along the western Antarctic Peninsula (WAP) is a region of rapid warming and sea ice loss, and in response there have been conspicuous trends in the ecosystem ranging from phytoplankton to krill and penguins. Despite the many ecosystem responses observed globally for phytoplankton and other trophic levels, there have been only a few observations of trends in heterotrophic bacteria, the most numerically dominant organisms on the planet. Here we report on a sustained increase in bacterial biomass over 2003–2019 that occurred throughout a 140,000 km2 area of the WAP. Concomitant with the rise in bacterial biomass, bacterial production, chlorophyll and primary production also increased throughout the region. The trends appear to be driven by the southward migration along the Peninsula of warm and moist conditions in the north into the cold and dry continental polar regime to the south. The extensive and sustained long-term increases in microbial biomass and activity are another sign of large changes in the WAP ecosystem.
{"title":"Multidecadal increase in microbial biomass and production along the western Antarctic Peninsula","authors":"Hugh W. Ducklow , Oscar M. Schofield , Sharon E. Stammerjohn , David L. Kirchman","doi":"10.1016/j.dsr.2026.104653","DOIUrl":"10.1016/j.dsr.2026.104653","url":null,"abstract":"<div><div>Marine pelagic ecosystems around the world are changing in response to climate change. The marine pelagic ecosystem extending along the western Antarctic Peninsula (WAP) is a region of rapid warming and sea ice loss, and in response there have been conspicuous trends in the ecosystem ranging from phytoplankton to krill and penguins. Despite the many ecosystem responses observed globally for phytoplankton and other trophic levels, there have been only a few observations of trends in heterotrophic bacteria, the most numerically dominant organisms on the planet. Here we report on a sustained increase in bacterial biomass over 2003–2019 that occurred throughout a 140,000 km<sup>2</sup> area of the WAP. Concomitant with the rise in bacterial biomass, bacterial production, chlorophyll and primary production also increased throughout the region. The trends appear to be driven by the southward migration along the Peninsula of warm and moist conditions in the north into the cold and dry continental polar regime to the south. The extensive and sustained long-term increases in microbial biomass and activity are another sign of large changes in the WAP ecosystem.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"228 ","pages":"Article 104653"},"PeriodicalIF":2.1,"publicationDate":"2026-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145986736","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 : 2026-01-02DOI: 10.1016/j.dsr.2026.104649
Mingxuan Lu , Zhao-Jun Liu , Min Wang , Xiao-Hua Zhu , Chuanzheng Zhang , Hua Zheng , Ze-Nan Zhu , Qun Ma
The Ryukyu Island chain is one of the major generation regions for internal tides in the western North Pacific, notably generating strong semidiurnal internal tides. However, due to limited in situ observational data, the characteristics of internal tides east of Ryukyu Island chain remain unclear. In this study, we used pressure-sensor-equipped inverted echo sounders (PIES) deployed southeast of Miyakojima to assess the spatial structure and temporal variability of the internal tides from June 2015 to June 2017. Observations indicated stronger semidiurnal internal tides with larger fluctuations onshore than offshore. Both PIES observations and the satellite-derived product indicated that the M2 internal tides propagated from the onshore to the offshore side; however, the amplitudes were substantially underestimated in the satellite product. The first mode of the Complex Empirical Orthogonal Function analysis revealed that the temporal amplitude exhibited clear seasonal variability, with larger amplitudes in spring (mean, 26.4 m) and autumn (mean, 22.2 m), and smaller amplitudes in summer (mean, 18.3 m) and winter (mean, 21.3 m). The pycnocline depth derived from the PIES observations also exhibited distinct seasonal variability, showing a strong correlation with sea level anomaly. These findings demonstrate that the temporal variability of the semidiurnal internal tides is likely attributable to mesoscale eddies, which modulate the pycnocline depth. Anticyclonic eddies deepen the pycnocline and suppress the amplitude of the semidiurnal internal tides. In nearly 70 % of the cases affected by mesoscale eddies during the observation period, decreased (increased) semidiurnal internal tide amplitudes occurred concurrently with a deepened (shoaled) pycnocline.
{"title":"Semidiurnal internal tides southeast of Miyakojima observed by the PIES array","authors":"Mingxuan Lu , Zhao-Jun Liu , Min Wang , Xiao-Hua Zhu , Chuanzheng Zhang , Hua Zheng , Ze-Nan Zhu , Qun Ma","doi":"10.1016/j.dsr.2026.104649","DOIUrl":"10.1016/j.dsr.2026.104649","url":null,"abstract":"<div><div>The Ryukyu Island chain is one of the major generation regions for internal tides in the western North Pacific, notably generating strong semidiurnal internal tides. However, due to limited in situ observational data, the characteristics of internal tides east of Ryukyu Island chain remain unclear. In this study, we used pressure-sensor-equipped inverted echo sounders (PIES) deployed southeast of Miyakojima to assess the spatial structure and temporal variability of the internal tides from June 2015 to June 2017. Observations indicated stronger semidiurnal internal tides with larger fluctuations onshore than offshore. Both PIES observations and the satellite-derived product indicated that the M<sub>2</sub> internal tides propagated from the onshore to the offshore side; however, the amplitudes were substantially underestimated in the satellite product. The first mode of the Complex Empirical Orthogonal Function analysis revealed that the temporal amplitude exhibited clear seasonal variability, with larger amplitudes in spring (mean, 26.4 m) and autumn (mean, 22.2 m), and smaller amplitudes in summer (mean, 18.3 m) and winter (mean, 21.3 m). The pycnocline depth derived from the PIES observations also exhibited distinct seasonal variability, showing a strong correlation with sea level anomaly. These findings demonstrate that the temporal variability of the semidiurnal internal tides is likely attributable to mesoscale eddies, which modulate the pycnocline depth. Anticyclonic eddies deepen the pycnocline and suppress the amplitude of the semidiurnal internal tides. In nearly 70 % of the cases affected by mesoscale eddies during the observation period, decreased (increased) semidiurnal internal tide amplitudes occurred concurrently with a deepened (shoaled) pycnocline.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104649"},"PeriodicalIF":2.1,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145924955","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 : 2025-12-31DOI: 10.1016/j.dsr.2025.104647
V.V.S.S. Sarma , B. Sridevi
The fraction of the primary production leaving the photic zone is important to understand the strength of the biological pump and carbon sequestration. This fraction intensifies the oxygen minimum zone by supporting life in the deeper ocean. The f-ratio, the new-to-total production ratio, represents the exportable production below the euphotic zone under specific conditions. Based on the measured f-ratios by 15N tracer and δ15N of suspended matter and their relation with sea surface temperature, salinity and chlorophyll-a (Chl-a), spatial and temporal variations in f-ratios were derived in the Bay of Bengal using remote sensing data. The 15N tracer and δ15N suspended matter methods give photic zone and mixed layer mean f-ratios, respectively. The basin-mean photic zone f-ratios were higher during winter, followed by summer and fall monsoon, with higher f-ratios along the coastal Bay of Bengal associated with the spread of riverine nutrients during fall and summer. The higher f-ratios in the northern Bay of Bengal during winter and spring were associated with atmospheric deposition of nutrients. The mixed layer and photic zone mean f-ratios in the Bay of Bengal were 0.37 ± 0.06, and 0.57 ± 0.10, respectively, suggesting that half of the primary production in the photic zone is exported to the aphotic zone. The estimated new production using external sources of nitrogen supported ∼59 ± 16 TgC annually. Based on total production from the Vertically Generalized Primary Production Model (VGPM), the f-ratio was estimated as 0.33 ± 0.05 using external sources, and it is consistent with the mixed layer mean f-ratio derived from δ15N of suspended matter (0.37 ± 0.06). Based on the mean f-ratio in the photic zone from external sources and VGPM production, about 60 ± 20 TgC y−1 of primary production sinks to the depth below the photic zone. The export production at the 100 m depth was measured to be ∼10 ± 5 TgC y−1 using thorium isotopes, suggesting that ∼50 ± 15 TgC y−1 of the primary produced organic matter may be utilized either through heterotrophic activity in a depth range between 60 and 100 m or transported horizontally. This estimate is consistent with the dark respiration rates in this depth zone and also the apparent oxygen utilization. The seasonal and spatial variations in f-ratios derived in this work may be used in the numerical model to improve the simulation and prediction of the carbon cycle in the Indian Ocean.
初级产物离开光带的比例对于了解生物泵和碳固存的强度很重要。这个部分通过支持深海中的生命而强化了最低氧区。f比，即新产量与总产量之比，代表特定条件下，在光区以下的可出口产量。基于15N示踪剂测得的f-比值和悬浮物δ15N及其与海温、盐度和叶绿素a （Chl-a）的关系，利用遥感资料推导了孟加拉湾f-比值的时空变化规律。15N示踪剂法和δ15N悬浮物法分别给出了光区和混合层平均f比。盆地平均光带f-比率在冬季较高，其次是夏季和秋季季风，在孟加拉湾沿岸较高的f-比率与秋季和夏季河流营养物质的扩散有关。孟加拉湾北部冬季和春季较高的f-比值与大气中营养物的沉积有关。孟加拉湾混合层和光区平均f比分别为0.37±0.06和0.57±0.10，表明光区初级产品的一半出口到光区。估计利用外部氮源的新产量每年支持~ 59±16 TgC。基于垂直广义初级生产模型（VGPM）估算的总产量f-ratio为0.33±0.05，与由悬浮物δ15N计算得到的混合层平均f-ratio（0.37±0.06）一致。根据光区外源平均f比和VGPM产量计算，初级产量约有60±20 TgC y−1沉到光区以下深度。使用钍同位素测量了100 m深度的出口产量为~ 10±5 TgC y - 1，这表明初级生产的有机质的~ 50±15 TgC y - 1可能通过60至100 m深度范围内的异养活动或水平运输被利用。这一估计与该深度区的暗呼吸速率和表观氧利用率一致。本研究得出的f比的季节和空间变化可用于数值模式，以改进印度洋碳循环的模拟和预测。
{"title":"Export production in the upper ocean using f-ratios in the Bay of Bengal using a remote sensing approach","authors":"V.V.S.S. Sarma , B. Sridevi","doi":"10.1016/j.dsr.2025.104647","DOIUrl":"10.1016/j.dsr.2025.104647","url":null,"abstract":"<div><div>The fraction of the primary production leaving the photic zone is important to understand the strength of the biological pump and carbon sequestration. This fraction intensifies the oxygen minimum zone by supporting life in the deeper ocean. The <em>f</em>-ratio, the new-to-total production ratio, represents the exportable production below the euphotic zone under specific conditions. Based on the measured <em>f</em>-ratios by <sup>15</sup>N tracer and δ<sup>15</sup>N of suspended matter and their relation with sea surface temperature, salinity and chlorophyll-a (Chl-a), spatial and temporal variations in <em>f</em>-ratios were derived in the Bay of Bengal using remote sensing data. The <sup>15</sup>N tracer and δ<sup>15</sup>N suspended matter methods give photic zone and mixed layer mean <em>f</em>-ratios, respectively. The basin-mean photic zone <em>f</em>-ratios were higher during winter, followed by summer and fall monsoon, with higher <em>f</em>-ratios along the coastal Bay of Bengal associated with the spread of riverine nutrients during fall and summer. The higher <em>f</em>-ratios in the northern Bay of Bengal during winter and spring were associated with atmospheric deposition of nutrients. The mixed layer and photic zone mean <em>f</em>-ratios in the Bay of Bengal were 0.37 ± 0.06, and 0.57 ± 0.10, respectively, suggesting that half of the primary production in the photic zone is exported to the aphotic zone. The estimated new production using external sources of nitrogen supported ∼59 ± 16 TgC annually. Based on total production from the Vertically Generalized Primary Production Model (VGPM), the <em>f</em>-ratio was estimated as 0.33 ± 0.05 using external sources, and it is consistent with the mixed layer mean <em>f</em>-ratio derived from δ<sup>15</sup>N of suspended matter (0.37 ± 0.06). Based on the mean <em>f</em>-ratio in the photic zone from external sources and VGPM production, about 60 ± 20 TgC y<sup>−1</sup> of primary production sinks to the depth below the photic zone. The export production at the 100 m depth was measured to be ∼10 ± 5 TgC y<sup>−1</sup> using thorium isotopes, suggesting that ∼50 ± 15 TgC y<sup>−1</sup> of the primary produced organic matter may be utilized either through heterotrophic activity in a depth range between 60 and 100 m or transported horizontally. This estimate is consistent with the dark respiration rates in this depth zone and also the apparent oxygen utilization. The seasonal and spatial variations in <em>f</em>-ratios derived in this work may be used in the numerical model to improve the simulation and prediction of the carbon cycle in the Indian Ocean.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104647"},"PeriodicalIF":2.1,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145924956","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 : 2025-12-29DOI: 10.1016/j.dsr.2025.104645
Lucas da Silva Salimene, José Luiz Lima de Azevedo, Leopoldo Rota de Oliveira, André Lopes Brum
The seasonal variability of Eddy Kinetic Energy (EKE) in the Brazil Current (BC) within the South Brazil Bight (22°S–28°S) remains poorly understood, particularly the role of energy conversion and redistribution terms. Using fourteen years of output from an eddy-resolving numerical simulation, we perform the first seasonal analysis of the EKE budget in this region. We find a pronounced along-stream asymmetry in the EKE seasonal cycle: upstream EKE peaks in summer, while downstream it peaks in winter. The barotropic instability is the primary modulator of EKE within the offshore flank of the mean BC jet. In contrast, baroclinic instability processes dominate beneath the jet core, as indicated by vertical eddy density fluxes. A key finding is that the advection of EKE exhibits the strongest correlation with EKE variability, identifying it as the principal mechanism for redistributing energy from generation sites. While eddy wind work shows no direct influence, pressure work peaks in the region of the Intermediate Western Boundary Current (IWBC), suggesting a potential energy pathway between the BC and the IWBC. Our results establish that the seasonal EKE cycle is not driven by local generation alone but is fundamentally controlled by the advective redistribution of energy from regions of high mesoscale activity.
{"title":"Seasonal variability of Eddy Kinetic Energy in the Brazil current, South Brazil Bight","authors":"Lucas da Silva Salimene, José Luiz Lima de Azevedo, Leopoldo Rota de Oliveira, André Lopes Brum","doi":"10.1016/j.dsr.2025.104645","DOIUrl":"10.1016/j.dsr.2025.104645","url":null,"abstract":"<div><div>The seasonal variability of Eddy Kinetic Energy (EKE) in the Brazil Current (BC) within the South Brazil Bight (22°S–28°S) remains poorly understood, particularly the role of energy conversion and redistribution terms. Using fourteen years of output from an eddy-resolving numerical simulation, we perform the first seasonal analysis of the EKE budget in this region. We find a pronounced along-stream asymmetry in the EKE seasonal cycle: upstream EKE peaks in summer, while downstream it peaks in winter. The barotropic instability is the primary modulator of EKE within the offshore flank of the mean BC jet. In contrast, baroclinic instability processes dominate beneath the jet core, as indicated by vertical eddy density fluxes. A key finding is that the advection of EKE exhibits the strongest correlation with EKE variability, identifying it as the principal mechanism for redistributing energy from generation sites. While eddy wind work shows no direct influence, pressure work peaks in the region of the Intermediate Western Boundary Current (IWBC), suggesting a potential energy pathway between the BC and the IWBC. Our results establish that the seasonal EKE cycle is not driven by local generation alone but is fundamentally controlled by the advective redistribution of energy from regions of high mesoscale activity.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104645"},"PeriodicalIF":2.1,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145884366","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 : 2025-12-29DOI: 10.1016/j.dsr.2025.104646
Zhenxuan Liu , Quanshu Yan , Xuefa Shi , Gang Yang , Yanguang Liu
The Kyushu-Palau Ridge (KPR), a remnant arc that split from the proto-Izu-Bonin-Mariana (IBM) arc, plays a significant role in understanding the intra-oceanic arc rifting and the geological evolution of the Philippine Sea Plate (PSP). There is still a paucity of data on the volcanism of the southern KPR, particularly, the influence of arc rifting on magma composition and arc evolution remains to be elucidated. This study presents new major and trace element geochemical compositions as well as K-Ar age of the basaltic lavas from the southern KPR (south of 22° N). Major and trace elements suggest that southern KPR lavas exhibit a strong tholeiitic affinity and limited contribution from subduction components (i.e., hydrous melts and aqueous fluids). Geochemically, the southern KPR shows similarities to the infant IBM arc and differs from the northern KPR as well as the more evolved mature island arc. The wide ranges in Nb/Yb (0.14–3.68) and Zr/Nb (6.43–115.44) ratios as well as the model calculations of samples demonstrate that the lavas were formed through low-degree (<15 %) partial melting of heterogeneous sub-arc mantle source in the spinel lherzolite facies. This study advances a conceptual model elucidating KPR evolution, proposing that the PSP kinematics with the variable arc rifting conditions of the proto-IBM arc led to the separation of the KPR. The arc rifting-spreading event prevented it from evolving into a mature arc.
{"title":"Petrogenesis of lavas from the southern Kyushu-Palau Ridge, Philippine Sea Plate: Implications for the arc rifting of the proto-Izu-Bonin-Mariana Arc","authors":"Zhenxuan Liu , Quanshu Yan , Xuefa Shi , Gang Yang , Yanguang Liu","doi":"10.1016/j.dsr.2025.104646","DOIUrl":"10.1016/j.dsr.2025.104646","url":null,"abstract":"<div><div>The Kyushu-Palau Ridge (KPR), a remnant arc that split from the proto-Izu-Bonin-Mariana (IBM) arc, plays a significant role in understanding the intra-oceanic arc rifting and the geological evolution of the Philippine Sea Plate (PSP). There is still a paucity of data on the volcanism of the southern KPR, particularly, the influence of arc rifting on magma composition and arc evolution remains to be elucidated. This study presents new major and trace element geochemical compositions as well as K-Ar age of the basaltic lavas from the southern KPR (south of 22° N). Major and trace elements suggest that southern KPR lavas exhibit a strong tholeiitic affinity and limited contribution from subduction components (i.e., hydrous melts and aqueous fluids). Geochemically, the southern KPR shows similarities to the infant IBM arc and differs from the northern KPR as well as the more evolved mature island arc. The wide ranges in Nb/Yb (0.14–3.68) and Zr/Nb (6.43–115.44) ratios as well as the model calculations of samples demonstrate that the lavas were formed through low-degree (<15 %) partial melting of heterogeneous sub-arc mantle source in the spinel lherzolite facies. This study advances a conceptual model elucidating KPR evolution, proposing that the PSP kinematics with the variable arc rifting conditions of the proto-IBM arc led to the separation of the KPR. The arc rifting-spreading event prevented it from evolving into a mature arc.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104646"},"PeriodicalIF":2.1,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145884365","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}
As terrestrial resources become increasingly scarce, the importance of developing deep-sea mineral resources has grown significantly. However, the harsh deep-sea environment and limited availability of species distribution data pose major challenges to the protection and management of deep-sea ecosystems. This study combined global marine environment data and limited deep-sea sponge distribution records to construct a high-resolution habitat suitability prediction model based on machine learning technology. By selecting six key environmental variables such as water depth, seawater nutrients, chemical composition, and seafloor topography, Random Forest, XGBoost, and the integrated learning algorithm Ensemble Median were used to predict the global potential distribution of deep-sea sponges. Model evaluation shows that the integrated model is significantly better than the single model in terms of prediction accuracy, AUC value, TSS value and Kappa coefficient, and has good robustness and reliability. The research results provide a scientific basis for the protection of deep-sea sponges, and provide an important reference for the rational development of deep-sea resources and maintenance of marine ecological balance, laying a theoretical foundation for the planning and policy formulation of deep-sea protected areas.
{"title":"Global distribution of suitable habitats for deep-sea sponges based on machine learning","authors":"Jichao Yang , Tongbo Xu , Xuelei Zhang , QinZeng Xu , Guoyu Xu , Guanhong Zhai , Minxing Dong","doi":"10.1016/j.dsr.2025.104642","DOIUrl":"10.1016/j.dsr.2025.104642","url":null,"abstract":"<div><div>As terrestrial resources become increasingly scarce, the importance of developing deep-sea mineral resources has grown significantly. However, the harsh deep-sea environment and limited availability of species distribution data pose major challenges to the protection and management of deep-sea ecosystems. This study combined global marine environment data and limited deep-sea sponge distribution records to construct a high-resolution habitat suitability prediction model based on machine learning technology. By selecting six key environmental variables such as water depth, seawater nutrients, chemical composition, and seafloor topography, Random Forest, XGBoost, and the integrated learning algorithm Ensemble Median were used to predict the global potential distribution of deep-sea sponges. Model evaluation shows that the integrated model is significantly better than the single model in terms of prediction accuracy, AUC value, TSS value and Kappa coefficient, and has good robustness and reliability. The research results provide a scientific basis for the protection of deep-sea sponges, and provide an important reference for the rational development of deep-sea resources and maintenance of marine ecological balance, laying a theoretical foundation for the planning and policy formulation of deep-sea protected areas.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104642"},"PeriodicalIF":2.1,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976688","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 : 2025-12-24DOI: 10.1016/j.dsr.2025.104644
Feng Wang , Sai Mei , Xianhai Bu , Fanlin Yang , Jianbing Chen , Zhao Zhao
Accurately quantifying the gas flux released by cold seeps into the water is significant for exploring gas hydrates and understanding the marine carbon cycle. While multibeam water column data (WCD) commonly used to detect gas plumes, its quantitative application may be limited by single frequency mode and inaccurately calibrated backscatter intensity. This study develops a novel WCD-based gas flux quantification method. First, a parallel genetic algorithm optimizes bubble size distribution (BSD) parameters by minimizing residuals between measured and theoretical backscatter intensities. Subsequently, kernel density estimation derives robust bubble volume from optimized BSD parameters. Finally, gas flux is calculated by combining bubble volume and bubble rising speed. Simulation experiments validate the robustness of the proposed method, with field application in the Shenhu area of the South China Sea yielding two key results: observed gas plumes exhibit maximum ascent heights of ∼820 m with the total gas flux reaching (6 ± 1) × 104 L/min, and statistically significant correlations between backscatter intensity and gas flux confirm methodological validity. The developed model establishes an efficient approach for WCD-based gas flux quantification, providing valuable insights for deep-sea emissions quantification and marine biogeochemical cycle modeling.
{"title":"Quantifying the deep-sea cold seep gas flux using multibeam water column data: A case study in the Shenhu area of the South China sea","authors":"Feng Wang , Sai Mei , Xianhai Bu , Fanlin Yang , Jianbing Chen , Zhao Zhao","doi":"10.1016/j.dsr.2025.104644","DOIUrl":"10.1016/j.dsr.2025.104644","url":null,"abstract":"<div><div>Accurately quantifying the gas flux released by cold seeps into the water is significant for exploring gas hydrates and understanding the marine carbon cycle. While multibeam water column data (WCD) commonly used to detect gas plumes, its quantitative application may be limited by single frequency mode and inaccurately calibrated backscatter intensity. This study develops a novel WCD-based gas flux quantification method. First, a parallel genetic algorithm optimizes bubble size distribution (BSD) parameters by minimizing residuals between measured and theoretical backscatter intensities. Subsequently, kernel density estimation derives robust bubble volume from optimized BSD parameters. Finally, gas flux is calculated by combining bubble volume and bubble rising speed. Simulation experiments validate the robustness of the proposed method, with field application in the Shenhu area of the South China Sea yielding two key results: observed gas plumes exhibit maximum ascent heights of ∼820 m with the total gas flux reaching (6 ± 1) × 10<sup>4</sup> L/min, and statistically significant correlations between backscatter intensity and gas flux confirm methodological validity. The developed model establishes an efficient approach for WCD-based gas flux quantification, providing valuable insights for deep-sea emissions quantification and marine biogeochemical cycle modeling.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104644"},"PeriodicalIF":2.1,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145840389","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 : 2025-12-23DOI: 10.1016/j.dsr.2025.104643
Amila Sandaruwan Ratnayake , Yoshikazu Sampei , Minoru Ikehara , David Lawrence Dettman
The Atlantis Massif (Mid-Atlantic Ridge, 30°N) provides a natural laboratory in the deep ocean for understanding the links among the hydrothermal system, serpentinization, abiogenic organic synthesis, and microbial activity in mantle-derived rocks. This study examined the potential origin of organic compounds in the subsurface geosphere. Subsurface rocks were recovered using seabed drilling during the International Ocean Discovery Program (IODP) Expedition 357 “Atlantis Massif Serpentinization and Life”. These samples include a range of lithologies such as dunite, gabbro, basalt, serpentinite, serpentinized dunite, and carbonate. Bulk and molecular organic geochemical parameters were evaluated for thirty-nine rock samples. Total organic carbon (TOC) values range from 0.010 % to 0.174 % (average = 0.058 % ± 0.04). Bulk δ13Ctotal and δ13CTOC values range from −24.6 ‰ to 5.6 ‰ (average = −14.3 ‰ ± 7.2) and from −28.4 ‰ to −26.3 ‰ (average = −27.7 ‰ ± 0.5), respectively. Bulk chemical composition, organic molecular composition, and stable isotope data (including compound-specific) show systematic changes for different lithologies at the Atlantis Massif. δ13C values of long-chain n-alkanes (C20 to C35) are higher in minerals of the rocks (average = −17.2 ‰ ± 2.1), indicating the traces of abiotic processes such as Fischer–Tropsch type synthesis. Sterane and hopane biomarkers suggest the occurrence of successive biotic processes in the Atlantis Massif. The low δ13C values of esters (i.e., fatty acid methyl ester after the esterification), phenol and alcohol molecules, and the approximate correlation between TOC and total sulfur (TS) contents may indicate a contribution of bacteria. The inverse isotopic trend could result from abiotic processes such as Fischer–Tropsch type synthesis during serpentinization with overprinting by biotic organic matter. Therefore, the submarine hydrothermal systems of the Atlantis Massif show a systematic process of abiotic hydrocarbon formation and their use by bacterial activity.
{"title":"Carbon cycle system and origin of organic molecules in subseafloor serpentinized rocks of the Atlantis Massif (Mid-Atlantic ridge, 30°N) oceanic core complex","authors":"Amila Sandaruwan Ratnayake , Yoshikazu Sampei , Minoru Ikehara , David Lawrence Dettman","doi":"10.1016/j.dsr.2025.104643","DOIUrl":"10.1016/j.dsr.2025.104643","url":null,"abstract":"<div><div>The Atlantis Massif (Mid-Atlantic Ridge, 30°N) provides a natural laboratory in the deep ocean for understanding the links among the hydrothermal system, serpentinization, abiogenic organic synthesis, and microbial activity in mantle-derived rocks. This study examined the potential origin of organic compounds in the subsurface geosphere. Subsurface rocks were recovered using seabed drilling during the International Ocean Discovery Program (IODP) Expedition 357 “Atlantis Massif Serpentinization and Life”. These samples include a range of lithologies such as dunite, gabbro, basalt, serpentinite, serpentinized dunite, and carbonate. Bulk and molecular organic geochemical parameters were evaluated for thirty-nine rock samples. Total organic carbon (TOC) values range from 0.010 % to 0.174 % (average = 0.058 % ± 0.04). Bulk δ<sup>13</sup>C<sub>total</sub> and δ<sup>13</sup>C<sub>TOC</sub> values range from −24.6 ‰ to 5.6 ‰ (average = −14.3 ‰ ± 7.2) and from −28.4 ‰ to −26.3 ‰ (average = −27.7 ‰ ± 0.5), respectively. Bulk chemical composition, organic molecular composition, and stable isotope data (including compound-specific) show systematic changes for different lithologies at the Atlantis Massif. δ<sup>13</sup>C values of long-chain <em>n</em>-alkanes (C<sub>20</sub> to C<sub>35</sub>) are higher in minerals of the rocks (average = −17.2 ‰ ± 2.1), indicating the traces of abiotic processes such as Fischer–Tropsch type synthesis. Sterane and hopane biomarkers suggest the occurrence of successive biotic processes in the Atlantis Massif. The low δ<sup>13</sup>C values of esters (i.e., fatty acid methyl ester after the esterification), phenol and alcohol molecules, and the approximate correlation between TOC and total sulfur (TS) contents may indicate a contribution of bacteria. The inverse isotopic trend could result from abiotic processes such as Fischer–Tropsch type synthesis during serpentinization with overprinting by biotic organic matter. Therefore, the submarine hydrothermal systems of the Atlantis Massif show a systematic process of abiotic hydrocarbon formation and their use by bacterial activity.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104643"},"PeriodicalIF":2.1,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145840300","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 : 2025-12-11DOI: 10.1016/j.dsr.2025.104640
Alice O. Matossian , Eoghan Daly , Sheena Fennell , Nadzeya Shymbaliova , Thomas Vandorpe , Martin White , David Van Rooij
The Belgica Mound Drift is a contourite drift located in the Porcupine Seabight, offshore Ireland, formed in association with cold-water coral mounds.
ROV imagery and bathymetry provided a close-up view of the drift seafloor, identifying multiple bedforms, including sinuous, linguoid and washed-out ripples as well as sediment waves. Three moorings equipped with current meters were deployed to better understand the spatial and temporal variations of the present-day hydrodynamic conditions over the drift moats and crest. Several velocity flows, ranging from 20 to 100 cm/s, were deduced from the interpretation of the bedforms and compared with the mooring-recorded flow values and character to evaluate the representativeness of the bedforms as a tool in the assessment of the strength and direction of bottom currents in deep environments. Both the tidally forced flows up to 50 cm/s, and the observed flow directions are consistent with the bedform estimation. While bedforms which require weaker bottom currents are currently formed during every tidal flow, the ripples created under stronger flows may be relic features formed during unrecorded peak flow events. This suggests that the drift and its moats are still being influenced by a strong hydrodynamic regime.
The spatial distribution of the bedforms suggests that the bottom current flow velocities are extremely variable, partly supported by the measured currents. This is likely related to the local topography which may have a very small spatial scale impact on the bottom flows.
{"title":"Evaluation of present-day hydrodynamic processes associated to the Belgica Mound contourite drift, offshore Ireland","authors":"Alice O. Matossian , Eoghan Daly , Sheena Fennell , Nadzeya Shymbaliova , Thomas Vandorpe , Martin White , David Van Rooij","doi":"10.1016/j.dsr.2025.104640","DOIUrl":"10.1016/j.dsr.2025.104640","url":null,"abstract":"<div><div>The Belgica Mound Drift is a contourite drift located in the Porcupine Seabight, offshore Ireland, formed in association with cold-water coral mounds.</div><div>ROV imagery and bathymetry provided a close-up view of the drift seafloor, identifying multiple bedforms, including sinuous, linguoid and washed-out ripples as well as sediment waves. Three moorings equipped with current meters were deployed to better understand the spatial and temporal variations of the present-day hydrodynamic conditions over the drift moats and crest. Several velocity flows, ranging from 20 to 100 cm/s, were deduced from the interpretation of the bedforms and compared with the mooring-recorded flow values and character to evaluate the representativeness of the bedforms as a tool in the assessment of the strength and direction of bottom currents in deep environments. Both the tidally forced flows up to 50 cm/s, and the observed flow directions are consistent with the bedform estimation. While bedforms which require weaker bottom currents are currently formed during every tidal flow, the ripples created under stronger flows may be relic features formed during unrecorded peak flow events. This suggests that the drift and its moats are still being influenced by a strong hydrodynamic regime.</div><div>The spatial distribution of the bedforms suggests that the bottom current flow velocities are extremely variable, partly supported by the measured currents. This is likely related to the local topography which may have a very small spatial scale impact on the bottom flows.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104640"},"PeriodicalIF":2.1,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790797","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 : 2025-12-11DOI: 10.1016/j.dsr.2025.104641
Hongxuan Pan , Hongwei Liu , Yongliang Duan , Chongguang Pang
This study investigates the seasonal variability and underlying mechanisms of sea surface temperature (SST) in the Somali upwelling region of the northwestern tropical Indian Ocean (TIO), based on high-resolution ocean reanalysis and observational datasets. Motivated by the distinct bimodal SST cycle in this region — featuring two warming (spring and autumn) and two cooling (summer and winter) periods — we conduct a detailed mixed-layer heat budget analysis to quantify the relative contributions of atmospheric forcing and oceanic processes. While net surface heat flux (NSHF) dominates both warming phases, the underlying mechanisms differ significantly. For spring warming, it is primarily driven by increased shortwave radiation and weakened winds. In contrast, autumn warming — despite stronger NSHF — is partially offset by vertical entrainment and horizontal advection. For the cooling phases, summer SST decline is driven by dynamic oceanic processes such as vertical entrainment and horizontal advection under the southwest monsoon, while winter cooling is controlled mainly by enhanced latent heat loss. Compared to the Java upwelling region, which displays a weaker unimodal SST pattern, the Somali system exhibits more complex monsoon–ocean interactions. While earlier basin-scale modeling studies have identified general seasonal controls in the northern Indian Ocean, our region-specific, observation-constrained analysis uncovers pronounced asymmetries between distinct warming and cooling phases. These findings emphasize the critical role of monsoon-driven, phase-dependent air–sea interactions in shaping the seasonal SST variability in the northwestern TIO.
{"title":"Seasonal sea surface temperature variability in the northwestern Indian ocean","authors":"Hongxuan Pan , Hongwei Liu , Yongliang Duan , Chongguang Pang","doi":"10.1016/j.dsr.2025.104641","DOIUrl":"10.1016/j.dsr.2025.104641","url":null,"abstract":"<div><div>This study investigates the seasonal variability and underlying mechanisms of sea surface temperature (SST) in the Somali upwelling region of the northwestern tropical Indian Ocean (TIO), based on high-resolution ocean reanalysis and observational datasets. Motivated by the distinct bimodal SST cycle in this region — featuring two warming (spring and autumn) and two cooling (summer and winter) periods — we conduct a detailed mixed-layer heat budget analysis to quantify the relative contributions of atmospheric forcing and oceanic processes. While net surface heat flux (NSHF) dominates both warming phases, the underlying mechanisms differ significantly. For spring warming, it is primarily driven by increased shortwave radiation and weakened winds. In contrast, autumn warming — despite stronger NSHF — is partially offset by vertical entrainment and horizontal advection. For the cooling phases, summer SST decline is driven by dynamic oceanic processes such as vertical entrainment and horizontal advection under the southwest monsoon, while winter cooling is controlled mainly by enhanced latent heat loss. Compared to the Java upwelling region, which displays a weaker unimodal SST pattern, the Somali system exhibits more complex monsoon–ocean interactions. While earlier basin-scale modeling studies have identified general seasonal controls in the northern Indian Ocean, our region-specific, observation-constrained analysis uncovers pronounced asymmetries between distinct warming and cooling phases. These findings emphasize the critical role of monsoon-driven, phase-dependent air–sea interactions in shaping the seasonal SST variability in the northwestern TIO.</div></div>","PeriodicalId":51009,"journal":{"name":"Deep-Sea Research Part I-Oceanographic Research Papers","volume":"227 ","pages":"Article 104641"},"PeriodicalIF":2.1,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145736981","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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