Pub Date : 2025-12-08DOI: 10.1016/j.dsr2.2025.105583
Longyun Lai , Moritz Müller , Rahayu Sukmaria Sukri , Changi Wong , Aazani Mujahid , Sumei Liu , Zhaomeng Xu , Tim Rixen , Thorsten Warneke , Justus Notholt , Shan Jiang
The Belait River is a typical blackwater river in Brunei, characterized by deep tea-brown water rich in dissolved organic matter (DOM) derived from surrounding peat swamps and rainforests. This study provides a systematic assessment of the chemical composition, transformation, and transport processes of dissolved nitrogen (N) in the Belait River during alternating wet and dry seasons by integrating nitrate (NO3−) stable isotope techniques with microbial analyses. Results indicate that dissolved organic nitrogen (DON) constitutes the primary component of total dissolved nitrogen (TDN), with its seasonal dynamics significantly controlled by hydrological climate and microbial activity. Along the salinity gradient, DON decreases due to dilution and degradation, while ammonium (NH4+) and NO3− accumulate significantly in densely populated areas owing to anthropogenic inputs. The extremely low dissolved inorganic phosphorus (DIP) concentrations in the Belait River highlight the crucial role of P limitation in maintaining the system's oligotrophic state. Through the investigation in this representative blackwater system, this study highlights complex N cycling mechanisms in blackwater and provides a critical gauge in land-ocean material fluxes at the Indo-Pacific Convergence Area.
{"title":"Dissolved nitrogen in a tropical river-sea continuum: a seasonal view on the distribution and transformation","authors":"Longyun Lai , Moritz Müller , Rahayu Sukmaria Sukri , Changi Wong , Aazani Mujahid , Sumei Liu , Zhaomeng Xu , Tim Rixen , Thorsten Warneke , Justus Notholt , Shan Jiang","doi":"10.1016/j.dsr2.2025.105583","DOIUrl":"10.1016/j.dsr2.2025.105583","url":null,"abstract":"<div><div>The Belait River is a typical blackwater river in Brunei, characterized by deep tea-brown water rich in dissolved organic matter (DOM) derived from surrounding peat swamps and rainforests. This study provides a systematic assessment of the chemical composition, transformation, and transport processes of dissolved nitrogen (N) in the Belait River during alternating wet and dry seasons by integrating nitrate (NO<sub>3</sub><sup>−</sup>) stable isotope techniques with microbial analyses. Results indicate that dissolved organic nitrogen (DON) constitutes the primary component of total dissolved nitrogen (TDN), with its seasonal dynamics significantly controlled by hydrological climate and microbial activity. Along the salinity gradient, DON decreases due to dilution and degradation, while ammonium (NH<sub>4</sub><sup>+</sup>) and NO<sub>3</sub><sup>−</sup> accumulate significantly in densely populated areas owing to anthropogenic inputs. The extremely low dissolved inorganic phosphorus (DIP) concentrations in the Belait River highlight the crucial role of P limitation in maintaining the system's oligotrophic state. Through the investigation in this representative blackwater system, this study highlights complex N cycling mechanisms in blackwater and provides a critical gauge in land-ocean material fluxes at the Indo-Pacific Convergence Area.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105583"},"PeriodicalIF":3.0,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145747822","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 : 2025-12-01DOI: 10.1016/j.dsr2.2025.105572
Ricardo Borrego-Santos , José M. Quintanilla , Raúl Laiz-Carrión , Alberto García , Estrella Malca , Francisco J. Abascal , David Die , Isabel Riveiro , Rasmus Swalethorp , Michael R. Landry
This study analyzed the growth patterns and survival of Southern bluefin tuna (SBT, Thunnus maccoyii) larvae collected during January–February 2022 in their only known spawning area in the eastern Indian Ocean (IO). Otolith microstructure was examined to characterize both population-level and intra-population growth (OPT-optimal and DEF-deficient group), with special emphasis on the flexion process, as well as to provide insights into larval survival. SBT larvae began flexion at sizes and ages comparable to those reported in other bluefin tuna species. At the intra-population level, OPT larvae reached flexion earlier in a better physical condition, with greater length, weight, and body depth, likely increasing their chances of survival at later stages. The observed larval growth rates (0.38 mm d−1) exceeded that from a historical study in 1987 (0.33 mm d−1), likely due to a ∼2 °C increase in sea surface temperature and shifts in prey availability. Larval survival appears to depend on a selective process based on growth, in which only a small proportion of individuals (<2 %) exhibited width increment in otoliths similar to those of surviving larvae, allowing for faster development and earlier access to larger prey. These findings highlight the need for expanded research on the early life stages of SBT, particularly in the context of ongoing ocean warming and climate change.
本研究分析了2022年1 - 2月在东印度洋唯一已知的南蓝鳍金枪鱼产卵区收集的南蓝鳍金枪鱼（SBT, Thunnus maccoyii）幼虫的生长模式和存活率。研究人员检查了耳石微观结构，以表征种群水平和种群内的生长（OPT-optimal和DEF-deficient组），特别强调了弯曲过程，并提供了对幼虫存活的见解。SBT幼虫在大小和年龄上开始弯曲，与其他蓝鳍金枪鱼物种相当。在种群内水平，OPT幼虫较早到达屈曲状态，身体状况较好，体长、体重和体深较大，可能增加其后期的生存机会。观察到的幼虫生长速率（0.38 mm d - 1）超过了1987年的历史研究（0.33 mm d - 1），可能是由于海面温度升高~ 2°C和猎物可得性的变化。幼虫的生存似乎依赖于一个基于生长的选择过程，在这个过程中，只有一小部分个体（2%）的耳石宽度增加与存活的幼虫相似，这使得它们能够更快地发育并更早地获得更大的猎物。这些发现突出表明，有必要扩大对SBT早期生命阶段的研究，特别是在持续的海洋变暖和气候变化的背景下。
{"title":"Revisiting daily growth and survival insights of Southern Bluefin Tuna (Thunnus maccoyii) larvae in the eastern Indian Ocean","authors":"Ricardo Borrego-Santos , José M. Quintanilla , Raúl Laiz-Carrión , Alberto García , Estrella Malca , Francisco J. Abascal , David Die , Isabel Riveiro , Rasmus Swalethorp , Michael R. Landry","doi":"10.1016/j.dsr2.2025.105572","DOIUrl":"10.1016/j.dsr2.2025.105572","url":null,"abstract":"<div><div>This study analyzed the growth patterns and survival of Southern bluefin tuna (SBT, <em>Thunnus maccoyii</em>) larvae collected during January–February 2022 in their only known spawning area in the eastern Indian Ocean (IO). Otolith microstructure was examined to characterize both population-level and intra-population growth (OPT-optimal and DEF-deficient group), with special emphasis on the flexion process, as well as to provide insights into larval survival. SBT larvae began flexion at sizes and ages comparable to those reported in other bluefin tuna species. At the intra-population level, OPT larvae reached flexion earlier in a better physical condition, with greater length, weight, and body depth, likely increasing their chances of survival at later stages. The observed larval growth rates (0.38 mm d<sup>−1</sup>) exceeded that from a historical study in 1987 (0.33 mm d<sup>−1</sup>), likely due to a ∼2 °C increase in sea surface temperature and shifts in prey availability. Larval survival appears to depend on a selective process based on growth, in which only a small proportion of individuals (<2 %) exhibited width increment in otoliths similar to those of surviving larvae, allowing for faster development and earlier access to larger prey. These findings highlight the need for expanded research on the early life stages of SBT, particularly in the context of ongoing ocean warming and climate change.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105572"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692360","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 : 2025-12-01DOI: 10.1016/j.dsr2.2025.105573
Claudia Traboni , Grace F. Cawley , Karen E. Selph , Michael R. Landry , Moira Décima
Prey removal incubations were conducted in the Argo Basin (eastern Indian Ocean) to investigate the trophic ecology of the zooplankton community supporting Southern Bluefin Tuna larvae. Copepod grazing and selectivity were evaluated considering prey trophic mode and size as food quality descriptors and compared with microzooplankton grazing. Copepods ingested between 3.4 and 138 ng carbon (C) ind−1 d−1. Diet was dominated by mixotrophic (5–89 %) and heterotrophic (0–84 %) prey, with autotrophs contributing 2–17 %. Nanoplankton provided the highest C intake to copepods (62–99 %) versus picoplankton (0.8–38 %), despite more picoplankton cells ingested. No measurable reduction in chlorophyll a (Chla) concentration occurred from copepod grazing through food removal, suggesting an indirect trophic pathway, although gut content revealed ingestion of 0.8 μg Chla ind−1 d−1. Calculations from disappearance incubations imply copepod selection on picoplankton (E = 0.3) over nanoplankton, but picoplankton were likely ingested as aggregates or depressed due to a trophic cascade of copepods ingesting nano-microzooplankton. Copepods ingested protistan consumers and/or metazoans fed on 15N-cyanobacteria with ∼5-fold higher N uptake from 1 to 2 μm 15N-Synechococcus than from <1 μm 15N-Prochlorococcus. Microzooplankton grazing on eukaryotes (0.07–2.5 d−1) and prokaryotes (0.3–2.1 d−1) greatly exceeded copepod grazing. Microzooplankton diet consisted mostly of heterotrophs (25–59 %) and mixotrophs (13–41 %) followed by autotrophs (12–33 %), with more nano- (95–98 %) than picophytoplankton (2–5 %). Overall, microzooplankton removed most daily production (111 %) in contrast to 7 % for copepods. Our findings indicate that mixotrophy, intraguild grazing and nutrient channeling support the food web in this oligotrophic region.
{"title":"Exploring the roles of trophic mode and microbial prey size in grazing pathways of tropical oligotrophic waters of the eastern Indian ocean","authors":"Claudia Traboni , Grace F. Cawley , Karen E. Selph , Michael R. Landry , Moira Décima","doi":"10.1016/j.dsr2.2025.105573","DOIUrl":"10.1016/j.dsr2.2025.105573","url":null,"abstract":"<div><div>Prey removal incubations were conducted in the Argo Basin (eastern Indian Ocean) to investigate the trophic ecology of the zooplankton community supporting Southern Bluefin Tuna larvae. Copepod grazing and selectivity were evaluated considering prey trophic mode and size as food quality descriptors and compared with microzooplankton grazing. Copepods ingested between 3.4 and 138 ng carbon (C) ind<sup>−1</sup> d<sup>−1</sup>. Diet was dominated by mixotrophic (5–89 %) and heterotrophic (0–84 %) prey, with autotrophs contributing 2–17 %. Nanoplankton provided the highest C intake to copepods (62–99 %) <em>versus</em> picoplankton (0.8–38 %), despite more picoplankton cells ingested. No measurable reduction in chlorophyll <em>a</em> (Chl<em>a)</em> concentration occurred from copepod grazing through food removal, suggesting an indirect trophic pathway, although gut content revealed ingestion of 0.8 μg Chl<em>a</em> ind<sup>−1</sup> d<sup>−1</sup>. Calculations from disappearance incubations imply copepod selection on picoplankton (E = 0.3) over nanoplankton, but picoplankton were likely ingested as aggregates or depressed due to a trophic cascade of copepods ingesting nano-microzooplankton. Copepods ingested protistan consumers and/or metazoans fed on <sup>15</sup>N-cyanobacteria with ∼5-fold higher N uptake from 1 to 2 μm <sup>15</sup>N-Synechococcus than from <1 μm <sup>15</sup>N-Prochlorococcus. Microzooplankton grazing on eukaryotes (0.07–2.5 d<sup>−1</sup>) and prokaryotes (0.3–2.1 d<sup>−1</sup>) greatly exceeded copepod grazing. Microzooplankton diet consisted mostly of heterotrophs (25–59 %) and mixotrophs (13–41 %) followed by autotrophs (12–33 %), with more nano- (95–98 %) than picophytoplankton (2–5 %). Overall, microzooplankton removed most daily production (111 %) in contrast to 7 % for copepods. Our findings indicate that mixotrophy, intraguild grazing and nutrient channeling support the food web in this oligotrophic region.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105573"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145747823","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 : 2025-12-01DOI: 10.1016/j.dsr2.2025.105558
Candice N. Cooper , Christopher A. Edwards , John L. Largier , Piero L.F. Mazzini
A descriptive analysis of remotely-sensed surface chlorophyll-a within the Gulf of the Farallones and nearby coastal waters occupying portions of three NOAA National Marine Sanctuaries along the central California coast is presented. The seasonal cycle from a 25-year chlorophyll-a record reveals elevated levels near the mouth of San Francisco Bay at the Golden Gate, with broad spatial extent climatologically from April through November. A 19-year time series of normalized water-leaving radiance at the 555 nm band (nLw555) was used to estimate the presence of waters representing the San Francisco Bay plume. Although the plume shows its largest spatial extent in winter, decreasing during spring and summer, chlorophyll-a was enhanced within plume waters relative to non-plume waters during all months; however, was not statistically different during upwelling months (April–June). Linear correlations between chlorophyll-a and a 20-year record of wind stress, a 10-year record of surface currents, and a 20-year record of sea surface temperatures reveal consistent, coherent regional spatial patterns. Weighted averages confirm that poleward winds and surface currents result in enhanced chlorophyll-a in nearshore waters north of the Golden Gate and around Point Reyes. Periods of equatorward winds and surface transport exhibit elevated chlorophyll-a and temperature south of the Golden Gate, offshore of Half Moon Bay, and are associated with nearby onshore currents. Correlations of plume concentrations (nLw555 W m−2 m−1 sr−1) with wind stress, however, do not show the same coherent patterns as with chlorophyll-a, and turbid plume waters are largely confined to the Gulf of the Farallones. These analyses suggest that surface chlorophyll-a within the inner Gulf of the Farallones close to San Francisco Bay is significantly influenced by outflow from the Bay, but the greater Gulf of Farallones is more strongly influenced by upwelling and relaxation effects.
本文对法拉隆湾和位于加州中部海岸的三个NOAA国家海洋保护区附近的沿海水域的遥感地表叶绿素- A进行了描述性分析。从25年的叶绿素记录的季节周期来看，在金门湾的旧金山湾口附近，从4月到11月，在气候上具有广泛的空间范围，叶绿素水平升高。在555nm波段（nLw555）的19年标准化水离开辐射时间序列被用来估计代表旧金山湾羽流的水的存在。尽管羽流的空间范围在冬季最大，在春夏两季逐渐减小，但在所有月份中，羽流水体内的叶绿素a均比非羽流水体增强；而在上升流月份（4 - 6月），差异无统计学意义。叶绿素-a与20年风应力记录、10年地表洋流记录和20年海面温度记录之间的线性相关揭示了一致的、连贯的区域空间格局。加权平均值证实，在金门以北和雷耶斯角附近的近岸水域，向极地方向的风和表面洋流导致叶绿素-a的增加。在金门以南，半月湾近海，赤道风和地面运输的时期，叶绿素-a和温度升高，并与附近的陆上洋流有关。然而，羽流浓度（nLw555≥12 W m−2 μm−1 sr−1）与风应力的相关性与叶绿素-a的相关性不一致，并且浑浊的羽流水主要局限于Farallones湾。这些分析表明，在靠近旧金山湾的Farallones内湾，表层叶绿素-a受到海湾流出物的显著影响，但Farallones大湾受上升流和松弛效应的影响更为强烈。
{"title":"Interaction of bay outflow and wind-driven upwelling in chlorophyll patterns in the Gulf of the Farallones","authors":"Candice N. Cooper , Christopher A. Edwards , John L. Largier , Piero L.F. Mazzini","doi":"10.1016/j.dsr2.2025.105558","DOIUrl":"10.1016/j.dsr2.2025.105558","url":null,"abstract":"<div><div>A descriptive analysis of remotely-sensed surface chlorophyll-<em>a</em> within the Gulf of the Farallones and nearby coastal waters occupying portions of three NOAA National Marine Sanctuaries along the central California coast is presented. The seasonal cycle from a 25-year chlorophyll-<em>a</em> record reveals elevated levels near the mouth of San Francisco Bay at the Golden Gate, with broad spatial extent climatologically from April through November. A 19-year time series of normalized water-leaving radiance at the 555 nm band (nLw555) was used to estimate the presence of waters representing the San Francisco Bay plume. Although the plume shows its largest spatial extent in winter, decreasing during spring and summer, chlorophyll-<em>a</em> was enhanced within plume waters relative to non-plume waters during all months; however, was not statistically different during upwelling months (April–June). Linear correlations between chlorophyll-<em>a</em> and a 20-year record of wind stress, a 10-year record of surface currents, and a 20-year record of sea surface temperatures reveal consistent, coherent regional spatial patterns. Weighted averages confirm that poleward winds and surface currents result in enhanced chlorophyll-<em>a</em> in nearshore waters north of the Golden Gate and around Point Reyes. Periods of equatorward winds and surface transport exhibit elevated chlorophyll-<em>a</em> and temperature south of the Golden Gate, offshore of Half Moon Bay, and are associated with nearby onshore currents. Correlations of plume concentrations (nLw555 <span><math><mrow><mo>≥</mo><mspace></mspace><mn>12</mn></mrow></math></span> W m<sup>−2</sup> <span><math><mi>μ</mi></math></span>m<sup>−1</sup> sr<sup>−1</sup>) with wind stress, however, do not show the same coherent patterns as with chlorophyll-<em>a</em>, and turbid plume waters are largely confined to the Gulf of the Farallones. These analyses suggest that surface chlorophyll-<em>a</em> within the inner Gulf of the Farallones close to San Francisco Bay is significantly influenced by outflow from the Bay, but the greater Gulf of Farallones is more strongly influenced by upwelling and relaxation effects.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"224 ","pages":"Article 105558"},"PeriodicalIF":3.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145620624","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 : 2025-11-25DOI: 10.1016/j.dsr2.2025.105570
Sven A. Kranz , Jared M. Rose , Michael R. Stukel , Karen E. Selph , Natalia Yingling , Michael R. Landry
Oligotrophic ocean regions are characterized by strong nutrient limitation, low standing phytoplankton biomass, and highly efficient nutrient recycling. During the BLOOFINZ-IO expedition (February 2022), we quantified nutrient inventories, primary productivity and N2 fixation in the Argo Basin of the eastern Indian Ocean, the sole known spawning ground for Southern Bluefin Tuna. Low concentrations of surface nitrate (<0.02 μmol L−1) and persistent residual phosphate indicated N as the limiting macronutrient, with photophysiological indices consistent with iron colimitation. Depth-integrated net primary production (NPP), from 14C-based in-situ incubations during 4 Lagrangian experiments, averaged ∼460 mg C m−2d−1, generally agreeing with mean satellite-based NPP estimates (459 mg C m−2d−1) but with spatial discrepancies. Nitrogen fixation provided a consistent new nitrogen source, contributing ∼16 % to local NPP in the upper euphotic zone. Gross primary production (GPP), from fast-repetition-rate-fluorometry-based estimates of electron transport, revealed significant autotrophic respiration losses, with mean GPP:NPP ratios of ∼1.8 consistent with metabolic costs under nutrient limitation. Net community production (NCP) from O2/Ar ratios averaged ∼20 % of NPP in the upper 30 m. This result, in combination with N2 fixation measurement, indicates that N2 fixation supports most of the export production in the region. Together, the multi-method approach revealed a recycling-dominated ecosystem affected by episodic mixing events, where primary productivity is maintained primarily through efficient nitrogen recycling and physiological photoacclimation. These results provide a comprehensive baseline of bottom-up support of ecosystem productivity for the Argo Basin for assessing future climate-driven changes in stratification, nutrient cycling, and food-web dynamics.
低营养海洋区具有养分限制强、浮游植物生物量低、养分循环效率高的特点。在BLOOFINZ-IO考察期间（2022年2月），我们量化了东印度洋Argo盆地（已知唯一的南蓝鳍金枪鱼产卵地）的营养库存、初级生产力和N2固定。低浓度的表面硝酸盐（<0.02 μmol L−1）和持久残留的磷酸盐表明N是限制性常量养分，其光生理指标与铁共生一致。在4次拉格朗日实验中，基于14c的原位孵育的深度综合净初级产量（NPP）平均为~ 460 mg C m−2d−1，与基于卫星的平均NPP估算值（459 mg C m−2d−1）大致一致，但存在空间差异。固氮提供了一致的新氮源，对高光区局部NPP贡献约16%。根据基于快速重复率荧光测量的电子传递估计，总初级产量（GPP）显示了显著的自养呼吸损失，GPP:NPP的平均比率为1.8，与营养限制下的代谢成本一致。O2/Ar比值产生的群落净产量（NCP）平均为30米上游NPP的20%。这一结果与N2固定测量相结合，表明N2固定支持该地区的大部分出口生产。总之，多方法方法揭示了一个以循环为主的生态系统，受偶发性混合事件的影响，其中初级生产力主要通过有效的氮循环和生理光驯化来维持。这些结果为Argo盆地生态系统生产力自下而上的支持提供了一个全面的基线，用于评估未来气候驱动的分层、养分循环和食物网动态变化。
{"title":"Primary productivity and N2-fixation in the eastern Indian ocean: Bottom-up support for an ecologically and economically important ecosystem","authors":"Sven A. Kranz , Jared M. Rose , Michael R. Stukel , Karen E. Selph , Natalia Yingling , Michael R. Landry","doi":"10.1016/j.dsr2.2025.105570","DOIUrl":"10.1016/j.dsr2.2025.105570","url":null,"abstract":"<div><div>Oligotrophic ocean regions are characterized by strong nutrient limitation, low standing phytoplankton biomass, and highly efficient nutrient recycling. During the BLOOFINZ-IO expedition (February 2022), we quantified nutrient inventories, primary productivity and N<sub>2</sub> fixation in the Argo Basin of the eastern Indian Ocean, the sole known spawning ground for Southern Bluefin Tuna. Low concentrations of surface nitrate (<0.02 μmol L<sup>−1</sup>) and persistent residual phosphate indicated N as the limiting macronutrient, with photophysiological indices consistent with iron colimitation. Depth-integrated net primary production (NPP), from <sup>14</sup>C-based <em>in-situ</em> incubations during 4 Lagrangian experiments, averaged ∼460 mg C m<sup>−2</sup>d<sup>−1</sup>, generally agreeing with mean satellite-based NPP estimates (459 mg C m<sup>−2</sup>d<sup>−1</sup>) but with spatial discrepancies. Nitrogen fixation provided a consistent new nitrogen source, contributing ∼16 % to local NPP in the upper euphotic zone. Gross primary production (GPP), from fast-repetition-rate-fluorometry-based estimates of electron transport, revealed significant autotrophic respiration losses, with mean GPP:NPP ratios of ∼1.8 consistent with metabolic costs under nutrient limitation. Net community production (NCP) from O<sub>2</sub>/Ar ratios averaged ∼20 % of NPP in the upper 30 m. This result, in combination with N<sub>2</sub> fixation measurement, indicates that N<sub>2</sub> fixation supports most of the export production in the region. Together, the multi-method approach revealed a recycling-dominated ecosystem affected by episodic mixing events, where primary productivity is maintained primarily through efficient nitrogen recycling and physiological photoacclimation. These results provide a comprehensive baseline of bottom-up support of ecosystem productivity for the Argo Basin for assessing future climate-driven changes in stratification, nutrient cycling, and food-web dynamics.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105570"},"PeriodicalIF":3.0,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692362","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 : 2025-11-24DOI: 10.1016/j.dsr2.2025.105569
Ankeeta Amonkar , Sridhar D. Iyer
Metalliferous sediments are known to exist at mid-ocean ridges and near active intraplate seamounts. Here we report the occurrence of metal-rich particles of variable compositions occurring in the sediments of the Central Indian Ocean Basin (CIOB) which is an intraplate basin. These metal-rich particles have been recovered from an average water depth of 5,000m from 79°E fracture zone (pelagic clays zone) and from seamount dominated area (from siliceous sediment, and siliceous-red clay transition zone).
The metal-rich particles observed in the studied sediment samples exhibit irregular, tabular, sub-rounded shapes and have a distinct crystalline structures. They occur both as native metals and as compounds such as oxides, sulphides, and sulphates. In addition to the previously reported magnetite and aluminium spherules from the CIOB sediments, our analysis reveals a high concentration of metal-rich particles containing zinc-copper and native copper, barium sulphides, lead-barium sulphates, native lead, and silver.
The sub-surface occurrence of these metal-rich particles in the sediments indicates their derivation from recent hydrothermal activity in the basin. The fracture zone and seamounts in the vicinity could be potential sites for degassing of volatiles and formation of metalloid elements and may have co-precipitated in the sediments that bear testimony of their hydrothermal origin. To our knowledge this is the first finding of metal-rich particles from abyssal depth of nearly 5000 m in the Indian Ocean.
{"title":"First findings of metal-rich particles from the central Indian ocean basin: Evidence of hydrothermal mineralization","authors":"Ankeeta Amonkar , Sridhar D. Iyer","doi":"10.1016/j.dsr2.2025.105569","DOIUrl":"10.1016/j.dsr2.2025.105569","url":null,"abstract":"<div><div>Metalliferous sediments are known to exist at mid-ocean ridges and near active intraplate seamounts. Here we report the occurrence of metal-rich particles of variable compositions occurring in the sediments of the Central Indian Ocean Basin (CIOB) which is an intraplate basin. These metal-rich particles have been recovered from an average water depth of 5,000m from 79°E fracture zone (pelagic clays zone) and from seamount dominated area (from siliceous sediment, and siliceous<em>-</em>red clay transition zone).</div><div>The metal-rich particles observed in the studied sediment samples exhibit irregular, tabular, sub-rounded shapes and have a distinct crystalline structures. They occur both as native metals and as compounds such as oxides, sulphides, and sulphates. In addition to the previously reported magnetite and aluminium spherules from the CIOB sediments, our analysis reveals a high concentration of metal-rich particles containing zinc-copper and native copper, barium sulphides, lead-barium sulphates, native lead, and silver.</div><div>The sub-surface occurrence of these metal-rich particles in the sediments indicates their derivation from recent hydrothermal activity in the basin. The fracture zone and seamounts in the vicinity could be potential sites for degassing of volatiles and formation of metalloid elements and may have co-precipitated in the sediments that bear testimony of their hydrothermal origin. To our knowledge this is the first finding of metal-rich particles from abyssal depth of nearly 5000 m in the Indian Ocean.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105569"},"PeriodicalIF":3.0,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692361","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}
Unlike earlier studies conducted in shallow coastal areas, this study is the first to examine the vertical distribution of meiofaunal communities at depths ranging from 10 to 93 m at five stations in the northern semi-enclosed Persian Gulf. Among the sampled stations, the highest meiofauna density was observed at Station 2, with an average of 2398 ± 921.4 individuals per 10 cm2, while the lowest abundance was recorded at Station 4, amounting to 444.3 ± 96.2 individuals per 10 cm2. A comprehensive analysis of 20311 meiofauna individuals representing 29 taxa revealed several dominant groups. Free-living nematodes (51.98 %), foraminifera (27.88 %), copepods (4.9 %), juvenile bivalves (2.79 %), polychaetes (2.76 %), and oligochaetes (2.39 %) comprised together 93 % of the community. The vertical distribution profile indicated that 91 % of the Persian Gulf meiofauna were concentrated in the top 2–3 cm sediment layer, although some were found at depths exceeding 5 cm. The nematode complex exhibited a diverse composition, with 90 genera from 30 families and 7 orders identified across the study sites. Environmental parameters, including sediment characteristics, i.e., dissolved oxygen (DO) as the strongest driver, total organic matter (TOM), grain size, and water depth, emerged as critical factors influencing meiofaunal abundance and diversity. Based on the Environmental Quality Standards (EQS) classification, the sampling stations demonstrated high to good EQS compliance.
{"title":"Vertical distribution and environmental drivers of meiofaunal communities in the Persian Gulf: insights into biodiversity and sediment dynamics","authors":"Narges Badri , Behrooz Abtahi , Abolfazl Saleh , Homira Agah , Hans-Peter Grossart","doi":"10.1016/j.dsr2.2025.105571","DOIUrl":"10.1016/j.dsr2.2025.105571","url":null,"abstract":"<div><div>Unlike earlier studies conducted in shallow coastal areas, this study is the first to examine the vertical distribution of meiofaunal communities at depths ranging from 10 to 93 m at five stations in the northern semi-enclosed Persian Gulf. Among the sampled stations, the highest meiofauna density was observed at Station 2, with an average of 2398 ± 921.4 individuals per 10 cm<sup>2</sup>, while the lowest abundance was recorded at Station 4, amounting to 444.3 ± 96.2 individuals per 10 cm<sup>2</sup>. A comprehensive analysis of 20311 meiofauna individuals representing 29 taxa revealed several dominant groups. Free-living nematodes (51.98 %), foraminifera (27.88 %), copepods (4.9 %), juvenile bivalves (2.79 %), polychaetes (2.76 %), and oligochaetes (2.39 %) comprised together 93 % of the community. The vertical distribution profile indicated that 91 % of the Persian Gulf meiofauna were concentrated in the top 2–3 cm sediment layer, although some were found at depths exceeding 5 cm. The nematode complex exhibited a diverse composition, with 90 genera from 30 families and 7 orders identified across the study sites. Environmental parameters, including sediment characteristics, i.e., dissolved oxygen (DO) as the strongest driver, total organic matter (TOM), grain size, and water depth, emerged as critical factors influencing meiofaunal abundance and diversity. Based on the Environmental Quality Standards (EQS) classification, the sampling stations demonstrated high to good EQS compliance.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105571"},"PeriodicalIF":3.0,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692359","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 : 2025-11-19DOI: 10.1016/j.dsr2.2025.105567
Evangeline Fachon , Robert S. Pickart , Jie Huang , Catherine Lalande , Donald M. Anderson
The persistent presence of a massive accumulation of resting cysts of the toxic dinoflagellate Alexandrium catenella on the Chukchi shelf represents a significant risk to Pacific Arctic ecosystems, as warming conditions are likely to promote harmful algal blooms of this species. While the majority of cysts are found in the benthos, cysts can also be suspended through the water column, allowing them to be transported by currents or to experience elevated temperature and light conditions that may accelerate germination. Spatial patterns of cyst suspension were investigated during a Fall 2020 survey, revealing broad presence of suspended cysts in near-bottom waters overlying benthic cyst accumulations. Enhanced suspension was observed at shallow, well-mixed stations – in some places extending beyond the bottom boundary layer into surface waters. Sinking particles collected continuously from 2017 to 2019 showed seasonal patterns of cyst flux, with export pulses during the late summer and wind-driven resuspension peaking during the fall. To evaluate the potential contribution of resuspension to bloom initiation, a hydrographic climatology of the southern Chukchi Sea was used to estimate cyst germination rates through the water column during the summer (June–September). This analysis was paired with wind-driven 1-D mixing simulations, demonstrating that cyst access to surface waters is enhanced under stormy conditions. While storm events are not currently common during the summer bloom season, a trend towards increasingly windy conditions points towards future potential for resuspended cysts to contribute to blooms in the shallow and warming waters of the Pacific Arctic region.
{"title":"Spatiotemporal patterns and implications of suspended Alexandrium catenella cysts in the Pacific Arctic region","authors":"Evangeline Fachon , Robert S. Pickart , Jie Huang , Catherine Lalande , Donald M. Anderson","doi":"10.1016/j.dsr2.2025.105567","DOIUrl":"10.1016/j.dsr2.2025.105567","url":null,"abstract":"<div><div>The persistent presence of a massive accumulation of resting cysts of the toxic dinoflagellate <em>Alexandrium catenella</em> on the Chukchi shelf represents a significant risk to Pacific Arctic ecosystems, as warming conditions are likely to promote harmful algal blooms of this species. While the majority of cysts are found in the benthos, cysts can also be suspended through the water column, allowing them to be transported by currents or to experience elevated temperature and light conditions that may accelerate germination. Spatial patterns of cyst suspension were investigated during a Fall 2020 survey, revealing broad presence of suspended cysts in near-bottom waters overlying benthic cyst accumulations. Enhanced suspension was observed at shallow, well-mixed stations – in some places extending beyond the bottom boundary layer into surface waters. Sinking particles collected continuously from 2017 to 2019 showed seasonal patterns of cyst flux, with export pulses during the late summer and wind-driven resuspension peaking during the fall. To evaluate the potential contribution of resuspension to bloom initiation, a hydrographic climatology of the southern Chukchi Sea was used to estimate cyst germination rates through the water column during the summer (June–September). This analysis was paired with wind-driven 1-D mixing simulations, demonstrating that cyst access to surface waters is enhanced under stormy conditions. While storm events are not currently common during the summer bloom season, a trend towards increasingly windy conditions points towards future potential for resuspended cysts to contribute to blooms in the shallow and warming waters of the Pacific Arctic region.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"225 ","pages":"Article 105567"},"PeriodicalIF":3.0,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145600479","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 : 2025-11-17DOI: 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":"2025-11-17","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 : 2025-11-11DOI: 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":"2025-11-11","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}
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