Deep-sea Research Part Ii-topical Studies in Oceanography最新文献_第2页

Seasonal and spatial variability of marine nepheloid layers in the deep South China Sea 南海深海海相网状层的季节和空间变异

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2026-01-13 DOI: 10.1016/j.dsr2.2026.105600

Zhuangcai Tian , Xiujun Guo , Jinjian Huang , Chao Xu , Lei Song , Jianhua Yue

Marine nepheloid layers are extensively distributed across the world's oceans and marginal seas, characterized by significantly high turbidity compared to adjacent layers. In this study, we measured four transects located at 6°N, 10°N, 18°N, and 113°E in the South China Sea (SCS), encompassing a total of 75 CTD stations each year, and conducted four sets of repeated measurements over a four-year period. Our findings indicate that the scale and concentration of Bottom Nepheloid Layer (BNL) and Intermediate Nepheloid Layer (INL) vary significantly across different subbasins and seasons. In the southwestern and northwestern subbasin of the SCS, BNL and multiple INLs persist year-round at different water depths. BNL is commonly observed on the continental slope with the INLs extending along the isopycnals, and both BNL and INLs always are stronger in summer. High turbidity has caused marked alterations in the isopycnal and isotherm structures of the water column, particularly near the slope. In the central basin of the SCS, multiple INLs also persist year-round, especially at water depths 400–1000 m. The changes in the water column by high turbidity in the central basin were weaker. The persistent presence of INLs indicates ongoing transport of particulate matter across the slope. Ocean currents and internal waves predominantly affect the slopes of the southwestern and northwestern subbasins, while the deeper central basin is primarily affected by the ocean currents. The interactions between internal waves or ocean currents and submarine topography contribute to the frequent occurrence of BNL and INLs around the seamounts. This paper aimed to provide a comprehensive analysis of the seasonal and spatial variability of BNLs and INLs in the deep SCS, serving as a reference for future research on the dynamic processes of marine ecological environment and associated source-sink systems.

海洋浊体层广泛分布在世界海洋和边缘海，其特点是与邻近层相比浊度明显高。研究中，我们在南海6°N、10°N、18°N和113°E的4个样带上进行了每年75个CTD站点的测量，并在4年的时间里进行了4组重复测量。研究结果表明，不同亚盆地、不同季节，底部和中间云雾层的规模和浓度存在显著差异。在南海西南和西北次海盆，在不同水深，BNL和多个inl全年持续存在。在大陆斜坡上普遍观测到BNL， inl沿等距平线延伸，夏季BNL和inl都较强。高浊度引起了水柱等平线和等温线结构的明显变化，特别是在斜坡附近。在南海的中央盆地，多个inl也全年持续存在，特别是在400-1000米的水深。中部盆地高浊度对水柱的影响较弱。INLs的持续存在表明颗粒物质正在通过斜坡进行输送。洋流和内波主要影响西南和西北次盆地的斜坡，而较深的中央盆地主要受洋流的影响。内波或海流与海底地形的相互作用是海底山附近频繁发生的海底低洼和海底低洼的重要原因。本文旨在全面分析南海深层生物碱和生物碱的季节和空间变异，为进一步研究海洋生态环境的动态过程和相关的源汇系统提供参考。

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引用次数: 0

Selective feeding of southern Bluefin Tuna (Thunnus maccoyii) larvae on appendicularians in their eastern Indian Ocean spawning region 南蓝鳍金枪鱼（Thunnus maccoyii）幼虫在东印度洋产卵区对尾尾鱼的选择性摄食

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2026-01-12 DOI: 10.1016/j.dsr2.2026.105591

Rasmus Swalethorp , Estrella Malca , Akihiro Shiroza , Lindsey Kim , Moira Decima , José M. Quintanilla , Ricardo Borrego-Santos , Claire H. Davies , David Die , Lynnath E. Beckley , Claudia Traboni , Grace F. Cawley , Kamran Walsh , Michael R. Landry , Raúl Laiz-Carrión

We investigated ontogenetic variability in feeding and prey selection by Southern Bluefin Tuna larvae (SBT; Thunnus maccoyii) in their only global spawning region, located in the eastern Indian Ocean between northwestern Australia and Indonesia. Zooplankton prey and SBT larvae were sampled during four multi-day Lagrangian experiments conducted in the southern Argo Basin during the peak midsummer spawning season in January–February 2022. The zooplankton were identified, enumerated, sizes measured, and their developmental stages ascertained both in situ and from the stomach contents of the larvae. Larval stomach contents revealed high feeding incidence of 95 % with at least one prey item ingested with an average of 3.9 zooplankton prey per larva. Diet and prey selection transitioned during larval ontogeny from copepod nauplii to calanoid and corycaeid copepodites, and ultimately to cladocerans, as well as fish larvae when these were available. However, for all developmental stages and experiments, appendicularians stood out as the most significant prey taxon, constituting an average of 57 % of prey carbon biomass consumed and up to 79 % for postflexion stages. We observed some indication of increasing selection for appendicularians and fish larvae where they were most abundant, even when other suitable prey items were more readily available. Our study documents unprecedented high feeding incidence and positive selection for appendicularians compared to previous investigations of bluefin species, highlighting a pathway that enhances food web transfer efficiency. Appendicularians are uniquely able to thrive in oligotrophic environments and could be an optimal food source supporting SBT larvae in the future ocean.

我们研究了南蓝鳍金枪鱼（SBT; Thunnus maccoyii）在其唯一的全球产卵区（位于澳大利亚西北部和印度尼西亚之间的东印度洋）的摄食和猎物选择的个体发育变异性。在2022年1 - 2月的盛夏产卵高峰期，在Argo盆地南部进行了4次多日拉格朗日实验，对浮游动物猎物和SBT幼虫进行了采样。对浮游动物进行了鉴定、枚举，测量了它们的大小，并在原位和从幼虫胃内容物中确定了它们的发育阶段。幼虫胃内容物的摄食率高达95%，至少有一种猎物被摄食，平均每只幼虫捕获3.9种浮游动物。在幼体发育过程中，饮食和猎物选择发生了转变，从鹦鹉螺类桡足类和喙类桡足类，到最终的枝海类，以及有条件的鱼类幼体。然而，在所有发育阶段和实验中，尾虫作为最重要的猎物分类群脱颖而出，平均占猎物碳生物量消耗的57%，在屈曲后阶段高达79%。我们观察到一些迹象表明，即使在其他合适的猎物更容易获得的情况下，尾虫和鱼类幼虫在它们最丰富的地方也会被选择。与以往的研究相比，我们的研究记录了蓝鳍金枪鱼前所未有的高摄食率和正选择，突出了提高食物网转移效率的途径。尾虫在低营养环境中茁壮成长的独特能力，可能是未来海洋中支持SBT幼虫的最佳食物来源。

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引用次数: 0

Sinking particle export within and beneath the euphotic zone in the eastern Indian Ocean 东印度洋光带内部和下方的下沉粒子输出

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2026-01-12 DOI: 10.1016/j.dsr2.2026.105590

Michael R. Stukel , Tristan Biard , Moira Décima , Christian K. Fender , Opeyemi Kehinde , Thomas B. Kelly , Sven A. Kranz , Manon Laget , Michael R. Landry , Natalia Yingling

The eastern Indian Ocean is substantially under sampled with respect to the biological carbon pump – the suite of processes that transport the carbon fixed by phytoplankton into the deeper ocean. Using sediment traps and other ecosystem measurements, we quantified sinking organic matter flux and investigated the characteristics of sinking particles in waters overlying the Argo Abyssal Plain directly downstream of the Indonesian Throughflow off northwest Australia. Carbon export from the euphotic zone averaged 7.0 mmol C m⁻² d⁻¹, which equated to an average export efficiency (export/net primary production) of 0.19. Sinking particle flux within the euphotic zone (beneath the mixed layer, but above the deep chlorophyll maximum) averaged slightly higher than flux at the base of the euphotic zone, suggesting that the deep euphotic zone was a depth stratum of net particle remineralization. Carbon flux attenuation continued into the twilight zone with a transfer efficiency (export at euphotic depth + 100m/export at euphotic depth) of 0.62 and an average Martin's b-value of 1.1. Within the euphotic zone, fresh phytoplankton (chlorophyll associated with sinking particles, possibly contained within appendicularian houses) were an important component of sinking particles, but beneath the euphotic zone the fecal pellets of herbivorous zooplankton (phaeopigments) were more important. Changes in carbon and nitrogen isotopic composition with depth further reflected remineralization processes occurring as particles sank. We show similarities with biological carbon pump functioning in a similar semi-enclosed oligotrophic marginal sea, the Gulf of Mexico, including net remineralization across the deep chlorophyll maximum.

东印度洋的生物碳泵（将浮游植物固定的碳输送到更深的海洋的一系列过程）的采样量基本上不足。利用沉积物捕集器和其他生态系统测量方法，我们量化了澳大利亚西北部印尼通流（印度尼西亚通流）下游Argo深海平原上的下沉有机质通量，并研究了下沉颗粒的特征。从光带出口的碳平均为7.0 mmol C m−2 d−1，相当于平均出口效率（出口/净初级生产）为0.19。透光区内下沉颗粒通量（低于混合层，但高于深层叶绿素最大值）平均略高于透光区底部的通量，表明深层透光区是一个净颗粒再矿化的深层地层。碳通量衰减继续进入过渡带，转移效率（出口在光深+ 100m/出口在光深）为0.62，平均马丁b值为1.1。在泛光带内，新鲜浮游植物（与下沉颗粒相关的叶绿素，可能包含在附属虫体内）是下沉颗粒的重要组成部分，但在泛光带下，食草浮游动物的粪便颗粒（phaeopigments）更为重要。碳和氮同位素组成随深度的变化进一步反映了颗粒下沉时发生的再矿化过程。我们展示了在类似的半封闭的低营养边缘海，墨西哥湾中生物碳泵的相似之处，包括深叶绿素最大值的净再矿化。

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引用次数: 0

An eastward branch of the east India coastal current off Sri Lanka: Dynamics, formation mechanisms, and impacts on Bay of Bengal salinity variability 斯里兰卡外东印度海岸流的东支：动力、形成机制和对孟加拉湾盐度变化的影响

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2026-01-08 DOI: 10.1016/j.dsr2.2025.105588

W.G. Indunil Tharaka Gunathilaka , JayarathnaW.N.D. Sandaruwan , Wang Tianyu , Yan Du

The East India Coastal Current (EICC) flows equatorward during early boreal winter, transporting low–salinity Bay of Bengal (BOB) waters southward along the Indian eastern coast. Using satellite measurements, in–situ observations, and ocean model data, we identify a recurrent eastward current (EC) that splits from the EICC off the eastern coast of Sri Lanka. While a weaker branch of the EICC continues equatorward along the coast, a section of rest flow diverts northeastward into the BOB as the EC, indicating a gyre structure in the northwest of BOB. Analysis of 28 years of data (1993–2020) reveals eight distinct EC events, occurring primarily during neutral Indian Ocean dipole years. These events are dynamically forced by two types of eddies, a westward–propagating anticyclonic eddy, linked to downwelling Rossby waves, impinging on the south eastern coast of Sri Lanka, while a cyclonic eddy forms to the north. These events are supported by the following coastal–trapped downwelling Kelvin wave, with the current appearing with increasing frequency over time. The EC, lasting about one-two weeks, exhibits a velocity of 0.3–0.5 m/s and transport flow volume ranging from 0.15 to 0.54 Sv. Despite its brief duration, EC plays a critical role in exporting low–salinity waters (<33 PSU) from Sri Lanka's eastern coast and subsequently transporting high–salinity central BOB waters toward the inner bay. By regulating EICC low–salinity water intrusion, the EC produces distinct freshening effects along Sri Lanka's eastern coast during active years, highlighting its important role in controlling western BOB freshwater distribution patterns.

东印度海岸流（EICC）在北纬初冬向赤道流动，将低盐度的孟加拉湾（BOB）水沿印度东海岸向南输送。利用卫星测量、现场观测和海洋模型数据，我们确定了一个从斯里兰卡东海岸的EICC分裂出来的周期性东流（EC）。当EICC的一个较弱分支沿着海岸继续向赤道方向移动时，一部分剩余气流转向东北进入BOB作为EC，表明BOB西北部存在环流结构。对28年（1993-2020）数据的分析揭示了8个不同的EC事件，主要发生在印度洋中性偶极子年。这些事件是由两种类型的涡流动态推动的，一种是向西传播的反气旋涡流，与下行的罗斯比波有关，撞击斯里兰卡的东南海岸，而一种是在北部形成的气旋涡流。这些事件是由以下海岸捕获的下潜开尔文波支持的，随着时间的推移，水流出现的频率越来越高。EC持续约1 - 2周，流速为0.3-0.5 m/s，输送流量为0.15 - 0.54 Sv。尽管持续时间很短，但东印度洋在从斯里兰卡东海岸出口低盐度水域（<33 PSU）以及随后将高盐度的BOB中部水域输送到内湾方面发挥了关键作用。通过调节EICC低盐度水入侵，EC在斯里兰卡东部沿海活跃年产生明显的清新效应，突出了其在控制西部BOB淡水分布模式中的重要作用。

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引用次数: 0

A prior-knowledge-integrated downscaling approach for subsurface thermal structure reconstruction in the tropical Indian Ocean 热带印度洋地下热结构重建的先验知识集成降尺度方法

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2025-12-31 DOI: 10.1016/j.dsr2.2025.105589

Zhongkun Feng , Jifeng Qi , Bowen Xie , Yuan Cao , Delei Li , Chuanyu Liu , Baoshu Yin

Accurately obtaining high-resolution ocean subsurface thermal structure (OSTS) is essential for resolving mesoscale dynamics in the tropical Indian Ocean (TIO), yet observations remain sparse and uneven. We present a Transformer-based neural network model, the Downscaling Vision Transformer (DSVIT), which integrates prior knowledge to reconstruct high-resolution OSTS in the TIO. Inputs include sea surface temperature (SST), absolute dynamic topography (ADT), and wind stress curl (WSC), as well as temporal, geographic, and climatological information. DSVIT enhances a standard Vision Transformer (ViT) with a geographic positional prior and a physics-aware loss that emphasizes thermocline and surface variability. On an independent test set, DSVIT achieves a Root Mean Square Error (RMSE) of 0.29 °C and a Coefficient of Determination (R²) of 0.9962 for reconstructed subsurface temperature, outperforming traditional recurrent neural network (RNN) and convolutional neural network (CNN) models. Moreover, a key innovation of this study lies in its novel downscaling strategy, which effectively improves the EN4 subsurface temperature resolution from 1° to 1/4° by altering the input segmentation. Compared with traditional interpolation and assessed against independent high-resolution products, the downscaled outputs exhibit lower RMSE and higher R², indicating enhanced physical consistency and mesoscale representation. SHapley Additive exPlanations (SHAP) analysis further reveals that climatology and SST are the dominant predictors, followed by ADT. This study provides a novel approach for downscaling OSTS and offers valuable insights for advancing oceanic and climatic research.

准确获取高分辨率海洋地下热结构（OSTS）对于解析热带印度洋（TIO）中尺度动力学至关重要，但观测数据仍然稀疏且不均匀。我们提出了一种基于变压器的神经网络模型，即降尺度视觉变压器（DSVIT），它集成了先验知识来重建TIO中的高分辨率OSTS。输入包括海温（SST）、绝对动力地形（ADT）、风应力旋度（WSC）以及时间、地理和气候信息。DSVIT增强了标准视觉变压器（ViT）的地理位置先验和强调温跃层和地表变化的物理感知损失。在独立测试集上，DSVIT重建地下温度的均方根误差（RMSE）为0.29°C，决定系数（R2）为0.9962，优于传统的递归神经网络（RNN）和卷积神经网络（CNN）模型。此外，本研究的一个关键创新在于其新颖的降尺度策略，通过改变输入分割，有效地将EN4地下温度分辨率从1°提高到1/4°。与传统插值方法相比，并通过独立的高分辨率产品进行评估，缩小后的输出显示出更低的RMSE和更高的R2，表明物理一致性和中尺度代表性增强。SHapley加性解释（SHAP）进一步揭示了气候和海温是主要的预测因子，其次是ADT。该研究为降低OSTS的尺度提供了一种新的方法，为推进海洋和气候研究提供了有价值的见解。

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引用次数: 0

Time series of dissolved organic carbon in the Fram Strait (2010–2021): Indications for increased river export of DOC to the East Greenland Current? Fram海峡溶解有机碳的时间序列（2010-2021）：DOC向东格陵兰洋流输出增加的迹象？

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2025-12-22 DOI: 10.1016/j.dsr2.2025.105586

Anja Engel , Anabel von Jackowski , Vanessa Lampe , Eva-Maria Nöthig

Climate change impacts the Arctic Ocean more profoundly than other regions, with uncertain consequences for carbon cycling. Additionally, allochthonous and autochthonous sources of organic carbon undergo extreme seasonal variability. Distinguishing climate-induced changes from seasonal variability in carbon cycling thus remains a significant challenge. We investigated interannual changes in dissolved organic carbon (DOC) concentration and lability. i.e., the lifetime of DOC, which we inferred from amino acid composition, in surface waters of the Fram Strait using time series data collected between 2010 and 2021. Sampling was conducted during summer with the RV POLARSTERN at or around the Long-Term Ecological Research observatory HAUSGARTEN. Our results show that the two major water masses in Fram Strait, the Polar Water (PW; T < 0 °C; S < 34.0) predominant in the East Greenland Current and the Atlantic Water (AW; T > 3 °C; S > 34.9) predominant in the West Spitzbergen Current, differ greatly in their DOC concentration and composition. PW carries high amounts of semi-labile DOC (SL-DOC) from the Arctic Ocean southwards, whereas AW contains less but more labile DOC. No clear trend in DOC concentration over the 10-year time series was detected for AW. In contrast, samples collected in PW between 2016 and 2021 showed a 15 % increase in DOC, which was attributable to an increase in SL-DOC. Interannual variability in DOC lability was most pronounced in the eastern Fram Strait, likely driven by differences in the seasonal progression of the pelagic ecosystem. Our data suggest that DOC dynamics in the Fram Strait are influenced by an enhanced riverine input of DOC to the Arctic Ocean, leading to an increased DOC export to the North Atlantic.

气候变化对北冰洋的影响比其他地区更深远，对碳循环的影响不确定。此外，外来和本地有机碳源经历了极端的季节变化。因此，将气候引起的变化与碳循环的季节变化区分开来仍然是一项重大挑战。研究了土壤中溶解有机碳（DOC）浓度和稳定性的年际变化。即，利用2010 - 2021年的时间序列数据，从氨基酸组成推断出海峡表层DOC的寿命。夏季，利用RV POLARSTERN在HAUSGARTEN长期生态研究观测站或其周围进行采样。结果表明，以东格陵兰海流为主的极地水（PW; T < 0°C; S < 34.0）和以西斯皮次卑尔根海流为主的大西洋水（AW; T < 3°C; S > 34.9）两大海峡水团DOC浓度和组成差异较大。PW从北冰洋向南携带大量的半不稳定DOC (SL-DOC)，而AW含有较少但较多的不稳定DOC。在10年时间序列中，没有检测到AW的DOC浓度的明显趋势。相比之下，2016年至2021年期间在PW收集的样本显示DOC增加了15%，这是由于SL-DOC的增加。DOC稳定性的年际变化在海峡东部最为明显，这可能是由远洋生态系统的季节变化所驱动的。我们的数据表明，弗拉姆海峡的DOC动态受到河流向北冰洋输入DOC增强的影响，导致DOC向北大西洋输出增加。

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引用次数: 0

Trophic specialization enhances growth performance in larvae of southern bluefin, albacore, and skipjack tunas from the eastern Indian ocean 营养特化提高了东印度洋南部蓝鳍金枪鱼、长鳍金枪鱼和鲣鱼幼虫的生长性能

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2025-12-19 DOI: 10.1016/j.dsr2.2025.105585

Raúl Laiz-Carrión , Ricardo Borrego-Santos , José María Quintanilla , Claudio Quezada- Romegialli , Estrella Malca , Rasmus Swalethorp , Francisco Abascal , María Grazia Pennino , Manuel Vargas-Yáñez , Carolina Johnstone , Miguel Ángel Godoy-Bermúdez , David Die , Michael R. Landry

We examined trophic ecology and its influence on larval growth variability for three scombrids, southern bluefin (Thunnus maccoyii, SBT), albacore (T. alalunga, ALB), and skipjack tunas (Katsuwonus pelamis, SKJ), that share a common spawning ground in the eastern Indian Ocean. We combined otolith-based ageing with bulk nitrogen and carbon stable isotope analysis (SIA) of individual larva. Significant interspecific differences in δ¹⁵N and δ¹³C indicate adaptive resource partitioning that allows these tunas to coexist during early ontogeny. Trophic position and isotopic niche were estimated with both frequentist and Bayesian approaches, enabling the evaluation of ontogenetic isotope shifts, niche overlap, and resource use in relation to growth. ALB grew fastest, had the highest trophic position, and the broadest isotopic niche. Optimally growing tuna larvae occupied the narrowest trophic niche and had lower trophic positions for all three species, supporting the hypothesis that strong trophic specialization supports better growth performance and that feeding on more efficient shorter food chains (e.g., microbial loop via appendicularians) can enhance larval fitness. Using lower C:N ratio as a proxy of larval condition found in optimal growing groups supports the broader hypothesis that growth potential is closely tied to energy allocation strategies during early ontogeny. A detailed understanding of how larval trophodynamics, niche breadth, and resource partitioning interact with growth and survival during these vulnerable stages is essential for ecosystem-based management, particularly in systems where growth rate modulates predation risk and competitive fitness.

我们研究了南蓝鳍金枪鱼（Thunnus maccoyii， SBT）、长鳍金枪鱼（T. alalunga， ALB）和鲣鱼（Katsuwonus pelamis， SKJ）这三种鲭鱼的营养生态学及其对幼虫生长变异的影响，这三种鲭鱼在东印度洋共享一个产卵地。我们将基于耳石的老化与个体幼虫的体积氮碳稳定同位素分析（SIA）相结合。δ15N和δ13C的显著种间差异表明，在个体发育早期，这些金枪鱼的适应性资源分配使其能够共存。利用频率和贝叶斯方法估算了营养位置和同位素生态位，从而评估了与生长相关的个体成因同位素变化、生态位重叠和资源利用。ALB生长最快，营养地位最高，同位素生态位最广。最佳生长的金枪鱼幼虫占据了最窄的营养生态位，并且在所有三个物种中都处于较低的营养位置，这支持了强营养专业化支持更好的生长性能的假设，以及更有效的短食物链（例如通过阑尾虫的微生物环）的摄食可以提高幼虫的适应性。利用较低的碳氮比作为最佳生长群体中幼虫状况的代表，支持了一个更广泛的假设，即生长潜力与个体发育早期的能量分配策略密切相关。在这些脆弱阶段，详细了解幼虫营养动力学、生态位宽度和资源分配如何与生长和生存相互作用，对于基于生态系统的管理至关重要，特别是在生长速度调节捕食风险和竞争适应性的系统中。

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引用次数: 0

Subsurface mixing and ventilation of oxygen minimum zone waters in the southern Bay of Bengal during summer monsoon 夏季风期间孟加拉湾南部氧最小带水域的地下混合和通气

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2025-12-15 DOI: 10.1016/j.dsr2.2025.105584

Rajdeep Roy , P.N. Vinayachandran , Jenson George , Amit Sarkar , Chandanlal Parida

During the summer monsoon, the influence of the cyclonic curl of local wind forcing around Sri Lanka causes the formation of a cold dome called the Sri Lanka Dome (SLD), which upwells subsurface water. To the east of SLD, the summer monsoon Current (SMC) flows into the Bay of Bengal (BoB), transporting Arabian Sea high salinity water. We show that SMC, alongside the upwelled waters of SLD, is ventilated episodically during the summer monsoon in the southern BoB, leading to a net exchange of low oxygen subsurface waters with the oxygen-saturated surface mixed layers. We observed the presence of a hypoxic boundary <63 μmol kg⁻¹ very close to the surface. Within the SLD, it shoaled between 35 and 40 m with oxygen concentrations reaching as low as 6 μmol kg⁻¹ at the bottom of the thermocline. Negative fluxes representing the in-gassing rates ranged between (-0.33 to - 9.43 μmol m⁻² sec⁻¹) within SLD and SMC. We emphasize that episodic ventilation observed during this investigation may lead to disequilibrium in the surface mixed layers and can contribute to mid-depth oxygen enrichment. Our present study possibly illustrates a likely mechanism that contributes to preventing denitrification in this region.

在夏季季风期间，斯里兰卡周围的气旋旋度的影响导致了一个被称为斯里兰卡圆顶（SLD）的冷圆顶的形成，该圆顶使地下水上升。在SLD以东，夏季风流（SMC）流入孟加拉湾（BoB），输送阿拉伯海高盐度水。研究表明，在夏季风期间，南太平洋的SMC与SLD上升水一起偶尔通风，导致低氧地下水与含氧饱和的地表混合层的净交换。我们观察到非常接近表面的低氧边界<；63 μmol kg−1的存在。在SLD内，它在35 ~ 40 m之间浅滩，在温跃层底部氧浓度低至6 μmol kg−1。负通量表示SLD和SMC的入气速率在（-0.33 ~ - 9.43 μmol m−2 sec−1）之间。我们强调，在本研究中观察到的间歇性通气可能导致表层混合层的不平衡，并有助于中深度的氧富集。我们目前的研究可能说明了一种可能的机制，有助于防止该地区的反硝化。

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引用次数: 0

Dissolved nitrogen in a tropical river-sea continuum: a seasonal view on the distribution and transformation 热带河海连续体中的溶解氮：分布和转变的季节性观点

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2025-12-08 DOI: 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.

Belait河是文莱典型的黑水河流，其特点是深茶色的水富含来自周围泥炭沼泽和雨林的溶解有机质（DOM）。本研究通过将硝酸盐（NO3−）稳定同位素技术与微生物分析相结合，系统地评估了干湿交替季节Belait河中溶解态氮(N)的化学组成、转化和运输过程。结果表明，溶解有机氮（DON）是总溶解氮（TDN）的主要组成部分，其季节动态受水文气候和微生物活动的显著控制。沿盐度梯度，DON因稀释和降解而减少，而在人口密集地区，铵（NH4+）和NO3−因人为输入而显著积累。Belait河中极低的溶解无机磷（DIP）浓度突出了P限制在维持系统寡营养状态中的关键作用。通过对这一具有代表性的黑水系统的调查，本研究突出了黑水中复杂的N循环机制，并为印太辐合区陆-海物质通量提供了一个关键指标。

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引用次数: 0

Revisiting daily growth and survival insights of Southern Bluefin Tuna (Thunnus maccoyii) larvae in the eastern Indian Ocean 重访东印度洋南部蓝鳍金枪鱼（Thunnus maccoyii）幼虫的日常生长和生存见解

IF 3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography

Pub Date : 2025-12-01 DOI: 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。

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引用次数: 0