Deep-sea Research Part Ii-topical Studies in Oceanography最新文献

{"title":"Impact of desalination plant brine discharge on macrobenthic communities in the Persian Gulf","authors":"Moslem Sharifinia,&nbsp;Mehrzad Keshavarzifard,&nbsp;Parisa Hosseinkhezri","doi":"10.1016/j.dsr2.2025.105465","DOIUrl":"10.1016/j.dsr2.2025.105465","url":null,"abstract":"<div><div>This research investigates the ecological impacts of desalination plant discharges on sediment quality and macrobenthic communities in the coastal waters of Bushehr City, Iran, located within the Persian Gulf. Spanning from November 2019 to October 2020, the study involved meticulous sampling of 288 sediment samples from 24 strategically selected stations—half of which were influenced by brine discharges from a desalination facility releasing approximately 45,000 cubic meters of treated wastewater daily, while the other half served as controls. The study employed a comprehensive methodology that integrated fieldwork focused on macrobenthos as biological indicators. A total of 62 macrobenthic taxa were identified, with a notable diversity of mollusks, including 35 gastropod taxa, which represented 56% of the total abundance. The application of ecological indices, including the AZTI Marine Biotic Index (AMBI), Margalef's richness, Shannon-Wiener diversity, and Pielou's evenness, revealed significant declines in biodiversity metrics near discharge points, highlighting the detrimental effects of pollution. Statistical analyses confirmed a negative correlation between the AMBI index and both the Shannon and Margalef indices, while a positive association was observed between the AMBI index and total organic matter (TOM), highlighting its effectiveness in assessing organic enrichment. These findings emphasize the complex interplay between ecological health indicators and environmental stressors, such as salinity, and highlight the importance of utilizing biological indices within coastal management frameworks. Ultimately, this research provides critical insights for developing targeted strategies to enhance the sustainable management of coastal ecosystems, ensuring the preservation of biodiversity and ecological integrity in the face of anthropogenic pressures.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105465"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143471556","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}

{"title":"Variable photosystem II thermal stress responses of reef-building corals Pocillopora indiania and Heliopora coerulea across latitudes from the Mascarene Plateau, Indian Ocean","authors":"Vikash Munbodhe ,&nbsp;Sundy Ramah ,&nbsp;Deepeeka Kaullysing ,&nbsp;Shakeel Yavan Jogee ,&nbsp;Mariette Dine ,&nbsp;Bryan Wilson ,&nbsp;Ranjeet Bhagooli","doi":"10.1016/j.dsr2.2025.105467","DOIUrl":"10.1016/j.dsr2.2025.105467","url":null,"abstract":"<div><div>The persistence of remote reef sites invariably depends on the ability of their corals to better respond and adapt to a continuing global environmental change, by way of their protection from additional and direct stressors as a result of their remoteness; such reefs are generally referred to as coral refugia. This study investigated the latitudinal thermal thresholds of two commonly occurring corals from reefs both remote from and close to human population centres, in the understudied Mascarene Plateau (MP), Central Indian Ocean. Thermal experimental trials at 26, 29 and 32 °C for a period of 22h focused on reef-building conspecifics: the regionally-endemic hard coral <em>Pocillopora indiania,</em> and heat-tolerant photo-physiologically understudied and threatened octocoral <em>Heliopora coerulea</em> from three sites of varying degrees of remoteness and human impact (Saya de Malha (SDM), St Brandon (SB) and Mauritius Island (MAU)), each with varying mean sea surface temperature (SST). Imaging Pulse-Amplitude-Modulation (Imaging-PAM) fluorometry was used to determine how the photosynthetic performances at the Photosystem II (PSII), in terms of effective quantum yield (Φ_PSII), of the conspecifics responded after exposure to these different temperature regimes. SST anomaly over the past 28 years showed an increment of 1.2 °C with no significant latitudinal variation within the MP. Moreover, the experimental results displayed significant differences in intra- and interspecific Φ_PSII when corals were exposed to 32 °C (p &lt; 0.0001); <em>P. indiania</em> from MAU suffered severe bleaching (over 90% surface area), with the highest degree of tissue sloughing leading to coral mortality, while conspecifics from SDM and SB exhibited better thermal threshold by being photosynthetically active, with 23% and 33% Φ_PSII, respectively. In contrast, <em>H. coerulea</em> from MAU thrived through the experiment indicating site-specific thermal threshold by displaying the lowest Φ_PSII (24%) as compared to conspecific from SDM (48%) and SB (58%). Although limited to Photosystem II responses, this study provides a first insight on the latitudinal variability in thermal vulnerability of conspecific corals from the MP and suggesting that corals from SDM and SB might be more resilient to the impacts of future warming events than corals at other sites.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105467"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143562732","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}

{"title":"Growth rates and ages of the small bamboo coral Acanella arbuscula in the Northwest Atlantic","authors":"Laura F. Piccirillo ,&nbsp;Evan Edinger ,&nbsp;Bárbara de Moura Neves ,&nbsp;Meghan Burchell ,&nbsp;Graham D. Layne ,&nbsp;Vonda E. Hayes","doi":"10.1016/j.dsr2.2025.105485","DOIUrl":"10.1016/j.dsr2.2025.105485","url":null,"abstract":"<div><div><em>Acanella arbuscula</em> is a common deep-water bamboo coral in the Northwest Atlantic and is considered a Vulnerable Marine Ecosystems indicator. Growth rates and ages of <em>A. arbuscula</em> have not been confirmed, despite the importance of these metrics to understand the species recovery potential when disturbed. One-hundred and fifteen <em>A. arbuscula</em> samples were analyzed to examine the relationship between age, location, and depth, and how environmental conditions influence growth rates. Colonies were collected during scientific trawl or remotely operated vehicle surveys from the SW Grand Banks, Northern Labrador shelf, and SE Baffin shelf from depths of 178–1354 m. Skeletons were cross-sectioned at the proteinaceous nodes and examined under reflected light and fluorescence microscopy to quantify growth rings and determine age and growth rates. The species exhibited both major and minor growth rings. Major growth rings were confirmed to represent annual growth by comparing size metrics and age from a previously bomb-¹⁴C dated specimen of <em>A. arbuscula</em> versus specimens aged by growth rings. Minor (sub-annual) growth rings were not consistently observed across specimens and the cause of their formation is unknown. Ages ranged from 8 to 29 years, with radial growth rates of 0.025–0.160 mm/year and axial growth rates of 1.87–16.1 mm/year. Longevity for <em>A. arbuscula</em> is lower than the bamboo coral <em>Keratoisis grayi</em> in the NW Atlantic, but growth rates were consistent with other documented bamboo corals. Multiple regressions revealed that age influenced radial and axial growth rates, with no significant influence of bottom temperature or chlorophyll-a observed for radial growth rates. This study confirms frequency of ring formation in <em>A. arbuscula</em> and that growth rates for the species do not vary significantly based on geographic or bathymetric location.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105485"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143935732","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}

{"title":"Blue carbon in an eastern boundary upwelling zone – A case study in Namibia","authors":"Simon H. Elwen ,&nbsp;Usman Khan ,&nbsp;Anja Kreiner ,&nbsp;Anja K. Van der Plas ,&nbsp;Margit R. Wilhelm ,&nbsp;David Barnes ,&nbsp;Kerry Howell ,&nbsp;Tara Pelembe","doi":"10.1016/j.dsr2.2025.105478","DOIUrl":"10.1016/j.dsr2.2025.105478","url":null,"abstract":"<div><div>Blue Carbon (BC) refers to Nature-Based Solutions in marine environments that aim to reduce greenhouse gases through carbon sequestration using natural processes. Much of the BC focus to date has been on tropical coastal habitats, especially salt marshes, mangroves, and seagrass beds, while research in temperate marine environments has lagged. In this paper, we investigate the BC potential in a cold-temperate eastern-boundary upwelling ecosystem, the northern Benguela off Namibia. We identified four areas, where the BC concept can be applied, identify data gaps and areas for future research. 1) Macroalgae play a large role in carbon sequestration globally, although many of the values and specifics remain debated. We recommend research to investigate the ultimate flows, fate and permanence of carbon in Namibian kelp forests, and the development of a high-quality national map of kelp biomass distribution. 2) The northern Benguela has a high abundance of gelatinous plankton, possibly associated with the collapse of the small pelagic fish stocks. Gelatinous plankton play an important role in the global carbon cycle and research into their role in carbon flow and sequestration in the northern Benguela is recommended. 3) Commercial fisheries are amongst the highest producers of carbon globally. We strongly support policies that promote the restoration of Namibian fish stocks, especially sardine and recommend undertaking analyses of the carbon-footprint of Namibian fisheries and their supply chains to identify areas where carbon production could be reduced through improved efficiency, reduced impact on the seabed and optimised transport solutions. 4) Namibia hosts some of the world's most carbon-rich marine sediments along its continental shelf. We recommend conducting a BC natural capital assessment of the environmental and financial value of these sediments and any impacts thereon. These actions could open new markets for Namibian products that prioritise low-carbon foodstuffs. Combined, a more thorough assessment of Namibia's BC ecosystems could contribute substantially to Namibia's nationally determined contributions.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105478"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatial and temporal variations in net primary production and long-term trends between 2003 and 2022 in the Indian Ocean: A synthesis using different models","authors":"V.V.S.S. Sarma ,&nbsp;B. Sridevi ,&nbsp;M.K. Ashitha","doi":"10.1016/j.dsr2.2025.105468","DOIUrl":"10.1016/j.dsr2.2025.105468","url":null,"abstract":"<div><div>The measurements of net particulate primary production (NPP) with reference to space and time are limited in the Indian Ocean. Therefore, models are the only source of understanding spatial, temporal, and long-term variations. Different models have been developed to use remote sensing data to estimate NPP in the Indian Ocean. However, the accuracy of these models has not been evaluated. Here, we used the measured NPP data collected between 2003 and 2022 in the Indian Ocean to compare with different models such as Vertically Generalized Production (VGPM), Carbon-based Production (CbPM), Eppley-VGPM, and Carbon, Absorption, Fluorescence, Euphotic resolved (CAFE) models. This comparison suggested that CbPM simulated NPP with 10% underestimation compared to measured NPP in the Arabian Sea and South Indian Ocean (SIO), whereas VGPM simulated NPP well in the Bay of Bengal (BoB). The Eppley-VGPM over (under) estimated measured NPP by 20–30% in the SIO (Arabian Sea), while the CAFE model underestimated NPP in the BoB by 25%. No single model simulated the NPP well in the entire Indian Ocean compared to the measurements. All models reproduced seasonality in the Arabian Sea and SIO, but they failed in the case of the BoB. Compared to the measured NPP, the VGPM and CAFE models underestimated NPP, whereas the CbPM and Eppley-VGPM models overestimated it. Variable rates of changes in NPP in the past two decades were simulated in the Indian Ocean by different models. The long-term trends simulated by CbPM suggest decreasing trends in NPP south of 12°N and no trends north of 12°N in the Arabian Sea and increasing trends in NPP south of 20°S and decreasing trends north of 20°S in the SIO. The VGPM model indicated no significant trends in the BoB. The trends by the other models are variable and contrast in some regions. Therefore, the selection of an appropriate model to study long-term trends in NPP in the Indian Ocean is crucial.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105468"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601498","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}

{"title":"Introducing a new method to determining the capacity of heavy metal absorption by macro algae on the coast of Persian Gulf based on Kullback-Leibler cumulative information","authors":"Mehdi Bibak ,&nbsp;Saeid Tahmasebi ,&nbsp;Eisa Safavi ,&nbsp;Najmaldin Ezaldin Hassan","doi":"10.1016/j.dsr2.2025.105466","DOIUrl":"10.1016/j.dsr2.2025.105466","url":null,"abstract":"<div><div>Researchers have continuously sought effective and affordable ways to address contamination. Application of both live and deceased algae biomass has emerged as a highly effective and promising approach for remediation. In this study, the efficacy of macroalgal species (<em>Padina gymnospora</em>, <em>Cladophoropsis membranacea</em>, and <em>Hypnea hamulosa</em>) harvested from the northern coast of the Persian Gulf was evaluated for their capacity to biosorb heavy metals, with a focus on nickel, lead, cadmium, and mercury. The study encompassed two key components. Firstlythe experimental methodology was meticulously design using Design-Expert software. Secondly, a novel approach involving – the analysis of scanning electron microscope (SEM) images of the algae was introduced, employing a measure known as cumulative Kullback–Leibler information. The results showed that <em>P. gymnospora</em> is capable of removing 50% of Pb. The highest percentage of Cd removal was observed in <em>H. hamulosa</em> (86.44%), while the highest percentage of Hg removal was recorded in <em>C. membranacea</em> (50%). Both, the experimental and analysis of image methods yielded consistent findings, corroborating their reliability. Based on the findings of this study, image analysis employing cumulative Kullback–Leibler information presents a novel and cost effective means of assessment, contributing to the arsenal methods available for contamination treatment.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105466"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143487678","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}

{"title":"Spatial variation of future trends in Atlantic upwelling cells from two CMIP6 models","authors":"Raquel Flügel ,&nbsp;Steven Herbette ,&nbsp;Anne-Marie Treguier ,&nbsp;Robin Waldman ,&nbsp;Malcolm Roberts","doi":"10.1016/j.dsr2.2025.105483","DOIUrl":"10.1016/j.dsr2.2025.105483","url":null,"abstract":"<div><div>Eastern Boundary Upwelling Systems (EBUS) are characterized by wind-triggered upwelling of deep waters along the coast. They are hotspots of biological productivity and diversity and therefore have a high economic, ecological and social importance. In the past, different methods using surface data have been used to estimate upwelling. Recently, the IPCC has suggested directly assessing vertical velocities as a promising method. We use this method to study the two Atlantic EBUS from CMIP6 models from the HadGEM3-GC3.1 and the CNRM6-CM6 family, for both the historical period and a high-emission future scenario with spatial resolutions in the ocean component ranging from 1°to 1/12°. The two major upwelling regions are divided in subregions depending on their seasonality. The vertical transport index shows similar values to a wind-derived Ekman index. Directly evaluating upwelling from transport processes further provides information about the depth of the upwelling, which has previously been identified as an important factor for nutrient availability. We show that depending on the subregion of the upwelling system, different cell structures can be seen in terms of depth and distance to the coast of maximum velocities. When looking at possible future changes, high interannual variability limits the significance of the trends but could indicate a poleward shift of the upwelling regions. A detailed comparison of the spatial structures and the distinction in subregions is important to explain contradictory trends in previous works.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105483"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143941074","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}

{"title":"Oceanic biophysical response to large-scale wind forcing observed southwest of Sumatra during December 2017","authors":"Takanori Horii ,&nbsp;Iwao Ueki ,&nbsp;Kelvin J. Richards ,&nbsp;Qoosaku Moteki ,&nbsp;Kentaro Ando ,&nbsp;Kazuhiko Matsumoto","doi":"10.1016/j.dsr2.2025.105479","DOIUrl":"10.1016/j.dsr2.2025.105479","url":null,"abstract":"<div><div>The water southwest of Sumatra is characterized by the seasonal and interannual occurrence of coastal upwelling, which drives biological variability and active fisheries. Although satellite observations show active biophysical variability at the surface, no observations of surface–subsurface physical and biogeochemical variations were available. Based on a field experiment conducted southwest of Sumatra (4.2°S, 101.5°E) by the research vessel <em>Mirai</em> from December 5, 2017 to January 1, 2018, this study reports observational results for ocean temperature, salinity, nutrients, and biological variations. During the observation period, westerly winds dominated the eastern equatorial Indian Ocean, with northwesterly winds southwest of Sumatra. This wind forcing was unfavorable for local coastal upwelling. Time series of <em>in situ</em> observations indicated gradual shoaling of the thermocline from mid-to late December 2017. This thermocline displacement was attributed to the propagation of equatorial and coastal Kelvin waves in response to the appearance of easterly winds (weakening of westerly winds) in the central (eastern) equatorial Indian Ocean. Concurrent with thermocline shoaling, we observed active mixing at the top of the thermocline, upward transport of nutrients to the euphotic layer, and subsurface phytoplankton growth. These biophysical responses demonstrate that even if local wind forcing is unfavorable for coastal upwelling, remote wind forcing can affect the nutrient supply that supports biological activity off Sumatra through Kelvin wave propagation. These results will provide fundamental data for validating biophysical models of the eastern Indian Ocean.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105479"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coral reefs health status variation around Kish Island before and after 2015 bleaching in the Persian Gulf: A case study of global warming effects","authors":"Askari-Hesni Majid ,&nbsp;Bolouki-Kourandeh Mehdi ,&nbsp;Somayeh Zangiabadi ,&nbsp;Ali Reza Rastgoo ,&nbsp;Mehdi Golestaninasab ,&nbsp;Douglas Fenner","doi":"10.1016/j.dsr2.2025.105484","DOIUrl":"10.1016/j.dsr2.2025.105484","url":null,"abstract":"<div><div>Despite the ecological importance of coral reefs in the Persian Gulf as one of the most sensitive and fragile marine ecosystems in this region, few ecological studies have been carried out in this area. The aims of the present study were to evaluate the species diversity of corals and cohabiting fishes, produce a health status assessment of hard corals in two different periods (2014 and 2020), identify the main destructive factors, and create a distribution map for coral reefs around Kish Island. During this survey, the density and percentage of live and dead corals were evaluated and compared in two periods. Cover percentage of live, bleached, and dead hard corals changed significantly from 2014 to 2020, and in most sites, biological communities are negatively affected. The situation is highly concerning for fishes that were examined as biological indicators of living conditions in the coral communities. Comparing 2014 and 2020 data, about half of fish species were not detected or rarely observed in 2020. Heat anomalies, fishing activities, and overtourism were found to be the most destructive factors on the coral reefs in Kish Island.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105484"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143903686","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}

{"title":"Variability of bottom dissolved oxygen on the southern Senegalese shelf at intraseasonal to interannual time scales using a modelling approach","authors":"Abdoul Wahab Tall ,&nbsp;Vincent Echevin ,&nbsp;Xavier Capet ,&nbsp;Eric Machu","doi":"10.1016/j.dsr2.2025.105464","DOIUrl":"10.1016/j.dsr2.2025.105464","url":null,"abstract":"<div><div>Recent in-situ measurements on the west African continental shelf have shown that the bottom waters undergo episodic hypoxia and even anoxia. In this study, we investigate the variability of bottom dissolved oxygen (DO) over the southern Senegalese shelf at seasonal, intraseasonal and interannual time scales over the period 2015–2019 using a high-resolution (2 km) regional coupled dynamical-biogeochemical model. The model is forced by daily winds to represent synoptic variability during the upwelling-favourable cold season (November-May). Near-bottom DO evaluation using data from the Melax mooring located over the mid shelf indicates that the model represents well the seasonal and intraseasonal variability. A bottom DO budget shows that advection of deep, low-oxygenated waters over the shelf edge during the upwelling season generates a DO loss, which is overcompensated by ventilation of the entire shelf due to vertical mixing. Biogeochemical processes compensate this DO supply: DO is consumed by organic matter and zooplankton respiration, slightly compensated by regenerated and new primary production. Because of a sluggish shelf circulation during the summer season (July–September, JAS), oxygen concentration declines in parts of the outer shelf bottom layer, in spite of a weaker surface primary production and organic matter export than during the heart of the cold season (February–April, FMA). Analysis of the synoptic variability reveals the complexity of the DO response to the duration and intensity of upwelling and relaxation events, with the largest DO decrease of <span><math><mrow><mo>∼</mo><mn>110</mn><mi>μ</mi><mi>m</mi><mi>o</mi><mi>l</mi><msub><mrow><mi>O</mi></mrow><mrow><mn>2</mn></mrow></msub><msup><mrow><mi>L</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span> associated with a strong upwelling event (cumulative upwelling index <span><math><mrow><mo>∼</mo><mn>2</mn><msup><mrow><mi>Nm</mi></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mi>d</mi><mi>a</mi><mi>y</mi></mrow></math></span>) obtained in 2016. Year to year variability indicates two periods of enhanced hypoxia in FMA 2017 and JAS 2016 characterized by a high retention of bottom waters over the shelf.</div></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":"221 ","pages":"Article 105464"},"PeriodicalIF":2.3,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143519959","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}