Pub Date : 2025-11-13DOI: 10.1016/j.pocean.2025.103619
Ruth G. Curry , Michael W. Lomas , Megan R. Sullivan , Damian Grundle
Despite decades of ship-based observations at the Bermuda Atlantic Timeseries Study (BATS) site, ambiguities linger in our understanding of the region’s annual carbon cycle. Difficulties reconciling geochemical estimates of annual net community production (ANCP) with direct measurements of nutrient delivery and carbon exports (EP) have implied either an insufficient understanding of these processes, and/or that they are playing out on shorter time and spatial scales than resolved by monthly sampling. We address the latter concern using autonomous underwater gliders equipped with biogeochemical sensors to quantify ANCP from mass balances of oxygen (O2) and nitrate (NO3−) over a full annual cycle. The timing, amplitude and distributions of O2 production, consumption, and NO3− fluxes reaffirm ideas about strong seasonality in physical forcing and trophic structure creating a dual system: i.e. production fueled by NO3− supplied to the photic zone from deeper layers in the first half of the year, versus being recycled within the upper ocean during the second half. The evidence also supports recently proposed hypotheses regarding the production and recycling of carbon with non-Redfield characteristics, depleted in nitrogen and phosphorus, to explain observed patterns of high NCP in the absence of significant NO3− supply. It further identifies significant contributions to ANCP and EP potentially linked to vertically migrating communities of salps in spring after all convective activity has ceased. The improved resolution of the datasets, combined with more precise definitions of photic and subphotic integration depths, brings the estimates of ANCP and EP into better alignment with each other.
{"title":"Annual net community production and carbon exports in the central Sargasso sea from autonomous underwater glider observations","authors":"Ruth G. Curry , Michael W. Lomas , Megan R. Sullivan , Damian Grundle","doi":"10.1016/j.pocean.2025.103619","DOIUrl":"10.1016/j.pocean.2025.103619","url":null,"abstract":"<div><div>Despite decades of ship-based observations at the Bermuda Atlantic Timeseries Study (BATS) site, ambiguities linger in our understanding of the region’s annual carbon cycle. Difficulties reconciling geochemical estimates of annual net community production (ANCP) with direct measurements of nutrient delivery and carbon exports (EP) have implied either an insufficient understanding of these processes, and/or that they are playing out on shorter time and spatial scales than resolved by monthly sampling. We address the latter concern using autonomous underwater gliders equipped with biogeochemical sensors to quantify ANCP from mass balances of oxygen (O<sub>2</sub>) and nitrate (NO<sub>3</sub><sup>−</sup>) over a full annual cycle. The timing, amplitude and distributions of O<sub>2</sub> production, consumption, and NO<sub>3</sub><sup>−</sup> fluxes reaffirm ideas about strong seasonality in physical forcing and trophic structure creating a dual system: i.e. production fueled by NO<sub>3</sub><sup>−</sup> supplied to the photic zone from deeper layers in the first half of the year, versus being recycled within the upper ocean during the second half. The evidence also supports recently proposed hypotheses regarding the production and recycling of carbon with non-Redfield characteristics, depleted in nitrogen and phosphorus, to explain observed patterns of high NCP in the absence of significant NO<sub>3</sub><sup>−</sup> supply. It further identifies significant contributions to ANCP and EP potentially linked to vertically migrating communities of salps in spring after all convective activity has ceased. The improved resolution of the datasets, combined with more precise definitions of photic and subphotic integration depths, brings the estimates of ANCP and EP into better alignment with each other.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103619"},"PeriodicalIF":3.6,"publicationDate":"2025-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145531208","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 : 2025-11-13DOI: 10.1016/j.pocean.2025.103620
Rhea K. Foreman , Benedetto Barone , Eric Grabowski , Karin M. Björkman , Fernanda Henderikx-Freitas , Catherine A. Garcia , Lauren E. Manck , Angelicque E. White , Matthew J. Church , David M. Karl
In the eastern portion of the oligotrophic North Pacific Subtropical Gyre (NPSG), summertime phytoplankton blooms are recurrent events whose frequency and spatial distribution are primarily known through satellite ocean color observations. Field sampling of blooms has been sparse, so their biogeochemical structure, ecosystem dynamics, and mechanisms of initiation have not been well described, except to show that they are commonly driven by diatom-diazotroph associations (DDAs). To better understand bloom dynamics, an oceanographic expedition in the summer of 2022 targeted a large (225,000 km2), long-lived (3 months) Hemiaulus-Richelia bloom north of the Hawaiian Islands for a comprehensive and multidisciplinary investigation into the bloom’s microbial community composition, nutrient dynamics, suspended and sinking particulate matter, primary production and nitrogen (N2) fixation, and abundances of genes catalyzing N2 fixation and ammonia oxidation (nifH and amoA genes). These novel observations were interpreted together with previous bloom and non-bloom observations from Station ALOHA, the nearby field site of the Hawaii Ocean Time-series program, to gain a general understanding of bloom ecology and the biogeochemical conditions that regulate bloom initiation and demise. We found that a bloom is likely initiated from a ubiquitous summertime seed population of DDAs in the presence of (1) an above-average concentration of phosphate and silicate, (2) a shallow mixed layer that retains DDAs in high light, and (3) low mortality. The build-up of biomass in a bloom leads to a substantial increase in light attenuation; for example, in the 2022 bloom, the depth of the 1% surface light level shoaled by 50 m compared to non-bloom conditions. Decreased photon flux to the lower euphotic zone (>50 m) had significant biological and chemical consequences for the water column, including a diminished abundance of Prochlorococcus and an accumulation of ammonium due to net heterotrophic conditions. The collapse of a bloom can be caused by nutrient depletion (most likely phosphorus in our study region), a deepening mixed layer, and/or enhanced mortality (e.g., a rise in the abundance of grazers, viruses, or parasites). The average carbon export efficiency is high from DDA blooms (in large part because they are mineral-ballasted organisms), and the contribution from blooms to annual, gyre-wide export of organic matter is expected to be substantial.
{"title":"Biogeochemical anatomy and ecosystem dynamics of a large phytoplankton bloom north of the Hawaiian Islands","authors":"Rhea K. Foreman , Benedetto Barone , Eric Grabowski , Karin M. Björkman , Fernanda Henderikx-Freitas , Catherine A. Garcia , Lauren E. Manck , Angelicque E. White , Matthew J. Church , David M. Karl","doi":"10.1016/j.pocean.2025.103620","DOIUrl":"10.1016/j.pocean.2025.103620","url":null,"abstract":"<div><div>In the eastern portion of the oligotrophic North Pacific Subtropical Gyre (NPSG), summertime phytoplankton blooms are recurrent events whose frequency and spatial distribution are primarily known through satellite ocean color observations. Field sampling of blooms has been sparse, so their biogeochemical structure, ecosystem dynamics, and mechanisms of initiation have not been well described, except to show that they are commonly driven by diatom-diazotroph associations (DDAs). To better understand bloom dynamics, an oceanographic expedition in the summer of 2022 targeted a large (225,000 km<sup>2</sup>), long-lived (3 months) <em>Hemiaulus-Richelia</em> bloom north of the Hawaiian Islands for a comprehensive and multidisciplinary investigation into the bloom’s microbial community composition, nutrient dynamics, suspended and sinking particulate matter, primary production and nitrogen (N<sub>2</sub>) fixation, and abundances of genes catalyzing N<sub>2</sub> fixation and ammonia oxidation (<em>nifH</em> and <em>amoA</em> genes). These novel observations were interpreted together with previous bloom and non-bloom observations from Station ALOHA, the nearby field site of the Hawaii Ocean Time-series program, to gain a general understanding of bloom ecology and the biogeochemical conditions that regulate bloom initiation and demise. We found that a bloom is likely initiated from a ubiquitous summertime seed population of DDAs in the presence of (1) an above-average concentration of phosphate and silicate, (2) a shallow mixed layer that retains DDAs in high light, and (3) low mortality. The build-up of biomass in a bloom leads to a substantial increase in light attenuation; for example, in the 2022 bloom, the depth of the 1% surface light level shoaled by 50 m compared to non-bloom conditions. Decreased photon flux to the lower euphotic zone (>50 m) had significant biological and chemical consequences for the water column, including a diminished abundance of <em>Prochlorococcus</em> and an accumulation of ammonium due to net heterotrophic conditions. The collapse of a bloom can be caused by nutrient depletion (most likely phosphorus in our study region), a deepening mixed layer, and/or enhanced mortality (e.g., a rise in the abundance of grazers, viruses, or parasites). The average carbon export efficiency is high from DDA blooms (in large part because they are mineral-ballasted organisms), and the contribution from blooms to annual, gyre-wide export of organic matter is expected to be substantial.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"241 ","pages":"Article 103620"},"PeriodicalIF":3.6,"publicationDate":"2025-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145531172","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 : 2025-11-10DOI: 10.1016/j.pocean.2025.103618
Juan Cruz Carbajal , Jacobo Martin , Maité P. Latorre , Facundo Barrera , Julieta Kaminsky , Andreana M. Cadaillón , Martin Saraceno
The continental margin south of Tierra del Fuego and the adjacent northwest Scotia Sea serves as a transition area between the Southern Chilean and the Southern Argentinian Patagonian ecosystems. Bounded by the Northern Boundary and the Sub-Antarctic Front of the Antarctic Circumpolar Current, circulation in this area transports water and properties from the Pacific to the Atlantic Ocean, influencing the ecology of southern ecosystems. The narrow continental margin hosts a network of submarine canyons, including the deeply incised Sloggett Canyon, which intercepts and likely modifies the along-shelf-break current. Combining in-situ hydrographic measurements from a multidisciplinary cruise conducted in November 2022 with coincident global atmospheric and oceanic reanalysis, we investigate the water masses and dynamics in this understudied area. Analysis of upper ocean variability exhibited two distinct phases associated with Ekman dynamics: a relaxation phase characterized by calm wind conditions, a weak along-shelf-break current (45 cm s−1), and well-defined mesoscale activity along the Sub-Antarctic Front, and an intensification phase marked by strong wind conditions, an intense along-shelf-break current (over 80 cm s−1), and increased meander activity offshore. Despite limited field data, we document a remarkable wind-driven upwelling episode in the upper portion of the Sloggett Canyon during the intensification phase, highlighting the role of wind stress and canyon geomorphology as possible mechanisms driving upwelling events. This episode was also coincident with near-surface chlorophyll-a maxima, emphasizing the canyon’s relevance as a biological hotspot. Our findings raise new questions, highlighting the need for longer time-series studies and more dedicated multidisciplinary research efforts.
火地岛南部的大陆边缘和邻近的西北斯科舍海是智利南部和阿根廷南部巴塔哥尼亚生态系统之间的过渡区域。受南极环极流的北部边界和亚南极锋的限制，该地区的环流将水和物质从太平洋输送到大西洋，影响了南部生态系统的生态。狭窄的大陆边缘拥有海底峡谷网络，包括深切的斯洛格特峡谷，它拦截并可能改变沿大陆架断裂的水流。结合2022年11月进行的多学科巡航的现场水文测量和同步的全球大气和海洋再分析，我们研究了这一研究不足地区的水团和动力学。上层海洋变率分析显示了与Ekman动力学相关的两个不同阶段：以平静风条件为特征的松弛阶段，弱的沿大陆架断裂流（45 cm s - 1），以及沿亚南极锋明确的中尺度活动；以及以强风条件为特征的强化阶段，强的沿大陆架断裂流（超过80 cm s - 1），以及近海蜿蜒活动的增加。尽管野外资料有限，但我们在加剧阶段记录了一个显著的风驱动上升流事件，突出了风应力和峡谷地貌作为驱动上升流事件的可能机制的作用。这一事件也与近地表叶绿素a的最大值一致，强调了峡谷作为生物热点的相关性。我们的发现提出了新的问题，强调需要更长的时间序列研究和更专注的多学科研究努力。
{"title":"Circulation and wind-driven processes in the Yaganes area","authors":"Juan Cruz Carbajal , Jacobo Martin , Maité P. Latorre , Facundo Barrera , Julieta Kaminsky , Andreana M. Cadaillón , Martin Saraceno","doi":"10.1016/j.pocean.2025.103618","DOIUrl":"10.1016/j.pocean.2025.103618","url":null,"abstract":"<div><div>The continental margin south of Tierra del Fuego and the adjacent northwest Scotia Sea serves as a transition area between the Southern Chilean and the Southern Argentinian Patagonian ecosystems. Bounded by the Northern Boundary and the Sub-Antarctic Front of the Antarctic Circumpolar Current, circulation in this area transports water and properties from the Pacific to the Atlantic Ocean, influencing the ecology of southern ecosystems. The narrow continental margin hosts a network of submarine canyons, including the deeply incised Sloggett Canyon, which intercepts and likely modifies the along-shelf-break current. Combining <em>in-situ</em> hydrographic measurements from a multidisciplinary cruise conducted in November 2022 with coincident global atmospheric and oceanic reanalysis, we investigate the water masses and dynamics in this understudied area. Analysis of upper ocean variability exhibited two distinct phases associated with Ekman dynamics: a relaxation phase characterized by calm wind conditions, a weak along-shelf-break current (45 cm s<sup>−1</sup>), and well-defined mesoscale activity along the Sub-Antarctic Front, and an intensification phase marked by strong wind conditions, an intense along-shelf-break current (over 80 cm s<sup>−1</sup>), and increased meander activity offshore. Despite limited field data, we document a remarkable wind-driven upwelling episode in the upper portion of the Sloggett Canyon during the intensification phase, highlighting the role of wind stress and canyon geomorphology as possible mechanisms driving upwelling events. This episode was also coincident with near-surface chlorophyll-a maxima, emphasizing the canyon’s relevance as a biological hotspot. Our findings raise new questions, highlighting the need for longer time-series studies and more dedicated multidisciplinary research efforts.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103618"},"PeriodicalIF":3.6,"publicationDate":"2025-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145485316","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 : 2025-11-07DOI: 10.1016/j.pocean.2025.103615
Laureline Dalaut, Nicolas Barrier, Matthieu Lengaigne, Olivier Maury
Pelagic ecosystems exhibit a strong regional heterogeneity, driven by physical and biogeochemical characteristics. Using the global 3D marine ecosystem model APECOSM, we simulate six high-trophic-level communities, capturing their size structure, spatial distribution, and trophic interactions up to 1,000 metres depth. We examine how different environments shape their contrasting organisation and interactions in three Pacific Ocean regions: the productive Humboldt Current System, the oligotrophic South Pacific Gyre, and the thermally stratified Pacific Warm Pool.
Simulations reveal strong regional contrasts in ecosystem responses. In the Humboldt, high primary production supports important biomass of small coastal pelagic fish. Seasonal warming enables tuna to forage in these productive waters, while low-oxygen conditions restrict the vertical range and abundance of mesopelagic organisms and concentrate epipelagic organisms close to the surface. In the Warm Pool, apex predators remain abundant despite low primary production, thanks to efficient trophic transfer and biomass import from neighbouring regions. Seamounts concentrate mesopelagic organisms into shallow layers, making them accessible to epipelagic predators. In contrast, the South Pacific Gyre supports sparse, imported high-trophic-levels with limited trophic coupling and strong intra-community predation. We quantify regional differences in trophic transfer efficiency and network complexity, identifying thresholds below which high-trophic-levels collapse.
These findings illustrate the emergent plasticity of pelagic ecosystems and the importance of bottom-up control of high-trophic-level biomass. They emphasise the importance of temperature, transport, light and oxygen in modulating horizontal and vertical distributions, controlling the co-occurrence of predators and prey, and influencing the formation of schools, ultimately impacting trophic interactions and community assemblages.
{"title":"How contrasted environments in the Humboldt Current System, Pacific Warm Pool and South Pacific Gyre, shape contrasted ecosystems. A modelling approach using APECOSM","authors":"Laureline Dalaut, Nicolas Barrier, Matthieu Lengaigne, Olivier Maury","doi":"10.1016/j.pocean.2025.103615","DOIUrl":"10.1016/j.pocean.2025.103615","url":null,"abstract":"<div><div>Pelagic ecosystems exhibit a strong regional heterogeneity, driven by physical and biogeochemical characteristics. Using the global 3D marine ecosystem model APECOSM, we simulate six high-trophic-level communities, capturing their size structure, spatial distribution, and trophic interactions up to 1,000 metres depth. We examine how different environments shape their contrasting organisation and interactions in three Pacific Ocean regions: the productive Humboldt Current System, the oligotrophic South Pacific Gyre, and the thermally stratified Pacific Warm Pool.</div><div>Simulations reveal strong regional contrasts in ecosystem responses. In the Humboldt, high primary production supports important biomass of small coastal pelagic fish. Seasonal warming enables tuna to forage in these productive waters, while low-oxygen conditions restrict the vertical range and abundance of mesopelagic organisms and concentrate epipelagic organisms close to the surface. In the Warm Pool, apex predators remain abundant despite low primary production, thanks to efficient trophic transfer and biomass import from neighbouring regions. Seamounts concentrate mesopelagic organisms into shallow layers, making them accessible to epipelagic predators. In contrast, the South Pacific Gyre supports sparse, imported high-trophic-levels with limited trophic coupling and strong intra-community predation. We quantify regional differences in trophic transfer efficiency and network complexity, identifying thresholds below which high-trophic-levels collapse.</div><div>These findings illustrate the emergent plasticity of pelagic ecosystems and the importance of bottom-up control of high-trophic-level biomass. They emphasise the importance of temperature, transport, light and oxygen in modulating horizontal and vertical distributions, controlling the co-occurrence of predators and prey, and influencing the formation of schools, ultimately impacting trophic interactions and community assemblages.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103615"},"PeriodicalIF":3.6,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145461749","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 : 2025-11-03DOI: 10.1016/j.pocean.2025.103616
Katharine T. Bigham , Ashley A. Rowden , Daniel Leduc , David A. Bowden
Sediment density flows are complex events that contain multiple flow types which can transport massive amounts of sediment across large distances. Turbidity flows are believed to have profound and lasting impacts on benthic communities in the deep sea. A canyon-flushing event in Kaikōura Canyon, New Zealand, triggered by the 2016 Mw 7.8 Kaikōura Earthquake, included significant submarine mass wasting, debris, and turbidity flows, and provided an opportunity to investigate the effects of this disturbance. Previous studies have analysed the mega-, macro-, and meiofauna community structure, before and after the event using a time series of imagery and sediment cores. Additionally, community recovery was investigated in relation to changes in the physical characteristics of the habitat, using environmental variables from images and bathymetric variables and sediment cores. However, no attempt has been made to examine the overall community response to turbidity flow disturbance or to consider interactions between the different size classes. To address this gap, the data and results for each size class in Kaikōura Canyon were synthesised here with an emphasis on assessing the overall deep-sea benthic community response, and predicting time to recovery for the full community in Kaikōura Canyon. Overall, the benthic community in Kaikoura Canyon appears to be resilient to the disturbance with meiofauna showing the fastest recovery time followed by megafauna and then macrofauna. Differences in the life-history characteristics of mega-, macro- and meiofauna, as well as various interactions among the faunal size class communities, likely have influenced the recovery patterns observed.
{"title":"Integrated understanding of benthic community response to disturbance from an earthquake-triggered turbidity flow event","authors":"Katharine T. Bigham , Ashley A. Rowden , Daniel Leduc , David A. Bowden","doi":"10.1016/j.pocean.2025.103616","DOIUrl":"10.1016/j.pocean.2025.103616","url":null,"abstract":"<div><div>Sediment density flows are complex events that contain multiple flow types which can transport massive amounts of sediment across large distances. Turbidity flows are believed to have profound and lasting impacts on benthic communities in the deep sea. A canyon-flushing event in Kaikōura Canyon, New Zealand, triggered by the 2016 M<sub>w</sub> 7.8 Kaikōura Earthquake, included significant submarine mass wasting, debris, and turbidity flows, and provided an opportunity to investigate the effects of this disturbance. Previous studies have analysed the mega-, macro-, and meiofauna community structure, before and after the event using a time series of imagery and sediment cores. Additionally, community recovery was investigated in relation to changes in the physical characteristics of the habitat, using environmental variables from images and bathymetric variables and sediment cores. However, no attempt has been made to examine the overall community response to turbidity flow disturbance or to consider interactions between the different size classes. To address this gap, the data and results for each size class in Kaikōura Canyon were synthesised here with an emphasis on assessing the overall deep-sea benthic community response, and predicting time to recovery for the full community in Kaikōura Canyon. Overall, the benthic community in Kaikoura Canyon appears to be resilient to the disturbance with meiofauna showing the fastest recovery time followed by megafauna and then macrofauna. Differences in the life-history characteristics of mega-, macro- and meiofauna, as well as various interactions among the faunal size class communities, likely have influenced the recovery patterns observed.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103616"},"PeriodicalIF":3.6,"publicationDate":"2025-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145427973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-30DOI: 10.1016/j.pocean.2025.103614
C. Yoshikawa , H. Yamaguchi , N.O. Ogawa , A. Makabe , M. Sato , Y. Mino , K. Matsumoto , Y. Nakano , S. Kawagucci , T. Fujiki , N. Harada , M. Kawachi , N. Ohkouchi
Nitrogen isotope compositions (δ15N) of phytoplankton, nitrate, and ammonium can reveal the fraction of nitrate versus ammonium utilization by phytoplankton. The δ15N values of ammonium in the open ocean has been rarely determined because of its low concentration. However, interpretations of phytoplankton nitrogen sources using δ15N values has required the ammonium δ15N values. Here, we determined the δ15N values of phytoplankton, nitrate, and ammonium in the summertime of 2012–2016 at contrasting stations in the subarctic and subtropical western North Pacific. We also developed a nitrogen isotope model to constrain the nitrogenous sources of the phytoplankton and compensate for the lack of observations. At the subarctic station, the δ15N values of nitrate and phytoplankton in the surface waters were 8.5 ‰ and − 5.9 ± 0.5 ‰ to − 3.3 ± 0.5 ‰, respectively. At the subtropical station, the δ15N values of nitrate and phytoplankton were 6.8 ‰ and1.0 ± 0.7 ‰, respectively. The differences in δ15N values between phytoplankton and nitrate were as large as 11.8 ‰ to 14.4 ‰ at the subarctic station and as small as 5.8 ‰ at the subtropical station. Although the ammonium concentration was below the detection limit at the subtropical station, it was 0.4 μM at the subarctic station and the δ15N value was 4.5 ± 1.9 ‰, much lower than that of nitrate. A model constrained by the nitrogen isotope measurements revealed that, during summer, the phytoplankton at the subarctic station assimilated more than half of their nitrogen from ammonium. At the subtropical station, ammonium assimilation was dominant.
{"title":"Nitrogenous sources for summertime phytoplankton at two contrasting stations in the subarctic and subtropical western North Pacific","authors":"C. Yoshikawa , H. Yamaguchi , N.O. Ogawa , A. Makabe , M. Sato , Y. Mino , K. Matsumoto , Y. Nakano , S. Kawagucci , T. Fujiki , N. Harada , M. Kawachi , N. Ohkouchi","doi":"10.1016/j.pocean.2025.103614","DOIUrl":"10.1016/j.pocean.2025.103614","url":null,"abstract":"<div><div>Nitrogen isotope compositions (<em>δ</em><sup>15</sup>N) of phytoplankton, nitrate, and ammonium can reveal the fraction of nitrate versus ammonium utilization by phytoplankton. The <em>δ</em><sup>15</sup>N values of ammonium in the open ocean has been rarely determined because of its low concentration. However, interpretations of phytoplankton nitrogen sources using <em>δ</em><sup>15</sup>N values has required the ammonium <em>δ</em><sup>15</sup>N values. Here, we determined the <em>δ</em><sup>15</sup>N values of phytoplankton, nitrate, and ammonium in the summertime of 2012–2016 at contrasting stations in the subarctic and subtropical western North Pacific. We also developed a nitrogen isotope model to constrain the nitrogenous sources of the phytoplankton and compensate for the lack of observations. At the subarctic station, the <em>δ</em><sup>15</sup>N values of nitrate and phytoplankton in the surface waters were 8.5 ‰ and − 5.9 ± 0.5 ‰ to − 3.3 ± 0.5 ‰, respectively. At the subtropical station, the <em>δ</em><sup>15</sup>N values of nitrate and phytoplankton were 6.8 ‰ and1.0 ± 0.7 ‰, respectively. The differences in <em>δ</em><sup>15</sup>N values between phytoplankton and nitrate were as large as 11.8 ‰ to 14.4 ‰ at the subarctic station and as small as 5.8 ‰ at the subtropical station. Although the ammonium concentration was below the detection limit at the subtropical station, it was 0.4 μM at the subarctic station and the <em>δ</em><sup>15</sup>N value was 4.5 ± 1.9 ‰, much lower than that of nitrate. A model constrained by the nitrogen isotope measurements revealed that, during summer, the phytoplankton at the subarctic station assimilated more than half of their nitrogen from ammonium. At the subtropical station, ammonium assimilation was dominant.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103614"},"PeriodicalIF":3.6,"publicationDate":"2025-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145404690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-28DOI: 10.1016/j.pocean.2025.103611
Cassandra Santos-Pacheco , Issah N. Suleiman , Erdal Tokat , Ana Martins
Understanding the implications of climate change is especially critical for the Cape Verde Islands, which are acutely vulnerable to climate variability and its associated impacts. This study characterised the temporal variability of surface and near-surface biophysical properties around Santo Antão using 20 years of MODIS-Aqua Level-2 imagery at 1 km resolution for Ocean Colour and Thermal Infrared parameters. The results of this study show that the waters around this island exhibited stable Sea Surface Temperature conditions with a pronounced seasonal cycle and no long-term warming over two decades, contrasting with global trends. Bio-optical parameters (Chlorophyll a, Diffuse Attenuation Coefficient and Particulate Organic Carbon) reflected the oligotrophic nature of the waters, with slight positive trends hinting at increasing concentrations of primary productivity. Consistently high levels of Photosynthetically Available Radiation affirmed light is not a limiting factor, with nutrient dynamics likely playing a dominant role. Particulate Inorganic Carbon displayed distinct variability, with no significant trends, underscoring the need for further research into its unique drivers. Based on ocean surface temperature cycles, the newly proposed seasonal classification successfully captured the dynamics of key parameters and demonstrated the value of satellite-derived data for long-term ecosystem monitoring. These findings enhanced the understanding of Santo Antão’s oceanographic dynamics and highlight the importance of regionally specific studies to complement global assessments. The results also provide a valuable baseline to support future research and inform conservation strategies and sustainable marine resource management in the Cape Verde region.
{"title":"Satellite-derived ocean climatology around Santo Antão Island: 20 years of surface and near-surface observations","authors":"Cassandra Santos-Pacheco , Issah N. Suleiman , Erdal Tokat , Ana Martins","doi":"10.1016/j.pocean.2025.103611","DOIUrl":"10.1016/j.pocean.2025.103611","url":null,"abstract":"<div><div>Understanding the implications of climate change is especially critical for the Cape Verde Islands, which are acutely vulnerable to climate variability and its associated impacts. This study characterised the temporal variability of surface and near-surface biophysical properties around Santo Antão using 20 years of MODIS-Aqua Level-2 imagery at 1 km resolution for Ocean Colour and Thermal Infrared parameters. The results of this study show that the waters around this island exhibited stable Sea Surface Temperature conditions with a pronounced seasonal cycle and no long-term warming over two decades, contrasting with global trends. Bio-optical parameters (Chlorophyll <em>a</em>, Diffuse Attenuation Coefficient and Particulate Organic Carbon) reflected the oligotrophic nature of the waters, with slight positive trends hinting at increasing concentrations of primary productivity. Consistently high levels of Photosynthetically Available Radiation affirmed light is not a limiting factor, with nutrient dynamics likely playing a dominant role. Particulate Inorganic Carbon displayed distinct variability, with no significant trends, underscoring the need for further research into its unique drivers. Based on ocean surface temperature cycles, the newly proposed seasonal classification successfully captured the dynamics of key parameters and demonstrated the value of satellite-derived data for long-term ecosystem monitoring. These findings enhanced the understanding of Santo Antão’s oceanographic dynamics and highlight the importance of regionally specific studies to complement global assessments. The results also provide a valuable baseline to support future research and inform conservation strategies and sustainable marine resource management in the Cape Verde region.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103611"},"PeriodicalIF":3.6,"publicationDate":"2025-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145396376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-28DOI: 10.1016/j.pocean.2025.103613
Anindya Wirasatriya , Arthur Mattews Basana , Elis Indrayanti , Agus Anugroho Dwi Suryoputro , R. Dwi Susanto , Retno Hartati , Nur Taufiq-SPJ , Jahved Ferianto Maro , Parichat Wetchayont , Mochamad Iqbal Herwata Putra , Achmad Sahri
An Extreme Upwelling Event (EUE), denoted by the sudden drop of sea surface temperature to less than 15 °C in a relatively short period, is a unique and recently reported oceanographic phenomenon. One and possibly the only place with confirmed EUE is the Mulut Kumbang Strait, Alor Kecil Village, Alor Island, Indonesia, since the phenomenon has never been reported in other tropical seas. The EUE occurred from August to November and lasted for 1 to 4 days, with a duration of only about an hour. The dramatic temperature drops during EUE caused small fish to become unconscious and attracted dolphins to come and feed. This is the first study to observe and quantify the dolphin sighting during EUE using closed-circuit television (CCTV). Full month observations were initially conducted in May and September 2022, which represented the months without and with EUE, respectively. In May 2022, the daytime minimum temperature was 24 °C (on May 19, 2022), with a total of 54 dolphin occurrences. In September 2022, the temperature reached 17.34 °C (on September 13, 2022), and the total dolphin occurrences increased to 87. With prior knowledge from 2022 EUEs, we conducted two additional EUE observations in 2023, focused around September: 2–4 September 2023 (period 1) and 30 September – 2 October 2023 (period 2). The temperatures in September and October 2023 were much lower than those in September 2022, with a minimum temperature of ∼ 12 °C. The total dolphin sightings in periods 1 and 2 of 2023 increased to 105 and 90, respectively, and both occurred within one hour during the peak of EUE. The frequent dolphin sightings during EUE have a potential to be developed as sustainable marine wildlife tourism, since people can watch dolphin occurrences only from the seashore along the Alor Kecil Village.
{"title":"Increasing dolphin occurrences during Extreme Upwelling Events: Potential nonharmful and sustainable marine wildlife tourism at Mulut Kumbang Strait, Alor Kecil Village, Alor Island, Indonesia","authors":"Anindya Wirasatriya , Arthur Mattews Basana , Elis Indrayanti , Agus Anugroho Dwi Suryoputro , R. Dwi Susanto , Retno Hartati , Nur Taufiq-SPJ , Jahved Ferianto Maro , Parichat Wetchayont , Mochamad Iqbal Herwata Putra , Achmad Sahri","doi":"10.1016/j.pocean.2025.103613","DOIUrl":"10.1016/j.pocean.2025.103613","url":null,"abstract":"<div><div>An Extreme Upwelling Event (EUE), denoted by the sudden drop of sea surface temperature to less than 15 °C in a relatively short period, is a unique and recently reported oceanographic phenomenon. One and possibly the only place with confirmed EUE is the Mulut Kumbang Strait, Alor Kecil Village, Alor Island, Indonesia, since the phenomenon has never been reported in other tropical seas. The EUE occurred from August to November and lasted for 1 to 4 days, with a duration of only about an hour. The dramatic temperature drops during EUE caused small fish to become unconscious and attracted dolphins to come and feed. This is the first study to observe and quantify the dolphin sighting during EUE using closed-circuit television (CCTV). Full month observations were initially conducted in May and September 2022, which represented the months without and with EUE, respectively. In May 2022, the daytime minimum temperature was 24 °C (on May 19, 2022), with a total of 54 dolphin occurrences. In September 2022, the temperature reached 17.34 °C (on September 13, 2022), and the total dolphin occurrences increased to 87. With prior knowledge from 2022 EUEs, we conducted two additional EUE observations in 2023, focused around September: 2–4 September 2023 (period 1) and 30 September – 2 October 2023 (period 2). The temperatures in September and October 2023 were much lower than those in September 2022, with a minimum temperature of ∼ 12 °C. The total dolphin sightings in periods 1 and 2 of 2023 increased to 105 and 90, respectively, and both occurred within one hour during the peak of EUE. The frequent dolphin sightings during EUE have a potential to be developed as sustainable marine wildlife tourism, since people can watch dolphin occurrences only from the seashore along the Alor Kecil Village.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103613"},"PeriodicalIF":3.6,"publicationDate":"2025-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145383422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-28DOI: 10.1016/j.pocean.2025.103612
Ping Du , Xiao Ma , Yuanli Zhu , Ruijie Ye , Shenran Zhang , WNC Priyadarshani , P.A.K.N. Dissanayake , Haifeng Zhang , Yibo Liao , Yanbin Tang , Zhibing Jiang , Hongliang Li , Feng Zhou , Lu Shou
The organic carbon produced by photosynthesis can only be stored over centennial time scales when it is transported to the meso- and bathypelagic zones. The increase in chlorophyll-a (Chla) influenced by positive Indian Ocean Dipole (pIOD) events and cold-core eddies, and the higher mesozooplankton biomass and abundance around cold-core eddies have been reported in the mixed layer. However, there is a gap in understanding the response of deep-sea mesozooplankton to pIOD events and eddies. Mesozooplankton communities within 0–3000 m were sampled in the eastern Equatorial Indian Ocean (EIO) and southern Bay of Bengal (BOB) between December 2019 and January 2020, and were used to analyze the responses of communities in epi- (0–100 m), meso- (100–1000 m), and bathypelagic (1000–3000 m) layers to the anomalous Chla in the upper water column caused by the pIOD event and eddies. The results found the higher mesozooplankton biomass in the epipelagic layer existed in the eastern EIO and south-central and south-eastern BOB, coinciding well with the higher surface and subsurface Chla concentration influenced by both the pIOD event and cold-core eddies. Meanwhile, cold-core eddies that lasted longer-time and caused a stronger upwelling process increased biomass and affected composition of mesozooplankton community in the mesopelagic layer. However, the pIOD event had little effect on the biomass and composition of mesopelagic mesozooplankton community. The study did not detect obvious effects of the pIOD event and eddies on the bathypelagic mesozooplankton community. This study highlights the important role of long-time lasting and strong cold-core eddies on carbon export and sequestration in the BOB.
{"title":"Responses of mesozooplankton to extreme positive Indian Ocean Dipole (pIOD) and cold-core eddy in the eastern Equatorial Indian Ocean and southern Bay of Bengal during 2019/2020 winter","authors":"Ping Du , Xiao Ma , Yuanli Zhu , Ruijie Ye , Shenran Zhang , WNC Priyadarshani , P.A.K.N. Dissanayake , Haifeng Zhang , Yibo Liao , Yanbin Tang , Zhibing Jiang , Hongliang Li , Feng Zhou , Lu Shou","doi":"10.1016/j.pocean.2025.103612","DOIUrl":"10.1016/j.pocean.2025.103612","url":null,"abstract":"<div><div>The organic carbon produced by photosynthesis can only be stored over centennial time scales when it is transported to the meso- and bathypelagic zones. The increase in chlorophyll-<em>a</em> (Chl<em>a</em>) influenced by positive Indian Ocean Dipole (pIOD) events and cold-core eddies, and the higher mesozooplankton biomass and abundance around cold-core eddies have been reported in the mixed layer. However, there is a gap in understanding the response of deep-sea mesozooplankton to pIOD events and eddies. Mesozooplankton communities within 0–3000 m were sampled in the eastern Equatorial Indian Ocean (EIO) and southern Bay of Bengal (BOB) between December 2019 and January 2020, and were used to analyze the responses of communities in epi- (0–100 m), meso- (100–1000 m), and bathypelagic (1000–3000 m) layers to the anomalous Chl<em>a</em> in the upper water column caused by the pIOD event and eddies. The results found the higher mesozooplankton biomass in the epipelagic layer existed in the eastern EIO and south-central and south-eastern BOB, coinciding well with the higher surface and subsurface Chl<em>a</em> concentration influenced by both the pIOD event and cold-core eddies. Meanwhile, cold-core eddies that lasted longer-time and caused a stronger upwelling process increased biomass and affected composition of mesozooplankton community in the mesopelagic layer. However, the pIOD event had little effect on the biomass and composition of mesopelagic mesozooplankton community. The study did not detect obvious effects of the pIOD event and eddies on the bathypelagic mesozooplankton community. This study highlights the important role of long-time lasting and strong cold-core eddies on carbon export and sequestration in the BOB.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103612"},"PeriodicalIF":3.6,"publicationDate":"2025-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145383387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-27DOI: 10.1016/j.pocean.2025.103601
Joanna Zanker , Emma F. Young , Paul Brickle , Ivan Haigh
Climate change is impacting high-latitude fjord circulation with consequences for the transport of marine biota essential for supporting local ecosystems. Currently, little is understood about oceanographic variability in sub-Antarctic island fjords such as Cumberland Bay, the largest fjord on the island of South Georgia in the Southern Ocean. Cumberland Bay is split into two arms, West Bay and East Bay, and is a key spawning site for the ecologically and commercially important mackerel icefish. Through the use of a high-resolution three-dimensional hydrodynamic model, the seasonal cycle in Cumberland Bay is found to be driven by a combination of boundary forcing influencing shelf exchange and deep inflow, atmospheric forcing influencing near surface temperatures and flows and freshwater forcing via subglacial discharge driving upwelling and strong outflow. There is a complex three-dimensional flow structure with a high degree of variability on short timescales due to wind forcing. Using model flow fields to drive an individual-based model parameterised for mackerel icefish larvae spawned in Cumberland Bay, we identify West Bay as a key retention zone. Successful retention of mackerel icefish larvae is found to be sensitive to complex circulation patterns driven by winds, freshwater and fjord-shelf exchanges and to changes in physical processes linked to climate change such as meltwater runoff and föhn wind events. This study highlights the importance of oceanographic variability in influencing ecological processes in fjords in our changing climate.
{"title":"Sub-Antarctic fjord circulation and associated icefish larval retention in a changing climate","authors":"Joanna Zanker , Emma F. Young , Paul Brickle , Ivan Haigh","doi":"10.1016/j.pocean.2025.103601","DOIUrl":"10.1016/j.pocean.2025.103601","url":null,"abstract":"<div><div>Climate change is impacting high-latitude fjord circulation with consequences for the transport of marine biota essential for supporting local ecosystems. Currently, little is understood about oceanographic variability in sub-Antarctic island fjords such as Cumberland Bay, the largest fjord on the island of South Georgia in the Southern Ocean. Cumberland Bay is split into two arms, West Bay and East Bay, and is a key spawning site for the ecologically and commercially important mackerel icefish. Through the use of a high-resolution three-dimensional hydrodynamic model, the seasonal cycle in Cumberland Bay is found to be driven by a combination of boundary forcing influencing shelf exchange and deep inflow, atmospheric forcing influencing near surface temperatures and flows and freshwater forcing via subglacial discharge driving upwelling and strong outflow. There is a complex three-dimensional flow structure with a high degree of variability on short timescales due to wind forcing. Using model flow fields to drive an individual-based model parameterised for mackerel icefish larvae spawned in Cumberland Bay, we identify West Bay as a key retention zone. Successful retention of mackerel icefish larvae is found to be sensitive to complex circulation patterns driven by winds, freshwater and fjord-shelf exchanges and to changes in physical processes linked to climate change such as meltwater runoff and föhn wind events. This study highlights the importance of oceanographic variability in influencing ecological processes in fjords in our changing climate.</div></div>","PeriodicalId":20620,"journal":{"name":"Progress in Oceanography","volume":"240 ","pages":"Article 103601"},"PeriodicalIF":3.6,"publicationDate":"2025-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145383393","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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