Pub Date : 2024-05-23DOI: 10.1016/j.dsr2.2024.105390
Alexei V. Chernyshev, Vasiliy G. Kuznetsov
To date, a total of 30 nemertean species have been described from depths greater than 1000 m. All deep-sea species of the infraorder Oerstediina belong to the genera found at great depths only. A new species of the genus Oerstedia Quatrefages, 1846 (O. sashae sp. nov.), whose described species inhabit shallow waters, has been collected on the Emperor Seamounts from a depth of 1407 m. Oerstedia sashae sp. nov. differs from the other species of the genus by the lack of eyes. Another new species, Oerstedia sofiae sp. nov., which is very close to the symbiotic Cryptonemertes actinophila (Bürger, 1904), has been described from the Sea of Okhotsk, from a depth of 250–490 m. A phylogenetic analysis based on five gene markers (COI, 16 S, 18 S, 28 S, and histone H3) has shown that O. sashae sp. nov., O. sofiae sp. nov., and C. actinophila belong to clade Paroerstediella of the genus Oerstedia. Cryptonemertes actinophila is here proposed to be transferred to the genus Oerstedia. Oerstedia sofiae sp. nov. and O. actinophila comb. nov. differ from the other species of the genus by the red blood and a very short proboscis and rhynchocoel.
{"title":"A description of two new deep-sea nemerteans from North Pacific with reconsideration of the genus Oerstedia (Hoplonemertea, Oerstediidae)","authors":"Alexei V. Chernyshev, Vasiliy G. Kuznetsov","doi":"10.1016/j.dsr2.2024.105390","DOIUrl":"https://doi.org/10.1016/j.dsr2.2024.105390","url":null,"abstract":"<div><p>To date, a total of 30 nemertean species have been described from depths greater than 1000 m. All deep-sea species of the infraorder Oerstediina belong to the genera found at great depths only. A new species of the genus <em>Oerstedia</em> Quatrefages, 1846 (<em>O. sashae</em> sp. nov.), whose described species inhabit shallow waters, has been collected on the Emperor Seamounts from a depth of 1407 m. <em>Oerstedia sashae</em> sp. nov. differs from the other species of the genus by the lack of eyes. Another new species, <em>Oerstedia sofiae</em> sp. nov., which is very close to the symbiotic <em>Cryptonemertes actinophila</em> (Bürger, 1904), has been described from the Sea of Okhotsk, from a depth of 250–490 m. A phylogenetic analysis based on five gene markers (COI, 16 S, 18 S, 28 S, and histone H3) has shown that <em>O. sashae</em> sp. nov., <em>O. sofiae</em> sp. nov., and <em>C. actinophila</em> belong to clade <em>Paroerstediella</em> of the genus <em>Oerstedia</em>. <em>Cryptonemertes actinophila</em> is here proposed to be transferred to the genus <em>Oerstedia</em>. <em>Oerstedia sofiae</em> sp. nov. and <em>O. actinophila</em> comb. nov. differ from the other species of the genus by the red blood and a very short proboscis and rhynchocoel.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141242085","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 : 2024-05-15DOI: 10.1016/j.dsr2.2024.105381
Jai Kumar, Smitha Ratheesh, Neeraj Agarwal, Rashmi Sharma
During the summer monsoon, the Somali region undergoes a significant upwelling phenomenon that enhances plankton productivity, thereby benefiting fisheries. Wind and coastal dynamics initially drive this upwelling, but eventually, eddy flows influence it. Our study explores the interplay between ocean currents, eddies, and chlorophyll-a concentrations using the backward Finite-Size Lyapunov Exponents (bFSLEs) technique. We also delve into the specific role of Ekman transport in distributing chlorophyll-a across the region. The Great Whirl (GW), an anticyclonic eddy, predominantly causes strong downwelling, interrupting the summer monsoon upwelling along the Somali coast longitudinally. Despite the GW's significant impact on moving upwelled water offshore, the influence of downwelling diminishes northward. As a result, the northern Somali coast, especially around 9°N and 10°N, showcases the most extensive offshore upwelling, reaching as far as 55°E. Our findings highlight a robust connection between chlorophyll-a levels and oceanic dynamics, influenced by both currents and eddies, as evidenced by bFSLEs, and by cross-shore Ekman transport, particularly within chlorophyll-a concentrations ranging from 0.2 to 0.6 mg m−3. The data suggests that Ekman transport-induced upwelling primarily drives coastal phytoplankton biomass. Furthermore, bFSLEs analysis underlines the supportive role of ocean currents and eddies in the offshore distribution of chlorophyll-a, especially near the coast. Further examination of lagged correlations reveals a temporal lag between peak concentrations of chlorophyll-a and Ekman transport; the lag increases offshore and is at least 9 days near the coast.
{"title":"Study of upwelling and mixing process in the Somali coastal region using satellite and numerical model observations: A Lagrangian approach","authors":"Jai Kumar, Smitha Ratheesh, Neeraj Agarwal, Rashmi Sharma","doi":"10.1016/j.dsr2.2024.105381","DOIUrl":"https://doi.org/10.1016/j.dsr2.2024.105381","url":null,"abstract":"<div><p>During the summer monsoon, the Somali region undergoes a significant upwelling phenomenon that enhances plankton productivity, thereby benefiting fisheries. Wind and coastal dynamics initially drive this upwelling, but eventually, eddy flows influence it. Our study explores the interplay between ocean currents, eddies, and chlorophyll-a concentrations using the backward Finite-Size Lyapunov Exponents (bFSLEs) technique. We also delve into the specific role of Ekman transport in distributing chlorophyll-a across the region. The Great Whirl (GW), an anticyclonic eddy, predominantly causes strong downwelling, interrupting the summer monsoon upwelling along the Somali coast longitudinally. Despite the GW's significant impact on moving upwelled water offshore, the influence of downwelling diminishes northward. As a result, the northern Somali coast, especially around 9°N and 10°N, showcases the most extensive offshore upwelling, reaching as far as 55°E. Our findings highlight a robust connection between chlorophyll-a levels and oceanic dynamics, influenced by both currents and eddies, as evidenced by bFSLEs, and by cross-shore Ekman transport, particularly within chlorophyll-a concentrations ranging from 0.2 to 0.6 mg m<sup>−3</sup>. The data suggests that Ekman transport-induced upwelling primarily drives coastal phytoplankton biomass. Furthermore, bFSLEs analysis underlines the supportive role of ocean currents and eddies in the offshore distribution of chlorophyll-a, especially near the coast. Further examination of lagged correlations reveals a temporal lag between peak concentrations of chlorophyll-a and Ekman transport; the lag increases offshore and is at least 9 days near the coast.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141068666","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 : 2024-05-03DOI: 10.1016/j.dsr2.2024.105380
Yingjun Zhang , Chuanmin Hu , Dennis J. McGillicuddy Jr. , Yonggang Liu , Brian B. Barnes , Vassiliki H. Kourafalou
The Gulf of Mexico (GoM) is characterized by strong mesoscale eddy activities that have been studied extensively, yet the comprehensive three-dimensional (3-D) kinematic properties of GoM eddies are still not well documented. In this study, the 3-D mesoscale eddy activities in the upper layer (0–800 m) of the GoM are characterized using 14-year (1997–2010) global Hybrid Coordinate Ocean Model (HYCOM) outputs. Most eddies in the upper layer (both cyclonic and anticyclonic) have radii of ∼30–60 km and lifespans shorter than 30 days. The spatial distributions of GoM eddies do not vary much with depth, while their intensity decreases with depth. The size of cyclonic eddies does not vary much with depth, while the size of anticyclonic eddies decreases slightly with depth. Cyclonic eddies are often found to be generated in the eastern GoM (especially in the Loop Current region), the Bay of Campeche, and on the continental slope of the Campeche Bank, while anticyclonic eddies are often generated on the northeastern and northwestern GoM continental slopes, and in the central GoM (near 24°N) and the Bay of Campeche (92–94°W). In addition, long-lived GoM eddies (e.g., lifespan >150 days) tend to have intermediate eddy intensity (e.g., 0.13–0.32 for cyclonic eddies at the 10 m level). Both cyclonic and anticyclonic eddies are found to play an important role in the horizontal and vertical transport of heat and salt, and eddy-induced anomalies of water temperature and salinity at both surface and subsurface are generally more pronounced in the eastern GoM than in the western GoM.
{"title":"Mesoscale eddies in the Gulf of Mexico: A three-dimensional characterization based on global HYCOM","authors":"Yingjun Zhang , Chuanmin Hu , Dennis J. McGillicuddy Jr. , Yonggang Liu , Brian B. Barnes , Vassiliki H. Kourafalou","doi":"10.1016/j.dsr2.2024.105380","DOIUrl":"https://doi.org/10.1016/j.dsr2.2024.105380","url":null,"abstract":"<div><p>The Gulf of Mexico (GoM) is characterized by strong mesoscale eddy activities that have been studied extensively, yet the comprehensive three-dimensional (3-D) kinematic properties of GoM eddies are still not well documented. In this study, the 3-D mesoscale eddy activities in the upper layer (0–800 m) of the GoM are characterized using 14-year (1997–2010) global Hybrid Coordinate Ocean Model (HYCOM) outputs. Most eddies in the upper layer (both cyclonic and anticyclonic) have radii of ∼30–60 km and lifespans shorter than 30 days. The spatial distributions of GoM eddies do not vary much with depth, while their intensity decreases with depth. The size of cyclonic eddies does not vary much with depth, while the size of anticyclonic eddies decreases slightly with depth. Cyclonic eddies are often found to be generated in the eastern GoM (especially in the Loop Current region), the Bay of Campeche, and on the continental slope of the Campeche Bank, while anticyclonic eddies are often generated on the northeastern and northwestern GoM continental slopes, and in the central GoM (near 24°N) and the Bay of Campeche (92–94°W). In addition, long-lived GoM eddies (e.g., lifespan >150 days) tend to have intermediate eddy intensity (e.g., 0.13–0.32 for cyclonic eddies at the 10 m level). Both cyclonic and anticyclonic eddies are found to play an important role in the horizontal and vertical transport of heat and salt, and eddy-induced anomalies of water temperature and salinity at both surface and subsurface are generally more pronounced in the eastern GoM than in the western GoM.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141066707","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 : 2024-04-16DOI: 10.1016/j.dsr2.2024.105377
Irina A. Vishnevskaya , Tatiana G. Okuneva , Daria V. Kiseleva , Natalia G. Soloshenko , Pavel E. Mikhailik
The Hawaiian–Emperor Seamount Chain is composed of seamounts capped with fossil coral reef deposits that originally formed close to sea level but are now covered by hundreds of meters of water owing to prolonged subsidence. These fossil reef deposits are important archives of paleoenvironmental change and retain possible traces of Aeolian input from continental Asian dust. We studied the trace and rare earth element composition of Oligocene-Miocene coral reef limestone of Koko guyot aged 25–6 Ma to assess the influence and possible increase of continental allothigenic material input that could persist in marine carbonates. The composition of trace and rare earth elements of modern coral and ancient limestones demonstrated that they had inherited the composition of sea water. Positive europium anomaly observed in modern coral and calcified echinoid spines aged 0–50 thousand years was absent in ancient limestones. This effect could be associated with a change in the oxidation state during diagenesis and recrystallization, which probably led to the loss of europium. The distribution of trace and rare earth elements was constant in carbonate rocks of different ages despite the increase of aeolian input, which confirmed the earlier conclusions about the restriction of incorporation of certain elements into the crystal lattice of carbonate minerals, and demonstrated the regulating role of seawater. In addition, trace and rare earth elements, even if they were adsorbed on the thin films of biological objects during their life, obviously didn't persist there after burial.
{"title":"The influence of aeolian input on the trace and rare earth element composition of Oligocene-Miocene corals of KOKO Guyot (Emperor seamount chain, Pacific Ocean)","authors":"Irina A. Vishnevskaya , Tatiana G. Okuneva , Daria V. Kiseleva , Natalia G. Soloshenko , Pavel E. Mikhailik","doi":"10.1016/j.dsr2.2024.105377","DOIUrl":"https://doi.org/10.1016/j.dsr2.2024.105377","url":null,"abstract":"<div><p>The Hawaiian–Emperor Seamount Chain is composed of seamounts capped with fossil coral reef deposits that originally formed close to sea level but are now covered by hundreds of meters of water owing to prolonged subsidence. These fossil reef deposits are important archives of paleoenvironmental change and retain possible traces of Aeolian input from continental Asian dust. We studied the trace and rare earth element composition of Oligocene-Miocene coral reef limestone of Koko guyot aged 25–6 Ma to assess the influence and possible increase of continental allothigenic material input that could persist in marine carbonates. The composition of trace and rare earth elements of modern coral and ancient limestones demonstrated that they had inherited the composition of sea water. Positive europium anomaly observed in modern coral and calcified echinoid spines aged 0–50 thousand years was absent in ancient limestones. This effect could be associated with a change in the oxidation state during diagenesis and recrystallization, which probably led to the loss of europium. The distribution of trace and rare earth elements was constant in carbonate rocks of different ages despite the increase of aeolian input, which confirmed the earlier conclusions about the restriction of incorporation of certain elements into the crystal lattice of carbonate minerals, and demonstrated the regulating role of seawater. In addition, trace and rare earth elements, even if they were adsorbed on the thin films of biological objects during their life, obviously didn't persist there after burial.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140621856","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 : 2024-03-02DOI: 10.1016/j.dsr2.2024.105369
Mario La Mesa , Federico Calì , Antonio Di Franco , Emilio Riginella , Fortunata Donato , Stefania Russo , Chiara Papetti , Pasquale Castagno , Francesco Memmola , Enrico Zambianchi
Early life stages of fish represent a key component in the food chain of the pelagic ecosystem of the Southern Ocean, connecting producer trophic levels to those of higher predators. Pelagic larvae and early juveniles of notothenioid fishes overwhelmingly dominate the ichthyoplankton community living on the continental shelf. Scientific research surveys targeting early life stages of fish in the pelagic realm have been mainly carried out in the western Ross Sea, whereas the eastern side can be considered unexplored. As source of high primary production, the presence and timing of formation of wide ice-free areas throughout the year in the Ross Sea play a fundamental role in structuring larval fish community. The Ross Ice Shelf Polynya (RISP) is a large coastal polynya, which is driven and maintained by local prevailing winds and oceanic currents. In the present study, we report the first data on species composition, relative abundance and spatial distribution of larval fish community found off the Bay of Whales in the eastern Ross Sea. As reported for other areas of the Ross Sea, the Antarctic silverfish Pleuragramma antarcticum was by far the most abundant species, followed by other nototheniids and channichthyids in smaller amounts. The huge abundance of P. antarcticum early larvae supports the hypothesis of a potential nursery area near the Bay of Whales. Present results strongly advocate for future investigations in these poorly known and remote areas.
{"title":"Larval fish community in the Bay of Whales (eastern Ross sea): Species composition, relative abundance and spatial distribution","authors":"Mario La Mesa , Federico Calì , Antonio Di Franco , Emilio Riginella , Fortunata Donato , Stefania Russo , Chiara Papetti , Pasquale Castagno , Francesco Memmola , Enrico Zambianchi","doi":"10.1016/j.dsr2.2024.105369","DOIUrl":"https://doi.org/10.1016/j.dsr2.2024.105369","url":null,"abstract":"<div><p>Early life stages of fish represent a key component in the food chain of the pelagic ecosystem of the Southern Ocean, connecting producer trophic levels to those of higher predators. Pelagic larvae and early juveniles of notothenioid fishes overwhelmingly dominate the ichthyoplankton community living on the continental shelf. Scientific research surveys targeting early life stages of fish in the pelagic realm have been mainly carried out in the western Ross Sea, whereas the eastern side can be considered unexplored. As source of high primary production, the presence and timing of formation of wide ice-free areas throughout the year in the Ross Sea play a fundamental role in structuring larval fish community. The Ross Ice Shelf Polynya (RISP) is a large coastal polynya, which is driven and maintained by local prevailing winds and oceanic currents. In the present study, we report the first data on species composition, relative abundance and spatial distribution of larval fish community found off the Bay of Whales in the eastern Ross Sea. As reported for other areas of the Ross Sea, the Antarctic silverfish <em>Pleuragramma antarcticum</em> was by far the most abundant species, followed by other nototheniids and channichthyids in smaller amounts. The huge abundance of <em>P. antarcticum</em> early larvae supports the hypothesis of a potential nursery area near the Bay of Whales. Present results strongly advocate for future investigations in these poorly known and remote areas.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0967064524000134/pdfft?md5=2a28f5d47d120b748c8357f27b5ae80d&pid=1-s2.0-S0967064524000134-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140052132","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}
Pub Date : 2024-02-10DOI: 10.1016/j.dsr2.2024.105368
Rachel R.-P. Rayne , Sarah L.C. Giering , Manuela Hartmann , Joost Brandsma , Richard D. Sanders , Claire Evans
As the major term in downward organic carbon flux attenuation, determining prokaryotic metabolism over depth in the mesopelagic ocean is crucial for constraining the efficiency of the gravitational biological carbon pump (BCP). We hypothesize that the enhancement of particulate organic carbon (POC) concentrations in the mesopelagic twilight zone during export events leads to a temporally dynamic prokaryotic metabolic response, which likely has consequences for the efficiency of the BCP. We tested this hypothesis by making repeated measurements of leucine assimilation and leucine respiration at in situ concentrations over six depths throughout the upper 500 m of the water column during the collapse of a large-scale Southern Ocean spring diatom bloom. Rates of prokaryotic leucine assimilation were used to indicate levels of prokaryotic heterotrophic production, and leucine assimilation efficiency (LAE; the proportion of leucine used for growth versus respiration) was taken as an indicator of prokaryotic growth efficiency. Thus, relative shifts in LAE are indicative of shifts in rates of prokaryotic production relative to respiration. The flux of POC through the oceans’ interior led to a dynamic prokaryotic response, characterized by a temporary elevation in mesopelagic prokaryote leucine assimilation rates, LAE and prokaryotic abundance. By the final measurement these changes had already begun to revert, despite POC concentrations still being enriched. As hypothesized, our data revealed distinctions in the phases of the mesopelagic system, likely due to an evolution in bulk prokaryotic metabolic status and the amount and composition of organic matter available. This indicates that estimating ocean carbon sequestration during export events necessitates a time course of measurements throughout the period of POC downward flux. Our findings also revealed distinctions in the ecophysiological prokaryotic responses to substrate regimes between the surface mixed layer and the mesopelagic. Specifically, in the latter in situ leucine concentrations appeared more significant in controlling prokaryote metabolism than POC concentration, and were more closely related to per cell leucine assimilation, than respiration. Whereas, in the mixed layer, the concentration of in situ leucine did not seem to drive rates of its assimilation, rather POC concentration was a strong negative driver of cell specific leucine respiration. These findings are suggestive of stronger levels of energy limitation in the deeper ocean. We surmised that ocean regions with sporadic substrate supply to the mesopelagic are likely to experience stronger energy limitation which favors prokaryotic respiration over production.
{"title":"Temporal shifts in prokaryotic metabolism in response to organic carbon dynamics in the mesopelagic ocean during an export event in the Southern ocean","authors":"Rachel R.-P. Rayne , Sarah L.C. Giering , Manuela Hartmann , Joost Brandsma , Richard D. Sanders , Claire Evans","doi":"10.1016/j.dsr2.2024.105368","DOIUrl":"https://doi.org/10.1016/j.dsr2.2024.105368","url":null,"abstract":"<div><p>As the major term in downward organic carbon flux attenuation, determining prokaryotic metabolism over depth in the mesopelagic ocean is crucial for constraining the efficiency of the gravitational biological carbon pump (BCP). We hypothesize that the enhancement of particulate organic carbon (POC) concentrations in the mesopelagic twilight zone during export events leads to a temporally dynamic prokaryotic metabolic response, which likely has consequences for the efficiency of the BCP. We tested this hypothesis by making repeated measurements of leucine assimilation and leucine respiration at in situ concentrations over six depths throughout the upper 500 m of the water column during the collapse of a large-scale Southern Ocean spring diatom bloom. Rates of prokaryotic leucine assimilation were used to indicate levels of prokaryotic heterotrophic production, and leucine assimilation efficiency (LAE; the proportion of leucine used for growth versus respiration) was taken as an indicator of prokaryotic growth efficiency. Thus, relative shifts in LAE are indicative of shifts in rates of prokaryotic production relative to respiration. The flux of POC through the oceans’ interior led to a dynamic prokaryotic response, characterized by a temporary elevation in mesopelagic prokaryote leucine assimilation rates, LAE and prokaryotic abundance. By the final measurement these changes had already begun to revert, despite POC concentrations still being enriched. As hypothesized, our data revealed distinctions in the phases of the mesopelagic system, likely due to an evolution in bulk prokaryotic metabolic status and the amount and composition of organic matter available. This indicates that estimating ocean carbon sequestration during export events necessitates a time course of measurements throughout the period of POC downward flux. Our findings also revealed distinctions in the ecophysiological prokaryotic responses to substrate regimes between the surface mixed layer and the mesopelagic. Specifically, in the latter in situ leucine concentrations appeared more significant in controlling prokaryote metabolism than POC concentration, and were more closely related to per cell leucine assimilation, than respiration. Whereas, in the mixed layer, the concentration of in situ leucine did not seem to drive rates of its assimilation, rather POC concentration was a strong negative driver of cell specific leucine respiration. These findings are suggestive of stronger levels of energy limitation in the deeper ocean. We surmised that ocean regions with sporadic substrate supply to the mesopelagic are likely to experience stronger energy limitation which favors prokaryotic respiration over production.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0967064524000122/pdfft?md5=6349d79dd5fcf14c715450d180363c1a&pid=1-s2.0-S0967064524000122-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139749635","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}
Pub Date : 2024-01-19DOI: 10.1016/j.dsr2.2024.105367
Shujie Wan , Xinjun Chen
Micronekton communities show large-scale spatiotemporal patterns in pelagic acoustic scattering layers. They are one of the most conspicuous and ecologically-important components of the vast mesopelagic zone of the world's oceans. They play an important role in fishery resources and marine ecology research. In this study, acoustic data from the southwestern Indian Ocean were used to perform a hotspot analysis exploring the differences in micronekton distribution at 16 different spatial scales. Moreover, a generalized additive model (GAM) was used to analyze the effects of environmental variables. The distribution of micronekton was found to be highly correlated with latitude at different spatial scales, with high-density areas (hotspots) distributed between 32°S and 42°S and low-density areas (coldspots) distributed between 43°S and 54°S. With increasing spatial scale, the centers of both high- and low-density micronekton areas tended to move southward. GAM analysis at 20′ × 20′ spatial scale revealed that the micronekton distribution was influenced by the interaction of multiple environmental variables, with photosynthetically active radiation and dissolved oxygen being the two key variables with the highest influence on hotspot and coldspot distributions. The present study provides indepth knowledge on which environmental variables influences the distribution of micronekton under hotspots and coldspots periods in the southwestern Indian Ocean.
{"title":"The spatial distribution and environmental effects on hotspots and coldspots of micronekton in the southwestern Indian Ocean","authors":"Shujie Wan , Xinjun Chen","doi":"10.1016/j.dsr2.2024.105367","DOIUrl":"10.1016/j.dsr2.2024.105367","url":null,"abstract":"<div><p><span><span>Micronekton<span><span> communities show large-scale spatiotemporal patterns in pelagic acoustic scattering layers. They are one of the most conspicuous and ecologically-important components of the vast </span>mesopelagic zone of the world's oceans. They play an important role in </span></span>fishery resources and </span>marine ecology<span> research. In this study, acoustic data from the southwestern Indian Ocean were used to perform a hotspot analysis exploring the differences in micronekton distribution at 16 different spatial scales. Moreover, a generalized additive model (GAM) was used to analyze the effects of environmental variables. The distribution of micronekton was found to be highly correlated with latitude at different spatial scales, with high-density areas (hotspots) distributed between 32°S and 42°S and low-density areas (coldspots) distributed between 43°S and 54°S. With increasing spatial scale, the centers of both high- and low-density micronekton areas tended to move southward. GAM analysis at 20′ × 20′ spatial scale revealed that the micronekton distribution was influenced by the interaction of multiple environmental variables, with photosynthetically active radiation and dissolved oxygen being the two key variables with the highest influence on hotspot and coldspot distributions. The present study provides indepth knowledge on which environmental variables influences the distribution of micronekton under hotspots and coldspots periods in the southwestern Indian Ocean.</span></p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139509413","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 : 2024-01-04DOI: 10.1016/j.dsr2.2024.105357
Hong G, Zuo F, Qin K
{"title":"Changing marine biosphere in the West Pacific Ocean","authors":"Hong G, Zuo F, Qin K","doi":"10.1016/j.dsr2.2024.105357","DOIUrl":"10.1016/j.dsr2.2024.105357","url":null,"abstract":"","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139104063","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 : 2024-01-01DOI: 10.1016/j.dsr2.2023.105356
Myounghee Kang , Sunyoung Oh , Wooseok Oh , Dong-Jin Kang , SungHyun Nam , Kyounghoon Lee
In this study, we describe the dynamics of the sound scattering layers (SSLs), particularly those of fish and macroplankton communities in the epipelagic layer, in the Seychelles-Chagos Thermocline Ridge (SCTR) of the southwest Indian Ocean using hydroacoustic data, net sampling, and oceanographic information. Overall, the acoustic backscattering values of the fish community were considerably higher than those of the macroplankton. Both communities were more densely distributed in the SCTR than in its surrounding region. On the vertical profile, the acoustic peak of the fish community was at 17 m during the day; however, considerably high values of up to 82 m were observed at night. Below 26 m, macroplankton was seldom found, regardless of the time. Hydrographic properties, such as temperature, salinity, dissolved oxygen (DO), and chlorophyll fluorescence, in the SCTR, were similar; however, an area at 5–8°S, 67°E was cooler, saltier, and had slightly lower DO. Weak or moderate positive correlations were observed between acoustic and hydrographic features. Based on all net samples, the most abundant taxon in terms of the total number of samples was found to be krill (Euphausiacea, 81%), followed by lantern fish (Myctophum punctatum, 12%). Understanding the dynamics of SSLs, particularly epipelagic organisms, will help to better clarify the important ecological roles of these organisms and their ability to facilitate vertical incorporation into marine food webs.
{"title":"Acoustic characterization of fish and macroplankton communities in the seychelles-chagos thermocline ridge of the southwest Indian ocean","authors":"Myounghee Kang , Sunyoung Oh , Wooseok Oh , Dong-Jin Kang , SungHyun Nam , Kyounghoon Lee","doi":"10.1016/j.dsr2.2023.105356","DOIUrl":"10.1016/j.dsr2.2023.105356","url":null,"abstract":"<div><p>In this study, we describe the dynamics of the sound scattering layers (SSLs), particularly those of fish and macroplankton communities in the epipelagic layer, in the Seychelles-Chagos Thermocline Ridge (SCTR) of the southwest Indian Ocean using hydroacoustic data, net sampling, and oceanographic information. Overall, the acoustic backscattering values of the fish community were considerably higher than those of the macroplankton. Both communities were more densely distributed in the SCTR than in its surrounding region. On the vertical profile, the acoustic peak of the fish community was at 17 m during the day; however, considerably high values of up to 82 m were observed at night. Below 26 m, macroplankton was seldom found, regardless of the time. Hydrographic properties, such as temperature, salinity, dissolved oxygen (DO), and chlorophyll fluorescence, in the SCTR, were similar; however, an area at 5–8°S, 67°E was cooler, saltier, and had slightly lower DO. Weak or moderate positive correlations were observed between acoustic and hydrographic features. Based on all net samples, the most abundant taxon in terms of the total number of samples was found to be krill (<em>Euphausiacea</em>, 81%), followed by lantern fish (<em>Myctophum punctatum</em>, 12%). Understanding the dynamics of SSLs, particularly epipelagic organisms, will help to better clarify the important ecological roles of these organisms and their ability to facilitate vertical incorporation into marine food webs.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0967064523001066/pdfft?md5=d961a1d4648ad011bd5cba3a7384fe79&pid=1-s2.0-S0967064523001066-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139077639","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}
Pub Date : 2024-01-01DOI: 10.1016/j.dsr2.2023.105355
Yi Xu , Ying Wu , Jing Zhang
A warming climate is expected to intensify the stratification of the upper ocean in tropical and subtropical regions, which in turn results in decreases in the primary productivity for these oligotrophic areas. To assess if there is trended change in primary productivity in the southern Indian Ocean (IO) with known striking temperature increase, we use 17-years of satellite chlorophyll (Chl) data and model output to examine the trended changes in Chl. The results exhibited a surprisingly increase in Chl concentrations in part of the southern IO over the gyre area. To investigate the potential mechanisms underlying this Chl increase, we used temperature/salinity observations to re-evaluate stratification in the southern IO. The southern IO experienced basin-wide surface warming over the time series however there was a region of subsurface cooling at 50–100 m around 10°S. In the subtropical IO gyre, subsurface warming occurs at faster rates compare to the surface. Through the calculation of buoyancy frequency (), we have confirmed the presence of subsurface instabilities caused by these inhomogeneous trends in the vertical thermohaline structure. This was particularly true over the southern IO gyre, which experienced sustained increase of surface mixing disturbances over the last decade—resulting in a more favorable environment for vertical transport of nutrients into the euphotic zone. A mixed layer nutrient budget analysis suggested that entrainment due to mixed layer deepening is crucial in delivering nutrients into the gyre's upper mixed layer, which fueled phytoplankton activity. This emphasizes the importance of considering subsurface instabilities when interpreting the factors that influence surface Chl variabilities. This study highlights the importance of a three-dimensional framework for examining stratification to assess future marine ecosystem responses to a changing climate.
{"title":"The role of subsurface instabilities for increasing chlorophyll concentrations in a warming southern Indian ocean","authors":"Yi Xu , Ying Wu , Jing Zhang","doi":"10.1016/j.dsr2.2023.105355","DOIUrl":"10.1016/j.dsr2.2023.105355","url":null,"abstract":"<div><p>A warming climate is expected to intensify the stratification of the upper ocean in tropical and subtropical regions, which in turn results in decreases in the primary productivity for these oligotrophic areas. To assess if there is trended change in primary productivity in the southern Indian Ocean (IO) with known striking temperature increase, we use 17-years of satellite chlorophyll (Chl) data and model output to examine the trended changes in Chl. The results exhibited a surprisingly increase in Chl concentrations in part of the southern IO over the gyre area. To investigate the potential mechanisms underlying this Chl increase, we used temperature/salinity observations to re-evaluate stratification in the southern IO. The southern IO experienced basin-wide surface warming over the time series however there was a region of subsurface cooling at 50–100 m around 10°S. In the subtropical IO gyre, subsurface warming occurs at faster rates compare to the surface. Through the calculation of buoyancy frequency (<span><math><mrow><msup><mi>N</mi><mn>2</mn></msup></mrow></math></span>), we have confirmed the presence of subsurface instabilities caused by these inhomogeneous trends in the vertical thermohaline structure. This was particularly true over the southern IO gyre, which experienced sustained increase of surface mixing disturbances over the last decade—resulting in a more favorable environment for vertical transport of nutrients into the euphotic zone. A mixed layer nutrient budget analysis suggested that entrainment due to mixed layer deepening is crucial in delivering nutrients into the gyre's upper mixed layer, which fueled phytoplankton activity. This emphasizes the importance of considering subsurface instabilities when interpreting the factors that influence surface Chl variabilities. This study highlights the importance of a three-dimensional framework for examining stratification to assess future marine ecosystem responses to a changing climate.</p></div>","PeriodicalId":11120,"journal":{"name":"Deep-sea Research Part Ii-topical Studies in Oceanography","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0967064523001054/pdfft?md5=5eab838ebc302fe0315c058764387acc&pid=1-s2.0-S0967064523001054-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139077738","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}