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Keywords = oligotrophic oceans

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19 pages, 4055 KiB  
Article
Open-Ocean Carbonate System and Air–Sea CO2 Fluxes Across a NE Atlantic Seamount Complex (Madeira–Tore, August 2024)
by Marta Nogueira and Alexandra D. Silva
Oceans 2025, 6(3), 46; https://doi.org/10.3390/oceans6030046 - 17 Jul 2025
Viewed by 478
Abstract
This study focused on the carbonate system dynamics and air–sea CO2 fluxes in the open-ocean waters of the Madeira–Tore Seamount Complex during August 2024. Surface water properties revealed pronounced latitudinal gradients in sea surface temperature (21.9–23.1 °C), salinity (36.2–36.7), and dissolved oxygen [...] Read more.
This study focused on the carbonate system dynamics and air–sea CO2 fluxes in the open-ocean waters of the Madeira–Tore Seamount Complex during August 2024. Surface water properties revealed pronounced latitudinal gradients in sea surface temperature (21.9–23.1 °C), salinity (36.2–36.7), and dissolved oxygen (228–251 µmol Kg−1), influenced by mesoscale eddies and topographically driven upwelling. Despite oligotrophic conditions, distinct phytoplankton assemblages were observed, with coccolithophores dominating southern seamounts and open-ocean stations, and green algae and diatoms indicating episodic nutrient input. Surface total alkalinity (TA: 2236–2467 µmol Kg−1), dissolved inorganic carbon (DIC: 2006–2183 µmol Kg−1), and pCO2 (467–515 µatm) showed spatial variability aligned with water mass characteristics and biological activity. All stations exhibited positive air–sea CO2 fluxes (2.8–11.5 mmol m−2 d−1), indicating the region is a CO2 source during summer. Calcite and aragonite saturation states were highest in stratified, warmer waters. Principal Component Analysis highlighted the role of physical mixing, carbonate chemistry, and biological uptake in structuring regional variability. Our findings emphasize and contribute to the complex interplay of physical and biogeochemical drivers in modulating carbon cycling and ecosystem structure across Atlantic seamounts. Full article
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19 pages, 3796 KiB  
Article
Comparative Genomics Reveals Evidence of the Genome Reduction and Metabolic Potentials of Aliineobacillus hadale Isolated from Challenger Deep Sediment of the Mariana Trench
by Shaofeng Yang, Jie Liu, Yang Liu, Weichao Wu, Jiahua Wang and Yuli Wei
Microorganisms 2025, 13(1), 132; https://doi.org/10.3390/microorganisms13010132 - 10 Jan 2025
Viewed by 1179
Abstract
Hadal zones account for the deepest 45% of oceanic depth range and play an important role in ocean biogeochemical cycles. As the least-explored aquatic habitat on earth, further investigation is still required to fully elucidate the microbial taxonomy, ecological significance, metabolic diversity, and [...] Read more.
Hadal zones account for the deepest 45% of oceanic depth range and play an important role in ocean biogeochemical cycles. As the least-explored aquatic habitat on earth, further investigation is still required to fully elucidate the microbial taxonomy, ecological significance, metabolic diversity, and adaptation in hadal environments. In this study, a novel strain Lsc_1132T was isolated from sediment of the Mariana Trench at 10,954 m in depth. Strain Lsc_1132T contains heterogenous 16S rRNA genes, exhibiting the highest sequence similarities to the type strains of Neobacillus drentensis LMG 21831T, Neobacillus dielmonensis, Neobacillus drentensis NBRC 102427T, Neobacillus rhizosphaerae, and Neobacillus soli NBRC 102451T, with a range of 98.60–99.10% identity. The highest average nucleotide identity (ANI), the highest digital DNA-DNA hybridization (DDH) values, and the average amino acid identity (AAI) with Neobacillus sp. PS3-40 reached 73.5%, 21.4%, and 75.54%, respectively. The major cellular fatty acids of strain Lsc_1132T included iso-C15:0, Summed Feature 3 (C16:1ω6c and/or C16:1ω7c), iso-C17:0, anteiso-C15:0, and iso-C17:1ω5c. The respiratory quinone of strains Lsc_1132T was MK-7. The G + C content of the genomic DNA was 40.9%. Based on the GTDB taxonomy and phenotypic data, strain Lsc_1132T could represent a novel species of a novel genus, proposed as Aliineobacillus hadale gen. nov. sp. nov. (type strain Lsc_1132T = MCCC 1K09620T). Metabolically, strain Lsc_1132T demonstrates a robust carbohydrate metabolism with many strain-specific sugar transporters. It also has a remarkable capacity for metabolizing amino acids and carboxylic acids. Genomic analysis reveals a streamlined genome in the organism, characterized by a significant loss of orthologous genes, including those involved in cytochrome c synthesis, aromatic compound degradation, and polyhydroxybutyrate (PHB) synthesis, which suggests its adaptation to low oxygen levels and oligotrophic conditions through alternative metabolic pathways. In addition, the reduced number of paralogous genes in strain Lsc_1132T, together with its high protein-coding gene density, may further contribute to streamlining its genome and enhancing its genomic efficiency. This research expands our knowledge of hadal microorganisms and their metabolic strategies for surviving in extreme deep-sea environments. Full article
(This article belongs to the Section Molecular Microbiology and Immunology)
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20 pages, 3134 KiB  
Article
Evaluating MULTIOBS Chlorophyll-a with Ground-Truth Observations in the Eastern Mediterranean Sea
by Eleni Livanou, Raphaëlle Sauzède, Stella Psarra, Manolis Mandalakis, Giorgio Dall’Olmo, Robert J. W. Brewin and Dionysios E. Raitsos
Remote Sens. 2024, 16(24), 4705; https://doi.org/10.3390/rs16244705 - 17 Dec 2024
Cited by 1 | Viewed by 1589
Abstract
Satellite-derived observations of ocean colour provide continuous data on chlorophyll-a concentration (Chl-a) at global scales but are limited to the ocean’s surface. So far, biogeochemical models have been the only means of generating continuous vertically resolved Chl-a profiles on a regular grid. MULTIOBS [...] Read more.
Satellite-derived observations of ocean colour provide continuous data on chlorophyll-a concentration (Chl-a) at global scales but are limited to the ocean’s surface. So far, biogeochemical models have been the only means of generating continuous vertically resolved Chl-a profiles on a regular grid. MULTIOBS is a multi-observations oceanographic dataset that provides depth-resolved biological data based on merged satellite- and Argo-derived in situ hydrological data. This product is distributed by the European Union’s Copernicus Marine Service and offers global multiyear, gridded Chl-a profiles within the ocean’s productive zone at a weekly temporal resolution. MULTIOBS addresses the scarcity of observation-based vertically resolved Chl-a datasets, particularly in less sampled regions like the Eastern Mediterranean Sea (EMS). Here, we conduct an independent evaluation of the MULTIOBS dataset in the oligotrophic waters of the EMS using in situ Chl-a profiles. Our analysis shows that this product accurately and precisely retrieves Chl-a across depths, with a slight 1% overestimation and an observed 1.5-fold average deviation between in situ data and MULTIOBS estimates. The deep chlorophyll maximum (DCM) is adequately estimated by MULTIOBS both in terms of positioning (root mean square error, RMSE = 13 m) and in terms of Chl-a (RMSE = 0.09 mg m−3). The product accurately reproduces the seasonal variability of Chl-a and it performs reasonably well in reflecting its interannual variability across various depths within the productive layer (0–120 m) of the EMS. We conclude that MULTIOBS is a valuable dataset providing vertically resolved Chl-a data, enabling a holistic understanding of euphotic zone-integrated Chl-a with an unprecedented spatiotemporal resolution spanning 25 years, which is essential for elucidating long-term trends and variability in oceanic primary productivity. Full article
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19 pages, 6463 KiB  
Article
Biogeochemical Fe-Redox Cycling in Oligotrophic Deep-Sea Sediment
by Di Zhan, Qingyin Xia, Gaoyuan Li, Xinyu Li, Yang Li, Dafu Hu, Jinglong Hu, Ziqi Zhou and Yizhi Sheng
Water 2024, 16(19), 2740; https://doi.org/10.3390/w16192740 - 26 Sep 2024
Cited by 1 | Viewed by 1497
Abstract
Biogeochemical redox cycling of iron (Fe) essentially governs various geochemical processes in nature. However, the mechanistic underpinnings of Fe-redox cycling in deep-sea sediments remain poorly understood, due to the limited access to the deep-sea environment. Here, abyssal sediment collected from a depth of [...] Read more.
Biogeochemical redox cycling of iron (Fe) essentially governs various geochemical processes in nature. However, the mechanistic underpinnings of Fe-redox cycling in deep-sea sediments remain poorly understood, due to the limited access to the deep-sea environment. Here, abyssal sediment collected from a depth of 5800 m in the Pacific Ocean was characterized for its elemental, mineralogical, and biological properties. The sedimentary environment was determined to be oligotrophic with limited nutrition, yet contained a considerable amount of trace elements. Fe-redox reactions in sediment progressed through an initial lag phase, followed by a fast Fe(II) reduction and an extended period of Fe(III) oxidation before achieving equilibrium after 58 days. The presence of an external H2 electron donor significantly increased the extent of Fe(III) bio-reduction by 7.73% relative to an amendment-free control under high pressure of 58 MPa. A similar enhancement of 11.20% was observed following lactate amendment under atmospheric pressure. Fe(II) bio-oxidation occurred after 16 days’ anaerobic culturing, coupled with nitrate reduction. During Fe bio-redox reactions, microbial community composition was significantly shaped by the presence/absence of an electron donor, while the hydrostatic pressure levels were the controlling factor. Shewanella spp. emerged as the primary Fe(III)-reducing microorganisms, and were stimulated by supplemented lactate. Marinobacter hydrocarbonoclasticus was the predominant Fe(II)-oxidizing microorganism across all conditions. Our findings illustrate continuous Fe-redox reactions occurring in the deep-sea environment, with coexisting Fe-redox microorganisms determining the oscillation of Fe valence states within the abyssal sediment. Full article
(This article belongs to the Special Issue Soil and Groundwater Quality and Resources Assessment)
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15 pages, 6666 KiB  
Article
Estimation of Phytoplankton Primary Productivity in Qinghai Lake Using Ocean Color Satellite Data: Seasonal and Interannual Variations
by Xuan Ban, Yingchao Dang, Peng Shu, Hongfang Qi, Ying Luo, Fei Xiao, Qi Feng and Yadong Zhou
Water 2024, 16(10), 1433; https://doi.org/10.3390/w16101433 - 17 May 2024
Cited by 2 | Viewed by 1478
Abstract
Estimation of primary production in Qinghai Lake is crucial for the aquatic ecosystem management in the northeastern Qinghai–Tibet Plateau. This study used the Vertically Generalized Production Model (VGPM) with ocean color satellite data to estimate phytoplankton primary productivity (PP) in Qinghai Lake during [...] Read more.
Estimation of primary production in Qinghai Lake is crucial for the aquatic ecosystem management in the northeastern Qinghai–Tibet Plateau. This study used the Vertically Generalized Production Model (VGPM) with ocean color satellite data to estimate phytoplankton primary productivity (PP) in Qinghai Lake during the non-freezing period from 2002 to 2023. Field data from 2018 and 2023 were used to calibrate and verify the model. The results showed a seasonal trend in chlorophyll-a and PP, with the lowest values in May and peaks from June to September. Qinghai Lake was identified as oligotrophic, with annual mean chlorophyl-a of 0.24–0.40 µg/L and PP of 40–369 mg C/m2/day. The spatial distribution of PP was low in the center of the lake and high near the shores and estuaries. An interesting periodic increasing trend in PP every 2 to 4 years was observed from 2002 to 2023. This study established a remote sensing method for PP assessment in Qinghai Lake, revealing seasonal and interannual variations and providing a useful example for monitoring large saline mountain lakes. Full article
(This article belongs to the Special Issue Impact of Environmental Factors on Aquatic Ecosystem)
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14 pages, 2799 KiB  
Article
Evaluation of Ocean Color Algorithms to Retrieve Chlorophyll-a Concentration in the Mexican Pacific Ocean off the Baja California Peninsula, Mexico
by Patricia Alvarado-Graef, Beatriz Martín-Atienza, Ramón Sosa-Ávalos, Reginaldo Durazo and Rafael Hernández-Walls
Remote Sens. 2024, 16(10), 1748; https://doi.org/10.3390/rs16101748 - 15 May 2024
Viewed by 1838
Abstract
Mathematical algorithms relate satellite data of ocean color with the surface Chlorophyll-a concentration (Chl-a), a proxy of phytoplankton biomass. These mathematical tools work best when they are adapted to the unique bio-optical properties of a particular oceanic province. Ocean color [...] Read more.
Mathematical algorithms relate satellite data of ocean color with the surface Chlorophyll-a concentration (Chl-a), a proxy of phytoplankton biomass. These mathematical tools work best when they are adapted to the unique bio-optical properties of a particular oceanic province. Ocean color algorithms should also consider that there are significant differences between datasets derived from different sensors. Common solutions are to provide different parameters for each sensor or use merged satellite data. In this paper, we use satellite data from the Copernicus merged product suite and in situ data from the southernmost part of the California Current System to test two widely used global algorithms, OCx and CI, and a regional algorithm, CalCOFI2. The OCx algorithm yielded the most favorable results. Consequently, we regionalized it and conducted further testing, leading to significant improvements, especially in eutrophic and oligotrophic waters. The database was then separated according to (a) dynamic boundaries in the area, (b) bio-optical properties, and (c) climatic conditions (El Niño/La Niña). Regional algorithms were obtained and tested for each partition. The Chl-a retrievals for each model were tested and compared. The best fit for the data was for the regional algorithms that considered the climatic conditions (El Niño/La Niña). These results will allow for the construction of consistent regionally adapted time series and, therefore, will demonstrate the importance of El Niño/La Niña events on the bio-optical properties of the area. Full article
(This article belongs to the Section Ocean Remote Sensing)
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19 pages, 1189 KiB  
Review
Mercury Biogeochemistry and Biomagnification in the Mediterranean Sea: Current Knowledge and Future Prospects in the Context of Climate Change
by Roberto Bargagli and Emilia Rota
Coasts 2024, 4(1), 89-107; https://doi.org/10.3390/coasts4010006 - 4 Feb 2024
Cited by 7 | Viewed by 3069
Abstract
In the 1970s, the discovery of much higher mercury (Hg) concentrations in Mediterranean fish than in related species of the same size from the Atlantic Ocean raised serious concerns about the possible health effects of neurotoxic monomethylmercury (MMHg) on end consumers. After 50 [...] Read more.
In the 1970s, the discovery of much higher mercury (Hg) concentrations in Mediterranean fish than in related species of the same size from the Atlantic Ocean raised serious concerns about the possible health effects of neurotoxic monomethylmercury (MMHg) on end consumers. After 50 years, the cycling and fluxes of the different chemical forms of the metal between air, land, and marine environments are still not well defined. However, current knowledge indicates that the anomalous Hg accumulation in Mediterranean organisms is mainly due to the re-mineralization of organic material, which favors the activity of methylating microorganisms and increases MMHg concentrations in low-oxygen waters. The compound is efficiently bio-concentrated by very small phytoplankton cells, which develop in Mediterranean oligotrophic and phosphorous-limited waters and are then transferred to grazing zooplankton. The enhanced bioavailability of MMHg together with the slow growth of organisms and more complex and longer Mediterranean food webs could be responsible for its anomalous accumulation in tuna and other long-lived predatory species. The Mediterranean Sea is a “hotspot” of climate change and has a rich biodiversity, and the increasing temperature, salinity, acidification, and stratification of seawater will likely reduce primary production and change the composition of plankton communities. These changes will likely affect the accumulation of MMHg at lower trophic levels and the biomagnification of its concentrations along the food web; however, changes are difficult to predict. The increased evasion of gaseous elemental mercury (Hg°) from warming surface waters and lower primary productivity could decrease the Hg availability for biotic (and possibly abiotic) methylation processes, but lower oxygen concentrations in deep waters, more complex food webs, and the reduced growth of top predators could increase their MMHg content. Despite uncertainties, in Mediterranean regions historically affected by Hg inputs from anthropogenic and geogenic sources, such as those in the northwestern Mediterranean and the northern Adriatic Sea, rising seawater levels, river flooding, and storms will likely favor the mobilization of Hg and organic matter and will likely maintain high Hg bioaccumulation rates for a long time. Long-term studies will, therefore, be necessary to evaluate the impact of climate change on continental Hg inputs in the Mediterranean basin, on air–sea exchanges, on possible changes in the composition of biotic communities, and on MMHg formation and its biomagnification along food webs. In this context, to safeguard the health of heavy consumers of local seafood, it appears necessary to develop information campaigns, promote initiatives for the consumption of marine organisms at lower trophic levels, and organize large-scale surveys of Hg accumulation in the hair or urine of the most exposed population groups. Full article
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24 pages, 2063 KiB  
Article
Insights into the Relative Abundance, Life History, and Ecology of Oceanic Sharks in the Eastern Bahamas
by Brendan S. Talwar, Edward J. Brooks, Debra L. Abercrombie, Brenda Anderson, Mark E. Bond, Annabelle M. L. Brooks, Demian D. Chapman, Gina M. Clementi, Candace Y. A. Fields, Jim Gelsleichter, R. Dean Grubbs, Lucy A. Howey, Lance K. B. Jordan, Jeremy J. Kiszka, Ryan J. Knotek, Yannis P. Papastamatiou, Cheston T. Peterson, Eric V. C. Schneider, Oliver N. Shipley, Sean Williams, Maggie M. Winchester and Michael R. Heithausadd Show full author list remove Hide full author list
Sustainability 2024, 16(1), 200; https://doi.org/10.3390/su16010200 - 25 Dec 2023
Cited by 1 | Viewed by 2816
Abstract
Fisheries-independent data on the diversity, relative abundance, and demographic structure of poorly studied, threatened oceanic sharks are absent from much of the western North Atlantic Ocean, where multiple oceanic shark species have experienced significant population declines. Resource-limited management approaches require the identification of [...] Read more.
Fisheries-independent data on the diversity, relative abundance, and demographic structure of poorly studied, threatened oceanic sharks are absent from much of the western North Atlantic Ocean, where multiple oceanic shark species have experienced significant population declines. Resource-limited management approaches require the identification of critical habitats or aggregation sites worthy of protection and enforcement. Data were collected on oceanic sharks using pelagic longline surveys, targeted baiting, and opportunistic encounters in oligotrophic open-ocean habitats of north-eastern Exuma Sound (NES), The Bahamas. The oceanic epipelagic shark community was also characterized using targeted baiting off Columbus Point, Cat Island (CI), a seamount north of San Salvador (SSSM), and the northwestern tip of Mayaguana. Pelagic longline surveys suggested that the relative abundance of sharks at NES was low (shark catch-per-unit-effort: 0.0007 sharks hook−1 h−1; 2.3 sharks per 1000 hooks). Silky sharks Carcharhinus falciformis, particularly juveniles (134 ± 39 cm stretched total length; mean ± SD STL), were the most common. Targeted baiting suggested oceanic whitetip sharks C. longimanus were abundant at CI, where large adults (245 ± 23 cm STL), most of which were females (83.8%, n = 98 of 117) that were gravid (65.7%; n = 46 of 70 assessed for pregnancy), dominated the aggregation. Many (20.5–26.5%, n = 24–31 of 117 depending on assumptions regarding tag loss) were recaptured or resighted at CI for up to five years. Silky sharks dominated catches at SSSM. Oceanic sharks, particularly adults, were sometimes caught or observed alongside short-finned pilot whales Globicephala macrorhynchus or tunas. Although The Bahamas offers threatened oceanic sharks refuge from fishing across its entire jurisdiction, these data suggest that some fixed features, including sites such as CI and potentially SSSM, are important aggregation sites with high regional conservation value and should be prioritized by fisheries managers and enforcement officials. Full article
(This article belongs to the Special Issue Aquatic Biodiversity and Marine Ecosystem Sustainability)
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18 pages, 2741 KiB  
Article
Use of Sentinel-3 OLCI Images and Machine Learning to Assess the Ecological Quality of Italian Coastal Waters
by Chiara Lapucci, Andrea Antonini, Emanuele Böhm, Emanuele Organelli, Luca Massi, Alberto Ortolani, Carlo Brandini and Fabio Maselli
Sensors 2023, 23(22), 9258; https://doi.org/10.3390/s23229258 - 18 Nov 2023
Cited by 4 | Viewed by 5246
Abstract
Understanding and monitoring the ecological quality of coastal waters is crucial for preserving marine ecosystems. Eutrophication is one of the major problems affecting the ecological state of coastal marine waters. For this reason, the control of the trophic conditions of aquatic ecosystems is [...] Read more.
Understanding and monitoring the ecological quality of coastal waters is crucial for preserving marine ecosystems. Eutrophication is one of the major problems affecting the ecological state of coastal marine waters. For this reason, the control of the trophic conditions of aquatic ecosystems is needed for the evaluation of their ecological quality. This study leverages space-based Sentinel-3 Ocean and Land Color Instrument imagery (OLCI) to assess the ecological quality of Mediterranean coastal waters using the Trophic Index (TRIX) key indicator. In particular, we explore the feasibility of coupling remote sensing and machine learning techniques to estimate the TRIX levels in the Ligurian, Tyrrhenian, and Ionian coastal regions of Italy. Our research reveals distinct geographical patterns in TRIX values across the study area, with some regions exhibiting eutrophic conditions near estuaries and others showing oligotrophic characteristics. We employ the Random Forest Regression algorithm, optimizing calibration parameters to predict TRIX levels. Feature importance analysis highlights the significance of latitude, longitude, and specific spectral bands in TRIX prediction. A final statistical assessment validates our model’s performance, demonstrating a moderate level of error (MAE of 0.51) and explanatory power (R2 of 0.37). These results highlight the potential of Sentinel-3 OLCI imagery in assessing ecological quality, contributing to our understanding of coastal water ecology. They also underscore the importance of merging remote sensing and machine learning in environmental monitoring and management. Future research should refine methodologies and expand datasets to enhance TRIX monitoring capabilities from space. Full article
(This article belongs to the Special Issue Advanced Remote Sensing Technologies in Ocean Observations)
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22 pages, 11000 KiB  
Review
A Review of Ocean Color Algorithms to Detect Trichodesmium Oceanic Blooms and Quantify Chlorophyll Concentration in Shallow Coral Lagoons of South Pacific Archipelagos
by Cécile Dupouy, Andra Whiteside, Jing Tan, Guillaume Wattelez, Hiroshi Murakami, Rémi Andréoli, Jérôme Lefèvre, Rüdiger Röttgers, Awnesh Singh and Robert Frouin
Remote Sens. 2023, 15(21), 5194; https://doi.org/10.3390/rs15215194 - 31 Oct 2023
Cited by 4 | Viewed by 2676
Abstract
The oceanic waters of the Southwest Tropical Pacific occupy a vast region including multiple Pacific Island Countries. The state of these waters is determinant for fisheries and the blue economy. Ocean color remote sensing is the main tool to survey the variability and [...] Read more.
The oceanic waters of the Southwest Tropical Pacific occupy a vast region including multiple Pacific Island Countries. The state of these waters is determinant for fisheries and the blue economy. Ocean color remote sensing is the main tool to survey the variability and long-term evolution of these large areas that are important for economic development but are affected by climate change. Unlike vast oligotrophic gyres, tropical waters are characterized by numerous archipelagos and islands, with deep and shallow lagoons subjected to the large impacts of the land. Strikingly large dendritic phytoplankton (Trichodesmium) blooms with high levels of chlorophyll, developing within archipelagos, as well as coastal enrichments from various origins may be observed. Algorithms to detect the presence of Trichodesmium have been developed or adapted, as well as algorithms to estimate the chlorophyll concentration ([Chl-a)]. Adapting existing [Chl-a] algorithms does not always yield high, i.e., sufficient, accuracy. A review of published regional bio-optical algorithms developed taking into account the specific phytoplankton composition and minimizing the adverse impacts of particles and the seabed bottom on [Chl-a] determination is presented, as well the bio-optical database that allowed their development. The interest of such algorithms for a variety of applications and scientific accomplishments is highlighted, with a view to further addressing the main biology and biogeochemistry questions, e.g., to determine the true impact of diazotrophs and assess lagoon [Chl-a] variability with the highest confidence. This work anticipates the use of future coarse and high-spatial-resolution and multi- and hyper-spectral satellite imagery in the Pacific. Full article
(This article belongs to the Special Issue Oceans from Space V)
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22 pages, 9627 KiB  
Article
Regional Models for Sentinel-2/MSI Imagery of Chlorophyll a and TSS, Obtained for Oligotrophic Issyk-Kul Lake Using High-Resolution LIF LiDAR Data
by Vadim Pelevin, Ekaterina Koltsova, Aleksandr Molkov, Sergei Fedorov, Salmor Alymkulov, Boris Konovalov, Mairam Alymkulova and Kubanychbek Jumaliev
Remote Sens. 2023, 15(18), 4443; https://doi.org/10.3390/rs15184443 - 9 Sep 2023
Cited by 3 | Viewed by 1893
Abstract
The development of regional satellite bio-optical models for natural waters with high temporal and spatial variability, such as inland seas, reservoirs, and coastal ocean waters, requires the implementation of an intermediate measuring link in the chain, “water sampling—bio-optical models”, and this link must [...] Read more.
The development of regional satellite bio-optical models for natural waters with high temporal and spatial variability, such as inland seas, reservoirs, and coastal ocean waters, requires the implementation of an intermediate measuring link in the chain, “water sampling—bio-optical models”, and this link must have certain intermediate characteristics. The most crucial of them are the high-precision measurements of the main water quality parameters, such as the concentration of chlorophyll a (Chl a), colored dissolved organic matter (CDOM), and total suspended sediments (TSS) in the upper water layer, together with a high operational rate and the ability to cover a large water area in a short time, which corresponds to a satellite overpass. A possible solution is to utilize laser-induced fluorescence (LIF) of water constituents measured by a marine LiDAR in situ with a high sampling rate from a high-speed vessel. This allows obtaining a large ground-truth dataset of the main water quality parameters simultaneously with the satellite overpass within the time interval determined by NASA protocols. This method was successfully applied to the oligotrophic Issyk-Kul Lake in Kyrgyzstan, where we obtained more than 4000 and 1000 matchups for the Chl a and TSS, respectively. New preliminary regional bio-optical models were developed on the basis of a one-day survey and tested for archive Sentinel-2A data for 2022. This approach can be applied for regular monitoring and further correction in accordance with seasonal variability. The obtained results, together with previously published similar studies for eutrophic coastal and productive inland waters, emphasize the applicability of the presented method for the development or adjustment of regional bio-optical models for water bodies of a wide trophic range. Full article
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16 pages, 2162 KiB  
Article
Metal Accumulations in Two Extreme-Environment Amphipods, Hadal Eurythenes gryllus and Antarctic Pseudorchomene plebs
by Shaojun Huang, Lingyue Zhu, Shouwen Jiang, Wanying Zhai, Binbin Pan, Zhichao Wu and Qianghua Xu
J. Mar. Sci. Eng. 2023, 11(8), 1515; https://doi.org/10.3390/jmse11081515 - 29 Jul 2023
Cited by 1 | Viewed by 1731
Abstract
The hadal zone and Antarctic Ocean are two of the least-explored habitats. Knowledge about human impacts on these two extreme environments is limited. Here, we analyzed the metal accumulations of two amphipod species, Eurythenes gryllus, from the Mariana Trench (6040 m, 11.36° [...] Read more.
The hadal zone and Antarctic Ocean are two of the least-explored habitats. Knowledge about human impacts on these two extreme environments is limited. Here, we analyzed the metal accumulations of two amphipod species, Eurythenes gryllus, from the Mariana Trench (6040 m, 11.36° N, 142.41° E) in the West Pacific Ocean, and Pseudorchomene plebs, from the Ross Sea (600 m, 77.12° S, 167,67° E) in the Antarctic. Bioaccumulation of thirteen elements (Na, Mg, K, Ca, Cu, Fe, Al, Cr, Mn, Zn, As, Se, and Cd) in three tissues (exoskeleton, leg muscle, and gut) of the two amphipods was investigated using inductively coupled plasma mass spectrometry (ICP-MS). Comparing the trace element concentrations between the different amphipoda species, we found higher element concentrations in the Antarctic amphipod, and an oligotrophication of the Mariana Trench. The concentrations of Cu, Zn, As, and Se in the three tissues all had a significant difference in abundance, and the Cd in the gut of P. plebs was comparably higher than that in E. gryllus, consistent with special environment adaptation. Compared with non-abyssal and shallow water decapoda and amphipoda species, hadal amphipods possessed comparably higher concentrations of Cd and Cr elements and displayed a very high environmental specificity for amphipods’ metal-element bioaccumulation strategy. This study reveals the amphipods of remote and uncontaminated areas as potential indicator species for metal-element bioaccumulation to measure anthropogenic impacts. Full article
(This article belongs to the Section Marine Biology)
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20 pages, 5056 KiB  
Article
Dynamics of the Seawater Carbonate System in the East Siberian Sea: The Diversity of Driving Forces
by Irina Pipko, Svetlana Pugach, Igor Semiletov and Oleg Konstantinov
Water 2023, 15(14), 2670; https://doi.org/10.3390/w15142670 - 24 Jul 2023
Cited by 1 | Viewed by 2058
Abstract
The East Siberian Sea (ESS) is a large and the shallowest part of the Arctic Ocean. It is characterized by high biogeochemical activity, but the seawater carbonate system remains understudied, especially during the late autumn season. Data from the research vessel (RV) “Professor [...] Read more.
The East Siberian Sea (ESS) is a large and the shallowest part of the Arctic Ocean. It is characterized by high biogeochemical activity, but the seawater carbonate system remains understudied, especially during the late autumn season. Data from the research vessel (RV) “Professor Multanovsky” cruise were used to assess the dynamics of the seawater carbonate system, air–sea CO2 fluxes, and the calcium carbonate corrosive waters in the two biogeochemical provinces of the ESS shortly before freeze-up. The ESS waters were mainly a sink for atmospheric CO2 due to the limited dispersion of river waters, autumn water cooling, and phytoplankton blooms in its eastern autotrophic province. The mean value of the CO2 air–sea flux was 11.2 mmol m−2 day−1. The rate of CO2 uptake in the eastern ESS was an order of magnitude larger than that in the western ESS. The specific waters and ice cover dynamics determined intensive photosynthesis processes identified on the eastern shelf and in the northern deep oligotrophic waters. A part of the surface and most of the bottom ESS waters were corrosive with respect to calcium carbonate, with the lowest saturation state of aragonite (0.22) in the bottom layer of the eastern ESS. The eastern ESS was the main source of these waters into the deep basin. The observed export of corrosive shelf waters to the deep sea can have a potential impact on the ocean water ecosystem in the case of mixing with layers inhabited by calcifying organisms. Full article
(This article belongs to the Special Issue Carbon Dynamics in Coastal and Deep Ocean)
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21 pages, 4853 KiB  
Article
Marine Bacterial Communities in the Xisha Islands, South China Sea
by Yihui Wang, Lei Wang, Yongliang Liu, Shengqi Su and Wenjin Hao
Diversity 2023, 15(7), 865; https://doi.org/10.3390/d15070865 - 18 Jul 2023
Cited by 6 | Viewed by 2610
Abstract
Oligotrophic marine environments are ecological funnels in marine ecosystems and are essential for maintaining the health and balance of the entire marine ecosystem. Bacterial communities are one of the most important biological populations, which can survive in low-nutrient environments and perform a variety [...] Read more.
Oligotrophic marine environments are ecological funnels in marine ecosystems and are essential for maintaining the health and balance of the entire marine ecosystem. Bacterial communities are one of the most important biological populations, which can survive in low-nutrient environments and perform a variety of important ecological functions, such as decomposing and absorbing organic waste in the ocean and converting nitrogen from the atmosphere into a usable nitrogen source, thus maintaining the health of marine ecosystems. The bacterioplankton community composition and potential function were analyzed using 16S rRNA gene amplicon sequencing in oligotrophic coral reef sea areas. The diversity of the bacterial community exhibited significant differences between the four studied regions. Proteobacteria (38.58–62.79%) were the most abundant in all sampling sites, followed by Cyanobacteria (15.41–37.28%), Bacteroidota (2.39–6.67%), and Actinobacteriota (0.45–1.83%). Although bacterioplankton communities presented no difference between surface and bottom water regarding community richness and α-diversity, the bacterial community composition presented significant differences between surface and bottom water regarding β-diversity. Alteromonadales, Rhodospirllales, and Chloroplast were identified as the significantly different communities between the surface and bottom (Q value < 0.01). Bacterial community distribution in different regions was mainly affected by pH, dissolved oxygen, and nutrients. Nitrite ammonification, chitinolysis, predatory or exoparasitic, chloroplasts, chemoheterotrophy, aerobic chemoheterotrophy, phototrophic, compound degradation (mostly nutrients and pollutants), nitrogen cycle, fermentation, and intracellular parasitism were the dominant functions in the four regions. Full article
(This article belongs to the Section Marine Diversity)
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22 pages, 9390 KiB  
Article
Evaluating the Performance of Sentinel-3A OLCI Products in the Subarctic Northeast Pacific
by Perumthuruthil Suseelan Vishnu and Maycira Costa
Remote Sens. 2023, 15(13), 3244; https://doi.org/10.3390/rs15133244 - 23 Jun 2023
Cited by 3 | Viewed by 2109
Abstract
The subarctic northeast Pacific (SNEP) is a high-nitrate, low-chlorophyll (HNLC) region in the ocean, where phytoplankton growth and productivity are limited by iron. Moreover, there is a limited application of high spatial (300 m) and temporal resolution (daily) ocean color (OC) satellite imagery [...] Read more.
The subarctic northeast Pacific (SNEP) is a high-nitrate, low-chlorophyll (HNLC) region in the ocean, where phytoplankton growth and productivity are limited by iron. Moreover, there is a limited application of high spatial (300 m) and temporal resolution (daily) ocean color (OC) satellite imagery in studying the phytoplankton dynamics in this region. To address this issue, we aim to validate the remote sensing reflectance (Rrs; sr−1(λ)) and chlorophyll-a (Chla) concentration derived from the Polymer atmospheric correction algorithm against in situ data for the SNEP obtained during 2019 and 2020. Additionally, we performed qualitative analysis using weekly binned surface Chla maps to determine whether the product reflects the general pattern over a latitudinal and longitudinal domain. We processed the daily Level-1 image using Polymer and binned them weekly using Graphic Processing Tool (GPT). The validation results indicate that Polymer exhibits higher radiometric performance in the blue and green bands and fails to represent in situ Rrs in the red band. Furthermore, the Polymer slightly over- and underestimates reflectance between 0.0012 and 0.0018 sr−1 in the green band. On the other hand, excellent agreement was found between satellite-derived versus in situ Chla, followed by a slight overestimation of in situ Chla in the range from 0.17 to 0.28 mg/m3. The weekly binned Chla spatial map revealed a spatially homogeneous distribution of surface Chla in Central Alaska, but a substantial increase in Chla (≥0.7 mg/m3) was recorded toward Southeast Alaska (SEA) and the British Columbia (BC) shelf. Furthermore, Chla derived from latitudinal and longitudinal transects indicates high Chla toward 57°N and −135°W, respectively. Overall, the results of this study emphasize the need to obtain high-quality matchups from under-sampled oligotrophic waters, which are crucial for satellite validation, in addition to highlighting the importance of using high spatial and temporal resolution satellite imagery to study phytoplankton dynamics in the SNEP. Full article
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