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Salaün J, Menn ML. In Situ Calibration of Wetlabs Chlorophyll Sensors: A Methodology Adapted to Profile Measurements. SENSORS (BASEL, SWITZERLAND) 2023; 23:2825. [PMID: 36905028 PMCID: PMC10007448 DOI: 10.3390/s23052825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 02/08/2023] [Accepted: 02/16/2023] [Indexed: 06/18/2023]
Abstract
Measurement of chlorophyll a content in the ocean is essential for biomass assessment, finding the optical properties of seawater, and calibration of satellite remote sensing. The instruments used for this purpose are mostly fluorescence sensors. The calibration of these sensors becomes a crucial point to ensure the reliability and quality of the data produced. The technology of these sensors is based on the principle that a concentration of chlorophyll a in µg per liter can be calculated from an in situ fluorescence measurement. However, the study of the phenomenon of photosynthesis and cell physiology teaches us that the yield of fluorescence depends on many factors that are difficult or impossible to reconstitute in a metrology laboratory. This is the case, for example, of the algal species, its physiological state, the greater or lesser presence of dissolved organic matter in the water, the turbidity of the environment, or the surface illumination. What approach should be adopted in this context to achieve a better quality of the measurements? This is the objective of the work we present here, which is the result of nearly ten years of experimentation and testing to optimize the metrological quality of chlorophyll a profile measurement. The results we obtained allowed us to calibrate these instruments with an uncertainty of 0.2-0.3 on the correction factor, with correlation coefficients higher than 0.95 between the sensor values and the reference value.
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2
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O’Brien T, Boss E. Correction of Radiometry Data for Temperature Effect on Dark Current, with Application to Radiometers on Profiling Floats. SENSORS (BASEL, SWITZERLAND) 2022; 22:6771. [PMID: 36146125 PMCID: PMC9505084 DOI: 10.3390/s22186771] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 08/31/2022] [Accepted: 09/01/2022] [Indexed: 06/16/2023]
Abstract
Measurements of daytime radiometry in the ocean are necessary to constrain processes such as photosynthesis, photo-chemistry and radiative heating. Profiles of downwelling irradiance provide a means to compute the concentration of a variety of in-water constituents. However, radiometers record a non-negligible signal when no light is available, and this signal is temperature dependent (called the dark current). Here, we devise and evaluate two consistent methods for correction of BGC-Argo radiometry measurements for dark current: one based on measurements during the day, the other based on night measurements. A daytime data correction is needed because some floats never measure at night. The corrections are based on modeling the temperature of the radiometer and show an average bias in the measured value of nearly 0.01 W m-2 nm-1, 3 orders of magnitude larger than the reported uncertainty of 2.5×10-5 W m-2 nm-1 for the sensors deployed on BGC-Argo floats (SeaBird scientific OCR504 radiometers). The methods are designed to be simple and robust, requiring pressure, temperature and irradiance data. The correction based on nighttime profiles is recommended as the primary method as it captures dark measurements with the largest dynamic range of temperature. Surprisingly, more than 28% of daytime profiles (130,674 in total) were found to record significant downwelling irradiance at 240-250 dbar. The correction is shown to be small relative to near-surface radiance and thus most useful for studies investigating light fields in the twilight zone and the impacts of radiance on deep organisms. Based on these findings, we recommend that BGC-Argo floats profile occasionally at night and to depths greater than 250 dbar. We provide codes to perform the dark corrections.
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Affiliation(s)
- Terence O’Brien
- Institute for the study of Earth, Ocean and Space, University of New Hampshire, Durham, NH 03824, USA
| | - Emmanuel Boss
- School of Marine Sciences, University of Maine, Orono, ME 04469, USA
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Zheng H, Ma Y, Huang J, Yang J, Su D, Yang F, Wang XH. Deriving vertical profiles of chlorophyll-a concentration in the upper layer of seawaters using ICESat-2 photon-counting lidar. OPTICS EXPRESS 2022; 30:33320-33336. [PMID: 36242374 DOI: 10.1364/oe.463622] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 08/16/2022] [Indexed: 06/16/2023]
Abstract
Chlorophyll-a concentration (chl-a) is a great indicator for estimating phytoplankton biomass and productivity levels and is also particularly useful for monitoring the water quality, biodiversity and species distribution, and harmful algal blooms. A great deal of studies investigated to estimate chl-a concentrations using ocean color remotely sensed data. With the development of photon-counting sensors, spaceborne photon-counting lidar can compensate for the shortcomings of passive optical remote sensing by enabling ocean vertical profiling in low-light conditions (e.g., at night). Using geolocated photons captured by the first spaceborne photon-counting lidar borne on ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2), this research reported methods for deriving vertical profiles of chl-a concentration in the upper layer of ocean waters. This study first calculates the average numbers of backscattered subaqueous photons of ICESat-2 at different water depths, and then estimates the optical parameters in water column based on a discrete theoretical model of the expected number of received signal photons. With the estimated optical parameters, vertical profiles of chl-a concentration are calculated by two different empirical algorithms. In two study areas (mostly with Type I open ocean waters and small part of Type II coastal ocean waters), the derived chl-a concentrations are generally consistent when validated by BGC-Argo (Biogeochemical Argo) data in the vertical direction (MAPEs<15%) and compared with MODIS (Moderate Resolution Imaging Spectroradiometer) data in the along-track direction (average R2>0.86). Using globally covered ICESat-2 data, this approach can be used to obtain vertical profiles of chl-a concentration and optical parameters at a larger scale, which will be helpful to analyze impact factors of climate change and human activities on subsurface phytoplankton species and their growth state.
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Liu X, Georgakakos AP. Chlorophyll a estimation in lakes using multi-parameter sonde data. WATER RESEARCH 2021; 205:117661. [PMID: 34560618 DOI: 10.1016/j.watres.2021.117661] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 08/30/2021] [Accepted: 09/08/2021] [Indexed: 06/13/2023]
Abstract
Algae blooms are of considerable concern in freshwater lakes and reservoirs worldwide. In-situ Chlorophyll a (Chl-a) fluorometers are widely used for rapid assessments of algae biomass. However, accurately converting Chl-a fluorescence to an equivalent concentration is challenging due to natural variations in the relationship as well as nonphotochemical quenching (NPQ) which occurs commonly in surface waters during daytime. This study is based on water quality data from a freshwater lake from October 2018 to December 2020. Initial analysis of sonde Chl-a fluorescence and laboratory extracted Chl-a concentrations shows that the two data sets exhibit a nonlinear relationship with positive correlation and significant errors. A bias correction method was next developed based on (1) concurrent sonde measurements of other water quality parameters (to account for nonlinearities) and (2) a bias correction approach for nonphotochemical quenching effects in surface waters. The new Chl-a model exhibits much improved accuracy, with a root mean square error (RMSE) less than 0.95 µg/L. The new method facilitates accurate Chl-a characterization in freshwater lakes and reservoirs based on readily obtainable in-situ fluorescence sonde measurements.
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Affiliation(s)
- Xiaofeng Liu
- Georgia Water Resources Institute, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Aris P Georgakakos
- Georgia Water Resources Institute, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
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Correction of Biogeochemical-Argo Radiometry for Sensor Temperature-Dependence and Drift: Protocols for a Delayed-Mode Quality Control. SENSORS 2021; 21:s21186217. [PMID: 34577421 PMCID: PMC8473398 DOI: 10.3390/s21186217] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 09/06/2021] [Accepted: 09/09/2021] [Indexed: 11/16/2022]
Abstract
Measuring the underwater light field is a key mission of the international Biogeochemical-Argo program. Since 2012, 0-250 dbar profiles of downwelling irradiance at 380, 412 and 490 nm besides photosynthetically available radiation (PAR) have been acquired across the globe every 1 to 10 days. The resulting unprecedented amount of radiometric data has been previously quality-controlled for real-time distribution and ocean optics applications, yet some issues affecting the accuracy of measurements at depth have been identified such as changes in sensor dark responsiveness to ambient temperature, with time and according to the material used to build the instrument components. Here, we propose a quality-control procedure to solve these sensor issues to make Argo radiometry data available for delayed-mode distribution, with associated error estimation. The presented protocol requires the acquisition of ancillary radiometric measurements at the 1000 dbar parking depth and night-time profiles. A test on >10,000 profiles from across the world revealed a quality-control success rate >90% for each band. The procedure shows similar performance in re-qualifying low radiometry values across diverse oceanic regions. We finally recommend, for future deployments, acquiring daily 1000 dbar measurements and one night profile per year, preferably during moonless nights and when the temperature range between the surface and 1000 dbar is the largest.
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Gbagir AMG, Colpaert A. Assessing the Trend of the Trophic State of Lake Ladoga Based on Multi-Year (1997-2019) CMEMS GlobColour-Merged CHL-OC5 Satellite Observations. SENSORS 2020; 20:s20236881. [PMID: 33271976 PMCID: PMC7731321 DOI: 10.3390/s20236881] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 11/20/2020] [Accepted: 11/27/2020] [Indexed: 11/20/2022]
Abstract
The trophic state of Lake Ladoga was studied during the period 1997–2019, using the Copernicus Marine Environmental Monitoring Service (CMEMS) GlobColour-merged chlorophyll-a OC5 algorithm (GlobColour CHL-OC5) satellite observations. Lake Ladoga, in general, is mesotrophic but certain parts of the lake have been eutrophic since the 1960s due to the discharge of wastewater from industrial, urban, and agricultural sources. Since then, many ecological assessments of the Lake’s state have been made. These studies have indicated that various changes are taking place in the lake and continuous monitoring of the lake is essential to update the current knowledge of its state. The aim of this study was to assess the long-term trend in chl-a in Lake Ladoga. The results showed a gradual reduction in chl-a concentration, indicating a moderate improvement. Chl-a concentrations (minimum-maximum values) varied spatially. The shallow southern shores did not show any improvement while the situation in the north is much better. The shore areas around the functioning paper mill at Pitkäranta and city of Sortavala still show high chl-a values. These findings provide a general reference on the current trophic state of Lake Ladoga that could contribute to improve policy and management strategies. It is assumed that the present warming trend of surface water may result in phytoplankton growth increase, thus partly offsetting a decrease in nutrient load. Precipitation is thought to be increasing, but the influence on water quality is less clear. Future studies could assess the current chemical composition to determine the state of water quality of Lake Ladoga.
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Affiliation(s)
- Augustine-Moses Gaavwase Gbagir
- School of Forest Sciences, University of Eastern Finland, Yliopistokatu 7, Borealis Building A 3rd Floor, 80101 Joensuu, Finland
- Correspondence:
| | - Alfred Colpaert
- Department of Geographical and Historical Studies, University of Eastern Finland, Yliopistokatu 7, Metria-Building, P.O. Box 111, FI-80101 Joensuu, Finland;
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Evaluation of Ocean Color Remote Sensing Algorithms for Diffuse Attenuation Coefficients and Optical Depths with Data Collected on BGC-Argo Floats. REMOTE SENSING 2020. [DOI: 10.3390/rs12152367] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The vertical distribution of irradiance in the ocean is a key input to quantify processes spanning from radiative warming, photosynthesis to photo-oxidation. Here we use a novel dataset of thousands local-noon downwelling irradiance at 490 nm (Ed(490)) and photosynthetically available radiation (PAR) profiles captured by 103 BGC-Argo floats spanning three years (from October 2012 to January 2016) in the world’s ocean, to evaluate several published algorithms and satellite products related to diffuse attenuation coefficient (Kd). Our results show: (1) MODIS-Aqua Kd(490) products derived from a blue-to-green algorithm and two semi-analytical algorithms show good consistency with the float-observed values, but the Chla-based one has overestimation in oligotrophic waters; (2) The Kd(PAR) model based on the Inherent Optical Properties (IOPs) performs well not only at sea-surface but also at depth, except for the oligotrophic waters where Kd(PAR) is underestimated below two penetration depth (2zpd), due to the model’s assumption of a homogeneous distribution of IOPs in the water column which is not true in most oligotrophic waters with deep chlorophyll-a maxima; (3) In addition, published algorithms for the 1% euphotic-layer depth and the depth of 0.415 mol photons m−2 d−1 isolume are evaluated. Algorithms based on Chla generally work well while IOPs-based ones exhibit an overestimation issue in stratified and oligotrophic waters, due to the underestimation of Kd(PAR) at depth.
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Claustre H, Johnson KS, Takeshita Y. Observing the Global Ocean with Biogeochemical-Argo. ANNUAL REVIEW OF MARINE SCIENCE 2020; 12:23-48. [PMID: 31433959 DOI: 10.1146/annurev-marine-010419-010956] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Biogeochemical-Argo (BGC-Argo) is a network of profiling floats carrying sensors that enable observation of as many as six essential biogeochemical and bio-optical variables: oxygen, nitrate, pH, chlorophyll a, suspended particles, and downwelling irradiance. This sensor network represents today's most promising strategy for collecting temporally and vertically resolved observations of biogeochemical properties throughout the ocean. All data are freely available within 24 hours of transmission. These data fill large gaps in ocean-observing systems and support three ambitions: gaining a better understanding of biogeochemical processes (e.g., the biological carbon pump and air-sea CO2 exchanges) and evaluating ongoing changes resulting from increasing anthropogenic pressure (e.g., acidification and deoxygenation); managing the ocean (e.g., improving the global carbon budget and developing sustainable fisheries); and carrying out exploration for potential discoveries. The BGC-Argo network has already delivered extensive high-quality global data sets that have resulted in unique scientific outcomes from regional to global scales. With the proposed expansion of BGC-Argo in the near future, this network has the potential to become a pivotal observation system that links satellite and ship-based observations in a transformative manner.
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Affiliation(s)
- Hervé Claustre
- Laboratoire d'Océanographie de Villefranche, Institut de la Mer de Villefranche, CNRS, Sorbonne Université, 06230 Villefranche-sur-Mer, France;
| | - Kenneth S Johnson
- Monterey Bay Aquarium Research Institute, Moss Landing, California 95039, USA; ,
| | - Yuichiro Takeshita
- Monterey Bay Aquarium Research Institute, Moss Landing, California 95039, USA; ,
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9
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Groom S, Sathyendranath S, Ban Y, Bernard S, Brewin R, Brotas V, Brockmann C, Chauhan P, Choi JK, Chuprin A, Ciavatta S, Cipollini P, Donlon C, Franz B, He X, Hirata T, Jackson T, Kampel M, Krasemann H, Lavender S, Pardo-Martinez S, Mélin F, Platt T, Santoleri R, Skakala J, Schaeffer B, Smith M, Steinmetz F, Valente A, Wang M. Satellite Ocean Colour: Current Status and Future Perspective. FRONTIERS IN MARINE SCIENCE 2019; 6:1-30. [PMID: 36817748 PMCID: PMC9933503 DOI: 10.3389/fmars.2019.00485] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Spectrally resolved water-leaving radiances (ocean colour) and inferred chlorophyll concentration are key to studying phytoplankton dynamics at seasonal and interannual scales, for a better understanding of the role of phytoplankton in marine biogeochemistry; the global carbon cycle; and the response of marine ecosystems to climate variability, change and feedback processes. Ocean colour data also have a critical role in operational observation systems monitoring coastal eutrophication, harmful algal blooms, and sediment plumes. The contiguous ocean-colour record reached 21 years in 2018; however, it is comprised of a number of one-off missions such that creating a consistent time-series of ocean-colour data requires merging of the individual sensors (including MERIS, Aqua-MODIS, SeaWiFS, VIIRS, and OLCI) with differing sensor characteristics, without introducing artefacts. By contrast, the next decade will see consistent observations from operational ocean colour series with sensors of similar design and with a replacement strategy. Also, by 2029 the record will start to be of sufficient duration to discriminate climate change impacts from natural variability, at least in some regions. This paper describes the current status and future prospects in the field of ocean colour focusing on large to medium resolution observations of oceans and coastal seas. It reviews the user requirements in terms of products and uncertainty characteristics and then describes features of current and future satellite ocean-colour sensors, both operational and innovative. The key role of in situ validation and calibration is highlighted as are ground segments that process the data received from the ocean-colour sensors and deliver analysis-ready products to end-users. Example applications of the ocean-colour data are presented, focusing on the climate data record and operational applications including water quality and assimilation into numerical models. Current capacity building and training activities pertinent to ocean colour are described and finally a summary of future perspectives is provided.
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Affiliation(s)
- Steve Groom
- Plymouth Marine Laboratory, Plymouth, United Kingdom
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, United Kingdom
- Correspondence: Steve Groom,
| | - Shubha Sathyendranath
- Plymouth Marine Laboratory, Plymouth, United Kingdom
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, United Kingdom
| | - Yai Ban
- State Key Laboratory of Satellite Ocean, Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China
| | - Stewart Bernard
- CSIR Earth Systems Earth Observation, CSIR – NRE, Cape Town, South Africa
| | - Robert Brewin
- Plymouth Marine Laboratory, Plymouth, United Kingdom
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, United Kingdom
| | - Vanda Brotas
- MARE, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
| | | | | | - Jong-kuk Choi
- KIOST-PML Science Lab, Korea Institute of Ocean Science and Technology, Plymouth, United Kingdom
| | | | - Stefano Ciavatta
- Plymouth Marine Laboratory, Plymouth, United Kingdom
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, United Kingdom
| | - Paolo Cipollini
- Telespazio VEGA UK Ltd. for ESA Climate Office, European Centre for Space Applications and Telecommunications, European Space Agency, Didcot, United Kingdom
| | - Craig Donlon
- European Space Research and Technology Centre, European Space Agency, Noordwijk, Netherlands
| | - Bryan Franz
- Goddard Space Flight Center, NASA, Greenbelt, MD, United States
| | - Xianqiang He
- State Key Laboratory of Satellite Ocean, Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China
| | | | - Tom Jackson
- Plymouth Marine Laboratory, Plymouth, United Kingdom
| | - Milton Kampel
- Instituto Nacional de Pesquisas Espaciais São Jose dos Campos, São Paulo, Brazil
| | - Hajo Krasemann
- Helmholtz-Zentrum Geesthacht – Zentrum für Materialund Küstenforschung GmbH, Geesthacht, Germany
| | | | | | - Frédéric Mélin
- European Commission, Joint Research Centre (JRC), Ispra, Italy
| | - Trevor Platt
- Plymouth Marine Laboratory, Plymouth, United Kingdom
| | | | - Jozef Skakala
- Plymouth Marine Laboratory, Plymouth, United Kingdom
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, United Kingdom
| | - Blake Schaeffer
- Office of Research and Development, United States Environmental Protection Agency, Research Triangle, NC, United States
| | - Marie Smith
- CSIR Earth Systems Earth Observation, CSIR – NRE, Cape Town, South Africa
| | | | - Andre Valente
- MARE, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
| | - Menghua Wang
- Marine Ecosystems and Climate Branch, NOAA NESDIS STAR, College Park, MD, United States
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Hemsley VS, Smyth TJ, Martin AP, Frajka-Williams E, Thompson AF, Damerell G, Painter SC. Estimating Oceanic Primary Production Using Vertical Irradiance and Chlorophyll Profiles from Ocean Gliders in the North Atlantic. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:11612-21. [PMID: 26301371 DOI: 10.1021/acs.est.5b00608] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
An autonomous underwater vehicle (Seaglider) has been used to estimate marine primary production (PP) using a combination of irradiance and fluorescence vertical profiles. This method provides estimates for depth-resolved and temporally evolving PP on fine spatial scales in the absence of ship-based calibrations. We describe techniques to correct for known issues associated with long autonomous deployments such as sensor calibration drift and fluorescence quenching. Comparisons were made between the Seaglider, stable isotope ((13)C), and satellite estimates of PP. The Seaglider-based PP estimates were comparable to both satellite estimates and stable isotope measurements.
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Affiliation(s)
- Victoria S Hemsley
- National Oceanography Centre , Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom
- Ocean and Earth Science, National Oceanography Centre Southhampton, University of Southampton, SO14 3ZH, United Kingdom
| | - Timothy J Smyth
- Plymouth Marine Laboratory , Prospect Place, The Hoe, Plymouth, PL1 3DH, United Kingdom
| | - Adrian P Martin
- National Oceanography Centre , Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom
| | - Eleanor Frajka-Williams
- Ocean and Earth Science, National Oceanography Centre Southhampton, University of Southampton, SO14 3ZH, United Kingdom
| | - Andrew F Thompson
- Environmental Science and Engineering, California Institute of Technology , Pasadena, California 91125, United States
| | - Gillian Damerell
- School of Environmental Sciences, University of East Anglia , Norwich, NR4 7TJ, United Kingdom
| | - Stuart C Painter
- National Oceanography Centre , Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom
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11
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Cullen JJ. Subsurface chlorophyll maximum layers: enduring enigma or mystery solved? ANNUAL REVIEW OF MARINE SCIENCE 2014; 7:207-39. [PMID: 25251268 DOI: 10.1146/annurev-marine-010213-135111] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The phenomenon of subsurface chlorophyll maximum layers (SCMLs) is not a unique ecological response to environmental conditions; rather, a broad range of interacting processes can contribute to the formation of persistent layers of elevated chlorophyll a concentration (Chl) that are nearly ubiquitous in stratified surface waters. Mechanisms that contribute to the formation and maintenance of the SCMLs include a local maximum in phytoplankton growth rate near the nutricline, photoacclimation of pigment content that leads to elevated Chl relative to phytoplankton biomass at depth, and a range of physiologically influenced swimming behaviors in motile phytoplankton and buoyancy control in diatoms and cyanobacteria that can lead to aggregations of phytoplankton in layers, subject to grazing and physical control. A postulated typical stable water structure characterizes consistent patterns in vertical profiles of Chl, phytoplankton biomass, nutrients, and light across a trophic gradient structured by the vertical flux of nutrients and characterized by the average daily irradiance at the nutricline. Hypothetical predictions can be tested using a nascent biogeochemical global ocean observing system. Partial results to date are generally consistent with predictions based on current knowledge, which has strong roots in research from the twentieth century.
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Affiliation(s)
- John J Cullen
- Department of Oceanography, Dalhousie University, Halifax B3H 4R2, Canada;
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12
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Green RE, Bower AS, Lugo-Fernández A. First autonomous bio-optical profiling float in the Gulf of Mexico reveals dynamic biogeochemistry in deep waters. PLoS One 2014; 9:e101658. [PMID: 24992646 PMCID: PMC4081586 DOI: 10.1371/journal.pone.0101658] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Accepted: 06/09/2014] [Indexed: 11/18/2022] Open
Abstract
Profiling floats equipped with bio-optical sensors well complement ship-based and satellite ocean color measurements by providing highly-resolved time-series data on the vertical structure of biogeochemical processes in oceanic waters. This is the first study to employ an autonomous profiling (APEX) float in the Gulf of Mexico for measuring spatiotemporal variability in bio-optics and hydrography. During the 17-month deployment (July 2011 to December 2012), the float mission collected profiles of temperature, salinity, chlorophyll fluorescence, particulate backscattering (bbp), and colored dissolved organic matter (CDOM) fluorescence from the ocean surface to a depth of 1,500 m. Biogeochemical variability was characterized by distinct depth trends and local "hot spots", including impacts from mesoscale processes associated with each of the water masses sampled, from ambient deep waters over the Florida Plain, into the Loop Current, up the Florida Canyon, and eventually into the Florida Straits. A deep chlorophyll maximum (DCM) occurred between 30 and 120 m, with the DCM depth significantly related to the unique density layer ρ = 1023.6 (R2 = 0.62). Particulate backscattering, bbp, demonstrated multiple peaks throughout the water column, including from phytoplankton, deep scattering layers, and resuspension. The bio-optical relationship developed between bbp and chlorophyll (R2 = 0.49) was compared to a global relationship and could significantly improve regional ocean-color algorithms. Photooxidation and autochthonous production contributed to CDOM distributions in the upper water column, whereas in deep water, CDOM behaved as a semi-conservative tracer of water masses, demonstrating a tight relationship with density (R2 = 0.87). In the wake of the Deepwater Horizon oil spill, this research lends support to the use of autonomous drifting profilers as a powerful tool for consideration in the design of an expanded and integrated observing network for the Gulf of Mexico.
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Affiliation(s)
- Rebecca E. Green
- Environmental Studies Section, Bureau of Ocean Energy Management, New Orleans, Lousiana, United States of America
- * E-mail:
| | - Amy S. Bower
- Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, United States of America
| | - Alexis Lugo-Fernández
- Environmental Studies Section, Bureau of Ocean Energy Management, New Orleans, Lousiana, United States of America
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13
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Antoine D, Babin M, Berthon JF, Bricaud A, Gentili B, Loisel H, Maritorena S, Stramski D. Shedding light on the sea: André Morel's legacy to optical oceanography. ANNUAL REVIEW OF MARINE SCIENCE 2013; 6:1-21. [PMID: 24015899 DOI: 10.1146/annurev-marine-010213-135135] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
André Morel (1933-2012) was a prominent pioneer of modern optical oceanography, enabling significant advances in this field. Through his forward thinking and research over more than 40 years, he made key contributions that this field needed to grow and to reach its current status. This article first summarizes his career and then successively covers different aspects of optical oceanography where he made significant contributions, from fundamental work on optical properties of water and particles to global oceanographic applications using satellite ocean color observations. At the end, we share our views on André's legacy to our research field and scientific community.
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Affiliation(s)
- David Antoine
- Laboratoire d'Océanographie de Villefranche, Centre National de la Recherche Scientifique (CNRS) and Université Pierre et Marie Curie (Paris 6), Villefranche-sur-Mer 06238, France; , ,
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14
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Rees AP. Pressures on the marine environment and the changing climate of ocean biogeochemistry. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2012; 370:5613-35. [PMID: 23129714 DOI: 10.1098/rsta.2012.0399] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The oceans are under pressure from human activities. Following 250 years of industrial activity, effects are being seen at the cellular through to regional and global scales. The change in atmospheric CO(2) from 280 ppm in pre-industrial times to 392 ppm in 2011 has contributed to the warming of the upper 700 m of the ocean by approximately 0.1°C between 1961 and 2003, to changes in sea water chemistry, which include a pH decrease of approximately 0.1, and to significant decreases in the sea water oxygen content. In parallel with these changes, the human population has been introducing an ever-increasing level of nutrients into coastal waters, which leads to eutrophication, and by 2008 had resulted in 245,000 km(2) of severely oxygen-depleted waters throughout the world. These changes are set to continue for the foreseeable future, with atmospheric CO(2) predicted to reach 430 ppm by 2030 and 750 ppm by 2100. The cycling of biogeochemical elements has proved sensitive to each of these effects, and it is proposed that synergy between stressors may compound this further. The challenge, within the next few decades, for the marine science community, is to elucidate the scope and extent that biological processes can adapt or acclimatize to a changing chemical and physical marine environment.
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Xing X, Morel A, Claustre H, D'Ortenzio F, Poteau A. Combined processing and mutual interpretation of radiometry and fluorometry from autonomous profiling Bio-Argo floats: 2. Colored dissolved organic matter absorption retrieval. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jc007632] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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