1,157 research outputs found

    Biological Oceanography by Remote Sensing

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    Sustenance of phytoplankton in the subpolar North Atlantic during the winter through patchiness

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    This study investigates the influence of two factors that change the mixed layer depth and can potentially contribute to the phytoplankton sustenance over winter: 1) variability of air-sea fluxes and 2) three-dimensional processes arising from strong fronts. To study the role of these factors, we perform several three-dimensional numerical simulations forced with air-sea fluxes at different temporal averaging frequencies as well as different spatial resolutions. Results show that in the winter, when the average mixed layer is much deeper than the euphotic layer and the days are short, phytoplankton production is relatively insensitive to the high-frequency variability in air-sea fluxes. The duration of upper ocean stratification due to high-frequency variability in air-sea fluxes is short and hence has a small impact on phytoplankton production. On the other hand, slumping of fronts creates patchy, stratified, shallow regions that persist considerably longer than stratification caused by changes in air-sea fluxes. Simulations show that before spring warming, the average MLD with fronts is about 700 m shallower than the average MLD without fronts. Therefore, fronts increase the residence time of phytoplankton in the euphotic layer and contribute to phytoplankton growth. Results show that before the spring warming, the depth-integrated phytoplankton concentration is about twice as large as phytoplankton concentration when there are no fronts. Hence, fronts are important for setting the MLD and sustaining phytoplankton in the winter. Model results also show that higher numerical resolution leads to stronger restratification, shallower mixed layers, greater variability in the MLD and higher production of phytoplankton

    Using remote sensing as a support to the implementation of the European Marine Strategy Framework Directive in SW Portugal

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    The exclusive economic zones (EEZ) of coastal countries are coming under increasing pressure from various economic sectors such as fishing, aquaculture, shipping and energy production. In Europe, there is a policy to expand the maritime economic sector without damaging the environment by ensuring that these activities comply with legally binding Directives, such as the Marine Strategy Framework Directive (MSFD). However, monitoring an extensive maritime area is a logistical and economic challenge. Remote sensing is considered one of the most cost effective, methods for providing the spatial and temporal environmental data that will be necessary for the effective implementation of the MSFD. However, there is still a concern about the uncertainties associated with remote sensed products. This study has tested how a specific satellite product can contribute to the monitoring of a MSFD Descriptor for "good environmental status" (GES). The results show that the quality of the remote sensing product Algal Pigment Index 1 (API 1) from the MEdium Resolution Imaging Spectrometer (MERIS) sensor of the European Space Agency for ocean colour products can be effectively validated with in situ data from three stations off the SW Iberian Peninsula. The validation results show good agreement between the MERIS API 1 and the in situ data for the two more offshore stations, with a higher coefficient of determination (R-2) of 0.79, and with lower uncertainties for the average relative percentage difference (RPD) of 24.6% and 27.9% and a root mean square error (RMSE) of 0.40 and 0.38 for Stations B and C, respectively. Near to the coast, Station A has the lowest R-2 of 0.63 and the highest uncertainties with an RPD of 112.9% and a RMSE of 1.00. It is also the station most affected by adjacency effects from the land: when the Improved Contrast between Ocean and Land processor (ICOL) is applied the R-2 increases to 0.77 and there is a 30% reduction in the uncertainties estimated by RPD. The MERIS API 1 product decreases from inshore to offshore, with higher values occurring mainly between early spring and the end of the summer, and with lower values during winter. By using the satellite images for API 1, it is possible to detect and track the development of algal blooms in coastal and marine waters, demonstrating the usefulness of remote sensing for supporting the implementation of the MSFD with respect to Descriptor 5: Eutrophication. It is probable that remote sensing will also prove to be useful for monitoring other Descriptors of the MSFD.EU (European Space Agency) [308392, 21464/08/1-0, 607325]; Portuguese FCT [FRH/BD/78354/2011, SFRH/BD/78356/2011]; Horizon 2020 AquaSpace [633476]info:eu-repo/semantics/publishedVersio

    A review of ocean color remote sensing methods and statistical techniques for the detection, mapping and analysis of phytoplankton blooms in coastal and open oceans

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    The need for more effective environmental monitoring of the open and coastal ocean has recently led to notable advances in satellite ocean color technology and algorithm research. Satellite ocean color sensors' data are widely used for the detection, mapping and monitoring of phytoplankton blooms because earth observation provides a synoptic view of the ocean, both spatially and temporally. Algal blooms are indicators of marine ecosystem health; thus, their monitoring is a key component of effective management of coastal and oceanic resources. Since the late 1970s, a wide variety of operational ocean color satellite sensors and algorithms have been developed. The comprehensive review presented in this article captures the details of the progress and discusses the advantages and limitations of the algorithms used with the multi-spectral ocean color sensors CZCS, SeaWiFS, MODIS and MERIS. Present challenges include overcoming the severe limitation of these algorithms in coastal waters and refining detection limits in various oceanic and coastal environments. To understand the spatio-temporal patterns of algal blooms and their triggering factors, it is essential to consider the possible effects of environmental parameters, such as water temperature, turbidity, solar radiation and bathymetry. Hence, this review will also discuss the use of statistical techniques and additional datasets derived from ecosystem models or other satellite sensors to characterize further the factors triggering or limiting the development of algal blooms in coastal and open ocean waters

    Reappraisal of meridional differences of factors controlling phytoplankton biomass and initial increase preceding seasonal bloom in the northwestern Pacific Ocean

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    Multiplatform observations of ocean biogeochemical data were used to elucidate meridional differences in the factors that limit phytoplankton biomass (Chl-a) and the mechanisms that trigger the seasonal winter or spring phytoplankton bloomin the northwestern Pacific Ocean (NWPO). During the winter, Chl-a north (south) of 30°N is limited by light (nutrients). During the spring and fall, Chl-a in much of the area east of the Japan/Kuril Islands and/or north of 40°N(south of 35°N) is limited by light (nutrients). During the summer, nutrients limit Chl-a over much of the NWPO, except in the areas east of the Japan/Kuril Islands and north of 45°N. In the area south of around 31°N, phytoplankton biomass is nutrient limited throughout the year, and the seasonal bloom emerges in the winter, begins in the fall which is associated with mixed layer deepening. Between 31°N and 40°N, the spring bloom onset is mainly associated with a cessation of mixed layer deepening. In much of the area north of 40°N, including the Oyashio area, the onset of the spring bloom is consistent with Sverdrup’s critical depth hypothesis. The spatial extents of the light- and nutrient-limited areas and the areas associated with a single bloom onset mechanism are by no means constant. They are expected to undergo meridional shifts as a result of large-scale climatic changes and global warming

    Relationships of interannual variability in SST and phytoplankton blooms with giant jellyfish (Nemopilema nomurai) outbreaks in the Yellow Sea and East China Sea

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    Giant jellyfish (Nemopilema nomurai) outbreaks in relation to satellite sea surface temperature (SST) and chlorophyll-a concentration (Chl-a) were investigated in the Yellow Sea and East China Sea (YECS) from 1998 to 2010. Temperature, eutrophication, and match-mismatch hypothesis were examined to explain long-term increases and recent reductions of N. nomurai outbreaks. We focused on the timing of SST reaching 15oC, a critical temperature enabling polyps to induce strobilation and enabling released ephyra to grow. We analyzed the relationship of the timing with intterannual variability of SST, Chl-a, and the timing of phytoplankton bloom. Different environmental characteristics among pre-jellyfish years (1998-2001), jellyfish year (2002-2007, 2009), and non-jellyfish year (2008, 2010) were assessed on this basis. The SST during late spring and early summer increased significantly from 1985 to 2007. This indicated that high SST is beneficial to the long-term increase in jellyfish outbreaks. SST was significantly lower in non-jellyfish years than in jellyfish years, suggesting that low SST might reduce the proliferation of N. nomurai. We identified three (winter, spring, and summer) major phytoplankton bloom regions and one summer decline region. Both Chl-a during non-blooming period and the peak increased significantly from 1998 to 2010 in most of the YECS. This result indicates that eutrophication is beneficial to the long-term increases in jellyfish outbreaks. Timing of phytoplankton blooms varied interannually and spatially, and their match and mismatch to the timing of SST reaching 15oC did not correspond to long-term increases in N. nomurai outbreaks and the recent absence

    Mapping Satellite Inherent Optical Properties Index in Coastal Waters of the Yucatán Peninsula (Mexico)

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    [EN] The Yucatan Peninsula hosts worldwide-known tourism destinations that concentrate most of the Mexico tourism activity. In this region, tourism has exponentially increased over the last years, including wildlife oriented tourism. Rapid tourism development, involving the consequent construction of hotels and tourist commodities, is associated with domestic sewage discharges from septic tanks. In this karstic environment, submarine groundwater discharges are very important and highly vulnerable to anthropogenic pollution. Nutrient loadings are linked to harmful algal blooms, which are an issue of concern to local and federal authorities due to their recurrence and socioeconomic and human health costs. In this study, we used satellite products from MODIS (Moderate Resolution Imaging Spectroradiometer) to calculate and map the satellite Inherent Optical Properties (IOP) Index. We worked with different scenarios considering both holiday and hydrological seasons. Our results showed that the satellite IOP Index allows one to build baseline information in a sustainable mid-term or long-term basis which is key for ecosystem-based management.This research was funded by CONACYT with a doctorate scholarship to Jesús A. Aguilar-Maldonado,with the announcement number 251025 in 2015. María-Teresa Sebastiá-Frasquet was a beneficiary of the BEST/2017/217 post-doctoral research grant, supported by the Valencian Conselleria d’Educació, Investigació,Cultura i Esport (Spain) during her stay at the Universidad Autónoma de Baja California (Mexico). The Secretariat of Public Education of Mexico (SEP) under the Program for Professional Development Teacher, covered the costs of publication in open access.Aguilar-Maldonado, J.; Santamaría-Del-Ángel, E.; González-Silvera, A.; Cervantes-Rosas, OD.; Sebastiá-Frasquet, M. (2018). Mapping Satellite Inherent Optical Properties Index in Coastal Waters of the Yucatán Peninsula (Mexico). 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Harmful Algae, 67, 144-152. doi:10.1016/j.hal.2017.06.001Harvey, E. T., Kratzer, S., & Philipson, P. (2015). Satellite-based water quality monitoring for improved spatial and temporal retrieval of chlorophyll-a in coastal waters. Remote Sensing of Environment, 158, 417-430. doi:10.1016/j.rse.2014.11.017Malthus, T. J., & Mumby, P. J. (2003). Remote sensing of the coastal zone: An overview and priorities for future research. International Journal of Remote Sensing, 24(13), 2805-2815. doi:10.1080/0143116031000066954Matthews, M. W. (2011). A current review of empirical procedures of remote sensing in inland and near-coastal transitional waters. International Journal of Remote Sensing, 32(21), 6855-6899. doi:10.1080/01431161.2010.512947Miller, R. L., & McKee, B. A. (2004). Using MODIS Terra 250 m imagery to map concentrations of total suspended matter in coastal waters. 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    Ash Deposition Triggers Phytoplankton Blooms at Nishinoshima Volcano, Japan

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    Volcanoes that deposit eruptive products into the ocean can trigger phytoplankton blooms near the deposition area. Phytoplankton blooms impact the global carbon cycle, but the specific conditions and mechanisms that facilitate volcanically triggered blooms are not well understood, especially in low nutrient ocean regions. We use satellite remote sensing to analyze the chlorophyll response to an 8-month period of explosive and effusive activity from Nishinoshima volcano, Japan. Nishinoshima is an ocean island volcano in a low nutrient low chlorophyll region of the Northern Pacific Ocean. From June to August 2020, during explosive activity, satellite-derived chlorophyll-a was detectable with amplitudes significantly above the long-term climatological value. After the explosive activity ceased in mid-August 2020, these areas of heightened chlorophyll concentration decreased as well. In addition, we used aerial observations and satellite imagery to demonstrate a spatial correlation between blooms and ash plume direction. Using a sun-induced chlorophyll-a fluorescence satellite product, we confirmed that the observed chlorophyll blooms are phytoplankton blooms. Based on an understanding of the nutrients needed to supply blooms, we hypothesize that blooms of nitrogen-fixing phytoplankton led to a 1010–1012 g drawdown of carbon. Thus, the bloom could have significantly mediated the output of carbon from the explosive phase of the eruption but is a small fraction of anthropogenic CO2 stored in the ocean or the global biological pump. Overall, we provide a case study of fertilization of a nutrient-poor ocean with volcanic ash and demonstrate a scenario where multi-month scale deposition triggers continuous phytoplankton blooms across 1,000s of km2

    The Oceanic Biological Pump: Rapid carbon transfer to depth at Continental Margins during Winter

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    The oceanic biological pump is responsible for the important transfer of CO2-C as POC “Particulate Organic Carbon” to the deep sea. It plays a decisive role in the Earth’s carbon cycle and significant effort is spent to quantify its strength. In this study we used synchronized daily time-series data of surface chlorophyll-a concentrations from the NASA’s MODIS satellite in combination with hourly to daily observations from sea surface buoys and from an Internet Operated Vehicle (IOV) on the seafloor within Barkley Canyon (Northeast Pacific) to investigate the importance of winter processes in the export of fresh phytodetritus. The results indicate that phytoplankton pulses during winter can be as important in POC transfer to depth as the pulses associated with spring and summer blooms. Short winter phytoplankton pulses were observed to disappear from surface waters after low-pressure systems affected the area. Pulses of chlorophyll reached the IOV, at 870 m depth on the canyon seafloor, 12–72 hours later. These observed short pulses of biological carbon production regularly observed in the region from December to March have not been considered a significant component of the biological pump when compared with the denser summer productivity blooms
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