Evaluation of ocean color remote sensing algorithms for diffuse attenuation coefficients and optical depths with data collected on BGC-Argo floats

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\u27s 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\u27s 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

SeaWiFS Technical Report Series

Two issues regarding primary productivity, as it pertains to the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Program and the National Aeronautics and Space Administration (NASA) Mission to Planet Earth (MTPE) are presented in this volume. Chapter 1 describes the development of a science plan for deriving primary production for the world ocean using satellite measurements, by the Ocean Primary Productivity Working Group (OPPWG). Chapter 2 presents discussions by the same group, of algorithm classification, algorithm parameterization and data availability, algorithm testing and validation, and the benefits of a consensus primary productivity algorithm

Carbon from Space: determining the biological controls on the ocean sink of CO2 from satellites, in the Atlantic and Southern Ocean

Increasing anthropogenic carbon dioxide (CO2) emissions to the atmosphere have partially been absorbed by the global oceans. The role which the plankton community contributes to this net CO2 sink, and how it may change under climate change has been identified as a key issue to address within the United Nations decade of ocean science (2021-2030) Integrated Ocean Carbon Research (IOC-R) programme. This thesis sets out to explore how the net community production (NCP; the balance between photosynthesis and respiration) of the plankton community contributes to the variability in air-sea CO2 flux in the South Atlantic Ocean. In Chapter 2, NCP is shown to be accurately and precisely estimated from satellite measurements with respect to in situ observations. For this, weighted statistics are used to account for satellite, in situ and model uncertainties. The accuracy of satellite NCP could be improved by up to 40% by reducing uncertainties in net primary production (NPP). In Chapter 3, these satellite NCP observations were then used within a feed forward neural network scheme (SA-FNN) to extrapolate partial pressure of CO2 in seawater (pCO2 (sw)) over space and time, which is a key component to estimating the CO2 flux. NCP improved the accuracy and precision of pCO2 (sw) fields compared to using chlorophyll a (Chl a); the primary pigment in phytoplankton which is often used as a proxy for the biological CO2 drawdown. Compared to in situ observations, the seasonal variability in pCO2 (sw) was improved using the SA-FNN in key areas such as the Amazon River plume and Benguela upwelling, which make large regional contributions to the air-sea CO2 flux in the South Atlantic Ocean. In Chapter 4, these complete pCO2 (sw) fields were used with a timeseries decomposition method to determine the drivers of air-sea CO2 flux over seasonal, interannual and multi-year timescales. NCP was shown to correlate with the variability in CO2 flux on a seasonal basis. At interannual and mutli-year timescales, NCP became a more important contributor to variability in CO2 flux. This has not been previously analysed for this region. Mesoscale eddies in the global ocean can modify the biological, physical, and chemical properties and therefore may modify the CO2 flux. In Chapter 5, the cumulative CO2 flux of 67 long lived eddies (lifetimes > 1 year) was estimated using Lagrangian tracking with satellite observations. The eddies could enhance the CO2 flux into the South Atlantic Ocean by up to 0.08 %, through eddy modification of biological and physical properties. Collectively this research has shown that the plankton community plays a more significant role in modulating the air-sea CO2 flux in the South Atlantic Ocean, which has significant implications for the global ocean

Marine aerosols, their precursors and their influence on clouds over the global ocean

Marine aerosols have a large potential to influence the Earth¿s climate through their effects on cloud properties. The CLAW hypothesis goes further, and suggests that marine aerosols formed by the sulphur cycle of the ocean and the atmosphere act as a mechanism for regulating the Earth's climate. This effect is produced through the influence of plankton emissions of sulphur compounds on cloud formation. Phytoplankton produces dimethylsulphide (DMS), a highly volatile sulphur compound. Once in the atmosphere, DMS is oxidized and becomes the main source of natural atmospheric sulphates. These sulphates act as condensation nuclei, particles that are essential for the formation of clouds. Those marine particles in the atmosphere play an important role in the Earth's radiation budget. Indirectly they produce a greater amount of cloud droplets. Higher cloud condensation nuclei imply smaller cloud droplets. The efficiency of smaller droplets in reflecting incident solar radiation is greater, resulting in an increase in cloud albedo, producing a cooling effect on the Earth's surface. To properly study the marine aerosols we need accurate knowledge of the global seawater distribution of the aerosol precursors. Our work focused on the ocean-to-atmosphere emissions of DMS and other biogenic gases that can have an impact on cloud microphysics. During the thesis we updated the monthly global DMS climatology taking advantage of the three-fold increased size and better resolved distribution of the observations available in the DMS database. The emerging patterns found with the previous versions of the database and climatology were explored with the updated version. The statistical relationships between the seasonalities of DMS concentrations and solar radiation doses and chlorophyll a concentrations were here re-examined. Analyses of nine years of satellite data suggested that there is a natural inverse correlation between the spatial cover of low marine clouds and the cloud droplet size, which is related to the presence of small aerosols. This coupled seasonality pushes cloud albedo to contribute higher negative radiative forcing in summer and lower in winter. This relation is disrupted in the marine atmosphere regions heavily impacted by anthropogenic aerosols. Consequently, the potential influence the aerosol precursors have on marine clouds was next analysed over unpolluted and polluted ocean, separately. The 9 years of global satellite data and ocean climatologies were used to derive parameterizations of the production fluxes of secondary aerosols formed by oxidation of DMS and other biogenic organic volatiles. Further, the emission fluxes of biogenic primary organic and sea salt aerosols ejected by wind action on sea surface were also globally studied. Series of weekly estimates of these fluxes were correlated to series of cloud droplet effective radius. The outcome of the statistical analyses indicated that sulphur and organic secondary aerosols might be important in seeding cloud nucleation and droplet activation over mid and high latitude unpolluted oceanic regions. Conversely, primary aerosols (organic and sea salt) showed that, despite contributing to large shares of the marine aerosol mass, they do not seem to be major drivers of the variability of cloud microphysics. Our results provide partial support for the feasibility of the CLAW hypothesis at the seasonal scale. Despite that DMS has drawn much of the attention on the links between marine biota and climate regulation, the implication of other biogenic precursors on cloud formation provides and suggests a wider scope on the formulation of such hypothesis.Los aerosoles marinos tienen un gran potencial para influir en el clima de la Tierra a través de sus efectos en las propiedades de las nubes. La hipótesis de CLAW va más allá y sugiere que los aerosoles marinos formados por el ciclo del azufre en océanos y atmósfera actúan como un mecanismo para la regulación del clima de la Tierra. Este efecto se produce a través de la influencia de las emisiones de plancton de compuestos de azufre en la formación de nubes. El fitoplancton produce sulfuro de dimetilo (DMS), un compuesto de azufre altamente volátil. Una vez en la atmósfera, el DMS se oxida y se convierte en la principal fuente de sulfatos naturales atmosféricos. Estos sulfatos actúan como núcleos de condensación, partículas esenciales para la formación de nubes. Estas partículas presentes en la atmósfera marina juegan un papel importante en el ciclo radiativo de la Tierra. Indirectamente, producen una mayor cantidad de gotas de las nubes. Mayor número de núcleos de condensación en las nubes implica gotas de nubes más pequeñas. La eficacia de las pequeñas gotas en reflejar la radiación solar incidente es mayor, lo que resulta en un aumento del albedo de las nubes, produciendo un efecto de enfriamiento en la superficie de la Tierra. Para estudiar adecuadamente los aerosoles marinos necesitamos tener un correcto conocimiento de la distribución oceánica global de los precursores de aerosoles. Nuestro trabajo se ha centrado en las emisiones del océano a la atmósfera de DMS y otros gases biogénicos que puede tener un impacto en la microfísica de nubes. Durante la tesis se ha actualizado la climatología mensual global de DMS, aprovechando el aumento en tres veces del número de observaciones y una mejor distribución global de las mismas, en la base de datos de DMS. Los patrones emergentes encontrados con las versiones anteriores de la base de datos y de la climatología se han re-evaluado con la versión actualizada. Las relaciones estadísticas encontradas entre la evolución temporal de las concentraciones de DMS y las dosis de radiación solar y concentraciones de clorofila han sido re-examinadas. Los análisis de nueve años de datos de satélite sugieren que existe una correlación inversa entre la cubierta espacial de nubes marinas bajas y el tamaño de las gotas de nubes, relacionado con la presencia de aerosoles pequeños. Esta estacionalidad acoplada conduce al albedo de las nubes a contribuir a un forzamiento radiativo negativo superior en verano, y más bajo en invierno. Esta relación se interrumpe en las regiones de la atmósfera marina con un alto impacto de los aerosoles antropogénicos. En consecuencia, la posible influencia de los precursores de aerosoles marinos en las nubes se ha analizado en una atmósfera marina limpia y contaminada, por separado. Los 9 años de datos satelitales globales y climatologías oceánicas se han utilizado para derivar las parametrizaciones de los flujos de producción de aerosoles secundarios, formados por la oxidación de DMS, y otros compuestos volátiles orgánicos biogénicos. Además, los flujos de emisiones biogénicas de aerosoles primarios orgánicos y aerosoles de sal marina expulsados por acción del viento sobre la superficie del mar se ha estudiado también a nivel global. Las series semanales de las estimaciones de estos flujos se han correlacionado con las series temporales de los radios de las gotas de nubes. El resultado de los análisis estadísticos ha indicado que el azufre orgánico y otros aerosoles secundarios pueden ser importantes en la nucleación y la activación de sus gotas sobre las regiones oceánicas no contaminadas en latitudes medias y altas. Por el contrario, aerosoles primarios (orgánico y la sal del mar) han mostrado que, a pesar de que contribuyen a una gran proporción de la masa de aerosol marino, no parecen ser los principales motores de la variabilidad de la microfísica de nubes. Nuestros resultados proporcionan un apoyo parcial a la viabilidad de la hipótesis de CLAW a escala estacional. A pesar de que el DMS ha llamado mucho la atención sobre los vínculos entre la biota marina y la regulación del clima, la implicación de otros precursores biogénicos en la formación de nubes ofrece y sugiere un mayor alcance en la formulación de esta hipótesis

Phytoplankton functional types from Space.

The concept of phytoplankton functional types has emerged as a useful approach to classifying phytoplankton. It finds many applications in addressing some serious contemporary issues facing science and society. Its use is not without challenges, however. As noted earlier, there is no universally-accepted set of functional types, and the types used have to be carefully selected to suit the particular problem being addressed. It is important that the sum total of all functional types matches all phytoplankton under consideration. For example, if in a biogeochemical study, we classify phytoplankton as silicifiers, calcifiers, DMS-producers and nitrogen fix- ers, then there is danger that the study may neglect phytoplankton that do not contribute in any significant way to those functions, but may nevertheless be a significant contributor to, say primary production. Such considerations often lead to the adoption of a category of “other phytoplankton” in models, with no clear defining traits assigned them, but that are nevertheless necessary to close budgets on phytoplankton processes. Since this group is a collection of all phytoplankton that defy classification according to a set of traits, it is difficult to model their physi- ological processes. Our understanding of the diverse functions of phytoplankton is still growing, and as we recognize more functions, there will be a need to balance the desire to incorporate the increasing number of functional types in models against observational challenges of identifying and mapping them adequately. Modelling approaches to dealing with increasing functional diversity have been proposed, for example, using the complex adaptive systems theory and system of infinite diversity, as in the work of Bruggemann and Kooijman (2007). But it is unlikely that remote-sensing approaches might be able to deal with anything but a few prominent functional types. As long as these challenges are explicitly addressed, the functional- type concept should continue to fill a real need to capture, in an economic fashion, the diversity in phytoplankton, and remote sensing should continue to be a useful tool to map them. Remote sensing of phytoplankton functional types is an emerging field, whose potential is not fully realised, nor its limitations clearly established. In this report, we provide an overview of progress to date, examine the advantages and limitations of various methods, and outline suggestions for further development. The overview provided in this chapter is intended to set the stage for detailed considerations of remote-sensing applications in later chapters. In the next chapter, we examine various in situ methods that exist for observing phytoplankton functional types, and how they relate to remote-sensing techniques. In the subsequent chapters, we review the theoretical and empirical bases for the existing and emerging remote-sensing approaches; assess knowledge about the limitations, assumptions, and likely accuracy or predictive skill of the approaches; provide some preliminary comparative analyses; and look towards future prospects with respect to algorithm development, validation studies, and new satellite mis- sions

Book of Abstracts & Lead Articles The Second International Symposium Remote Sensing for Ecosystem Analysis and Fisheries

SAFARI (Societal Applications in Fisheries and Aquaculture using Remotely-Sensed Imagery) is an initiative which provides a forum for coordination, at the international level, of activities in global fisheries research and management. The forum is open to all interested parties, including policy makers, research scientists, government managers, and those involved in the fishing industries. SAFARI organizes international workshops and symposia as a platform to discuss the latest research in Earth observation and fisheries management, information sessions aimed at the fisheries industry, government officials and resource managers, representation at policy meetings, and producing publications relevant to the activities. SAFARI gains worldwide attention through collaboration with other international networks, such as ChloroGIN (Chlorophyll Global Integrated Network), IOCCG (International Ocean-Colour Coordinating Group), POGO (Partnership for Observation of the Global Oceans) and the oceans and society: Blue Planet Initiative of the intergovernmental organization, the Group on Earth Observations (GEO)

Inter-annual and decadal variation in the pelagic marine ecosystem of the Yellow and East China seas

The water-leaving radiance measurements and chlorophyll concentrations of the Coastal Zone Color Scanner (CZCS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) were compared to investigate decadal trends in the Yellow and East China Seas (YECS). A unified bio-optical algorithm was derived to convert CZCS pigments to SeaWiFS chlorophyll concentrations. The conversion is applied to level-2 CZCS data. We established monthly variations in the stratified and well-mixed areas using a coupled ocean wave-circulation model and the ocean color satellite data for estimating primary productivity in the Yellow Sea using satellite observations. The model results were compared with remotely sensed sea surface temperature and water-leaving radiance at 667nm derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) to develop a method to differentiate stratified and well-mixed waters using remote sensing data. We used and modified an existing primary productivity algorithm to estimate phytoplankton primary production using satellite data in the Yellow Sea. The Yellow Sea was first partitioned into three subregions based on the bathymetry and physical features to parameterize the algorithm. A local empirical chlorophyll algorithm was applied to derive more accurate chlorophyll concentration in the Yellow Sea and an approach was presented for estimating the diffuse attenuation coefficient. We investigated whether it was necessary to model the vertical biomass profile. Finally, the algorithm was applied to derive the primary production in the Yellow Sea. The primary production derived using the local algorithm was higher in the middle of the Yellow Sea in May and September than in the shallower (\u3c50 m) coastal areas. The low primary production in the coastal areas is caused by high turbidity due to strong tides and shallow depths. Lower turbidity in the middle of the Yellow Sea allows the light energy for primary production to penetrate to a deeper depth. Our computation of daily total primary production for the entire the Yellow Sea is 19.7 x 104 tonC d-1 in May and 15.8 x 10 4 tonC d-1 in September, and the annual total primary production in the Yellow Sea was 50.1 x 106 tonC yr-1. The resulting maps of primary production calculated from the remotely sensed data provide the first synoptic views of primary production in the Yellow Sea. (Abstract shortened by UMI.)

Are the world\u27s oceans optically different?

With satellite technology, the dynamics of oceanic photosynthesis can be analyzed on a global scale using remotely sensed estimates of chlorophyll concentration. Such work is dependent on the performance of empirical ocean color algorithms that produce the chlorophyll estimates. In hopes to understand the sources of algorithm uncertainty, the NASA bio-Optical Marine Algorithm Data set (NOMAD) was analyzed. The OC4v.4 algorithm estimates were compared to NOMAD\u27s in situ measurements, and a bias was apparent when the data were sorted by ocean (Atlantic, Pacific, and Southern). Several instrumental artifacts were found to be insignificant to the oceanic algorithm bias. Using a subset of NOMAD that contained absorption measurements with each observation, the oceanic bias was independently verified, and explained through differences in the concentration of non-algal organic matter and the phytoplankton community structure. Ultimately, the world\u27s oceans were found to be optically different as a result of differences in biogeochemical processes