Improved determination of particulate absorption from combined filter pad and PSICAM measurements

Filter pad light absorption measurements are subject to two major sources of experimental uncertainty: the so-called pathlength amplification factor, β, and scattering offsets, o, for which previous null-correction approaches are limited by recent observations of non-zero absorption in the near infrared (NIR). A new filter pad absorption correction method is presented here which uses linear regression against point-source integrating cavity absorption meter (PSICAM) absorption data to simultaneously resolve both β and the scattering offset. The PSICAM has previously been shown to provide accurate absorption data, even in highly scattering waters. Comparisons of PSICAM and filter pad particulate absorption data reveal linear relationships that vary on a sample by sample basis. This regression approach provides significantly improved agreement with PSICAM data (3.2% RMS%E) than previously published filter pad absorption corrections. Results show that direct transmittance (T-method) filter pad absorption measurements perform effectively at the same level as more complex geometrical configurations based on integrating cavity measurements (IS-method and QFT-ICAM) because the linear regression correction compensates for the sensitivity to scattering errors in the T-method. This approach produces accurate filter pad particulate absorption data for wavelengths in the blue/UV and in the NIR where sensitivity issues with PSICAM measurements limit performance. The combination of the filter pad absorption and PSICAM is therefore recommended for generating full spectral, best quality particulate absorption data as it enables correction of multiple errors sources across both measurements

Estimation of suspended matter, organic carbon and chlorophyll-A concentrations estimation from particle size and refractive index distributions

Models of particle density and of organic carbon and chlorophyll-a intraparticle concentration were applied to particle size distributions and particle real refractive index distributions determined from flow cytometry measurements of natural seawater samples from a range of UK coastal waters. The models allowed for the estimation of suspended particulate matter, organic suspended matter, inorganic suspended matter, particulate organic carbon, and chlorophyll-a concentrations. These were then compared with independent measurements of each of these parameters. Particle density models were initially applied to a simple spherical model of particle volume, but generally overestimated independently measured values, sometimes by over two orders of magnitude. However, when the same density models were applied to a fractal model of particle volume, successful agreement was reached for suspended particulate matter and both inorganic and organic suspended matter values (RMS%E: 57.4, 148.5, and 83.1% respectively). Non-linear organic carbon and chlorophyll-a volume scaling models were also applied to a spherical model of particle volume, and after an optimization procedure achieved successful agreement with independent measurements of particulate organic carbon and chlorophyll-a concentrations (RMS%E: 45.6% and 51.8% respectively). Refractive index-based models of carbon and chlorophyll-a intraparticle concentration were similarly tested, and were also found to require a fractal model of particle volume to achieve successful agreement with independent measurements, producing RMS%E values of 50.2% and 45.2% respectively after an optimization procedure. It is further shown that the non-linear exponents of the volume scaling models are mathematically equivalent to the fractal dimensionality coefficients that link cell volume to mass concentration, reflecting the impact of non-uniform distribution of intracellular carbon within cells. Fractal models of particle volume are thus found to be essential to successful closure between results provided by models of particle mass, intraparticle carbon and chlorophyll content, and bulk measurements of suspended mass and total particulate carbon and chlorophyll when natural mixed particle populations are concerned. The results also further confirm the value of determining both size and refractive index distributions of natural particle populations using flow cytometry

Eddy Study to Understand Physical-Chemical-Biological Coupling and the Biological Carbon Pump as a Function of Eddy Type off West Africa, Cruise No. M160, 23.11.2019 - 20.12.2019, Mindelo (Cabo Verde) - Mindelo (Cabo Verde)

Cruise M160 is part of concerted MOSES/REEBUS Eddy Study featuring three major research expeditions (M156, M160, MSM104). It aims to develop both a qualitative and quantitative understanding of the role of physical-chemical-biological coupling in eddies for the biological pump. The study is part of the MOSES “Ocean Eddies” event chain, which follows three major hypotheses to be addressed by the MOSES/REEBUS field campaigns: (1) Mesoscale and sub-mesoscale eddies play an important role in transferring energy along the energy cascade from the large-scale circulation to dissipation at the molecular level. (2) Mesoscale and sub-mesoscale eddies are important drivers in determining onset, magnitude and characteristics of biological productivity in the ocean and contribute significantly to global primary production and particle export and transfer to the deep ocean. (3) Mesoscale and sub-mesoscale eddies are important for shaping extreme biogeochemical environments (e.g., pH, oxygen) in the oceans, thus acting as a source/sink function for greenhouse gases. In contrast to the other two legs, MOSES Eddy Study II during M160 did not include any benthic work but focused entirely on the pelagic dynamics within eddies. It accomplished a multi-disciplinary, multi-parameter and multi-platform study of two discrete cyclonic eddies in an unprecedented complexity. The pre-cruise search for discrete eddies suitable for detailed study during M160 had already started a few months prior to the cruise. Remote sensing data products (sea surface height, sea surface temperature, ocean color/chlorophyll a) were used in combination with eddy detection algorithms and numerical modelling to identify and track eddies in the entire eddy field off West Africa. In addition, 2 gliders and 1 waveglider had been set out from Mindelo/Cabo Verde for pre-cruise mapping of the potential working area north of the Cabo Verdean archipelago. At the start of M160, a few suitable eddies – mostly of cyclonic type – had been identified, some of which were outside the safe operation range of the motorglider plane. As technical problems delayed the flight operations, the first eddy (center at 14.5°N/25°W) for detailed study was chosen to the southwest of the island of Fogo. It was decided to carry out a first hydrographic survey there followed by the deployment of a suite of instruments (gliders, waveglider, floats, drifter short-term mooring). Such instrumented, we left this first eddy and transited – via a strong anticyclonic feature southwest of the island of Santiago – to the region northeast of the island of Sal, i.e. in the working range of the glider plane. During the transit, a full suite of underway measurements as well as CTD/RO section along 22°W (16°-18.5°N) were carried in search for sub-surface expressions of anticyclonic eddy features. In the northeast, we had identified the second strong cyclonic eddy (center at 18°N/22.5°W) which was chosen for detailed study starting with a complete hydrographic survey (ADCP, CTD/RO, other routine station work). After completion of the mesoscale work program, we identified a strong frontal region at the southwestern rim of the cyclonic eddy, which was chosen for the first sub-mesoscale study with aerial observation component. There, the first dye release experiment was carried out which consisted of the dye release itself followed by an intense multi-platforms study of the vertical and horizontal spreading of the initial dye streak. This work was METEOR-Berichte, Cruise M160, Mindelo – Mindelo, 23.11.2019 4 – 20.12.2019 supported and partly guided by aerial observation of the research motorglider Stemme, which was still somewhat compromised by technical issues and meteorological conditions (high cloud cover, Saharan dust event). Nevertheless, this first dye release experiment was successful and showed rapid movement of the dynamic meandering front. After completion of work on this second eddy and execution of a focused sampling program at the Cape Verde Ocean Observation, RV METEOR returned to the first eddy for continuation of the work started there in the beginning of the cruise. This was accompanied by a relocation of the airbase of Stemme from the international airport of Sal to the domestic airport of Fogo. The further execution of the eddy study at this first eddy, which again included a complete hydrographic survey followed by a mesoscale eddy study with dye release, was therefore possible with aerial observations providing important guidance for work on RV METEOR. Overall, M160 accomplished an extremely intense and complex work program with 212 instrument deployments during station work, 137 h of observation with towed instruments and a wide range of underway measurements throughout the cruise. Up to about 30 individually tracked platforms (Seadrones, glider, wavegliders, drifters, floats) were in the water at the same time providing unprecedented and orchestrated observation capabilities in an eddy. All planned work components were achieved and all working groups acquired the expected numbers of instrument deployments and sampling opportunities

Chlorophyll a fluorescence measured from water bottle samples during METEOR cruise M160

This dataset includes measured and calculated data over the epi-mesopelagic layer (0-450 m depth) of 29 stations with 4 stations within a cyclonic eddy nearby Brava island, 5 stations within a cyclonic eddy nearby Sal island, and one station within an anticyclonic eddy around the Cabo Verde islands in the eastern Tropical North Atlantic during the M160 cruise on the RV Meteor from November 22nd to December 20th, 2019. Chlorophyll−a was determined from a modified version of the method described in Garrido et al. (2003). The concentration of Chl−a was determined by separation through HPLC and was detected fluorometrically (Shimadzu)

Water inherent optical properties and concentrations of water constituents from the German Bight and adjacent regions: spectral data of the phytoplankton light absorption coefficient

A regional data set of water constituent concentrations and inherent optical properties (light absorption and scattering coefficient) for the German Bight and adjacent waters (River Elbe, North Sea, UK waters, and Southern Norwegian Sea) is presented. The data provide high quality results of in situ measurements and laboratory analysis of samples taken at sea, mainly from the mixed layer, during the years 2008 to 2021. Parameters of the water constituents include concentrations of chlorophyll a, particulate organic and dissolved organic carbon (POC, DOC), total suspended matter (TSM), organic suspended matter (OSM) together with water depth, temperature, salinity, and turbidity. Inherent optical properties (IOPs) are given spectrally as light attenuation, scattering and absorption coefficients. This includes coefficients of light attenuation by all non-water matter (cgp) and particulate matter alone (cp), light absorption by all non-water matter (agp), particulate (ap) and dissolved matter (Gelbstoff, ag), non-algal matter (anap) and phytoplankton (aph), and total scattering (bp) and backscattering (bbp) by particulate matter. The combination of concentrations and IOPS is used to determine specific IOPs of German Bight water and in optical modelling of coastal waters to interpret surface reflectance spectra like in satellite remote sensing approaches

Water inherent optical properties and concentrations of water constituents from the German Bight and adjacent regions: spectral data of the dissolved fraction light absorption coefficient (CDOM)

A regional data set of water constituent concentrations and inherent optical properties (light absorption and scattering coefficient) for the German Bight and adjacent waters (River Elbe, North Sea, UK waters, and Southern Norwegian Sea) is presented. The data provide high quality results of in situ measurements and laboratory analysis of samples taken at sea, mainly from the mixed layer, during the years 2008 to 2021. Parameters of the water constituents include concentrations of chlorophyll a, particulate organic and dissolved organic carbon (POC, DOC), total suspended matter (TSM), organic suspended matter (OSM) together with water depth, temperature, salinity, and turbidity. Inherent optical properties (IOPs) are given spectrally as light attenuation, scattering and absorption coefficients. This includes coefficients of light attenuation by all non-water matter (cgp) and particulate matter alone (cp), light absorption by all non-water matter (agp), particulate (ap) and dissolved matter (Gelbstoff, ag), non-algal matter (anap) and phytoplankton (aph), and total scattering (bp) and backscattering (bbp) by particulate matter. The combination of concentrations and IOPS is used to determine specific IOPs of German Bight water and in optical modelling of coastal waters to interpret surface reflectance spectra like in satellite remote sensing approaches

Water inherent optical properties and concentrations of water constituents from the German Bight and adjacent regions: spectral data of the particulate light absorption coefficient

A regional data set of water constituent concentrations and inherent optical properties (light absorption and scattering coefficient) for the German Bight and adjacent waters (River Elbe, North Sea, UK waters, and Southern Norwegian Sea) is presented. The data provide high quality results of in situ measurements and laboratory analysis of samples taken at sea, mainly from the mixed layer, during the years 2008 to 2021. Parameters of the water constituents include concentrations of chlorophyll a, particulate organic and dissolved organic carbon (POC, DOC), total suspended matter (TSM), organic suspended matter (OSM) together with water depth, temperature, salinity, and turbidity. Inherent optical properties (IOPs) are given spectrally as light attenuation, scattering and absorption coefficients. This includes coefficients of light attenuation by all non-water matter (cgp) and particulate matter alone (cp), light absorption by all non-water matter (agp), particulate (ap) and dissolved matter (Gelbstoff, ag), non-algal matter (anap) and phytoplankton (aph), and total scattering (bp) and backscattering (bbp) by particulate matter. The combination of concentrations and IOPS is used to determine specific IOPs of German Bight water and in optical modelling of coastal waters to interpret surface reflectance spectra like in satellite remote sensing approaches

Water inherent optical properties and concentrations of water constituents from the German Bight and adjacent regions: spectral data of the total non-water light absorption coefficient

A regional data set of water constituent concentrations and inherent optical properties (light absorption and scattering coefficient) for the German Bight and adjacent waters (River Elbe, North Sea, UK waters, and Southern Norwegian Sea) is presented. The data provide high quality results of in situ measurements and laboratory analysis of samples taken at sea, mainly from the mixed layer, during the years 2008 to 2021. Parameters of the water constituents include concentrations of chlorophyll a, particulate organic and dissolved organic carbon (POC, DOC), total suspended matter (TSM), organic suspended matter (OSM) together with water depth, temperature, salinity, and turbidity. Inherent optical properties (IOPs) are given spectrally as light attenuation, scattering and absorption coefficients. This includes coefficients of light attenuation by all non-water matter (cgp) and particulate matter alone (cp), light absorption by all non-water matter (agp), particulate (ap) and dissolved matter (Gelbstoff, ag), non-algal matter (anap) and phytoplankton (aph), and total scattering (bp) and backscattering (bbp) by particulate matter. The combination of concentrations and IOPS is used to determine specific IOPs of German Bight water and in optical modelling of coastal waters to interpret surface reflectance spectra like in satellite remote sensing approaches