Assessing the impact of climate change on phytoplankton in Fram Strait: 1. particle absorption properties from continuous measurements of spectral absorption attenuation sensor meter (AC-S)

The decline of ArcGc sea ice as well as its resulting feedbacks is asserted to have great impacts on the Arctic phytoplankton, and caused large regional variations in primary production range in the Arctic Ocean and its marginal seas. Understanding and quantifying such impacts are critical to appreciate the Arctic as a system and allow diagnostic modeling of its current status and dynamics. To assess the above impacts of reduction in sea ice and then the changes in physical properties on Arctic phytoplankton, numerical models have emerged as valuable tools. In order to generate reliable results, a high quality Arctic Chl-a dataset is essential to improve parameterizations in the coupled ice-ecosystem-ocean circulation models. With the emergency of autonomous platforms (e.g. floats (Argo), autonomous vehicles), high spatial and temporal resolution measurements of biooptical parameters are achievable. However, new challenges arise from the automated way of observing the bio-optical properties of the ocean. Indeed, conversely to what happens when the same kinds of equipment are operated from a ship, these bio-optical data are collected in environmental condiGons that are out of the operator’s control. Therefore, new specific data processing and management procedures have to be developed for in situ bio-optical sensors which generate high spatial and temporal resolution measurements of bio-optical data. In this study, analytical bio-optical techniques are applied to develop quality controlled high quality pan-Arctic long-term information on total biomass of phytoplankton. The quantitative distribution of phytoplankton will be determined on long time scales covering the Fram Strait in the Arctic Ocean by the integration of measurements from various platforms that enable to retrieve the total biomass of phytoplankton

High resolution water column phytoplankton composition across the Atlantic Ocean from ship-towed vertical undulating radiometry.

Different phytoplankton groups dominate ocean biomes and they drive differently the marine food web and the biogeochemical cycles. However, their distribution over most parts of the global ocean remains uncertain due to limitations in the sampling resolution of currently available in situ and satellite data. Information below surface waters are especially limited because satellite sensors only provide information on the first optical depth. We present measurements obtained during Polarstern cruise PS113 (May–June 2018) across the Atlantic Ocean from South America to Europe along numerous transects. We measured the hyperspectral underwater radiation field continuously over several hours from a vertical undulating platform towed behind the ship. Equivalent measurements were also taken at specific stations. The concentrations of phytoplankton pigments were determined on discrete water samples. Via diagnostic pigment analysis we derived the phytoplankton group chlorophyll a concentration (Chla) from this pigment data set. We obtained high resolution phytoplankton group Chla data from depth resolved apparent optical properties derived from the underwater radiation data by applying an empirical orthogonal function (EOF) analysis to the spectral data set and subsequently developing regression models using the pigment based phytoplankton group Chla and selected EOF modes. To our knowledge, this is the first data set with high horizontal coverage (50–150 km) and resolution (∼1 km) that is also resolved vertically for the Chla of major taxonomic phytoplankton groups. Subsampling with 500 permutations for cross validation verified the high robustness of our estimates to enable predictions of seven different phytoplankton groups’ Chla and of total Chla (R2 and median percent differences of the cross validation are within 0.45–0.68 and 29–53%, respectively). Our depth resolved phytoplankton groups’ Chla data reflect well the different biogeochemical provinces within the Atlantic Ocean transect and follow the distributions encountered by previous point observations. This verifies the high quality of our retrievals and provides the prospect to put similar radiometers on profiling floats or gliders which would enable the large-scale collection of vertically resolved phytoplankton data at much improved horizontal coverage relative to discrete sampling

Underway observations of inherent optical properties for the estimation of near-surface chlorophyll-a in the Fram Strait

Chlorophyll-a, the most important photosynthetic pigment of marine phytoplankton, is one of the basic marine biogeochemical variables. Chlorophyll-a concentration can be measured by applying high-performance liquid chromatography (HPLC) techniques to filtered water samples, which is greatly limited by time and number of samples. The inherent optical properties (IOPs) of seawater are proved to have good linkage to biogeochemical variables. With the emergency of in situ optical sensors, high spatial and temporal resolution measurements of bio-optical properties are achievable, making it possible to understand ocean biogeochemical processes on a broader scale. However, data quality control of the optical sensors remains challenging because of biofouling and the instrumental instability. In this study, we established a ship-based flow-through system of Absorption Attenuation Spectra Meter (AC-s) and conducted continuous underway measurements of hyperspectral IOPs during the PS93.2 expedition to the Fram Strait. The system collected periodical measurements of total and 0.2 μm cartridge filtered absorption and attenuation, allowing for the calculation of particulate absorption and attenuation by differencing the corresponding IOPs of the total and filtered seawater. The continuous particulate absorption coefficients were then averaged to 1-min intervals, compared and corrected with discrete filter-pad measurements. The near-surface phytoplankton Chlorophyll-a concentrations were finally retrieved from the quality controlled hyperspectral particulate absorption based on empirical orthogonal functions in the Fram Strait

Underway spectrophotometry in the Fram Strait (European Arctic Ocean): a highly resolved chlorophyll a data source for complementing satellite ocean color

Satellite remote sensing of chlorophyll a concentration (Chl-a) in the Arctic Ocean is spatially and temporally limited and needs to be supplemented and validated with substantial volumes of in situ observations. Here, we evaluated the capability of obtaining highly resolved in situ surface Chl-a using underway spectrophotometry operated during two summer cruises in 2015 and 2016 in the Fram Strait. Results showed that Chl-a measured using high pressure liquid chromatography (HPLC) was well related (R2 = 0.90) to the collocated particulate absorption line height at 676 nm obtained from the underway spectrophotometry system. This enabled continuous surface Chl-a estimation along the cruise tracks. When used to validate Chl-a operational products as well as to assess the Chl-a algorithms of the aqua moderate resolution imaging spectroradiometer (MODIS-A) and Sentinel-3 Ocean Land Color Imager (OLCI) Level 2 Chl-a operational products, and from OLCI Level 2 products processed with Polymer atmospheric correction algorithm (version 4.1), the underway spectrophotometry based Chl-a data sets proved to be a much more sufficient data source by generating over one order of magnitude more match-ups than those obtained from discrete water samples. Overall, the band ratio (OCI, OC4) Chl-a operational products from MODIS-A and OLCI as well as OLCI C2RCC products showed acceptable results. The OLCI Polymer standard output provided the most reliable Chl-a estimates, and nearly as good results were obtained from the OCI algorithm with Polymer atmospheric correction method. This work confirms the great advantage of the underway spectrophotometry in enlarging in situ Chl-a data sets for the Fram Strait and improving satellite Chl-a validation and Chl-a algorithm assessment over discrete water sample analysis in the laboratory

Towards Cost-Effective Operational Monitoring Systems for Complex Waters: Analyzing Small-Scale Coastal Processes with Optical Transmissometry

21 pages, 13 figures, 1 table, data availability https://doi.org/10.1594/PANGAEA.863589The detection and prediction of changes in coastal ecosystems require a better understanding of the complex physical, chemical and biological interactions, which involves that observations should be performed continuously. For this reason, there is an increasing demand for small, simple and cost-effective in situ sensors to analyze complex coastal waters at a broad range of scales. In this context, this study seeks to explore the potential of beam attenuation spectra, c(λ), measured in situ with an advanced-technology optical transmissometer, for assessing temporal and spatial patterns in the complex estuarine waters of Alfacs Bay (NW Mediterranean) as a test site. In particular, the information contained in the spectral beam attenuation coefficient was assessed and linked with different biogeochemical variables. The attenuation at λ = 710 nm was used as a proxy for particle concentration, TSM, whereas a novel parameter was adopted as an optical indicator for chlorophyll a (Chla) concentration, based on the local maximum of c(λ) observed at the long-wavelength side of the red band Chl-a absorption peak. In addition, since coloured dissolved organic matter (CDOM) has an important influence on the beam attenuation spectral shape and complementary measurements of particle size distribution were available, the beam attenuation spectral slope was used to analyze the CDOM content. Results were successfully compared with optical and biogeochemical variables from laboratory analysis of collocated water samples, and statistically significant correlations were found between the attenuation proxies and the biogeochemical variables TSM, Chl-a and CDOM. This outcome depicted the potential of high-frequency beam attenuation measurements as a simple, continuous and cost-effective approach for rapid detection of changes and patterns in biogeochemical properties in complex coastal environmentsThis study was supported by the Spanish Ministry of Economy and Competitiveness (MESTRAL project, CTM2011-30489-C02-01) and by Total Foundation (PHYTOSCOPE project). MR-P was supported by a PhD fellowship from the Spanish Ministry of Economy and Competitiveness (grants: BES-2012-054205 and EEBB-I-2014-08231). RG-A was supported by a PhD fellowship from the Coordination for the Improvement of Higher Level Personnel (CAPES-Brazil, grant 12362/12-3) in collaboration with the German Academic Exchange Service (DAAD)Peer Reviewe

Towards cost-effective operational monitoring systems for complex waters: analyzing small-scale coastal processes with optical transmissometry.

The detection and prediction of changes in coastal ecosystems require a better understanding of the complex physical, chemical and biological interactions, which involves that observations should be performed continuously. For this reason, there is an increasing demand for small, simple and cost-effective in situ sensors to analyze complex coastal waters at a broad range of scales. In this context, this study seeks to explore the potential of beam attenuation spectra, c(λ), measured in situ with an advanced-technology optical transmissometer, for assessing temporal and spatial patterns in the complex estuarine waters of Alfacs Bay (NW Mediterranean) as a test site. In particular, the information contained in the spectral beam attenuation coefficient was assessed and linked with different biogeochemical variables. The attenuation at λ = 710 nm was used as a proxy for particle concentration, TSM, whereas a novel parameter was adopted as an optical indicator for chlorophyll a (Chl-a) concentration, based on the local maximum of c(λ) observed at the long-wavelength side of the red band Chl-a absorption peak. In addition, since coloured dissolved organic matter (CDOM) has an important influence on the beam attenuation spectral shape and complementary measurements of particle size distribution were available, the beam attenuation spectral slope was used to analyze the CDOM content. Results were successfully compared with optical and biogeochemical variables from laboratory analysis of collocated water samples, and statistically significant correlations were found between the attenuation proxies and the biogeochemical variables TSM, Chl-a and CDOM. This outcome depicted the potential of high-frequency beam attenuation measurements as a simple, continuous and cost-effective approach for rapid detection of changes and patterns in biogeochemical properties in complex coastal environments

Importance of deep mixing and silicic acid in regulating phytoplankton biomass and community in the iron-limited Antarctic Polar Front region in summer

En prens