4D IOPs profiles of upper 70 m layer of the Black Sea: bio-argo floats and ocean color satellite products

The deep chlorophyll maximum (DCM) is a well known feature of the global ocean. However, its description and the study of its formation are a&#160; challenge, especially in the peculiar environment that is the Black Sea. The retrieval of chlorophyll a (Chla) from fluorescence (Fluo) profiles recorded by biogeochemical-Argo (BGC-Argo) floats is not trivial in the Black Sea, due to the very high content of colored dissolved organic matter (CDOM) which contributes to the fluorescence signal and produces an apparent increase of the Chla concentration with depth.Here, we revised Fluo correction protocols for the Black Sea context using co-located in-situ high-performance liquid chromatography (HPLC) and BGC-Argo measurements. The processed set of Chla data (2014&#8211;2019) is then used to provide a systematic description of the seasonal DCM dynamics in the Black Sea and to explore different hypotheses concerning the mechanisms underlying its development.Our results show that the corrections applied to the Chla profiles are consistent with HPLC data. In the Black Sea, the DCM begins to form in March, throughout the basin, at a density level set by the previous winter mixed layer. During a first phase (April-May), the DCM remains attached to this particular layer. The spatial homogeneity of this feature suggests a hysteresis mechanism, i.e., that the DCM structure locally influences environmental conditions rather than adapting instantaneously to external factors.In a second phase (July-September), the DCM migrates upward, where there is higher irradiance, which suggests the interplay of biotic factors. Overall, the DCM concentrates around 45 to 65% of the total chlorophyll content within a 10 m layer centered around a depth of 30 to 40 m, which stresses the importance of considering DCM dynamics when evaluating phytoplankton productivity at basin scale.

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Dynamics of the Deep Chlorophyll Maximum in the Black Sea as depicted by BGC-Argo floats

10.5194/bg-2020-295 ◽

2020 ◽

Author(s):

Florian Ricour ◽

Arthur Capet ◽

Fabrizio D'Ortenzio ◽

Bruno Delille ◽

Marilaure Grégoire

Keyword(s):

Black Sea ◽

High Performance ◽

Global Ocean ◽

The Black Sea ◽

Fluorescence Signal ◽

Deep Chlorophyll Maximum ◽

Lateral Loads ◽

Spatial Homogeneity ◽

Argo Floats ◽

Chlorophyll Maximum

Abstract. The Deep Chlorophyll Maximum (DCM) is a well known feature of the global ocean. However, its description and the study of its formation are a challenge, especially in the peculiar Black Sea environment. The retrieval of Chlorophyll a (Chla) from fluorescence (Fluo) profiles recorded by Biogeochemical-Argo (BGC-Argo) floats is not trivial in the Black Sea, due to the very high content of Colored Dissolved Organic Matter (CDOM) which contributes to the fluorescence signal and produces an apparent increase of the Chla concentration with depth. Here we revised Fluo correction protocols for the Black Sea context using co-located in-situ High-Performance Liquid Chromatography (HPLC) and BGC-Argo measurements. The processed set of Argo Chla data (2014–2019) is then used to provide a systematic description of the seasonal DCM dynamics in the Black Sea, and to explore different hypotheses concerning the mechanisms underlying its development. Our results show that the corrections applied to Chla profiles are consistent with HPLC data. In the Black Sea, the DCM is initiated in March, throughout the basin, at a pycnal level set by the previous winter mixed layer. The DCM then remains attached to this particular layer until the end of September. The spatial homogeneity of this feature suggests a self-sustaining DCM structure, locally influencing environmental conditions rather than adapting instantaneously to external factors. In summer, the DCM concentrates around 50 to 65 % of the total chlorophyll content around a depth of 30 m, where light conditions ranged from 0.5 to 4.5 % of surface incoming irradiance. In October, as the DCM structure is gradually eroded, a longitudinal gradient appears in the DCM pycnal depth, indicating that autumnal mixing induces a relocation of the DCM which is this time driven by regional factors, such as nutrients lateral loads and turbidity.

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Regional empirical algorithm for an improved retrieval of chlorophyll a concentrations in the Black Sea using Sentinel 3 ocean color data

10.5194/egusphere-egu21-1743 ◽

2021 ◽

Author(s):

Violeta Slabakova ◽

Snejana Moncheva ◽

Nataliya Slabakova ◽

Nina Dzembekova

Keyword(s):

Remote Sensing ◽

Chlorophyll A ◽

Black Sea ◽

Ocean Color ◽

The Black Sea ◽

Ocean Color Remote Sensing ◽

Color Data ◽

Cubic Polynomial ◽

Polynomial Formulation

The Black Sea is an extraordinarily complex water body for ocean color remote sensing, as it belong to Case 2 waters, which are characterized by relatively high absorption by Colored Dissolved Organic Matter (CDOM) while the concentration of non-pigmented particulate matter does not co-vary in a predictable manner with chlorophyll a . The optical complexity of the Black Sea is the reason why the standard bio-optical algorithms developed for Case 1 waters, are the source of large uncertainties (of the order of hundreds of percent) of chlorophyll a concentration in the coastal and shelf regions. In the framework of ESA contract &#8220;BIO-OPTICS FOR OCEAN COLOR REMOTE SENSING OF THE BLACK SEA - Black Sea Color&#8221; we developed empirical ocean color algorithm for chlorophyll a retrieval from Sentinel 3A/OLCI primary ocean color products using the in situ reference bio-optical datasets collected in the Black Sea in the period 2012-2019. Results obtained from the assessment of operational S3A/OLCI chlorophyll products, highlighted and confirmed that the specific regional algorithm is essential for the Black Sea. The coefficients of the regional algorithm were derived from the regression of log-transformed pigment concentrations and remote sensing reflectance ratio at 490nm and 560 nm with determination coefficient R2 =0.88 and number of samples N=186. The algorithm predicts chlorophyll a values using a cubic polynomial formulation. The result of assessment of the regional chlorophyll a product against independent in situ measurements from the data utilized for algorithm development, showed relatively high accuracy (31.7%), fewer underestimations (MPD=-9.2%) and a good agreement (R2=0.66) between datasets indicating that the regional algorithm is more effective in reproducing the&#160; pigment concentration in the Black Sea waters in comparison to the standard Sentinel 3A/OLCI algorithms. Our analysis revealed the importance of providing regional algorithms strictly required to suit the peculiar bio-optical properties featuring this basin. However, this requires collection of accurate in situ measurements in the different parts of the Black Sea. The validity of the reported empirical algorithm obviously depends on the size of the dataset used for its development. The Black Sea waters vary at a basin level due to the sub-regional features, environmental factors and seasonal variability, consequently the presented regional algorithm might have a limited generalization capability. Clearly, more in situ data with improved spatial and temporal coverage are critically needed for further calibration and validation of the ocean color products in the Black Sea.

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Photosynthetically available radiation on surface of the Black Sea based on ocean color data

10.1117/12.2203660 ◽

2015 ◽

Cited By ~ 7

Author(s):

V. V. Suslin ◽

S. N. Korolev ◽

A. A. Kucheryaviy ◽

T. Ya. Churilova ◽

O. V. Krivenko

Keyword(s):

Black Sea ◽

Ocean Color ◽

The Black Sea ◽

Photosynthetically Available Radiation ◽

Color Data

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Dynamics of the deep chlorophyll maximum in the Black Sea as depicted by BGC-Argo floats

Biogeosciences ◽

10.5194/bg-18-755-2021 ◽

2021 ◽

Vol 18 (2) ◽

pp. 755-774

Author(s):

Florian Ricour ◽

Arthur Capet ◽

Fabrizio D'Ortenzio ◽

Bruno Delille ◽

Marilaure Grégoire

Keyword(s):

Black Sea ◽

Global Ocean ◽

The Black Sea ◽

Second Phase ◽

Deep Chlorophyll Maximum ◽

Phytoplankton Productivity ◽

Chl A ◽

Argo Floats ◽

Chlorophyll Maximum ◽

Basin Scale

Abstract. The deep chlorophyll maximum (DCM) is a well-known feature of the global ocean. However, its description and the study of its formation are a challenge, especially in the peculiar environment that is the Black Sea. The retrieval of chlorophyll a (chl a) from fluorescence (Fluo) profiles recorded by Biogeochemical Argo (BGC-Argo) floats is not trivial in the Black Sea, due to the very high content of coloured dissolved organic matter (CDOM) which contributes to the fluorescence signal and produces an apparent increase in the chl a concentration with depth. Here, we revised Fluo correction protocols for the Black Sea context using co-located in situ high-performance liquid chromatography (HPLC) and BGC-Argo measurements. The processed set of chl a data (2014–2019) is then used to provide a systematic description of the seasonal DCM dynamics in the Black Sea and to explore different hypotheses concerning the mechanisms underlying its development. Our results show that the corrections applied to the chl a profiles are consistent with HPLC data. In the Black Sea, the DCM begins to form in March, throughout the basin, at a density level set by the previous winter mixed layer. During a first phase (April–May), the DCM remains attached to this particular layer. The spatial homogeneity of this feature suggests a hysteresis mechanism, i.e. that the DCM structure locally influences environmental conditions rather than adapting instantaneously to external factors. In a second phase (July–September), the DCM migrates upward, where there is higher irradiance, which suggests the interplay of biotic factors. Overall, the DCM concentrates around 45 % to 65 % of the total chlorophyll content within a 10 m layer centred around a depth of 30 to 40 m, which stresses the importance of considering DCM dynamics when evaluating phytoplankton productivity at basin scale.

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Assessment of Applicability of Satellite-Derived Ocean Color Data for Studying Variability of Total Suspended Matter in the Surface Layer of the Deep Part of the Black Sea

Physical Oceanography ◽

10.22449/1573-160x-2020-5-547-556 ◽

2020 ◽

Vol 27 (5) ◽

Author(s):

A. S. Kukushkin ◽

V. V. Suslin ◽

Keyword(s):

Surface Layer ◽

Black Sea ◽

Suspended Matter ◽

Temporal Variability ◽

Ocean Color ◽

Total Suspended Matter ◽

The Black Sea ◽

Backscattering Coefficient ◽

Color Data

Purpose. Studies of spatial-temporal variability of total suspended matter are necessary for understanding the biochemical processes which form and support stable functioning of a marine ecosystem. The aim of the work is to assess applicability of satellite data for studying total suspended matter variability in the surface layer of the deep part of the Black Sea. Methods and Results. Application of the regression analysis yielded the linear regression equations that unite the in situ measurements of the total suspended matter concentrations in the surface layer in the northeastern (June, 2005–2015) and western (November, 2016, 2017 and December, 2017) deep sea areas, and the regional satellite products (the particulate backscattering coefficient, the absorption coefficient of colored detrital matter and the chlorophyll a concentration). Based on the measured and calculated data arrays, the maps of the total suspended matter concentrations in the surface layer of the northeastern Black Sea were constructed. The interannual changes in the in situ measured concentrations of the total suspended and lithogenic matters, as well as in the quasi-synchronous satellite regional products (the light absorption coefficient of colored detrital matter at 490 nm and the particulate backscattering coefficient at 555 nm) in June, 2005–2015 were considered. High total suspended matter concentrations were noted in 2012, just when extreme growth of the coccolithophorid population was observed in the Black Sea. The correlation coefficients were used to evaluate whether the relation between the total suspended matter concentration and the individual analyzed parameters was fast. Conclusions. Spatial distributions of the measured and calculated total suspended matter contents showed satisfactory agreement. In course of the whole observation period, difference between the values of the measured and calculated total suspended matter concentrations was on average 6–23 %. Possibility of application of the satellite-derived ocean color data for studying spatial-temporal variability of the total suspended matter content is shown.

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