Cyanobacterial blooms cause heating of the sea surface

Abstract

A series of AVHRR (Advanced Very High Resolution Radiometer) satellite images and simultaneous ship transects in July 1992 were used to show that surface accumulations of cyanobacteria (blue-green algae) in the southern Baltic Sea can cause local increases in the satellite-derived sea surface temperature (SST) by up to 1.5 'C. The warmer SST is attributed to increased absorption of sunlight due to increased phytoplankton pigment concentration. The distribution of surface cyanobacterial accumulations detected as increased reflectance in the visible channel of the AVHRR satellite sensor was correlated with chlorophyll concentration at 5 m depth. Warm SST anomalies ('hot spots') appeared both in accumulations of surface-floating cyanobacteria and in areas of high chlorophyll concentration (detected by shipboard measurements). The 'hot spots' followed the detailed boundaries of the cyanobacterial plumes and probably represented a shallow, diurnally heated top layer that appeared by afternoon in conditions of low wind (2 m ss1) and weak mixing, disappeared during the night due to thermal convection and were hardly detectable on days with wind speed of 6 to 8 m S -l . The vertical extension of the top diurnally heated layer was probably less than 1 m and definitely less than 5 m, at which depth no temperature increase was detected. It is suggested that the day/night SST difference in low-wind conditions may be an indicator of near-surface phytoplankton pigment concentration.

Seasonal Dynamics of Nutrient Loading and Chlorophyll A in a Northern Prairies Reservoir, Saskatchewan, Canada

“…This is in accordance with earlier studies that that found correlations between NDVI and surface cyanobacteria concentrations [36,37]. The overall distribution of algal biomass along the river from upstream to downstream locations could be clearly identified by satellite image analysis.…”

“…Thus, the VI was used as a surrogate and has been applied to indirectly estimate the spatial distribution of algal biomass. Two VIs were applied in this study, first the Normalized Difference Vegetation Index (NDVI) [36], which is defined as the normalized difference of brightness values indicating relative distribution and activity from the satellite image (Equation (1)). …”

Screening Assessment of Cyanobacteria and Cyanotoxins in Southern California Lentic Habitats

“…Our results also demonstrated a cut point of approximately 15 µg L -1 chlorophyll-a, above which cyanobacteria consistently dominated the phytoplankton assemblage. Thus, our results reinforce the concept that chlorophyll-a can be a meaningful screening variable for cyanoHABs, either through direct field measures or via remote sensing (Kahru et al 1993;Kahru 1997), and can be prioritized for more intensive field monitoring. ISSN 2164-7682 2015 www.macrothink.org/emsd 106 TN had the strongest linear relationship with chlorophyll-a and cyanobacterial cell counts, with the particulate and dissolved organic fraction driving the strength of the relationship, indicating that nutrients have been incorporated into cyanobacterial growth or were recycling as dissolved organic forms within the water column.…”

Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea) and its impact on trace metal concentrations in seawater

“…As soon as the wind abates, cyanobacteria float rapidly towards the surface due to their 'over-buoyancy' (Sellner, 1997). The surface accumulations are quickly dispersed over the water column by wind-induced mixing at wind speeds over 6e 8 m s À1 (Kahru et al, 1993). If the wind energy is not strong enough to redisperse the cells into the water column, cyanobacteria accumulate on the water surface as observed in the present study (Table 2).…”