Quantifying effects of phytoplankton on the heat budgets of two large limnetic enclosures

Abstract

1. The aestival heat budgets of two large limnetic enclosures within a small lake in the English Lake District were studied. During summer, these enclosures had different nutrient supplies and consequently different phytoplankton populations. 2. As initial temperature profiles were similar and the incoming surface heat and momentum fluxes for the two enclosures were identical, subsequent changes in the heat budget were assumed to be induced by the biological differences between the enclosures. The proposed mechanism is an increased surface absorption of solar radiation leading to extra surface warming and a consequent excess loss of heat to the atmosphere through long-wave emittance and sensible and latent heat fluxes, conservatively estimated to be of the order of 10-30 W m )2 . 3. Theoretical calculations show that potential effects on a heat budget could be considerably larger than those observed here. The inherent non-linearity of the heat fluxes implies that such effects will be more important in warmer lakes than in colder ones. 4. Thermocline depth and strength were also altered by the response to differences in phytoplankton. 5. Any changes in climate or in nutrient loading from the catchment which substantially affect abundance or timing of phytoplankton populations in a lake will consequently also change the thermal structure of the lake.

HESS Opinions "Biological catalysis of the hydrological cycle: life's thermodynamic function"

“…which is consistent with the measurements of Jones et al (2005) who find maximum increases in surface temperatures of approximately 1.5 • C for induced phytoplankton blooms. The percentage increase in evaporation rate is, therefore,…”

“…One important exception is Jones et al (2005) who have determined that phytoplankton can, through increased photon absorption, increase surface temperatures and therefore the outgoing latent heat flux of a lake. Irrespective of other factors such as wind speed and humidity, evaporation rates should at least correlate with the amount of solar radiation absorbed in the sea-surface layer.…”

“…By absorbing and dissipating UV and visible light on the surface of oceans and lakes, life therefore augments the entropy production of the Earth in its solar environment. Without life at the surface, a greater portion of light would be reflected, increasing the albedo of Earth (Clarke et al, 1970, give measurements for the reduction of water albedo at different frequencies due to the presence of organic material), and light would penetrate deeper into the ocean, thereby augmenting the overall bulk black-body temperature of the ocean (see, for example, Jones et al, 2005 for the effect of phytoplankton on the temperature profile with depth for a lake). Both effects reduce the entropy production of Earth; greater albedo reduces the amount of available light to dissipate, and penetration of light to greater depth shifts the radiated spectrum (day + night integrated) to shorter wavelengths (see Eq.…”

Thermodynamic dissipation theory for the origin of life

“…Cyanobacterial blooms have been shown to cause considerable additional heating of the sea-surface (Kahru et al, 1993). The effect of a nutrient enriched phytoplankton bloom on the energy exchange at the surface of a lake has been quantified by Jones et al (2005). They found a 1.8 K increase in the daytime surface temperature of the lake.…”

“…Bacterial lysing by viruses augments the production of cyanobacteria and other phytoplankton by cycling through necessary nutrients such as phosphor and nitrogen (Wommack and Colwell, 2000;and references therein). This floating organic material, in effect, increases the absorption and dissipation of sunlight at the surface of lakes and oceans today (Jones et al, 2005;Michaelian, 2010a).…”