Primary Production: Sensitivity to Surface Irradiance and Implications for Archiving Data

Abstract

An equation is derived to express the sensitivity of daily, watercolumn production by phytoplankton in the ocean to variations in irradiance at the sea surface. Assuming no spectral effects, and a vertically uniform chlorophyll profile, the sensitivity is a function only of the dimensionless irradiance. Spectral effects can be accounted for as a function of the chlorophyll concentration. At the global scale, the relative reduction in daily production consequent on halving the surface irradiance (representing the expected scope for variation in surface irradiance under natural conditions) is found to be from 30 to 40%. Choice of data source for irradiance may incur a further systematic error of up to 15%. Given that local irradiance (the principal forcing for primary production) may vary from day to day, the issue of how to archive production data for the most generality is discussed and recommendations made in this regard.

A 55-Year Time Series Station for Primary Production in the Adriatic Sea: Data Correction, Extraction of Photosynthesis Parameters and Regime Shifts

“…The light grey curve represents P Z,T calculated with the climatological noon irradiance, and the dark grey curve represents P Z,T calculated with half the climatological noon irradiance. This reduction represents the effect of cloud cover [15] and as such gives the lower limit on production that would be achieved by using remotely-sensed chlorophyll. In principle, cloud cover removes the direct component of solar radiation, leaving only the diffuse component, which corresponds to a reduction of about 50% in total irradiance.…”

“…Therefore, by keeping the same chlorophyll and reducing light intensity in such a way, the effect of cloud cover on primary production was simulated. Following Platt et al [15], these two calculations represent the possible range of water column production that can be calculated from climatological data on irradiance.…”

“…When deciding on in situ incubation time, an important factor that needs to be taken into account is the competing assignments that the ship may be required to perform [15], and usually (when the incubation line is tethered to the ship), a compromise has to be made between ideal incubation time and the time required to execute such other duties. Complementary to in situ, two alternative implementations of the 14 C method are available that do not affect ship time: phytoplankton incubated on deck under controlled light conditions, typically during shorter incubation intervals [16] or phytoplankton incubated on deck under simulated light conditions [17].…”

Comparação entre estimativas de taxas de produção primária no canal de São Sebastião e a influência das condições oceanográficas

“…Esta situação leva à fotoinibição, sendo que esta depende da profundidade em que a célula se encontra, o horário do dia, da região, estação do ano e o grupo taxonômico do fitoplâncton (Platt et al, 1981, Platt et al, 2017.…”

“…Os resultados do presente trabalho indicam, como esperado (Ciotti et al, 2018 (Platt et al, 1981;Platt et al, 2017). Uma vez que o método não considera o processo de fotoinibição, nestes casos, pode haver superestimava da PP em relação ao método de referência (PPB), em ambientes como o CSS.…”