Abstract
Over the past decade, a number of methods have been developed to estimate size-class primary production from either in situ phytoplankton pigment data or remotely-sensed data. In this context, the first objective of this study was to compare two methods of estimating size class specific (micro-, nano- and pico-phytoplankton) photosynthesis-irradiance (PE) parameters from pigment data. The second objective was to analyse the relationship between environmental variables (temperature, nitrate and PAR) and PE parameters in the different size-classes. A large dataset was used of simultaneous measurements of the PE parameters (n=1260) and phytoplankton pigment markers (n=2326), from 3 different institutes was used. There were no significant differences in mean PE parameters of the different size classes between the chemotaxonomic method of Uitz et al. (2008) and the pigment markers and carbon-to-Chl a ratios method of Sathyendranath et al. (2009). For both methods, mean maximum photosynthetic rates ( ) for micro-phytoplankton were significantly lower than those for pico-phytoplankton and nano-phytoplankton. The mean light limited slope (αB) for nano-phytoplankton were significantly higher than for the other size taxa. For micro-phytoplankton dominated samples identified using the Sathyendranath et al. (2009) method, both and αB exhibited a significant, positive linear relationship with temperature, whereas for pico-phytoplankton the correlation with temperature was negative. Nano-phytoplankton dominated samples showed a positive correlation between and temperature, whereas for αB and the light saturation parameter (Ek) the correlations were not significant. For the Uitz et al. (2008) method, only micro-phytoplankton , pico-phytoplankton αB, nano- and pico-phytoplankton Ek. The temperature ranges occupied by the size classes derived using these methods differed. The Uitz et al. (2008) method exhibited a wider temperature range compared to those derived from the Sathyendranath et al. (2009) method. The differences arise from the classification of mixed populations. Based on these patterns, we therefore recommend using the Sathyendranath et al. (2009) method to derive micro-phytoplankton PE parameters at sea water temperatures up to 8 oC during monospecific blooms and the Uitz et al. (2008) method to derive PE parameters of mixed populations over the temperature range from 8 to 18 oC.
Highlights
Increased interest in predicting future effects of climate change on marine ecosystems has led to a concerted effort to understand how large-scale patterns in ocean productivity vary in response to changing environmental properties, especially to sea-surface temperature, which is routinely monitored from satellite
One principal conclusion from these studies was that a better understanding of the temperature regulation and parameterisation of photosynthesis is required to improve the accuracy of remotely-sensed models of marine primary production (Carr et al, 2006)
Data from Bedford Institute of Oceanography (BIO) were collected from 1997 to 2001 along the Scotian Shelf and from the NW sub-tropical Atlantic in March 1999; data from Laboratoire d’Océanographie de Villefranche-sur-Mer (LOV) were from the tropical NE Atlantic in June 1992 and data from Plymouth Marine Laboratory (PML) were from AMT6 in May-June 1998 and the Irish Sea in May, June and July 2001
Summary
Increased interest in predicting future effects of climate change on marine ecosystems has led to a concerted effort to understand how large-scale patterns in ocean productivity vary in response to changing environmental properties, especially to sea-surface temperature, which is routinely monitored from satellite. One principal conclusion from these studies was that a better understanding of the temperature regulation and parameterisation of photosynthesis is required to improve the accuracy of remotely-sensed models of marine primary production (Carr et al, 2006). To estimate primary productivity at basin or global scales, it is necessary to understand how the PE parameters; the light limited slope (αB), the maximum photosynthetic rate (PmB ), and the light saturation parameter (Ek) or associated parameters such as the optimum photosynthetic rate (Pbopt) vary as a function of environmental variables that can be measured from remote sensing (Behrenfeld and Falkowski, 1997; Bouman et al, 2005; Platt et al, 2005). At temperatures above 20◦C, commonly associated with stratified oligotrophic conditions and high surface irradiance, the maximum rate of carbon fixation is often reduced, which may be explained in part by an increased investment of resources in photo-protection, repair of photo-damage (Raven, 2011), and to endure nutrient limitation (Behrenfeld and Falkowski, 1997)
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