Computation of primary production from remote sensing of ocean colour at the northwestern Atlantic C-SOLAS Lagrangian site

Abstract

At the C-SOLAS Lagrangian Study site, the phytoplankton community was dominated by diatoms in declining bloom conditions, which were characterised by a decrease in primary production over time. Measurements of primary production were performed using photosynthesis-light experiments and simulated in situ incubations. Several methods were used to assign photosynthetic parameters for estimation of primary production from remote-sensing of ocean colour: (1) the nearestneighbour method (NNM), (2) a temperature-dependent model, (3) an iterative approach to retrieve photosynthetic parameters from in situ measurements of phytoplankton production, and (4) average values of measured parameters. Owing to the declining status of the diatom population and its patchy distribution, the magnitude of primary production measured from in situ incubations was highly variable. Under bloom conditions, all methods underestimated production compared with results of simulated in situ measurements; however, the NNM provided the closest estimates to the in situ measurements. In the declining bloom phase, the NNM overestimated primary production, whereas the iterative method returned estimates of production in good agreement with the in situ observations. In conditions characterized by mixed-phytoplankton populations, the NNM returned estimates in agreement with the observations. A new method is proposed for classifying image pixels using criteria accessible to remote sensing, according to the phase of the diatom bloom (bloom versus declining conditions) and according to community composition (diatom versus mixed population). Upon separating the database used for parameter assignment into 2 parts, one representing the general phytoplankton community and the other representing declining diatom conditions, estimates of chlorophyll a-normalised water-column production were in good agreement with in situ observations. KEY WORDS: Response · Primary production · Remote sensing of ocean colour · Photosynthetic parametersResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 352: 27-38, 2007 through phytoplankton photosynthesis in the ocean amounts to 50 Gt C yr -1 and is equivalent in magnitude to terrestrial primary production , Behrenfeld & Falkowski 1997, Behrenfeld et al. 2001. Moreover, through the biological pump, a proportion of this carbon will be transferred to the ocean floor via sedimentation of organic material (Longhurst & Harrison 1989). Quantification of primary production in the ocean is therefore of central importance to programmes such as SOLAS.Remote sensing of ocean colour is an effective method for computing primary production on a global scale , Antoine et al. 1996, Behrenfeld & Falkowski 1997. The method relies on estimation of chl a at the surface, estimation of the attenuation coefficient for downwelling light and the assignment of parameters describing the biomass profile at each image pixel, as well as the photosynthetic response to available light . The first 2 est...

Direct observations of diel biological CO<sub>2</sub> fixation on the Scotian Shelf, northwestern Atlantic Ocean

“…The corresponding respiration rate, assumed to be constant throughout the day, is estimated to be 0.05 µmol C (l h) −1 ; the rates of NCP and GPP are 0.26 µmol C (l h) −1 and 0.31 µmol C (l h) −1 , respectively, both lasting approximately 10 h per day. This compares well with the GPP estimates given by Forget et al (2007, their Table 2), which, when combined with an assumed 30 m MLD, yield GPP rates of 13 µmol C (l d) −1 . It must be noted, however, that their station is somewhat further offshore at the shelf break than the mooring location of the CARIOCA buoy and the SeaHorse.…”

“…4d). Again, this compares well with the GPP rates of 1-3 µmol C (l d) −1 as reported by Forget et al (2007) for this period. Charette et al (2001) reported 14 C-based GPP rates, determined for the area in September 1997, of 0.9-13 µmol C (l d) −1 , assuming a 30 m MLD.…”

Particulate organic carbon export in the upper twilight zone during the decline of the spring bloom

“…3500 m; Fig. 1) as part of a Lagrangian survey of the decline of the spring bloom in the northwest Atlantic Ocean (Forget et al 2007a). A water mass within which a phytoplankton bloom had developed was sampled from 25 April (Day 1) to 1 May 2003 (Day 7).…”

Influence of Amur River discharge on phytoplankton photophysiology in the Sea of Okhotsk during late summer

“…Furthermore, Forget et al . [] found a decrease in the photosynthetic parameters during the declining phase of the phytoplankton bloom in the northwestern Atlantic. Although the values of α B at Stns.…”