Nick J. Hardman-Mountford

Validation of MERIS reflectance and chlorophyll during the BENCAL cruise October 2002: preliminary validation of new demonstration products for phytoplankton functional types and photosynthetic parameters

We measured water leaving reflectance, phytoplankton pigments, optical properties and photosynthetic parameters in the southern Benguela ecosystem in October 2002. These data were used to validate MERIS standard products: reflectance (MERIS wavelengths) and Case 1 Chlorophyll‐a. In this heterogeneous area, accurate validation required sampling within a few minutes of the satellite overpass. Inter‐pigment relationships e.g. Total Chlorophyll (TChla) to Total Pigment (TP) were robust (R2∼0.99) yet pigment ratios (TChla/TP) were not constant (range 0.44 to 0.62) increasing log‐linearly with biomass (R2∼0.7). Photosynthetic parameters (e.g. Photosynthetic Quantum Efficiency, PQE) and optical ratios (a676/a440) also increased log‐linearly with biomass (R2∼0.8). PQE, pigment and optical ratios were linearly inter‐correlated (R2∼0.7 to 0.8). From these data we derived the bio‐optical traits for several phytoplankton functional types (PFTs): micro‐plankton (diatoms and dinoflagellates) had high biomass, pigment ratios and PQE; nano‐flagellates had low to intermediate biomass, pigment ratios and PQE; prokaryotes had very low biomass, pigment ratios and PQE. We present MERIS data analysed for PFTs and new products (PQE).

Model of phytoplankton absorption based on three size classes

Using the phytoplankton size-class model of Brewin et al. [Ecol. Model.221, 1472 (2010)], the two-population absorption model of Sathyendranath et al. [Int. J. Remote. Sens.22, 249 (2001)] and Devred et al. [J. Geophys. Res.111, C03011 (2006)] is extended to three populations of phytoplankton, namely, picophytoplankton, nanophytoplankton, and microphytoplankton. The new model infers total and size-dependent phytoplankton absorption as a function of the total chlorophyll-a concentration. A main characteristic of the model is that all the parameters that describe it have biological or optical interpretation. The three-population model performs better than the two-population model at retrieving total phytoplankton absorption. Accounting for the contributions of picophytoplankton and nanophytoplankton, rather than the combination of both as in the two-population model, improved significantly the retrieval of phytoplankton absorption at low chlorophyll-a concentrations. Class-dependent specific absorption of phytoplankton derived using the model compares well with previously published models. However, the model presented in this paper provides the specific absorption of three size classes and is applicable to a continuum of chlorophyll-a concentrations. Absorption obtained from remotely sensed chlorophyll-a using our model compares well with in situ absorption measurements.

Particle backscattering as a function of chlorophyll and phytoplankton size structure in the open-ocean

Using an extensive database of in situ observations we present a model that estimates the particle backscattering coefficient as a function of the total chlorophyll concentration in the open-ocean (Case-1 waters). The parameters of the model include a constant background component and the chlorophyll-specific backscattering coefficients associated with small (<20 μm) and large (>20 μm) phytoplankton. The new model performed with similar accuracy when compared with a traditional power-law function, with the additional benefit of providing information on the role of phytoplankton size. The observed spectral-dependency (γ) of model parameters was consistent with past observations, such that γ associated with the small phytoplankton population was higher than that of large phytoplankton. Furthermore, γ associated with the constant background component suggests this component is likely attributed to submicron particles. We envisage that the model would be useful for improving Case-1 ocean-colour models, assimilating light into multi-phytoplankton ecosystem models and improving estimates of phytoplankton size structure from remote sensing.

Impacts of light shading and nutrient enrichment geo-engineering approaches on the productivity of a stratified, oligotrophic ocean ecosystem

Geo-engineering proposals to mitigate global warming have focused either on methods of carbon dioxide removal, particularly nutrient fertilization of plant growth, or on cooling the Earths surface by reducing incoming solar radiation (shading). Marine phytoplankton contribute half the Earths biological carbon fixation and carbon export in the ocean is modulated by the actions of microbes and grazing communities in recycling nutrients. Both nutrients and light are essential for photosynthesis, so understanding the relative influence of both these geo-engineering approaches on ocean ecosystem production and processes is critical to the evaluation of their effectiveness. In this paper, we investigate the relationship between light and nutrient availability on productivity in a stratified, oligotrophic subtropical ocean ecosystem using a one-dimensional water column model coupled to a multi-plankton ecosystem model, with the goal of elucidating potential impacts of these geo-engineering approaches on ecosystem production. We find that solar shading approaches can redistribute productivity in the water column but do not change total production. Macronutrient enrichment is able to enhance the export of carbon, although heterotrophic recycling reduces the efficiency of carbon export substantially over time. Our results highlight the requirement for a fuller consideration of marine ecosystem interactions and feedbacks, beyond simply the stimulation of surface blooms, in the evaluation of putative geo-engineering approaches.

Mapping size-specific phytoplankton primary production on a global scale

Abstract Please click here to download the map associated with this article. Since the initiation of satellite-borne visible spectral radiometry (ocean colour), oceanographers have developed techniques to map phytoplankton biomass on a global scale, with a major application being to model primary production and the ocean carbon cycle in the context of climate change. However, we now recognise that marine carbon cycling links specifically to the activity of particular phytoplankton functional groups. From the perspective of primary production and the global carbon cycle, cell size is thought to be sufficient for defining these functional groups. This has led to a variety of bio-optical methods that use satellite data to differentiate between phytoplankton size classes. Here we combine an established phytoplankton size class algorithm which is integrated into an available-light primary production model in order to partition and map primary production estimates from microplankton (>20μm) and combined nano-picoplankton (<20μm) on a global scale for the year 2005. We estimate global primary production in 2005 to be 51.20 ± 0.29 Gt C y−1 of which, combined nano-picoplankton contributes to 48.58 ± 0.34 Gt C y−1 (94.8%) and microplankton 2.62 ± 0.07 Gt C y−1 (5.2%). This approach can supply data for large-scale maps of size-specific primary production and an example of May and November 2005 is shown.

Comparing satellite-based phytoplankton classification methods

Satellite Phytoplankton Functional Type Algorithm Intercomparison Workshop; Sapporo, Japan, 22–23 November 2011 Satellite observations of ocean color have become synonymous with derivations of chlorophyll a concentration as a proxy for phytoplankton biomass. In addition, a number of satellite algorithms for estimating the phytoplankton community structure have been developed that provide size-structure estimates of phytoplankton and detect taxonomic groups (termed phytoplankton functional types, or PFTs). These new algorithms provide an increased level of observational detail for ecosystem and biogeochemical studies of the role of phytoplankton in marine systems.

Supplement to physical exchanges at the air-sea interface: UK-SOLAS Field Measurements

This document is a supplement to “Physical Exchanges at the Air–Sea Interface: UK–SOLAS Field Measurements,” by Ian M. Brooks, Margaret J. Yelland, Robert C. Upstill-Goddard, Philip D. Nightingale, Steve Archer, Eric d’Asaro, Rachael Beale, Cory Beatty, Byron Blomquist, A. Anthony Bloom, Barbara J. Brooks, John Cluderay, David Coles, John Dacey, Michael DeGrandpre, Jo Dixon, William M. Drennan, Joseph Gabriele, Laura Goldson, Nick Hardman-Mountford, Martin K. Hill, Matt Horn, Ping-Chang Hsueh, Barry Huebert, Gerrit de Leeuw, Timothy G. Leighton, Malcolm Liddicoat, Justin J. N. Lingard, Craig McNeil, James B. McQuaid, Ben I. Moat, Gerald Moore, Craig Neill, Sarah J. Norris, Simon O’Doherty, Robin W. Pascal, John Prytherch, Mike Rebozo, Erik Sahlee, Matt Salter, Ute Schuster, Ingunn Skjelvan, Hans Slagter, Michael H. Smith, Paul D. Smith, Meric Srokosz, John A. Stephens, Peter K. Taylor, Maciej Telszewski, Roisin Walsh, Brian Ward, David K. Woolf, Dickon Young, and Henk Zemmelink (Bull. Amer. Meteor. Soc., 90, 629–644) • ©2009 American Meteorological Society • Corresponding author: Ian M. Brooks, Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom • E-mail: i.brooks@see.leeds.ac.uk • DOI:10.1175/2008BAMS2578.2