The Use of Solar Radiation Products in Understanding the Structure, Function and Dynamics of Marine Ecosystems Heather Bouman Department of Earth Sciences University of Oxford The path of radiation from the sun through the watercolumn Solar energy (100%) absorbed, scattered and reflected by clouds (50% of total) Ultraviolet (< 400 nm) Small fraction of total radiation Rapidly scattered and absorbed Infrared (> 780 nm) (ca. 50% of total surface radiation) Absorbed and converted to heat near surface average surface reflection (4% of PAR) Visible spectrum/PAR (400-700nm) (ca. 50% of total surface radiation) decreasing with depth (up to ~ 200m) (adapted from Lalli & Parsons) Solar Heating Increased solar heating of the surface water leads to more stable density stratification, reducing the penetration of wind-driven mixing. Phytoplankton absorption can further enhance surface heating of the surface ocean leading for example to changes in the dynamics across oceanic fronts. Solar Heating Chlorophyll gradient gives rise to a differential heat rate across the front. Horizontal gradient of heating rate induces secondary vertical circulation at the front, enhancing nutrient flow. Edwards et al. (2001) J. Geophys. Res. Solar Heating Sea Ice Melts Ocean absorbs more heat Surface albedo decreases Park et al. PNAS 2015 Light quantity: its ecological and biogeochemical relevance Implications of cell size for photon acquisition by phytoplankton cells of various sizes. Incident light John Raven Absorption (m-1) Transmitted light Incident light Transmitted light Absorption spectra for phytoplankton pigments, proteins and DNA Barbara Prézelin Solar Irradiance as a Stressor SOLAR RADIATION (PAR+UVR) NET STRESS Energy demand Cell composition Growth rate Mortality Increased solar radiation Vincent & Roy 1993 Envrion. Rev. Ocean Biogeochemistry Cao & Miller (2015) J. Geophys. Res. Oceans Ocean Biogeochemistry Carbon Cycle: Depth Integrated Carbon Monoxide Photoproduction JAN APR JUL Fichot & Miller 2010 Vertical mixing and light A zm B πΌπΌππ = πΌπΌ 0 [1 β exp(βπ§π§ππ πΎπΎππ )] π§π§ππ πΎπΎππ zm β’ Turbulent mixing causes cells to be mixed deeper in the water column, exposing them to a lower average PAR and UVR. Mixing, light and ecology Bouman et al. Science 2006 Mixing, light and ecology Pacific Atlantic Indian 20 Australia 40 Africa 60 South America 80 Australia % Pigment biomass 100 Other Carotenoids Diat + Diad Zeax Chl b 19' Hexan 19' Butan Chl c3 Fucox Chl c1+2 0 160oE 160oW 120oW 80oW 40oW 0o 40oE 80oE 120oE Bouman et al. Science 2006 Mixing, light and ecology Bouman et al. Science 2006 Light quality: its ecological and biogeochemical relevance β’ The effects spectral light on photosynthesis have been widely studied by plant and algal physiologists. β’ Increasing evidence that the quality of available light is important determinant of the ecology and photophysiology of marine primary producers. β’ Generally spectral properties of light have not received the attention they deserve in ecosystem and climate models. Spectral niches within a stratified water column 0 Open Ocean 50 β’ Surface assemblages are exposed to a broad spectrum, with potentially damaging levels of UV and visible radiation. 100 150 200 0 50 100 150 200 Coastal Waters β’ Deep assemblages are exposed to a spectrum of blue light at irradiance levels limiting phytoplankton growth. β’ Deep assemblages are exposed to a spectrum of green light at irradiance levels limiting phytoplankton growth. Sathyendranath & Platt Oceanologia 2007 Sathyendranath & Platt Oceanologia 2007 Distribution of Common Proteorhodopsin Variants across GOS Samples and its relationship with Ocean Colour Models of Marine Primary Production Surface Irradiance Biomass (Chlorophyll) Light Penetration Model Water-column irradiance Photosynthetic Parameters Photosynthesis Light Model Water-column Primary Production Spectral formalism of Model PAR(0) = πΌπΌππ ππ, 0 + πΌπΌπ π (ππ, 0) Surface Irradiance Biomass (Chlorophyll) Light Penetration Model Water-column irradiance πππππ΅π΅ π§π§ , πΌπΌ π΅π΅ ππ, π§π§ ππ π§π§ = π΅π΅ π§π§ Ξ π§π§ 1 + where Photosynthesis Light Model Photosynthetic Parameters Ξ π§π§ πππππ΅π΅ π§π§ 1 2 β2 Ξ π§π§ = cos ππππ ππ ππ, π§π§ + ππππ (ππ, π§π§) cos ππ πΌπΌππ ππ, π§π§ , πΌπΌπ π (ππ, π§π§) πΎπΎππ ππ, π§π§ = Water-column Primary Production β1 οΏ½ πΌπΌ π΅π΅ ππ, π§π§ πΌπΌππ ππ, π§π§ ππππ + cos πππ π β1 οΏ½ πΌπΌ π΅π΅ ππ, π§π§ πΌπΌπ π (ππ, π§π§) ππππ IRRADIANCE (Wm-2µm-1) OUTSIDE ATMOSPHERE SEA LEVEL 0 WAVELENGTH (nm) Surface Irradiance Biomass (Chlorophyll) 50 100 Light Penetration Model 150 200 0 Water-column irradiance Photosynthetic Parameters Open Ocean 50 Photosynthesis Light Model 100 150 Water-column Primary Production 200 Coastal Waters Conclusions I β’ Solar radiation has numerous and diverse effects on the structure of aquatic ecosystems, and its impact is observed at the molecular, organism, community, and environmental levels. β’ There is increasing need to examine solar radiation in the spectral and UV domain to assess the significance of photoacclimation, photoinhibition and photodamage on the structure and function of pelagic marine ecosystems. β’ Impacts of solar radiation on the physical and biogeochemical dynamics of aquatic ecosystems and potential biological feedbacks have been taken into account in recent studies using models of varying complexity (water-column to earth system). Conclusions II β’ Combining incident solar irradiance products with information on the mixed layer provided by ARGO arrays and global models will allow us to estimate the average daily growth irradiance of phytoplankton within the upper layer of the global ocean. β’ Spectral models of primary production are routinely used to estimate NPP and can incorporate the rich information embedded in the reflectance signal. β’ Information on the spectral structure of incident solar radiation will deepen our understanding of the influence of light on global primary production.
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