Beam attenuation and chlorophyll concentration as alternative optical indices of phytoplankton biomass

Chlorophyll has long functioned as the prominent field metric for phytoplankton biomass, but its variability can be strongly influenced by (even dominated by) physiological shifts in intracellular pigmentation in response to changing growth conditions (light, nutrients, temperature). The particulate beam attenuation coefficient (cp) may offer an alternative optical measure of phytoplankton biomass that is readily assessed in situ and relatively insensitive to changes in intracellular pigment content. Unlike chlorophyll, however, cp is not uniquely associated with phytoplankton and varies as well with changes in inorganic, detrital, and heterotrophic particles. In open ocean environments, particles in the size range of ∼0.5 to 20 μm (i.e., within the phytoplankton size domain) dominate cp. Multiple field studies have indicated that the ratio of cp to chlorophyll (i.e., c*p) registers first-order changes in algal physiology, suggesting that cp covaries with phytoplankton carbon biomass. Here we use approximately 10,000 measurements of cp and fluorescence-based chlorophyll estimates (ChlFl) to evaluate the correspondence between these two phytoplankton biomass proxies. Our study focuses on a region of the eastern equatorial Pacific where mixed layer growth conditions are relatively homogeneous, thereby constraining phytoplankton chlorophyll:carbon ratios and allowing chlorophyll to function as a reliable measure of phytoplankton biomass. Over our 6600 km transect, cp was exceptionally well correlated with ChlFl (r2 = 0.93). Our results contribute additional support for cp as a viable index of phytoplankton carbon biomass in the open ocean

Accountant\u27s Business Manual: Fall Tax Supplement 1991

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General business issues : selected chapters from the Accountant\u27s business manual

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Employment Issues, Selected Chapters from the Accountant\u27s Business Manual

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Business Entities: Selected Chapters form the Accountant\u27s Business Manual

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Global assessment of ocean carbon export by combining satellite observations and food-web models

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of ~6 Pg C yr−1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump

Carbon-Based Primary Productivity Modeling With Vertically Resolved Photoacclimation

Net primary production (NPP) is commonly modeled as a function of chlorophyll concentration (Chl), even though it has been long recognized that variability in intracellular chlorophyll content from light acclimation and nutrient stress confounds the relationship between Chl and phytoplankton biomass. It was suggested previously that satellite estimates of backscattering can be related to phytoplankton carbon biomass (C) under conditions of a conserved particle size distribution or a relatively stable relationship between C and total particulate organic carbon. Together, C and Chl can be used to describe physiological state (through variations in Chl:C ratios) and NPP. Here, we fully develop the carbon-based productivity model (CbPM) to include information on the subsurface light field and nitracline depths to parameterize photoacclimation and nutrient stress throughout the water column. This depth-resolved approach produces profiles of biological properties (Chl, C, NPP) that are broadly consistent with observations. The CbPM is validated using regional in situ data sets of irradiance-derived products, phytoplankton chlorophyll: carbon ratios, and measured NPP rates. CbPM-based distributions of global NPP are significantly different in both space and time from previous Chl-based estimates because of the distinction between biomass and physiological influences on global Chl fields. The new model yields annual, areally integrated water column production of similar to 52 Pg C a(-1) for the global oceans

Satellite observations of chlorophyll, phytoplankton biomass, and Ekman pumping in nonlinear mesoscale eddies

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 118 (2013): 6349–6370, doi:10.1002/2013JC009027.Nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms. The relative importance of these two processes depends on the polarity of an eddy (cyclones versus anticyclones) and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation. Eddies originating in the eastern South Indian Ocean are unique in that anticyclones, typically associated with downwelling, contain elevated levels of chlorophyll-a, enhanced primary production and phytoplankton communities generally associated with nutrient-replete environments. From analysis of 9 years of concurrent satellite measurements of sea surface height, chlorophyll, phytoplankton carbon, and surface stress, we present observations that suggest eddy-induced Ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the South Indian Ocean. The biological response to this eddy-induced Ekman upwelling is evident only during the Austral winter. During the Austral summer, the biological response to eddy-induced Ekman pumping occurs deep in the euphotic zone, beyond the reach of satellite observations of ocean color.This work was funded by NASA grants NNX08AI80G, NNX08AR37G, NNX10AO98G, and NNX13AD78G.2014-06-0