Hargreaves, Bruce: Lehigh University (Project Lead)
Project Funding:
2007 - 2010
NRA: 2006 NASA: Ocean Biology and Biogeochemistry
Funded by NASA
Abstract:
NASA's goal for the Southern Ocean (SO) Carbon Program is to resolve uncertainties in
the size, dynamics, and global significance of the SO as a carbon sink as well as
processes controlling this sink. The field component of this program (the GASEX-III
cruise) aims to improve models of air-sea CO2 flux and related remotely sensed data.
Accurate measurement of photosynthesis from space can contribute to modeling sea-air
flux of CO2 at the basin scale because photosynthesis influences near-surface pCO2.
Photosynthesis rates have been modeled using phytoplankton pigment concentration
(chlorophyll) but results have been spatially and temporally variable and the SO has often
been treated as a special case. An alternative hypothesis proposed by Marra et al.(2007)
suggests that photosynthesis is better modeled from phytoplankton absorption than from
chlorophyll concentration.
To test this hypothesis we propose to make coordinated measurements of phytoplankton
spectral absorption and photosynthesis rates together while collecting in situ and satellite
optical and bio-optical data during the GASEX-III cruise. Because all methods for
measuring phytoplankton absorption used to date have limitations, the approach for this
cruise is to compare multiple methods via separate proposals (from Marra, Subramaniam,
Vaillancourt, Lee, and Hargreaves). The best combination of in situ measurements will
then be used to estimate phytoplankton absorption for modeling photosynthesis rates
from satellite data.
The specific objectives of this proposal (Hargreaves) are to:
1.Measure spectral absorption of phytoplankton in samples collected during the GASEXIII
cruise using a Filter Pad Technique that incorporates both Transmittance and
Reflectance (FPT-TR);
2.Develop and test (through rigorous on-site and laboratory calibrations) a universal
equation for the Beta function that is required to interpret FPT data;
3.Compare two FPT-compatible methods for separating absorption into pigment and nonpigment
components (bleaching versus alcohol extraction);
4.Improve detection of protective pigments that influence photosynthesis models by
using the broad spectral response (225-800 nm) and rapid processing features of a new
portable instrument (pFPT-TR) to analyze freshly filtered samples;
5.Improve estimates of the package effect in phytoplankton that suppresses absorption by
pigments in living cells.
One outcome of the proposed research is the rigorous comparison of methods for
measuring phytoplankton spectral absorption that should improve future in situ and
satellite studies of phytoplankton ecology. A direct product of this study will be a unique
data set of optical and bio-optical properties and phytoplankton photosynthesis rates for
the Southern Ocean, providing an important test of a general model of phytoplankton
productivity based on absorbance, and for the role of photosynthesis as a modulator of
air-sea carbon flux.
2008 NASA Carbon Cycle & Ecosystems Joint Science Workshop Posters
- Phytoplankton spectral absorption in the Southern Ocean: preliminary results from SO-GASEX
-- (Bruce Robert Hargreaves)
[abstract]
[poster]
More details may be found in the following project profile(s):
