primary productivity and the basic photosynthetic parameters (absorption cross section, 

 turnover time of photosynthesis, and photoconversion efficiency photosynthesis). The 

 estimates of primary productivity and photosynthetic parameters will be related to ^'*C-based 

 measurements. The deck FRR fluorometer will be used in conjunction with immunological 

 investigations to study the effects of nutrient limitation and light regime on the photosynthetic 

 parameters of phytoplankton. The photosynthetic parameters will be related to nutrient- 

 pigment data acquired over the same spatial and temporal scale. The immunological 

 measurements will be done using fluorescentiy tagged antibodies on preserved phytoplankton 

 samples and will be analyzed by microscopy. 



Over a much larger scale, satellite images establish the distribution of chlorophyll, which 

 when coupled with irradiance measurements can be used to infer the broad-scale distribution 

 of primary production. However, over continental shelves with high concentrations of 

 chlorophyll and dissolved organic matter, standard reflectance algorithms used to derive 

 chlorophyll from satellite-based measurements are notoriously inaccurate. Ground truth 

 verification and development of satellite algorithms for estimating pigment biomass and 

 primary production is therefore critical for the Ocean Margins Program. It can be achieved 

 using moored, vertically-resolving optical sensors that provide near-surface and subsurface 

 information. Satellite remote sensing and in-situ (mooring-based) measurements are 

 complementary: as well as providing ground-truth, the latter can cover periods during which 

 satellites cannot "see" the sea-surface (e.g. at night, periods of cloud cover) as well as 

 providing essential depth resolution; the former provides the areal coverage that would be 

 prohibitively expensive to obtain with moored instrumentation. 



B. Respiration 



Water-column respiration rates will be determined from direct measurements of oxygen 

 consumption in seawater samples using a high-precision automatic titration system with a 

 potentiometric detector during relatively short-term (2-12 h) bottie incubations. In conjunction 

 with direct measurements of oxygen consumption, measurements of total CO2 will also be 

 made using coulometry. This high-precision method (ca. 1 |xM C) is capable of making direct 

 measurements of carbon mineralization and thereby provides an independent assessment of 

 respiration. These complementary measurements will provide an estimate of total POC and 

 DOC remineralization rates in the water column. 



Dissolved oxygen is one of the few chemical parameters that can currentiy be measured 

 in situ from long-term moorings. Recentiy, a sensor has been developed to measure total 

 dissolved gas tension, and an in-situ PCO2 sensor is currentiy under development. Total 

 dissolved gas tension measurements (from moorings) combined with oxygen measurements 

 allows the partial pressure of nitrogen gas (PN2) to be calculated. Combination of pN2, PO2 

 and PCO2 time-series data permits the physical processes affecting p02 and PCO2 to be 

 quantified (e.g. air-sea gas exchange and mixing) and therefore permits direct estimation of 

 bulk rates of net community production and respiration from moored chemical sensor time- 

 series data. Note that neither p02 nor PCO2 measurements alone can fuUy characterize the 

 biological transformations of carbon because of the potentially complicating effects of 

 alkalinity changes arising from biological calcification and river inputs. These measurements 

 are therefore complementary: p02 changes reflect soft-tissue formation and degradation, 



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