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Seasonal variability of light availability and utilization in the Sargasso SeaA 2 year time series of optical, biogeochemical, and physical parameters, taken near the island of Bermuda, is used to evaluate the sources of temporal variability in light avaliability and utilization in the Sargasso Sea. Integrated assessments of light availability are made by examining the depth of constant percent incident photosynthetically available radiation (% PAR) isolumes. To first order, changes in the depth %PAR isolumes were caused by physical processes: deep convection mixing in the winter which led to the spring bloom and concurrent shallowing of %PAR depths and the occurrence of anomalous thermohaline water masses during the summer and fall seasons. Spectral light availability variations are assessed using determinations of diffuse attenuation coefficient spectra which illustrates a significant seasonal cycle in colored detrital particulate and/or dissolved materials that is unrelated to changes in chlorophyll pigment concentrations. Temporal variations in the photosynthetic light utilization index Psi are used to assess vertically intergrated light utilization variations. Values of Psi are highly variable and show no apparent seasonal pattern which indicates that Psi is not simply a 'biogeochemical constant.' Determinations of in situ primary production rates and daily mean PAR fluxes are used to diagnose the relative role of light limitation in determining vertically integrated rates of primary production integral PP. The mean depth of the light-saturated zone (the vertical region where the daily mean PAR flux was greater than or equal to the saturation irradiance) is only approximately 40 m, although more than one half of interal PP occurred within this zone. Production model results illustrate that accurate predictions of integral PP are dependent upon rates of light-saturated production rather than upon indices of light limitation. It seems unlikely that significant improvements in simple primary production models will come from the partitioning of the Earth's seas into biogeochemical provinces.
Document ID
19950056047
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Siegel, David A.
(Univ. of California, Santa Barbara, CA United States)
Michaels, Anthony F.
(Bermuda Biological Station for Research Ferry Reach, Bermuda)
Sorensen, Jens C.
(Univ. of California, Santa Barbara, CA United States)
O'Brein, Margaret C.
(Univ. of California, Santa Barbara, CA Us, United States)
Hammer, Melodie A.
(Bermuda Biological Station for Research Ferry Beach, Bermuda)
Date Acquired
August 16, 2013
Publication Date
May 15, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: C5
ISSN: 0148-0227
Subject Category
Oceanography
Accession Number
95A87646
Funding Number(s)
CONTRACT_GRANT: NSF OCE-93-01950
CONTRACT_GRANT: NAGW-3145
CONTRACT_GRANT: NSF OCE-88-01089
CONTRACT_GRANT: NSF OCE-91-16372
CONTRACT_GRANT: NSF OCE-90-16990
Distribution Limits
Public
Copyright
Other

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