Date of Award

Winter 1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

E. E. Hofmann

Committee Member

L. P. Atkinson

Committee Member

A. J. Busalacchi

Committee Member

J. M. Klinck

Abstract

A one dimensional coupled bio-optical and mixed layer model is developed and applied to problems involving the role of phytoplankton-induced turbidity (PIT) on the vertical structure and heating of the upper ocean in the Equatorial Pacific Ocean. The bio-optical and mixed layer model for optically pure sea water was forced with climatological environmental conditions to provide a reference simulation for 140°W in the eastern Equatorial Pacific Ocean. This reference simulation was used for comparison to other simulations which considered the effects of variations in wind stress and solar input for a homogeneous chlorophyll a profile and variations in the magnitude and location of the chlorophyll a maximum concentration from the surface to 150 meters and variation in the chlorophyll a specific phytoplankton absorption spectrum. Additional simulations were used to investigate the role of phytoplankton induced turbidity on the mixed layer for ENSO (warm SST) and Non-ENSO (cold SST) conditions at 140°W.

In general, the simulations show that the mixing cycle has a daytime phase in which the mixed layer is shallow (5 to 10 m) and stable and a nighttime phase in which maximum mixing occurs evidenced by the deeper mixed layer (40 to 60 m). These simulations suggest that wind stress and surface cooling are the primary environmental factors controlling the spatial and temporal variations of the mixing cycle. Simulations have shown that the inclusion of either a constant or variable vertical distribution of chlorophyll a can reduce the average day-night temperature difference by 6% and 16%, respectively; and reduces the rate of change in heat content by 4% and 2%, respectively. Spatial variations in the phytoplankton biomass produced a maximum mixed layer depth (40 to 55 m) with the deepest occurring for the 30 m chlorophyll a maximum concentration greater than 0.5 mg m−3 and the depth of the average mixed layer varied from 36 m to 18 m with the smallest variation occurring for the chlorophyll a maximum at the surface and 100 m over the range of chlorophyll a concentrations. The spectral variation in the specific absorption spectrum showed that large phytoplankton underestimate the Δ SST by 15% and the maximum depth of the mixed layer by 1% and overestimate the average mixed layer depth by 1% relative to small phytoplankton.

The physical processes dominate the influence of phytoplankton induced turbidity (PIT) by an order of magnitude with respect to the mixing and surface temperature for both ENSO and Non-ENSO conditions. The PIT caused the average depth of the mixed layer to shoal by 3% for ENSO conditions and results in an increase of the rate of change of heat content of 10% and 7% for the Non-ENSO and ENSO simulations.

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DOI

10.25777/tf94-tt61

ISBN

9780599652712

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