Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Oceanography



First Advisor

John McN. Sieburth


Dissolved polysaccharide (PCHO), monosaccharide (MCHO) and total carbohydrate (TCHO) have been determined at two to four hour intervals in three marine environments, and related to several other chemical and biological parameters, to study the dynamics and biological interactions of dissolved carbohydrate (CHO).

Six vertical CHO arid dissolved organic carbon (DOC) profiles from a preliminary study across the North Atlantic were compaired with those of particulate ATP (< 3 um and > 3 um size fractions), chlorophyll a phaeopigments and dissolved oxygen. Carbohydrate peaks were associated with accumulations of > 3 um organisms which were low in chlorophyll a possibly indicative of collections of protozooplankton.

A total of ten follow up diel studies in an enclosed salt marsh and a 13 m3 simulated estuarine ecosystem (MERL tank) show evidence of biologically mediated CH0 fluctuations. During five of the six marsh studies, PCHO underwent periods of sustained accumulation commencing in the late morning or early afternoon and continuing through at least two sampling periods into the early evening. Accumulations during this time period seem to be related to the rate of primary production. They may result from the release of recently synthesized PCHO from phototrophs since their magnitude was a significant multiple linear function of daily solar radiation and mean daily temperature for the six studies spanning all seasons. Similar periods of sustained release were not found in the MERL tank but a significant direct correlation between the rates of change of PCHO and phaeopigments in the combined data from all four tank studies suggests that zooplankton excretion was an important source of PCHO. Bacterioplankton counts and PCHO levels, in one study, varied directly in the late morning and inversely through the afternoon and evening, indicating that the bacteria were active and able to respond rapidly and control the natural PCHO concentrations on a time scale of a few hours.

Data from two stations in the western Sargasso Sea, sampled at three or four hour intervals while following a drogued buoy, indicate that in-situ CHO concentrations were closely related to the phototrophic nanoplankton (PNAN), heterotrophic nanoplankton (HNAN) and heterotrophic bacterioplankton (HBAC) populations determined by epifluorescence microscopy. Significant inverse correlations of PCHO and of TCHO with PNAN numbers were found in two diel data sets from off the Carolina coast. Off central Florida, TCHO and/or PCHO were significant multiple linear functions of PNAN, HBAC and sometimes HNAN counts. Partial regression coefficients for PNAN and HNAN were always negative and positive, respectively. HBAC was not consistent in this respect but inverse relations dominated.

Very similiar relationships were found during a similiar drogue study in the Caribbean Sea. Significant inverse relations between PCHO and PNAN levels and between their apparent rates of change were found in the combined data from five diel studies. These correlations may reflect an inverse relation between the rates of cell division and CHO excretion by PNAN. A similiar inverse diel relation between the accumulation rates of TCHO and cell numbers was found in a nutrient replete Isochrysis galbana culture grown under natural sunlight. Fluctuations in HBAC populations were inversely and directly related to the apparent rates of change of PCHO and MCHO, respectively. This appears to be partially due to bacterial extracellular enzymatic hydrolysis of PCHO to MCHO during periods of rapid bacterial reproduction, however actual net heterotrophic PCHO uptake by HBAC also occurred. The combined PNAN and HNAN or HBAC fluctuations accounted for a more significant proportion of the variation in the apparent rates of change of TCHO and PCHO than did any single population parameter, indicating that intimate interactions between these groups of planktonic microorganisms are important in the regulation of in-situ CHO in the Caribbean as well as in the Sargasso Sea.

Net hourly rates of in-situ TCHO release and uptake in the salt marsh frequently exceeded 40 ug C L-1h-1 (maximum of 70 and 98 ug C L-1h-1 for release and uptake respectively) in August, with rates up to 17 ug C L-1h-1 in February. Lower rates were found in the MERL tank, with maximum TCHO release and uptake of 35 ug C L-1h-1 in June and 5 ug C L-1h-1 in February.

Rate estimation from the open water measurements in the Sargasao and Caribbean Seas is tenuous because of the possibility of spatial patchiness. It is possible, however, that the observed CHO fluctuations in the Caribbean, primarily represent true temporal dynamics occurring in homogeneous water masses because sample sigma-t variations in each study were small and apparently unrelated to fluctuations in CHO or the populations of microbial plankton. There was no evidence of significant horizontal plankton patchiness. Assuming temporal dynamics, TCHO release and uptake rate~ averaged 7.4 and 5.4 ug C L-1h-1 with maximal values of 29 and 15 ug C L-1h-1, respectively. Away from the influence of shallow waters, the total net apparent TCHO flux over 3 days in the Caribbean accounted for 33 and 48% of the total net apparent DOC release and uptake, respectively. At one 48 h station with complete data, DOC release was 50% of the net apparent primary production.



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