Sources, cycling, and deposition of organic matter in northern Newfoundland fjords and bays

Ostrom, Nathaniel Emil (1989) Sources, cycling, and deposition of organic matter in northern Newfoundland fjords and bays. Masters thesis, Memorial University of Newfoundland.

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Abstract

An understanding of sources, cycling and deposition of organic matter in northern Newfoundland fjords and bays was gained through the use of stable carbon and nitrogen isotopic and elemental analyses. Seston from terrestrial stations was characterized by two groups: 1) stations which had a dominant influence of runoff had respective average δ¹⁵N, δ¹³C and C/N compositions of 2.2°/oo, -25.5°/oo and 12.3 and 2) stations which appeared to be influenced by freshwater phytoplankton had average values of 5.1°/oo, -24.9°/oo and 8.1 for δ¹³C, δ¹⁵N , and C/N, respectively. A macroalgae endmember was defined by a δ¹⁵N, δ¹³C and C/N of 4.6°/oo, -20.3°/oo and 9.2, respectively. Surface water seston which was not influenced by terrestrial detritus or macroalgae had average values of 8.2°/oo, -24.6°/oo, and 6.5 for δ¹⁵N, δ¹³C, and C/N, respectively, and was considered to be representative of a phytoplankton endmember. -- The isotopic and elemental composition of POM isolated from the water column shifted in response to source, diagenesis and resuspension. Surficial sediments reflected contributions from both macroalgae and phytoplankton and showed little alteration by diagenesis. Degradation was evidenced by loss of organic matter with depth in all sediment cores analyzed. With the exception of one location isotopic ratios were not altered by this process. -- The retreat of the Wisconsinan ice sheet was recorded by variations in the geochemistry of sediment cores. The average δ¹⁵N, δ¹³C and C/N of glacial till collected from the base of one core, 4.3°/oo, -25.3°/oo and 6.0, respectively, indicated a terrigenous origin. This till was a major contributor of organic matter to the lowermost 3 sedimentary units of that core. Shifts in δ¹⁵N from 5.5 to 9.2 °/oo and δ¹³C from -24.4 to -21.8°/oo above these units were related to changes in the relative contribution of phytoplankton and macroalgae. The isotopic and elemental composition of organic matter within Holocene sediments throughout all bays studied indicated a mixture of phytoplankton and macroalgae.

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