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Carbon flow through inshore marine environments of the Vestfold Hills, East Antarctica

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Gibson, John Andrew Edwin,1959- (1997) Carbon flow through inshore marine environments of the Vestfold Hills, East Antarctica. PhD thesis, University of Tasmania.

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Abstract

The first integrated study in the Antarctic region of the marine carbon cycle over an
entire annual period, including organic carbon formation, remineralisation,
sedimentation and burial, was undertaken during two summers and the intervening
winter from December 1993 to February 1995 at two sites in the Vestfold Hills region,
East Antarctica: offshore at O'Gorman Rocks and in semi-enclosed Ellis Fjord.
A single peak in uptake of dissolved inorganic carbon (DIC) occurred at the O'Gorman
Rocks site in the first summer, while three peaks, resulting from different
phytoplankton communities, were observed in the second. Net organic carbon (OC)
production calculated from the uptake of DIC reached 2.1 mg kg-1. The sum of
particulate and dissolved OC was typically only 30 % of the calculated total,
suggesting rapid sedimentation of OC or transfer to higher trophic levels. After the end
of OC production in autumn the concentrations of DIC and nutrients increased slowly
and steadily to late winter maxima, primarily as the result of remineralisation rather
than nutrient supply by deep-water upwelling.
Sediment trap flux of OC at O'Gorman Rocks totalled 10 g m -2 year-1, with peak
sedimentation coinciding with maximum OC production, but with a significant
proportion (30 %) occurring outside summer. The development of a bottom ice algal
community in October contributed a pulse of sedimentation which was characterised
by OC with high 813C (-13 % compared to the annual average -19 %0). Comparison of
the fluxes with the OC content of a sediment core showed that 2 gm-2 year-1 OC was
buried, with the majority (80 %) remineralised by the benthic community.
In Ellis Fjord DIC and nutrient uptake began earlier and ended later than at O'Gorman
Rocks, though total DIC uptake and annual OC sedimentation were similar to those
offshore. Early in summer the C:N uptake ratio calculated from concentrations in the water column reached 40, considerably higher than the expected Redfield Ratio of
16:1. Sedimentation of bottom ice algae again resulted in the transfer of particulate
matter with high 613C to the sediment.
This study shows that OC production in the nearshore Antarctic environment does not
necessarily occur in a single pulse after the loss of the ice cover, but rather can begin
under the ice and continue after refreezing. Furthermore, OC production can be of
similar magnitude in ice-covered systems to areas which are ice-free for part of the
summer. Bottom ice algae play an important role in total OC production, and are a
source of OC for sedimentation before and after the period of peak water column
production. This community is also important in the formation of OC with elemental
ratios and 613C different to material produced in open water. Interannual variability in
OC production and the algal and phytoplankton communities, however, can be large.
These factors must be taken into account when developing biological carbon uptake
estimates from models of nutrient utilisation, in interpreting sedimentary isotope
records, and considering the effects of climate change on Antarctic ecosystems.

Item Type: Thesis (PhD)
Keywords: Marine ecology, Carbon cycle (Biogeochemistry)
Copyright Holders: The Author
Copyright Information:

Copyright 1997 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1997. Includes bibliographical references

Date Deposited: 09 Dec 2014 00:02
Last Modified: 16 Sep 2016 04:10
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