Organic Carbon Dynamics in Fjords: A Case Study of Fiordland, New Zealand
Abstract
Fjords have been identified as sites of enhanced organic carbon (OC) burial and may play an important role in regulating climate change on glacial-interglacial timescales. In this study, we use sediments from Fiordland, New Zealand to examine the relative importance of different terrestrially derived OC in fjord sediments and assess the role of hydrodynamic sorting in distributing sediments and OC along fjords. Sediments and terrestrial end-members were collected for organic geochemistry analysis to examine the efficiency of terrestrial OC burial, both in this system and in fjords globally. In addition, selective surface sediment samples were used for density fractionation separation, bulk OC and compound specific radiocarbon analysis (CSRA). End-member models indicated that 69% and 61% of OC in Fiordland and global fjord sediments were terrestrially derived, respectively. There was a decreasing trend of terrestrially derived OC down fjords, which was contributed by hydrodynamic sorting. Comparatively, less hydrodynamic sorting in fjords than large river estuary -coastal systems contributed to high burial rates of OC in fjords. However, our bulk OC radiocarbon and CSRA results suggested minimal contribution of petrogenic OC by bedrock erosion. Here we suggest that global fjords may play an important role in regulating atmospheric CO2 levels by burying purely modern OC, in contrast to other systems. Globally, fjords bury 11.3 ± 4.4 × 1012 g OCterr, which accounts for 18% of all the OCterr buried in all marine sediments annually. This new information has now increased the total global OCterr pool buried in marine sediments from 58 to 63 (× 1012 g), which better constrains the "missing sink" in OCterr burial in the global ocean. Our results indicate that watershed soil residence times, fjord water depth, and dissolved oxygen levels were more important than mass accumulation rates (MAR) in controlling OC burial.
- Publication:
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American Geophysical Union, Ocean Sciences Meeting
- Pub Date:
- February 2016
- Bibcode:
- 2016AGUOSEC41B..03C
- Keywords:
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- 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4850 Marine organic chemistry;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4217 Coastal processes;
- OCEANOGRAPHY: GENERALDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL