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Quantifying Labile Organic Carbon Dynamics in Antarctic Peninsula Sediments: A Radiocarbon Approach.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Quantifying Labile Organic Carbon Dynamics in Antarctic Peninsula Sediments: A Radiocarbon Approach./
作者:	Taylor, Richard.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	204 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-05, Section: B.
Contained By:	Dissertations Abstracts International80-05B.
標題:	Chemical Oceanography. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=11007227
ISBN:	9780438599239

Quantifying Labile Organic Carbon Dynamics in Antarctic Peninsula Sediments: A Radiocarbon Approach.
Taylor, Richard.

Quantifying Labile Organic Carbon Dynamics in Antarctic Peninsula Sediments: A Radiocarbon Approach. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 204 p.

Source: Dissertations Abstracts International, Volume: 80-05, Section: B.

Thesis (Ph.D.)--North Carolina State University, 2018.

This item must not be sold to any third party vendors.

Sediments from the former Larsen A ice shelf offer a unique opportunity to investigate the buildup of labile organic carbon (LOC) from a patchy, oligotrophic system (with an ice shelf) to a regime with a LOC-rich food bank (no ice shelf). This rapidly transitioning ecosystem on the Larsen A shelf is in contrast to that of the West Antarctic Peninsula (WAP), where there is a slow progressive change with time, and diagenetic processes affecting LOC can be examined under more steady-state conditions. Thus, the intent of this dissertation is to compare and contrast the abundances, distributions, and mean residence times of LOC (recently produced from marine plankton) in two quite different depositional regimes, aiming to understand the dominant biogeochemical processes affecting this important food source for the benthic community. The sediments under the former Larsen A were sampled along an East-West transect, where stations represent successive ice-shelf retreat or collapse dates (15->170 years). The supply of LOC to the seabed from plankton was considered to start immediately upon ice shelf collapse/retreat. On the WAP, a variety of shelf environments were sampled, including a fjord basin, a local sediment depocenter, as well as across shelf transects at different latitudes. In this study, the abundance of LOC was measured using a recently developed, radiocarbon technique applied to the organic fraction of Antarctic shelf sediments. To establish LOC distributions, inventories, and mean residence times (τ-LOC) for both WAP and the Larsen A sediments, a simple binary mixing model was invoked, utilizing the 14C age of plankton to represent the labile end-member and the 14C age at depth for the refractory component (DeMaster et al., 2016; Isla and DeMaster, 2018). The LOC profiles were fit to a diagenetic model in which bioturbation intensity (assumed diffusive) was calculated using the naturally occurring radioisotopes: 234Th (WAP) and 210Pb (Larsen A). Results from the former Larsen A shelf show a decrease in LOC inventory from E-W (74.9-9.2 mg/cm2), and a general decrease in τ-LOC (from ~60y to ~6y). Results suggest that as the more LOC gets remineralized, the LOC "ages" (τ-LOC increases), as the time from shelf retreat increases. On the WAP, shelf LOC inventories ranged from 17.3-70.4 mg/cm 2. τ-LOC s were much shorter on a 100-day timescale (0.8-9.8y) in near-surface sediments, compared to 100-year timescales (32y-4.9ky), which represented LOC dynamics below the rapidly mixed surface layer. The increase in τ-LOC between near-surface and sub-surface sediments on the WAP is believed to be a result of rapid and efficient LOC processing in the rapidly mixed surface layer by benthic fauna and microbes, causing the remaining LOC at depth to be less reactive. The third part of this research involved using Ramped Pyrolysis Oxidation (RPO), to test the assumptions of the two-endmember 14C mixing model made by Isla and DeMaster (2018) and this dissertation. RPO analysis was carried out on bulk sediment samples from a Larsen A core. CO2 thermographs were decomposed into 3 constituent components (Rosenheim et al., 2008), representing organic matter with different combustion temperatures and reactivities, i.e., labilities. All components decreased in absolute abundance down core. The 14C age of each component increased substantially with depth in the sediment column. Component 1 (C1; the lowest temperature peak), associated with the LOC fraction of the sediment, had a 14C age of 1690y at the surface (representing ~40% of the total organic carbon) and an age of ~12ky at 10-12cm (where it was reduced to 6.8% of the TOC). Per gram of sediment, C1 abundance was reduced by 95% down core (199.7-8.1 μmol/g). The RPO abundances of the C1 peak down core were in good agreement with the LOC abundances predicted from the two-endmember 14C mixing model, corroborating 14C mixing model assumptions, and clearly showing that the sedimentary organic matter could accurately be treated as a combination of a labile and a refractory organic carbon component.

ISBN: 9780438599239Subjects--Topical Terms:

1674678
Chemical Oceanography.

Quantifying Labile Organic Carbon Dynamics in Antarctic Peninsula Sediments: A Radiocarbon Approach.
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520 $a Sediments from the former Larsen A ice shelf offer a unique opportunity to investigate the buildup of labile organic carbon (LOC) from a patchy, oligotrophic system (with an ice shelf) to a regime with a LOC-rich food bank (no ice shelf). This rapidly transitioning ecosystem on the Larsen A shelf is in contrast to that of the West Antarctic Peninsula (WAP), where there is a slow progressive change with time, and diagenetic processes affecting LOC can be examined under more steady-state conditions. Thus, the intent of this dissertation is to compare and contrast the abundances, distributions, and mean residence times of LOC (recently produced from marine plankton) in two quite different depositional regimes, aiming to understand the dominant biogeochemical processes affecting this important food source for the benthic community. The sediments under the former Larsen A were sampled along an East-West transect, where stations represent successive ice-shelf retreat or collapse dates (15->170 years). The supply of LOC to the seabed from plankton was considered to start immediately upon ice shelf collapse/retreat. On the WAP, a variety of shelf environments were sampled, including a fjord basin, a local sediment depocenter, as well as across shelf transects at different latitudes. In this study, the abundance of LOC was measured using a recently developed, radiocarbon technique applied to the organic fraction of Antarctic shelf sediments. To establish LOC distributions, inventories, and mean residence times (τ-LOC) for both WAP and the Larsen A sediments, a simple binary mixing model was invoked, utilizing the 14C age of plankton to represent the labile end-member and the 14C age at depth for the refractory component (DeMaster et al., 2016; Isla and DeMaster, 2018). The LOC profiles were fit to a diagenetic model in which bioturbation intensity (assumed diffusive) was calculated using the naturally occurring radioisotopes: 234Th (WAP) and 210Pb (Larsen A). Results from the former Larsen A shelf show a decrease in LOC inventory from E-W (74.9-9.2 mg/cm2), and a general decrease in τ-LOC (from ~60y to ~6y). Results suggest that as the more LOC gets remineralized, the LOC "ages" (τ-LOC increases), as the time from shelf retreat increases. On the WAP, shelf LOC inventories ranged from 17.3-70.4 mg/cm 2. τ-LOC s were much shorter on a 100-day timescale (0.8-9.8y) in near-surface sediments, compared to 100-year timescales (32y-4.9ky), which represented LOC dynamics below the rapidly mixed surface layer. The increase in τ-LOC between near-surface and sub-surface sediments on the WAP is believed to be a result of rapid and efficient LOC processing in the rapidly mixed surface layer by benthic fauna and microbes, causing the remaining LOC at depth to be less reactive. The third part of this research involved using Ramped Pyrolysis Oxidation (RPO), to test the assumptions of the two-endmember 14C mixing model made by Isla and DeMaster (2018) and this dissertation. RPO analysis was carried out on bulk sediment samples from a Larsen A core. CO2 thermographs were decomposed into 3 constituent components (Rosenheim et al., 2008), representing organic matter with different combustion temperatures and reactivities, i.e., labilities. All components decreased in absolute abundance down core. The 14C age of each component increased substantially with depth in the sediment column. Component 1 (C1; the lowest temperature peak), associated with the LOC fraction of the sediment, had a 14C age of 1690y at the surface (representing ~40% of the total organic carbon) and an age of ~12ky at 10-12cm (where it was reduced to 6.8% of the TOC). Per gram of sediment, C1 abundance was reduced by 95% down core (199.7-8.1 μmol/g). The RPO abundances of the C1 peak down core were in good agreement with the LOC abundances predicted from the two-endmember 14C mixing model, corroborating 14C mixing model assumptions, and clearly showing that the sedimentary organic matter could accurately be treated as a combination of a labile and a refractory organic carbon component.
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