9 research outputs found
The temporal dynamics of terrestrial organic matter transfer to the oceans : initial assessment and application
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2007This thesis employs compound-specific stable carbon and radiocarbon isotopic
analysis of organic biomarkers to (a) resolve petrogenic from pre-aged vascular plant
organic carbon (OC) in continental margin sediments, (b) investigate the underlying
mechanisms controlling the anomalously old ages that are often observed for the
terrestrial component of sedimentary OC, and (c) address the associated consequences for
biomarker-based climate reconstructions. In Chapters 2 and 3, coupled molecular isotope
mass balances demonstrate that the amount of petrogenic OC residing on the Beaufort
Shelf (Arctic Ocean) and the Eel River Margin (coastal California) has been previously
overestimated due to the presence of significantly âpre-agedâ terrestrial OC. However,
even though the contribution of organic matter emanating from sedimentary rocks may be
smaller, these results reinforce the emerging notion that it is not completely oxidized
during weathering and subsequent seaward transport. In Chapter 4, comparison of the
down-core radiocarbon profiles for certain vascular plant biomarkers extracted from
Cariaco Basin (Caribbean Sea) and Saanich Inlet (coastal British Columbia) sediments
with the radiocarbon evolution of atmospheric carbon dioxide reveals that the vast
majority of the terrestrial OC experiences multi-millennial residence times on land prior
to entering the sea. Most of the remaining inventory is deposited in sediments within one
or two decades, providing direct evidence that very little terrestrial organic matter is
rapidly transferred to the marine environment. With this in mind, the striking modulation
in the signal amplitude of a biomarker-based tropical paleoaridity record presented in
Chapter 5 was instead used to evaluate the role of low versus high latitude forcing in
abrupt paleoclimate oscillations during the last full glacial cycle. Seasonal variations in
the position of the Intertropical Convergence Zone were interpreted to be a response to
both high latitude adjustments in meridional overturning circulation and precessionally-driven
modifications in local insolation. Finally, Chapter 6 addresses the broader
implications of multi-millennial terrestrial residence times for paleoclimate records based
on vascular plant biomarkers.The scientific analyses described herein were funded by the National Science
Foundation through grants OCE-9907129 (T.I.E.), OCE-052626800 (T.I.E.), OCE-
0137005 (T.I.E. and K.A.H.), DEB-0447281 (K.A.H.), and the Stanley Watson Chair for
Excellence in Oceanography (T.I.E.). N.J.D.âs tuition and stipend were supported by the
graduate fellowships from the Stanley Watson Foundation, Schlanger Ocean Drilling
Program, and Environmental Protection Agencyâs Science to Achieve Results (STAR)
Program, as well as by the WHOI Academic Programs Office
Blank assessment for ultra-small radiocarbon samples : chemical extraction and separation versus AMS
Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 1322-1335.The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed
protocols for analyzing radiocarbon in samples as small as ~0.001 mg of carbon (C). Mass-balance background corrections
for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern
standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach
can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary
sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination
of ~0.6 ± 0.3 Όg C, while DC is ~0.3 ± 0.15 Όg C. Today, the laboratory routinely analyzes graphite samples as small
as 0.015 mg C for external submissions and â
0.001 mg C for internal research activities with a precision of ~1% for ~0.010
mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods
(such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with
combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so
high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination
encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented
to illustrate how extraction chemistry blanks are determined
Late Holocene sea-surface temperature and precipitation variability in northern Patagonia, Chile (Jacaf Fjord, 44°S)
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Research 72 (2009): 400-409, doi:10.1016/j.yqres.2009.06.010.A high-resolution multi-proxy study including the elemental and isotopic
composition of bulk organic matter, land plant-derived biomarkers, and alkenone-based sea
surface temperature (SST) from a marine sedimentary record obtained from the Jacaf Fjord
in northern Chilean Patagonia (~ 44°20'S) provided a detailed reconstruction of continental
runoff, precipitation, and summer SST spanning the last 1750 years. We observed two
different regimes of climate variability in our record: a relatively dry/warm period before
900 cal yr BP (lower runoff and average SST 1°C warmer than present-day) and a wet/cold
period after 750 cal yr BP (higher runoff and average SST 1°C colder than present-day).
Relatively colder SSTs were found during 750-600 and 450-250 cal yr BP, where the latter
period roughly corresponds to the interval defined for the Little Ice Age (LIA). Similar
climatic swings have been observed previously in continental and marine archives of the
last two millennia from central and southern Chile, suggesting a strong latitudinal
sensitivity to changes in the Southern Westerly Winds, the main source of precipitation in
southern Chile, and validating the regional nature of the LIA. Our results reveal the
importance of the Chilean fjord system for recording climate changes of regional and
global significance.The preparation of this article was made possible by the support of the Comité
OceanogrĂĄfico Nacional Chile through the Special Fund to Promote Interdisciplinary
Publications of the CIMAR Program. Sampling was funded by the CIMAR FIORDO-7
Program (Grant CPF 01-10)
Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds
Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core 14C profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called âbomb-spikeâ, and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times (âresidence timesâ).
Using a modeling framework, we find that, in addition to a "young" (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (±9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (±5.0) and 2.4 (±0.50) to 3.2 (±0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir.
Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences
Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 244 (2019): 502-521, doi:10.1016/j.gca.2018.09.034.Relatively little is known about the amount of time that lapses between the
photosynthetic fixation of carbon by vascular land plants and its incorporation into the
marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have
important implications for the carbon cycle. Vascular plant carbon may encounter
multiple potential intermediate storage pools and transport trajectories, and the age of
vascular plant carbon accumulating in marine sediments will reflect these different predepositional
histories. Here, we examine down-core 14C profiles of higher plant leaf waxderived
fatty acids isolated from high fidelity sedimentary sequences spanning the socalled
âbomb-spikeâ, and encompassing a ca. 60-degree latitudinal gradient from tropical
(Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to
constrain integrated vascular plant carbon storage/transport times (âresidence timesâ).
Using a modeling framework, we find that, in addition to a "young" (conditionally
defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the
fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the
environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old
pool of 28 ky (±9.4, standard deviation), indicating extensive pre-aging in permafrost
soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger,
7.9 (±5.0) and 2.4 (±0.50) to 3.2 (±0.54) ky, respectively, indicating less protracted
storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for
Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool,
respectively), likely reflecting episodic transport of OC from steep hillside slopes
surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta,
respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay
of OC inflow, potentially related to transport time to the offshore basin. Modeling results
also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30
years of age), pointing to the presence of an intermediate reservoir.
Overall, these results show that a significant fraction of vascular plant C
undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine
sediments. The age distribution, reflecting both storage and transport times, likely
depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the
degree of soil buildup and preservation. We show that catchment-specific carbon
residence times across landscapes can vary by an order of magnitude, with important
implications both for carbon cycle studies and for the interpretation of molecular
terrestrial paleoclimate records preserved in sedimentary sequences.Financial support was provided by a Schlanger Ocean
Drilling Graduate Fellowship (NJD), an EPA STAR Graduate Fellowship (NJD), a Dutch
NWO Veni grant #825.10.022 (JEV), US NSF grants #OCE-0137005 (TIE and KAH),
#OCE-052626800 (TIE), #OCE-0961980 (ERMD), and #EAR-0447323 (ERMD and
JRS), a Swiss SNF grant #200021_140850 (TIE), a Swedish Research Council grant
#2013-05204 (MS), as well as the Stanley Watson Chair for Excellence in Oceanography
at WHOI (TIE) and the WHOI Arctic Research Initiative (TIE and LG)
Western Atlantic Intertropical Convergence Zone variability over the last full glacial cycle
Pptn. changes in the western tropical Atlantic over the past 180,000 years are reconstructed using the stable
carbon and deuterium isotopic compns. of higher plant leaf waxes preserved in Cariaco Basin sediments.
Results indicate that less (more) pptn. fell over northern South America during stadial (interstadial) periods
relative to today. Moreover, this trend is highly modulated by precessionally driven oscillations in Nov.
insolation, such that dry events concurrent with periods of increased solar heating were less arid than those
occurring when that heating was diminished (and visa versa). Together, these findings suggest that the
duration of the seasonal displacement of the Intertropical Convergence Zone (ITCZ) was modified in
response to changes in both the high latitude North Atlantic (presumably due to variations in the rate of
meridional overturning circulation) and tropical insolation during the last glacial cycle, thus establishing an
important link between seasonality and abrupt climate change
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