isotopes
Evaluation of the fidelity of isotope records as an environmental proxy in the coral Montastraea
Tue, 01/24/2012 - 13:52 — leonmiWatanabe, T., A. Winter, T. Oba, R. Anzai, and H. Ishioroshi. 2002. Evaluation of the fidelity of isotope records as an environmental proxy in the coral montastraea. Coral Reefs 21 (2) (JUL): 169-78.
Abstract:
Many studies of climate variability in the
Tropical Ocean have used high-resolution chemical
tracer records contained in coral skeletons. The complex
architecture of coral skeletons may lead to the
possibility of biases in coral records and it is therefore
important to access the fidelity of coral geochemical
records as environmental proxies. Coral skeletal records
from the same coral colony, and even the same
corallite, may show large variation due to differing
extension rates, formational timing of the skeletal elements,
colony topography, and sampling resolution. To
assess the robustness of the skeletal record, we present
d13C and d18O data based on different sampling resolutions,
skeletal elements, and coral colonies of Montastraea
faveolata species complex, the primary coral
used for climate reconstruction in the Atlantic. We
show that various skeletal elements produce different
isotopic records. The best sampling rate to resolve the
full annual range of sea surface temperature (SST) is 40
samples per year. This sampling frequency also consistently
recovered SST variability measured at weekly
intervals. A sampling rate of 12 times per year recovered
84% of the annual range recording average
monthly SST changes through the year. Six samples per
year significantly decreased the ability to resolve the
annual SST range. The d18O recorded from two adjacent
colonies were very similar, suggesting that this
isotope can be trusted to record environmental changes.
The d13C, on the other hand, remained highly variable,
perhaps as a result of the activity of symbiotic algae
(zooxanthellae).
Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of Puerto Rico
Tue, 01/24/2012 - 12:47 — leonmiLachnicht, SL, PF Hendrix, and X. Zou. 2002. Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of puerto rico. Biology and Fertility of Soils 36 (1) (AUG): 43-52.
Abstract:
Investigation of single or mixed assemblages of
native Estherella sp. and exotic Pontoscolex corethrurus
from a rain forest in Puerto Rico was undertaken to understand
resource use patterns, and linkages with C and N
mineralization in a 19-day incubation. Resource use was
explored with addition of 15N-enriched leaf litter and 13Cenriched
glucose to reconstructed organic and mineral soil
horizons. Juvenile Estherella sp. became at least 6.06‰
more enriched in 13C than sub-adult Estherella sp. or adult
P. corethrurus. Sub-adult Estherella sp. became >3.6‰
enriched in 13C over P. corethrurus. δ15N acquired by P.
corethrurus was greater by 0.83–1.56‰ in the mixed-species
than the single-species assemblages. δ15N of subadult
Estherella sp. was enriched by 0.73–0.81‰ over juvenile
Estherella sp. in the single-species assemblage. Net
N immobilization occurred in the organic layer of all 15Nenriched
treatments. Net N mineralization in mineral soil
layers was significantly greater in microcosms with P.
corethrurus than in those containing only Estherella sp..
Cumulative respiration was greatest in P. corethrurus assemblages,
however, assemblages with only Estherella sp.
released more 13C in respiration. P. corethrurus assimilated
different N resources when incubated with, as compared
to without, native Estherella sp.. δ13C and δ15N signatures
acquired by assimilation of 13C and 15N differed
by species, developmental stage, and competitive interactions.
The results showed that alone, exotic P. corethrurus
induced higher mineralization rates than native Estherella
sp., but that the interaction of exotic and native species
impinged on resource use by P. corethrurus, reducing the
effect of the exotic species on C and N mineralization. Invasion
of exotic P. corethrurus may change the mineralization
potentials of C and N and their biogeochemical cycling
in soils.
Greater Soil Carbon Sequestration under Nitrogen-Fixing Trees Compared with Eucalyptus Species
Tue, 01/24/2012 - 12:38 — leonmiResh, SC, D. Binkley, and JA Parrotta. 2002. Greater soil carbon sequestration under nitrogen-fixing trees compared with eucalyptus species RID A-2703-2010. Ecosystems 5 (3) (APR): 217-31.
Abstract:
Forests with nitrogen-fixing trees (N-fixers) typically
accumulate more carbon (C) in soils than similar
forests without N-fixing trees. This difference
may develop from fundamentally different processes,
with either greater accumulation of recently
fixed C or reduced decomposition of older soil C.
We compared the soil C pools under N-fixers with
Eucalyptus (non-N-fixers) at four tropical sites: two
sites on Andisol soils in Hawaii and two sites on
Vertisol and Entisol soils in Puerto Rico. Using stable
carbon isotope techniques, we tracked the loss
of the old soil organic C from the previous C4 land
use (SOC4) and the gain of new soil organic C from
the C3, N-fixer, and non-N-fixer plantations
(SOC3). Soils beneath N-fixing trees sequestered
0.11 + 0.07 kg m-2 y-' (mean ± one standard
error) of total soil organic carbon (SOCT) compared
with no change under Eucalyptus( 0.00 ± 0.07 kg
m-2 y-1; P = 0.02). About 55% of the greater
SOCT sequestration under the N-fixers resulted
from greater retention of old SOC4, and 45% resulted
from greater accretion of new SOC3. Soil N
accretion under the N-fixers explained 62% of the
variability of the greater retention of old SOC4 under
the N-fixers. The greater retention of older soil
C under N-fixing trees is a novel finding and may
be important for strategies that use reforestation or
afforestation to offset C emissions.
Review of Use of Isotopes in Studying the Natural History of Puerto Rico
Thu, 01/19/2012 - 14:43 — leonmiEvaristo J. Review of Use of Isotopes in Studying the Natural History of Puerto Rico. University of Pennsylvania. 2012.
Abstract:
This review summarizes the earth and environmental science research papers in Puerto Rico that used isotopic techniques between 1965 and 2011. The range of applications in isotope-related research in Puerto Rico has grown steadily, led by the ubiquitous utility of stable isotope ratios in biogeochemical (δ13C, δ15N) and ecological (δ13C, δ15N, δD) research. Moreover, research in climatology has grown in recent years, spanning from the evaluation of the fidelity of isotope records (δ18O, δ13C) as an environmental proxy to the elucidation of multidecadal variability for paleoclimate reconstructions (δ18O and Sr/Ca). On the other hand, in addition to using isotope ratios, hydrological studies in Puerto Rico have also used trace element data to answer flow source (δD, δ18O, 87Sr/86Sr) and solute source (Ge/Si) questions, as well as in examining groundwater/surface flow relationships (222Rn). Finally, various isotope data have been used in trying to understand geomorphological (10Be, δ30Si) and geophysical (Pb, Nd, and Sr) phenomena. It is hoped that this review will be able to contribute to stimulating future interests in isotope-related research as applicable in the LCZO or Puerto Rico, in particular, and/or in comparable humid tropical settings, in general.
Cloud water in windward and leeward mountain forests: The stable isotope signature of orographic cloud water
Thu, 07/28/2011 - 16:09 — ckassScholl, M. A., T. W. Giambelluca, S. B. Gingerich, M. A. Nullet, and L. L. Loope (2007), Cloud water in windward
and leeward mountain forests: The stable isotope signature of orographic cloud water, Water Resour. Res., 43, W12411,
doi:10.1029/2007WR006011.
Abstract:
Cloud water can be a significant hydrologic input to mountain forests. Because it is a
precipitation source that is vulnerable to climate change, it is important to quantify
amounts of cloud water input at watershed and regional scales. During this study, cloud
water and rain samples were collected monthly for 2 years at sites on windward and
leeward East Maui. The difference in isotopic composition between volume-weighted
average cloud water and rain samples was 1.4% d18O and 12% d2H for the windward site
and 2.8% d18O and 25% d2H for the leeward site, with the cloud water samples enriched
in 18O and 2H relative to the rain samples. A summary of previous literature shows
that fog and/or cloud water is enriched in 18O and 2H compared to rain at many locations
around the world; this study documents cloud water and rain isotopic composition
resulting from weather patterns common to montane environments in the trade wind
latitudes. An end-member isotopic composition for cloud water was identified for each site
and was used in an isotopic mixing model to estimate the proportion of precipitation
input from orographic clouds. Orographic cloud water input was 37% of the total
precipitation at the windward site and 46% at the leeward site. This represents an estimate
of water input to the forest that could be altered by changes in cloud base altitude resulting
from global climate change or deforestation.
Sr isotopes as a tracer of weathering processes and dust inputs in a tropical granitoid watershed, Luquillo Mountains, Puerto Rico
Thu, 07/28/2011 - 15:52 — ckassPett-Ridge J. C., Derry L. A. and Kurtz A. C. (2009) Sr isotopes as
a tracer of weathering processes and dust inputs in a tropical
granitoid watershed, Luquillo Mountains, Puerto Rico. Geochim.
Cosmochim. Acta 73, 25–43.
Abstract:
Sr isotope data from soils, water, and atmospheric inputs in a small tropical granitoid watershed in the Luquillo Mountains
of Puerto Rico constrain soil mineral development, weathering fluxes, and atmospheric deposition. This study provides
new information on pedogenic processes and geochemical fluxes that is not apparent in watershed mass balances based on
major elements alone. 87Sr/86Sr data reveal that Saharan mineral aerosol dust contributes significantly to atmospheric inputs.
Watershed-scale Sr isotope mass balance calculations indicate that the dust deposition flux for the watershed is
2100 ± 700 mg cm2 ka1. Nd isotope analyses of soil and saprolite samples provide independent evidence for the presence
of Saharan dust in the regolith. Watershed-scale Sr isotope mass balance calculations are used to calculate the overall
short-term chemical denudation velocity for the watershed, which agrees well with previous denudation rate estimates based
on major element chemistry and cosmogenic nuclides. The dissolved streamwater Sr flux is dominated by weathering of plagioclase
and hornblende and partial weathering of biotite in the saprock zone. A steep gradient in regolith porewater 87Sr/86Sr
ratio with depth, from 0.70635 to as high as 0.71395, reflects the transition from primary mineral-derived Sr to a combination
of residual biotite-derived Sr and atmospherically-derived Sr near the surface, and allows multiple origins of kaolinite to be
identified
