11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 4: Coral Reef Organisms as Recorders of Local and Global Environmental Change
4-26
Biologic Influence On Proxies Of Scleractinian Coral Skeleton
Anne JUILLET-LECLERC* 1 , Stéphanie REYNAUD 2
1 LSCE, CNRS, Gif sur Yvette, France, 2 CSM, Monaco, France
The coral skeleton d18O is the most commonly used SST proxy essentially depending on
external factors such as SST and water d18O.
Acropora cultured under variable light (equivalent to seasonal light variation) show
systematic d18O fractionation. But, temperature and light lead to opposite responses with
a lower effect due to light. This effect is associated to metabolic processes underlining
the strong relationship between metabolism of symbiotic algae and skeleton formation.
However, isotopic fractionation obeys to physical rules. Weber and Woodhead (1972)
provided annual mean isotope values, statistically significant, partly rejecting vital effect.
By using these data and introducing seawater d18O, we derived from these data Acropora
calibration similar to ones of Epstein.
The question arises if this effect is specific to cultured Acropora? In order to estimate the
influence of seasonality, we compared data measured on Porites colonies that developed
close to each other in a well-constrained environment. Although deposited under identical
conditions we obtain highly variable SST calibrations for different species, different
colonies and even different sampling on a single head. This can be only explained by
additional seasonal biologic effects. Light and temperature being the main seasonal
changes, we conclude that both temperature and light, in addition to the physical SST
influence, affect d18O through metabolism.
Based on these evidences we developed a new method using multi-proxies, which
revealed that corals are likely a better archive than a simple isotopic thermometer.
4-27
High-Resolution Acropora Cervicornis δ 18 o: Implications For Early Holocene
Caribbean Temperatures And Position Of The Intertropical Convergence Zone
Lida TENEVA* 1 , Lisa GREER 2 , William PATTERSON 3
1 Earth and Environmental Sciences, Columbia University, Palisades, NY, 2 Geology,
Washington and Lee University, Lexington, VA, 3 Geological Sciences, University of
Saskachewan, Saskatoon, SK, Canada
High-resolution coral 18O data, coupled with precise dating techniques, have the
potential to provide critical information on paleoclimate variability and tropical oceanatmosphere
interactions through time. Here we present paleotemperature data from welldated
pristine early Holocene (~9360-8900 years BP) Acropora cervicornis of the
Enriquillo Valley, Dominican Republic. A new paleotemperature reconstruction equation
based on previous Acropora coral culture studies (Reynaud et al. 2007) was used to
calculate Holocene temperature variability. Taking into account deglacial changes in
seawater 18O (∆ 18O) in the early Holocene, our data reveal lower temperatures than
previously estimated using equations based on molluskan calcite (Epstein et al. 1953,
O’Neil et al. 1969) and molluskan aragonite (Grossman and Ku 1986). Our calculations
show the early Holocene in the Dominican Republic was ~4oC cooler than today’s
average (26.5-29.5oC). We consider this temperature difference unrealistic, and propose
Dominican Holocene coral 18O data can be attributed to combined temperature and
salinity effects. The latter refers to a precipitation effect associated with a northward
incursion of the Intertropical Convergence Zone (ITCZ) in the early Holocene. Using the
culture-based temperature equation, the modern annual temperature range of 3oC for the
Dominican Republic would correspond to half the 18O amplitude observed in our
study. Thus, precipitation changes likely played an important role in 18O signal
variability since the deglacial ∆ 18O contribution peaked at ~0.46‰. On first order,
oxygen isotope records from this study show covariability in time with tropical ice cap
18 O data from Huascaran, Peru and Sajama, Bolivia. This may imply that at least in the
early Holocene, the northern Caribbean and northern South America may have derived
their moisture from the same source at the same time (i.e. enhanced ITCZ precipitation).
4-28
Eighty Years Long Oxygen And Carbon Isotopic Data Series From A Southwestern
Atlantic Coral
Ruy KIKUCHI* 1 , Henning KUHNERT 2 , Jürgen PÄTZOLD 3 , Zelinda LEAO 1 , Alexandre
COSTA 4 , Ricardo DOMINGUES 5 , Marília OLIVEIRA 1 , Carlos LENTINI 4
1 Geophysics and Geology Research Center, Universidade Federal da Bahia, Salvador, Brazil,
2 RCOM Research Centre for Ocean Margins, Universitaet Bremen, Bremen, Germany,
3 Universitaet Bremen, Bremen, Germany, 4 Institute of Physics, Universidade Federal da Bahia,
Salvador, Brazil, 5 Institute of Geosciences, Universidade Federal da Bahia, Salvador, Brazil
The oldest sea surface temperature instrumental records available in Brazilian Navy records
date from 1973, and climate proxy indicators in the Southwestern Atlantic are scarce, if not
absent. Our project aim to evaluate the quality and reconstruct the longer possible time series of
temperature record based on isotopic proxies in the endemic coral Mussismilia braziliensis
skeleton. This species is the main reef builder in Abrolhos Reef Complex. Seasonal temperature
amplitude in the region is about 4-5oC varying from about 23.5oC to 28.5oC. Turbidity and
cloudiness are greater during winter when southern polar fronts tend to reach Brazilian Eastern
Coast as far as 12oS. Among 15 cores taken in the region, one 70 cm long coral core (from
17o47,173'S, 39o02,935'W) was cut as a slab of 1,5 cm thick, X-rayed and sampled along a
growth axis from top to bottom every 0,5 mm with a 0,8 mm wide drill. The analyses were
made in a Finnigan MAT mass spectrometer coupled with an automated sampler. Both d18O
and d13C exhibited a cyclical pattern that, in general, conforms to the density banding. Oxygen
and carbon curves have inverse behavior relative do each other. d18O varies from -3.42 to -
3.70‰ (VPDB) and d13C from 2.04 to -2.46‰ (VPDB). The seasonality in d18O, in the order
of 0.4‰ is low compared to the expected seasonality 0.8‰-1.0‰, but is explained by the
depletion in 16O that occurs during the summer in seawater (ca. 0.5‰). The 80 years
represented by the isotopic data exhibit a decadal (ca. 12 years) variability and milder
temperatures before the 70's. Highest temperature signal occur in the end of the 70's and
beginning of the 80's and in 2001-2003.
4-29
Corals As Recorders Of Land-Ocean Carbon Transport in Puerto Rico Using δ 13 c And
Ba/ca
Ryan MOYER* 1 , Andrea GROTTOLI 1
1 School of Earth Science, The Ohio State University, Columbus, OH
Rivers link terrestrial and marine ecosystems and influence the abundance, composition, and
timing of carbon delivered to the coastal ocean. During periods of sustained high river
discharge, the stable carbon isotope (δ13C) signature of coastal seawater DIC is likely
influenced by the δ13C of the organic and inorganic carbon of the adjacent catchment. In
coastal areas where coral reefs occur in close proximity to the mouths of rivers, coral skeletal
δ13C should record deviations in seawater DI- δ13C during periods of high river discharge.
Additionally, Ba in coral skeletons acts as a conservative tracer of freshwater pulses in coastal
marine systems, and can be used to identify past flood events in coral cores. To further establish
this connection and extend the record of river discharge, coral skeletal δ13C and Ba/Ca were
measured in a Montastraea faveolata coral core collected approximately 400 m from the mouth
of the Fajardo River (Puerto Rico). Cross-spectral analysis of coral skeletal Ba/Ca and river
discharge yields significant bi-weekly coherence for the portion of the record where
instrumental river discharge records are available (1979 - 2004). Coral δ 13 C and river discharge
are annually coherent over this same time interval, with δ 13 C decreasing as discharge increases.
Coral Ba/Ca and δ 13 C are also annually coherent over the entire 56-year record. These data
suggest that such a multi-proxy approach is extremely valuable in elucidating periods of heavy
river discharge where coral δ 13 C is likely affected by terrestrial carbon transport. In combination
with previous work, the data also suggest that skeletal δ 13 C in corals growing near the mouths
of small tropical rivers provide a record of terrestrial carbon delivery to the coastal ocean and
coral reefs, as well as the land-use history of the river catchment.
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