SEMINAR: MGG Student seminar, Tuesday, at noon

["Katherine Inderbitzen" <kinderbitzen@rsmas.miami.edu>]

MGG presents its weekly student seminar at 12:00 PM, Tuesday, in the CIMAS
conference room.  This week's speakers are:

Kelly Gibson
A multi-proxy, high resolution record of Termination I in Cariaco Basin

The Cariaco Basin, located off the northern coast of Venezuela, provides an
opportunity to examine the response of the tropics to the deglaciation at
high
resolution.  Though previous studies have utilized the sediment record of
the basin
to explore this interval, inconsistencies between some proxies complicate the
interpretation of changes in surface water productivity, riverine input,
and basin
ventilation. Early oxygen isotope data allow for little to no YD cooling
of surface
waters in the basin, while more recent Mg/Ca data suggest a decrease of
3-4oC,
equivalent to a return to glacial sea surface temperatures (SST). Regional
data
support a southward shift of the Intertropical Convergence Zone (ITCZ)
during the
YD, which could at least partially explain cooler SST through stronger
trade winds
and increased upwelling; however, standard paleoproductivity proxies yield
conflicting interpretations of the direction and magnitude of productivity
changes
that would be expected of stronger upwelling. In addition, sediment
concentrations
of the redox-sensitive trace metal molybdenum and the presence of a
limited benthic
fauna in YD sediments both suggest some degree of bottom water
oxygenation, contrary
to the expected state of anoxia that is presently understood to be
generated by high
levels of surface productivity in the basin.  We attempt to resolve some
of these
inconsistencies by presenting a high resolution, multi-proxy record of
Termination I
in the Cariaco Basin from IMAGES Calypso core MD03-2621, including its
onset and
termination. Paired, multi-species Mg/Ca and oxygen isotope records
provide sea
surface temperature and sea surface salinity records, while benthic
foraminiferal
census and oxygen isotope data, combined with elemental data generated by
scanning
XRF, illuminate the nature of basin oxygenation and deep water conditions
during
this period. The timing and magnitude of paleoenvironmental changes in the
Cariaco
Basin during the YD can be expected to provide insights into the response
of the
tropics to abrupt climate changes.


Noelle Van Ee
Capturing Carbonate Heterogeneity in Multiple Dimensions and Scales,
Glover?s Reef, Belize

Glover?s Reef is a 260-km2 reef-rimmed platform off the coast of Belize.
In the modern, the windward-leeward asymmetry and over 800 patch reefs in
the lagoon introduce considerable heterogeneity in both facies and
morphology. Rotary cores, over 100 km of seismic lines, satellite imagery,
petrophysical measurements, and sediment samples from patch reefs and the
marginal reef allow rigorous quantitative assessment of carbonate
heterogeneity in multiple dimensions and scales for the first time.
A single-channel seismic survey of approximately 111 km of grid lines with
0.5-2 km spacing and six rotary cores is used to determine relationships
between antecedent topography and the modern facies. The Pleistocene top
is imaged by a transparent to chaotic facies with a set of high amplitude
reflections forming an irregular top. In the Holocene section, two seismic
facies are identified; high amplitude, continuous reflections in the
topographic lows between the patch reefs, and a chaotic to transparent
facies that occurs within the Holocene highs. Even when accounting for the
pull-up effects caused by the Holocene reefs, Pleistocene topography
exists beneath the majority of patch reefs within the lagoon. What is
apparent in the cores but lacking from the seismic data; however, is that
topography is created by at least two stacked Pleistocene reefs.
Classification of Landsat (30-m resolution) and IKONOS (4-m resolution)
satellite imagery compared to ground-truthed bathymetry and sediment
samples illustrates facies heterogeneity on different scales.
Landsat-based classification images windward-leeward asymmetry on a
platform scale, while high-resolution IKONOS imagery is needed to capture
asymmetric morphology and facies changes on a patch reef scale (10s to
100s of meters).
Finally, core investigations reveal that vertical variability is dependent
on location with respect to the platform. While cores taken from the rim
record up to 9 m of Holocene framestone and boundstone, Holocene sections
of patch reef cores are comprised almost entirely of loose sand and coral
rubble.  The Pleistocene and Holocene of patch reefs record an ecological
succession of biogenic grainstone and branching corals followed
Montastraea annularis coral framestones and finally coral rubble. Higher
diversity rim cores illustrate both aggrading and prograding successions.



***************************
Katherine Inderbitzen
Rosenstiel School of Marine & Atmospheric Science
Marine Geology & Geophysics
kinderbitzen@rsmas.miami.edu


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