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Background to the ANDRILL Southern McMurdo Sound Project, Antarctica
No full textDuring the austral spring of 2007, the Southern
McMurdo (SMS) Project recovered a 1138.54 meter
long drill core (AND-2A) from a 8.5 m thick floating seaice
platform (~8.5 meters thick) over approximately
380 meters of water (77°45.488S; 165°16.613E)
(Fig. 1). This demonstrated the ANDRILL Program’s
continuing success in recovering high quality marine
and glacimarine sedimentary drill core (> 98% core
recovery) from high latitude ice-covered areas. A
primary goal of the SMS Project, the second drillhole
of the McMurdo Sound Portfolio (Harwood et al.,
2006), was to recover an Antarctic marine sediment
record depositied during the middle Miocene, which
has long been held as one of the fundamental time
intervals in development of the modern Antarctic
ice sheets (e.g., Zachos et al., 2001; Shevenell et
al., 2004). Deep-sea stable isotope records suggest
the middle Miocene encompassed a change from
the warm Mid-Miocene Climatic Optimum (MMCO),
approximately 17.5 to 14.5 million years ago (Ma),
to the onset of major cooling between approximately
14.5 to 13.5 Ma, which is commonly interpreted as the
major cause of the formation of a quasi-permanent
ice sheet in East Antarctica (e.g., Haywood et al.,
2008, and references contained therein).
The AND-2A drill core, Pleistocene to early Miocene
in age (e.g., Acton et al., this volume), confirms its
potential to establish a robust history of Neogene
Antarctic ice sheet variation and climate evolution
that can be integrated into continental and global
records toward a better understanding of Antarctica’s
role in the past, present and future global system. In
particular, the recovery of middle Miocene Antarctic
stratigraphic sequences will greatly improve the
evaluation of global proxy records that invoke a
change from a warm climatic optimum to the onset
of major Miocene cooling. The uppermost section of
AND-2A core, Pliocene to Pleistocene in age, shows
a similar importance in providing an original record
that will complement and build on coastal and fjord
sediment records from previous drillcores west of
the drill site (Dry Valley Drilling Project (DVDP) -
10, -11 and Cenozoic Investigation in the Western
Ross Sea Project (CIROS) -2), and on the deeper
water sedimentary record from the AND-1B drillcore
in the McMurdo Ice Shelf area, all interpreted to
reflect repeated Late Neogene alternation between
‘interglacial’ and ‘glacial’ conditions (Barrett, 2007;
Naish et al., 2007, Naish et al., 2009).
In addition to their paleoclimatic implications, the
ongoing study of the drilled strata, with their variable
clast compositions reflecting an evolving provenance,
high content in Cenozoic volcanic detritus and fallout
products, abundant structures related to brittle
deformation, and a rich paleontological resource,
have already demonstrated that they will provide
important new information about the glacial history of
the Ross Embayement, the volcanic evolution of the
Erebus Volcanic Province and the tectonic evolution
of both the Antarctic Rift system (Victoria Land Basin
- VLB) and the adiacent sector of the Transantarctic
Mountains (TAM).
This volume presents the initial science results
of the AND-2A drill-hole. It derives from the Webbased
On-Ice Report and includes the results of corecharacterization
activities conducted by science team
members off-ice, prior to the core workshop held at
Florida State University, Antarctic Marine Geology
Research Facility, 30 April - 4 May 2008, where nearly
95 individuals presented their ongoing research on the
AND-2A recovered material. This contribution provides
background on the geological setting, site surveys,
and stratigraphic prognosis prior to drilling. The rest
of the volume contains 11 chapters and provides an
operational overview of the drilling operations, the
curation and management of the cores, ANDRILL’s
education and outreach program, and the initial
characterization of the drill core set out under major
discipline areas
Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica
No full textSampling of interstitial fl uids during deep coring in southern McMurdo Sound, Antarctica,
revealed the presence of seawater-sourced, hypersaline brine at depths >200 m below the seafl
oor. Na-Cl-Br and SO4-Cl-Br relationships are consistent with a concentration mechanism
that involves the removal of pure H2O as ice and precipitation of mirabilite (Na2SO4·10H2O)
during progressive freezing of seawater. The brine is in Neogene subglacial, glacimarine, and
marine facies that record advance and retreat of glaciers through the Ross Sea embayment.
In this environment, sea ice formation in semi-isolated marine basins that occupied fl exural
troughs along ice sheet margins produced dense brines that sank and infi ltrated the permeable
subglacial sediment. Repeated cycles of glacial advance and retreat provided multiple
opportunities for batches of seawater to be transformed into brine that now is in the subsurface
of southern McMurdo Sound. Results demonstrate the feasibility of brine formation via
seawater freezing and attest to the potential of a cryogenic origin for subsurface brines in
high-latitude regions of the Northern Hemisphere, as proposed by some workers
Total clast numbers per meter in sediment core AND-2A
No full textTotal clast numbers per meter in sediment core AND-2
Core description of Hole AND-2A (resolution: 600 m)
No full textCore description of Hole AND-2A (resolution: 600 m
Splitcore images of the AND-2A drill core, working half
No full textSplitcore images of the AND-2A drill core, working hal
Core description of Hole AND-2A (resolution: 100 m)
No full textCore description of Hole AND-2A (resolution: 100 m
Total clast numbers per 10 cm in sediment core AND-2A
No full textTotal clast numbers per 10 cm in sediment core AND-2
Core description of Hole AND-2A (resolution: 4 m)
No full textCore description of Hole AND-2A (resolution: 4 m
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