7 research outputs found
Quantifying bioturbation of a simulated ash fall event
<p>Tephrochronology allows the establishment of ‘isochrons’ between marine, lacustrine, terrestrial and ice cores, typically
based on the geochemical fingerprint of the tephra. The development of cryptotephrochronology has revealed a vast inventory
of isochrons which hold the potential to improve stratigraphic correlation and identify systemic leads and lags in periods
of rapid climate change. Unfortunately, bioturbation acts to blur these isochrons, reducing the temporal resolution in marine
and lacustrine records. In order to better resolve these event horizons, we require a better understanding of bioturbative
processes, and the depth and time over which they operate. To this end, an ash fall event was simulated on the intertidal
zone of the Eden Estuary, Fife, Scotland and sediment cores were collected over 10 days. A novel approach to tephra quantification
was developed, using the imaging software ImageJ. Our results showed limited bioturbation (mixed depth=18 mm), most likely
owing to the fine grain size, low-energy environment and the resulting faunal composition of the sediments. These results
imply a strong ecological control on bioturbation, and suggest that inferences may be made about palaeoenvironments from the
observed bioturbation profiles.
</p
Iceberg-rafted tephra as a potential tool for the reconstruction of ice-sheet processes and ocean surface circulation in the glacial North Atlantic
<p>Ice-rafted tephra deposits, of Marine Isotope Stage 6 (MIS 6) age, from Site U 1304 on the Gardar Drift, North Atlantic were
examined for their shard size distribution and major element composition. The heterogeneous composition, large shard sizes
and association with ice-rafted debris (IRD) indicate that these late MIS 6 deposits were transported by iceberg-rafting from
Iceland to Site U 1304. Comparison of individual shard geochemistry with the geochemistry of Holocene volcanic systems from
Iceland allows the identification of different potential volcanic source regions. This detailed geochemical analysis, when
combined with Icelandic Ice Sheet (IIS) flow models for the Last Glacial Maximum (LGM), suggests that the IIS had calving
margins to both the north and south during the late MIS 6 and that icebergs could have been transported to the Site U 1304
by following surface ocean circulation patterns similar to those that prevailed during the LGM. We demonstrate that the descriptive
concept of Icelandic glass in the characterization of tephra components within North Atlantic IRD can be significantly improved
through quantitative characterization and that such data hold the potential to help constrain surface ocean circulation models,
while also potentially yielding new information about the IIS during earlier glacial periods.
</p
Scanning electron micrographs of <i>Haynesina germanica</i> following exposure to each of the CO<sub>2</sub> treatments.
<p>SEM images of specimens taken at 380(A & B), 750 ppm (C & D) and 1000 ppm (E & F). (A) Side view of apertural region showing numerous sharp tubercles. Note diatom impaled on ornamentation (*). (B) Scanning electron micrograph of test surface of specimen 2A. (C) Side view of apertural region, showing tubercles and teeth. (D) Scanning electron micrograph of test surface of specimen 2C. (E) Side view of apertural region. Note the distinct absence of the numerous conical tubercles present in 2A. (F) Scanning electron micrograph of test surface of specimen 2E. Note surface dissolution and cracking damage.</p
Summary of main morphological features at each CO<sub>2</sub> treatment.
<p>Summary of main morphological features at each CO<sub>2</sub> treatment.</p
Scanning electron micrographs of <i>Haynesina germanica</i>.
<p>(A) Scanning electron micrograph of typical test, side view. (B) Higher magnification view of apertural region, showing tubercles and teeth lining the aperture. (C) Scanning electron micrograph of typical test, apertural view. (D) Higher magnification view of apertural region. Note impaled diatom (*).</p
Fjord systems and archives: a review
<p>Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters
from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally
controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that
represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence
of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still
possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the
removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial
cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjords
ideal depositional environments for preserving continuous records of climate and environmental change with high temporal resolution.
In addition to acting as high-resolution environmental archives, fjords can also be thought of as mini-ocean sedimentary basin
laboratories. Fjords remain an understudied and often neglected sedimentary realm. With predictions of warming climates, changing
ocean circulation and rising sea levels, this volume is a timely look at these environmentally sensitive coastlines.
</p
Fjord systems and archives: a review
<p>Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters
from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally
controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that
represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence
of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still
possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the
removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial
cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjords
ideal depositional environments for preserving continuous records of climate and environmental change with high temporal resolution.
In addition to acting as high-resolution environmental archives, fjords can also be thought of as mini-ocean sedimentary basin
laboratories. Fjords remain an understudied and often neglected sedimentary realm. With predictions of warming climates, changing
ocean circulation and rising sea levels, this volume is a timely look at these environmentally sensitive coastlines.
</p