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Papers by Matt Konfirst

Palaeogeography, Palaeoclimatology, Palaeoecology, 2012

ABSTRACT In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo ... more ABSTRACT In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo Ice Shelf) project recovered a 1285 m sediment core from beneath the Ross Ice Shelf near Ross Island, Antarctica. Contained within the upper ~ 600 m of this core are sediments recording 38 glacial/interglacial cycles of Early Pliocene to Pleistocene time, including 13 discrete diatomite units (DU). The thickest of these, DU XI, is ~ 76 m thick, has been assigned an Early Pliocene age (5–3 Ma), and represents several extended periods of uninterrupted sediment accumulation. A combination of geochemical and biological data was used to examine the role of changes in sediment source areas on diatom community composition. Peak-area count-ratios from the data collected with the XRF core scanner include K:Fe and Ti:K. K is lower and Ti higher in the volcanic series sampled. K:Fe is an indicator of the source area of fine-grained sediment delivered to the site by terrestrial and marine sedimentary processes (glacial, fluvial, eolian, gravitational, marine currents), while Ti:K is primarily associated with Ross Sea volcanic sources. A comparison of these two elemental ratios shows an anti-correlation, indicating changes in source rocks with time. Furthermore, relative abundance of the diatom genus, Chaetoceros, varies in the same sense and magnitude as K:Fe, suggesting that climatically-driven changes in sediment source regions are related to variations in abundance. It is suggested that increases in TAM-sourced sediment at the ANDRILL AND-1B site caused increased nutrient levels in the water column, leading to blooms of this genus, which is consistent with current known ecological preferences.

Marine Micropaleontology, 2012

ABSTRACT The goal of this study is to assess the changes that have occurred during the Mid-Pleist... more ABSTRACT The goal of this study is to assess the changes that have occurred during the Mid-Pleistocene Transition, an important transitional period in cryosphere evolution, by examining the siliceous microfossil record of sediments collected proximal to a major ice drainage outlet for the West Antarctic Ice Sheet. Core PS58/254 was collected from a sediment drift on the upper continental rise in the Amundsen Sea, directly offshore from Pine Island Bay, one of the three main discharge areas for the West Antarctic Ice Sheet (WAIS). Published data on physical properties, geochemical composition, grain size and clay mineral assemblages are complemented here by a high-resolution record (sample spacing 10 cm) of the siliceous microfossil assemblages (diatoms and silicoflagellates). Between 1200 ka and 621 ka, the assemblage is relatively diverse, with Actinocyclus ingens, Thalassiothrix antarctica and Fragilariopsis kerguelensis dominating the assemblages, but diatom abundance is variable from low to barren. Additionally, the occurrence of A. ingens, Thalassiosira elliptipora and Thalassiosira fasciculata is used to confirm and further refine the existing age model and extend it back to 1200 ka. Species composition during the last ca. 621 ka is dominated by F. kerguelensis, which consistently comprises 80-90% of the assemblage. A clear relationship between diatom abundance and glacial/interglacial variability is apparent after 621 ka, which resembles the glacial-interglacial variability previously observed in other proxy data. A significant change in both sediment composition and diatom assemblages is observed at 621 ka. This change concurs with the last abundant occurrence of A. ingens and the end of the Mid-Pleistocene Transition (MPT, i.e. the onset of modern eccentricity/precession-paced glacial cycles around 650 ka). We suggest that during interglacial periods after 621 ka the Amundsen Sea Low pressure system shifted seasonally southwestwards towards the shelf and thereby increased the advection of relatively warm Circumpolar Deep Water (CDW) onto the Amundsen Sea shelf, which is a major factor for present ice-sheet melting in this part of West Antarctica.

Marine Micropaleontology, 2011

Journal of Paleolimnology, 2011

Marine Micropaleontology, 2015

article i nfo Accumulation of fossil diatoms in marine sediments is variably affected by the prod... more article i nfo Accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of diatom frustules across space and time. No quantitative proxy exists for estimating the amount of silica lost to dissolution in Southern Ocean sediment cores. To address this gap, cultured valves of Fragilariopsis kerguelensis, the dominant planktonic diatom in the Pleistocene to recent Southern Ocean, were dissolved progressively under controlled laboratory conditions. Expansion, and eventual conjoining, of the areolae of F. kerguelensis advances through several phases, which are presented herein as a measure of diatom dissolution. In order to evaluate the validity of laboratory methods, this proxy is applied to sediments from piston core PS58/254 from the Amundsen Sea. Dissolution-induced degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in sediments, thus suggesting the laboratory conditions accurately reflect the natural process of dissolution. These resultsrepresentthe firstapplication of afullyquantitativeproxyfordiatomdissolution toSouthernOcean sediments, revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of diatom valves. Intensity of diatom dissolution in core PS58/254 does not correspond to the relative abundance of any diatom species, clay mineralogy, or linear sedimentation rates. However, a correlation does exist between glacial cyclicity and diatom dissolution, indicating that variation in average wall thickness and susceptibility to dissolution reflects primary conditions during formation of the silica wall, transit through the water column, and eventual deposition. Higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during interglacials. This result is consistent with the predictions of the silicic acid leakage hypothesis (SALH), whereby reduced rates of Si usage in the Southern Ocean lead to shifts in marine primary productivity in the tropics from coccolithophoriddominance duringinterglacialstodiatomdominanceduringglacials.Thiswouldfuela decrease in atmospheric pCO2duringglacials. Silica acidleakage isdrivenbya decreaseinthe Si:Nratioofdiatoms,caused by increased iron input to glacial-aged Southern Ocean waters. This resulted in more lightly silicified diatom valves in the Southern Ocean, which dissolved more quickly in the upper water column, thereby maintaining the high silica content of glacial-aged SO waters, and allowing for export of Si to upwelling zones in the lower latitudes.

In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo Ice Shelf... more In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo Ice Shelf) project
recovered a 1285 m sediment core from beneath the Ross Ice Shelf near Ross Island, Antarctica. Contained
within the upper ~600 m of this core are sediments recording 38 glacial/interglacial cycles of Early Pliocene
to Pleistocene time, including 13 discrete diatomite units (DU). The thickest of these, DU XI, is ~76 m thick,
has been assigned an Early Pliocene age (5–3 Ma), and represents several extended periods of uninterrupted
sediment accumulation. A combination of geochemical and biological data was used to examine the role of
changes in sediment source areas on diatom community composition. Peak-area count-ratios from the data
collected with the XRF core scanner include K:Fe and Ti:K. K is lower and Ti higher in the volcanic series sampled.
K:Fe is an indicator of the source area of fine-grained sediment delivered to the site by terrestrial and
marine sedimentary processes (glacial, fluvial, eolian, gravitational, marine currents), while Ti:K is primarily
associated with Ross Sea volcanic sources. A comparison of these two elemental ratios shows an anticorrelation,
indicating changes in source rocks with time. Furthermore, relative abundance of the diatom
genus, Chaetoceros, varies in the same sense and magnitude as K:Fe, suggesting that climatically-driven
changes in sediment source regions are related to variations in abundance. It is suggested that increases in
TAM-sourced sediment at the ANDRILL AND-1B site caused increased nutrient levels in the water column,
leading to blooms of this genus, which is consistent with current known ecological preferences.

The goal of this study is to assess the changes that have occurred during the Mid-Pleistocene Tra... more The goal of this study is to assess the changes that have occurred during the Mid-Pleistocene Transition, an
important transitional period in cryosphere evolution, by examining the siliceous microfossil record of sediments
collected proximal to a major ice drainage outlet for the West Antarctic Ice Sheet. Core PS58/254 was
collected from a sediment drift on the upper continental rise in the Amundsen Sea, directly offshore from
Pine Island Bay, one of the three main discharge areas for the West Antarctic Ice Sheet (WAIS). Published
data on physical properties, geochemical composition, grain size and clay mineral assemblages are complemented
here by a high-resolution record (sample spacing 10 cm) of the siliceous microfossil assemblages (diatoms
and silicoflagellates). Between 1200 ka and 621 ka, the assemblage is relatively diverse, with
Actinocyclus ingens, Thalassiothrix antarctica and Fragilariopsis kerguelensis dominating the assemblages, but
diatom abundance is variable from low to barren. Additionally, the occurrence of A. ingens, Thalassiosira
elliptipora and Thalassiosira fasciculata is used to confirm and further refine the existing age model and extend
it back to 1200 ka. Species composition during the last ca. 621 ka is dominated by F. kerguelensis, which
consistently comprises 80-90% of the assemblage. A clear relationship between diatom abundance and
glacial/interglacial variability is apparent after 621 ka, which resembles the glacial-interglacial variability
previously observed in other proxy data.
A significant change in both sediment composition and diatom assemblages is observed at 621 ka. This
change concurs with the last abundant occurrence of A. ingens and the end of the Mid-Pleistocene Transition
(MPT, i.e. the onset of modern eccentricity/precession-paced glacial cycles around 650 ka). We suggest that
during interglacial periods after 621 ka the Amundsen Sea Low pressure system shifted seasonally southwestwards
towards the shelf and thereby increased the advection of relatively warm Circumpolar Deep
Water (CDW) onto the Amundsen Sea shelf, which is a major factor for present ice-sheet melting in this
part of West Antarctica.

We present a diatom record from a sediment core taken in Lake Fryxell, Taylor Valley, Antarctica.... more We present a diatom record from a
sediment core taken in Lake Fryxell, Taylor Valley,
Antarctica. Six zones were defined using diatom
assemblage changes that indicate varying limnological
conditions. The early lake stage, ca. 35,000 cal
years BP, is characterized by Mayamea atomus f.
permitis, a species rarely reported in modern Antarctic
Dry Valley environments. An extended period
from ca. 35,000 to 19,000 cal years BP is characterized
by low diatom abundance, with dominant taxa
Luticola spp., Muelleria spp., and Diadesmis contenta.
The modern assemblage was established ca.
13,000 cal years BP, after two relatively brief transitional
stages. One key species for this recent period,
Navicula lineola var. perlepida, is absent in surface
sediments and the modern environment, indicating an
environmental change within the last several centuries.
The diatom assemblage is compared to modern
diatom communities in Dry Valley streams, which
provide the most complete information on diatom
distributions in this region. Although precise environmental
interpretation of the core is hampered by
limited knowledge of environmental constraints on many of the diatom taxa present in the lake core, the
data provide important new insights into the history
of Glacial Lake Washburn.

In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing-McMurdo Ice Shelf)... more In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing-McMurdo Ice Shelf) project
recovered a 1285 m sediment core from beneath the Ross Ice Shelf near Ross Island, Antarctica in a flexural
moat associated with volcanic loading. The upper ~600 m of this core contain sediments recording 38 glacial/
interglacial cycles of Early Pliocene to Pleistocene time, including 13 discrete diatomite units (DUs). The
longest of these, DU XI, is ~76 m-thick, and has been assigned an Early to Mid-Pliocene age (5–3 Ma). A
detailed record of the siliceous microfossil assemblages in DU XI is used in conjunction with geochemical and
sedimentological data to subdivide DU XI into four discrete subunits of continuous sedimentation. Within
each subunit, changes in diatom assemblages have been correlated with the δ18O record, providing a temporal
resolution up to 600 yr, and allowing for the construction of a detailed age model and calculation of associated
sediment accumulation rates within DU XI. Results indicate a productivity-dominated sedimentary record
with greater proportions of hemipelagic mud accumulating during relatively cool periods. This implies that
even during periods of substantial warmth, Milankovitch-paced changes in Antarctic ice volume can be linked
to ecological changes recorded in diatom assemblages.

In the ANDRILL (ANtarctic geologic DRILLing project) AND-1B core, an ~80 m-long interval of early... more In the ANDRILL (ANtarctic geologic DRILLing project) AND-1B core, an ~80 m-long interval of early Pliocene
diatomite was obtained (382.98–440.12 m below sea floor). To better understand the role of fragmentation
on diatom preservation within this unit, data were collected from 154 samples on the size and number of
fragments of specimens of the diatom genus, Rouxia. The number of frustule fragments was classified into
categories based on the amount of intact raphe and then evaluated using a formula created to characterize
the nature and degree of fragmentation in each sample. Variations in fragmentation were compared with
the age model and indicate a relationship between fragmentation and sediment accumulation rates for the
lower ~37 m with higher fragmentation related to lower accumulation rates of hemipelagic mud during
warmer intervals. This relationship is not as pronounced in the upper ~20 m, which can be related to the frequent
occurrence of sandstone layers, lenses and laminated intervals. After evaluating a number of hypotheses,
the most plausible explanation is that the presence of greater proportions of hemipelagic mud
produces a cushioning effect, which prohibits the interaction of diatom frustules with sand grains or other
diatoms, thereby reducing fragmentation.

Accumulation of fossil diatoms in marine sediments is variably affected by the production and dis... more Accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of
diatom frustules across space and time. No quantitative proxy exists for estimating the amount of silica lost to
dissolution in Southern Ocean sediment cores. To address this gap, cultured valves of Fragilariopsis kerguelensis,
the dominant planktonic diatom in the Pleistocene to recent Southern Ocean, were dissolved progressively
under controlled laboratory conditions.
Expansion, and eventual conjoining, of the areolae of F. kerguelensis advances through several phases, which
are presented herein as a measure of diatom dissolution. In order to evaluate the validity of laboratory methods,
this proxy is applied to sediments from piston core PS58/254 from the Amundsen Sea. Dissolution-induced
degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in
sediments, thus suggesting the laboratory conditions accurately reflect the natural process of dissolution.
These results represent the first application of a fully quantitative proxy for diatomdissolution to Southern Ocean
sediments, revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of
diatom valves. Intensity of diatom dissolution in core PS58/254 does not correspond to the relative abundance
of any diatom species, clay mineralogy, or linear sedimentation rates. However, a correlation does exist between
glacial cyclicity and diatom dissolution, indicating that variation in average wall thickness and susceptibility to
dissolution reflects primary conditions during formation of the silica wall, transit through the water column,
and eventual deposition.
Higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during
interglacials. This result is consistent with the predictions of the silicic acid leakage hypothesis (SALH), whereby
reduced rates of Si usage in the Southern Ocean lead to shifts in marine primary productivity in the tropics from
coccolithophorid dominance during interglacials to diatomdominance during glacials. Thiswould fuel a decrease
in atmospheric pCO2 during glacials. Silica acid leakage is driven by a decrease in the Si:N ratio of diatoms, caused
by increased iron input to glacial-aged Southern Ocean waters. This resulted in more lightly silicified diatom
valves in the Southern Ocean, which dissolved more quickly in the upper water column, thereby maintaining
the high silica content of glacial-aged SO waters, and allowing for export of Si to upwelling zones in the lower
latitudes.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2012

Marine Micropaleontology, 2012

Marine Micropaleontology, 2011

Journal of Paleolimnology, 2011

Marine Micropaleontology, 2015