Quantitative precipitation estimation in Antarctica using different ZE-SR relationships based on snowfall classification combining ground observations by radar and disdrometer

2020 ◽  
Author(s):  
Alessandro Bracci ◽  
Nicoletta Roberto ◽  
Luca Baldini ◽  
Mario Montopoli ◽  
Elisa Adirosi ◽  
...  
Keyword(s):  
Quantitative Estimate ◽  
Global Climate ◽  
Ice Sheet ◽  
Estimation Methods ◽  
Antarctic Ice Sheet ◽  
Numerical Weather ◽  
Precipitation Estimation ◽  
Antarctic Continent ◽  
The Antarctic ◽  
Reflectivity Factor

<p>The Antarctic Ice Sheet plays a major role in regional and global climate variability and represents, probably, the most critical factor of future sea-level rise. Snow and solid precipitation more broadly have been recognized as primary mass input for ice sheet. However, despite its fundamental role in the surface mass balance estimation, precipitation over Polar region and in the Antarctica particularly, remains largely unknown, being not well assessed by numerical weather/climate models, by ground observations and satellite measurements as well. More accurate estimations of precipitation in the Antarctic continent are desirable not only in understanding the behavior of the Antarctic Ice Sheet, but also in validating global climate and numerical weather prediction models and also in order to constrain measurements from space during validation/calibration satellite campaigns.</p><p>Recently, several observatories in Antarctica have been equipped with equipment for cloud and precipitation measurements, such as the two Italian stations “Mario Zucchelli”, Terra Nova Bay, and Concordia, in the Antarctic Plateau. At “Mario Zucchelli”, instrumentation includes 24-GHz vertical pointing radar Micro Rain Radar (MRR) and optical disdrometer. The synergetic use of such set of instruments allows for characterizing and quantifying precipitation, even if quantitative estimate of precipitation from radar is extremely demanding, especially in snowfall, because of variability microphysical features of hydrometeors.</p><p>Usually precipitation estimation methods with weather radar are based on relationships between radar equivalent reflectivity factor (Ze) and liquid equivalent snowfall rate (SR). Several relationships are reported in literature, derived from comparison between radar and ground sensors but very few are suitable for the Antarctic continent and none also considers the microphysical characterization of hydrometeors.</p><p>This work shows quantitative estimate of the Antarctic precipitation for several snow episodes at the Mario Zucchelli station using specific ZE-SR relationships also taking into account the snowfall classification according to dominating hydrometeor type (e.g. pristine, aggregate, dendrite, plate). Microphysical properties of precipitation are inferred by comparing radar measurements with simulations obtained from disdrometer measurements in terms of reflectivity factor. Specifically, the Ze directly derived by radar has been compared with the Ze calculated by disdrometer observations coupling particle size distributions and NASA database of hydrometeor backscattering values based on the Discrete Dipole Approximation. More challenging are estimations at Concordia, where ice particles have very small sizes and are hardly detectable by laser disdrometer, and where MRR lacks of adequate sensitivity.</p>

scholarly journals Climate, the Antarctic ice sheet and ground heat flux

1995 ◽  
Vol 21 ◽  
pp. 144-148
Author(s):  
Garth W. Paltridge ◽  
Christopher M. Zweck
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Global Climate Models ◽  
Balance Model ◽  
Antarctic Ice Sheet ◽  
Ground Heat Flux ◽  
The Antarctic

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state height h and potential basal temperature Tb. Tb determines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values of h and Tb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.

scholarly journals Climate, the Antarctic ice sheet and ground heat flux

1995 ◽  
Vol 21 ◽  
pp. 144-148 ◽  
Author(s):  
Garth W. Paltridge ◽  
Christopher M. Zweck
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Global Climate Models ◽  
Balance Model ◽  
Antarctic Ice Sheet ◽  
Ground Heat Flux ◽  
The Antarctic

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state heighthand potential basal temperatureTb.Tbdetermines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values ofhandTb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.

scholarly journals Ice Induced Sea Level Change in the Late Neogene

2021 ◽  
Author(s):  
◽  
Gary Steven Wilson
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Level Fluctuation ◽  
Antarctic Ice Sheet ◽  
Continental Scale ◽  
Base Level ◽  
Late Neogene ◽  
Antarctic Continent ◽  
Sea Level Fluctuation ◽  
The Antarctic

<p>Two independent records of latest Neogene (2,0 - 6.0 Ma.) glacioeustasy are presented, one of Antarctic ice volume from East Antarctica and the other of eustatic sea level from the South Wanganui Basin, New Zealand. Glacial deposits in the Transantarctic Mountains (Sirius Group) and sediment at the Antarctic continental margin provide direct evidence of Antarctic ice sheet fluctuation. Evidence for deglaciation includes the occurrence of Pliocene marine diatoms in Sirius Group deposits, which are sourced from the East Antarctic interior. K/Ar and 39Ar/40Ar dating of a tuff in the CIROS-2 drill-core confirms their Pliocene age at high latitudes (78 [degrees] S) in Antarctica. Further evidence for Antarctic ice volume fluctuation is recorded by glaciomarine strata from the Ross Sea Sector cored by the CIROS-2 and DVDP-11 drill-holes. Magnetostratigraphy integrated with Beryllium-10, K/Ar and 39Ar/40Ar dating provides a high resolution ([plus or minus] 50 k.y.) chronology of events in these strata. In the Wanganui Basin, New Zealand, a 5 km thick succession of continental shelf sediments, now uplifted, records Late Neogene eustatic sea level fluctuation. In the Late Neogene, basin subsidence equalled sediment input allowing eustatic sea level fluctuation to produce a dynamic alternation of highstand, transgressive, and lowstand sediment wedges. This record of Late Neogene sea level variation is unequalled in its resolution and detail. Magnetostratigraphy provides a high resolution chronology for these sedimentary cycles as well as magnetic tie lines with the Antarctic margin record in McMurdo Sound. These two independent records of Late Neogene glacioeustasy are in good agreement and record the following history: The Late Miocene and Late Pliocene are times of low 'base level' glacioeustasy (here termed glacialism, rather than glacial), with growth of continental-scale ice sheets on the Antarctic continent causing a lowering of global sea level. The Early Pliocene was a time of high 'base level' glacioeustasy (here termed interglacialism, rather than interglacial), driven by collapsing of continental-scale ice sheets to local and subcontinental ice caps. The middle Pliocene is marked by a move into glacialism with an increasing 'base level' of glacioeustatic fluctuation. Higher-order glacial advances and associated eustatic sea-level lowering occurred at approximately 3.5 and 4.3 Ma., separating the Early Pliocene into 3 sea-level stages. Still higher-order glacioeustatic fluctuations are recognised in this study, with durations of 50 Ka. and 100 - 300 Ka.. The 100 - 300 Ka. duration cycles are prominent during interglacialisms, and the 50 Ka. duration cycles are prominent during glacialisms. These shorter duration fluctuations in glacioeustasy have already been recognised as glacial/deglacial cycles from detailed studies of the Quaternary. Four orders of sea-level fluctuation are recognised within the Late Neogene, these are of approximately 0.05 Ma., 0.1-0.3 Ma., 2 Ma., and 4 Ma. in duration. The 2 Ma. and 4 Ma. duration cycles are subdivisions of the third order cyclicity recognised by Vail et al. (1991) (referred to here as cyclicity orders 3a and 3b). The 0.1-0.3 Ma. duration cycles are a subset of the fourth order cyclicity recognised Vail et al. (1991), and the 0.05 Ma. Duration cycles are a subset of the 5 th order cyclicity recognised by Vail et al. (1991). 3a, 3b and 4 th order sea level fluctuations are driven by fluctuations in the volume of the Antarctic Ice Sheet. Fifth order sea level fluctuations are also suggested to be at least partially driven by fluctuations in the volume of the Antarctic Ice Sheet. Milankovitch cyclicities in glacioeustasy (<100 Ka., fifth order cyclicity) are prominent in the geologic record at times when there is large scale glaciation (glacialism) of the Antarctic Continent (e.g. for the Pleistocene). Conversely, at times when the Antarctic continent is in a deglaciated state (deglacialism) fourth order cyclicity is more prominent, with Milankovitch cyclicities present at a parasequence level.</p>

scholarly journals Ice Induced Sea Level Change in the Late Neogene

2021 ◽  
Author(s):  
◽  
Gary Steven Wilson
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Level Fluctuation ◽  
Antarctic Ice Sheet ◽  
Continental Scale ◽  
Base Level ◽  
Late Neogene ◽  
Antarctic Continent ◽  
Sea Level Fluctuation ◽  
The Antarctic

<p>Two independent records of latest Neogene (2,0 - 6.0 Ma.) glacioeustasy are presented, one of Antarctic ice volume from East Antarctica and the other of eustatic sea level from the South Wanganui Basin, New Zealand. Glacial deposits in the Transantarctic Mountains (Sirius Group) and sediment at the Antarctic continental margin provide direct evidence of Antarctic ice sheet fluctuation. Evidence for deglaciation includes the occurrence of Pliocene marine diatoms in Sirius Group deposits, which are sourced from the East Antarctic interior. K/Ar and 39Ar/40Ar dating of a tuff in the CIROS-2 drill-core confirms their Pliocene age at high latitudes (78 [degrees] S) in Antarctica. Further evidence for Antarctic ice volume fluctuation is recorded by glaciomarine strata from the Ross Sea Sector cored by the CIROS-2 and DVDP-11 drill-holes. Magnetostratigraphy integrated with Beryllium-10, K/Ar and 39Ar/40Ar dating provides a high resolution ([plus or minus] 50 k.y.) chronology of events in these strata. In the Wanganui Basin, New Zealand, a 5 km thick succession of continental shelf sediments, now uplifted, records Late Neogene eustatic sea level fluctuation. In the Late Neogene, basin subsidence equalled sediment input allowing eustatic sea level fluctuation to produce a dynamic alternation of highstand, transgressive, and lowstand sediment wedges. This record of Late Neogene sea level variation is unequalled in its resolution and detail. Magnetostratigraphy provides a high resolution chronology for these sedimentary cycles as well as magnetic tie lines with the Antarctic margin record in McMurdo Sound. These two independent records of Late Neogene glacioeustasy are in good agreement and record the following history: The Late Miocene and Late Pliocene are times of low 'base level' glacioeustasy (here termed glacialism, rather than glacial), with growth of continental-scale ice sheets on the Antarctic continent causing a lowering of global sea level. The Early Pliocene was a time of high 'base level' glacioeustasy (here termed interglacialism, rather than interglacial), driven by collapsing of continental-scale ice sheets to local and subcontinental ice caps. The middle Pliocene is marked by a move into glacialism with an increasing 'base level' of glacioeustatic fluctuation. Higher-order glacial advances and associated eustatic sea-level lowering occurred at approximately 3.5 and 4.3 Ma., separating the Early Pliocene into 3 sea-level stages. Still higher-order glacioeustatic fluctuations are recognised in this study, with durations of 50 Ka. and 100 - 300 Ka.. The 100 - 300 Ka. duration cycles are prominent during interglacialisms, and the 50 Ka. duration cycles are prominent during glacialisms. These shorter duration fluctuations in glacioeustasy have already been recognised as glacial/deglacial cycles from detailed studies of the Quaternary. Four orders of sea-level fluctuation are recognised within the Late Neogene, these are of approximately 0.05 Ma., 0.1-0.3 Ma., 2 Ma., and 4 Ma. in duration. The 2 Ma. and 4 Ma. duration cycles are subdivisions of the third order cyclicity recognised by Vail et al. (1991) (referred to here as cyclicity orders 3a and 3b). The 0.1-0.3 Ma. duration cycles are a subset of the fourth order cyclicity recognised Vail et al. (1991), and the 0.05 Ma. Duration cycles are a subset of the 5 th order cyclicity recognised by Vail et al. (1991). 3a, 3b and 4 th order sea level fluctuations are driven by fluctuations in the volume of the Antarctic Ice Sheet. Fifth order sea level fluctuations are also suggested to be at least partially driven by fluctuations in the volume of the Antarctic Ice Sheet. Milankovitch cyclicities in glacioeustasy (<100 Ka., fifth order cyclicity) are prominent in the geologic record at times when there is large scale glaciation (glacialism) of the Antarctic Continent (e.g. for the Pleistocene). Conversely, at times when the Antarctic continent is in a deglaciated state (deglacialism) fourth order cyclicity is more prominent, with Milankovitch cyclicities present at a parasequence level.</p>

scholarly journals Sequence Stratigraphy, Chronostratigraphy  and Zircon Geochronology of the CIROS-1  Drill Core, Ross Sea, Antarctica:  Implications for Cenozoic Glacial and  Tectonic Evolution

2021 ◽  
Author(s):  
◽  
Evelien Van de Ven
Keyword(s):  
Trace Element ◽  
Ross Sea ◽  
Global Climate ◽  
Ice Sheet ◽  
Late Eocene ◽  
Late Oligocene ◽  
Antarctic Ice Sheet ◽  
History Of ◽  
The Antarctic ◽  
East Antarctic Ice Sheet

<p>Antarctica plays a central role in the global climate system. Understanding the continent's past climate interactions is key to predicting its future response to, and influence on, global climate change. In recent decades, sediment cores drilled on the Antarctic continental margin have provided direct evidence of past climatic and tectonic events. Drilled in 1986 from sea ice in western McMurdo Sound, the pioneering 702 m-long CIROS-1 core extended back to the Late Eocene and provided some of the first evidence of the antiquity and history of the Antarctic ice sheets. The CIROS-1 drill core recovered a depositional history of the western margin of the Victoria Land Basin adjacent to the Trans-Antarctic Mountains. It was located directly offshore from where the Ferrar Glacier, which drains the East Antarctic Ice Sheet, discharges into the Ross Sea. Consequently CIROS-1 contains a record of both the glacial and tectonic Cenozoic evolution of the Antarctic margin. This thesis provides a timely re-evaluation of the CIROS-1 core with new analysis techniques that enable further insights into the glacial and tectonic history of the western Ross Sea region, and includes three key objectives:  (1) Re-examine CIROS-1 sedimentology and stratigraphy and provide a new facies and sequence stratigraphic analysis using modern methods developed from recent drilling projects (e.g. CRP, ANDRILL).  (2) Develop a new integrated chronostratigraphic model through an assessment and compilation of previous studies, which provides a context for the interpretation of detrital zircon data, climate and tectonic history. (3) Undertake a detailed examination of the provenance of CIROS-1 sediments using cutting edge in situ analysis techniques of detrital zircons (U-Pb and trace element analysis using LA-ICP-MS).  Glaciomarine sequence stratigraphic analysis identifies 14 unconformity-bound sequences occurring in two distinctive stratigraphic motifs. The four sequences located beneath the 342 mbsf unconformity contain relatively complete vertical facies succession. They were deposited in shallow marine, fluvio-deltaic conditions with distal glaciers terminating on land, and possibly calving into the ocean in adjacent valleys as evidenced by occasional ice-rafted debris. The ten sequences located above ~342 mbsf have a fundamentally different architecture. They are incomplete (top-truncated), contain subglacial and ice proximal facies grading upsequence into distal glaciomarine and shelf conditions. Top truncation of these sequences represents overriding of the CIROS-1 site by the paleo-Ferrar Glacier during glacial phases.  A revised age model for CIROS-1 is presented that utilises new calibrations for Antarctic diatom zones and compiles three previously published age models for different sections of the core (Roberts et al., 2003; Wilson et al., 1998; Hannah et al., 1997). The new age model allows correlation of Late Oligocene cycles with coeval cycles in CRP-2/2A, 80 km to the north. A fundamental orbital control on the dynamics of these East Antarctic Ice Sheet outlet glaciers is evident from this comparison. Both glacier systems respond in-phase to longer-period orbital components (e.g. eccentricity 100 kyr and 400 kyr), but differ in their sensitivity to precession (20 kyr). It appears that during the Late Oligocene the Ferrar catchment responded to 20 kyr precession cycles, whilst the larger MacKay Glacier, which is more directly connected to the East Antarctic Ice Sheet, responded to longer duration 125 kyr (eccentricity) forcing.  CIROS-1 zircons group into four distinct geochemical suites. Zircons formed in felsic igneous environments dominate the CIROS-1 population, with 89 % of zircons analysed showing geochemical characteristics inherent to granitic/rhyolitic zircons. Approximately 7 % of CIROS-1 zircons have a highly trace element enriched igneous provenance and were most probably sourced from enriched enclaves in granitic/rhyolitic units or from pegmatites. Approximately 3 % of CIROS-1 zircons show a metamorphic geochemical signature, and ~1 % formed in trace element depleted igneous environments. The zircons were sourced from the local basement (Koettlitz, Granite Harbour Groups), the Beacon Supergroup, and potentially, lithologies of the East Antarctic Craton located under the ice, or components of the Trans-Antarctic Mountains located under the current baseline of geologic exposure.  Large-scale, systematic temporal trends in zircon characteristics have been divided into three distinct climatic periods: Zone 1 (702-366 mbsf, Late Eocene), Zone 2 (366-250 mbsf, Late Oligocene) and Zone 3 (< 250 mbsf, Late Oligocene and Early Miocene). Zircons deposited during these periods show unique properties. During Zone 1, Antarctica experienced a relatively warm temperate climate and alpine style glaciers flowed eastwards through the Trans-Antarctic Mountains. Zircons in this zone contain a subtle record of unroofing of geochemically zoned Granite Harbour and Koettlitz units located in the Ferrar Valley. During Zone 2 deposition, glaciers flowed though the Trans-Antarctic Mountains draining a large and ephemeral EAIS, which oscillated on orbital time scales. Zircons in this interval show variable properties, high numbers and were most probably deposited as the paleo-Ferrar Glacier deeply incised the Ferrar Fiord. In contrast, Zone 3 is characterised by a flux of McMurdo Volcanic Complex derived sediments, together with systematic changes in zircon characteristics. These patterns indicate a Late Oligocene shift in ice flow to the site (above ~250 mbsf). Due to a cooling that culminated in the Mi-1 glaciation, ice flow to the site changed from an eastward to a northward flow, in response to an increased ice volume in the Ross embayment.</p>

scholarly journals Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene

2011 ◽  
Vol 7 (3) ◽  
pp. 869-880 ◽  
Author(s):  
D. Liebrand ◽  
L. J. Lourens ◽  
D. A. Hodell ◽  
B. de Boer ◽  
R. S. W. van de Wal ◽  
...  
Keyword(s):  
Global Climate ◽  
Ice Sheet ◽  
Early Miocene ◽  
High Temporal Resolution ◽  
Short Term ◽  
Antarctic Ice Sheet ◽  
Oxygen Isotope Record ◽  
Isotope Record ◽  
The Antarctic

Abstract. Stable isotope records of benthic foraminifera from ODP Site 1264 in the southeastern Atlantic Ocean are presented which resolve the latest Oligocene to early Miocene (~24–19 Ma) climate changes at high temporal resolution (<3 kyr). Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded episodically during the declining phase of the long-term (~400 kyr) eccentricity cycle and subsequent low short-term (~100 kyr) eccentricity cycle. The largest glaciations are separated by multiple long-term eccentricity cycles, indicating the involvement of a non-linear response mechanism. Our modelling results suggest that during the largest (Mi-1) event, Antarctic ice sheet volume expanded up to its present-day configuration. In addition, we found that distinct ~100 kyr variability occurs during the termination phases of the major Antarctic glaciations, suggesting that climate and ice-sheet response was more susceptible to short-term eccentricity forcing at these times. During two of these termination-phases, δ18O bottom water gradients in the Atlantic ceased to exist, indicating a direct link between global climate, enhanced ice-sheet instability and major oceanographic reorganisations.

scholarly journals Sequence Stratigraphy, Chronostratigraphy  and Zircon Geochronology of the CIROS-1  Drill Core, Ross Sea, Antarctica:  Implications for Cenozoic Glacial and  Tectonic Evolution

2021 ◽  
Author(s):  
◽  
Evelien Van de Ven
Keyword(s):  
Trace Element ◽  
Ross Sea ◽  
Global Climate ◽  
Ice Sheet ◽  
Late Eocene ◽  
Late Oligocene ◽  
Antarctic Ice Sheet ◽  
History Of ◽  
The Antarctic ◽  
East Antarctic Ice Sheet

<p>Antarctica plays a central role in the global climate system. Understanding the continent's past climate interactions is key to predicting its future response to, and influence on, global climate change. In recent decades, sediment cores drilled on the Antarctic continental margin have provided direct evidence of past climatic and tectonic events. Drilled in 1986 from sea ice in western McMurdo Sound, the pioneering 702 m-long CIROS-1 core extended back to the Late Eocene and provided some of the first evidence of the antiquity and history of the Antarctic ice sheets. The CIROS-1 drill core recovered a depositional history of the western margin of the Victoria Land Basin adjacent to the Trans-Antarctic Mountains. It was located directly offshore from where the Ferrar Glacier, which drains the East Antarctic Ice Sheet, discharges into the Ross Sea. Consequently CIROS-1 contains a record of both the glacial and tectonic Cenozoic evolution of the Antarctic margin. This thesis provides a timely re-evaluation of the CIROS-1 core with new analysis techniques that enable further insights into the glacial and tectonic history of the western Ross Sea region, and includes three key objectives:  (1) Re-examine CIROS-1 sedimentology and stratigraphy and provide a new facies and sequence stratigraphic analysis using modern methods developed from recent drilling projects (e.g. CRP, ANDRILL).  (2) Develop a new integrated chronostratigraphic model through an assessment and compilation of previous studies, which provides a context for the interpretation of detrital zircon data, climate and tectonic history. (3) Undertake a detailed examination of the provenance of CIROS-1 sediments using cutting edge in situ analysis techniques of detrital zircons (U-Pb and trace element analysis using LA-ICP-MS).  Glaciomarine sequence stratigraphic analysis identifies 14 unconformity-bound sequences occurring in two distinctive stratigraphic motifs. The four sequences located beneath the 342 mbsf unconformity contain relatively complete vertical facies succession. They were deposited in shallow marine, fluvio-deltaic conditions with distal glaciers terminating on land, and possibly calving into the ocean in adjacent valleys as evidenced by occasional ice-rafted debris. The ten sequences located above ~342 mbsf have a fundamentally different architecture. They are incomplete (top-truncated), contain subglacial and ice proximal facies grading upsequence into distal glaciomarine and shelf conditions. Top truncation of these sequences represents overriding of the CIROS-1 site by the paleo-Ferrar Glacier during glacial phases.  A revised age model for CIROS-1 is presented that utilises new calibrations for Antarctic diatom zones and compiles three previously published age models for different sections of the core (Roberts et al., 2003; Wilson et al., 1998; Hannah et al., 1997). The new age model allows correlation of Late Oligocene cycles with coeval cycles in CRP-2/2A, 80 km to the north. A fundamental orbital control on the dynamics of these East Antarctic Ice Sheet outlet glaciers is evident from this comparison. Both glacier systems respond in-phase to longer-period orbital components (e.g. eccentricity 100 kyr and 400 kyr), but differ in their sensitivity to precession (20 kyr). It appears that during the Late Oligocene the Ferrar catchment responded to 20 kyr precession cycles, whilst the larger MacKay Glacier, which is more directly connected to the East Antarctic Ice Sheet, responded to longer duration 125 kyr (eccentricity) forcing.  CIROS-1 zircons group into four distinct geochemical suites. Zircons formed in felsic igneous environments dominate the CIROS-1 population, with 89 % of zircons analysed showing geochemical characteristics inherent to granitic/rhyolitic zircons. Approximately 7 % of CIROS-1 zircons have a highly trace element enriched igneous provenance and were most probably sourced from enriched enclaves in granitic/rhyolitic units or from pegmatites. Approximately 3 % of CIROS-1 zircons show a metamorphic geochemical signature, and ~1 % formed in trace element depleted igneous environments. The zircons were sourced from the local basement (Koettlitz, Granite Harbour Groups), the Beacon Supergroup, and potentially, lithologies of the East Antarctic Craton located under the ice, or components of the Trans-Antarctic Mountains located under the current baseline of geologic exposure.  Large-scale, systematic temporal trends in zircon characteristics have been divided into three distinct climatic periods: Zone 1 (702-366 mbsf, Late Eocene), Zone 2 (366-250 mbsf, Late Oligocene) and Zone 3 (< 250 mbsf, Late Oligocene and Early Miocene). Zircons deposited during these periods show unique properties. During Zone 1, Antarctica experienced a relatively warm temperate climate and alpine style glaciers flowed eastwards through the Trans-Antarctic Mountains. Zircons in this zone contain a subtle record of unroofing of geochemically zoned Granite Harbour and Koettlitz units located in the Ferrar Valley. During Zone 2 deposition, glaciers flowed though the Trans-Antarctic Mountains draining a large and ephemeral EAIS, which oscillated on orbital time scales. Zircons in this interval show variable properties, high numbers and were most probably deposited as the paleo-Ferrar Glacier deeply incised the Ferrar Fiord. In contrast, Zone 3 is characterised by a flux of McMurdo Volcanic Complex derived sediments, together with systematic changes in zircon characteristics. These patterns indicate a Late Oligocene shift in ice flow to the site (above ~250 mbsf). Due to a cooling that culminated in the Mi-1 glaciation, ice flow to the site changed from an eastward to a northward flow, in response to an increased ice volume in the Ross embayment.</p>

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