More Like this

1. Topographic evolution of WAIS subglacial bedrock: Insights from low-temperature thermochronology and thermo-kinematic modeling in Marie Byrd Land, West Antarctica

   Taylor, Jennifer ; Swope, Fiona ; Siddoway, Christine ; Thomson, Stuart ; and Teyssier, Christian ( September 2022 , 29th West Antarctic Ice Sheet Workshop)

   Bedrock topography is a key boundary condition for ice sheet modeling, and determining changes in subglacial topography through time can provide insight into the timing of ice sheet development, the magnitude of glacial erosion, and the co-development of glaciers and glacial topography. West Antarctica hosts an unusually high geothermal gradient supported by hot, low-viscosity mantle which likely enhanced the lithospheric response to West Antarctic Ice Sheet (WAIS) cycles of growth and increased the sensitivity of thermochronometers to landscape evolution on million-year timescales. Thus, a valuable record of glacial landscape change might be recovered from apatite fission track [AFT 80-130°C range] and (U-Th)/He [AHe; 50-90°C] dating, provided that landscape evolution can be distinguished from tectonic signals, including the effects of faults. This study utilizes AFT-AHe thermochronology and thermo-kinematic Pecube modeling to investigate interactions between the hot geotherm, glacial erosion, and inferred crustal structures in the Ford Ranges and the DeVicq Glacier trough in western and central Marie Byrd Land (MBL), respectively. The Ford Ranges host glacial troughs (up to 3km relief) dissecting a low-relief erosional surface. Previous work suggests a majority of bedrock exhumation and cooling occurred at/by 80 Ma. However, new data hint at renewed exhumation linked to glacial incision since WAIS formation at 34 or 20 Ma. Prior (U-Th)/He zircon dates from exposures of crystalline bedrock span 90 – 67 Ma. New AHe bedrock dates are 41 to 26 Ma, while two glacial erratics (presumed to be eroded from walls or floor of glacial troughs) yielded AHe dates of 37 Ma and 16 Ma. Initial modeling results suggest a tectonic boundary between the Ford Ranges and Edward VII Peninsula separating regions with distinct exhumation histories. The boundary may cause differential WAIS incision at 34 or 20 Ma, a possibility being investigated with new models. The DeVicq Glacier trough (>3.5km relief) coincides with a prominent crustal lineament but lacks temperature-time information compared to other regions. The crustal structure may have accommodated motion between elevated central MBL and the subdued crust of the Ford Ranges. Here, owing to the lack of onshore non-volcanic bedrock exposure, we have employed AHe and AFT dating of glacial sediment marine core samples offshore of the DeVicq Glacier to investigate the timing and rates of exhumation of the bedrock carved by the DeVicq trough, with initial results revealing detrital AHe ages as young as 24 Ma. Our new Pecube models test a series of thermal, tectonic, and landscape evolution scenarios against a suite of thermochronologic data, allowing us to assess the timing of glacial incision and WAIS initiation in the Ford Ranges, and to seek evidence of an inferred tectonic boundary at DeVicq Trough. Modeling efforts will be aided by new AHe and AFT analyses from ongoing work. These models combine topographic, tectonic, thermal, and key thermochronologic datasets to produce new insight into the unique cryosphere-lithosphere interactions affecting landscape change in West Antarctica. 

   more » « less
2. Development of Glacial Topography over a Hot Geotherm: Insights from Low-Temperature Thermochronology and Thermo-Kinematic Modeling in Marie Byrd Land, WestAntarctica

   Taylor, Jennifer M. ; Swope, Fiona ; Siddoway, Christine S. ; Thomson, Stuart N. ; Teyssier, Christian P. ( October 2021 , 2021 AGU Fall Meeting)

   West Antarctica hosts an unusually high geothermal gradient supported by hot, low-viscosity mantle which likely enhanced the lithospheric response to West Antarctic Ice Sheet [WAIS] cycles of growth and increased the sensitivity of thermochronometers to landscape evolution. Thus a valuable record of glacial landscape change might be recovered from apatite fission track [AFT 80-130°C range] and (U-Th)/He [AHe; 50-90°C]dating, provided that landscape evolution can be distinguished from tectonic signals, including the effects of faults. This study utilizes AFT-AHe thermochronology and thermo-kinematic Pecube modeling to investigate interactions between the hot geotherm, glacial erosion, and inferred crustal structures in the Ford Ranges and the DeVicq Glacier trough in Marie Byrd Land (MBL). The Ford Ranges host glacial troughs (up to 3km relief) dissecting a low-relief erosional surface. Previous work suggests a majority of bedrock exhumation and cooling occurred at/by 80 Ma. However, new data hint at renewed exhumation linked to glacial incision since WAIS formation at 34 or 20 Ma. Prior (U-Th)/He zircon dates from exposures of crystalline bedrock span 90 – 67 Ma. New AHe bedrock dates are 41 to 26 Ma, while two glacial erratics (presumed to be eroded from walls or floor of glacial troughs) yielded AHe dates of 37 Ma and 16 Ma. The DeVicq Glacier trough (>3.5km relief) likely coincides with a regional fault but lacks temperature-time information compared to other regions. The structure may have accommodated motion between elevated central MBL and the subdued crust of the Ford Ranges. We are acquiring AHe and AFT for onshore and offshore samples to compare uplift and exhumation rates for bedrock flanking DeVicq trough. Our new Pecube models test a series of thermal, tectonic, and landscape evolution scenarios against a suite of thermochronologic data, allowing us to assess the timing of glacial incision and WAIS initiation in the FordRanges, and to seek evidence of an inferred tectonic boundary at DeVicq Trough. Modeling efforts will be aided by new AHe analyses from ongoing work. These models combine topographic, tectonic, thermal, and key thermochronologic datasets to produce new insight into the unique cryosphere-lithosphere interactions affecting landscape change in West Antarctica. 

   more » « less
3. Amundsen Sea West Antarctic Ice Sheet History

   https://doi.org/10.14379/iodp.proc.379.2021  

   Gohl, K. ; Wellner, J.S. ; Klaus, A. ( February 2021 , Proceedings of the International Ocean Discovery Program)

   The Amundsen Sea sector of Antarctica has long been considered the most vulnerable part of the West Antarctic Ice Sheet (WAIS) because of the great water depth at the grounding line, a subglacial bed seafloor deepening toward the interior of the continent, and the absence of substantial ice shelves. Glaciers in this configuration are thought to be susceptible to rapid or runaway retreat. Ice flowing into the Amundsen Sea Embayment is undergoing the most rapid changes of any sector of the Antarctic ice sheets outside the Antarctic Peninsula, including substantial grounding-line retreat over recent decades, as observed from satellite data. Recent models suggest that a threshold leading to the collapse of WAIS in this sector may have been already crossed and that much of the ice sheet could be lost even under relatively moderate greenhouse gas emission scenarios. Drill cores from the Amundsen Sea provide tests of several key questions about controls on ice sheet stability. The cores offer a direct offshore record of glacial history in a sector that is exclusively influenced by ice draining the WAIS, which allows clear comparisons between the WAIS history and low-latitude climate records. Today, relatively warm (modified) Circumpolar Deep Water (CDW) is impinging onto the Amundsen Sea shelf and causing melting under ice shelves and at the grounding line of the WAIS in most places. Reconstructions of past CDW intrusions can assess the ties between warm water upwelling and large-scale changes in past grounding-line positions. Carrying out these reconstructions offshore from the drainage basin that currently has the most substantial negative mass balance of ice anywhere in Antarctica is thus of prime interest to future predictions. The scientific objectives for this expedition are built on hypotheses about WAIS dynamics and related paleoenvironmental and paleoclimatic conditions. The main objectives are: 1. To test the hypothesis that WAIS collapses occurred during the Neogene and Quaternary and, if so, when and under which environmental conditions; 2. To obtain ice-proximal records of ice sheet dynamics in the Amundsen Sea that correlate with global records of ice-volume changes and proxy records for atmospheric and ocean temperatures; 3. To study the stability of a marine-based WAIS margin and how warm deepwater incursions control its position on the shelf; 4. To find evidence for the earliest major grounded WAIS advances onto the middle and outer shelf; 5. To test the hypothesis that the first major WAIS growth was related to the uplift of the Marie Byrd Land dome. International Ocean Discovery Program (IODP) Expedition 379 completed two very successful drill sites on the continental rise of the Amundsen Sea. Site U1532 is located on a large sediment drift, now called the Resolution Drift, and it penetrated to 794 m with 90% recovery. We collected almost-continuous cores from recent age through the Pleistocene and Pliocene and into the upper Miocene. At Site U1533, we drilled 383 m (70% recovery) into the more condensed sequence at the lower flank of the same sediment drift. The cores of both sites contain unique records that will enable study of the cyclicity of ice sheet advance and retreat processes as well as ocean-bottom water circulation and water mass changes. In particular, Site U1532 revealed a sequence of Pliocene sediments with an excellent paleomagnetic record for high-resolution climate change studies of the previously sparsely sampled Pacific sector of the West Antarctic margin. Despite the drilling success at these sites, the overall expedition experienced three unexpected difficulties that affected many of the scientific objectives: 1. The extensive sea ice on the continental shelf prevented us from drilling any of the proposed shelf sites. 2. The drill sites on the continental rise were in the path of numerous icebergs of various sizes that frequently forced us to pause drilling or leave the hole entirely as they approached the ship. The overall downtime caused by approaching icebergs was 50% of our time spent on site. 3. A medical evacuation cut the expedition short by 1 week. Recovery of core on the continental rise at Sites U1532 and U1533 cannot be used to indicate the extent of grounded ice on the shelf or, thus, of its retreat directly. However, the sediments contained in these cores offer a range of clues about past WAIS extent and retreat. At Sites U1532 and U1533, coarse-grained sediments interpreted to be ice-rafted debris (IRD) were identified throughout all recovered time periods. A dominant feature of the cores is recorded by lithofacies cyclicity, which is interpreted to represent relatively warmer periods variably characterized by sediments with higher microfossil abundance, greater bioturbation, and higher IRD concentrations alternating with colder periods characterized by dominantly gray laminated terrigenous muds. Initial comparison of these cycles to published late Quaternary records from the region suggests that the units interpreted to be records of warmer time intervals in the core tie to global interglacial periods and the units interpreted to be deposits of colder periods tie to global glacial periods. Cores from the two drill sites recovered sediments of dominantly terrigenous origin intercalated or mixed with pelagic or hemipelagic deposits. In particular, Site U1533, which is located near a deep-sea channel originating from the continental slope, contains graded silts, sands, and gravels transported downslope from the shelf to the rise. The channel is likely the pathway of these sediments transported by turbidity currents and other gravitational downslope processes. The association of lithologic facies at both sites predominantly reflects the interplay of downslope and contouritic sediment supply with occasional input of more pelagic sediment. Despite the lack of cores from the shelf, our records from the continental rise reveal the timing of glacial advances across the shelf and thus the existence of a continent-wide ice sheet in West Antarctica during longer time periods since at least the late Miocene. Cores from both sites contain abundant coarse-grained sediments and clasts of plutonic origin transported either by downslope processes or by ice rafting. If detailed provenance studies confirm our preliminary assessment that the origin of these samples is from the plutonic bedrock of Marie Byrd Land, their thermochronological record will potentially reveal timing and rates of denudation and erosion linked to crustal uplift. The chronostratigraphy of both sites enables the generation of a seismic sequence stratigraphy for the entire Amundsen Sea continental rise, spanning the area offshore from the Amundsen Sea Embayment westward along the Marie Byrd Land margin to the easternmost Ross Sea through a connecting network of seismic lines. 

   more » « less
4. Expedition 355 Scientific Prospectus: Arabian Sea Monsoon

   https://doi.org/10.14379/iodp.sp.355.2014  

   Pandey, D.K. ; Clift, P.D. ; Kulhanek, D.K. ( June 2014 , Scientific prospectus)

   null (Ed.)

   Interactions between the solid Earth and climate system represent a frontier area for geoscientific research that is strongly emphasized in the International Ocean Discovery Program (IODP) Science Plan. The continental margin of India adjoining the Arabian Sea offers a unique opportunity to understand tectonic-climatic interactions and the net impact of these on weathering and erosion of the Himalaya. Scientific drilling in the Arabian Sea is designed to understand the coevolution of mountain building, weathering, erosion, and climate over a range of timescales. The southwest monsoon is one of the most intense climatic phenomena on Earth. Its long-term development has been linked to the growth of high topography in South and Central Asia. Conversely, the tectonic evolution of the Himalaya, especially the exhumation of the Greater Himalaya, has been linked to intensification of the summer monsoon rains, as well as to plate tectonic forces. Weathering of the Himalaya has also been linked to long-term drawdown of atmospheric CO2 during the Cenozoic, culminating in the onset of Northern Hemisphere glaciation. No other part of the world has such intense links between tectonic and climatic processes. Unfortunately, these hypotheses remain largely untested because of limited information on the history of erosion and weathering recorded in the resultant sedimentary prisms. This type of data cannot be found on shore because the proximal foreland basin records are disrupted by major unconformities, and depositional ages are difficult to determine with high precision. We therefore propose to recover longer records of erosion and weathering from the Indus Fan that will allow us to understand links between paleoceanographic processes and the climatic history of the region. The latter was partially addressed by Ocean Drilling Program (ODP) Leg 117 on the Oman margin, and further studies are proposed during IODP Expedition 353 (Indian Monsoon Rainfall) that will core several sites in the Bay of Bengal. Such records can be correlated to structural geological and thermochronology data in the Himalaya and Tibetan Plateau to estimate how sediment fluxes and exhumation rates change through time. The drilling will be accomplished within a regional seismic stratigraphic framework and will for the first time permit an estimation of sediment budgets together with quantitative estimates of weathering fluxes and their variation through time. Specific goals of this expedition include 1. Testing whether the timing of the exhumation of Greater Himalaya correlates with an enhanced erosional flux and stronger chemical weathering after ~23 Ma, 2. Determining the amplitude and direction of the environmental change at 8 Ma, and 3. Dating the age of the base of the fan and the underlying basement to constrain the timing of India-Asia collision. Drilling through the fan base and into the underlying basement in the proposed area will permit additional constraints to be placed on the nature of the crust in the Laxmi Basin (Eastern Arabian Sea), which has a significant bearing on paleogeographic reconstructions along conjugate margins in the Arabian Sea and models of continental breakup on rifted volcanic margins. 

   more » « less
5. Expedition 379 Preliminary Report: Amundsen Sea West Antarctic Ice Sheet History

   https://doi.org/10.14379/iodp.pr.379.2019  

   Gohl, K. ; Wellner, J.S. ; Klaus, A. ( May 2019 , Preliminary report)

   null (Ed.)

   The Amundsen Sea sector of Antarctica has long been considered the most vulnerable part of the West Antarctic Ice Sheet (WAIS) because of the great water depth at the grounding line and the absence of substantial ice shelves. Glaciers in this configuration are thought to be susceptible to rapid or runaway retreat. Ice flowing into the Amundsen Sea Embayment is undergoing the most rapid changes of any sector of the Antarctic Ice Sheet outside the Antarctic Peninsula, including changes caused by substantial grounding-line retreat over recent decades, as observed from satellite data. Recent models suggest that a threshold leading to the collapse of WAIS in this sector may have been already crossed and that much of the ice sheet could be lost even under relatively moderate greenhouse gas emission scenarios. Drill cores from the Amundsen Sea provide tests of several key questions about controls on ice sheet stability. The cores offer a direct record of glacial history offshore from a drainage basin that receives ice exclusively from the WAIS, which allows clear comparisons between the WAIS history and low-latitude climate records. Today, warm Circumpolar Deep Water (CDW) is impinging onto the Amundsen Sea shelf and causing melting of the underside of the WAIS in most places. Reconstructions of past CDW intrusions can assess the ties between warm water upwelling and large-scale changes in past grounding-line positions. Carrying out these reconstructions offshore from the drainage basin that currently has the most substantial negative mass balance of ice anywhere in Antarctica is thus of prime interest to future predictions. The scientific objectives for this expedition are built on hypotheses about WAIS dynamics and related paleoenvironmental and paleoclimatic conditions. The main objectives are 1. To test the hypothesis that WAIS collapses occurred during the Neogene and Quaternary and, if so, when and under which environmental conditions; 2. To obtain ice-proximal records of ice sheet dynamics in the Amundsen Sea that correlate with global records of ice-volume changes and proxy records for atmospheric and ocean temperatures; 3. To study the stability of a marine-based WAIS margin and how warm deep-water incursions control its position on the shelf; 4. To find evidence for earliest major grounded WAIS advances onto the middle and outer shelf; 5. To test the hypothesis that the first major WAIS growth was related to the uplift of the Marie Byrd Land dome. International Ocean Discovery Program (IODP) Expedition 379 completed two very successful drill sites on the continental rise of the Amundsen Sea. Site U1532 is located on a large sediment drift, now called Resolution Drift, and penetrated to 794 m with 90% recovery. We collected almost-continuous cores from the Pleistocene through the Pliocene and into the late Miocene. At Site U1533, we drilled 383 m (70% recovery) into the more condensed sequence at the lower flank of the same sediment drift. The cores of both sites contain unique records that will enable study of the cyclicity of ice sheet advance and retreat processes as well as bottom-water circulation and water mass changes. In particular, Site U1532 revealed a sequence of Pliocene sediments with an excellent paleomagnetic record for high-resolution climate change studies of the previously sparsely sampled Pacific sector of the West Antarctic margin. Despite the drilling success at these sites, the overall expedition experienced three unexpected difficulties that affected many of the scientific objectives: 1. The extensive sea ice on the continental shelf prevented us from drilling any of the proposed shelf sites. 2. The drill sites on the continental rise were in the path of numerous icebergs of various sizes that frequently forced us to pause drilling or leave the hole entirely as they approached the ship. The overall downtime caused by approaching icebergs was 50% of our time spent on site. 3. An unfortunate injury to a member of the ship's crew cut the expedition short by one week. Recovery of core on the continental rise at Sites U1532 and U1533 cannot be used to precisely indicate the position of ice or retreat of the ice sheet on the shelf. However, these sediments contained in the cores offer a range of clues about past WAIS extent and retreat. At Sites U1532 and U1533, coarse-grained sediments interpreted to be ice-rafted debris (IRD) were identified throughout all recovered time periods. A dominant feature of the cores is recorded by lithofacies cyclicity, which is interpreted to represent relatively warmer periods variably characterized by higher microfossil abundance, greater bioturbation, and higher counts of IRD alternating with colder periods characterized by dominantly gray laminated terrigenous muds. Initial comparison of these cycles to published records from the region suggests that the units interpreted as records of warmer time intervals in the core tie to interglacial periods and the units interpreted as deposits of colder periods tie to glacial periods. The cores from the two drill sites recovered sediments of purely terrigenous origin intercalated or mixed with pelagic or hemipelagic deposits. In particular, Site U1533, which is located near a deep-sea channel originating from the continental slope, contains graded sands and gravel transported downslope from the shelf to the abyssal plain. The channel is likely the path of such sediments transported downslope by turbidity currents or other sediment-gravity flows. The association of lithologic facies at both sites predominantly reflects the interplay of downslope and contouritic sediment supply with occasional input of more pelagic sediment. Despite the lack of cores from the shelf, our records from the continental rise reveal the timing of glacial advances across the shelf and thus the existence of a continent-wide ice sheet in West Antarctica at least during longer time periods since the late Miocene. Cores from both sites contain abundant coarse-grained sediments and clasts of plutonic origin transported either by downslope processes or by ice rafting. If detailed provenance studies confirm our preliminary assessment that the origin of these samples is from the plutonic bedrock of Marie Byrd Land, their thermochronological record will potentially reveal timing and rates of denudation and erosion linked to crustal uplift. The chronostratigraphy of both sites enables the generation of a seismic sequence stratigraphy not only for the Amundsen Sea rise but also for the western Amundsen Sea along the Marie Byrd Land margin through a connecting network of seismic lines. 

   more » « less