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1. NW Greenland Glaciated Margin

   https://doi.org/10.14379/iodp.proc.400.2025  

   Knutz, PC; Jennings, AE; Childress, LB (March 2025, International Ocean Discovery Program)

   Elucidating the geologic history of the Greenland ice sheet (GrIS) is essential for understanding glacial instability thresholds, identified as major climate system tipping points, and how the cryosphere will respond to anthropogenic greenhouse gas emissions. To address current knowledge gaps in the evolution and variability of the GrIS and its role in Earth’s climate system, International Ocean Discovery Program (IODP) Expedition 400 obtained sedimentary records from Sites U1603–U1608 across the northwest Greenland margin into Baffin Bay where thick Cenozoic sedimentary successions can be directly linked to the evolution of the northern GrIS (NGrIS). The strategy of drilling along this transect was to retrieve a composite stratigraphic succession representing the late Cenozoic era from the Oligocene/early Miocene to the Holocene. The proposed sites targeted high–accumulation rate deposits associated with contourite drifts and potential interglacial deposits within a trough mouth fan system densely covered by seismic data. The principal objectives were to (1) test if the NGrIS underwent near-complete deglaciations in the Pleistocene and assess the ice sheet’s response to changes in orbital cyclicities through the mid-Pleistocene transition, (2) ascertain the timing of the NGrIS expansion and examine a hypothesized linkage between marine heat transport through Baffin Bay and high Arctic warmth during the Pliocene, and (3) provide new understandings of climate-ecosystem conditions in Greenland during the geologic periods with increased atmospheric CO2 compared to preindustrial values, encompassing the last 30 My. The deep time objective was attained by coring at Site U1607 on the inner shelf to 978 meters below seafloor, capturing a succession of mainly Miocene and Oligocene age. The six sites drilled during Expedition 400 resulted in 2299 m of recovered core material, and wireline downhole logging was completed at Sites U1603, U1604, U1607, and U1608. This unique archive will provide the basis for understanding the full range of forcings and feedbacks—oceanic, atmospheric, orbital, and tectonic—that influence the GrIS over a range of timescales, as well as conditions prevailing at the time of glacial inception and deglacial to interglacial periods. We anticipate that the shipboard data and further analytical work on Expedition 400 material can constrain predictive models addressing the GrIS response to global warming and its impending effects on global sea levels. 

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2. Preliminary Report: NW Greenland Glaciated Margin

   Knutz, P.C.; Jennings, A.; Childress, L.B. (January 2024, Preliminary report)

   Elucidating the geologic history of the Greenland Ice Sheet (GrIS) is essential for understanding glacial instability thresholds, identified as major climate system tipping points, and how the cryosphere will respond to anthropogenic greenhouse gas emissions. To address current knowledge gaps in the evolution and variability of the GrIS and its role in Earth's climate system, International Ocean Discovery Program (IODP) Expedition 400 obtained sedimentary records from Sites U1603–U1608 across the northwest Greenland margin into Baffin Bay where thick Cenozoic sedimentary successions can be directly linked to the evolution of the northern GrIS (NGrIS). The strategy of drilling along this transect was to retrieve a composite stratigraphic succession representing the late Cenozoic era from the Oligocene/early Miocene to Holocene. The proposed sites targeted high–accumulation rate deposits associated with contourite drifts and potential interglacial deposits within a trough mouth fan system densely covered by seismic data. The principal objectives were to (1) test if the NGrIS underwent near-complete deglaciations in the Pleistocene and assess the ice sheet’s response to changes in orbital cyclicities through the mid-Pleistocene transition; (2) ascertain the timing of the NGrIS expansion and examine a hypothesized linkage between marine heat transport through Baffin Bay and high Arctic warmth during the Pliocene; and (3) provide new understandings of climate-ecosystem conditions in Greenland during the geologic periods with increased atmospheric CO2 compared to preindustrial values, encompassing the last 30 My. The deep time objective was attained by coring at Site U1607 on the inner shelf to 978 meters below seafloor, capturing a succession of mainly Miocene and Oligocene age. The six sites drilled during Expedition 400 resulted in 2299 m of recovered core material, and wireline downhole logging was completed at Sites U1603, U1604, U1607, and U1608. This unique archive will provide the basis for understanding the full range of forcings and feedbacks—oceanic, atmospheric, orbital, and tectonic—that influence the GrIS over a range of timescales, as well as conditions prevailing at the time of glacial inception and deglacial to interglacial periods. We anticipate that the shipboard data and further analytical work on Expedition 400 material can constrain predictive models addressing the GrIS response to global warming and its impending effects on global sea levels. 

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3. Thermodynamic Modeling of the Tso Morari UHP Eclogite, NW Himalaya

   Pan, R; Macris, C.A.; Menold, C.A. (December 2019, AGU Fall Meeting 2020)

   Thermodynamic modeling is an important technique to interpret metamorphic phase relations and calculate model pressure-temperature (P-T) paths for metamorphic rocks. This study uses representative, coesite-bearing eclogites from the Tso Morari UHP terrane of the NW Himalaya to simulate its prograde metamorphism using multiple modeling programs and thermobarometry. Our modeling yields a peak metamorphism P-T of ~32-33 kbar and ~560-570 °C by the THERMOCALC345 and Theriak-Domino programs (Green et al., 2016), which is ~5 kbar higher in pressure and ~15 °C lower in temperature than that determined by using THERMOCALC333 (White et al., 2007) (~27.8 kbar and ~580 °C). The significantly higher pressure obtained using the THERMOCALC345 and Theriak-Domino is likely a result of the upgrade of thermodynamic parameters of minerals (i.e. garnet Wpy-gr and agr) in the newer a-x relations. The modeled effective bulk compositions and mineral stabilities along the calculated P-T path show different patterns under the two modeling techniques. Modeling by the Theriak-Domino programs is preferred in this case because the results are more consistent with the measured mineral compositions of our rocks. Multiple thermobarometers by garnet-omphacite-phengite, garnet-omphacite, garnet-phengite on the garnet rim, high-Si phengite and matrix omphacite yield a peak metamorphism of ~ 28.5-29.0 kbar and ~ 650-728 °C, which is generally consistent with the modeled P-T path. Based on our model calculations, the initial bulk composition measured by XRF does not represent the reactant bulk composition at the time of garnet nucleation, and this compositional discrepancy possibly is caused by the crystallization of pre-garnet minerals (i.e. hematite), reaction overstepping, or partial reequilibration. In summary, by implementing and evaluating multiple modeling strategies and considering the petrography and metamorphic mineralogy of the rocks, this study finds that the eclogite modeling using Theriak-Domino programs in the Tso Morari terrane provide more consistent metamorphic phase relations and more reasonable thermodynamic simulations regarding fractionation of the bulk composition and prograde metamorphism. References: Green et al. J Metamorph Geol 34, 845-869 (2016) White et al. J Metamorph Geol 25, 511-527 (2007) 

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4. Expedition 400 Scientific Prospectus: NW Greenland Glaciated Margin

   https://doi.org/10.14379/iodp.sp.400.2022  

   Knutz, P.; Jennings, A.; Childress, L.B. (September 2022, Scientific prospectus)

   Elucidating the long-term history of the Greenland Ice Sheet (GrIS) is essential for understanding glacial instability thresholds, identified as major climate system tipping points, and how the cryosphere will respond to anthropogenic greenhouse gas emissions. To address current knowledge gaps in the evolution and variability of the GrIS and its role in Earth's climate system, International Ocean Discovery Program (IODP) Expedition 400 will obtain cores from seven sites across the northwest Greenland margin into Baffin Bay where thick Cenozoic sedimentary successions can be directly linked to the evolution of the northern GrIS (NGrIS). The strategy of drilling along this transect is to retrieve a composite stratigraphic succession representing the Late Cenozoic era from the Oligocene/Early Miocene to Holocene. The proposed sites will specifically target high–accumulation rate deposits associated with contourite drifts and potential interglacial deposits within a trough mouth fan system densely covered by seismic data. We seek to test if the NGrIS underwent near-complete deglaciations in the Pleistocene and to assess the ice sheet’s response to changes in orbital cyclicities through the mid-Pleistocene transition. Paleoclimate records will be obtained that can provide chronology on the NGrIS expansion and unravel potential linkages between marine heat transport through Baffin Bay and high Arctic warmth during the Pliocene. A deep coring site (980 meters below seafloor) targeting a Miocene and Oligocene strata succession will examine possible linkages between changes in atmospheric CO2 and climate-ecosystem conditions in Greenland. The overall aim is to investigate the full range of forcings and feedbacks—oceanic, atmospheric, orbital, and tectonic—that influence the GrIS over a range of timescales, as well as conditions prevailing at the time of glacial inception and deglacial to interglacial periods. The data and results gathered from Expedition 400 will effectively constrain predictive models addressing the GrIS response to global warming and its impending effects on global sea levels. 

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5. A westerly dominated Early Cretaceous eolian system in the Hami Basin, NW China

   https://doi.org/10.1130/B37436.1  

   Zhang, Dehai; Wang, Guocan; Pullen, Alex; Abell, Jordan T; Cheng, Feng; Shen, Tianyi; Ji, Junliang; Zhang, Meng (June 2024, Geological Society of America Bulletin)

   Cretaceous eolian deposits provide evidence of variations in the tropical-subtropical atmospheric circulation under greenhouse conditions. However, the misinterpretation of many such deposits as fluvial or deltaic originally hindered precise paleoclimatic reconstructions. Here we report a newly identified Early Cretaceous desert in the Hami Basin, China, which helps understand spatial-temporal variations in aridity and atmospheric circulations within central East Asia during the Early Cretaceous. The Liushuquan Formation is composed of >300-m-thick eolian deposits interpreted as an intermontane erg environment. Paleocurrent indicators within the straight-crested dunes of the Liushuquan Formation yield a mean trend of 101.3° (± 10.1°, 1 standard deviation) throughout the formation, consistent with near-surface westerly winds. Paleo-atmospheric circulation superimposed on topographic effects led to widespread eolianite accumulation during the Early Cretaceous. Combined with the spatiotemporal changes in desert distributions and prevailing surface wind patterns in East Asia, these observations are consistent with the migration of the subtropical high-pressure belt during the Early Cretaceous. We propose the following paleo-atmospheric model: (1) During the late Berriasian−Valanginian, the subtropical high belt drifted southward and northward over shorter time scales within the spatial domain of the paleo-Ordos Basin, then shifted southward at least past the Ordos Basin; (2) until the late Hauterivian−Barremian, the subtropical high-pressure zone was primarily located between the northwestern Tarim Basin and the Ordos Basin; and (3) a significant southward shift of the subtropical high-pressure zone occurred during the Aptian−Albian. 

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