Climate-controlled submarine landslides on the Antarctic continental margin

Antarctica’s continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

Climate-controlled submarine landslides on the Antarctic continental margin

Antarctica’s continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude

Early to Middle Miocene sea-level oscillations of approximately 40-60 m estimated from far-field records1-3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth2. This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene4,5. Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72-17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution

Petrography and provenance study of gravel size clasts from Miocene glacio-marine sequences in the IODP_exp374 Ross Sea drillcores (Antarctica): preliminary study

The International Ocean Discovery Program (IODP) Expedition 374 drilled five sites from the outer continental shelf to rise in the eastern Ross Sea (Antarctica) to investigate the West Antarctic Ice Sheet evolution during Neogene and Quaternary. Detailed petrographic investigation of gravel size clasts is a key to identify the rocks source of those sediments and consequently the paleo-ice flow shifts during time. Sites U1521 and U1522 are located in the outer continental shelf and present thick sequences of glacio-marine sediments. Results presented here show the clasts logging of 421m of cores, where more than 26.000 clasts (>2mm) were macroscopically identified and sub-divided in six major lithological groups: igneous rocks, quartz fragments, volcanic rocks, dolerite clasts, sedimentary/meta-sedimentary rocks and metamorphic rocks. Moreover, 220 clasts were sampled for detailed petrographic and minero-geochemical analysis. The number of clasts along the core shows a wide variability, with 0-10 clasts/m in the clast-poor diamictite intervals to 10-47 clasts/m in the clast-rich diamictite, indicating oscillations of the sediment supply at the ice front. In the westernmost site (U1521), located in the Pennel Basin, the Early(?) Miocene drilled sequence shows five major clasts assemblage variations, marked by the percentage variability of basalt and dolerite, while the two major populations, consisting of low-grade fine-grained meta-sedimentary rocks (40-55%) and felsic granitoids (25-45%) remain constant. Sedimentary rocks, such as quartz-arenite, were found; limestones, meta-limestones and limestone’s conglomerates also occur and medium to high-grade metamorphic rocks, such as schists and gneisses, are not abundant. This lithological assemblage would be consistent with a source in the Transantarctic Mountains basement type; however, a local provenance from basement highs in the Ross Sea can not be excluded. In the easternmost studied site (U1522), located in the Glomar Challenger Basin, the Late Miocene drilled sequence, shows two major clasts assemblage variations, marked by the basalt abundance changes. The main lithological group is represented by low-grade fine-grained meta-sedimentary rocks (45-70%); secondary felsic to mafic granitoid rocks are present (20-40%). Dolerite clasts of the Ferrar Group are almost absent, instead basalts are common (1-5%) and medium- to high-grade metamorphic rocks (schist ang migmatitic gneiss) occur along cores. The Late Miocene sequence of the site U1522 shows a quite different clasts assemblage compared to the Early Miocene assemblage of the site U1521. Further detailed petrographic analysis are needed to better identify the source of clasts; moreover, geochronological analysis of heavy minerals of granitoid rocks could provide essential data to constrain provenance models in both sites

Data report: IODP Site U1523 composite section and stratigraphic splice based on X-ray fluorescence data

Contribution of melting Antarctic Ice Sheets (AIS) to rising sea level remains one of the least quantified inputs to models for the future. To improve these estimates, International Ocean Discovery Program (IODP) Expedition 374 cored five sites in the Ross Sea, Antarctica to examine the stability of the AIS to past intervals of global warmth. While most sites consisted of a single hole, Site U1523 cored 3 holes with overlapping stratigraphy in an attempt to recover as complete of a stratigraphic section as possible despite challenging coring conditions due to the presence of gravel lags and indurated intervals. Given these challenges, no attempt was made to create a composite depth scale or stratigraphic splice during the expedition. Here we use a combination of physical property data (primarily magnetic susceptibility and natural gamma radiation), X-ray fluorescence core scanning, and visual core description to construct a core composite depth below seafloor (CCSF) to the base of Hole U1523B. This composite depth scale is discontinuous due to challenging coring conditions and variable core recovery, although there are several intervals of reasonably good stratigraphic continuity between 0 and 26 m CCSF and 82 and 96 m CCSF. We also created a stratigraphic splice from 0 to 93.95 m CCSF, although the splice is only continuous to 15.82 m CCSF. Additionally, we mapped the off-splice interval of Core U1523E-1H to the composite depth scale over several intervals with significant core disturbance by stretching and squeezing to obtain a best fit. Development of the composite depth scale and stratigraphic splice will improve post-cruise research results by allowing scientists to compare samples from different holes on the same depth scale

Pleistocene depositional environments and links to cryosphere-ocean interactions on the eastern Ross Sea continental slope, Antarctica (IODP Hole U1525A)

The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic condition

Tephrochronology and Provenance of an Early Pleistocene (Calabrian) Tephra From IODP Expedition 374 Site U1524, Ross Sea (Antarctica)

Abstract We present a full characterization of a 20 cm‐thick tephra layer found intercalated in the marine sediments recovered at Site U1524 during International Ocean Discovery Program (IODP) Expedition 374, in the Ross Sea, Antarctica. Tephra bedforms, mineral paragenesis, and major‐ and trace‐element composition on individual glass shards were investigated and the tephra age was constrained by 40Ar‐39Ar on sanidine crystals. The 40Ar‐39Ar data indicate that sanidine grains are variably contaminated by excess Ar, with the best age estimate of 1.282 ± 0.012 Ma, based on both single‐grain total fusion analyses and step‐heating experiments on multi‐grain aliquots. The tephra is characterized by a very homogeneous rhyolitic composition and a peculiar mineral assemblage, dominated by sanidine, quartz, and minor aenigmatite and arfvedsonite‐riebeckite amphiboles. The tephra from Site U1524 compositionally matches with a ca. 1.3 Ma, rhyolitic pumice fall deposit on the rim of the Chang Peak volcano summit caldera, in the Marie Byrd Land, located ca. 1,300 km from Site U1524. This contribution offers important volcanological data on the eruptive history of Chang Peak volcano and adds a new tephrochronologic marker for the dating, correlation, and synchronization of marine and continental early Pleistocene records of West Antarctica