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This study reports that substantial chemical weathering occurs at subzero temperatures in ice-and-salt-rich permafrost in the McMurdo Dry Valleys, Antarctica. Chemical weathering is documented in a 30.0-m core collected in Beacon Valley by measuring the ionic composition, pH, and Mg isotopes of water extracted from thawed ice-rich sediment. Evidence of rock weathering is revealed by coinciding increases in the Mg isotopic composition and pH values. The primary factor that controls weathering is the salt content that leads to unfrozen brine; this is most apparent in the upper 7.0 m where salt content is high, temperatures rise above −21 °C and modeled unfrozen water reaches up to 4.0% of ice-content. In the upper 7.0 m, up to 60% of soluble Mg in the thawed permafrost ice is sourced from Ferrar Dolerite (δ26Mg = −0.22 ± 0.07‰) weathering, resulting in δ26Mg values ranging from of −0.82 ± 0.05‰ to −0.64 ± 0.05‰. Below 7.0 m, temperatures remain below −21 °C, unfrozen water is less than 2.0% of ice-content, and on average, 5% of soluble Mg is sourced from dolerite weathering with δ26Mg values ranging from −1.05 ± 0.05‰ to −0.76 ± 0.05‰. Regions of the core that are modeled to have no unfrozen water show little or no evidence of chemical weathering and relatively constant δ26Mg values close to Taylor Glacier and Beacon Valley snowfall values (–0.93 ± 0.06‰). This study demonstrates that significant chemical weathering occurs at subzero temperatures in permafrost where liquid brines form. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile strategy was reported to fabricate multifunctional PVA-based material. • The strength and toughness of material increased by 210% and 860%, respectively. • The material sets an impressive new record of folding-failure (900 000 times). • The material shows excellent self-healing, UV-blocking, and fluorescent properties. In the quest of materials that can tolerate extreme environments (i.e. , aerospace, polar regions of earth), facile design of self-healing, high fatigue-resistant and multifunctional nanocomposite materials with excellent ultralow temperature toughness, especially by utilizing inexpensive and sustainable bioresources is still currently challengeable. In current study, we deliver a general method by mixing PVA/BN and hydrogen bond cross-linked polymers to fabricate a nanocomposite material with ultralow temperature toughness, which shows excellent toughness (107.3 MJ·m−3) at − 196 °C and maintains high mechanical strength in highly humid environments. This material is a spider silk-inspired, poly(vinyl alcohol) (PVA)-based, autonomous room temperature self-healable nanocomposite by complexation of boron nitride (BN), quantum dots (QDs) and soy protein isolate grafted lignin (SPI-lignin). The fabricated material, namely PVA-BN-QDs-SPI-lignin, simultaneously exhibits outstanding tensile strength (53.3 MPa), toughness (182.8 MJ·m−3), fatigue-resistance as well as antiultraviolet and fluorescent properties and sets an impressive new record of folding-failure (900 000 times) and toughness, which are 10.6 to 45.7 times higher than other graphene-based nanocomposites. It can be impressively self-healed within only 2 min. Of particular interest is its facile, green, mild and inexpensive preparation method that can be easily scaled up. It is believed that this work, beginning with abundant biodegradable resources, opens the door to develop biobased multifunctional materials in practical applications, which may satisfy the demands of applications in ultralow environments such as in Antarctica, Moon, and Mars. [ABSTRACT FROM AUTHOR]