Spatiotemporal variations in formation conditions of cryogenic brines: Insights from aragonite cements in New Harbor, western Ross Sea, Antarctica

• Published in: Earth and planetary science letters Vol. 632; p. 118641
• Main Authors: Yang, Mingyu, Frank, Tracy D., Fielding, Christopher R., Chang, Biao
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2024
• Subjects: Diagenesis; Early–middle Pleistocene Transition; Isotope geochemistry; McMurdo Dry Valleys; McMurdo Sound; Middle Miocene Climatic Transition; Middle Miocene Climatic Transition; Diagenesis; McMurdo Dry Valleys; Early–middle Pleistocene Transition; Isotope geochemistry; McMurdo Sound
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2024.118641

•Aragonite cements in all sediment cores beneath New Harbor are analyzed.•Cement patterns indicate diverse brine-forming conditions in outlet glacial valleys.•Brine formation further illustrates how climate and ice sheets varied over time.•Guide to identify similar cryogenic processes elsewhere is provided. Cryogenic-brine precipitated carbonates (cryogenic-brine carbonates) have proven to be a valuable proxy for tracing the origin, nature, and distribution of Cenozoic brines that reside beneath McMurdo Sound (MMS) and adjacent McMurdo Dry Valleys (MDV), Antarctica. Of particular significance is the predominance of cryogenic-brine aragonite cements found in several stratigraphic sections in this region, reflecting the initial chemistry and conditions under which the brines formed. To fully explore this aspect, this paper presents a comprehensive examination of cryogenic-brine aragonite cements in all sediment cores recovered in New Harbor, an embayment that connects the MDV and MMS. Petrographic and isotopic analyses of the cements reveal a diverse range of brine-forming environments in the glacial outlet system during the middle Miocene Climatic Transition and the Early–Middle Pleistocene Transition. These environments span subglacial and ice-contact proglacial lakes to sub-ice-shelf fjords, occurring as cold-based, continent-sized Antarctic ice sheets expanded over the continental margin. Subsurface infiltration of the brines triggered almost instantaneous precipitation of aragonite cements below the sediment-water interface at low temperatures near 0 °C. Driven by the hydraulic gradient, the brines facilitated slow yet pervasive precipitation of an unusual form of aragonite characterized by coarse, blocky and poikilotopic morphologies—distinct from the typical acicular and fibrous aragonite dominating near-surface strata. The oxygen isotopic compositions of brines, as derived from aragonite precipitates, vary among different environments, displaying an increasing trend from ∼ –30 to –5 ‰ VSMOW toward MMS. The 18O depletion is primarily controlled by the availability of periodic saline water replenishment and the relative contribution of seawater versus meltwater during the cryoconcentration process. The ubiquity of brine-forming environments on the Antarctic continental margin suggests their potential existence during past ice ages, which may be identified by the presence of distinct cryogenic-aragonite cement patterns as documented in this study.