Ca isotopic geochemistry of an Antarctic aquatic system

Abstract

The McMurdo Dry Valleys, Antarctica, are a polar desert ecosystem. The hydrologic system of the dry valleys is linked to climate with ephemeral streams that flow from glacial melt during the austral summer. Past climate variations have strongly influenced the closed‐basin, chemically stratified lakes on the valley floor. Results of previous work point to important roles for both in‐stream processes (e.g., mineral weathering, precipitation and dissolution of salts) and in‐lake processes (e.g., mixing with paleo‐seawater and calcite precipitation) in determining the geochemistry of these lakes. These processes have a significant influence on calcium (Ca) biogeochemistry in this aquatic ecosystem, and thus variations in Ca stable isotope compositions of the waters can aid in validating the importance of these processes. We have analyzed the Ca stable isotope compositions of streams and lakes in the McMurdo Dry Valleys. The results validate the important roles of weathering of aluminosilicate minerals and/or CaCO3 in the hyporheic zone of the streams, and mixing of lake surface water with paleo‐seawater and precipitation of Ca‐salts during cryo‐concentration events to form the deep lake waters. The lakes in the McMurdo Dry Valleys evolved following different geochemical pathways, evidenced by their unique, nonsystematic Ca isotope signatures.

Dissolved major ions, Sr and 87 Sr/ 86 Sr of coastal lakes from Larsemann hills, East Antarctica: Solute sources and chemical weathering in a polar environment

“…Like for any chemical constituent, the dissolved (Ca + Mg) concentrations of these LH lakes are likely to be supplied through oceanic sources and/or weathering processes (Lyons et al, ). To better constrain the weathering process, we estimated the non‐sea‐salt component of all the elements using the following equation where, the subscripts lake, SW and NSS stand for the measured lake water composition, seawater composition and non‐seasalt component of the element, X (= Na, K, Ca, Mg, SO 4 , HCO 3 and Sr) respectively.…”

“…Average elemental ratios for these major sources are compiled from available literature and provided in Table 2. In addition to these major sources, freezing of seawater in polar regions may precipitate mirabilite (Na 2 SO 4 ), hydrohalites (NaCl, 2H 2 O) and Ca-Mg rich salts (Bein & Arad, 1992;Lyons et al, 2017;Wilson, 1979). Dissolution of these minerals may also supply solutes to these lakes.…”

“…Like for any chemical constituent, the dissolved (Ca + Mg) concentrations of these LH lakes are likely to be supplied through oceanic sources and/or weathering processes (Lyons et al, 2017). To better constrain the weathering process, we estimated the non-sea-salt component of all the elements using the following equation…”

“…In absence of perennial rivers/streams, these lakes are the only archive to study solute dynamics, biogeochemical cycling and on‐going surficial process in Antarctica. A large numbers of surface and subglacial lakes (approximately 10,000) have been reported from Antarctica, however, only a few of them have been studied to understand water chemistry and their solute sources (Lyons et al, ; Lyons et al, ; Lyons, Bullen, & Welch, ; Sabbe, Verleyen, Hodgson, Vanhoutte, & Vyverman, ). Multiple factors may contribute to the solute chemistry of these lakes which include chemical weathering of the bedrocks, biogeochemical processes, snow‐ice melting, evaporation, precipitation, aerosol induced dust deposition, sea salt spray and anthropogenic activities (Sabbe et al, ; Verleyen et al, ; Wilson, ).…”

“…In absence of perennial rivers/streams, these lakes are the only archive to study solute dynamics, biogeochemical cycling and on-going surficial process in Antarctica. A large numbers of surface and subglacial lakes (approximately 10,000) have been reported from Antarctica, however, only a few of them have been studied to understand water chemistry and their solute sources (Lyons et al, 2003;Lyons et al, 2005;Lyons, Bullen, & Welch, 2017;Sabbe, Verleyen, Hodgson, Vanhoutte, & Vyverman, 2003).…”