High latitude mountain environments are experiencing disproportionately adverse effects from climate change. The Gulf of Alaska (GoA) region is an embodiment of this change, particularly concerning a shifting hydrologic balance. Even so, the magnitude and contribution of fresh submarine groundwater discharge (fresh SGD) remains virtually unexplored within the region, though it has gained increasing attention globally due to its chemical significance and influence on coastal ecosystems. Here we provide the first regional estimates of fresh SGD to the GoA using two established water balance approaches. This is an effective way to distinguish the contribution of terrestrially derived fresh SGD, rather than the more commonly quantified total SGD which includes discharge that is driven by marine forces such as sea-level oscillations and density gradients. We compare the approaches and assess their capabilities in computing the magnitude of fresh SGD over a large regional scale. Mean annual fresh SGD flux ranges between 26.5 to 86.8 km3 yr-1 to the GoA, equivalent to 3.5-11.4% of the total freshwater discharge. Contributions are highest in the Southeastern panhandle and lowest in the Cook Inlet basin, with the highest area normalized contribution occurring in the Prince William Sound. Fresh SGD exhibits high spatial and temporal variability throughout the region. Although freshwater discharge to the GoA is investigated considerably, the importance of fresh SGD has, thus far, been overlooked.

Accelerating demand for energy storage has led to increasing development of brine resources in the “Lithium Triangle”, estimated to hold about 75% of the planet’s Li reserves but persistent and fundamental questions regarding the source and transit time of groundwater have confounded efforts to manage these resources effectively. The basins containing these brines lie within the massive Altiplano-Puna Plateau, home to people whose ancestors have inhabited this land for thousands of years and fragile ecosystems that exist nowhere else on Earth. This region is very dry, bordering Earth’s driest non-polar desert and as such, groundwater is the predominant and, in many areas the only source of water. Fundamental questions about the spatiotemporal dimensions of these groundwater systems have only begun to be addressed. In much of this extreme and remote region, there is a severe lack of quality baseline understanding of the regional hydrological system and connections between surface and groundwater bodies. To address these questions, we utilize an exhaustive set (~2,500 individual analyses) of environmental tracer data (δ18O, δ2H, 3H, 87Sr/86Sr), and dissolved major and minor elements in waters collected from over a dozen field campaigns in the Salar de Atacama and Altiplano of Chile and on the Puna Plateau of Argentina. Our integrated analysis pairs these data with rigorous geochemical modelling and physical hydrological measurements from the field and remote sensing products. 3H data show much of the groundwater currently discharging into these basins is non-modern (>60 yrs. old), stable isotope and geochemical data show strong connectivity but also a marked disconnect between some recharge and discharge areas. We show that “fossil” groundwater, 100-10,000 yrs. or older is widespread and fundamental to the system, sharp disconnects exist between the modern hydrological system, the water bodies it sustains, and those sustained by paleo-recharge water. By defining these connections in spatial detail and within a regional integrated framework, we greatly improve the fundamental mechanistic understanding of this and other groundwater-sustained systems. This will greatly improve the ability of communities, governments and industry to manage of these water resources in a way that is genuinely sustainable.

Demand for lithium for batteries is growing rapidly with the global push to decarbonize energy systems. The Salar de Atacama, Chile holds ~42% of the planet’s reserves in the form of brines hosted in massive evaporite aquifers. The mining of these brines and associated freshwater use has raised concerns over the sustainability of lithium extraction, yet large uncertainties remain regarding fundamental aspects of governing hydrological processes in these environments. This incomplete understanding has led to the perpetuation of misconceptions about what constitutes sustainable or renewable water use and therefore what justifies responsible allocation. We present an integrated hydrological assessment using tritium and stable oxygen & hydrogen isotopes paired with remotely sensed and terrestrial hydroclimate data to define unique sources of water distinguished by their residence time, physical characteristics, and connectivity to modern climate. Our results describe the impacts of major drought on surface and groundwaters and demonstrate that nearly all inflow to the basin is composed of water recharged >65 years ago. Still, modern precipitation is critical to sustaining important wetlands around the salar. Recent large rain events have increased surface water and vegetation extents and terrestrial water storage while mining-related water withdrawals have continued. As we show in this basin, poor conceptualizations of these complex hydrological systems have perpetuated the misallocation of water and the misattribution of impacts. These fundamental issues apply to many similar regions globally. Our new framework for hydrological assessment in these arid basins moves beyond calculating gross inputs-outputs at a steady-state to include all compartmentalized stores that constitute “modern” budgets.

High latitude glacierized coastal catchments of the Gulf of Alaska (GoA) are undergoing rapid hydrologic changes in response to climate change and glacial recession. These catchments deliver important nutrients in the form of both inorganic and organic matter to the nearshore marine environment, yet are relatively understudied with respect to characterization of the solute generation processes and total yields. Using multiple linear regression informed by Bayesian Information Criterion analysis we empirically demonstrate how watershed characteristics affect solute generation as represented by concentration-discharge relationships. We find that watershed mean slope and relief control solute generation and that solute yields are influenced most by glacier coverage. We contribute a new flux and concentration-discharge based conceptualization for understanding solute cycles across a hydroclimatic gradient of GoA watersheds that can be used to better understand future watershed responses to rapid hydrologic change.