Tides regulate the flow and density of Antarctic Bottom Water from the western Ross Sea.

Antarctic Bottom Water (AABW) stores heat and gases over decades to centuries after contact with the atmosphere during formation on the Antarctic shelf and subsequent flow into the global deep ocean. Dense water from the western Ross Sea, a primary source of AABW, shows changes in water properties and volume over the last few decades. Here we show, using multiple years of moored observations, that the density and speed of the outflow are consistent with a release from the Drygalski Trough controlled by the density in Terra Nova Bay (the "accelerator") and the tidal mixing (the "brake"). We suggest tides create two peaks in density and flow each year at the equinoxes and could cause changes of ~ 30% in the flow and density over the 18.6-year lunar nodal tide. Based on our dynamic model, we find tides can explain much of the decadal variability in the outflow with longer-term changes likely driven by the density in Terra Nova Bay.

The role of tides in bottom water export from the western Ross Sea.

Approximately 25% of Antarctic Bottom Water has its origin as dense water exiting the western Ross Sea, but little is known about what controls the release of dense water plumes from the Drygalski Trough. We deployed two moorings on the slope to investigate the water properties of the bottom water exiting the region at Cape Adare. Salinity of the bottom water has increased in 2018 from the previous measurements in 2008-2010, consistent with the observed salinity increase in the Ross Sea. We find High Salinity Shelf Water from the Drygalski Trough contributes to two pulses of dense water at Cape Adare. The timing and magnitude of the pulses is largely explained by an inverse relationship with the tidal velocity in the Ross Sea. We suggest that the diurnal and low frequency tides in the western Ross Sea may control the magnitude and timing of the dense water outflow.

anem: A Simple Web-Based Platform to Build Stakeholder Understanding of Groundwater Behavior.

Groundwater supports essential societal and ecological functions by acting as a reservoir that buffers against natural variability. Increasing water scarcity and climate variability have resulted in more intensive management of groundwater resources, but groundwater often remains difficult to understand and manage. With this in mind, we develop a simple platform that provides a straightforward, web-based user interface applicable to a wide variety of end-user scenarios. Groundwater behavior is modeled using the method of images in a new R package, anem, which serves as the engine for the web platform, anem-app, produced using R Shiny. Both tools allow users to define aquifer properties and pumping wells, view maps of hydraulic head, and simulate particle tracking under steady-state conditions. These tools have the advantage of being platform independent and open source, so that they are freely available to anyone with a web browser and internet connection (anem-app) or computing platform with R installed (anem). We designed both tools to lower the learning curve and up-front costs to building simple groundwater models. The simplicity of the web application allows exploration of groundwater behavior under various conditions, and should be especially valuable in low-budget applications where advanced analysis may not be practical or necessary. Integration with the R language allows for advanced analysis and deeper exploration of groundwater dynamics. In this manuscript, we describe how anem and anem-app are built in the R environment and demonstrate how they might be used by planners or stakeholders.

A large population of king crabs in Palmer Deep on the west Antarctic Peninsula shelf and potential invasive impacts.

Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic continental shelf waters for more than 14 Myr. The west Antarctic Peninsula shelf is warming rapidly and has been hypothesized to be soon invaded by lithodids. A remotely operated vehicle survey in Palmer Deep, a basin 120 km onto the Antarctic shelf, revealed a large, reproductive population of lithodids, providing the first evidence that king crabs have crossed the Antarctic shelf. DNA sequencing and morphology indicate the lithodid is Neolithodes yaldwyni Ahyong & Dawson, previously reported only from Ross Sea waters. We estimate a N. yaldwyni population density of 10 600 km(-2) and a population size of 1.55 × 10(6) in Palmer Deep, a density similar to lithodid populations of commercial interest around Alaska and South Georgia. The lithodid occurred at depths of more than 850 m and temperatures of more than 1.4°C in Palmer Deep, and was not found in extensive surveys of the colder shelf at depths of 430-725 m. Where N. yaldwyni occurred, crab traces were abundant, megafaunal diversity reduced and echinoderms absent, suggesting that the crabs have major ecological impacts. Antarctic Peninsula shelf waters are warming at approximately 0.01°C yr(-1); if N. yaldwyni is currently limited by cold temperatures, it could spread up onto the shelf (400-600 m depths) within 1-2 decades. The Palmer Deep N. yaldwyni population provides an important model for the potential invasive impacts of crushing predators on vulnerable Antarctic shelf ecosystems.