“Meltwater On, In, & Under the Greenland Ice Sheet”

I was fortunate to be invited to give a public lecture at the Carnegie Science Institute in Washington, DC as part of their Carnegie Capital Science evening lecture series. It was a fantastic experience!

Each summer, a volume of water equivalent to 10 Chesapeake Bays melts off of the Greenland Ice Sheet. Much of this meltwater reaches the ocean, but its path is neither direct nor simple. On its way, the meltwater interacts with the glacier itself in ways that can affect ice flow and further sea-level rise. Dr. Poinar uses numeric models and remotesensing observations to understand the water-ice interactions that affect the glacier’s long-term behavior. She will discuss her analyses of water systems — including large meltwater lakes and rivers that form on top of the ice, aquifers within the ice, deep crevasses that move water from these systems through the glacier to its base, and the water flow networks that develop under the glacier — that change the flow speed and patterns of the ice on its slow, or sometimes not-so-slow, journey to the ocean. Ultimately, Dr. Poinar wants to discover: how much is the Greenland Ice Sheet likely to raise sea levels and how fast will it happen?

A top-notch video recording of the lecture is available at https://carnegiescience.edu/greenland.

Though the total carbon content of the mantle is largely unknown, the isotopic signatures of its sources and sinks suggests much about how the mantle operates. Together, geochemical and mineralogical analyses of a new diamond, a compendium of studies of the magnitude of carbon fluxes into and out of the mantle, and a simple geophysical model suggest that the mantle acts as two interacting reservoirs of carbon: (1) subducting slabs (the reservoir for depleted carbon) descend deep into (2) the bulk mantle (the enriched-carbon reservoir) to possibly as deep as the core-mantle boundary. These reservoirs mix to a small degree; that degree is a function of the isotopic composition of the bulk mantle (δ13C from -8 to -3.5 parts per thousand) and the residence time of carbon in the mantle (1-10 Gyr). The residence time is a function of the net flux out of the mantle, which is itself a sum of seafloor spreading rates, oceanic sediment deposition rates, calcium carbonate precipitation rates, and arc volcanism fluxes. This paper summarizes many studies of these fluxes to estimate those above quantities relevant to mantle convection.

We visited the Eternal Flame, a methane seep at a local waterfall, on a beautiful fall Saturday. Eternal Flame Falls is a short hike from a huge parking lot at Chestnut Ridge County Park, outside Buffalo. We also explored the rest of the park on our hike and met a local mushroom photography expert on the trail!

This month, I had the pleasure to be a guest at Canisius Conservation Conversations, a student-produced podcast at the Institute for the Study of Human-Animal Relations at Canisius College, Buffalo. It was a great experience!

I like the paper “Distortion of isochronous layers in ice revealed by ground-penetrating radar” by Vaughan, Corr, Doake, and Waddington (1999), Nature, 398(6725), 323–326, doi:10.1038/18653. The paper describes the field discovery of a Raymond Bump. The online Supplement, however, is not so good. (Thanks, Nature.) I wanted to be able to read it without squinting and scratching my head, so I rewrote it. Maybe it will prove useful to someone out there at some time. See link at end of page.

If you don’t know what a Raymond Bump is, you should learn about it from Jesse Johnson’s page.

And finally… the Supplement of Vaughan et al. (1999)… rewritten!