All posts by kpoinar

About kpoinar

I am a glaciologist employed as an Assistant Professor in the Geology Department at the University of Buffalo.

News article “The future of the planet is written in Greenland”

Argemino Barro, a New York-based journalist, interviewed Kristin Poinar for El Ágora, the first Spanish-speaking media entirely devoted to water and climate change. His article is about the future of the Greenland Ice Sheet.

(also see Google translation to English)
La pérdida de hielo de lugares como Groenlandia está aumentando el nivel del mar.
De “El futuro del planeta se escribe en Groenlandia” por Argemino Barro.

GML in person

We had our first and only in-person lab meeting of Spring 2021. It was a brisk spring day on UB’s South Campus, where none of us had ever spent much time. We took a walk around and even spied the Mackay Tower, where a pair of peregrine falcons make their nest. (UB has a webcam — UB Falcon Cam — highly recommended viewing in April through the end of May.)

Congratulations Jeremy Stock, MS!

Jeremy Stock successfully defended his MS thesis, “Modeled Patterns of Crevassing Induced by Supraglacial Lake Drainage in Western Greenland”, and turned in a very nice dissertation this May. Congratulations, Jeremy!

Abstract:

The Greenland Ice Sheet is expected to contribute substantially to global sea level rise over the next century in response to climate change. As increasing volumes of surface meltwater are delivered to the glacier bed via moulins during supraglacial lake drainage events, it has been hypothesized that new crevasses may form upflow, causing a cascade of lake drainages. This upflow expansion could alter ice sheet dynamics, leading to ice sheet instability and even greater sea level rise contributions. To investigate this hypothesis, we applied an analytical ice-flow model (Gudmundsson, 2008) to calculate surface strain rates and infer the pattern of crevassing induced by a modeled rapidly drained lake. We calibrate the model using data collected during a lake drainage event in the summer of 2011 in the Pakitsoq region of Western Greenland. The patterns and extent of crevassing we see in our model results are highly dependent on the bed topography, basal sliding ratio, dimensions of the slipperiness patch, and the seasonal timing of the drainage event. Our model results show evidence of considerable crevassing occurring within 3-5.5 km upstream of the modeled lake drainage, with crevassing enhanced by a factor of 5-6 within a 3 km radius of the rapidly drained lake. Because lakes in this area are spaced by roughly 2-4 km, our results support the hypothesis for cascading lake drainage. This research improves our understanding of how meltwater may affect ice sheet dynamics, which are a major factor in how much the Greenland Ice Sheet will contribute to sea level rise in the future.

G. H. Gudmundsson. Analytical solutions for the surface response to small amplitude perturbations in boundary data in the shallow-ice-stream approximation. The Cryosphere, 2(2):77–93, 2008. http://doi.org/10.5194/tc-2-77-2008

Modeled Patterns of Crevassing Induced by Supraglacial Lake Drainage in Western Greenland

A few figure excerpts:

Figure 2.12: Flow chart of the data inputs (colored blocks), required parameters (gray circles), and outputs (white circles) produced by the analytical perturbation model (Gudmundsson, 2008). The model outputs are responses to basal perturbations and represent changes to the mean surface elevation (s), mean longitudinal velocity (u), mean transverse velocity (v), and mean vertical velocity (w).
Figure 4.1: Most likely new crevasse locations in response to supraglacial lake drainage. Model results when the study area is centered around lakes 55, 52, 44, 64, 59, and 54. Lake 52 is always shown as a bold circle. Supraglacial lakes are shown as black circles, with the lakes involved in the drainage event outlined twice (Morriss et al., 2013) and GPS stations shown as black triangles (Andrews et al., 2014). The colors indicate where all 3 theoretical strain rate thresholds are exceeded (deep red), 2 thresholds are exceeded (red), 1 threshold is exceeded (orange), and no thresholds are exceeded (tan). The concentric circles are separated by 1 km. We used constant values for mean slip ratio ( ̄C), time (t), and the amplitude of the basal slipperiness patch (Ac) across all tests shown. The diameter of the basal slipperiness patch (Dc) is scaled relative to mean ice thickness ( ̄h) in each location.

Carnegie Capital Science evening lecture

“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.

The carbon cycle in the mantle

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.


The isotopic fractionation of carbon by biological processes also has wide-reaching implications. Geological evidence shows that the fractionation has been quite constant over the age of the Earth, yet the mismatch between the δ13C of the bulk mantle and of subducting sediment suggest that subducting slabs descend to a largely separate reservoir. The δ13C of diamonds suggest that this reservoir is deeper than the transition zone, and may even be at the core-mantle boundary. Thus, analysis centered on the relatively inaccessible carbon content of the mantle could provide evidence for full- rather than layered-mantle convection, one of the largest questions in geophysics.
We know from the amount of accumulated carbon on the Earth’s surface that the net flux of carbon out of the mantle over the age of the earth has been of order 10^8 to 10^9 kg/yr.
Photo by Meacham Wood, tartanscot.blogspot.com

Vaughan et al., 1999 Supplementary Information

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.

This is the Raymond Bump under the ice divide at Siple Dome, West Antarctica. It’s a radargram. From Gades et al. (2000).

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