Holocene glacier length variations along the American Cordilleras from paired ¹⁴C-¹⁰Be measurements

Andrew Jones

Abstract: Rising global temperatures in the industrial era have led to the smallest observed glacier lengths since record keeping began a few centuries ago. The degree to which modern glacier size is anomalous within the context of the Holocene, however, remains largely unknown. Here, we present cosmogenic in situ ¹⁴C and ¹⁰Be measurements in recently exposed proglacial bedrock for 10 glaciers spanning 60º N to 60º S along the American Cordilleras in order to quantitatively assess if modern alpine glaciers are at their smallest extents of the Holocene.

We collected ~5 bedrock samples at each glacier abutting modern ice along a transect perpendicular to flow. ¹⁰Be exposure ages represent cumulative exposure durations during the Holocene, while ¹⁴C is used to infer burial, as ¹⁴C will experience significant decay (t_1/2 = 5,700 years) when shielded from nuclide production by ice on Holocene time scales. Because nuclide concentrations can only provide cumulative exposure and burial durations, observed ¹⁴C/¹⁰Be ratios were compared to 100,000 possible exposure-burial histories by Monte Carlo simulation to quantify when glaciers advanced or retreated during the Holocene.

Modeled glacier extents for 4 tropical glaciers, 1 glacier in the Sierra-Nevada, CA, and 1 in Patagonia, CL are at their smallest extent of the Holocene, providing evidence that present-day warming may have already exceeded the warmest periods of the Holocene. Other study sites in the Northern and Southern hemispheres (30-60º) exhibit a transition from smaller to larger glaciers during the mid-Holocene, suggesting a late Holocene cooling trend that is in agreement with global proxy data, but contrasts climate model simulations.

Time: April 22nd (11:45)

Advisor: Shaun Marcott

Co-Authors: Andrew L Gorin, Tori M Kennedy, Shaun A Marcott, Jeremy D Shakun, Brent M Goehring, Gordon R Bromley, Douglas H Clark, Andrew Hein, Vincent Jomelli, Emilio Mateo, Bryan Mark, Brian Menounos, Don Rodbell, Andrew Wickert.

Stream: Zoom

Email: agjones3@wisc.edu