2021 Kirk Bryan Award

Presented to Maureen H. Walczak

Maureen H. Walczak

Maureen H. Walczak

Awarded for: 2020, Phasing of millennial-scale climate variability in the Pacific and Atlantic Oceans: Science, vol. 370, p. 716-720. DOI: 10.1126/science.aba7096.


Citation by John M. Jaeger

It is my honor to be the citationist for this year’s Kirk Bryan award-winning paper by Maureen (Mo) Walczak entitled “Phasing of millennial-scale climate variability in the Pacific and Atlantic Oceans”. Mo directed an all-star cast of co-authors in their landmark 2020 Science paper that directly tackles a fundamental question in Quaternary geomorphology: “What part of the planet drives late Pleistocene climate change?” The paradigm is that the global chain-of-climate-events starts in the sub-polar north Atlantic, associated with changes in North Atlantic Deep Water production disturbed by meltwater release from the Laurentide ice sheet. Resulting changes in Atlantic meridional overturning circulation (AMOC) then lead to a long list of down-stream climate impacts. Mo and colleagues provide the strongest evidence to date that the primary driver lies not in the north Atlantic but in the Pacific Ocean.

They challenge this AMOC paradigm with a high temporal resolution sediment record from the relatively under-sampled Gulf of Alaska. Mo’s radiocarbon analysis of an exceptional foraminifera database (82 benthic-planktic radiocarbon pairs spanning the past ~50,000 years BP) from Integrated Ocean Drilling Program Site U1419 on the upper continental slope. This independently dated northeast Pacific record is essential because most global studies of late Pleistocene paleoclimate showing a north Atlantic control tune/adjust their chronologies to match Greenland ice core records.

Walczak et al. suggest armadas of icebergs, “Siku Events” (Inupiat/Inuit word for ice) that are analogous to the Laurentide Heinrich events, calved episodically from the marine-terminating Cordilleran Ice Sheet (CIS), when regional atmospheric temperatures were relatively warm, representing a massive influx of icebergs from regional retreat of marine-terminating outlet glaciers.

Critically, the atmospheric and oceanic changes triggering Siku Events observed in their records follow Asian Monsoon changes by 1000-3000 years but precede north Atlantic Heinrich Events and Antarctic and global atmospheric CO2 millennial-scale changes by 1000-1500 years. This pattern of leads and lags supports the hypothesis that the Pacific is not a passive recipient of north Atlantic climate changes, but rather that a western Pacific moisture and heat source initiates millennial-scale climate perturbations.

Mo’s meticulous lab study and careful explanation of the response of Quaternary ice sheets on millennial-timescales is based on fundamental glacilogical principals (e.g., glacial mass balances, moisture/heat delivery) rather than the more circuitous route implicit in the AMOC hypothesis of ice dynamics. Her paper should make us reconsider the climatic paradigm driving much of Quaternary paleoclimatology and thus merits this prestigious award.



Response forthcoming.