From the Asian monsoon to North Atlantic climate

As an early Christmas present, Francesco Muschitiello’s and my manuscript Time-transgressive environmental shifts across Northern Europe at the onset of the Younger Dryas is now online! After years of excursions into the Asian monsoon, it seems that I am back again into something that has always interested me deeply: chronology and timescales and the dramatic climatic shifts at the end of the last ice age.

Francesco has done an excellent job compiling data sets, placing them on the same chronological framework, and comparing the different records. By doing so, we were able to show that the rapid cooling leading into the Younger Dryas was not felt equally and at the same time in records from Norway, Sweden, Denmark and Ireland. Thus, the start of the Younger Dryas cooling, or better the response to this cooling was time-transgressive. Hopefully, this article leads to the understanding that tuning and assuming synchronicity does not help science forward, and that good radiocarbon chronologies and age models are a way forward to solve the many mysteries surrounding the timing of the response to this cold interval on land.

Here is the link to the article for those who might be interested and the abstract:

Until lately, it has commonly been assumed that the last major reorganization of the North Atlantic ocean–atmosphere system, the Younger Dryas climatic reversal, spread synchronously on continental to hemispheric scales. This assumption arose because reliable chronologies, which would allow capturing the complexity surrounding local responses to abrupt climate change, were lacking. To better understand the temporal structure at the inception of the Younger Dryas across the North Atlantic, we revised, updated and compared the chronological framework of four Northern European sediment sequences (Lake Kråkenes, Lake Madtjärn, Lake Gammelmose, Sluggan Bog) by applying classical Bayesian modelling. We found distinct and spatially consistent age differences between the inferred ages of the Allerød interstadial – Younger Dryas stadial pollen zone boundaries among the four sites. Our results suggest an earlier vegetation response at sites along latitude 56–54°N as compared to sites located at 60–58°N. We explain this time lag by a gradual regional cooling that started as early as c. 12,900–13,100 cal. BP. This phenomenon was probably linked to cooling around the Nordic Seas as a result of enhanced iceberg calving from the Fennoscandian Ice Sheet during the final stage of the Allerød interstadial. By contrast, vegetation shifts at sites located further north occurred significantly later and in concert with the establishment of full stadial climate conditions (c. 12,600–12,750 cal. BP). Our study emphasizes the need to develop solid regional 14C chronologies and to employ the same age modelling approach to determine the temporal and spatial response to a climatic shift.

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