Atmospheric Δ14C in the northern and southern hemispheres over the past two millennia : Role of production rate, southern hemisphere westerly winds and ocean circulation changes
Goosse, Hugues ; Brovkin, Victor ; Meissner, Katrin J. ; Menviel, Laurie ; Mouchet, Anne ; Muscheler, Raimund LU
and Nilsson, Andreas
LU
(2024)
In Quaternary Science Reviews
326.
- Abstract
The variations of atmospheric Δ14C over the past two millennia are classically attributed to changes in its production rate in the upper atmosphere, which in turn is related to changes in solar activity and the Earth's magnetic field. However, the potential contribution of atmospheric and oceanic circulation changes during this period has not been precisely quantified. This has been achieved here using a coupled climate model simulating explicitly the evolution of the different carbon isotopes, driven by a new estimate of 14C production derived from 10Be measurements, and using different production rates for each hemisphere. Our results confirm that changes in global and hemispheric atmospheric... (More)
The variations of atmospheric Δ14C over the past two millennia are classically attributed to changes in its production rate in the upper atmosphere, which in turn is related to changes in solar activity and the Earth's magnetic field. However, the potential contribution of atmospheric and oceanic circulation changes during this period has not been precisely quantified. This has been achieved here using a coupled climate model simulating explicitly the evolution of the different carbon isotopes, driven by a new estimate of 14C production derived from 10Be measurements, and using different production rates for each hemisphere. Our results confirm that changes in global and hemispheric atmospheric Δ14C are primarily driven by changes in production rate. The very good agreement between our results and observed atmospheric Δ14C also highlights the strong consistency of current interpretations of 10Be and 14C measurements. By contrast, the interhemispheric difference in atmospheric Δ14C is controlled by changes in the intensity of southern hemisphere westerly winds (SHWW) that impact atmosphere-ocean exchange and the upwelling of 14C depleted water masses in the Southern Ocean. Changes in deep water formation in both hemispheres or open ocean polynyas in the Southern Ocean only have a small impact on atmospheric Δ14C over that period. When driven by changes in the SHWW proportional to three existing reconstructions of the Southern Annular Mode (SAM) index, the model reproduces some key characteristics of the observed interhemispheric Δ14C gradient. These include the low values in the 15th century and the peak in the 16th century, but there are also clear differences between the experiments and Δ14C observations. This suggests that while SAM reconstructions capture some robust features in the centennial variability, large uncertainties remain.
(Less)
- author
- Goosse, Hugues
; Brovkin, Victor
; Meissner, Katrin J.
; Menviel, Laurie
; Mouchet, Anne
; Muscheler, Raimund
LU
and Nilsson, Andreas
LU
- organization
- publishing date
- 2024-02-15
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Cosmogenic isotopes, Global, Holocene, Ocean circulation, Paleoclimate modeling, Past millennium, Southern Ocean, Westerly winds
- in
- Quaternary Science Reviews
- volume
- 326
- article number
- 108502
- publisher
- Elsevier
- external identifiers
-
- scopus:85182607558
- ISSN
- 0277-3791
- DOI
- 10.1016/j.quascirev.2024.108502
- language
- English
- LU publication?
- yes
- id
- 6c41478f-38b8-4642-9bee-958d00ccb3fb
- date added to LUP
- 2024-04-12 14:49:15
- date last changed
- 2024-04-12 14:49:38
@article{6c41478f-38b8-4642-9bee-958d00ccb3fb,
abstract = {{<p>The variations of atmospheric Δ<sup>14</sup>C over the past two millennia are classically attributed to changes in its production rate in the upper atmosphere, which in turn is related to changes in solar activity and the Earth's magnetic field. However, the potential contribution of atmospheric and oceanic circulation changes during this period has not been precisely quantified. This has been achieved here using a coupled climate model simulating explicitly the evolution of the different carbon isotopes, driven by a new estimate of <sup>14</sup>C production derived from <sup>10</sup>Be measurements, and using different production rates for each hemisphere. Our results confirm that changes in global and hemispheric atmospheric Δ<sup>14</sup>C are primarily driven by changes in production rate. The very good agreement between our results and observed atmospheric Δ<sup>14</sup>C also highlights the strong consistency of current interpretations of <sup>10</sup>Be and <sup>14</sup>C measurements. By contrast, the interhemispheric difference in atmospheric Δ<sup>14</sup>C is controlled by changes in the intensity of southern hemisphere westerly winds (SHWW) that impact atmosphere-ocean exchange and the upwelling of <sup>14</sup>C depleted water masses in the Southern Ocean. Changes in deep water formation in both hemispheres or open ocean polynyas in the Southern Ocean only have a small impact on atmospheric Δ<sup>14</sup>C over that period. When driven by changes in the SHWW proportional to three existing reconstructions of the Southern Annular Mode (SAM) index, the model reproduces some key characteristics of the observed interhemispheric Δ<sup>14</sup>C gradient. These include the low values in the 15th century and the peak in the 16th century, but there are also clear differences between the experiments and Δ<sup>14</sup>C observations. This suggests that while SAM reconstructions capture some robust features in the centennial variability, large uncertainties remain.</p>}},
author = {{Goosse, Hugues and Brovkin, Victor and Meissner, Katrin J. and Menviel, Laurie and Mouchet, Anne and Muscheler, Raimund and Nilsson, Andreas}},
issn = {{0277-3791}},
keywords = {{Cosmogenic isotopes; Global; Holocene; Ocean circulation; Paleoclimate modeling; Past millennium; Southern Ocean; Westerly winds}},
language = {{eng}},
month = {{02}},
publisher = {{Elsevier}},
series = {{Quaternary Science Reviews}},
title = {{Atmospheric Δ<sup>14</sup>C in the northern and southern hemispheres over the past two millennia : Role of production rate, southern hemisphere westerly winds and ocean circulation changes}},
url = {{http://dx.doi.org/10.1016/j.quascirev.2024.108502}},
doi = {{10.1016/j.quascirev.2024.108502}},
volume = {{326}},
year = {{2024}},
}