Bivalves Indicate That the North Atlantic Was Under Stress Before the Onset of the Little Ice Age

Bivalves indicate that the North Atlantic was under stress before the onset of the Little Ice Age

Beatriz Arellano-Nava, Paul R. Halloran, Chris A. Boulton, Timothy M. Lenton [email protected], [email protected]

College of Life and Environmental Sciences University of Exeter

April, 2021

University of Exeter April, 2021 1/9 The Little Ice Age

Climate reconstructions from the last millennium exhibit a transition from warm conditions during the Medieval Climate Anomaly to colder temperatures during the Little Ice Age. The transition occurred between 1300 and 1400 in the Arctic and Northern Eurasia [12]. The most accepted hypothesis to explain the transition argues that sea-ice ocean feedbacks ampliﬁed an initial cooling caused by frequent strong volcanic eruptions. The initial cooling led to an increase of Arctic sea ice exported to the subpolar North Atlantic, reducing surface density and convection in the Labrador Sea. This might have weakened the subpolar gyre, resulting in reduced northward heat transport, further reinforcing sea ice formation in the Arctic. [5, 8, 11, 16].

University of Exeter April, 2021 2/9 Bivalve shell derived records

Isotope ratios and the width of annual growth bands measured on bivalve shells provide precisely dated and annually resolved reconstructions of the marine environment. Increment width is determined by environmental conditions (food supply and temperature) akin to tree rings. Overlapping of individual shell measurements allows the creation of long-term records.

University of Exeter April, 2021 3/9 Resilience indicators

University of Exeter April, 2021 4/9 Changes in resilience in the subpolar North Atlantic

University of Exeter April, 2021 5/9 Comparison with other environmental reconstructions

The second period of loss of resilience coincides with the Great Sea Ice Anomaly [7] when the amount of Arctic Sea Ice exported to the subpolar North Atlantic increased significantly. Sea ice Medieval Climate Anomaly anomaly Little Ice Age First episode Second episode of loss of resilience After the second event of declining resilience, SSTs in the Norwegian shelf dropped abruptly (D), and the influence of Labrador Sea Water (LSW) in the Northeast Atlantic decreased rapidly (E), indicating a potential weakening of the subpolar gyre. The first period of destabilisation finished when the strongest volcanic eruption of the millennium occurred in 1257. Around that time, there was a brief episode of cold SSTs in the North Icelandic Shelf (B), and a mid-depth coral recorded an abrupt decrease in LSW, suggesting a weakening of the subpolar gyre (C). Between 1200 and 1260, there is evidence for high sea ice concentrations (F) and colder and fresher waters (G and H) in the northwestern Atlantic. During this period, frequent and Reduced LSW in the NE Atlantic relatively strong volcanic eruptions occurred (A). However, previous petrographic analyses suggest that the sea ice originated in South Greenland due to glacier calving during the warm conditions of the Medieval Climate Anomaly [6].

Reduced LSW in the Iceland Basin

Labrador sea

Subpolar S Gyre

Inﬂuence of colder and fresher waters in the Labrador Sea

A) Global volcanic stratospheric aerosols (Gao et al., 2008). B) Summer SST reconstructions based on alkenone paleothermometry in North Iceland (Sicre et al., 2011). C) Neodymium isotopic composition in deep-sea corals from the northeastern Atlantic (Copard et al., 2012). D) August SST from the Eastern Norwegian Sea inferred from diatom assemblages (Berner et al., 2011). E) Iceland Scotland Overflow Water (ISOW) near bottom flow-speeds measured as the sortable silt mean grain size (SS), faster ISOW speeds indicate a reduced influence of Labrador Sea water in South Iceland (Moffa-Sánchez et al., 2017). F) Sea ice concentration (SIC) in central-east Greenland inferred from diatom assemblages (Miettinen et al., 2015). G) Relative abundance of the polar foraminifera species Neogloboquadrina pachyderma (sinistral) in the Labrador Sea (Moffa‐Sánchez et al., 2014). H) SST in Newfoundland derived from alkenone paleothermometry (Sicre et al., 2014). Shaded areas correspond to the episodes in which we detect loss of resilience.

University of Exeter April, 2021 6/9 Summary

Our results indicate loss of stability in the marine environment before the transition to the Little Ice Age ∼1400, providing evidence for the action of internal feedbacks. The ﬁrst event of loss of resilience occurred before the cluster of major volcanic eruptions ∼1257, and large amounts of Arctic sea ice were exported to the subpolar North Atlantic, indicating that the region was already under stress. Bivalve shell derived reconstructions constitute valuable tools to assess changes in stability in the shelf seas environment since they are annually resolved and precisely dated.

University of Exeter April, 2021 7/9 References [1] Berner, K. S., Ko¸c,N., Godtliebsen, F., and Divine, D. (2011). Holocene climate variability of the Norwegian Atlantic Current during high and low solar insolation forcing: HOLOCENE CLIMATE VARIABILITY. Paleoceanography, 26(2):n/a–n/a. [2] Butler, P. G., Wanamaker, A. D., Scourse, J. D., Richardson, C. A., and Reynolds, D. J. (2013). Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica. Palaeogeography, Palaeoclimatology, Palaeoecology, 373:141–151. [3] Copard, K., Colin, C., Henderson, G., Scholten, J., Douville, E., Sicre, M.-A., and Frank, N. (2012). Late Holocene intermediate water variability in the northeastern Atlantic as recorded by deep-sea corals. Earth and Planetary Science Letters, 313-314:34–44. [4] Gao, J., Barzel, B., and Barabási, A.-L. (2016). Universal resilience patterns in complex networks. Nature, 530(7590):307–312. [5] Lehner, F., Born, A., Raible, C. C., and Stocker, T. F. (2013). Amplified Inception of European Little Ice Age by Sea Ice–Ocean–Atmosphere Feedbacks. Journal of Climate, 26(19):7586–7602. [6] Miettinen, A., Divine, D. V., Husum, K., Ko¸c,N., and Jennings, A. (2015). Exceptional ocean surface conditions on the SE Greenland shelf during the Medieval Climate Anomaly. Paleoceanography, 30(12):1657–1674. [7] Miles, M. W., Andresen, C. S., and Dylmer, C. V. (2020). Evidence for extreme export of Arctic sea ice leading the abrupt onset of the Little Ice Age. Science Advances, 6(38):eaba4320. [8] Miller, G. H., Geirsdóttir, A.,´ Zhong, Y., Larsen, D. J., Otto-Bliesner, B. L., Holland, M. M., Bailey, D. A., Refsnider, K. A., Lehman, S. J., Southon, J. R., Anderson, C., Björnsson,H., and Thordarson, T. (2012). Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks. Geophysical Research Letters, 39(2). [9] Moffa-Sánchez,P. and Hall, I. R. (2017). North Atlantic variability and its links to European climate over the last 3000 years. Nature Communications, 8(1):1726. [10] Moffa-Sánchez,P., Hall, I. R., Barker, S., Thornalley, D. J. R., and Yashayaev, I. (2014). Surface changes in the eastern Labrador Sea around the onset of the Little Ice Age. Paleoceanography, 29(3):160–175. [11] Moreno-Chamarro, E., Zanchettin, D., Lohmann, K., and Jungclaus, J. H. (2017). An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes. Climate Dynamics, 48(3):727–744. [12] PAGES 2k Consortium (2013). Continental-scale temperature variability during the past two millennia. Nature Geoscience, 6(5):339–346. [13] Reynolds, D. J., Scourse, J. D., Halloran, P. R., Nederbragt, A. J., Wanamaker, A. D., Butler, P. G., Richardson, C. A., Heinemeier, J., Eir´ıksson,J., Knudsen, K. L., and Hall, I. R. (2016). Annually resolved North Atlantic marine climate over the last millennium. Nature Communications, 7(1). [14] Sicre, M.-A., Hall, I. R., Mignot, J., Khodri, M., Ezat, U., Truong, M.-X., Eir´ıksson,J., and Knudsen, K.-L. (2011). Sea surface temperature variability in the subpolar Atlantic over the last two millennia. Paleoceanography, 26(4):2011PA002169. [15] Sicre, M.-A., Weckström,K., Seidenkrantz, M.-S., Kuijpers, A., Benetti, M., Masse, G., Ezat, U., Schmidt, S., Bouloubassi, I., Olsen, J., Khodri, M., and Mignot, J. (2014). Labrador current variability over the last 2000 years. Earth and Planetary Science Letters, 400:26–32. [16] Zhong, Y., Miller, G. H., Otto-Bliesner, B. L., Holland, M. M., Bailey, D. A., Schneider, D. P., and Geirsdottir, A. (2011). Centennial-scale climate change from decadally-paced explosive volcanism: A coupled sea ice-ocean mechanism. Climate Dynamics, 37(11-12):2373–2387. University of Exeter April, 2021 8/9 ACKNOWLEDGEMENT: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989 (project COMFORT, Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points). DISCLAIMER: This work, reflects only the authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.

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