Samþætting fornveðurvísa - verkefni lokið

Integrating paleoclimate reconstructions with modeling to understand abrupt climate change in the northern North Atlantic region - ANATILS (Abrupt North Atlantic Transitions: Ice, Lakes, and Sea)


The goal of the ANATILS project (Abrupt North Atlantic Transitions; Ice, Lake and Sea) was to improve our understanding of the nature and causes of abrupt climate changes.

Fréttatilkynning verkefnisstjóra

The goal of the ANATILS project (Abrupt North Atlantic Transitions; Ice, Lake and Sea) was to improve our understanding of the nature and causes of abrupt climate changes. Current Arctic warming was evaluated in a Holocene context to better constrain the nature of sustained and often abrupt climate changes in the recent past. We focused on the past 8 ka, a time when boundary conditions were broadly similar to present, whereas the early Holocene (12-to-8 ka) was dominated by residual Northern Hemisphere ice sheets and the occasional release of vast quantities of meltwater and icebergs that obscured primary non-glacial climate variability. Our three-pronged strategy, reflected in our ANATILS acronym, was to test hypotheses on the evolution of the Holocene climate in the northern North Atlantic with: 1) new, high-resolution marine and terrestrial paleoclimate reconstructions, 2) icecap modeling, and 3) climate modeling.

One of the primary goals under this award was to produce new glacier and climate reconstructions from NW Iceland. We developed new lake sediment climate proxy records across northeastern Vestfirdir, constrained by radiocarbon-dated macrofossils and/or tephra of known age. These records indicate that although proto-Drangajökull still covered much of northeastern Vestfirdir ca 10 ka, the ice cap rapidly receded to dimensions smaller than present by ~9.2 ka, likely forced by elevated Northern Hemisphere (NH) summer insolation and increasing regional sea surface temperatures (SSTs). Strong summer insolation and SST forcing after 9.2 ka make it highly unlikely that residuals of Drangajökull survived the Holocene Thermal Maximum (7.9-5.5 ka). Although summer insolation declined through the Holocene, the first evidence demonstrating re-nucleation of Drangajökull is not until ~2.3 ka, much later than for Langjokull in central Iceland. Two threshold lake sediment records from Drangajökull's SE margin, combined with radiocarbon dating of entombed vegetation emerging from beneath cold-based portions of the ice cap provide the basis for late Holocene expansion. Our composite proxy records suggest that Drangajökull was advancing at 320 BCE, 180 CE, 560 CE, 950 CE and 1400 CE. Moraine mapping and lake sediment records along the southern margin suggest that the ice cap attained its maximum late Holocene dimensions during the Little Ice Age (1250-1850 CE), covering an area nearly twice it's modern dimensions. A new sea ice record from the north Iceland shelf developed with this project suggests that sea ice and SSTs modulated the first-order cooling trend, resulting in a non-linear response of the ice cap to the NH summer insolation decline.

Our geological constraints provide key targets for the numerical glacier modeling experiments. The modeling experiments showed that Drangajökull did not reform until the late Holocene, about 2 ka, consistent with our lake sediment and dead vegetation records. The low elevation of Vestfirdir and the strong marine influence result in Drangajökull being sensitive to changes in climate. The ice cap is sensitive to air temperature and precipitation, which can lead to rapid retreat if air temperatures continue to warm. The glaciological record developed under this grant, suggests that contrary to popular belief, Drangajökull has actually behaved quite similar to other Icelandic ice caps during the Holocene, and is likely to disappear in the future if the present warming trend persists.

Planktic and benthic foraminiferal assemblages document a decline in summer SST throughout the last 8 ka. The highest SST occurred between 6 and 4 ka, similar to the periods of warmest air temperature. There was a pronounced SST drop at 3.8 ka BP. After 4 ka SST lows correspond with peaks in IP25, a proxy for drift ice and with ice rafted quartz supporting the association between low IRF final report Page 2 of 6 SSTs, Polar surface water and drift-ice advection toward North Iceland from the north. Abrupt increases in IP25 at ca 1.5 and 0.7 ka are coincident with periods of rapid cooling in our lake proxy records, suggesting coupling between the marine and terrestrial systems. The contribution of sea ice to the broader climate system is further evidenced through the identification of statistically significant periodicities (ca 1000 yr and ca 200-230 yr) in the drift ice proxy data that have counterparts in previous studies concerning atmospheric and oceanic variability and solar forcing mechanisms.

A transient simulation for the past 2 ka, was performed from 1 CE to 2005 CE using NCAR's Community Earth System Model (CESM) and forcings compiled by Paleoclimate Modeling Intercomparison Project version 4 (PMIP4). This is the first high-resolution transient simulation for the past 2 ka to be made with a fully coupled high-resolution GCM. Our 2 ka simulation was compared to proxy data from Past Global Changes 2K (PAGES 2K) Arctic sub-program and CESM Last Millennium Ensemble simulation that covers the period from 850 to 2005 CE. Moreover, a series of experiments with the CESM perturbed by idealized volcanic forcing were carried out to test the hypothesis that periods of sustained cryosphere expansion in the northern North Atlantic during the last 2ka was caused by volcanism. Our modeling experiment simulates overall cooling both over land and over ocean in the North Atlantic Arctic during the last 2ka, with simulated cooling rates much greater around the North Atlantic Arctic than in the North Pacific Arctic, and statistically significant at sites over Canadian Arctic Archipelago, southern Greenland, Svalbard, Norway, and Finland, but not over Iceland. Proxy reconstructions indicate sustained expansion of sea ice cover around Iceland, but CESM Past2K fails to reproduce this continued expansion. Additional experiments are in progress to evaluate the reliability of the sea ice component of CESM in a colder world.

Heiti verkefnis: Samþætting fornveðurvísa og loftslagslíkana til skilnings á snöggum loftslagsbreytingum í norðurhluta Norður Atlantshafs / Integrating paleoclimate reconstructions with modeling to understand abrupt climate change in the northern North Atlantic region - ANATILS (Abrupt North Atlantic Transitions: Ice, Lakes, and Sea)
Verkefnisstjórar: Áslaug Geirsdóttir og Clifford H. Miller, Háskóla Íslands, INSTAAR & University og Colorado
Tegund styrks: Öndvegisstyrkur
Styrkár: 2014-2016
Fjárhæð styrks: 96,906 millj. kr. alls

Publications derived from the ANATILS project 2014-2017

Andrews, J.T., Cabedo-Sanz, P., Jennings, A.E., Ólafsdóttir, S., Belt, S., Geirsdóttir, Á., accepted. Sea ice, icerafting, and ocean climate across Denmark Strait during rapid deglaciation (~16 to 12 cal ka BP) of the Iceland and East Greenland shelves. Journal Quaternary Sciences.

Pendleton, S.L., Miller, G.H., Anderson, R.A., Crump, S.E., Zhong, Y., Jahn, A., Geirsdóttir, Á., accepted. Episodic Neoglacial expansion and rapid 20th Century retreat of a small ice cap on Baffin Island, Arctic Canada and modeled temperature change. Clim. Past Discuss., doi:10.5194/cp-2017-27, 2017.

Geirsdóttir, Á., Miller, G.H., Larsen, D.J., 2016. Glacial landforms in Hvítárvatn, central Iceland. In: Dowdeswell, J. A., Canals, M., Jakobsson, M., Todd, B. J., Dowdeswell, E. K. & Hogan, K. A. (eds) Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient. Geological Society, London, Memoirs, 1-4. © The Geological Society of London, 2016.

Magnússon, E., Belart, J.M.C.; Pálsson, F., Anderson, L.S., Gunnlaugsson, Á. T., Berthier, E., Ágústsson, H. And Geirsdóttir, Á., 2016. The subglacial topography of Drangajökull ice cap, NW-Iceland, deduced from dense RESprofiling. Jökull 66, 1-26.

Harning,D., Geirsdóttir, Á., Miller, G.H., Zalzal, K., 2016. Very early Holocene deglaciation of Drangajökull, Vestfirdir, Iceland. Quaternary Science Reviews 153, 192-198.

Harning, D., Geirsdóttir, Á., Miller, G.H., Anderson, L., 2016. Episodic expansion of Drangajökull, Vestfirdir, Iceland, over the last 3 ka culminating in its maximum dimension during the Little Ice Age. Quaternary Science Reviews 152, 118-131.

Gunnarson, S., 2016. Holocene Climate and Landscape Evolution in the West Central Highlands, Iceland. Unpublished MS thesis. University of Iceland.

Florian C.R. 2016. Multi-Proxy Reconstructions of Holocene Environmental Change and Catchment

Biogeochemistry using algal pigments and stable isotopes preserved in lake sediment from Baffin Island and Iceland. PhD thesis Faculty of Earth Sciences, School of Engineering and Natural Sciences, University of Iceland Reykjavík, May 2016

Magnússon, E., Belart, J.M.C., Pálsson, F., Ágæústsson, H., Crochet, P., 2016. Geodet mass balance record with rigorous uncertainty estimates deduced from aerial photographs and lidar data – Case study from DRangajökull ice cap, NW Iceland. The Cryosphere 10, 159-177. Doi:10.5194/tc-10-159-2016.

Belart, J.M.C., Berthier, E., Magnússon, E., Anderson, L.A., Pálsson, F., Thorsteinsson, Th., Howat, I.M., Adalgeirsdóttir, G., Jóhannesson, T., and Jarosch, A.H., 2017. Winter mass balance of DRangajökull ice cap (NW Iceland) derived from satellite sub-meter stereo images. The Cryosphere 11, 1501-1517.

Kristjánsdóttir, G.B., Moros, M., Andrews, J.T., Jennings, A.E., 2016. Holocene Mg/Ca, alkenones, and light stable isotope measurements on the outer North Iceland shelf (MD99-2269): A comparison with other multi-proxy data and sub-division of the Holocene. The Holocene 1-11. DOI: 10.1177/0959683616652703

Alsos IG, Ehrich D, Seidenkrantz M-S, Bennike O, Kirchhefer AJ, Geirsdottir A. 2016 The role of sea ice for vascular plant dispersal in the Arctic. Biol. Lett. 12: 20160264.

Solomina, O.N., Bradley, R.S., Jomelli, V., Geirsdóttir, Á., Kaufman, D.S., Koch, J., McKay, N.P., Masiokas, M., Miller, G, Nesje, A., Owen, L.A., Putnam, A.E., Wanner, H., Wiles, G., Yang, B., 2016. Glacier fluctuations during the past 2000 years. Quaternary Science Reviews 149, 61-90.

Sejrup, H.P., Seppä, H., McKay, N.P., Kaufman, D.S., Geirsdóttir, Á., de Vernal, A., Rensen, H., Husum, K., Jennings, A.E., Andrews, J.T., 2016. North Atlantic –Fennoscandian Holocene climate trends and mechanisms. Quaternary Science Reviews, online.

Capedo-Sanz, P., Belt, S.T., Jennings, A.E., Andrews, J.T., Geirsdóttir, Á., 2016. Variability in drift ice export from the Arctic Ocean to the North Icelandic Shelf over the last 8000 years: A multi-proxy evaluation. Quaternary Science Reviews 146, 99-115.

Jónsdóttir, I.R., Ólafsdóttir, S., Geirsdóttir, Á., 2015. A 2000 year record of marine climate variability from Arnarfjördur, NW Iceland. JÖKULL.

Blair, C., Geirsdóttir, Á., Miller, G.H., 2015. A high resolution multi-proxy lake record of Holocene environmental change in southern Iceland. Journal of Quaternary Sciences 30 (3) 281-292 ISSN0267-8179, DOI: 10,1002/jqs.2780.

Larsen, D.J. Geirsdóttir, Á. & Miller, G.H. 2015. Precise chronology of Little Ice Age expansion and repetitive surges of Langjökull, central Iceland. Geology 43, 167-170., doi:10.1130/G36185.1.

Florian, C.R., Miller, G.H., Fogel, M.L., Wolfe, A.P., Vinebrooke, R.D., Geirsdóttir, Á., 2015. Algal pigments in Arctic lake sediments record biogeochemical changes due to Holocene climate variability and anthropogenic global change. J. Paleolimnol 54, 53-69.

Jennings, A.E., Thordarson, T., Zalzal, K.,Stoner, J., Hayward, C., Geirsdóttir, Á., Miller, G. 2014. SE Greenland shelf archive of Icelandic and Alaskan volcanic eruptions during the Holocene. In: Austin, W. E. N., Abbott, P. M., Davies, S. M., Pearce, N. J. G. & Wastega°rd, S. (eds) Marine Tephrochronology. Geological Society, London, Special Publications, 398, # The Geological Society of London 2014. Publishing disclaimer:

In review

Gunnarson S., Geirsdóttir, Á., Miller, G.H., Ólafsdóttir, S., in review. Holocene Climate and Landscape Evolution in the West Central Highlands, Iceland. The Holocene.

Harning, D.J., Thordarson, T., Geirsdóttir, Á., Zalzal, K., Miller, G.H., in review. Provenance, stratigraphy and chronology of Holocene tephra from Vestfirdir, Iceland. Quat Geochronol.

Harning, D.J., Geirsdóttir, Á., Miller, G.H., in review. Holocene climate of Vestfirdir, Iceland, linked to oceanographic conditions along North Iceland Shelf. Earth and Planetary Science Letters.

Florian, C.R., Crump, S., Geirsdóttir, Á., Miller, G.H., Zalzal, K., in revision. Catchment geometry influences proxy response in late Holocene records from two proximal lakes located in north Iceland. Journal of Paleolimnology.

Andrews, J.T., Jónsdóttir, I., Geirsdóttir, Á. in review. Tracking Holocene drift-ice limits on the NW/SW Iceland shelf. ArcticAntarctic&AlpineResearch.

In Preparation

Florian, C.R., Geirsdóttir, Á., Miller, G.H. in prep. A 12 ka record of aquatic productivity and landscape stability from Torfdalsvatn, North Iceland. Quaternary Science Reviews.

Anderson et al., in prep. Holocene evolution of Drangajökull – numerical modeling. QSR/ JGR Surface.

Thordarson et al. in prep. The Grímsvatna tephra series Geology.

Geirsdóttir et al., in prep. Holocene climate variability and rapid transitions in the northern North Atlantic – Icelandic lake records QSR.

Yafang et al., in prep. Modeling North Atlantic sea ice and circulation changes during the last 2 ka (Draft end of year). Clim. Dyn/Climate of the Past.

Jennings et al., in prep. Planktic and Benthic Foraminifera. Marine Micro/Holocene/QSR.

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