Melting ice in the Arctic

Declining Arctic sea ice drives divergent shrub growth around the north

The implications of shrub growth responses to sea ice-induced changes in climate are Pan Arctic wide with global consequences including: landscape carbon sequestration, diets of caribou, reindeer and muskoxen as well as strengthening positive albedo feedbacks to future climate warming.

Dwarf shrubs are the most widespread woody plants in the Arctic and, like trees in lower latitudes, they form annual growth rings. These rings can be measured under a microscope to reveal the history of plant growth during past climates while also revealing growth responses to the recent climate changes that is vividly present in the Arctic. A new study shows how currently ongoing sea ice decline controls shrub growth across the Arctic.

Arctic sea ice has been in steep decline over the last two decades. Meanwhile, tundra shrub abundance has been increasing in many regions of the Arctic. A new study published in the Proceedings of the National Academy of Sciences of the United States of America reveals that declining Arctic sea ice extent has been associated with increasing shrub growth in some regions of the Arctic and decreasing growth in other, generally drier, regions.

The results are featured in Arctic Today, written by science writer, Yereth Rosen and can be found below.

An international team from eight countries led by Dr. Agata Buchwal from Adam Mickiewicz University in Poznan, Poland, Dr. Paddy Sullivan from University of Alaska Anchorage (UAA) and Professor Jeff Welker from the University of Oulu (UOulu) and UAA. This consortium gathered 23 existing shrub-ring chronologies from around the Arctic Basin and investigated shrub ring widths compared to changes in sea ice extent, air temperature and precipitation over the past 100 years.

UArctic Research Chair & Professor of Arctic Ecology and Biogeochemistry at the UOulu and UAA, Dr. Jeff Welker, sponsored and orchestrated the research in part with NSF, UArctic and UOulu funding in conjunction with Dr. Buchwal’s Polish Fulbright and Ministry of Science and Education postdoctoral fellowships to join Welkers lab.

Welker says “This research provides a mechanistic understanding of how divergent shrub growth responses to the Arctic wide warming and sea ice loss is predicated in part on the ecohydrology of the different landscapes where shrubs grow.

In particular, so long as shrubs do not experience drought conditions, they display positive growth responses to declining sea ice and warming.  However, populations of shrubs in drought prone regions are more likely to exhibit reduced growth with sea ice loss and warming.  These findings also point to the role of snow melt water and prior winter conditions in supporting divergent shrub ecophysiology and growth that the Welker lab has show recently with isotope studies (Jespersen et al. 2018). 

While Arctic tundra greening and browning have received increasing attention over the past decade, one comparatively under-studied area is the ultimate role of sea ice dynamics and decline as drivers of terrestrial vegetation change. Sea ice decline is emerging as a powerful driver of warming and associated precipitation changes across the Arctic, and tundra shrubs are recognized as climatically sensitive proxies of Arctic environmental change. However, sea ice – shrub interactions had not been studied at the Pan-Arctic scale. “The comprehensive assessment reported in our synthesis not only addresses that knowledge gap, but also, more importantly, documents contrasting influences of declining sea ice on summer climate and shrub growth at the biome scale”, says Buchwal.

Why we should care about the tundra shrubs? The implications of increasing heterogeneity in shrub growth responses to sea ice-induced changes in climate might be widespread, with local to global consequences, including carbon sequestration and albedo effects. While tundra areas dominated by increasers have the potential to take up and store more carbon from the atmosphere, areas dominated by decreasers might be areas of increasing carbon loss to the atmosphere.

Changes in shrub growth and abundance can have additional consequences across the Arctic that are linked to food webs as ungulates like caribou, reindeer and muskoxen use this life form as a forage source.  Ideal tundra landscapes for ungulates typically consist of both shrub and grass life forms.  But an over abundance or complete lack of shrubs can prove detrimental to ungulate health and potentially lead to herd reductions that can in turn effect subsistence communities that rely on ungulate protein.  

Articles:

Divergence of Arctic shrub growth associated with sea ice decline
https://doi.org/10.1073/pnas.2013311117

Arctic Today: How tiny growth rings revealed the secret link between sea ice loss and tundra ‘greening’ and ‘browning’

 

Last updated: 12.1.2021