Demise of a glacier, uncovering a fjordDemise of a glacier, uncovering a fjord gudrun Thu, 11/12/2020 - 14:17 Demise of a glacier, uncovering a fjord When the last ice age was over, a large glacier covering the 1000 meter deep Hardangerfjord collapsed. These events at the end of the ice age in Norway, resemble what we are about to witness in today’s Greenland.
The Hardanger region in southwestern Norway is famous for a mild climate, steep rock walls and delicious apples. Towards the end of the last ice age, things were different. Climate was frigid, too cold for humans to settle, let alone apple trees. The Hardangerfjord Glacier reached from the Hardangervidda plateau in the east, towards the island Halsnøy towards the west. These gravelly islands were themselves created a few centuries earlier, by the bulldozing force of the glacier. This Norwegian ice-age landscape reminds us of the coasts of Greenland, with impressive fjords hosting glaciers and icebergs.
A new study reveals how climate warming at the end of the last ice age caused the great glacier covering Hardanger to collapse around 11.000 years ago. The study is done by a team of scientists from the University of Bergen, the Bjerknes Centre for Climate Research, the University of Svalbard, Stockholm University, and the Bolin Centre for Climate Research. The findings are now published in the journal Quaternary Science Reviews.
Among the fastest glacier retreats worldwide
During the ice age, a large cold blanket of ice covered the British Isles, Scandinavia and parts of Russia. Norway was covered by kilometres of ice, including the Hardangerfjord. As climate warmed, the glacier in the fjord started to melt and retreat fast.
"When the ice age was over, things got quite dramatic. Temperatures rose several degrees in a matter of decades. The retreat of the Hardangerfjord Glacier was incredibly quick, actually one of the fastest lasting meltdowns of a glacier that we know of," says Henning Åkesson, who has lead the study.
Åkesson is a post-doctoral researcher at Stockholm University, previously at the University of Bergen and the Bjerknes Centre. The study gives new insights into how the Hardangerfjord Glacier vanished, and is the result of a close collaboration between glaciologists, geologists and climate scientists.
Through computer simulations, the scientists have reconstructed a detailed picture of the rapid melting. The glacier reacted strongly to the climate warming when the last ice age ended, and retreated 125 km over a period of 500 years, giving a mean long-term retreat rate of 250 metres per year. The retreat was a combination of melting at the surface and by the warming fjord waters, and iceberg calving.
This is similar to what is measured in the fjords of Greenland today, as a result of global warming.
The submarine landscape controls the speed
"When temperatures rise, glaciers melt. This is obvious, but the pace of retreat can vary greatly. We find that the landscape of the seafloor is the the deciding factor," says Åkesson.
He points at an example close to the fjord-side village of Jondal, where the fjord is nearly 900 m deep.
Further towards the coast, between the villages of Rosendal and Jondal, the retreat was slow. Along this part of the fjord, the fjord bottom shoals moving inland, until we reach a fjord sill at 500 metres depth. Such sills are known to slow down the retreat of fjord glaciers. A melting glacier can be left hanging several decades on such “submarine hills” at the fjord floor, even though the known climate warming indicates that the glacier would continue to retreat quickly.
"In such settings, we may easily be misled and think that the retreat has stopped, while in reality, it is just a short breather for the glacier. Therefore we really need to know what the submarine landscape looks like," Åkesson points out.
Over the submarine hills
As a glacier loses its grip at a sill, things literally go downhill.
The study of Hardangerfjorden is a great example of this. From the sill, the fjord floor plunges “downhill” for almost 30 kilometres, before getting gradually shallower towards the village Eidfjord at the fjord head.
The scientists show that during the most dramatic period, the glacier retreated 10 meters per day, or several kilometres every year.
"If you were using the local ferry to Jondal at this time, you could have witnessed the glacier melting back with your own eyes," Åkesson says.
Clues from the past
The simulation of the collapse of Hardangerfjord Glacier gives clues about the impact of climate change on glaciers today, according to Åkesson, for example in Greenland.
A temperature rise similar to that at the end of the ice age, will occur in the near future due to global warming, unless man-made emissions of greenhouse gases are drastically reduced. Such climate warming is critical in deciding the fate of the ice on Greenland and in the fjords around the continent.
Scientists have long been troubled about the health of the Greenland Ice Sheet, where many glaciers have started to flow faster and have retreated many kilometres over the last 20 years.
Ice melt in Greenland is of great consequence for the coastal landscape, wildlife and the local people, while also adding to an already steadily rising global sea level. In the long-run, the entire ice sheet on Greenland is in danger. In the worst-case scenario, the ice sheet will melt away, causing global sea level to rise with seven metres, though this is not expected in at least another 1000 years from now.
Henning Åkesson, Richard Gyllencreutz, Jan Mangerud, John Inge Svendsen, Faezeh M. Nick, Kerim H. Nisancioglu,
Rapid retreat of a Scandinavian marine outlet glacier in response to warming at the last glacial termination, Quaternary Science Reviews,
Volume 250, 2020, 106645, ISSN 0277-3791, https://doi.org/10.1016/j.quascirev.2020.106645
The sea can nurture or calm stormsThe sea can nurture or calm storms Anonymous (not verified) Mon, 11/02/2020 - 11:58 The sea can nurture or calm storms The ocean is a questionable babysitter. Kristine Flacké Haualand takes us to the cradle of midlatitude cyclones.
Written by Kristine Flacké Haualand, PhD candidate at the Bjerknes Centre and the Geophysical Institute at the University of Bergen. The article was first published on Scisnack.
Between the warm tropics and the cold polar regions exists a broad belt of strong latitudinal temperature contrasts: the midlatitudes. The weather here is dominated by cyclones, associated with wet and windy weather, and anticyclones, associated with calm and sunny weather. Before these weather systems hit land and affect our daily lives and picnic plans, they have often formed and traveled over open ocean, from which they’ve picked up a lot of heat and moisture. Let’s start at the cradle of midlatitude cyclones and see how the ocean influences their intensity before they potentially grow to mature storms and make landfall.
Many baby storms are born along the Gulf Stream, where warm, tropical water flows poleward. With the warm ocean below, the cold sector of the storm gets heated by the ocean such that the horizontal temperature contrast across the storm core weakens. This is sad news for the baby storm because temperature contrasts provide an important energy source for her growth. But someone is happy! Further down the path of the storm sit people like us enjoying the benefits of calmer weather.
While the ocean provides heat that calms down the weather, the ocean also provides moisture to the storms. With more moisture comes more clouds that intensify the storms. The role of the ocean is therefore two-fold, with the heat from the ocean weakening storm development, and the moisture from the ocean intensifying it.
For typical environmental conditions, especially in a warmer climate, the effect of moisture dominates, such that the overall effect of the ocean is storm intensification. Maybe just enough to postpone those picnic plans?
Read about how clouds and rain influence lows here.
Haualand, K. F., and T. Spengler, 2020: Direct and Indirect Effects of Surface Fluxes on Moist Baroclinic Development in an Idealized Framework. J. Atmos. Sci., 77, 3211–3225, https://doi.org/10.1175/JAS-D-19-0328.1.
Unormalt store mengder sjøis i drift sørover i byrjinga av 1300-tallet kan ha satt i gang den vesle istida, og viser eit nytt studie. Tilfeldige og spontane klimaendringar kan vere grunnen til at det kom så mykje is – som igjen sette i gang mange hundre år med kulde i Europa.
Foraminifera trace anthropogenic CO2 in the Iceland Sea by 1950Foraminifera trace anthropogenic CO2 in the Iceland Sea by 1950 Anonymous (not verified) Wed, 09/30/2020 - 09:18 Foraminifera trace anthropogenic CO2 in the Iceland Sea by 1950 Margit Simon and her colleagues have detected anthropogenic CO2 from the 1950s and onwards in sediments from the Icelandic shelf. Here she writes about their new study.
Written by Margit Simon, researcher at the Bjerknes Centre and NORCE.
In a new study published in PLoS ONE we show that marine sediments from the ocean floor off Iceland overlap with the historical era providing a record of oceanographic changes and the carbon cycle in unprecedented temporal resolution.
The CO2 emitted from fossil fuel burning has a distinct carbon isotope ratio compared to the preindustrial background level. Since the industrial revolution, nearly 30 percent of CO2 emissions have been taken up by the ocean. This absorption is not uniform; therefore, understanding local CO2 uptake rates is essential for assessing the strength and climate sensitivity of the ocean carbon sink, as well as the risk for future ocean acidification.
We find evidence that the imprint of this fossil fuel‐derived CO2 in the waters of the NW Icelandic Shelf became detectable from ~1950 CE (±8 years) onwards. These new results are based on the carbon isotope (δ13C) signature in planktic foraminifera, marine zooplankton that forms a calcium carbonate shell in the water they live. Their carbon isotope time series reveals a negative excursion driven by anthropogenic CO2 penetration into the ocean, the so called “Suess effect” signal.
A trend in productivity?
However, this decline in the carbon isotope ratio over time is smaller than what we would expect at this location in the Iceland Sea. Our results imply a reduced Suess effect. The reason for that is, that the Suess effect is counteracted by a concurrent increase in surface ocean productivity, since the 1940/50´s (causing a positive shift in the foraminiferal δ13C).
This mechanism agrees with a recent study on the same core material that finds that enhanced freshwater discharge from melting Arctic Ocean drift sea ice and the eastern Greenland Ice Sheet has contributed to nutrient-driven fertilization of the upper ocean and consequently increased the marine primary productivity since the 1940s/50s on the North Icelandic Shelf.
Reconstructed ocean properties
Unfortunately, missing detailed instrumental observations before the 1950s limits our understanding of how the ocean–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing.
The sedimentary material on the Iceland Shelf has allowed us to produce a multi-proxy record of ocean variability in the region. Proxies are substitute measurements that reflect ocean properties in the past. By doing so, we extend the oceanographic observational record ~100 years back in time for this area.
Our results show natural multi-decadal variability related to the Iceland Sea 's response to easterly wind forcing. Moreover, we are able to trace the poleward propagation of warm water moving with the currents from the south, the subtropics, into the Nordic Seas, via the Icelandic inflow branch.
Simon MH, Muschitiello F, Tisserand A, Olsen A, Moros M, Perner K, et al. A multi-decadal record of oceanographic changes of the past ~165 years (1850-2015 AD) from Northwest of Iceland. PLoS ONE. 2020. doi: 10.1371/journal.pone.0239373.