Category Archives: Greenland

Viking and Inuit in Greenland

Posted on December 28, 2022 by | 1 comment

While Viking rulers of Kyiv in Ukraine formally converted to Christianity in 988 CE at the outer limits of eastern Europe, two small viking settlements emerged at the southern tip of Greenland close to the Americas. The Norse settlers of Greenland left Iceland with 25 ships, but 11 of these either turned back to Iceland or were lost at sea. The remaining 14 boats arrived near 61 N latitude to establish an “Eastern” settlement which over time grew to more than 190 farms and 12 churches. Farther north near 64 N latitude a smaller “Western” settlement eventually grew to about 90 farms and four churches near Nuuk, today’s capital of Greenland. The “Western” settlement had a warmer and milder continental climate, because their farms were located far inland within a wide and complex fjord system that sheltered the farmers from atrocious coastal storms. The “Eastern” settlement was hit harder by these storms, because here the farms were closer to shore, closer to the icesheet, and closer to the center of the North-Atlantic storm activity.

North-Atlantic location map with Norse trading routes between Europe and Greenland adapted from Jackson et al. (2018)

For about 200-300 years the settlements flourished and reached a population of about 4,000 people. They paid taxes to the King of Norway, donated tithes to their churches, and imported clothing, iron, and food stuff from Scandinavia. They paid with ivory from narwhales and walrus that they hunted in Disko Bay at 69 N latitude. Three viking hunters scratched their names in stone on a cairn they built about 1333 CE on an island near Upernavik at 73 N latitude (Francis, 2011). At these “Northern Hunting Grounds” the vikings from both “Eastern” and “Western” settlements likely met the Inuit of the Thule culture who at the time were moving south along West Greenland after a 3000 km migration from coastal Alaska within a few generations.

Runestone of Kingittorsuaq found at 72°57′55″N 56°12′45″W stating “Erlingur the son of Sigvat and Bjarni Þorðar’s son and Eindriði Oddr’s son, the washingday (Saturday) before Rogation Day, raised this mound and rode…” [Photo Credit: Ukendt /Nationalmuseet, Danmark]

The modern Inuit of the Thule culture arrived in Greenland about 200-300 years after the vikings did. They arrived on foot, by dog sled, and in umiaks from the Bering Sea area of Alaska and Siberia (Friesen, 2016). They were equally adept to hunt caribou on land with bow and arrow, seals on sea ice with spears, and whales on open ocean with sophisticated harpoons. They crossed Smith Sound at 79 N latitude about 1300 CE to reach Greenland spreading south towards the viking settlements and north-east towards Fram Strait separating Greenland from Svalbard. On a beach off Independence Fjord in North-East Greenland at almost 83 N latitude Eigil Knuth found the frame of one of their skin-hulled umiak in 1949 (Knuth, 1952).

Umiak in Greenland as depicted by Carl Rasmussen in 1875 adapted from https://en.wikipedia.org/wiki/Umiak

The vikings built “permanent” houses of stone, farmed the land, and kept sheep, goat, and cows. They hunted walrus and narwhal for its ivory to trade with Europe to import metals, clothes, and foods. Their diet until about 1300 CE was high on terrestrial and low on marine resources as indicated by isotopic studies of their bone structure. This changed when a cooling climate challenged animal husbandry in Greenland and the Norse transitioned towards a marine-based diet of fish, seals, and marine mamals (Jackson et al., 2018).

Map of Greenland and Ellesmere Islands adapted from Gullov (2008). Red symbols indicate Norse artifacts found at Inuit sites occupied in the 13th and 14th century while black dots represent location of such artifacts at 15th and 16th century.

In contrast, the Inuit embraced a more mobile life-style as entire family units moved large distances to new sites from year to year and seasonally from summer to winter camps. Their hunting was tied to the sea ice and they developed fancy techniques to hunt larger whales, walrus, and polar bears for food, fuel, and clothing. Their technologies and behaviors adapted rapidly in an extreme environment and climate that kept changing in time. Inuit often viewed themselves and their animal prey as mutually connected with energies flowing from animal to Inuit and vice versa. Both were part of one nature which changes in time on many different cycles that one needs to read and understand for survival. This view differed from that of the more pastoral vikings who saw themselves and their homes as “safe inner spaces” and everything on the outside as “wild and hostile” nature. They constantly tried to modify, improve, and control the landscape while the Inuit moved and adapted within it (Jackson et al., 2018).

Viking settlement on Greenland (left), chess figures from walrus ivory (center), and viking longboat from the 10th century.

The vikings vanished without a trace in the 15th century. Their fate is still researched and debated in academic and popular outlets alike. In contrast, the Inuit expanded their range along all of Greenland where in the 18th and 19th centuries they were “re-discovered” in the South by Danish and Moravian colonists and missionaries and in the North by the English Navy, American adventurers, and Danish scientists.

In 1910 two Danes Knut Rasmussen and Peter Freuchen established a trading post at North Star Bay near 77 N Latitude. They called “Thule.” Over the next 20 years Thule became a focal point of about 200 nomadic Inughuit that all are direct descendants of the Thule culture Inuit. There are about 700 of them today and most still live in Qaanaaq. Linguist Stephen Pax Leonard lived among them for a year in 2010/11 when he produced a 10 minute video that documents contemporary Inuit life and language.

Contemporary photos of Qaanaaq and Thule region. Photos on left panel by Dr. Steffen Olsen near Tracy Glacier in Inglefield Fjord while images in right panel are of North Star Bay and Thule Air Base by the author.

References:

Francis, C.S., 2011: The Lost Western Settlements of Greenland, 1342, California State Univ. Sacramento, MA Thesis, 84 pp.

Friesen, T.M., 2016: Pan-Arctic Population Movements, Chap.-28 of “The Prehistoric Arctic,” Oxford Univ. Press, 988 pp.

Gullov, H.C., 2008: The Nature of Contact between Native Greenlanders and Norse, J. North Atlantic, 1, 16-24.

Jackson, R., J. Arneborg, A. Dugmore, C. Madsen, T. McGovern, K. Smiarowski, R. Streeter, 2018: Disequilibrium, Adaptation, and the Norse Settlement of Greenland, Human Ecology, 46 (5), https://doi.org/10.1007/s10745-018-0020-0.

Kintsch, E., 2016: Why did Greenland’s Vikings disappear? Science, 10.1126/science.aal0363, accessed as https://www.science.org/content/article/why-did-greenland-s-vikings-disappear

Knuth, E., 1952: An Outline of the Archaeology of Peary Land, Arctic, 5(1), pp. 17-33.

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Posted in Greenland, History, Iceland, Thule, vikings

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Greenland Glacier-Driven Ocean Circulation

Posted on November 16, 2022 by | Leave a comment

Greenland’s coastal glaciers melt, shrink, and add to globally rising sealevel. They also drive local ocean currents that move icebergs around unless they are stuck on the bottom. The glaciers’ melt is cold fresh water while the adjacent ocean is both salty and warm. Checking on what we may expect against observations, I here use data from NASA’s Ocean Melts Greenland initiative that dropped ocean probes from an airplane into the ice waters off coastal Greenland to measure ocean temperature and salinity.

For six years these data show how the coastal ocean off Greenland varies from location to location next to glaciers as well as from year to year. More specifically, I picked Melville Bay in North-West Greenland for both its many glaciers and many dropped NASA ocean sensors. The ocean data allow me to estimate ocean currents by using a 100 year old physics method. I just taught this to a small class of undergraduate science students at the University of Delaware. My students are strong in biology, but weak on ocean physics. This essay is for them.

Melville Bay is a coastal area off north-west Greenland between the town of Upernavik (Kalaallisut in Greenlandic) near 73 N latitude where 1100 people live and the village of Savissivik (Havighivik in Inuktun) at 76 N latitude where 60 Inuit live. There are no other towns or settlements between these two villages that are about as far apart as Boston is from Philadelphia, PA. Imagine there were no roads from Boston to New York to Philadelphia but only one large glacier next to another large glacier. This is Melville Bay.

Below I show an excellent set of photos of Savissivik by a French husband and wife team who visited in 2013/14. Their photographic gallery captures elements of contemporary subsistence living in remote Greenland where animals like seals, birds, fish, narwhal, and polar bears provide food, fuel, clothing, and income.

NASA dropped some 50 ocean sensors into Melville Bay froma plane during the short summer seasons each year 2016 through 2021. I met NASA pilots, engineers, and scientists doing their experiments when I was doing mine from a snowmobile in April of 2017 and again with Danish friends from a Navy ship in August of 2021, but these are stories for another day.

Let me start with a map of where NASA dropped their ocean profiling floats into Melville Bay and thus introduce the data. While the surface waters are usually near the freezing point, waters 300-400 meters deep down are much warmer. They originate from the Atlantic Ocean to the south and one of the goals of NASA’s “Ocean Melts Greenland” campaigns was to determine if and how these Atlantic waters reach the coastal glaciers. Most glaciers of Melville extend into this warm ocean layer and thus are melted by the ocean.

In the map above I paint the maximal temperatures in red and the bottom depths in blue tones. The profile on the right shows data for all depths at one station. As salinity increases uniformly (red curve) the temperature increases to a maximum near 300-m depth (black curve). It is this maximal subsurface temperature that I extract for each station and then put on the contour and station map on the left. The straight blue line connects Upernavik in the south with Sassivik in the north. It is an arbitrary line, coast-to-coast cutting across Melville Bay.

The warmest warm waters we find near Upernavik in the south and within a broad submarine canyon that brings even warmer waters from Baffin Bay towards the coast. Temperatures here exceed 2.4 or even 2.7 degrees Celsius. Most coastal waters along Melville Bay have a temperature maximum of about 1.5 to 1.8 degrees Celcius (about 35 Fahrenheit) and this “warm Atlantic” ocean water melts the coastal glaciers. The ocean melts the glaciers summer and winter while the warm air melts it only in summer.

There is more, because the glaciers’ melt also discharge fresh water into the ocean where it mixes to to form a layer of less dense or buoyant water. The buoyant waters create a local sealevel that is a little higher along the coast than farther offshore. The map above indicates that this “little higher sealevel” comes to about 4 cm or 2 inches. If this pressure difference across the shore is balanced by the Coriolis force, as it often does, then an along-shore coastal current results. This coastal current would move all icebergs from south to north unless they get stuck on the bottom. Along the northern coastline of Melville Bay the surface flow is from east to west. The coastal current is strongest near Savissivik where we find a (geostrophic) surface current larger than 40 cm/s. At that speed an iceberg would move more than 21 miles per day. Such strong surface flows are exceptional and diminish rapidly with depth. Hence a freely floating iceberg with a draft of several hundred meters would move much slower than the surface current.

I met a hunter from Savissivik in April of 2017 and for a fast-moving night we discussed the state of local fishing, hunting, living, traveling, and working on the sea ice next to the glaciers of Melville Bay. He invited me to become his apprentice. As such I would now ask him about the surface currents outside his home. Which way does he observe the icebergs to move in summer or winter? Has hunting on the sea ice in winter changed over his life time? When is it safe to travel there with a dog-sled? Could he and I perhaps work together during the spring to deploy ocean sensors through the sea ice? I am dreaming again …

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Posted in Arctic Glacier, Greenland, Oceanography, Thule

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Adaptations of Genetically Isolated Polar Bears in Southeast Greenland

Posted on November 3, 2022 by | Leave a comment

Ms. Amanda Winton wrote this essay as an extra-curricular activity developed from a science communication assignment for MAST383 – Introduction to Ocean Sciences. The editor teaches this course at the University of Delaware and was assisted by Ms. Terri Gillespie in a final formal edit. ~Editor

“… The intense winds blow against my white fur. The chunks of white, frosty glacial ice float below me. I lift my eyes, scanning my surroundings for my next meal. I see a dark gray mass sliding along the ice a few hundred feet away. My mouth waters as my paws ready for the hunt. I have not eaten, nor seen any prey, in 12 days. I begin my slow and steady pursuit. The terrain below me is rough, unlike the abundant flat sea ice that was my ancestors’ hunting grounds.

It is a little bit more difficult to maneuver, taking more time to get to my prey than I would have hoped. Minutes later, I jump into the water, about to swim to the ice my prey is lounging on. Unfortunately, I grossly underestimated how far away it is, and by the time I swim to this meal, it’s gone. Now I am left with no food, and my stomach grumbles for the fifth time today.”

This short, first-person narrative is written from the perspective of a Greenland polar bear in the summertime. In particular, this polar bear is part of a subpopulation that hunts on a glacial mélange within fjords, rather than on larger frozen ice caps. Of course, I do not know what polar bears think in their pursuits, migration, or other actions. I can only use my own experiences and compassion to imagine their point of view and desires. Based on my biocentric view, all animals have their own importance in the world and are worthy of preservation. Since human intervention causes polar bears to struggle in their own environment, people have the responsibility to save them and recover their habitat.

Figure 1. This depicts the types of glaciers that can be present in different places, depending on the snow and ice available as well as the pressure and heat present. [adapted from National Snow and Ice Data Center]

Polar bears are losing their land due to the indirect and direct effects of human interaction with the environment, called climate change. Atmospheric warming leads to scarce and thinner glaciers, as well as less advancement in the growth season. The breakup of ice in the spring due to melting occurs nine days earlier than it did before global warming was identified in 1938 (Maslin, 2016), and the freezing of ice in the fall occurs ten days later (EPA, 2022). Not only is there less ice, but the ice exists for a shorter period of time. This leads to less territory, which can be detrimental to any species.

When Glacier National Park in Montana was established in 1910, about 150 glaciers existed. Now, less than 30 remain (Glick, 2021). Polar bears are forced to look for land and food elsewhere because they do not have as much space to hunt and breed. There is not much land or food present, so the natural selection rate for this animal is increasing dramatically every day, at a rate as fast as climate change (Peacock, 2022). Polar bears are forced by their environment to either die or adapt. This is not an easy adaptation, either.

Polar bears are forced to adapt quickly, since glacier ice is very limited in the Arctic. On the southeast coast of Greenland, polar bears have implemented a new habitat: fjords. These bears live at the front of glaciers in fjords, called the glacial mélange, which is a mixture of sea ice, icebergs, and snow. Only polar bears in southeast Greenland live there all year round, using this habitat to breed, hunt, and sleep.

Figure 2. This Glacier-Ocean-Mélange System depicts the forces acting upon this mechanism at all times. These forces are important for keeping the system at equilibrium and habitable for polar bears. [adapted from Amundson et al. (2020)]

In a recent research study led by Kristin Laidre, Northeast and Southeast Greenland polar bear population migrations were tracked. The median distance of the polar bears in the northeast was 40km per four days. The median distance traveled for the southeast population was 10km per four days, which is statistically significantly lower. Laidre et al. (2022) found that the southeast polar bears traveled between neighboring fjords, or stayed in the same fjord all year. This adaptation shows behavioral plasticity (Peacock, 2022), as Southeast Greenland bears have not become locally extinct.

This subpopulation of polar bears is one out of 20, and is very small. They are smaller in size and have a slower reproduction rate, most likely due to trouble finding a mate in a small population, as well as their long generation time and low natality. It’s important to preserve this genetically isolated population to preserve their genetic diversity. Without this element, birth defects, either mental or physical, will occur. This leads to a population less fit for its environment. Genetic diversity is necessary for surviving natural selection and thriving in an ecosystem. 

Figure 3. This photograph presents polar bears walking in the snowy fjords. Fjords are not flat, which makes it harder for these bears to travel, versus the flat ice that other polar bears have been hunting on for centuries. [adapted from Laidre et al. 2022]

“… I leave my fjord the next day, hoping to find another nearby, hopefully unoccupied. To my luck, one appears in my field of vision a few hundred meters away. To my surprise, a bob of seals rests on the glacial mélange. They are oblivious and unsuspecting of my presence. Minutes pass, and my stomach no longer rumbles. A successful hunt is always satisfactory. Now I can focus on my next need: my desire to find a mate and pass on my strong genes. It will not be too hard for me as I am a big male, with thick, insulated fur. I advance through the neighboring fjord, hopeful and confident. My story is just beginning.”

References:

Amundson, J., Kienholz, C., Hager, A., Jackson, R., Motyka, R., Nash, J., Sutherland, D., 2020: Formation, flow and break-up of ephemeral ice mélange at LeConte Glacier and Bay, Alaska. Journal of Glaciology, 66(258), 577-590. doi:10.1017/jog.2020.29.

Environmental Protection Agency, 2022: Climate Change Indicators: Arctic Sea Ice, https://www.epa.gov/climate-indicators/climate-change-indicators-arctic-sea-ice.

Dunham, W., 2022: Isolated Greenland Polar Bear Population Adapts to Climate Change. Reuters, Thomson Reuters, https://www.reuters.com/business/environment/isolated-greenland-polar-bear-population-adapts-climate-change-2022-06-16.

Glick, D., 2021: The Big Thaw. National Geographic, https://www.nationalgeographic.com/environment/article/big-thaw.

Greenfieldboyce, N., 2022: In a Place with Little Sea Ice, Polar Bears Have Found Another Way to Hunt, KTOO, https://www.ktoo.org/2022/06/20/in-a-place-with-little-sea-ice-polar-bears-have-found-another-way-to-hunt/.

Laidre, K. L. and 18 others, 2022: Glacial Ice Supports a Distinct and Undocumented Polar Bear Subpopulation Persisting in Late 21st-Century Sea-Ice Conditions, vol. 376(6599), 1333–1338, https://doi.org/10.1126/science.abk2793.

Maslin, M. , 2016: Forty years of linking orbits to ice ages, Nature, 540, 208–209, https://doi.org/10.1038/540208a.

Ogasa, N., 2022: Some Polar Bears in Greenland Survive on Surprisingly Little Sea Ice, Science News, https://www.sciencenews.org/article/polar-bear-greeland-sea-ice-glacial-melange-climate-change.

Peacock, E., 2022: A new polar bear Population, Science, vol. 376(6599), 1267–1268, https://doi.org/10.1126/science.abq5267.

National Snow and Ice Data Center, 2022: Glaciers, https://nsidc.org/learn/parts-cryosphere/glaciers/science-glaciers.

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Posted in Global Warming, Greenland, Wild Life

Ice, ocean, and glacier change in northern Greenland

Posted on April 7, 2022 by | Leave a comment

Steffen Olsen is a Danish physical oceanographer with a skill to present beauty to an artist like my wife and a scientist like me. Three days ago he posted a photo on Twitter with these words

“Local hunters from Qaanaaq navigating our CTD system in the frozen ice mélange in front of Tracy Galcier 66W 77N to measure the ocean below. Heat loss to melting of glacial ice leaves the ocean at sub-zero temperatures down to 400m @arctic_passion @dmidk @ruth_mottram“

Photo: Dogsled from Qaanaaq near the northern edge of Tracy Gletscher in Inglefield Fjord April 2022. [Credit: Dr. Steffen Olsen, Danish Meteorological Institute.]

Steffen’s photo shows his study area, research platform, and mode of transportation. There is a glacier in the background between the rocks on the left (north) and unseen mountains to the right (south). Equally unseen is the ocean under all this crushed and broken and piled up sea ice covered by fresh snow. We see tracks of people walking to the vantage point from where the photo is taken. The dogs rest on a small patch of level sea ice perhaps 3-5 feet (1 to 1.5 meters) thick.

There are boxes on the sled that contain gear to drill through the sea ice and then to send a probe down towards the ocean bottom to measure ocean temperature, saltiness, and oxygen during its decent. I did similar work with a snowmobile in 2017 based at Thule Air Base for 6 weeks. Steffen and I work together on such data. He collected these every year since 2011 both adjacent to Tracy Gletscher and along most of the ~120 km long and ~1000 meter deep fjord. I am grateful to Steffen to share this photo: It helps me to focus on my passions rather than my outrage at soldiers and leaders of the Russian Federation in their war to destroy Ukraine and its people building a free, vibrant, and democratic country for themselves. There is more, but I stop here now.

Let me start with a map of where in Greenland the photo was taken and where Steffen collected his data each since 2011. The red star in the insert top-right shows the location of the map between Canada and Greenland. I color ocean bottom depths in blue shades and land heights in green, yellow, and brown shades. The glacier in Steffen’s photo is at the north-eastern end of Inglefield Fjord where I placed the label Tracy. The label Qaanaaq shows where about 650 Inughuit live along the coast near the center of the fjord. It probaby took the dogs about 2-3 days to travel with their cargo from Qaanaaq to Tracy Gletscher. Red dots are stations served by a Danish Navy ship in the summer of 2015, but I here only talk about the blue dots.

Figure: Map of the study area with ocean sampling stations in Inglefield Fjord (blue dots) and adjacent northern Baffin Bay. [Unpublished own work.]

The blue dots are stations where Steffen and his companions drilled through the sea ice in 2018. Note that some of those ocean stations appear on land. This cannot be, but the glacier has retreated between the time the topographic data was collected and 2018 when Steffen collected the ocean data. Three LandSat satellite images below show how the glacier changed from 1973 to July and August of 2021. Icebergs are visible, too. A citizen scientist with the handle “Espen” at the Arctic Sea Ice Forum extracted these satellite photos from public U.S. databases. He is part of an online international community of Greenland and sea ice enthusiasts who posts at this forum for over a decade making daily discovers. These are people with regular jobs that in their spare time post satellite imagery and open data they found which they share openly often with insightful interpretations. It is citizen science at its very best. I go there often to read, ask, and learn. I even met a prominent member once for lunch when visiting Copenhagen on my way to Greenland. He gifted me LandSat imagery of my favorite glaciers printed on cloth that I framed for its scientific and artistic beauty. Thank you, Espen 😉

Gallery: Space photography (LandSat) of glaciers terminating from the Greenland ice sheet in Inglefield Fjord in 1973 (right), July 2021 (center), and August 2021 showing the retreat of Tracy but not Heilprin Gletscher. [Credit: Espen Olsen at Arctic Sea Ice Forum.]

So how does the ocean below all this ice next to a glacier look? Well, lets look at a set of station from Qaanaaq to Tracy Gletscher that shows how temperature, salinity, and oxygen of the water changes both with depth and along the fjord. We always find very cold, somewhat fresher, and highly oxygenated water near the ocean surface about 40 m (near glacier) to 100 m (near Qaanaaq) below the sea ice and warmer, saltier, and less oxygenated water below with a temperature maximum of 1 degree Celsius near 300 m depth. It is this warm water that melts the adjacent glacier. As Dr. Olsen says “… Heat loss to melting of glacial ice leaves the ocean at sub-zero temperatures …” In other words, the deeper waters 1. enter the fjord at temperatures above zero degrees Centigrade, 2. reach the glacier, 3. cool down as they melt the glacier, and 4. leave the fjord at temperatures below zero degrees Centigrade. This is why the two stations near the glacier show slightly fresher and cooler waters between 300 and 500 m depth. This water contains the glacial melt. The section represents the 10 year average from 2011 through 2020.

Figure: Section of salinity (bottom), temperature (center), and dissolved oxygen (top) along Inglefield Fjord as an average of data collected annually between 2011 and 2020. [Unpublished own work.]

Earlier this year I tried to visit Copenhagen to finish this work that places this emerging story into both a historical and spatial context, but Covid restrictions derailed this and other plans. Nevertheless, have excellent data from 1928 when this fjord was first surveyed by Danish oceanographers. At that time the waters had dramatically different temperatures (much colder) and salinities (a little fresher) both inside the fjord and in Baffin Bay adjacent to it. The changes are probably related to a much changed sea ice cover and perhaps ocean circulation that relates how the winds impact the ocean with and without sea ice. For the 1979 to present satellite record, we can quantify how much sea ice covers both the fjord and adjacent ocean. I made the graph below last week from 14073 almost daily satellite images whose data the U.S. National Snow and Ice Data Center distributes freely. I show annual averages for each of the 42 years that these SSM/I satellites have been measuring sea areal coverage from space.

Figure: Annual averages of sea ice cover 1979 through 2021 with linear trend lines for two 21-year subsets (blue) and the entire 42-year record (red). [Unpublished own work.]

Before the year 2000 the sea ice cover fluctuated between 26,000 and 39,000 km2 and if one for how these changes are trending between 1979 and 2002, one finds a slight increase in the blue line, however, this increase is not significantly different from zero at a high 95% level of confidence. For the second period after 2002, the ice covered area fluctuates much less, from about 22,000 to 28,000 km2 and the trend line in blue now indicates decreasing sea ice cover. As before, however, this blue trend line is no different from zero at the same high level of confidence. We also notice that there is a red trend line that I derive from using all 42 years of data. This line is very different and statistically significant, but it does not quiet do justice to the almost step-like change that appears to happen around 2000 through 2005. What happened then? I do not know, yet, but this is the fun of doing science: There is always more to discover. The sea ice cover in northern Greenland does not always follow a straight line. This is not different from our climate or life. Expect the unexpected, adjust, and keep moving. Or in Dr. Olsen’s words:

“… you have a number of years where conditions don’t follow the more linear track of (predicted) scenarios,” explained Dr. Olsen. “A warming tendency can be reversed for some years, for example.” [From https://phys.org, Oct.-13, 2021]

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Rotations, Spin, and People

Posted on August 23, 2020 by | Leave a comment

I hate to rotate. It makes me sick. And yet, every day I spin at 800 miles per hour, because living on a spinning earth does this to me. Why does the earth spin at all? [CalTech answer.] Did it always spin the way it does now? [No.] Could it spin in the other direction that would make the sun rise above the horizon in the West rather than the East? [No.] If not, why not? [Not sure yet.] I am pondering these questions as I will teach my first undergraduate class in ten days:

I plan to introduce how oceans and atmospheres circulate to distribute heat, water, and “stuff” like food and plastics across the globe. There is lots of rotation, lots of angular momentum, lots of torque and I am unsure, if a text book and lecture via Zoom will make much sense. So, today I discovered several fun and smart and insightful videos that I may even pose to my students as Homework or Exam questions 😉

The first set of videos I discovered today is Derek Muller’s Veritasium channel on YouTube. He covers a range of physics, math, and even biology topics, but I here focus on his wing nut problem. He entertains by explaining a strange and even bizarre observation made in space some 30 years ago. A Russian engineering astronaut noticed a rotating wing nut change its rotational axis repeatedly. Russia kept the observation top secret for over 10 years for reasons not entirely clear, but here is a modern attempt to explain what happened. It also applies to how tennis rackets rotate:

Now this reminded me of a problem that I encountered during my third year studying physics in Germany. I never solved or understood this so-called spinning-hard-boiled-egg problem that the Physics Girl describes so well. Her real name is Dianne Cowern and I use her videos in my graduate statistics class where her voice and physics shatters wine glasses via resonance. Today I discovered many more of her PBS Digital videos that all are filled with fun, beauty, and smart explanations. She plays with vortices in air and water and in between.

Now how does this relate to oceanography and meteorology? Well, we all live somewhere on the spinning top or egg or peanut that we call earth. Gravity keeps us grounded, but rotating objects can do strange things as the above two videos show. And when rotation becomes important we are not just dealing with linear momentum, but also angular momentum. When rotation becomes important, we must consider torques that generate angular momentum in ways similar to how forces generate linear momentum.

Rotation adds a strong and often counter-intuitive element because unlike a force that accelerates a car in the same direction that the force is applied, a force applied to a rotating system generates a torque perpendicular to both the force and the direction to the rotational axis. This can be confusing and one has to either watch the movies or go through advanced vector calculus. Furthermore, a rotating sphere acts differently than a rotating spheroid which acts differently from a rotating triaxial spheriod. Our peanut earth is the latter and thus has at least three axes of orientation (a and b and c) that all have different kinetic energy and angular momentum states. This makes for wobbly rotations which are sensitive to changes in both force balances and the distribution of masses like ice and water that can move to different locations at different times and stay there for a while.

For a perfect sphere three perpendicular lines from the center to the surface all have the same distance a (top) while for a spheriod only two of the three perpendicular lines have the same distance from the center (bottom right). If all three perpendiculars are different then we have something called a triaxial spheroid [Adapted from WikiPedia].

And how does this relate to climate science and my beloved glaciers in Greenland? Well, there is the “global wobbling” that caused ice ages and warm periods as the earth’s principal axis or rotation changes or wobbles. The “global wobble” was discussed in hilarious way a few years ago by the United States House of Representative’s “Committee on Science, Space, and Technology.” Closing this essay, I let Jon Steward of the Comedy Channel speak and hope you find his commentary and live experiment as funny as I do:

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