A Geological Perspective of Polar Bears

A Geological Perspective of Polar Bears

Guest "Geological Perspective" by David Middleton

A popular story

Polar bears (Ursus maritimus) are the poster child for the effects of climate change on species, and rightly so. So far, global warming has been most pronounced in the Arctic and this trend is expected to continue. There are suggestions that we could have an almost ice-free Arctic by the middle of the century. This increases the urgency with which we must act to reduce our greenhouse gas emissions in order to delay or avoid some of the worst effects of climate change.


Figure 1. Change.org

A geological perspective

Figure 2. “Estimation of the global polar bear population through 2018. From Chapter 10 of the polar bear disaster that never happened (Crockford 2019).” Polar bear science.

Effects of ice retreat on polar bear behavior and habitat selection

Among all polar bear subpopulations, those found in the Beaufort and Chukchi seas have experienced some of the greatest losses of sea ice in the entire Arctic Ocean. However, the mechanisms that link the habitat to population development have not been described quantitatively. The role of habitat preference in behavior (i.e. movement and activity), or whether some habitats are important to life story requirements, is uncertain. Polar bear movements are associated with foraging and energy costs. Therefore, as a proxy for behavior and energetics, movements can indicate habitat value and represent a quantifiable means of elucidating the mechanisms of the reaction of the polar bear population to a changing Arctic. We use polar bear location data collected by the USGS since 1985 to develop models of polar bear distribution that take into account long-term changes in behavior and habitat function. This research will provide products that can be used by managers to mitigate the adverse effects of anthropogenic activity on polar bears and polar bear habitats.


Key passage:

Among all polar bear subpopulations, those found in the Beaufort and Chukchi seas have experienced some of the greatest losses of sea ice in the entire Arctic Ocean. However, the mechanisms that link the habitat to population development have not been described quantitatively. The role of habitat preference in behavior (i.e. movement and activity), or whether some habitats are important to life story requirements, is uncertain.


"The mechanisms that link living space with population development" cannot be "described quantitatively".

November 14, 2018
The first record of polar bears between the USA and Russia shows a healthy population
Hannah Hickey
UW News

Not all polar bears are in the same emergency situation due to the retreating sea ice, at least not at the moment. Off the west coast of Alaska, the Chukchi Sea is rich in marine life, but the number of polar bears in the area has never been counted. The first formal study of this population suggests that it has been healthy and relatively abundant in recent years, numbering around 3,000 animals.

The study by researchers from the University of Washington and federal agencies will be published November 14 in Scientific Reports, an open access journal from the Nature Publishing Group.

"This work represents a decade of research that gives us an initial estimate of the abundance and status of the subpopulation in the Chukchi Sea," said first author Eric Regehr, a researcher at the UW's Polar Science Center who is a biologist on the project the US Fish and Wildlife Service started in Alaska. “Although we had about a month less time to hunt for preferred sea ice habitats compared to 25 years ago, we found that the Chukchi Sea subpopulation did well from 2008-2016.


Of the 19 polar bear subpopulations in the world, the US shares two with neighboring countries. The other US subpopulation – the polar bears of the southern Beaufort Sea, whose territory intersects with Canada – are showing signs of stress.

"The southern Beaufort Sea subpopulation is well-studied, and there is growing body of evidence to suggest it is performing poorly due to the loss of sea ice," Regehr said.


Recent ecological observations had shown that the Chukchi fur seals are fine. A study conducted by co-author Karyn Rode at the US Geological Survey showed that the top predators have similar amounts of body fat as they did 25 years ago, a good indicator of their overall health.

The current study is the first assessment of subpopulation size using modern methods. Almost 3,000 animals with generally good reproduction rates and survival of the young are estimated.


For the first time, the model also took into account local and traditional ecological knowledge that Alaska's North Slope Borough has gathered from local hunters and community members with generations of polar bear experience.

"It was important to bring our science together with the observations and expertise of people who live in polar bear land all year round and understand the animals in different ways," said Regehr.

University of Washington

If the loss of sea ice due to global warming is burdening the polar bears of the Beaufort Sea, why are they doing so well in the Chukchi Sea?

The Chukchi Sea is more ice-free than the Beaufort Sea …

Figure 3. Arctic sea ice. NASAFigure 4. Extent of the Arctic sea ice. NASA

The "core study area" was that between Lisburne and Seward Peninsulas …

Figure 5. “The striped area on the left shows the range of the polar bear subpopulation in the Chukchi Sea. The sea ice extends south to the dotted line in winter and retreats to the solid black line in summer. The image on the right shows a close-up of the study area off the coast of Alaska. White circles show where polar bears were marked between 2008 and 2016. Regehr et al. / Scientific reports "(UW)

The "core study area" is particularly badly affected by the loss of sea ice …

Figure June 6, 1979Figure June 7, 2019Figure 8. Animation

Aside from the fact that polar bear populations do not seem to be declining overall, how did polar bears manage to survive the vast majority of the Holocene when the sea ice was far less large than it is today? How did they survive the interglacial stage of the Eemian (Sangamonian) when the Arctic was 5-10 ° C warmer than today?

The holocene epoch

The Chukchi Sea, the place where the polar bear population appears stable and healthy, was virtually ice-free for much of the Holocene.

Figure 9. “Modern sea ice cover in the study area, expressed here as the number of months / year with> 50% cover, an average of 10.6 ± 1.2 months / year … Today's SST and SSS in August are 1.1 ± 2.4 8C and 28.5 ± 1.3 … In the Holocene record of the core HLY0501-05, the sea ice cover was between 5.5 and 9 months / year, the summer SSS between 22 and 30 and the summer SST between 3 and 7, 5 8C (Figure 7). (McKay et al., 2008)

During most of the Holocene, sea ice cover of> 50% occurred between 5.5 and 9 months per year. During the “Anthropocene”, sea ice cover of> 50% was between 9 and 12 months per year.

Figure 10. How did polar bears survive with so little sea ice?

Stein et al., 2017 (H / T tty) provide a great description of a fairly novel method for determining the extent of paleo sea ice.

In a seminal study by Belt et al. (2007) the ability to (semi-) quantitative reconstruction of paleo-sea ice distributions was significantly improved by a biomarker approach based on the determination of a highly branched isoprenoid (HBI) with 25 carbons (C25 HBI monoene = IP25). This biomarker is only biosynthesized by certain diatoms in the arctic sea ice (Brown et al., 2014) and appears to be a specific, sensitive and stable proxy for arctic sea ice in sedimentary sections that represent the late Miocene until recently (Stein et al., 2014) ., 2012, 2016; Belt and Müller, 2013; Stein and Fahl, 2013; Knies et al., 2014). The presence of IP25 in the sediments studied is direct evidence of the presence of sea ice.


For more semi-quantitative estimates of current and past sea ice cover, Müller et al. (2011) combined the sea ice proxy IP25 and phytoplankton biomarkers in a phytoplankton IP25 index, the so-called "PIP25 index":

PIP25 = (IP25) / ((IP25) + ((phytoplankton marker) x c))

with c is the mean IP25 concentration / mean phytoplankton biomarker concentration for a given dataset or core.

Stein et al., 2017

This schematic diagram from Belt et al., 2013 relates the PIP25 index to sea ice conditions:

Figure 11. Relationship of sea ice conditions to the PIP25 index (Belt ea al., 2013). Click to enlarge.

In general, the PIP25 index correlates with sea ice extent as follows:

  • > 0.7 = extended, multi-year (year-round) ice cover
  • 0.5-0.7 = seasonal ice cover / ice edge location
  • 0.1-0.3 = reduced ice cover
  • <0.1 = ice-free all year round

Stein et al. In 2017, a cross-section of PIP25 curves across the Arctic from the Fram Strait to the Chukchi Sea was created.

Figure 12. Location plan of the sediment cores and cross-section A-A “. (modified from Stein et al., 2017)

All four core locations currently reflect seasonal ice cover / ice edge situations (PIP25 index 0.5-0.7), with Fram Strait being an ice edge situation and the other three reflecting seasonal ice cover situations.

Figure 13. Cross section A-A “. High and low refer to solar radiation in the northern hemisphere.

Three important takeaways:

  1. The maximum Holocene sea ice extent occurred at every location in the last 500-1000 years.
  2. The current sea ice extent at all locations is greater than over 50% to 85% of the Holocene.
  3. Polar bears survived most of the Holocene with little sea ice extent.

If I draw the cross-section on Kinnard's probability map, we can see that all of the low-ice area, which is larger than today, was seasonal for most of the Holocene.

Figure 14. Probability of sea ice occurrence (1870-2003) A = maximum, B = minimum. (Kinnard et al., 2008)

A significant decrease in Arctic summer sea ice compared to today would revert to the conditions of the early Holocene. In fact, if we have an "Anthropocene in the Arctic" right now, it is more icy than most Holocene "Goldilocks" conditions.

When did polar bears first evolve?

Nobody really knows.

The polar bear evolution was quick and furious

By Elizabeth Pennisi May. 8, 2014 at 12:00 PM

For polar bears, being limp is a way of life. Fat can make up 50% of your body weight; The bacon-laden seals they eat make bacon look downright healthy. A new, comprehensive comparison of the genomes of polar bears and their closest relative, the brown bear, has now shown how polar bears survive such unhealthy diets.

The work also suggests that the bears developed these changes relatively quickly, likely because they had to adapt to extreme conditions that forced them to switch to a diet that would be toxic to other mammals. "It's a textbook example of evolution," says Eske Willerslev, an evolutionary geneticist at the University of Copenhagen who led the research.

Brown bears – some of which are called grizzlies – and polar bears are closely related and can even crossbreed. In recent years, researchers have used genetic information to clarify this relationship and understand how polar bears thrive in the cold Arctic. They feed primarily on seals and other marine life that have been caught from holes in the ice. This work involved sequencing the genome of the animals, which suggests that polar bears are really a distinct species that lived apart from brown bears at times, and sometimes mixed and mingled with them. However, researchers disagree on when the polar bear began to split off from the brown bears. Estimates range from around 600,000 years to 5 million years.

In the most recent sequencing effort, Willerslev and researchers from Denmark, China, and the United States analyzed the genome of 80 polar bears from Greenland and 10 brown bears from North America and Europe. "For bears it is the most comprehensive genome dataset to date," says Frank Hailer, evolutionary biologist at Goethe University Frankfurt in Germany.

From this data, Willerslev and his colleagues conclude that polar bears split off from brown bears between 343,000 and 479,000 years ago. Although from an evolutionary point of view this was little more than a flash of time long enough for important genetic differences to develop, they state today in a report in Cell.



Estimates were between 70,000 and 5,000,000 years ago. The oldest confirmed polar bear fossil dates from 110,000 to 130,000 years ago. This means that polar bears survived the Eemian interglacial stage.

The highest warmth of the interglacial stage of Eem marks the boundary between the late Pleistocene Tarantian and the Middle Pleistocene Ionic ages.

Figure 15. Pleistocene stratigraphic nomenclature, SQS.Figure 16. “The oxygen isotopes in the ice indicate that the climate during the last interglacial period was stable and temperatures were 5 ° C warmer than today.” Members of the North Greenland Ice Core Project, 2004

If sea ice is so important to polar bears' survival, how did they survive the Eemian? Well it seems that despite:

The last time temperatures in the Arctic were significantly higher than today was the early Holocene thermal maximum9, 10. However, the Holocene is an as yet unfinished interglacial cycle. This certainly justifies climatic assessments of older, completed warm interglacial cycles like the last interglacial (LIG), i.e. the Marine Isotope Stage (MIS) 5e (Eemian), which last between 130 and 115 ka and is often suggested as a possible analog for our in the nearer Future climatic conditions on earth11, 12. Based on proxy records from ice, land and sea archives, the LIG is characterized by an atmospheric CO2 concentration of around 290 ppm, ie similar to the pre-industrial (PI) value13 air temperatures in northeast Siberia , which were about 9 ° C higher than today14, air temperatures above the Greenland NEEM ice core location of about 8 ± 4 ° C above the mean value of the past millennium15, North Atlantic sea surface temperatures of about 2 ° C higher than modern (PI) temperatures12, 16 and a global sea level 5–9 m above the current sea level17. In the Nordic seas, on the other hand, the Eemian may have been cooler than the Holocene, as the flow of Atlantic surface water northwards towards the Fram Strait and Arctic Ocean was less, indicating the complexity of the interglacial climate system and its development in the northern high latitudes12, 18, 19th

Stein et al., 2017

The arctic sea ice has not completely disappeared …

Figure 17. “Simulation of the Arctic sea ice cover of the last interglacial and the pre-industrial climate. The last interglacial (LIG) conditions were simulated for three time slices: LIG-130 (130 ka), LIG-125 (125 ka) and LIG-120 (120 ka). White circles indicate the positions of the four examined sediment cores. Stein et al., 2017Figure 18. Too fun to frack!


Belt S.T., Müller J. "The Arctic Sea Ice Biomarker IP25: An Overview of Current Understanding, Recommendations for Future Research, and Applications in Paleo Sea Ice Reconstruction". (2013) Quaternary Science Reviews, 79, pp. 9-25. Belt_2013

Crockford, Susan J, and Global Warming Policy Foundation. The polar bear disaster that never happened. London, The Global Warming Policy Foundation, 2019.

Fetterer, F., K. Knowles, W.N. Meier, M. Savoie and A.K. Wind nail. 2017, updated daily. Sea ice index, version 3. (sea ice monthly by year). Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: https://doi.org/10.7265/N5K072F8. (Accessed October 16, 2019).

Kinnard, C., Zdanowicz, C. M., Koerner, R., Fisher, D. A., 2008. "A Changing Arctic Seasonal Ice Zone – Observations from 1870-2003 and Possible Oceanographic Consequences". 35, L02507. Kinnard_2008

McKay, J.L., A. de Vernal, C. Hillaire-Marcel, C. Not, L. Polyak, and D. Darby. 2008. Holocene Fluctuations in Arctic Sea Ice Cover: Dinocyst-based Reconstructions for the Eastern Chukchi Sea. Can. J. Earth Sci. 45: 1377-1397

Middleton, David. “Back to the Anthropocene! Arctic Sea Ice Edition. “Watts Up With That ?, October 17, 2019, wattsupwiththat.com/2019/10/17/back-to-the-anthropocene-arctic-sea-ice-edition/.

Members of the North Greenland Ice Core Project. 2004. “High-resolution recording of the climate of the northern hemisphere up to the last interglacial period”. Nature 431 (7005): 147-137; 151

Stein, R., Fahl, K., Gierz, P. et al. Sea ice cover of the Arctic Ocean during the penultimate glacier and the last interglacial. Nat Commun 8th, 373 (2017). https://doi.org/10.1038/s41467-017-00552-1

Stein, R., Fahl, K., Schade, I., Manerung, A., Wassmuth, S., Niessen, F. and Nam, S. (2017), Holocene variability in sea ice cover, primary production and the Pacific water influx and climate change in the Chukchi and East Siberian Seas (Arctic Ocean). J. Quaternary Sci., 32: 362-362; 379. doi: 10.1002 / jqs.2929 stein2017

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