Roundup: Siberia, Serpentine and Seasonal Cycling

Roundup: Siberian Glaciers, Vegetation Succession and Sea Ice

 

Glaciers in Siberia During the Last Glacial Maximum

From Palaeogeography, Palaeoclimatology, Palaeoecology: “It is generally assumed that during the global Last Glacial Maximum (gLGM, 18–24 ka BP) dry climatic conditions in NE Russia inhibited the growth of large ice caps and restricted glaciers to mountain ranges. However, recent evidence has been found to suggest that glacial summers in NE Russia were as warm as at present while glaciers were more extensive than today… We hypothesize that precipitation must have been relatively high in order to compensate for the high summer temperatures… Using a degree-day-modelling (DDM) approach, [we] find that precipitation during the gLGM was likely comparable to, or even exceeded, the modern average… Results imply that summer temperature, rather than aridity, limited glacier extent in the southern Pacific Sector of NE Russia during the gLGM.”

Read more about the study here.

 

Siberia experiences very cold temperatures but has relatively few glaciers (Source: Creative Commons)
Siberia experiences very cold temperatures but has relatively few glaciers (Source: Creative Commons).

 

Plant Communities in the Italian Alps

From Plant and Soil: “Initial stages of pedogenesis (soil formation) are particularly slow on serpentinite… Thus, a particularly slow plant primary succession should be observed on serpentinitic proglacial (in front of glaciers) areas..Ssoil-vegetation relationships in such environments should give important information on the development of the “serpentine syndrome” .Pure serpentinite supported strikingly different plant communities in comparison with the sites where the serpentinitic till was enriched by small quantities of sialic (rich in silica and aluminum) rocks. While on the former materials almost no change in plant species composition was observed in 190 years, four different species associations were developed with time on the other. Plant cover and biodiversity were much lower on pure serpentinite as well.”

Read more about “serpentine syndrome” here.

 

Plant communities in the Italian Alps can differ depending on the underlying bed rock (Source: Creative Commons)
Plant communities in the Italian Alps can differ depending on the underlying bed rock (Source: Creative Commons).

 

Carbon Cycling and Sea Ice in Ryder Bay

From Deep Sea Research Part II: Topical Studies in Oceanography: “The carbon cycle in seasonally sea-ice covered waters remains poorly understood due to both a lack of observational data and the complexity of the system… We observe a strong, asymmetric seasonal cycle in the carbonate system, driven by physical processes and primary production. In summer, melting glacial ice and sea ice and a reduction in mixing with deeper water reduce the concentration of dissolved organic carbon (DIC) in surface waters… In winter, mixing with deeper, carbon-rich water and net heterotrophy increase surface DIC concentrations… The variability observed in this study demonstrates that changes in mixing and sea-ice cover significantly affect carbon cycling in this dynamic environment.”

Read more about carbon cycling in West Antarctica here.

 

Seasonal sea ice melting influences the cycling of carbon in West Antarctica (Source: Jason Auch / Creative Commons).
Seasonal sea ice melting influences the cycling of carbon in West Antarctica (Source: Jason Auch/Creative Commons).

Prehistoric Glaciation Influenced Frog Evolution

Extensive studies in continental regions have discovered that climate variations can have strong impacts on the distribution and evolutionary history of species. Now, a study of mountainous areas, where few studies have been conducted, has found similar patterns in the current distribution and population isolation of a frog species on the Tibetan Plateau.

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Nanorana parkeri from Tibetan Plateau (Source: Kai Wang/CalPhotos).

The study, published in Scientific Reports by Jun Liu, of the Institute of Zoology, Chinese Academy of Sciences, and his colleagues looked at how historical processes might play the role in contemporary geographic distributions of frogs, a concept they refer to as phylogeography. Researchers discovered that ancient climate change impacted the demographic history of Nanorana parkeri, a frog species on the Tibetan Plateau, by facilitating population divergence.

Nanorana parkeri, also known as the High Himalaya Frog, is a frog species only found in the southern Tibetan Plateau with an altitudinal range of 2850 to 4700 meters above sea level. No other frog species lives in altitudes as high as N. parkeri.

Despite its limited geographical distribution, this medium-sized frog is very common in high-altitude grasslands, forests, marshes, and streams in the plateau. The varying topography, complex drainage system as well as high peaks make the region a biodiversity hotspot, where endemic species including N. parkeri can be spotted.

The researchers analyzed the sequences of one mitochondria and three nuclear DNA from N. parkeri to investigate the genetic diversity of this frog. The species distribution modeling was applied to examine whether this species survived locally during the Pleistocene glaciations and how the recolonization process was during postglacial times.

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Nanorana parkeri from Tibetan Plateau (Source: Kai Wang/CalPhotos).

Through their analysis, the researchers discovered that there were two distinct lineages of this one frog species, East and West. More importantly, there was no overlap between these two lineages. Researchers estimated that this divergence in lineages may have occurred during the Middle Pleistocene, about 1.4 to 3.7 million years ago.

The divergence occurred long before the Last Glacial Maximum (LGM), which was 0.72 to 0.5 million years ago. This indicates that the genetic lineages survived during the maximum glaciation in glacial refugia. During LGM, ice sheets covered much of North America, northern Europe, and Asia, including the Tibetan Plateau.

Moreover, multiple refugia must have been existed for N. parkeri; otherwise, the genes would be mixed if the lineages were living in a single refuge. The researchers suggest that the Yarlung Zangbo valley in eastern region and the Kyichu catchment in the west might have been the refugia for the two lineages during historical glaciations.

Yarlung Zangbo valley where Nanorana parker can be found (source: Preston Rhea/Flickr).
Yarlung Zangbo valley where Nanorana parkeri is found (source: Preston Rhea/Flickr).

The researchers also proposed that other climatic factors might have affected this historical divergence as well. They found that the boundary between the two lineages coincides with the 400mm annual precipitation level. The eastern region is relatively humid while the western region is more arid and drier. The shift in climatic factors might act as a barrier to the dispersal of the frog.

Although the frog is currently abundant, this study could have implications for conservation of frog species on the Tibetan Plateau. The two N. parkeri lineages have diverged for a long time with limited gene flow between them. Therefore, they each need to be protected separately. As a potential refugia for the frog, the Yarlung Zangbo valley and Kyichu catchment need to be conserved.

Melting Glaciers Give Earth a Pop

Southeast Alaska shown in the red rectangle (Source: Google Earth).
Southeast Alaska shown in the red rectangle (Source: Google Earth).

Though the Earth often seems solid and fixed, it is not. You’ve probably heard of continental drift—the horizontal movement of continent-sized bodies of rock—but fewer of you may appreciate that the earth can move vertically as well. Studies have shown that North America and Europe are rebounding, slowly but steadily, due to the removal of thick ice sheets which once covered them during the last ice age, which ended about 21,000 years ago.

This process of postglacial upward movement is called glacial isostatic adjustment (GIA). Researchers have established that some materials have a viscous response when a surface load is placed on them, flowing like slow-moving honey, and remaining deformed when the load is removed; others have an elastic response, stretching like rubber and bouncing back to their original form. The substances that compose the upper sections of the earth are somewhere between these extremes, and have what is termed a viscoelastic response. As a result, when a mass of an icesheet is removed, the solid Earth underneath may display some degree of rebound. It was observed that the uplift rate in North America and Europe can reach 1 cm/yr.

Researchers have established that the formation of icesheets generated pressure on the underlying rocks, pushing them downward. In addition to this downward dislocation of the crust, the mantle beneath might be compressed as well. Previous studies on GIA have seldom included this compressibility of the Earth in their calculations, because of the complexities and uncertainties that it would introduce into quantitative models. But a paper published by Tanaka et al. earlier this year in the Journal of Geodynamics established a model which includes compressibility for the GIA in southeast Alaska and compared this model to another which did not include compressibility.

Geographic map of southeast Alaska (Source: Carrera et al./USGS).
Geographic map of southeast Alaska (Source: Carrera et al./USGS).

Southeast Alaska, which is also referred to as the Alaska Panhandle, lies west of the Canadian province of British Columbia. This region is known to have the largest GIA rate in North America, approximately 30 mm/yr. The reseachers anticipated that the compressibility effects would be larger and easier to detect in this region. In this region, models of GIA integrate the effect of ice sheet mass variations over three periods: the Last Glacial Maximum (LGM) about 20,000 years ago, the Little Ice Age a few centuries ago (LIA) and present-day (PD).

Measurements of rebound at different locations can serve to test these models, since information is available on the extent of icesheets in different periods. It is known, for example, that icesheets retreated earlier at lower elevations, so effects from earlier periods will be stronger there. In the case of southeast Alaska, rebound results primarily from post-LIA and PD ice melting; the former, larger in magnitude, was incorporated into the compressibility model. This model examined the rheological properties of the Earth’s mantle—the geological processes which allow rocks to flow on long time scales, and a second set of properties, called flexural rigidity, which determine the capacity of the earth’s crust to bend.

Glacier Bay in Southeast Alaska (Source:Kool Cats/flickr).
Glacier Bay in Southeast Alaska (Source:Kool Cats/flickr).

The authors conclude that their modeling efforts demonstrate the value of including compressibility. Without this element, the current uplift rate in southeast Alaska would be 27% (4 mm/yr) slower, and as a result would not match field measurements as well. Phrased in simpler language, they show that the vast ice sheets of the past not only pushed the mantle down, but squeezed it as well. This study demonstrates the great power of ice to alter our planet’s surface, and indicates that it can have measurable effects centuries, or millennia, after it melts.