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.

Roundup: Climate Science and International Adaptation

Integration of Glacier and Snow

“Energy budget-based distributed modeling of snow and glacier melt runoff is essential in a hydrologic model to accurately describe hydrologic processes in cold regions and high-altitude catchments. We developed herein an integrated modeling system with an energy budget-based multilayer scheme for clean glaciers, a single-layer scheme for debris-covered glaciers, and multilayer scheme for seasonal snow over glacier, soil, and forest within a distributed biosphere hydrological modeling framework.”

Read more of the article here.

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Climate Science on Glaciers

“The 2001–2013 sum of positive temperatures (SPT) record, as a proxy of snow/ice ablation, has been obtained for the high-mountain glaciarized Munku-Sardyk massif, East Sayan Mountains, using daily NCEP/NCAR reanalysis data. The SPT (and ice melt) demonstrates a significant decreasing trend, with the highest values in 2001, 2002, and 2007, and the lowest in 2013. We have investigated relationships between potential summer ablation and synoptic-scale conditions over the study area.”

Read more of this article here.

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International Adaptation to Glacier Retreat

“The transboundary Himalayan Rivers flowing through Bhutan to India and Bangladesh constitute an enormous asset for economic development in a region which contains the largest number of poor people in the world. However, the rapid retreat of Himalayan glaciers has made South Asia vulnerable to variety of water-related natural hazards and disasters such as floods, landslides, and glacial lake outburst.”

Read more of this book chapter here.

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Glacial Retreat Encourages Seaweed Colonization

Newly ice-free areas exposed by glacial retreat in Potter Cove, Antarctica, are being colonized by seaweed. With glaciers melting, the original white, mostly lifeless Antarctica is now becoming darker and lively with seaweed. These macroalgae not only produce oxygen for marine species through photosynthesis but also serve as the base of the marine food chain. Scientists predict this seaweed colonization could lead to a higher rate of carbon sequestration and higher productivity in marine system, but the local biodiversity might be reduced.

South Shetland Islands in Antarctica (Source: David Stanley/Flickr).
South Shetland Islands in Antarctica (Source: David Stanley/Flickr).

Glacial retreat has a major influence on coastal ecosystems – it creates ice-free areas which can then be taken over by marine species. However, the process is not always that simple. A recent study published in Polar Biology by D. Deregibus et al. discovered that although newly exposed ice-free areas favor colonization, sediments carried by glacial runoff makes seawater less clear and affects coastal marine species adversely by reducing the survival or reproductive rate. Nonetheless, seaweed in Potter Cove has adapted to shade and can tolerate darkness for a long period as it is accustomed to ice cover blocking sunlight. Increased turbidity, or cloudiness, caused by sediments affects the distribution rather than survival of Antarctic seaweed, Deregibus and his colleagues found.

The study investigated how the availability of incoming sunlight affects seaweed distribution in newly ice-free areas in Potter Cove, South Shetland Islands in Antarctica. Researchers found that the more sunlight breaks the surface of the water, the more seaweed can thrive. Levels of sunlight are influenced by the amount of sediments that runoff glaciers as they melt as sediments can decrease water clarity and light penetration.

Palmaria decipiens (Source: Berkeley University).
Palmaria decipiens, found on sub-Antarctic islands (Source: University of California, Berkeley).

In Potter Cove, high loads of sediment are produced during the summer melting season. This phenomenon is more evident in newly ice-free areas closer to glacial runoff. Both seasonal and spatial variations in water clarity affect the depth distribution of macroalgae. The vertical distribution in areas close to glacier runoff is reduced due to higher concentration of sediments, researchers found.

In this study, three major factors – turbidity, salinity and temperature – were examined to assess their influence on seaweed’s vertical distribution. The results indicate that changes in salinity and temperature do not significantly affect photosynthetic performance of seaweed; instead, turbidity is the main controlling factor.

Specifically, how deep the light can penetrate determines the maximal depth distribution limit of seaweed. The depth at which seaweed can survive is controlled by the amount of available light. In addition, carbon balance also affects what kinds of seaweed can be found at different depths.

Himantothallus grandifolius (Source: Oikonos).
Himantothallus grandifolius, a type of seaweed can only be found in Antarctica (Source: Oikonos).

The mystery of how these two seaweeds survive even when there is little light lies in carbon balance. During spring, when more sunlight reaches deep water, the seaweed starts accumulating extra carbon storage compounds. These accumulated carbon compounds can then be used to sustain their metabolism in summer, when inflowing sediments block the sun.

The rapid increase in temperature has caused significant glacial retreat as well as sea ice decrease in the Western Antarctic Peninsula. This glacial retreat has lead to an increase in the rate of sediment deposition. Such inflow of sediment into the marine system will affect the coastal ecosystems, especially distribution of species, according to researchers.

As temperatures continue to rise in the future, the spatial distribution of seaweed is expected to expand further in new coastal areas. However, how exactly such expansion will affect the coastal ecosystem remains a question for future study.

 

Photo Friday: Glacier Illuminated by Aurora

This week’s photos feature the Athabasca Glacier in Alberta, Canada with Northern Lights in the background. Photographer Paul Zizka captured ice climber Stuart and Takeshi Tani hanging from the glacier when the Northern Light hits the sky.

Paul Zizka is a professional mountain landscape and adventure photographer based in Banff, Alberta. He has a passion for shooting alpine sports and capturing the unique features of nature. “My hope is that through my photography, people will rediscover the precious connection they can have with the wonders of our planet,” he said.

For more photos from Paul Zizka, please look here.

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Photo Friday highlights photo essays and collections from areas with glaciers. If you have photos you’d like to share, let us know in the comments, by Twitter @glacierhub or email us at glacierhub@gmail.com

Glacier Retreat Threatens Insect with Extinction

As glaciers retreat, a species of glacier-dependent stonefly faces extinction.

In 2010, the Center for Biological Diversity petitioned for Zapada glacier, a western glacier stonefly only found in alpine streams of Glacier National Park, Montana, to be listed as endangered species under the U.S. Endangered Species Act. This species – one of more than 3500 species of stonefly –  is highly restricted to cold, glacial meltwater with limited dispersal ability.

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Zapada glacier adult female from the Grinnell Glacier Basin in Glacier National Park (approximate length is 12 mm) (Source: Giersch et al./Freshwater Science).

Now, in an effort to save this endangered stonefly, the Center for Biological Diversity filed a lawsuit against the U.S. Fish and Wildlife Service to address the urgency of protecting this stonefly. The insect could potentially be taken to other clean cold streams outside its established range, perhaps further north or at higher elevation where it might survive – but time is running out.

Species evolve to survive in specific temperature ranges; however, when the environmental conditions have exceeded the range, species are unable to adapt to new conditions immediately. Climate change has put many species in danger, but this is the first time that an insect species has been threatened with extinction by glacier retreat.

“Protection can’t come soon enough for this stonefly,” said Tierra Curry, a senior scientist at the Center for Biological Diversity. “Glacier National Park will have no glaciers in 15 years if we don’t take action to curb climate change.”

Stoneflies are a particularly ancient order of insects that spend most of their lives in water. They are considered the most sensitive indicators of water quality in streams as they require fresh, clean water and don’t tolerate pollution. The insects have a one to two-year life cycle starting in the nymph stage in fresh meltwater. They usually emerge from the water in late spring when the stream is uncovered by melting snow. Z. glacier has a narrow temperature preference around 3.3 degrees Celsius. It is this narrow temperature preference that makes this insect especially susceptible to climate change.

Between 1960 to 2012, the average summer temperature in Glacier National Park has risen by approximately 1 degree Celsius. Additionally, since 1850, 125 of the 150 glaciers in Glacier National Park have melted away while the remaining 25 are predicted to disappear by 2030. The loss of glaciers as well as restricted suitable environmental conditions and limited dispersal ability of the stonefly threaten the species’ ability to survive.

Many Glacier in GNP (Source: Esther Lee/Flickr).
Glaciers in Glacier National Park (Source: Esther Lee/Flickr).

Few studies have investigated the impacts of climate change on alpine species distributions. To compensate for this knowledge gap, J. Joseph Giersch from US Geological Survey and other researchers looked at the current status and distribution of Z. glacier. Their results were published in Freshwater Science.

Giersch et al. sampled 6 alpine streams, where Z. glacier was historically known to live, to examine the relationship between species occurrence and environmental variations of temperature and glacial extent. In order to identify the current geographic distribution and distinguish Z. glacier from the other 6 Zapada species in Glacier National Park, the researchers used morphological characteristics, the outward appearance of adults and the DNA of nymphs.

Giersch et al. identified 28 suitable alpine locations in Glacier National Park as potential habitats for Z. glacier. From this study, Z. glacier was only found in 1 of the 6 historically occupied streams – the outlet of Upper Grinnell Lake. The results suggest increased temperature and glacier retreat have already caused local extinction of Z. glacier from several historical locations.

Upper Grinnell Lake in Glacier National Park, where Zapada glacier can be found (Source: GlacierNPS/Flickr).
Upper Grinnell Lake in Glacier National Park, where Zapada glacier can be found (Source: GlacierNPS/Flickr).

The stonefly was also detected in 2 new high-elevation locations in Glacier National Park. Therefore, only 3 out of the 28 potential habitats have Z. glacier. The results indicate that the historical distribution of this stonefly in Glacier National Park was already restricted and its distribution will be further reduced in the future due to increased stream temperatures and habitat loss.

“The plight of the glacier stonefly is a wakeup call that unless the United States takes major action to reduce our greenhouse gas emissions, this special insect and more than one-third of all plants and animals on Earth could go extinct by 2050,” said Curry.

For more stories on invertebrates near glaciers, read here and here.

Roundup: Black Carbon, Winds, and Supraglacial Lakes

Light-absorbing Particles in Peru

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“Glaciers in the tropical Andes have been rapidly losing mass since the 1970s. In addition to the documented increase in temperature, increases in light-absorbing particles deposited on glaciers could be contributing to the observed glacier loss. Here we report on measurements of lightabsorbing particles sampled from glaciers during three surveys in the Cordillera Blanca Mountains in Peru.”

Read more here.

Winds on Glaciers

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“We investigate properties of the turbulent flow and sensible heat fluxes in the atmospheric surface layer of the high elevation tropical Zongo glacier (Bolivia) from data collected in the dry season from July to August 2007, with an eddy-covariance system and a 6-m mast for wind speed and temperature profiles. Focus is on the predominant downslope wind regime.”

Read more here.

Supraglacial Lakes in Central Karakoram Himalaya

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“This paper discusses the formation and variations of supraglacial lakes on the Baltoro glacier system in the Central Karakoram Himalaya during the last four decades. We mapped supraglacial lakes on the Baltoro Glacier from 1978 to 2014 using Landsat MSS, TM, ETM+ and LCDM images. Most of the glacial lakes were formed or expanded during the late 1970s to 2008. After 2008, the total number and the area of glacial lakes were found to be lesser compared to previous years.”

Read more here.

 

Photo Friday: Kyrgyz Glaciers

Kyrgyzstan, located in Central Asia, is a country with enormous glaciers. About 30% of the total land area in Kyrgyzstan is covered by permanent snow and 4% is covered by glaciers. The total amount of glaciers in Kyrgyzstan is equivalent to 580 billion cubic meters of water, which can cover the whole country to a depth of 3 meters. The most famous glacier is the Enilchek Glacier in the Eastern Tien Shan mountain range. The Kyrgyz are semi-nomadic herders and their nomadic movements still take place seasonally.

To learn about political controversies surrounding mining near glaciers in Kyrgyzstan, click here.

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Photo Friday highlights photo essays and collections from areas with glaciers. If you have photos you’d like to share, let us know in the comments, by Twitter @glacierhub or email us at glacierhub@gmail.com

New Discovery: Record of Glacial Cycles on Sea Floor

The history of the world’s hot and cold periods can be read on the ocean floor, according to a new study.

The Earth has gone through cycles of glacial periods, when the great continental ice sheets advanced during colder periods, and interglacial periods – warmer climate cycles like like present day. These glacial-interglacial cycles are caused by the slow cycle of shifts in the Earth’s orbit, called Milankovitch cycles, which affect the amount of sunlight reaching the Earth.

Now, scientists discovered that these ancient glacial-interglacial cycles are recorded on the sea floor through ocean ridges. A recent study by Crowley et al. in Oceanography demonstrated that new mapping of the sea floor from the Australian-Antarctic ridge showed statistically significant match with the Earth’s glacial cycles.

“Step back and think about this: Small variations in the orbital parameters of the Earth—tilt and eccentricity and wobble—are recorded on the sea floor, it kind of blows my mind.” says Richard Katz, one of the researchers told Science Magazine.

Each time the world passed between glacial and interglacial periods, global water distribution shifted. Specifically, when the Earth enters an ice age, the cold temperature freezes the sea water into glaciers, causing sea level to drop significantly. During the last glacial cycle, sea level dropped by 35 meters, which is more than twice the volume of the Greenland and West Antarctic ice sheets. As sea level drops, the pressure on the sea floor decreases accordingly. The ease in pressure allows magma beneath the seafloor to erupt and break the Earth’s surface, leading to divergence of the oceanic plates and forming the seafloor spreading center. This eruption thickens the crusts on teh sea floor and forms the abyssal hills – elevated landforms along the seaward margin parallel to mid-ocean ridges.

The sea floor spreading mechanism. The upwelling of mantle pushes the plate away and forms the abyssal hills. (Source: Conrad/Science).
The sea floor spreading mechanism. The upwelling of mantle pushes the plate away and forms the abyssal hills. (Source: Conrad/Science).

So how did the researchers discover the record of glacial cycles on sea floor? The answer lies in the variations in crustal thickness at the seafloor spreading center. They examined the crustal thickness response to sea level change by computing the physical mechanisms beneath the sea floor, such as mantle flow, thermal structure, melting, and pathways of melt transport. The model they used, which predicts the time series of crustal thickness caused by sea level change, was used to simulate the dynamics of mid-ocean ridge.

Map of the ocean floor. The mid-ocean ridges are shown as dark bands (Source: Earthguide).
Map of the ocean floor. The mid-ocean ridges are shown as dark bands (Source: Earthguide).

The numerical model results from this study contradict previous findings. Earlier research indicated an inverse relationship between variations in crustal thickness and spreading rate, which did not include the effects of sea level change. However, the new study reveals that melting or sensitivity to sea level variation does not simply decrease with increasing spreading rate. Instead, the crustal thickness response depends on changes in sea level and how long it took for melted magma to reach the surface. This newly discovered crustal response illustrates the link between glacial cycles and sea floor, contrary to findings from previous studies.

 

Roundup: Rock Avalanche, Melting Sound, Black Carbon

Landslides on Glaciers

“The chapter looks mainly at massive rock slope failures that generate high-speed, long- runout rock avalanches onto glaciers in high mountains, from subpolar through tropical latitudes. Drastic modifications of mountain landscapes and destructive impacts occur, and initiate other, longer-term hazards. Worst-case calamities are where mass flows continue into inhabited areas below the glaciers. Travel over glaciers can change landslide dynamics and amplify the speed and length of runout.”

Read more about this chapter here.

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Noise from Melting Glaciers

“According to research accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union, the underwater noise levels are much louder than previously thought, which leads scientists to ask how the noise levels influence the behavior of harbor seals and whales in Alaska’s fjords.”

Read more of this article.

 

Black Carbon in Tibetan Plateau

“High temporal resolution measurements of black carbon (BC) and organic carbon (OC) covering the time period of 1956–2006 in an ice core over the southeastern Tibetan Plateau show a distinct seasonal dependence of BC and OC with higher respective concentrations but a lower OC / BC ratio in the non-monsoon season than during the summer monsoon. We use a global aerosol-climate model, in which BC emitted from different source regions can be explicitly tracked, to quantify BC source–receptor relationships between four Asian source regions and the southeastern Tibetan Plateau as a receptor.”

Read the paper here.

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Researchers collect ice cores with soot deposition recordsthat span back to the 1950s. Credit: Institute of Tibetan Plateau Research, Chinese Academy of Science

 

 

Photo Friday: Alpine Photography by Fi Bunn

Fiona Bunn, a landscape photographer and alpinist, has been traveling to the Alps for over 25 years. Her alpine photography work has been frequently shared on social media, including The Alpine Club as well as Zermatt Tourism. Her work was recently included in an exhibition for a second time at The Brick Lane Gallery in the Shoreditch district of London’s East End. The exhibition featured the relationship between photographers and alpinists. Fi finds the worldwide alpine community to be supportive, with a desire to appreciate and express their interest in art. She  wrote “my aim is that my work highlights this vibrant, friendly, international community, who celebrate a shared interest for alpine exploration which literally crosses borders.” In addition, Fi is also concerned about climate change and glacial retreat. In her travels she has seen a large reduction in the size of glaciers firsthand. In an email she told GlacierHub,”I hope that my photos of these amazing mountains and glaciers perhaps help focus attention on how environmentally essential they are.

For more alpine photographs by Fi, please check out her website.

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Photo Friday highlights photo essays and collections from areas with glaciers. If you have photos you’d like to share, let us know in the comments, by Twitter @glacierhub or email us at glacierhub@gmail.com

Where Can Alpine Plants Hide from Global Warming?

Androsace alpine living on rock glaciers as well as moraine ridges and deglaciated forelands (Source: Apollonio Tottoli/Flickr).

Environmental conditions, including climate, strongly influence the distribution of plant species. As temperatures continue to rise around the world, many people are concerned about the possible shifts in distribution of plant species, since plants are immobile, and many of them have a limited ability to disperse. These restrictions to changes in their distribution are particularly severe for plants that are adapted to cold conditions, such as those found in high mountain regions.

Studies by Valenti Rull and others have shown that during interglacial periods in the geological past, alpine plants were able to disperse to microrefugia, small-scale sites which allowed species to persist when most of their ranges became unsuitable for them. Thus, in the current era of warming, such sites, with locally favorable climate, could once again prove to be important for the survival of cold-adapted alpine species. A newly published study by Rodolfo Gentili of the Department of Environmental Sciences at the University of Milan and several co-authors in Ecological Complexity establishes a fresh approach to the study  of microrefugia. The authors examined the geomorphological and ecological features of microrefugia during earlier interglacial stages and used these features to identify potential microrefugia areas for alpine plants in and near glaciers, in both the present and the near future.

Leucanthemopsis alpine living on mountain summits (Source: Apollonio Tottoli)
Leucanthemopsis alpine living on mountain summits (Source: Apollonio Tottoli/Flickr).

In general, there are three recognized strategies which alpine plants can adapt to survive under a warming climate. They can migrate to higher elevation, remain at local microrefugia or evolve through genetic differentiation to adapt to new climate. However, there had been no overview to date of how plants in the Alps and other high mountains of Europe could respond to future warming. Gentili and his co-authors conducted  a thorough literature review, focusing in particular on geomorphological processes and landforms associated with plant communities in alpine environment. (They found only one study which addressed the genetic evolution of an alpine plant.)

The authors developed a typology of alpine landforms and characterized each one according to its “vegetation features, climatic controls, microclimate features of active landforms and microrefugium functions.” They recognized eight landform types, which differ in terms of the processes that generate them. These landforms are mountain summits, debris-covered glaciers, moraine ridges and deglaciated forelands, nivation niches or snow patches,rock glaciers, alpine composite debris cones (debris slopes and scree), alpine corridors (composite channels, including avalanche channels and tracks), and ice caves.

Saxifraga oppositifolia living on alpine corridors (Source: Alastair Rae/Flickr).
Saxifraga oppositifolia living on alpine corridors (Source: Alastair Rae/Flickr).

Taken individually, all of these eight landforms have been documented in the published literature as serving currently as microrefugia, except for the debris-covered glaciers, which nonetheless are promising as future microrefugia because of their relatively cool temperatures which result from the presence of sub-surface ice. The other landforms all have been shown to function as microrefugia. They offer a number of advantages, including suitable sites for colonization (moraine ridges and deglaciated forelands), cooler temperatures (debris-covered glaciers, rock glaciers, nivation niches or snow patches, ice caves), a vertical range that facilitates dispersal (alpine corridors) and a large variety of niches (alpine composite debris cones). Taken together, these landforms provide a very wide range of habitats, increasing the likelihood that any given alpine species could have a favorable spot to which it could disperse. These relations are indicated in the figure from the paper, shown below, which demonstrates that the geomorphological heterogeneity—the diversity of habitats within and across landforms—promotes the survival of species.

The relation of geomorphological diversity to species survival (Source: Gentili et al./Ecological Complexity).
The relation of geomorphological diversity to species survival (Source: Gentili et al./Ecological Complexity).

The researchers note that these glacial and pre-glacial landforms are potential microrefugia for alpine plants under warming conditions. They recognize that human intervention—purposive translocation of plants—may assist in the survival of species. In addition, they point out that the plant species themselves may adapt genetically to changing environmental conditions. They conclude by suggesting that researchers could profitably direct their attention to evolutionary processes within this geomorphologically complex and climatically dynamic environment, seeing whether species, pressed by climate change, can adapt, or even evolve into new species.

Saxigrada bryoides living on debris-covered glaciers (Source: /Flickr).
Saxigrada bryoides living on debris-covered glaciers (Source: Benoit Deniaud/Flickr).

Glaciers Influence Marine Invertebrates in Chile

Bivalves larvae – Swimming Manila Clam. The width of the picture is slightly over 1mm (Source: Dick/Flickr).
Bivalves larvae – Swimming Manila Clam. The width of the picture is slightly over 1mm (Source: Dick/Flickr).

Zooplankton are tiny creatures that drift in water bodies. A recent study by Meerhoff et al. in Progress in Oceanography describes linkages which connect them with glaciers. The researchers observed meroplankton—organisms which have planktonic features in their larval stages, but live sessile in the bottom as adults. They worked in the fjords of the Baker River, which is located between the Northern and Southern Patagonian ice fields in Chile. Physical and chemical conditions vary widely in these fjords, due to tides and to seasonal fluctuations in glacier meltwater and other contributions to river flow. These varying conditions, in turn, influence the dynamics of zooplankton communities, including productivity patterns, biomass, and community structure (the distribution and interactions of different species).

Zooplankton community dynamics in fjords are influenced by the strong vertical and horizontal gradients in hydrographic structure, such as freshwater discharge and tides. Studies have shown that temporal and spatial distributions of zooplankton are controlled by environmental conditions. Temperatures influence temporal scale by influencing metabolic rates and swimming behaviors of zooplankton. The salinity of water constrains the spatial distribution of estuarine zooplankton because each species can tolerate only certain levels of salinity. These two environmental factors also influence food availability and predation stress, which also affects the community structure of zooplankton.

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A fjord from the southern Patagonian in Chile (Source: NASA/Flickr).

The input of freshwater from glacial meltwater can change salinity, generate internal tides and reshape the circulation pattern in estuarine systems. Moreover, the turbidity of the water is influenced by glacial input. Even though the glaciers are virtually pristine, the meltwater is able to carry sediments along its way, known as rock flour. These finely ground particles, formed by the interaction of glaciers with their beds, are so small that they remain in suspension, making the water less transparent. This increase in turbidity limits light penetration and thus restricts primary production through photosynthesis by phytoplankton—the minute plants which float in the water column.

The study area of Baker river fjord in Chile (Source: Meerhoff et al./Progress in Oceanography).
The study area of Baker river fjord in Chile (Source: Meerhoff et al./Progress in Oceanography).
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CTD profiling for hydrographic measurements by the research group (Source: Erika Meerhoff).

Using vertical tows, Meerhoff and her associates collected samples in three sites close to the river mouth, during the Baker river minimum outflow season (October 2012) and during the maximum outflow season (February 2013). They observed strong hydrographic gradients, both horizontal and vertical, in early spring (October) and late summer (February). They have also found that these two seasons are significantly distinct in water-column conditions. Such variations are largely caused by freshwater discharges from nearby glaciers.

This study found a number of kinds of meroplankton in these fjords; the dominant organisms are larval forms of barnacles, squat lobsters, crabs, snails and bivalves. The study also indicated that zooplankton community shows seasonal variations. Specifically, barnacle larvae are favored in spring, when river outflow is at its minimum, while its food sources, phytoplankton, are more abundant. In contrast, bivalve larvae are dominant in summer due to higher surface water temperature. At this time, river outflow is at its maximum and phytoplankton availability is much lower than in spring, reflecting the greater turbidity of the water that carries glacier rock flour. Studies are needed to demonstrate whether bivalve larvae in this estuary feed on bacteria when phytoplankton are unavailable, as they do in other regions.

Adult stage of barnacles (Source: Abraham Puthoor/Flickr).
Adult stage of barnacles (Source: Abraham Puthoor/Flickr).

This study shows how freshwater input, along with other factors, affects zooplankton composition and distribution. It is remarkable to think of the numerous marine invertebrate larvae whose populations respond to glaciers located well inland of their estuarine home.

Look here for other stories about invertebrate life near and on glaciers.