Krill Contribute to Ocean Carbon Storage in Patagonia

Waters in the sub-Antarctic region of Chilean Patagonia are fed by glaciers in one of the largest freshwater systems on Earth, the North and South Patagonian Icefields. A recent study published in Marine Ecology Progress Series found that Euphasia vallentini, the most abundant species of krill in Chilean Patagonian waters, play a key role in food webs. The study also discovered that this species of krill helps to sequester carbon in the oceansthey consume plankton, which take in carbon during photosynthesis, and discharge some of the carbon into deeper ocean waters through the production of fast-sinking fecal pellets. This is increasingly important as atmospheric carbon concentrations rise, as it contributes to the role of the oceans as a carbon sink.

The North Patagonian Icefield (Source: McKay Savage / Creative Commons).
The North Patagonian Icefield (Source: McKay Savage/Creative Commons).

Krill are small, shrimp-like crustaceans that are found in all of the world’s oceans. In an interview with GlacierHub, Humberto E. González, the lead author of the study from the Austral University of Chile, explained that krill form “a trophic [related to food and nutrition] bridge between the microbial community [bacteria, nanoplankton, microzooplankton] and the upper trophic layers [seals, whales, penguins, etc.]. Thus, they play a pivotal role in trophic flows.”

The study by González et al. focused on the region between the Magellan Strait and Cape Horn because of the unique biological, chemical and physical conditions created by the hydrological input from three different sources: nutrient-rich Pacific and Atlantic Sub-Antarctic Waters (waters that lie between 46°– 60° south of the Equator), and cold and nutrient depleted freshwater from Patagonian rivers and glaciers.

Waters that are more saline or that are colder have higher densities. However, as explained in the study, the effect of salinity exceeds the effect of temperature on density within this region, giving rise to strong saline stratification in the mixture of oceanic and freshwater terrestrial environments. This reduces the movement of important species between the benthic (the lowest level) and pelagic (open water) ecosystems in southern Patagonia.

The stratification also reduces upward and downward mixing of ocean water. This reduces carbon fluxes in the region, as the transport of carbon dioxide to deeper parts of the ocean through diffusion across layers occurs more slowly than the circulation of ocean waters with different carbon dioxide concentrations.

A map of the Strait of Magellan and the region where the study took place (Source: / Creative Commons).
A map of the region where the study took place. The icefields are located further north (Source: Creative Commons).

The team of scientists embarked on a research cruise in the region in October and November 2010, collecting chemical and biological samples at about forty different stations. Using a variety of techniques, they studied features such as the types and distribution of organic carbon in the waters, and the abundance and diet of E. vallentini. All this was done to better understand the role of E. vallentini in the region’s food web structures and in the transport of carbon to deeper layers of the ocean despite strong stratification.

In conversation with GlacierHub, González stated that “the species of the genus Euphausia (a functional group of zooplankton) play a paramount role in many disparate environments from high to low latitude ecosystems. Euphausia superba in the Southern Ocean and Euphausia mucronata in the Humboldt Current System are some examples.In this study, González et al. found that E. vallentini play a similarly important role in Southern Chilean Patagonia, consuming a range of plankton from nano- to phytoplankton and forming the dominant prey of several fish, penguin and whale species.

Krill, such as E. vallentini, form an important link in food chains between phytoplankton and larger animals (Source: Uwe Kils / Creative Commons)
Krill, such as E. vallentini, form an important link in food chains between phytoplankton and larger animals (Source: Uwe Kils/Creative Commons)

The study also found that E. vallentini play an important role in passive fluxes of carbon through the sequestration of carbon in fast-sinking fecal pellets, or poop. The plankton ingested by E. vallentini takes in carbon dioxide during photosynthesis, and about a quarter of the plankton ingested by E. vallentini is then passed out in fecal matter. These fecal pellets form the dominant component of particulate organic carbon (organic carbon particles that are larger than a certain size) fluxes in the region’s waters, helping to sequester carbon as they sink to the ocean floor.

This process is accelerated by E. vallentini’s vertical diurnal migrations, which occur despite the strong saline stratification of waters in southern Patagonia. Their vertical movements, from deeper parts of the ocean during the day to the surface of the ocean in search of food at night, occurs more quickly than the rate at which their fecal pellets sink, speeding up the transport of carbon to deeper ocean layers. As González explained, “the Patagonian krill [and] the squat lobster (Munida gregaria) are the main species responsible for the carbon export towards deeper layer of the fjords and channels (in southern Patagonia).”

Although scientists from the Commission for the Conservation of Antarctic Marine Living Resources estimate that the total weight of Antarctic krill exceeds that of humans on Earth, they may not be immune from the effects of anthropogenic climate change. Indeed, González stated that a greater input of freshwater to the ocean could reduce nutrient levels in upper layers of the ocean. This will reduce the productivity of fjords and channels, reducing the availability of food for krill, and creating serious implications for the marine ecosystems that they are part of. This research serves as a reminder that biological organisms play an important role in the effects of marine ecosystems on the world’s climate, as they do in terrestrial ecosystems. 

Patagonian Ice Holds the Key to Unlocking the Past

A research team recently conducted a study in the Northern Patagonia Ice Field (NPI) to uncover some of the mystery behind Earth’s ancient climate. Along the way, the team made important observations about the current state of glacial ice thinning and climate change.

Through their investigation of ancient paleoclimates (climates prevalent in the geological past), the scientists were able to identify time periods where major glacial growth and decline occurred in the Patagonian Ice Field, contributing important information to our understanding of our planet’s climate following the last ice age. Developing a strong comprehension of glacial advance and retreat over the last 10,000 years in places like the Patagonian Ice Field provides the scientific community with tools to augment our understanding of the past, as the planet’s climate is intrinsically related to its ecology at any given point in our recent geological history.

An astronaut’s photo of a glacier outlet meeting a fjord in the Southern Patagonia Icefield. (Source: NASA)

Patagonia hosts a wide variety of largely untouched landscapes, possessing a range of environments from mountains and deserts to glaciers and grasslands. In addition to its mountainous beauty, the Northern Patagonia Icefield is special in that it is the most glaciated terrain on the planet within its latitude of 46.5 to 47.5 degrees south. The region where the ice field lies is a barren sector of South America spanning nearly 3 million square kilometers across southern Argentina and Chile.

In the glaciated terrain, thick layers of ice and rock hold a wealth of information regarding global climates of the last 25,000 years, offering a glimpse of where we are headed given the recent anthropogenic (human-caused) acceleration of climate change. The study provided scientists with valuable climate data from the Late Pleistocene and Holocene time periods, which began approximately 125,000 years ago following the final episode of widespread global glaciation.

The lead researchers of the study, David Nimick and Daniel McGrath, focused specifically on the the largest outlet glacier draining in the region, the Colonia Glacier on the eastern flank of the ice field. The team sought to constrain the ages of major glacial events by using a variety of dating techniques, including dendrochronology (tree-ring dating), radiocarbon dating, lichenometry (utilizing lichen growth to determine the age of exposed rock) as well as optically stimulated luminescence (dating the last time quartz sediments were exposed to sunlight). Employing such a wide variety of experimental techniques can be a valuable tool in improving the confidence of data and allowed the team to study a diversity of unique properties of the same glacial medium.  

Lichen covered quartz ideal for lichenometry and luminescense. (Source: Tigerente/Wikimedia Commons)

By examining properties of lichen and quartz grains (when they were last exposed to sunlight), the research team was able to  constrain the time at which specific rocks were uncovered from the ice sheets. The age at which the ice melted away to reveal these rocks corresponds to events of retreat (and subsequent advance) of glacial ice across the last few millennia. The determination of major glacial events using these techniques sheds light on the climatic events that not only influenced South American paleoclimate but also may affect present and future glacial retreat given the recent spike in atmospheric carbon dioxide levels.

Results from dating analyses indicated that the most prominent increase in glaciated terrain occurred 13,200 years ago, 11,000 years ago and 4,960 years ago, with the last major advance defining the onset of Neoglaciation – the period of significant cooling during the Holocene or present day epoch. Analysis of a local ice-dammed lake revealed that glacial growth occurred 2,900 years ago and 810 years ago, with ice retreating during the intervening periods. This data points to the idea that in a general sense, warming and cooling even within the last 11,000 year Holocene interglacial period is highly cyclical. Significant Colonia Glacier thinning has been observed since the late 1800’s which has opened up low elevation channels for the local Lago Cachet Dos, a possible reflection of our warming climate and the greenhouse effect.

This knowledge provides an effective framework to which we can compare our actively changing climate. The timing between periods of glacial advance and subsequent retreat are useful metrics for judging the speed at which terrestrial ice is currently disappearing.

Glacial ice melts as it floats in a region north of the NPI. (Source: Adam Derewecki)

Nimick’s team’s findings show advance of the Colonia Glacier occurring approximately every 1,000 years under a climate with generally stable atmospheric carbon dioxide levels. Given the recent benchmark event of passing the 400ppm atmospheric carbon dioxide threshold, it is undeniable that human activity, particularly in the form of carbon emissions, is altering global climate and atmospheric carbon dioxide levels.

As we continue to release more carbon dioxide into the atmosphere, the stable conditions that contributed to the glacial patterns discovered in the study may no longer be present. Increases in greenhouse gases and a warming planet may spell disaster for ice sheets, yet the current speed and extent of glacial melting remain uncertain. Nevertheless, understanding glacial patterns in the Northern Patagonia Ice Field has improved our understanding of paleoclimate following the last ice age and may in fact contribute to our ability to improve forecasts for glacial retreat in the coming years.