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Glaciers Enhance the Biosphere — By Design

Evolution News
Photo: Greenland Ice Sheet.

The exquisite suitability of our planet for life depends on many non-biological factors. In his latest book The Miracle of the Cell, Michael Denton explores some aspects of chemical elements that seem finely tuned — even foreseen — to allow biological processes to excel at their daily work. These include the nature of the carbon atom, the strength differences between covalent and weak bonds, and the properties of metals and trace elements that permit particular enzymes to function. Among the non-biological factors of the earth that are life-enhancing, glaciers may not have been among the oft-considered candidates.

Glaciers, crawling slowly with their loads of ice, carve valleys and deposit rock in moraines. What’s biological about that? There may be ice-tolerant organisms living in parts of the ice, but there are hidden life-enhancing processes not visible to the casual observer. Underneath their thick ice bedloads, rivers of meltwater flow downhill. And with those rivers come cargo needed by living organisms.

Plankton

Fresh water, certainly, is one of the main cargoes. Consider what it does when it reaches the ocean. A new paper in the American Geophysical Union’s journal Geophysical Research Letters, by C. W. Lester et al., uncovered a major role this freshwater plays at the base of the marine food chain.

In the Arctic, each spring the appearance of the sun awakens the region’s ecosystem. In particular, the blooming of phytoplankton – which form the base of the Arctic marine food web — is an early phenomenon that depends on the availability of sunlight. In this study we present a model that supports the idea that sunlight alone is not enough to drive large plankton blooms in the open ocean: an influx from sea‐ice meltwater is also needed. This meltwater (which is fresh and light) acts to maintain an ocean surface layer that is thin and separated from the ocean below. The plankton are confined to this surface layer where they can absorb plentiful sunlight and grow into large blooms. Our model sheds light on this central role of sea‐ice meltwater for the growth of Arctic phytoplankton. [Emphasis added.]

The bloom of plankton brings fish like krill to feast on its abundance, and with the krill come other creatures all the way up the food chain. In Flight: The Genius of Birds, Illustra Media shows how arctic terns time their migrations to the annual feast. Having flown over 12,000 miles from the arctic circle, the birds arrive in time to enjoy the vast numbers of krill, which they share with the humpback whales featured in Living Waters, another documentary in Illustra’s Design of Life trilogy. The largest mammals on earth feast on the krill which feed on the plankton which depend on the fresh water delivered by glacial meltwater. 

Trace Element Delivery

Denton expounded on water’s multi-faceted chemical suitability for life in his previous book The Wonder of Water (2017). He pointed out that the peculiarly low viscosity of ice relative to rock (10 orders of magnitude smaller) allows glaciers to move on a thin sheet of liquid water, carving out U-shaped valleys and other characteristic glacial landforms. 

Mineral-laden glaciers humble the hardest mountain rock, carrying vast stores of material into flood plains and oceans. As glaciers flow down river valleys or across great continental land masses, sliding over the bedrock, they drag along rocks and rock fragments across the underlying surface, grinding away the underlying rocks and reducing them to “rock flour,” material made up of tiny grains of rock, fractions of a millimeter in size. This greatly increases the area available for chemical weathering. 

The Wonder of Water, pp. 23-24

The process of chemical weathering, in turn, delivers the minerals organisms need to thrive, including metals like iron, calcium, sodium, potassium, magnesium, manganese, zinc, and molybdenum. Denton describes the particular qualities of each of these elements for their roles in cellular processes in Chapter 6 of The Miracle of the Cell.

A recent paper adds to the wonder of this geophysical delivery system. In PNAS, a team of over 16 scientists with Jon R. Hawking as lead author measured trace elements in the glacial meltwater emerging from under the Greenland Ice Sheet and Antarctic Ice Sheet. They were surprised to find that subglacial rivers carry ten times more biologically essential trace elements than rivers on land. In their paper, “Enhanced trace element mobilization by Earth’s ice sheets,” they explain the significance of their findings:

Trace elements are integral to biogeochemical processes at the Earth’s surface and play an important role in the carbon cycle as micronutrients to support biological productivity. We present data from the Greenland and Antarctic ice sheets to demonstrate the importance of subglacial biogeochemical processes in mobilizing substantial quantities of these elements. Usually immobile elements are found in subglacial meltwaters at elevated concentrations compared with typical rivers, with most exhibiting distinctive size fractionation due to adsorption onto nanoparticles. Our findings suggest that ice sheets need to be included in models of global biogeochemical cycles of trace elements and studies of the fertilization of adjacent marine systems, especially the Southern Ocean, due to large export fluxes of micronutrients, most notably iron.

Iron is not the only essential element delivered to the oceanic food chain by these processes. They also found elevated levels of cobalt, manganese, and zinc. Cobalt (atomic number 27), that hard, lustrous, silver-gray trace metal more commonly thought of for its uses in magnets and alloys, plays an essential role in our bodies, too — it occupies the center of vitamin B12, “the only vitamin known to contain such a heavy element” (Britannica). Denton explains the importance of manganese and zinc (Miracle of the Cell, pp. 106-109). Here again, non-biological processes cooperate with biological processes in a complex interaction of geophysics and biophysics. Life might be uncommon, locally isolated to places having the largest concentrations of trace elements (TEs), were it not for the glacial delivery system that bulldozes rock, grinds it down to small particles, washes the nutrients into estuaries for further processing, and finally carries them out into the oceans.

Concentrations of TEs in subglacial meltwaters are generally high despite low temperatures, which likely reflects weathering of rock microparticles and/or long water residence times in high rock:water subglacial drainage systems. The importance of colloidal/nanoparticulate species depends on the element in question, but our data indicate a prevalence of elemental species 0.02 to 0.45 µm in size compared with truly soluble (<0.02-µm) aqueous species. Nanoparticulate oxyhydroxide minerals are therefore important in subglacial environments with a high sorption capacity and have important implications for lability and the ultimate fate of TEs in the downstream cascade. The role of subglacial export of TEs to adjacent/downstream polar ecosystems can elevate micronutrient availability and therefore, the carbon cycle by sustaining or altering biological productivity.

The Result of Chance?

Could these fortuitous circumstances be the result of chance? Toby Tyrrell thinks so, in a recent paper in Communications Earth & Environment, “Chance played a role in determining whether Earth stayed habitable.” He disagrees with a common notion that given a habitable planet, life will be inevitable. That’s something to ponder when reporters become enthusiastic about the increasing number of exoplanets being discovered. 

As Michael Denton points out in his Privileged Species series of books, videos and podcasts, there are too many coincidences from the atomic level to the geophysical and astrophysical level working in harmony to imagine that complex life might be a result of sheer dumb luck. It appears uncannily like foresight, enough to make even materialists take note. The late Freeman Dyson was struck by it all. He famously said, “As we look out into the Universe and identify the many accidents of physics and astronomy that have worked together to our benefit, it almost seems as if the Universe must in some sense have known that we were coming.”