Antarctic terrestrial life – challenging the history of the frozen continent?

Abstract

Antarctica is a continent locked in ice, with almost 99.7% of current terrain covered by permanent ice and snow, and clear evidence that, as recently as the Last Glacial Maximum (LGM), ice sheets were both thicker and much more extensive than they are now. Ice sheet modelling of both the LGM and estimated previous ice maxima across the continent give broad support to the concept that most if not all currently ice-free ground would have been overridden during previous glaciations. This has given rise to a widely held perception that all Mesozoic (pre-glacial) terrestrial life of Antarctica was wiped out by successive and deepening glacial events. The implicit conclusion of such destruction is that most, possibly all, contemporary terrestrial life has colonised the continent during subsequent periods of glacial retreat. However, several recently emerged and complementary strands of biological and geological research cannot be reconciled comfortably with the current reconstruction of Antarctic glacial history, and therefore provide a fundamental challenge to the existing paradigms. Here, we summarise and synthesise evidence across these lines of research. The emerging fundamental insights corroborate substantial elements of the contemporary Antarctic terrestrial biota being continuously isolated in situ on a multi-million year, even pre-Gondwana break-up timescale. This new and complex terrestrial Antarctic biogeography parallels recent work suggesting greater regionalisation and evolutionary isolation than previously suspected in the circum-Antarctic marine fauna. These findings both require the adoption of a new biological paradigm within Antarctica and challenge current understanding of Antarctic glacial history. This has major implications for our understanding of the key role of Antarctica in the Earth System.

Geothermal activity helps life survive glacial cycles

“…Recent geological estimates of ice thicknesses during the past 10 million years suggest that the ice cover was generally thinner than was previously thought, raising the likelihood of small, icefree rocky patches ("nunataks") being present (25,26). However, although such nunataks could have harbored some life, many nunatak fauna are unique to such environments or to specific parts of the continent (27)(28)(29), and nunataks thus cannot explain the persistence of a wider range of Antarctic species, especially coastal species, throughout the LGM (30). Similarly, although the McMurdo Dry Valleys are known to have been partly icefree at the LGM (31,32), supporting some life, typically low moisture levels drastically limit diversity in this region (24,25).…”

“…With the exception of wind-dispersed taxa, such as mosses and lichens, most Antarctic terrestrial species are likely to be relatively poor dispersers that rely on rare, chance events, such as transport via birds (30), to colonize distant territory (e.g., greater than tens of kilometers). Geothermal heating from volcanic activity is generally limited to within a few kilometers of the summit crater or caldera.…”

“…Whereas poor sampling is the most parsimonious explanation for this pattern, other factors might also be important. Most plausible among these factors is a larger influence of survival on LGM nunataks on invertebrates than on other taxa (19), although, as stated above, contemporary nunataks do not host the same suite of invertebrates as found in coastal regions (30). Genetic research on intraspecific spatial patterns of diversity could shed light on whether invertebrates have recolonized much of the continent primarily from geothermal refugia or whether nunataks have played a larger role.…”

Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star

“…This for instance could have resulted in species ranges being restricted to the northern continental shelves of South Georgia and South America, while Antarctic shelf populations went extinct (Clarke and Crame, 1989). The onset of glaciation caused extinction in most, but not all, of the terrestrial flora and fauna (Convey et al, 2008), but in the more constant marine environment, much of the fauna has adapted successfully and has become comparably rich (Clarke and Johnston, 2003). There has long been debate regarding the origins of the Antarctic fauna and how much movement there has been of fauna into and out of the Antarctic realm over time since its isolation (Hedgpeth, 1969;Dell, 1972;Clarke and Crame, 1989;Clarke et al, 2005;Barnes et al, 2006;Griffiths et al, 2009).…”

Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia

“…Convey et al 2008). To this end, we employed molecular phylogenetic techniques, including molecular clock analysis of nuclear encoded 18S rRNA gene sequences of original Antarctic microchlorophyte isolates, along with an extensive set of other green algal sequences.…”