Every season of fieldwork in Antarctica answers some questions, but often raises just as many or more new ones. Steve has progressed southward in his quest to reconstruct the occupation history of the continent’s penguins. He began his work in the northern Antarctic Peninsula and found that the record of penguin occupation only stretches back to around 700 years ago, but populations have recently shifted from the colder-adapted Adélie penguins to the warmer-adapted Gentoo and Chinstrap penguins (Emslie, 1995; Emslie et al. 1998). He then explored further south in the peninsula, and found abandoned Adélie sites as old as 6000 year before present (Emslie, 2001; Emslie and McDaniel, 2002). We worked southward into the Ross Island region around McMurdo in 2000-2001, and found the record for Adélies also stretched back to about 6000 years ago on the southern Victoria Land Coast, with occupation beginning in the north and working southwards until peaking during the “penguin optimum” around 4000 years ago. Some time around 2000 years ago the entire southern region was apparently abandoned, then the Ross Island sites (Capes Barne, Royds, Bird, and Crozier) were all colonized starting about 1000 years ago and most were apparently occupied continuously to the present (Emslie et al., 2003). Last season Steve worked on the other side of the continent in Wilkes Land, out of the Australian Casey base, and found abandoned sites that date back to roughly 8000 years ago, with occupation taking place as soon as land was exposed by retreat of the glaciers at the end of the Pleistocene (Emslie in preparation).
But one important question has remained unanswered: where were the Adélie penguins during the last glaciation? Baroni and Orombelli (1994) analyzed sediments containing guano from a site at Cape Hickey that may date to the late-Pleistocene (10,000-15,000 years ago), but it is important to get more secure dates on bone or eggshell to confirm or reject these dates. Now that we have visited the site (Update #7), occupation of this area during the full glacial seems unlikely, as large glaciers surround the Hickey West point, and could easily have buried it with more ice during a colder period. Also the sites do not appear much older than others we have sampled in the Ross Sea (ie. with excellent preservation of shell and bone) and I would expect Pleistocene sites to be less well preserved. We await the radiocarbon results from Cape Hickey (and elsewhere) with great interest.
Two locations that seemed very likely to have been home for Adélies during the glacial period have turned out to be less likely than previously thought. Steve had hypothesized that Cape Hallett, or especially Cape Adare, may have been likely refugia for the penguins during the ice age, as these sites are the most northerly on the Ross Sea west coast. But now that we have visited Cape Hallett, and seen photos of Cape Adare (image provided by whale researcher Catarina Fortuna at Terra Nova), this appears less likely. With more glacial ice on the landscape, beach lines were depressed during the full glacial, and low elevation sites such as Hallett and Adare should have been submerged beneath the sea. The remaining hillslopes are steep and today only contain spillover for the large colonies. It is more likely that older colonies will be found on higher terraces, resembling this one at Adélie Cove or possibly the Cape Hickey site. Or Adélies may have vacated the continent entirely, colonizing the sub-Antarctic islands or the tips of South America and Africa. These sites may be found someday, or may be lost forever under ocean waves or glacial ice. Meanwhile, the search for Ice-age penguin fossils continues.
Jurek found many fewer plant species than on the Antarctic Peninsula, documenting several species of mosses and lichens growing around the abandoned and active rookeries, some of these endemic to Antarctica. Field identification of these is difficult, so he is bringing samples back to Poland to examine in detail under the microscope to confirm his identifications. Many of these specimens may end up as reference specimens in the Polish Academy of Sciences for future work down here. Steve is bringing back 650 lbs. of sediment to process, and Ed has a lot of isotopic work to do on all the modern and fossil eggshells. So that just about does it for this year’s fieldwork. For now the plan is to return to the Ross Sea next season; cleaning up some loose ends (Cape Royds, Cape Adare, etc.) and revisit sites that produced the most interesting dates. Stay tuned.
Baroni, C and Orombelli, G. 1994. Abandoned penguin rookeries as Holocene paleoclimate indicators in Antarctica. Geology 22, 23-26.
Emslie, S. D. 1995. Age and taphonomy of abandoned penguin colonies in the Antarctic Peninsula region. Polar Record 31, 409-418.Emslie, S. D. 2001. Radiocarbon dates from abandoned penguin colonies in the Antarctic Peninsula region. Antarctic Science 13, 289-295.
Emslie, S. D. and McDaniel, J. 2002. Adélie penguin diet and climate change during the middle to late Holocene in northern Marguerite Bay, Antarctic Peninsula. Polar Biology 25, 222-229.Emslie, S. D., Fraser, W., Smith, R., Walker, W. 1998. Abandoned penguin colonies and environmental change in the Palmer Station area, Anvers Island, Antarctic Peninsula. Antarctic Science 10, 257-268.
Emslie, S. D., Berkman, P., Ainley, D., Coats, L., and Polito, M. 2003. Late-Holocene initiation of ice-free ecosystems in the southern Ross Sea, Antarctica. Marine Ecology Progress Series 262, 19-25.