Wider Implications

The link between southernmost Patagonia and Antarctica would be expected. The climate of southern most Patagonia is influenced by the circumpolar current sweeping around Antarctica. The tip of South America protrudes into this current and diverts water northwards along the coast for some hundreds of km. Sea surface temperatures influence the temperature and moisture content of westerly air masses crossing the ocean before they encounter the Andes and drop their precipitation as rain or snow. If temperatures fall below those of the present then existing glaciers will expand and vice versa. In such a situation the glaciers can respond quickly to changes in the offshore sea surface temperatures, even those on sub-decadal time scales such as that of El Niño. Thus it is to be expected that southernmost Patagonian glaciers will respond to millennial-scale fluctuations of the Southern Ocean. One outstanding issue is to establish how far north this Antarctic effect extends.

The antiphase behaviour during the transition from a full glacial global climate to an interglacial climate is an exciting discovery. It is the first firm evidence to be gained from high-resolution terrestrial records in such a southerly latitude (see Figure below). It supports the idea of an oceanic bipolar seesaw mechanism whereby cooling in the south is matched by warming in the north and vice versa. The implications for our present world are fascinating. It means it is possible for climatic change to lead to both warming and cooling at the same time. Whether a place warms or cools depends on its location. Thus it becomes even more important to take care in interpreting the record from any single location unless it is put in its wider context. It also implies that any predictions of the effects of global warming on society will be complex.

(left)The Timing of the Magellan late-glacial advance compared with ice core records from Greenland and Antarctica. The ice core records demonstrate asynchrony at a millennial scale during late-glacial times. The Magellan climatic signal represented by the duration of the ice-dammed lake mirrors the climate signal of the southern hemisphere and is out of phase with that of the northern hemisphere. The onset of the lake phase is based on the mean calibrated age of the Reclus Tephra and is a minimum, since the lake was already present. The end of the lake phase is the mean calibrated age of surface peat at Cabo Valentin II. Ice core records after Blunier et al. (1998)

The coincidence between the southern and northern hemispheres of the peak of the last Ice Age, the onset of deglaciation and the start of the present interglacial suggests wholesale reorganisation of the Earth’s climate system at the time. Perhaps the system is stable enough in its Ice Age mode and Interglacial mode to be able to dominate the world’s climate and this leads to global synchrony in the main events. The antiphase behaviour during the transition from one state to the other is suggestive of instability. Perhaps it is during the change from one state to the other that ocean instability is able to dominate global climate change.