Interhemispheric comparisons

Returning to the conundrum in post 13, one of the most important finds in the study of millennial-scale climate variability is that the response of the North and South hemispheres are out of phase.

The Southern hemisphere has not received much attention so far in the blog post, but as we shall we see in this post and the next post, it holds vital importance for our understanding of global ocean circulation) (Blunier et al., 1998). Blunier et al. (1998) showed that Greenland warming around 36 and 45 kyr before present (BP) lagged Antarctica by 1 kyr. Therefore, in order to synchronize both records, the authors use methane (CH₄) records from the last glaciation from 2 Antarctic ice cores (Byrd station 80°S, 120°W, Vostok 78.47°S, 106.80°E ) and 1 Greenland ice core (GRIP ice core summit, 72.58 °N, 37.64 °W). CH₄ has an approximate residence times of c. 10 years in the atmosphere. The advantage of using CH₄ as a tool for synchronisation is that it has a residence time that is long enough to become globally homogenous but is also short enough to react quickly to budget imbalance linked to climate changes. Therefore any changes in concentration should be synchronous between Antarctica and Greenland (Figure 1).

Figure 1: GRIP, Byrd and Vostok isotopic and CH₄ records on the common timescale (GRIP timescale in years before 1989).Antarctic warming as indicated by A1 and A2, with vertical dashed lines  indicating the location of Greenland warmings 1,8 and 12 in the Antarctic cores.

Source: Blunier et al. (1998)

On average, the authors found that the change in Antarctic climate leads Greenland on an average of 1 1±2.5 kyr across the period 47±23kyr BP. One of the greatest findings of Blunier et al. (1998)’s observation is that the records dispelled any notion of a coupling between Northern and Southern hemispheres via the atmosphere, an idea postulated by Bond et al. (1993). Crucially, the findings potentially favour an ocean connection in order to conceptualise this behaviour.

One of the greatest challenges in climate science is the ability to derive a mechanism that accounts for the observed behaviour of high-latitude north and south hemispheres.

Any such mechanism would need to address the following conundrum (forgive my use of intertextuality with reference to arguably one of the most famous authors in English literature):

To be in Phase or To be in Antiphase?

That is the question…