Kaufman et al 2004

Catchy title huh? I've just finished reading a really impressive and interesting article by Kaufman et al (2004) called "Holocene thermal maximum in the western Arctic (0–180 W)". The (many) authors included Holocene records from 140 sites, incorporating ice core, peat bog, marine and lake records distributed around the Western Arctic and considered in four major regions shown below. Unlike many of the palaeo-studies available in this region and in general, the authors sought to investigate the spatial distribution and timing of the 'Holocene Thermal Maximum' (HTM), a period in the early-to-mid Holocene in which averaged Northern Hemisphere temperatures peaked. Just as with the paper we considered in the last 'scientific' post, the authors used multiple proxies, all with varying reaction times and resolutions, giving them a fuller picture. By taking this approach they found some interesting and important results. Follow the jump for a summary...

Area considered by Kaufman et al (2004). Palaeo-records were taken from the whole region and considered in these four areas. Dominant ocean currents are also shown (Key in paper)

The sites and methods can be found here (the link in the article no longer works), and it is possible to locate the data used for each site used in the paper. I found this a great way to interact with the paper, something which I hope is used by other authors, hopefully with a working link! Oh, and don't be put off by the funny map they use.

Why so many sites, records and proxies? Well, there are a number of problems including those specific to the Arctic which can be limited by the use of many records and multiple proxies. For example, the paper mentions that most of the data in this synthesis are from pollen and plant macrofossil records. These are often used together because of their known limitations, but the authors admit difficulty in finding available macrofossils in the lake cores due to sparse vegetation in the region, especially shortly after the last glaciation. By using a greater number of records they can compare, contrast, and hopefully 'average out' erroneous findings as well as gaining a decent spatial resolution and distribution of results. Also, finding reliable ¹⁴C dates in these long cores is difficult where there may be a lack of organic material. Therefore, the authors have used only records with >3 ¹⁴C dates included in the record. As the trends dealt with in the paper are millenial in scale, a greater number of dates was not required in order to be sure of centennial-scale trends.

Their results indicated a high spatial variability in the HTM timing, with it reaching a peak at 11Kyr BP in the 'Central-Eastern Beringia' region, before the southern Hudson bay area (Northern Continental Canada) at 7Kyr BP, when the Laurentide Ice Sheet finally melted. This was likely, the authors suggest, caused by insolation forcing at the different latitudes in the region as well as complex feedback mechanisms which acted to amplify the gradual changes.

This paper uses palaeo-records in an interesting way and raises a number of points. Firstly, Holocene climate has been variable, even in this relatively limited region. Also, it illustrates the sensitivity of the Arctic to insolation forcing, which makes the recent warming trend even more significant in the light of a negative insolation trend. The results also suggest that feedback mechanisms, such as the ocean currents, took a significant role in influencing regional climate during the later ice-melt. Therefore, it is likely that similar mechanisms would be established during current and future ice melt, although on a different scale.

More interestingly in my opinion, however, the spatial variation in the timing of the HTM throughout this limited region in the paper shows the use of global averages, both in 'palaeo' and modelling disciplines has very limited applicability*. It would also suggest that similar syntheses in other areas would yield interesting results if attempted.

Now that I've very briefly looked at climate history of the Arctic and placed it in relation to the modern trends, the following posts will shift slightly to consider the ecological impacts in the Arctic of climatic changes and then human activities. Where possible, this will include a palaeo-aspect to give a long-term view. After that, I will consider some forecasts of future ecological and ecosystem change.
______

*As an example, here's something has been following me round the past few weeks as I've been looking up quirky and interesting things to fill gaps between serious posts:

This figure pops up on all number of websites, mostly in those sceptical of recent man-made warming. Ignoring the region on the very right of the graph for the moment (the part which shows no recent rise!) the graph shows a conceptualised 'average' Northern Hemisphere temperature record. In relation to this discussion only, considering the Northern hemisphere as a single unit seems to be ignoring much of the detail in the record. By the way, who else has come across this in their recent travels?