January 29, 2011 — andyextance

The water flowing from the Atlantic Ocean into the Arctic through the Fram Strait is warmer today than any time in the past 2,000 years. That’s what microscopic seabed deposits have told Robert Spielhagen of the Academy of Sciences, Humanities, and Literature in Mainz, Germany, and his colleagues. The scientists have shown that the average temperature of water flowing into the Arctic since 1890 is 2ºC higher than it has been on average in the previous two millennia. This sends a stark message about the prospects for the Northern polar region. “I am afraid that my children – now 14 and 17 years old – will be able to see a summer ice-free Arctic Ocean,” Spielhagen told Simple Climate.

On August 4, 2007 Spielhagen and his co-workers extracted the key deposits when they drilled a 46 cm long cylinder of rock from the sea bed. Such “sediment cores” had previously been used to look at temperature changes as far as 12,000 years into the past, but could only provide measurements for periods of a few hundred years at a time. That’s down to how much sediment settles to the sea bed, with too little deposition for high-resolution temperature measurements occurring where cores have been taken before. By contrast, Spielhagen’s team was able to give temperatures on a scale of 2-3 decades at a time. “We took our core in a place where a lot of fine-grained particles settle, due to diminished bottom currents,” he explained. “We were the first to find such a spot.”

The key element needed to determine temperature within the deposits are the shells of single-celled animals called foraminifers. Together with researchers from the US, Norway and Germany, Spielhagen investigated the shells in two different ways. “Method one uses the various species of foraminifers in the sediment,” the scientist explained. “There is only one species which prefers very cold water, from -2 to +2ºC, and several species which live in warmer waters.” Comparing the percentages of different species in the sample can give historical temperature values. The second method uses the ratio of the elements magnesium and calcium in foraminifer shells, which is directly linked to temperature.

Method Pre-1850 minimum temperature (°C) Pre-1850 average temperature (°C) Pre-1850 maximum temperature (°C) Post 1890 minimum temperature (°C) Post 1890 average temperature (°C) Post 1890 maximum temperature (°C) 1 2.8 3.4 4.4 4.1 5.2 6 2 N/A 3.6 N/A 4.4 5.8 7.1

The team found that the proportion of foraminifer species typically found in warmer water in the sample has seen an “unprecedented increase” at the location they sampled in the past 120 years. Spielhagen admitted that the corresponding rate of temperature increase that they reported in top journal Science on Friday was unexpected. “Publications about the dramatic atmospheric temperature increase in the Arctic made me expect that we should find something similar for the ocean waters,” he said. “I was somewhat surprised, however, how strong the temperature increase in the last 100-120 years was, according to our data.”

While such efforts to reconstruct historical temperatures can attract a lot of scepticism, Spielhagen asserted that his findings are robust. “The results from both methods are very similar,” Spielhagen underlined. “The very good correspondence make us very confident about the data. The methods we have applied for our records are well established and have been found to give very reliable results in many different ocean basins.”

These findings were published just a week after measurements showing that the proportion of the year in which the Greenland ice sheet was melting rather than freezing in 2010 was a record 50 days longer than average. Spielhagen emphasised that warmer water flowing into the Arctic could be contributing to this. “Warm water releases heat to the atmosphere,” he explained. “The warmer and stronger the transport of Atlantic Water to the Arctic is, the more heat may be released to the Arctic atmosphere and distributed there – potentially also reaching Greenland.”