8000ka (again)

7 Jul 2017

At https://phys.org/print418470684.html ... sediment cores from Pine Island Bay in West Antarctica were collected by the British Antarctic Survey and an international team of scientists that used the German research vessel RV Polarstern. The findings are interesting as it has shown wind driven incursions of warm water forced the retreat of glaciers in the peninsular over the last 11,000 years. One has to take that statement at face value. Was it wind driven - or current driven? Or both. It happened on many occasions, it is inferred, but the shells of minute sea creatures do not provide an exact run of dates. They are therefore indicative rather than exact. In spite of that it comes up with some surprising data that fits studies in other parts of the world. For example, we know from data collected over the last 20 years that episodes of ice loss in West Antarctica result from warm water in the deep ocean, with an origin in the tropical Pacific, flowing on to the shallow continental shelf system around the peninsular. When it reaches the coastline it triggers substantial melting of floating ice bergs as well as a thinning of glaciers upstream. The reconstruction shows that warm water flooded Pine Island Bay at the end of the Younger Dryas (around 11,000 years ago). This coincided with a retreat of the ice. The process is then said to have come to an end around 7500 years ago which involved, they say, a switch in westerly winds. The change in wind is interesting as the date of 7500ka appears to be the aftermath of global events in 8000ka which may have involved a change in the axis of rotation. A change in wind direction, and the ocean conveyor current, is to be expected in such a situation. The authors don't say this of course as the shells of small sea creatures are not encyclopedic. The idea it solely involved a change in wind direction (the cause of which is left unsaid in the Phys Org piece), is an explanation, or an hypothesis - and so is the idea of a change in the axis of rotation. It is something that has been aired before in the News as there were contemporary changes in global sea level. Did sea levels go up, or down, in West Antarctica, 7500ka? As it involved, according to the research, an end to warm water affecting the peninsular, one suspects that indeed the sea level declined in this part of the world, and that would have been attributed to a build up of ice on the peninsular.

Little information is provided in the Phys Org piece for what occurred between 7500 years ago and the present. The compulsory reference to global warming appears to be the claim that in the 1940s there was a renewal of warm water affecting the continental shelf around the West Antarctic peninsular - which is then used to explain modern ice loss over the last 20 years (in a series of episodes). What it omits is that ice was regained in between the losses and the situation is little altered from what it was in the 1940s. Indeed, the 1940s represents the end of the 1920s/1930s warm period (the El Nino dominated 30 year half of the 60 year solar cycle) which was followed by a dominance of La Nina (colder weather on average) in the 1950s, 1960s and 1970s. A renewed bout of El Nino dominance kicked in during the 1980s,1990s, and 2000s. The million dollar question might be framed - have we entered a La Nina dominated 30 year phase (in the 2010s 2020s and 2030s period)? Might the so called 60 year cycle be a bit longer and we are still at the edge looking inwards as the 2015 El Nina was a major weather changing event. A La Nina dominance doesn't cause El Nino's to go away - just as in an El Nino dominated period they are still intersected and divided by La Nina events. Only time will tell. Theories abound. What the research has highlighted, which most of the sceptic climate blogs have failed to note, is that something big happened at the end of the Younger Dryas period, and something big happened in the period around 8000 years ago (or framed as 7500 years ago in this research article).