olelog

As a long-term average the Baltic Sea is ice covered for about 45% of its surface area at maximum annually. The ice-covered area during such a typical winter includes the Gulf of Bothnia, the Gulf of Finland, Gulf of Riga and Väinameri in the Estonian archipelago. The remainder of the Baltic itself does not freeze during a normal winter, with the exception of sheltered bays and shallow lagoons such as the Curonian Lagoon. The ice reaches its maximum extent in February or March; typical ice thickness in the northernmost areas in the Bothnian Bay, the northern basin of the Gulf of Bothnia, is about 70 cm for landfast sea ice. The thickness decreases further south.


Freezing begins in the northern coast of Gulf of Bothnia typically in middle of November, reaching the open waters of Bothnian Bay in early January. The Bothnian Sea, the basin south of it, freezes on average in late February. The Gulf of Finland and the Gulf of Riga freeze typically in late January.

The ice extent depends on whether the winter is mild, moderate or severe. Severe winters can lead to ice formation around Denmark and southern Sweden, and on rare occasions the whole sea is frozen, such as in 1942 and 1966. In 1987, some 96% of the Baltic Sea was ice-covered, leaving only a small patch of open water in the south-west around Bornholm. However, in milder winters only restricted parts of the Bay of Bothnia and Gulf of Finland are ice covered, in addition to coastal fringes in more southerly locations such as the Gulf of Riga. In recent years a typical winter produces only ice in the northern and eastern extremities of the Sea. In 2007 there was almost no ice formation except for a short period in March.

From Wikipedia.

The extent of ice covering the Baltic sea this winter (2007/2008) reached an all-time low. New figures from Sweden's meteorological agency (SMHI) indicate the lowest levels since measurements began more than a century ago. Overall, 49,000 km2 of the Baltic sea were covered in ice compared to the usual 180,000 km2. That was just over a quarter of the normal level, and the ice season had ended two weeks early. The highest levels of ice cover in the Baltic came in the winter of 1986 and 1987 when 420,000 km2 of its waters were covered.

The ringed seal had to change its usual habits and give birth much closer to land.

I would like to stress than one warm winter in a local area like the Baltic Sea proves nothing about global warming. Global warming is about a trend in climate change over many years. At the same time I would like to stress that Americans should NOT take their cold winter that same winter 2007/2008 as a sign that this global warming trend has suddenly stopped.

• http://www.thelocal.se/11526/20080503/
• http://www.terradaily.com/reports/Baltic_sea_ice_cover_hits_an_all-time_low_meteorologists_999.html

More in Swedish from SMHI at
http://www.smhi.se/cmp/jsp/polopoly.jsp?d=103&a=34774&l=sv

Much has been written about the impact from volcanic eruptions on climate change (cooling) and sea level changes. Less has been said about the impact from global warming and sea level rise on volcanism.

Sea level rise can reactivate volcanoes situated near sea level. Alaska's Pavlof volcano erupts every winter when (local) sea levels are higher - well just about 30 centimetres. Thirteen of sixteen magmatic eruptions of Pavlof Volcano in nine of the years from 1973 to 1998 have occurred between 9 September and 29 December. A significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading. (See this abstract). The melting of polar ice sheets from global warming and the resulting stress placed on the earth's crust from rising sea levels will cause more magma and increase volcanic eruptions on a global scale in the years to come.

Carolina Pagli of the University of Leeds, UK, and Freysteinn Sigmundsson of the University of Iceland in Reykjavik calculated how shrinkage of the Icelandic ice cap Vatnajökull affects what is happening below ground. Their findings will shortly be published in Geophysical Research Letters.

Pagli, C., and F. Sigmundsson (2008), Will present day glacier retreat increase volcanic activity? Stress induced by recent glacier retreat and its effect on magmatism at the Vatnajokull ice cap, Iceland, Geophys. Res. Lett., doi:10.1029/2008GL033510, in press.

When ice disappears, the added weight it forced upon the crust below it disappears as well. As a result this is increasing the rate at which the rocks under the ice sheet melt into magma. Iceland is home to several active volcanoes that exist underneath the ice, including Gjàlp, home of the last big eruption in 1996, and 58 years earlier in 1938. But according to Pagli and Sigmundsson the extra magma produced over the past century and more could reduce that time down to a gap of 30 years between each eruption. Volcanoes in Antarctica and Alaska will be at risk of similar increased volcanic activity. The shifting stresses could even cause eruptions in unexpected places.

And now that I am talking about Icelandic volcanoes - according to Iceland Review Online a giant volcano has recently been discovered off Reykjanes peninsula, Southwest Iceland, almost as large as the peninsula itself, and expected to erupt at any time. In the centre of the volcano there is a caldera measuring ten kilometres in diameter.

Since the volcano is at a depth of 1,500 metres eruptions would not have any effect on Iceland, except perhaps causing earthquakes (and tsunamis?). The volcano’s discovery is considered significant because it was believed it couldn’t exist in that area. Such large volcanoes are not supposed to be located on oceanic ridges. They are always drifting apart and that prevents a volcano from being created, so the volcano’s existence really came as a surprise.

• http://www.dailygalaxy.com/my_weblog/2008/04/will-a-warmer-w.html#more
• http://environment.newscientist.com/channel/earth/mg19826515.100-melting-ice-caps-may-trigger-more-volcanic-eruptions.html
• http://www.abc.net.au/news/stories/2007/09/14/2033161.htm?section=justin
• http://environment.newscientist.com/channel/earth/climate-change/mg19626324.600-volcanoes-give-sea-level-a-temporary-boost.html
• http://www.abc.net.au/science/news/stories/2005/1494475.htm

RedOrbit regularly posts satellite images of the day. I have the impression that it is mostly more than one image per day. Thank You RedOrbit. They often give new insights in larger geological structures. On 13 February 2008 they posted an image of the Pingualuit Meteorite Crater

The Pingualuit Crater was created 1.4 ± 0.1 million years ago (Pleistocene) by a meteorite impact. The 3.4-km diameter crater rises 160 m above the surrounding tundra and is 400 m deep. On the bottom of the crater, a lake with a measured depth of 267 m, contains some of the purest water in the world. The lake has no inlets or apparent outlets, so the water accumulates from rain and snow and is only lost through evaporation. The residence time of the water in the lake has been estimated at 330 years. It has a salinity level of less than 3 parts per million. In terms of transparency, it is second only to Lake Masyuko in Japan. It is one of the youngest and best-preserved craters in the world.

During World War II (in 1943), the singular landmark was noted by Allied pilots ferrying planes north and eastwards to Europe. Fred Chubb, a diamond prospector, visited the crater in July 1950 and the crater was subsequently identified as the "Chubb Crater". In the summer of 1951, the National Geographic Society and the Royal Ontario Museum lead the first scientific expedition to the crater. In 1968, it was renamed "Cratère du Nouveau-Québec" (New Quebec Crater ) by the Quebec government. Then in 1999, the name was changed to "Pingualuit", which means "where the land rises" in the local Inuit language. The crater and surrounding area is now a Provincial Park. Having a surface area of 1,133.9 km2, this park was officially created on 1 January 2004. The park’s main characteristic is the Pingualuit crater.

Recognising Pingualuit Crater’s unique characteristics - the lake has no surface connection to other surrounding water bodies - a research team from the University of Arkansas collected samples of the lake’s sediments, paying special attention to diatoms. Communities of these single-celled, silica-shelled algae change in response to environmental changes, including changes in climate. Deep within the crater’s lake sediments, the research team found two separate layers of diatoms and other organic material that indicate they were created during relatively warm conditions. The layers probably dated back before the Holocene Epoch — the geologic time period that covers Earth’s history since the end of the Pleistocene Ice Age about 10 thousand years ago. In short, the team’s findings suggested that at two different times before the Holocene Epoch, the area around Pingualuit Crater enjoyed ice-free conditions.

• http://www.unb.ca/passc/ImpactDatabase/images/new-quebec.htm
• http://www.redorbit.com/images/images-of-the-day/img/18878/pingualuit_crater_canada/index.html?source=r_earthiod
• http://www.ottawa.rasc.ca/articles/odale_chuck/earth_craters/pingualuit/index.html
• http://www.bivouac.com/MtnPg.asp?MtnId=4469
• http://www.sciencedaily.com/releases/2007/12/071215212916.htm
• http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17919
• http://dailyheadlines.uark.edu/11974.htm

Chronology is the science of dating (past) events and their sequence, and an important issue in geology (chronostratigraphy). A lot of different methods are used for dating, a.o. depending on time scale. At some time I mentioned the use of lichens for dating in my post on Earthquakes and Lichenometry.

Tephra is solid material of all sizes (ash, bombs, cinders, etc.) explosively ejected from a volcano into the atmosphere, and dating by use of tephra is called tephrochronology. Tephrochronology is a geochronological technique that utilises discrete layers of tephra (or volcanic ash layers if you like) from a single eruption to create a chronological framework in which palaeoenvironmental records can be placed. Such an established event provides a "tephra horizon". The tephra layers are deposited relatively instantaneously over a wide spatial area. Because each volcanic event has a unique and identifiable chemical 'fingerprint', volcanic ash layers can be relatively easily identified in many sediments.

Until the 1960’s, tephrochronological studies in north-west Europe were restricted to Iceland, the only country with active volcanoes in the region. - Although I remember that we counted volcanic ash layers even before that time in sediments on the island of Fur in Denmark. More than 200 layers of volcanic ash of predominantly basaltic composition have been found within the Mo-clay of the Fur Formation of early Eocene age. 180 volcanic ash layers of the c. 60 m thick Fur Formation have been numbered. - Through new developments in geochemical analysis the scope of tephrochronology as a potential tool to investigate and precisely determine rates of climate change has been much enhanced. Much of the analysed material is extremely small - microscopic glass shards <100 µm in size referred to as ‘microtephras’ or ‘cryptotephras’.

A paper titled “Three new distal tephras in sediments spanning the Last Glacial-Interglacial Transition in Scotland” published in the Journal of Quaternary Science of September 2007 reports the results of tephrostratigraphic investigations at a number of Last Glacial-Interglacial Transition sites from the Inner Hebrides and Scottish mainland.

As they say at the Tephrochronological Database at http://www.tephrabase.org : “Tephra layers are now an invaluable tool in palaeoenvironmental studies. The data produced by such research can be difficult to handle and disseminate. Tephrabase is a database of tephra layers found in Iceland, north-west and northern Europe, Russia and central Mexico. Details on the location, name, age and geochemistry of tephra layers are stored in the database, as well as information about relevant volcanoes and volcanic systems. A comprehensive reference database is also included.“

• http://www3.interscience.wiley.com/cgi-bin/abstract/113521548/ABSTRACT?CRETRY=1&SRETRY=0
• http://en.wikipedia.org/wiki/Tephrochronology
• http://www.tephrabase.org/tephrochron.html

Distinctive radioactive signals from fallout from atmospheric nuclear tests during the 1950s and 1960s are routinely used as event markers when analysing ice cores. And as sedimentological time markers in rivers as well for that matter. In 2006, a joint U.S.-Chinese team drilled four ice cores from the summit of Naimona'nyi, a large glacier 6,050 meters high on the Tibetan Plateau, and discovered that these signals were missing in their cores.

A reasonable conclusion is that this Tibetan ice field has been shrinking at least since the A-bomb test half a century ago.

The 7,694 meter high Mt. Naimona'nyi (also known as Gurla Mandhata) lies in the western tip of the mid-Himalayas in Burang County of the Tibetan Autonomous Region.

As the Tibetan glaciers release meltwater each year and feed the rivers that support nearly 500 million people in that region this is bad news. The loss of these ice fields might eventually create critical water shortages for people who depend on glacier-fed streams. If what is happening on Naimona'nyi is characteristic of the other Himalayan glaciers, glacial meltwater will eventually dwindle with substantial consequences for a tremendous number of people.


* http://researchnews.osu.edu/archive/radsignl.htm
* http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2007/2007121126010.html
* http://www.gov.cn/english/2006-11/10/content_438741.htm
* http://english.cas.cn/eng2003/news/detailnewsb.asp?infono=26273