Climate Change and Scientific Language
Friday, 3. August 2007, 15:56:17
Scientific publications are written by experts for their colleague experts within the same field. There is nothing wrong with that, but it makes most of them extremely difficult (if not impossible) to read for the rest of us. I find this a pity with all the important research going on with implications for everybody and relevant as basis for political decisions.
There is, for example, a pressing need to understand the mechanisms of rapid climate change. Research in that direction is reported in the journal Science vol. 317 of 27 July 2007 under the title Four Climate Cycles of Recurring Deep and Surface Water Destabilizations on the Iberian Margin. Let me quote one of the easier sentences in that important report: “In these cores, the ∂18O record of benthic foraminifera resembled the Antarctic temperature signal, whereas the ∂18O of planktic foraminifera exhibited changes similar to those found in Greenland ice cores.”
We are talking about deep sea sediment cores taken off the cost of Southern Portugal (that is what is called the Iberian margin in the title). The data collected made it possible to construct a detailed picture of the climate history of the past 420,000 years - that is covering four climate cycles each of around 100,000 years.
I have the impression that most of my readers are geologists having no problems with the sentence I quoted. I, for myself, happened once upon a time to have taken a one year university course in oceanography, so I have no problem either. If however you don’t know anything about foraminifera, benthos, plankton, and isotopes (like ∂18O), you may have a serious problem with this in itself simple sentence.
Foraminifera are microorganisms living in the sea. They typically produce a calcareous shell (called a test) composed of calcium cabonate. When they die their shells sink to the bottom of the ocean to become a substantial part of the deep sea sediments. Foraminifera have been studied more extensively than any other group of oceanic microfossils. The microscopic formaninifera are the most important for sediemtological studies, although larger foraminifera (up to 16 mm) do exist. See my post on Ocean Drilling for Earth's Climate History.
Some foraminifera are bottom-dwelling. Organisms which live on, in, or near the seabed are called Benthos. So
benthic foraminifera are bottom-dwelling microorganisms.
Other foraminifera drift with ocean currents. They are plankton. So planktic foraminifera live in surface water.
When their shells sink to the bottom of the ocean they will end up in sediment layers side by side with shells of bottom-dwelling foraminifera, which make them ideal for study of (currents in) surface waters and deepsea waters at a specific time.
The chemical formula for calcium carbonate is CaCO3 (calcium + carbon + oxygen). Here we shall concentrate on the oxygen. The oxygen is extracted from water, H2O (hydrogen + oxygen).
Oxygen isotopes. Isotopes are not necessarily radioactive. Isotopes of an element have nuclei with the same number of protons but different numbers of neutrons. Oxygen has seventeen known isotopes. Three are stable, 16O, 17O, and 18O, of which 16O is the most abundant (over 99.7%). That they are stable means that they don’t change after their formation. Oxygen-16 or 16O has 8 protons and 8 neutrons, whereas Oxygen-18 has 8 protons and 10 neutron, which makes it heavier. Oxygen isotope analysis considers the ratio of O-18 to O-16 present in a core sample taken from deposits in the ocean floor. In fact it is more like a ratio of a ratio, because the delta values (∂18O) are calculated on the basis of ratios of the ratio of oxygen-16 and oxygen-18 in the sample and the ratio of oxygen-16 and oxygen-18 in average ocean water (Standard Mean Ocean Water, SMOW).
Today the ∂18O values for rainwater (or meteoric water as it is called by geologists) range from close to -50 per mil at the South Pole to close to zero per mil in some tropical areas. The observed ∂18O concentration in average annual precipitation is proportional to the mean annual air temperature. The isotopic composition of seawater does not only depend on temperature, but to a larger degree on other factors like continental ice volume.
Now: In samples from deep sea sediments off the coast of Portugal analysis of the oxygen content of bottom-dwelling microorganisms pointed to temperatures at the Antarctic, while the oxygen content in microorganisms, that had lived near the surface, was more like in Greenland ice cores.
Apart from a story about temperatures and ice caps. this also told that the surface current came from the north (Greenland) and the bottom current came from the south (Antarctic Bottom Water, AABW - and NOT North Atlantic Deep Water. NADW - see my post on the Gulf Stream).
There is, for example, a pressing need to understand the mechanisms of rapid climate change. Research in that direction is reported in the journal Science vol. 317 of 27 July 2007 under the title Four Climate Cycles of Recurring Deep and Surface Water Destabilizations on the Iberian Margin. Let me quote one of the easier sentences in that important report: “In these cores, the ∂18O record of benthic foraminifera resembled the Antarctic temperature signal, whereas the ∂18O of planktic foraminifera exhibited changes similar to those found in Greenland ice cores.”
We are talking about deep sea sediment cores taken off the cost of Southern Portugal (that is what is called the Iberian margin in the title). The data collected made it possible to construct a detailed picture of the climate history of the past 420,000 years - that is covering four climate cycles each of around 100,000 years.
I have the impression that most of my readers are geologists having no problems with the sentence I quoted. I, for myself, happened once upon a time to have taken a one year university course in oceanography, so I have no problem either. If however you don’t know anything about foraminifera, benthos, plankton, and isotopes (like ∂18O), you may have a serious problem with this in itself simple sentence.
Foraminifera are microorganisms living in the sea. They typically produce a calcareous shell (called a test) composed of calcium cabonate. When they die their shells sink to the bottom of the ocean to become a substantial part of the deep sea sediments. Foraminifera have been studied more extensively than any other group of oceanic microfossils. The microscopic formaninifera are the most important for sediemtological studies, although larger foraminifera (up to 16 mm) do exist. See my post on Ocean Drilling for Earth's Climate History.
Some foraminifera are bottom-dwelling. Organisms which live on, in, or near the seabed are called Benthos. So
benthic foraminifera are bottom-dwelling microorganisms.
Other foraminifera drift with ocean currents. They are plankton. So planktic foraminifera live in surface water.
When their shells sink to the bottom of the ocean they will end up in sediment layers side by side with shells of bottom-dwelling foraminifera, which make them ideal for study of (currents in) surface waters and deepsea waters at a specific time.
The chemical formula for calcium carbonate is CaCO3 (calcium + carbon + oxygen). Here we shall concentrate on the oxygen. The oxygen is extracted from water, H2O (hydrogen + oxygen).
Oxygen isotopes. Isotopes are not necessarily radioactive. Isotopes of an element have nuclei with the same number of protons but different numbers of neutrons. Oxygen has seventeen known isotopes. Three are stable, 16O, 17O, and 18O, of which 16O is the most abundant (over 99.7%). That they are stable means that they don’t change after their formation. Oxygen-16 or 16O has 8 protons and 8 neutrons, whereas Oxygen-18 has 8 protons and 10 neutron, which makes it heavier. Oxygen isotope analysis considers the ratio of O-18 to O-16 present in a core sample taken from deposits in the ocean floor. In fact it is more like a ratio of a ratio, because the delta values (∂18O) are calculated on the basis of ratios of the ratio of oxygen-16 and oxygen-18 in the sample and the ratio of oxygen-16 and oxygen-18 in average ocean water (Standard Mean Ocean Water, SMOW).
Today the ∂18O values for rainwater (or meteoric water as it is called by geologists) range from close to -50 per mil at the South Pole to close to zero per mil in some tropical areas. The observed ∂18O concentration in average annual precipitation is proportional to the mean annual air temperature. The isotopic composition of seawater does not only depend on temperature, but to a larger degree on other factors like continental ice volume.
Now: In samples from deep sea sediments off the coast of Portugal analysis of the oxygen content of bottom-dwelling microorganisms pointed to temperatures at the Antarctic, while the oxygen content in microorganisms, that had lived near the surface, was more like in Greenland ice cores.
Apart from a story about temperatures and ice caps. this also told that the surface current came from the north (Greenland) and the bottom current came from the south (Antarctic Bottom Water, AABW - and NOT North Atlantic Deep Water. NADW - see my post on the Gulf Stream).
- http://www.sciencemag.org/cgi/content/short/317/5837/502
- http://www.pro-physik.de/Phy/leadArticle.do?laid=9352 (in German)
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By 11thhouraction, # 3. August 2007, 16:50:53