Shulou(Shulou.com)11/24 Report--

The weather is cold, we will put on thick clothes to keep warm. Similarly, when other creatures on earth feel the changes in the external environment, they will also add or subtract their "clothes" to adapt to the changes in the temperature of the environment. The behind-the-scenes contributors to this process are the magic elements we are going to introduce today. So how on earth did they do it, and what use are they for us to explore the mysteries of the ancient environment?

Where are the magic molecules? Let's start with long-chain ketenes.

1. When Coccolithophores mentions long-chain ketene, it has to mention its parent material source-Chlorophyta. In 1836, Ehrenberg first discovered stone algae in the Baltic Sea, and then scientists discovered various types of stone algae in the oceans all over the world. Calcareous algae, also known as Chlorella, is a kind of widespread marine algae, which belongs to single-celled calcareous phytoplankton, living in the upper sea water less than 200 meters. Most of the lithophytes are autotrophs that photosynthesize with the help of carbon dioxide, nitrates and other non-organic salts in sunlight and water. The algae vary in size (5-100 μ m in diameter) and have unique morphological characteristics, with cells and organic matter inside, while the outside is surrounded by many disc-shaped calcium carbonate "bones" (pebbles) with unique patterns.

Schematic diagram of the algae and its cellular structure (Billard & Innouye, 2004) when the cells of the algae die, part of the cells in the body decay and decompose, while the calcareous "bones" will sink to the bottom of the sea with impurities in water or biological feces, and gradually form fossils, which will be preserved in marine sediments for a long time, leaving clues for us to explore the paleo-marine environment.

2. Long-chain ketene long-chain ketene (LCAs, long-chain alkenones) is a long-chain unsaturated methyl or ethyl ketone (C37-C39) with 2 to 4 double bonds, which is mainly produced from the cytoplasm and cell membrane of a few species of lithophytes, of which the main contributors are Emiliania huxleyi and Gephyrocapsa oceanica. These two kinds of algae belong to wide temperature (adapt to a wide range of temperatures for life) and are widely distributed in the world's oceans. For example, the temperature range of Huxley algae is 2-29 ℃. According to the temperature of living water, it can be divided into polar type, cold water type and warm water type. The distribution of long-chain ketene determines that long-chain ketene also exists in every sea area of the world.

In life, we may notice that when the weather is cold, animal oils tend to solidify more easily than vegetable oils. This phenomenon occurs not only because the freezing points of the two are different, but also because animal fats contain more fat, mainly saturated fatty acids, which are easy to solidify, while vegetable oils contain more oil. oil molecules contain high levels of unsaturated fatty acids (that is, relatively more unsaturated bonds) and are not easy to solidify. In that case, the same is true of the cell membrane of Schizophyllum. When the ambient temperature changes, in order to maintain the fluidity of the cell membrane, it will adjust the proportion of unsaturated bonds of ketones in the process of biosynthesis to adapt to external changes. At high latitudes, when the sea surface temperature is low, the algae tend to synthesize more unsaturated bonds of C37V3 and C37R4 to maintain the fluidity of the cell membrane. However, at low latitudes, the sea surface temperature is higher, and the algae synthesize a large number of C37glucons with fewer unsaturated bonds. This is like Harbin's "cotton-padded jacket and body feel especially cold", my "T-shirt shorts are still too hot" in Sanya. It is this characteristic of C37 Ketene that makes the unsaturation of C37 ketene a good index to indicate the change of water temperature.

Long-chain ketene molecular structure diagram long-chain ketene unsaturation usually refers to the unsaturation of long-chain ketene containing 37 carbon atoms, expressed as or. Among them, U refers to unsaturated (Unsaturation), K refers to ketone (Ketone or Alkeno-ne), 37 refers to the number of carbon atoms of long-chain ketene. In practical application, the calculation formula is as follows:

That is, the proportion of C37GRV 2.

The experiment shows that

It has a very good corresponding relationship with the global sea surface temperature, and has a good application in both warm (28 °C) and cold (- 6 °C) sea areas. However, because the growth of calcareous algae is also controlled by environmental factors other than temperature,

The linear relationship between the sea surface temperature and the sea surface temperature is not completely consistent and needs to be determined according to the actual situation.

The relationship between the measured water temperature and the measured water temperature of the surface mixed layer (0-30m) (Conte, 2006, GGG)

However, this does not affect the wide application of the indicators in the global sea area. From a spatial point of view, the indicators can be applied to global sea areas, depicting a unique picture of different sea areas. In terms of time, the indicators can span the time scale of millions or even tens of millions of years, telling the magnificence of climate evolution.

Seeing here, you should know something about this magical molecule, right? Although long-chain ketene can not be seen or touched, through organic extraction experiments and testing instruments, we can determine its existence, and make use of the relationship between its unsaturation and sea surface temperature to establish a "paleo-ocean thermometer". Tracing back to the changes of sea water temperature in the past few million years, it provides a valuable "historical file" for scientists to study the changes of the earth's land and sea and climate. It seems that the magic of this molecule is that it tells the story of climate change in the transformation of undressing and dressing.

The figure is based on the estimated sea surface temperature (Herbert, et al, 2010, science) Reference of four sites measured by ketene paleotemperature.

[1] Billard C, Inouye I. What is new in coccolithophore biology? [M] / / Coccolithophores. Springer, Berlin, Heidelberg, 2004: 1-29.

Conte M H, Sicre M A, R ü hlemann C, et al. Global temperature calibration of the alkenone unsaturation index () in surface waters and comparison with surface sediments [J]. Geochemistry, Geophysics, Geosystems, 2006, 7 (2).

[3] Herbert T D, Peterson L C, Lawrence K T, et al. Tropical ocean temperatures over the past 3.5 million years [J]. Science, 2010, 328 (5985): 1530-1534.

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Zhixing

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