Name: sea surface temperature from alkenone ratios
Uploaded: 2023-04-30T06:47:01.000Z
Duration: 10 min 10 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.2.3

an-overview-of-alkenone-biomarker-analysis-for-paleothermometry

An Overview of Alkenone Biomarker Analysis for Paleothermometry

<div class="chapter_text" id="script_0">
Paleothermometry is the calculation of past temperatures by analysis of specific chemicals in natural samples, like those left behind by prehistoric algae.
Algae are a diverse group of organisms that have been abundant in Earth&#39;s oceans and lakes for millennia. Certain chemical compounds, which are deposited in sediment by ancient algae, act as biomarkers &#8211; organic compounds that can provide researchers with valuable insight into Earth&#8217;s history. In fact, analysis of algal biomarker content in sediment allows researchers to determine the Earth&#8217;s temperature hundreds of millions of years ago.
One such record comes from some species of coccolithophores. These algae produce varying amounts of alkenones, a class of robust biomarkers, based on the temperature of their environment. Alkenone analysis is primarily used to calculate the sea surface temperature of Earth&#39;s oceans eons and eons ago.
This video will illustrate the use of alkenones in paleoclimatology and describe the process of isolating, purifying, and analyzing alkenones to calculate past sea surface temperature.
</div>
<div class="chapter_text" id="script_1">
As its name implies, &#8220;Alkenone paleothermometry&#8221; is based on the analysis of lipids, known as&#160;alkenones.&#160;Alkenone paleothermometry is based on alkenones; long-chain, unsaturated alkyl ketones that contain 37 carbon atoms and 2 to 4 double bonds. Each double bond is a site of unsaturation. At low sea surface temperatures, alkenone producers generate more unsaturated alkenones than saturated. The ratio of saturation to unsaturation is known as the Alkenone Unsaturation Index.
The alkenones usually evaluated are C37:2&#160;and C37:3, which have 37 carbons and two or three double bonds, respectively. The Unsaturation Index of these alkenones, or the UK&#39;37, is positively related to sea surface temperature. The analytical method know as gas chromatography is generally sensitive enough to separate these alkenones from one another. However, alkenone-producing algae often also generate chemically-similar fatty acid methyl esters, or alkenoates, which cannot be distinguished from alkenones using this technique.&#160;Hydrocarbon contamination from pollution may also further muddy chromatographic analysis. To accurately determine relative alkenone concentration, alkenoates and unknown hydrocarbons must be removed before analysis by the methods of saponification and urea adduction.
Now that the relationship of sediment alkenone ratios to sea surface temperature has been reviewed, let&#39;s look at the techniques for their purification from a total lipid extract and analysis of the unsaturation ratio.
</div>
<div class="chapter_text" id="script_2">
Once marine sediment has been collected and extracted, the total lipid extract, or TLE, must go through a multistep purification process, and analyzed. First, the extract undergoes saponification to convert alkenoates into carboxylate salts and methanol using a strong base and heat. Other fatty acid esters present in the TLE will be saponified into salts and glycerol.
After cooling the mixture to room temperature, an aqueous salt solution is added to form salts and glycerol. The mixture is then acidified to protonate the carboxylate anions, producing fatty acids. Finally, the alkenones and fatty acids are extracted from the mixture with hexane.
Silica gel chromatography is then performed to remove both apolar compounds and the polar fatty acids produced by saponification. The dried and saponified TLE is dissolved in hexane and then loaded onto a column. Silica retains polar compounds more strongly than apolar ones.
First, apolar compounds are removed with an apolar solvent, like hexane. Next, alkenones are eluted by a moderately polar solvent, such as dichloromethane, leaving the highly polar fatty acids and other unwanted polar compounds on the column.
If the original sediment sample was collected from a highly polluted area, urea adduction is performed to remove any remaining highly branched or cyclic hydrocarbons. The dried mid-polarity fraction is dissolved in a solvent mixture in which the strongly polar urea is minimally soluble, such as DCM and hexane. A concentrated solution of urea in methanol is then added to the TLE, causing urea crystals to precipitate.
Straight-chain molecules such as alkenones fit into the spaces between molecules in the urea crystal lattice, but highly branched and cyclic molecules do not, and are expelled.
Once crystal growth has finished, the urea crystals are dried and then washed with an apolar solvent to remove expelled compounds. Then, the crystals are dissolved in a small amount of water. The alkenones are extracted from the water with an apolar solvent for analysis.
</div>
<div class="chapter_text" id="script_3">
While all previous purification steps did not differentiate between alkenone species, small differences in boiling point and molecular structure are sufficient for separation on a gas chromatography column. When paired with a flame-ionization detector, relative concentrations of the&#160;alkenones, can be determined.
Molecules are identified on the chromatogram by their retention time, or the time needed for the compound to be exit the column. The retention times of the desired compounds are ascertained with alkenone standards.
The relative concentrations of the alkenones are determined from analysis of the areas under the peaks of interest. The UK&#39;37&#160;value is then calculated from the concentrations of C37:2and C37:3&#160;in the sample. With the sea surface temperature proxy relationship and the UK&#39;37&#160;value, the analyst can solve for sea surface temperature at the time of the sediment deposition.
</div>
<div class="chapter_text" id="script_4">
Many different facets of Earth&#39;s history can be investigated by analysis of sediment and sedimentary rock.
Biostratigraphy is the study of determining the ages of layers, or strata, of rock by analysis of the fossils present. As there are many sources of sediment, sedimentary rocks from the same time period may have dramatically different compositions around the world. Certain sets of species throughout Earth&#39;s history, such as the ammonites, existed worldwide and underwent rapid evolution. If visually dissimilar rock strata both contain the same species of ammonite, then a temporal correlation between the strata can be drawn. When combined with techniques such as paleothermometry, extensive information about Earth&#39;s history can be determined from fossil records in natural samples.
Many species of foraminifera, or forams, are found in marine sediments worldwide. Forams have calcium carbonate shells and have existed throughout Earth&#39;s oceans for millions of years. Many species&#160;live on the ocean floor, and thus can provide temperature information about deeper parts of the ocean. The magnesium to calcium ratio of forams&#160;corresponds to temperature, as they incorporate more magnesium into their shells in warmer climates. The multitude of species and the abundance of forams makes their fossil record useful for tracking changes in ocean currents throughout Earth&#39;s history and for biostratigraphy.
As tectonic plates diverge, new rock forms between them. Correspondingly, the properties of the rock surrounding a divergent plate boundary provide information about plate movements over time. For instance, changes in Earth&#39;s magnetic field are preserved in some minerals found in fossils, rock, and sediment. The discovery of symmetric changes in magnetism about mid-ocean ridges significantly contributed to the current understanding of seafloor spreading and plate tectonics.
</div>
<div class="chapter_text" id="script_5">
You&#39;ve just watched JoVE&#39;s Overview of Alkenone Paleothermometry. You should now understand the principles of paleothermometry and the relationship of alkenone ratios in marine sediment to sea surface temperature. The following videos in this series will go into more detail about this complex process.
Thanks for watching!
</div>

an overview of alkenone biomarker analysis for paleothermometry

Source: Laboratory of Jeff Salacup&#160;- University of Massachusetts Amherst
Throughout this series of videos, natural samples were extracted and purified in search of organic compounds, called biomarkers, that can relate information on climates and environments of the past. One of the samples analyzed was sediment. Sediments accumulate over geologic time in basins, depressions in the Earth into which sediment flows through the action of fluid (water or air), movement, and gravity. Two main types of basins exist, marine (oceans and seas) and lacustrine (lakes). As one might guess, very different types of life live in these settings, driven in large part by the difference in salinity between them. Over the last few decades, organic geochemists discovered a toolbox of biomarker proxies, or compounds that can be used to describe climate or environment, some of which work in marine environments and some of which work in lacustrine. We turn our attention here to the marine realm and alkenone paleothermometry using the Uk&#39;37 sea surface temperature proxy.
The most well-established and widely applied open-ocean biomarker sea surface temperature (SST) proxy is Uk&#39;37.
Uk&#39;37 = (C37:2) / (C37:2 + C37:3) (see Herbert1 for a review)
The index is based on the ratio of two polyunsaturated long-chain alkyl ketones, called alkenones, produced by some classes of haptophyte algae2,3. Culture4,5&#160;and core-top sediment6&#160;calibration studies led to the development of the Uk&#39;37 Index as a quantitative SST proxy. Amazingly, the culture-based calibration of Prahl et al.4:
Uk&#39;37 = 0.034(SST) + 0.039,
And the core-top calibration of M&#252;ller et al.6,
Uk&#39;37 = 0.033(SST) + 0.044,
are statistically identical.
Reconstructed Uk&#39;37 temperatures correlate best with mean annual SST for a variety of climate and haptophyte production regimes in the global ocean7. Alkenones are detected in marine sediment cores of early Eocene to modern age8, and in exposed outcrops of uplifted marine sediment9&#160;suggesting they are very stable over geologic time, and thus useful as a paleoclimate tool. Uk&#39;37 has been used to document paleo sea surface temperature changes at decadal10&#160;to orbital11,12&#160;timescales and are therefore very versatile.
In the open ocean, the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica are responsible for most alkenone production. It is not yet known why these haptophytes alter the unsaturation ratio of alkenones based on growth temperature. It was initially thought that alkenones were components of haptophyte cell walls and that their unsaturation was adjusted in order to keep the membrane fluid, much like saturated fats are solid at room temperature, while unsaturated fats are fluid. However, experiments aimed at this question found that instead of being associated with the cell membranes, alkenones were associated with energy storage structures inside the cell. Thus, their use inside the cell remains an open question.
Recently, alkenones have been found in lacustrine environments. However, their utility has so far been limited. Different alkenone producers than those in the marine realm dwell in lakes and thus the calibration between water temperature and unsaturation (Uk&#39;37) is different. Moreover, this calibration is different between lakes, making the creation of a &#39;global&#39; calibration unlikely. Unfortunately, the creation of local calibrations is expensive and time consuming and so the future for Uk&#39;37 in lakes is also currently limited.
Alkenones are usually extracted from marine sediments. Very often the same organisms that produce alkenones produce fatty acid methyl esters of those alkenones called alkenoates. These compounds co-elute with the alkenones on a gas chromatograph and complicate their quantification. Therefore, these extracts will often undergo a saponification to remove alkenoates. Because the saponification produces carboxylic acids that are not gas chromatograph amenable, a silica gel column must be performed after the saponification to remove the carboxylic acids from the extract. The alkenones come out in the middle polarity ketone fraction that elutes in dichloromethane while the acids are left on the column. Lastly, in extreme cases, such as in sediments acquired from highly polluted areas, like estuaries near industrial centers, a urea adduction may also be required to remove unknown compounds that coelute with the alkenones on the gas chromatograph.
Once the total lipid extract is purified, the extracted and purified sample is run on a gas chromatograph coupled to a flame ionizing detector. The relative concentration of the two alkenones is determined by obtaining the area under the curve for each of the compounds on computer software designed for just this purpose (such as Agilent Chemstation). These areas are then put into the Uk&#39;37 ratio equation shown above to get a Uk&#39;37 value that ranges between 0 and 1. These Uk&#39;37 values are then mapped to sea surface temperature value using a calibration such as those described above.
<div class="chapter_text" id="script_0">
Paleothermometry is the calculation of past temperatures by analysis of specific chemicals in natural samples, like those left behind by prehistoric algae.
Algae are a diverse group of organisms that have been abundant in Earth&#39;s oceans and lakes for millennia. Certain chemical compounds, which are deposited in sediment by ancient algae, act as biomarkers &#8211; organic compounds that can provide researchers with valuable insight into Earth&#8217;s history. In fact, analysis of algal biomarker content in sediment allows researchers to determine the Earth&#8217;s temperature hundreds of millions of years ago.
One such record comes from some species of coccolithophores. These algae produce varying amounts of alkenones, a class of robust biomarkers, based on the temperature of their environment. Alkenone analysis is primarily used to calculate the sea surface temperature of Earth&#39;s oceans eons and eons ago.
This video will illustrate the use of alkenones in paleoclimatology and describe the process of isolating, purifying, and analyzing alkenones to calculate past sea surface temperature.
</div>
<div class="chapter_text" id="script_1">
As its name implies, &#8220;Alkenone paleothermometry&#8221; is based on the analysis if lipids, known as alkenones Alkenone paleothermometry is based on alkenones; long-chain, unsaturated alkyl ketones that contain 37 carbon atoms and 2 to 4 double bonds. Each double bond is a site of unsaturation. At low sea surface temperatures, alkenone producers generate more unsaturated alkenones than saturated. The ratio of saturation to unsaturation is known as the Alkenone Unsaturation Index.
The alkenones usually evaluated are C37:2 and C37:3, which have 37 carbons and two or three double bonds, respectively. The Unsaturation Index of these alkenones, or the UK&#39;37, is positively related to sea surface temperature. The analytical method know as gas chromatography is generally sensitive enough to separate these alkenones from one another. However, alkenone-producing algae often also generate chemically-similar fatty acid methyl esters, or alkenoates, which cannot be distinguished from alkenones using this technique.&#160;Hydrocarbon contamination from pollution may also further muddy chromatographic analysis. To accurately determine relative alkenone concentration, alkenoates and unknown hydrocarbons must be removed before analysis by the methods of saponification and urea adduction.
Now that the relationship of sediment alkenone ratios to sea surface temperature has been reviewed, let&#39;s look at the techniques for their purification from a total lipid extract and analysis of the unsaturation ratio.
</div>
<div class="chapter_text" id="script_2">
Once marine sediment has been collected and extracted, the total lipid extract, or TLE, must go through a multistep purification process, and analyzed. First, the extract undergoes saponification to convert alkenoates into carboxylate salts and methanol using a strong base and heat. Other fatty acid esters present in the TLE will be saponified into salts and glycerol.
After cooling the mixture to room temperature, an aqueous salt solution is added to form salts and glycerol. The mixture is then acidified to protonate the carboxylate anions, producing fatty acids. Finally, the alkenones and fatty acids are extracted from the mixture with hexane.
Silica gel chromatography is then performed to remove both apolar compounds and the polar fatty acids produced by saponification. The dried and saponified TLE is dissolved in hexane and then loaded onto a column. Silica retains polar compounds more strongly than apolar ones.
First, apolar compounds are removed with an apolar solvent, like hexane. Next, alkenones are eluted by a moderately polar solvent, such as dichloromethane, leaving the highly polar fatty acids and other unwanted polar compounds on the column.
If the original sediment sample was collected from a highly polluted area, urea adduction is performed to remove any remaining highly branched or cyclic hydrocarbons. The dried mid-polarity fraction is dissolved in a solvent mixture in which the strongly polar urea is minimally soluble, such as DCM and hexane. A concentrated solution of urea in methanol is then added to the TLE, causing urea crystals to precipitate.
Straight-chain molecules such as alkenones fit into the spaces between molecules in the urea crystal lattice, but highly branched and cyclic molecules do not, and are expelled.
Once crystal growth has finished, the urea crystals are dried and then washed with an apolar solvent to remove expelled compounds. Then, the crystals are dissolved in a small amount of water. The alkenones are extracted from the water with an apolar solvent for analysis.
</div>
<div class="chapter_text" id="script_3">
While all previous purification steps did not differentiate between alkenone species, small differences in boiling point and molecular structure are sufficient for separation on a gas chromatography column. When paired with a flame-ionization detector, relative concentrations of the&#160;alkenones, can be determined.
Molecules are identified on the chromatogram by their retention time, or the time needed for the compound to be exit the column. The retention times of the desired compounds are ascertained with alkenone standards.
The relative concentrations of the alkenones are determined from analysis of the areas under the peaks of interest. The UK&#39;37 value is then calculated from the concentrations of C37:2and C37:3 in the sample. With the sea surface temperature proxy relationship and the UK&#39;37 value, the analyst can solve for sea surface temperature at the time of the sediment deposition.
</div>
<div class="chapter_text" id="script_4">
Many different facets of Earth&#39;s history can be investigated by analysis of sediment and sedimentary rock.
Biostratigraphy is the study of determining the ages of layers, or strata, of rock by analysis of the fossils present. As there are many sources of sediment, sedimentary rocks from the same time period may have dramatically different compositions around the world. Certain sets of species throughout Earth&#39;s history, such as the ammonites, existed worldwide and underwent rapid evolution. If visually dissimilar rock strata both contain the same species of ammonite, then a temporal correlation between the strata can be drawn. When combined with techniques such as paleothermometry, extensive information about Earth&#39;s history can be determined from fossil records in natural samples.
Many species of foraminifera, or forams, are found in marine sediments worldwide. Forams have calcium carbonate shells and have existed throughout Earth&#39;s oceans for millions of years. Many species&#160;live on the ocean floor, and thus can provide temperature information about deeper parts of the ocean. The magnesium to calcium ratio of forams&#160;corresponds to temperature, as they incorporate more magnesium into their shells in warmer climates. The multitude of species and the abundance of forams makes their fossil record useful for tracking changes in ocean currents throughout Earth&#39;s history and for biostratigraphy.
As tectonic plates diverge, new rock forms between them. Correspondingly, the properties of the rock surrounding a divergent plate boundary provide information about plate movements over time. For instance, changes in Earth&#39;s magnetic field are preserved in some minerals found in fossils, rock, and sediment. The discovery of symmetric changes in magnetism about mid-ocean ridges significantly contributed to the current understanding of seafloor spreading and plate tectonics.
</div>
<div class="chapter_text" id="script_5">
You&#39;ve just watched JoVE&#39;s Overview of Alkenone Paleothermometry. You should now understand the principles of paleothermometry and the relationship of alkenone ratios in marine sediment to sea surface temperature. The following videos in this series will go into more detail about this complex process.
Thanks for watching!
</div>

Source: Laboratory of Jeff Salacup&#160;- University of Massachusetts Amherst
Throughout this series of videos, natural samples were extracted and ...

Paleothermometry is the calculation of past temperatures by analysis of specific chemicals in natural samples, like those left behind by prehistoric algae.Algae are a diverse group of organisms that have been abundant in Earth's oceans and lakes for millennia. Certain chemical compounds, which are deposited in sediment by ancient algae, act as biomarkers ? organic compounds that can provide researchers with valuable insight into Earth?s history. In fact, analysis of algal biomarker content in sediment allows researchers to determine the Earth?s temperature hundreds of millions of years ago.One such record comes from some species of coccolithophores. These algae produce varying amounts of alkenones, a class of robust biomarkers, based on the temperature of their environment. Alkenone analysis is primarily used to calculate the sea surface temperature of Earth's oceans eons and eons ago.This video will illustrate the use of alkenones in paleoclimatology and describe the process of isolating, purifying, and analyzing alkenones to calculate past sea surface temperature.As its name implies, ?Alkenone paleothermometry? is based on the analysis of lipids, known as?alkenones.?Alkenone paleothermometry is based on alkenones; long-chain, unsaturated alkyl ketones that contain 37 carbon atoms and 2 to 4 double bonds. Each double bond is a site of unsaturation. At low sea surface temperatures, alkenone producers generate more unsaturated alkenones than saturated. The ratio of saturation to unsaturation is known as the Alkenone Unsaturation Index.The alkenones usually evaluated are C37:2?and C37:3, which have 37 carbons and two or three double bonds, respectively. The Unsaturation Index of these alkenones, or the UK'37, is positively related to sea surface temperature. The analytical method know as gas chromatography is generally sensitive enough to separate these alkenones from one another. However, alkenone-producing algae often also generate chemically-similar fatty acid methyl esters, or alkenoates, which cannot be distinguished from alkenones using this technique.?Hydrocarbon contamination from pollution may also further muddy chromatographic analysis. To accurately determine relative alkenone concentration, alkenoates and unknown hydrocarbons must be removed before analysis by the methods of saponification and urea adduction.Now that the relationship of sediment alkenone ratios to sea surface temperature has been reviewed, let's look at the techniques for their purification from a total lipid extract and analysis of the unsaturation ratio.Once marine sediment has been collected and extracted, the total lipid extract, or TLE, must go through a multistep purification process, and analyzed. First, the extract undergoes saponification to convert alkenoates into carboxylate salts and methanol using a strong base and heat. Other fatty acid esters present in the TLE will be saponified into salts and glycerol.After cooling the mixture to room temperature, an aqueous salt solution is added to form salts and glycerol. The mixture is then acidified to protonate the carboxylate anions, producing fatty acids. Finally, the alkenones and fatty acids are extracted from the mixture with hexane.Silica gel chromatography is then performed to remove both apolar compounds and the polar fatty acids produced by saponification. The dried and saponified TLE is dissolved in hexane and then loaded onto a column. Silica retains polar compounds more strongly than apolar ones.First, apolar compounds are removed with an apolar solvent, like hexane. Next, alkenones are eluted by a moderately polar solvent, such as dichloromethane, leaving the highly polar fatty acids and other unwanted polar compounds on the column.If the original sediment sample was collected from a highly polluted area, urea adduction is performed to remove any remaining highly branched or cyclic hydrocarbons. The dried mid-polarity fraction is dissolved in a solvent mixture in which the strongly polar urea is minimally soluble, such as DCM and hexane. A concentrated solution of urea in methanol is then added to the TLE, causing urea crystals to precipitate.Straight-chain molecules such as alkenones fit into the spaces between molecules in the urea crystal lattice, but highly branched and cyclic molecules do not, and are expelled.Once crystal growth has finished, the urea crystals are dried and then washed with an apolar solvent to remove expelled compounds. Then, the crystals are dissolved in a small amount of water. The alkenones are extracted from the water with an apolar solvent for analysis.While all previous purification steps did not differentiate between alkenone species, small differences in boiling point and molecular structure are sufficient for separation on a gas chromatography column. When paired with a flame-ionization detector, relative concentrations of the?alkenones, can be determined.Molecules are identified on the chromatogram by their retention time, or the time needed for the compound to be exit the column. The retention times of the desired compounds are ascertained with alkenone standards.The relative concentrations of the alkenones are determined from analysis of the areas under the peaks of interest. The UK'37?value is then calculated from the concentrations of C37:2and C37:3?in the sample. With the sea surface temperature proxy relationship and the UK'37?value, the analyst can solve for sea surface temperature at the time of the sediment deposition.Many different facets of Earth's history can be investigated by analysis of sediment and sedimentary rock.Biostratigraphy is the study of determining the ages of layers, or strata, of rock by analysis of the fossils present. As there are many sources of sediment, sedimentary rocks from the same time period may have dramatically different compositions around the world. Certain sets of species throughout Earth's history, such as the ammonites, existed worldwide and underwent rapid evolution. If visually dissimilar rock strata both contain the same species of ammonite, then a temporal correlation between the strata can be drawn. When combined with techniques such as paleothermometry, extensive information about Earth's history can be determined from fossil records in natural samples.Many species of foraminifera, or forams, are found in marine sediments worldwide. Forams have calcium carbonate shells and have existed throughout Earth's oceans for millions of years. Many species?live on the ocean floor, and thus can provide temperature information about deeper parts of the ocean. The magnesium to calcium ratio of forams?corresponds to temperature, as they incorporate more magnesium into their shells in warmer climates. The multitude of species and the abundance of forams makes their fossil record useful for tracking changes in ocean currents throughout Earth's history and for biostratigraphy.As tectonic plates diverge, new rock forms between them. Correspondingly, the properties of the rock surrounding a divergent plate boundary provide information about plate movements over time. For instance, changes in Earth's magnetic field are preserved in some minerals found in fossils, rock, and sediment. The discovery of symmetric changes in magnetism about mid-ocean ridges significantly contributed to the current understanding of seafloor spreading and plate tectonics.You've just watched JoVE's Overview of Alkenone Paleothermometry. You should now understand the principles of paleothermometry and the relationship of alkenone ratios in marine sediment to sea surface temperature. The following videos in this series will go into more detail about this complex process.Thanks for watching!

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sea surface temperature from alkenone ratios

Sea surface temperature can be reconstructed from alkenone ratios preserved in marine sediment. Alkenones are long-chain, unsaturated alkyl ketones made by some haptophyte algae, especially coccolithophores such as Emiliania huxleyi and Gephyrocapsa oceanica in the open ocean. The most widely used proxy is the U K'37 index, which compares the C37:2 and C37:3 alkenones. Because the ratio changes with growth temperature, it can be used to estimate past sea surface temperature.

The U K'37 proxy was developed from both culture studies and core-top sediment calibration work. The culture-based relationship reported by Prahl and colleagues and the core-top relationship reported by Müller and colleagues are statistically very similar. Reconstructed U K'37 temperatures tend to match mean annual sea surface temperature across many ocean settings. Alkenones are also stable enough to be found in marine sediment cores from the early Eocene to modern deposits and in exposed outcrops of uplifted marine sediment. That long record makes them useful for studying climate change across both short and long time scales.

Scientists first thought alkenones were part of algal cell walls and helped control membrane fluidity, similar to how unsaturated fats stay fluid. Later work showed that alkenones are associated with energy storage structures inside the cell instead. Their exact role in the cell is still not fully known. Alkenones have also been found in lakes, but lacustrine use is more limited because the producers are different and the calibration between temperature and unsaturation changes from one lake to another. A single global lake calibration is unlikely, and making local calibrations takes time and money.

Marine sediment samples usually need several cleanup steps before analysis. Alkenone-producing algae often make alkenoates, which are fatty acid methyl esters that can co-elute with alkenones on a gas chromatograph and make quantification harder. To remove them, the total lipid extract is saponified, which converts the alkenoates into carboxylic acids and salts. The mixture is then acidified, and the resulting fatty acids are separated from the alkenones by silica gel chromatography. In polluted samples, such as sediment from estuaries near industrial centers, urea adduction may also be needed to remove unknown compounds that co-elute with the target molecules.

After purification, the sample is analyzed by gas chromatography with a flame ionization detector. The alkenones are identified by retention time using standards, and the areas under the peaks are used to determine the relative amounts of C37:2 and C37:3. Those values are inserted into the U K'37 equation to obtain a number between 0 and 1. A temperature calibration then converts that value into sea surface temperature at the time the sediment was deposited. This approach helps researchers study past ocean climates using biomarkers preserved in natural samples.

Alkenone paleothermometry is one part of a larger field of paleothermometry, which uses chemicals in sediments and rocks to estimate past temperatures. Algal biomarkers can preserve climate information from hundreds of millions of years ago. Sediment records can also be compared with other tools from Earth science, including biostratigraphy, which uses fossils to match rock layers by age. For example, ammonites can link separate strata, and foraminifera can provide temperature clues because their magnesium-to-calcium ratio changes with warmer water. Together with evidence from magnetism in rocks and sediment, these methods help scientists rebuild Earth’s history and track processes such as seafloor spreading and plate tectonics.

Sea Surface Temperature from Alkenone Ratios

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Igneous rocks form when hot liquid rock, called magma, cools and crystallizes. Magma temperatures typically range from about 800 °C to 1,200 °C. These rocks record the freezing of molten material inside Earth.

an overview of bgdgt biomarker analysis for paleoclimatology

an-overview-of-bgdgt-biomarker-analysis-for-paleoclimatology

Sediment Biomarkers for Past Climate Records

Sediment biomarkers can record past climate conditions, and branched GDGTs are one example used to study temperature in freshwater basins. These organic compounds are extracted from natural samples, purified, and then measured to help reconstruct environments from the past. In paleoclimatology, scientists use these records to better understand climate change over time. Sediments build up over geologic time in sedimentary basins, which are low areas in the Earth’s crust where material is...

Sea surface temperature can be reconstructed from alkenone ratios preserved in marine sediment. Alkenones are long-chain, unsaturated alkyl ketones made by some haptophyte algae, especially coccolithophores such as Emiliania huxleyi and Gephyrocapsa oceanica in the open ocean. The most widely used proxy is the U K'37 index, which compares the C37:2 and C37:3 alkenones. Because the ratio changes with growth temperature, it can be used to estimate past sea surface temperature. The U K'37 proxy...

sonication extraction of lipid biomarkers from sediment

sonication-extraction-of-lipid-biomarkers-from-sediment

How Organic Carbon Becomes Biomarkers

Organic material and inorganic material are chemically different. In an ecosystem, living material includes leaves, fungi, bark, and tissue. Non-living material includes rocks, their minerals, oxygen, water, and metals. Organic matter contains carbon linked to other carbon and hydrogen molecules, which sets it apart from inorganic matter. Carbon is especially flexible in the kinds of bonds it can form. Its valence range from -4 to +4 lets it make up to four separate covalent bonds with nearby...

soxhlet extraction of lipid biomarkers from sediment

soxhlet-extraction-of-lipid-biomarkers-from-sediment

Large-Volume Sediment Extraction for Standards

Large-volume sediment extraction is used to isolate compounds for chemical standards. These standards help labs track the performance, accuracy, and precision of instruments over time. That way, a measurement made today can be compared with one made a year later. Because standards must be checked over long periods, labs often need large amounts of material. Many chemical standards can be bought from companies such as Sigma-Aldrich and Fisher. But some natural compounds needed for paleoclimatic...

extraction of biomarkers from sediments - accelerated solvent extraction

extraction-of-biomarkers-from-sediments-accelerated-solvent-extraction

Sediment biomarkers can help scientists reconstruct past air and water temperatures. In this method, a group of organic biomarkers called glycerol-dialkyl glycerol-tetraethers, or GDGTs, is studied in modern sediments and in older sediment layers of known age. GDGTs are produced by a suite of archaea and bacteria. Their distribution changes in a predictable way in response to temperature. That pattern lets researchers use sediment records to track how climate changed over time. These...

conversion of fatty acid methyl esters by saponification for uk'37 paleothermometry

conversion-fatty-acid-methyl-esters-saponification-for-uk-37

Saponification for Cleaner GC-FID Analysis

Saponification helps clean up complex lipid samples before gas chromatography analysis. A total lipid extract, or TLE, from an organic solvent extraction can contain hundreds or even thousands of compounds. Researchers may only need a few target compounds. They may also need to remove unwanted material that gets in the way or co-elutes, meaning it comes off the gas chromatograph at the same time as another compound. This sample cleanup supports measurement on a gas chromatograph coupled to a...

purification of a total lipid extract with column chromatography

purification-of-a-total-lipid-extract-with-column-chromatography

Separating Lipid Classes by Column Chromatography

Column chromatography is used to separate lipid classes in a total lipid extract. A total lipid extract, or TLE, is often a complex mixture made up of hundreds or even thousands of compounds. Researchers may only need a few target compounds, so they remove the compounds they are not studying. Those target compounds can belong to different classes, including alkanes, ketones, alcohols, and acids. In some studies, a sample may contain many compounds, but only a small set matters for analysis.

removal of branched and cyclic compounds by urea adduction for uk'37 paleothermometry

removal-branched-cyclic-compounds-urea-adduction-for-uk-37

Urea Adduction Separates Lipid Shapes

Urea adduction separates straight-chain lipids from branched and cyclic compounds in a total lipid extract. Researchers use this step when they want only a small set of target molecules from a sample that may contain hundreds or even thousands of compounds. For paleothermometry, the target compounds are the alkenones used in U k'37 and the isoprenoidal glycerol dialkyl glycerol tetraethers, or GDGTs, used in MBT/CBT. Together, these organic paleothermometers depend on only six compounds: two...

earth science

This collection features topics ranging from geology to geochemistry; with a variety of demonstrations including physical and chemical properties of minerals and the analysis of rock formations. 

Learn how alkenone biomarkers in marine sediment are purified and measured with gas chromatography to estimate past sea surface temperature using the U K'37 proxy.

Sea Surface Temperature from Alkenone Ratios | JoVE K12

Pennsylvania State Academic Standards

Earth and Space Science

3.3.9-12.I

History of Earth

3.3.9-12.F

3.3.9-12.G

3.3.9-12.J

Weather and Climate

3.3.9-12.E

Louisiana Student Standards for Science

High School

Earth’s Systems

HS-ESS2-1

HS-ESS2-3

HS-ESS2-4

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Physical Geology

Minerals

properties-minerals-hardness-luster-cleavage-streak-crystal-shape

Properties of minerals (hardness, luster, cleavage, streak, crystal shape, fluorescence, flammability, density/specific gravity, malleability)

Earth's History

The geologic rock record

Plate Tectonics

Internal Earth

Historical review

Virginia  Standards of Learning

HIgh School

ES.5

ES.5.a

ES.9

ES.9.a

ES.10

ES.10.d

Texas Essential Knowledge and Skills

Earth Systems Science

112.49.c.11

112.49.c.11.E.

Alabama Course of Study Science

9-12.ESS.2.5.d

Florida Department of Education

SC.912.E.6

SC.912.E.6.3

SC.912.E.7

SC.912.E.7.7

Georgia Standards of Excellence

Geology

Geologic Time

SG3.a

new-york-state-science-learning-standards

New York State Science Learning Standards

Physical Science

HS. Structure and Properties of Matter

HS-PS1-10.

HS. Waves and Electromagnetic Radiation

HS-PS4-5.

Life Science

matter-and-energy-in-organisms-and-ecosystems

Matter and Energy in Organisms and Ecosystems

HS-LS1-6.

HS-LS2-4.

Earth and Space Sciences

HS-ESS2-2.

HS-ESS2-6.

HS-ESS2-7.

Jeff Salacup

Overview

Principles of Alkenone Paleothermometry

Alkenone Purification

Analysis of Relative Alkenone Concentrations

Applications

Summary

Igneous Volcanic Rock

Source: Laboratory of Alan Lester - University of Colorado Boulder
Igneous rocks are the products of cooling and crystallization of magma. Volcanic rocks ...

The Carbon Cycle

Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among ...

Igneous Intrusive Rock

Source: Laboratory of Alan Lester - University of Colorado Boulder
Igneous rocks are products of the cooling and crystallization of high temperature ...

Using Topographic Maps to Generate Topographic Profiles

Source: Laboratory of Alan Lester - University of Colorado Boulder
Topographic maps are &#34;plan-view&#34; representations of Earth&#39;s ...

Determining Spatial Orientation of Rock Layers with the Brunton Compass

Source: Laboratory of Alan Lester - University of Colorado Boulder
Most rock units exhibit some form of planar surfaces or linear features. Examples ...

Making a Geologic Cross Section

Source: Laboratory of Alan Lester - University of Colorado Boulder
Geologic maps were first made and utilized in Europe, in the mid-to-late 18th century. ...

Use models to explain how mantle convection powers plate tectonics.

ESS.EES.2.1

Analyze and interpret data to predict locations of volcanoes and earthquakes based on plate boundaries.

ESS.EES.2.2

Topographic Surveying and Contours

Topographic surveying is critical for documenting the Earth's surface, focusing on capturing elevations, slopes, and natural and man-made features. It is ...

Plotting of Topographic Maps

Topographic maps represent the Earth's surface features using contour lines, which connect points of equal elevation to create a two-dimensional ...

Methods of Obtaining Topography

Topography involves measuring and mapping land elevations, natural features, and artificial structures to create accurate representations of the terrain. ...

Use models to explain how plate tectonics influence topography.

The Soil Ecosystem

Plants obtain inorganic minerals and water from the soil, which acts as a natural medium for land plants. The composition and quality of soil depend not ...

Conditions on Early Earth

What are Biogeochemical Cycles?

The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited ...

The Water Cycle

The Earth&rsquo;s hydrosphere includes all of the areas where the storage and movement of water occurs. Since water is the basis of all living processes, ...

The Nitrogen Cycle

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of ...

The Phosphorus Cycle

Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, ...

The Sulfur Cycle

Sulfur, an important element in the chemical makeup of proteins, is recycled through the atmosphere and aquatic and terrestrial environments. Found in the ...

Bioremediation

Bioremediation is the use of prokaryotes, fungi, or plants to remove pollutants from the environment. This process has been used to remove harmful toxins ...

Carry out investigations to explain how the rock cycle and rates of weathering, erosion, and soil formation influence Earth's systems.

ESS.EES.2.4

What is Climate?

Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, &#8220;Climate is what you expect. ...

What is Weather?

Overview

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the ...

Variation of Atmospheric Pressure

Change in atmospheric pressure with height is particularly interesting. The decrease in atmospheric pressure with increasing altitude is due to the ...

/files/media/science-education/science-education-thumbs/14711.jpg

Analyze and interpret data to explain how volcanic activity influences changes in Earth's atmosphere, geosphere, biosphere, and hydrosphere.

ESS.EES.2.5

Analyze how the geosphere is shaped by plate tectonics and the rock cycle.

Sea Surface Temperature from Alkenone Ratios

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