User:Benjah-bmm27/degree/2/RDP

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Marine chemistry, RDP

"Marine Chemistry"

Physical oceanography
Chemical oceanography
Seawater, salinity: conservative ions (99.8% of ocean solutes) are nacklecamgsok: Na⁺, Cl⁻, Ca²⁺, Mg²⁺, SO₄²⁻, K⁺
Ocean current, hydrothermal circulation
Thermohaline circulation: halocline, thermocline, pycnocline, sea surface temperature
Upwelling
Carbon cycle
Redfield–Richards ratio in marine plankton – C:H:P – 106:16:1
Nitrification, Anammox, Sulfur assimilation, Denitrification, Methanogenesis
Remineralisation
Biological pump - faecal pellet packaging (particulate) and downwelling (dissolved) transport organic carbon from the surface to the deep ocean
Paleocene–Eocene Thermal Maximum
Methane clathrate
Archaeol
Sulfate-reducing bacteria
Dissolved inorganic carbon: CO₂, CO₃²⁻, HCO₃⁻, H₂CO₃, CaCO₃
Lysocline, Carbonate Compensation Depth
Ocean acidification, UNESCO ocean acidification FAQ
Biomarkers, haptophytes, dinoflagellates, diatoms, maitotoxin
Methanogens and methanotrophs are archaea and have ether lipid membranes
- they probably developed in warm conditions, so needed lipids resistant to acid hydrolysis – an ester lipid would not do
- ether lipids are used to trace methanogenic and methanotrophic archaea

Isorenieratene

Anoxygenic photosynthesis by Chlorobium (green sulfur bacteria):
- H₂S + CO₂ + hν → SO₄²⁻ + organic C
- needs reduced sulfur so strictly anaerobic, but also needs light – rare combination of conditions, found in very stratified water columns (constrained basin with fresh water flowing in to achieve sharp density gradient), e.g. the Black Sea
- Lives ~100 m depth, so wavelength of sunlight is altered, ∴ uses its own special light harvesting pigment, isorenieratene:
- Brocks & Summons, Nature 437, 866-870: "Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea"
- Indicator of photic zone anoxia (Isorenieratene Biosynthesis in Green Sulfur Bacteria (2008))
Anoxic event

Anammox

Also from the anoxic Black Sea – anammox:
- NH₄⁺ + NO₂⁻ → (intermediates: N₂H₄, NH₂OH) → N₂ + 2H₂O
- Membrane lipids of planctomycetes: ladderanes e.g. pentacycloanammoxic acid from Brocadia anammoxidans, stack flat making an impermeable membrane to keep toxic intermediates isolated inside anammoxosome

Alkenones

E. huxleyi (a haptophyte) uses alkenones as membrane lipids:

In colder seas, it makes more triunsaturated alkenone (37:3) which is more kinked as so remains fluid at low temperatures
In warmer seas, it makes for diunsaturated alkenone (37:2), which is less kinked and would solidify in the cold
Use ratio of the two alkenones as a proxy for sea surface temperature: $U_{37}^{K}={\frac {37:2}{37:2+37:3}}$
First work on alkenones for SST done in Bristol in the 1980s:
- Br. Phycol. J. (1980) 19, 2619-2622
- Phys. Chem. Earth (1980) 12, 219-227
- Nature (1986) 320, 129-133
- Org. Geochem. (1988) 13, 727-734 – C₃₇ alkenones unexpectedly have all-trans (E) stereochemistry
Further reading:

37:2 (15E,22E)-heptatriaconta-15,22-dien-2-one, C₃₇H₇₀O:

37:3 (8E,15E,22E)-heptatriaconta-8,15,22-trien-2-one, C₃₇H₆₈O:

Tetraether lipids

Pelagic crenarchaea use tetraether lipids, which they adapt to different temperatures:
- more rings help membranes stack at stay well-ordered at high temperatures
- fewer rings help disorder membranes, so they don't freeze at low temperatures

News reports

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