Altklausurfragen

• fold belts (Appalachians - Caledonides)

• Age provinces: geological age provinces are found on different continents )e.g. Precambrium rocks of Soth American and African shields can be correlated across the Atlantic

• Igneous provinces: Similarity of belts of extrusive and intrusive rocks (e.g. South Africa, Antarctica and Tasmania)

• Stratigraphic sections

• Metallogenic provinces: Similarities of natural mineral depositts (e.g. Mn, Fe, Au, Zn)

• Fossils of tropic plants found in Antarctica, South South America and Australia

• Marsupials show similar species until 100 Ma ago; Later: diverging development in South America and Australia

• Found and described by Marie Tharp

• V-shaped structure running continuously through the axis of MORs indicated rift valley characteristics

• Suggests that the rift valley was formed when new material welled up to the surface, pushing either side of the ridge apart

• everywhere on earth the magnetic field has a well defined direction

• however, true north and magnetic north have an offset which is called magnetic declination

• as the earths magnetic field changes orientation over large timescales, the orientation of newly formed freezes the current orientation at time of cooling

• the magnetic field reverses randomly (183x in 83 Ma)

• patterns on both sides of the MORs are identicl

The seismic activity patterns align with Marie Tharps map of tectonic plates.

• geometric fit of continents

• Paleontological evidence: identical or similar fossil assemblages found

• Geological: features like mountain ranges could be correlated across vast distances

• Glacial: glaciers once covered areas that are now sperated by oceans

• Paleoclimatic: climates are inconsistent with current locations of continents (e.g. fossils of tropical plants in Antarctica)

• North American Plate

• Pacific Plate

• Eurasian Plate

• Australien Plate

• South American Plate

• African Plate

• Antarctic Plate

• Nazca Plate

• Indian Plate

• Arabien Plate

• (Caribbean Plate)

• (Cocos Plate)

• (Scotia Plate)

• (Filipino Plate)

• Continental/Oceanic Crust

• Lithosphere (Crust and uppermost solid Mantle)

• Asthenosphere

• Mantle

• Outer Core

• Inner Core

• GPS -> gives information about speed and direction

• Volcanic islands tell us how the plates moved above hot spots (age of rocks is important)

10-40mm/yr but some make it up to 160mm per year

• Convergent boundary: plates are colliding -> compressional

• Divergent boundary: plates are pulling apart -> extensional

• Transform boundary: plates are sliding past each other -> `strike slip´

Convergent (typified by subduction/compressional/reverse faulting):

• Tonga

• Himalayas

• Chile

Divergent (typified by rifting/divergent/normal faulting):

• East African Rift System

• Mid Ocean Ridges

Transform (strike slip/transform):

• San Andreas Fault

• Normal Faulting -> Extensional (divergent)

• Reverse Faulting -> Compressional (convergent)

• Strike-Slip Faulting -> Transform (strike slip)

• A stress field comprises three principal components (sigma 1-3) taht are orthogonal to each other

• sigma 1 is the strongest force

• Normal faulting occurs when sigm,a 1 is vertical

• Reverse faulting and strike slip occur when sigma 1 is horizontal

• physics

• chemistry

• biology

• mathematics

• astronomy

• sedimentology

• tectonics

• volcanology

• micro-paleontology

• biogeochemistry

• seismology

• mineralogy

• petrology

• Igneous and metamorphic rocks are created and uplifted (mountains)

• Erosion transfers them into sediments

• Compaction and cementation turn them into sedementary rock

• Sedimemntary rocks are buried deep and heat and pressure lets minerals recrystalize to form metamorphic rock

• These can be burried so deep that they melt and form new igneous rock

• lose sediments are compacted and cemented (lithified)

• Conglomerate, Breccia, Sandstone, Shale, Mudstone

• compacted and cemented evaporites (salt)/ charbonate mud with particles of biogenic origin (e.g. pyramids, cliffs of dover)

• coal from organic material

• chert from silicious material like sponge spicule, radiolarian, diatoms (often occus in limestones)

• Oxygen (O) 46.6%

• Silicon (Si) 27.7%

• Aluminium (Al) 8.1%

• Iron (Fe) 5%

• Calcium (Ca) 3.6%

• Sodium (Na) 2.8%

• Potassium (K) 2.6%

• Magnesium (Mg) 2.1%

• magmatic rocks (main component is SiO44-)

• Magma = Lava (in a chemical sense)

• Cooling of Magma -> intrusive rock

• Cooling of Lava -> extrusive rock

Two pathways to form minerals as Magma cools:

1. Discontinuous series: One mineral is transformed into a different mineral through chemical reaction

2. Continuous series: palioglase feldspar goes from being rich in Calcium to being rich in Sodium

• X-ray diffractometry

• determination of mineral due to its physical/optical properties

-> O2- as anion

-> when OH- as anion than its called hydroxide mineral

• Hematite - Fe2O3

• Magnetite - Fe3O4

• Bauxite - Al2O3*2H2O

• Corundum - Al2O3 (Ruby)

-> carbonate anion combines with 2+ cations

• Calcite/Aragonite - CaCO3

• Dolomite - (Ca,Mg)CO3

• Magnesite - MgCO3

In reverse order of their solubility:

1. Calcite and Dolomite

2. Gypsum and Anhydrite

3. Halite

4. Potassium and Magnesium salts

chemically identical but different chrystal structure

-> They definetly have an S somewhere

• Galena - PbS

• Pyrite - FeS2

• Chalcopyrite - CuFeS2

• Sphalerite - ZnS

-> Their anion is SO4

• Anhydrite - CaSO4

• Gypsum - CaSO4*2H2O

• Barite - BaSO4

• Celestite - SrSO4

-> They include halogen elements like chloride, fluorine adn bromine

• Cryolite - Na3AlF6

• Fluorite - CaF2

• Halite - NaCl

-> They have a PO4 somewhere

• Apatite - Ca5(PO4)3(F,Cl,OH)

• Turquoise

The comprising elements resemble the Redfield Ratio

-> they all consist of SiO44- tetrahedra (four-sided pyramid shape)

• Olivine - (Mg,Fe)2SiO4

• Pyroxene - Fe2Si2O6/Mg2Si2O6

• Quartz - SiO2

• Neosilicates: isolated SiO4 bonded to iron and/or Mg ions

• Inosilicates: single chain of SiO4 where two SiO4 share one oxygen atom -> fewer O in the structure (expression as O:Si ratio -> Olivine 4:1 and Pyroxene 3:1). Can also be double chain silicates such as Amphibole (here the O:Si ratio goes down to 2.75:1)

• Phyllosilicates: continuous sheets where each SiO4 shares 3 Si atoms with adjacent SIO4. These sheets are linked with Mg or Al octahedron layers.

• Tectosilicates: framework silicates (very different types) e.g. Talc, Mica, Illite. Layers of tetrahedrons/octahedrons -> T-O-T in Talc, ..X+T-O-T+X… in Mica

• Study sediemnt itself (age dating, source determination, mineral composition, deposition environment)

• Study pore water (geochemical analysis, diagenesis)

• Investigate fauna and related processes

-> gravity corer

-> piston corer

-> multi corer

-> box corer

• minerological, geochemical or geotechnical studies (source, age, alteration processes, element content

-> Dredge

-> TV grab

-> Drilling

• see what is on seafloor/changes over time

• quantitative measurements

-> towed systems

-> lander systems

-> submersibles

-> AUVs

-> ROVs

-> Divers

Hydroacoustic signal to measure depth. Generates pressure wave (longitudinal) that travels through water. Time of return to transducer is measured and used to calculate depth.

-> depth = sound speed*travel time/2

-> wave length = sound speed/signal frequency

also important: transmit angle

Backscatter = intensity of the signal that is returned to the transducer

Area of beam increases with depth while resolution decreases.

Lead sounding (1-2k soundings/survey)

Single beam echosounding

Dual-swath Multibeam

Multibeam echosounding (400-1000M soundings/survey)

• visualize the sub-seafloor structures for tectonic/geological interpretations

• Detect and trace oil and gas resources and fluid pathways

• Derive sediment sound velocities for accurate depth determination (-Y hydrocarbon exploration), state of cementation/porosity

• Sand, slit and clay particles derived from continents by physical erosion

• Deposited in the coastal zone and at the continental margins

• Dust particles derived from continents deposited at the deep-sea floor (red clay)

• Biogenous particles formed by marine plankton (calcium carbonate, biogenic opal, OM)

• Carbonate formed at tropical shelves by calcifying benthic organisms (e.g. corals)

• Shell sand, oyster banks, etc.

• Precipitated from seawater or sediment pore water

• Evaporites (salt), manganese nodules, phosphorite concretions, etc.

Deposited at the deep-sea floor

Mixture of terrigenous and biogenous pelagic sediment

• Strong currents move coarse grained materials -> sand abundant in seafloor areas with high current velocities (coastal zone and continental shelf)

• Fine grained particles (clays) are transported over long distances even at low current velocities (found at continental slope and rise)

• During glacials, when sea levles are lower, deposition of riverine particles is shifted to the shelf edge, slope and rise

• motion of large sediment volumes at continental slopes

• strong currents at shelf break -> move particles across the shelf edge -> deposition at upper slope

• Accumulated material is mechanically unstable and likely to move downslope

• Slope failure can be spontaneous or triggered by earthquakes, fluid flow or melting of gas hydrates

• Massive slope failure events can trigger tsunamis

• Turbidity currents: high-velocity density currents carrying large amounts of suspended sediment

• They incise submarine canyons and form submarine fans and abyssal plains. Also break submarine cables

• Sedimentary deposits formed by turbidity currents are called turbidites

Describes the typical sediment sequence in turbidite areas that is formed by decreasing velocity of turbidity currents which leads to deposition of sediments.

From successive turbidite deposits burying the rough topography beneath. They cover large areas of the deep sea floor.

Dust transported by winds bypasses the coastal zone and is partly deposited in the open ocean. Iron and other nutreints are released from the dust into the water and fertilize the ocean. Red clay sediments are formed by the deposition of eolian dust.

Terrigenous particles deposited at the seafloor are generated on the continents by physicale erosion.

Erosion is induced by water, wind and ice (glaciers).

The largest mass flux of particles into the ocean is caused by rivers.

• Relief in the drainage area: erosion is enhanced in steep terrain

• Water discharge (i.e. transport capacity): erosion is enahnced at high water discharge; seasonal effects (monsoon) and events (heavy rain fall) are more important than continuous precipitation and runoff

• Geology of the river basin: sediment loads are high when rivers are flowing through areas where erodible materials are abundant (loess, volcanic ash, rock debris from glacial grinding)

• Presence of lakes and dams along the river bed: decrease the sediments discharge into the ocean

• Increase of erosion due to deforestation and cultivation of land, overgrazing and construction

• Decrease results from building of dams and reservoirs

• Surface waters in the ocean are oversaturated with respect to calcite and aragonite: 2HCO3- + Ca2+ —> CaCO3 + CO2 + H2O

• Because of higehr pressure and CO2 concentrations, deep water masses are often under-saturated with respect to CaCO3

• Therefore, the remains of calcerous plankton are partly dissolved in the deep ocean: CaCO3 + CO2 + H2O —> 2HCO3- + Ca2+

• The water depth below which all the carbonate delivered is dissolved is called CCD

Boundary between well preserved and poorly preserved carbonates

Rate of carbonate rain > rate of carbonate dissolution -> some carbonate accumulation

• Surface waters and deep waters of the ocean are strongly under-saturated with respect to biogenic opal

• To build their shells, siliceous phytoplankton organisms actively transport silicic acid into their cell, where biogenic opal (SiO2*nH2O) is precipitated

• Biogenic opal dissolves slowly and the dissolution rate is further diminshed by organic coatings covering and protecting the fragile biogenic opal shells

• Biogenic opal is, thus, found in sediments where the rain rate of biogenic opal to the seafloor is faster than the dissolution rate

Dissolution of minerals by CO2 and other weathering agents during continental weathering

• Climate (temperature, runoff): chemical weathering is enahnced under warm and humid conditions

• Mineralogy: carbonates and feldspars are dissolved more rapidly than quartz and clay materials

• Erosion and exposure of mineral surfaces: enhances the dissolution of minerals

• Vegetation: increases the pCO2 of soil solutions and the concentratoin of other weathering agents thereby the rate of chemcal weathering

• The dissoliution of carbonate minerals consumes CO2 and produces dissolved calcium and bicarbonate ions: CaCO3 + CO2 + H2O —> Ca2+ + 2HCO3-

• The dissolution of feldspars consumes CO2 and produces clay minerals, dissolved silica and bicarbonate ions

• Anthropogenic CO2 will be removed from the atmosphere within the next 100.000 yrs

• in isolated shallow basins where evaporation >> precipitation

• The type of mineral precipitated depends on the degree of evaporation

• Calculated from mass accumulation rate (MAR = g/cm2/yr), burial velocity (w = cm/yr), porosity (P) and density of dry solid (ds)

• Bural velocity can be derived by sediment dating (via 14C)

• Typical mean values for surface sediments are P = 0.8 and ds 0 2.5 g/cm3

• MAR = ds * (1-P) * w

From fast to slow:

• terrigenous

• calcerous

• hemipelagic

• red clays

• siliceous

• volcanogenic

Sites where magma extrudes/erupts on the earrths surface

• melt formation at depth

• differentation during ascent

• environment at surface

• converging plate boundary -> volcanic

• diverging plate boundary -> volcanic

• tranforming plate boun dary -> non-volcanic

West- and east-Eifel

• Melting of mantle rock

• Ascent of melts through mantle and crust

• Storage in large reservoirs and compositional evolution

• Magma degassing

• Volcanic eruption

• increase in temperature: frictional heating on fault planes, walls of magma chambers, belown thick lava flows, magma underplating crust

• decompression: fast and sufficiently voluminous convective upwelling/tectonic upthrusting to orevent thermal equilibration with the surrounding mantle (often under MORs and in hot-spot-plumes)

• addition of volatiles (e.g. water): causes drop in solidus temperature below geotherm (common in subduction zones where downgoing slabs release water into the overlying mantle)

MORs or divergent-margin volcanism

• In melt veins 0.1-100m wide

• 1-200m apart

• Diapir: lower density in lower magma -> isolated balloon shaped magma batch rises due to high buoyancy force (high resistance due to large surface)

• Isolated dike: blade-shaped magma filled crack -> lower buoyancy force but also low resistance -> tip effect

• Feeded dike: dike connected to magma -> high buoyancy and low resistance -> tip effect

Magma filled crack with a volatile filled tip cavity

• Mafic melts ascent from the mantle due to their density being lower than that of ambient rock

• But upper crust is less dense than basaltic melt/magma -> rising until neutral buoyancy -> magma chambers

• Volatiles are dissolved in the melt which, when they exsolve, form a fluid or gas phase

• Gas can also be formed by vaporization of ambient water

• Expansion of gas is the most important control on explosive volcanic eruptions

-> exsolution of gas phases dissolved in the melt lead to magmatic eruptions

-> vaporization of water in contact with hot magma lead to phreatomagmatic eruptions

• formation due to a nucleus (e.g. mineral)

• groowth due to diffusion putting gas into already existing gas bubbles

• decompression as magma rises

hindered bubble growth generates gas overpressure

-> fast ascent increases gas pressure faster in the ubbles than it can be compensated by growth (higher pressure is delivered to shallow depths)

-> explosivity increases

-> fragmentation easier and more complete

Effusive -> lava flows, lava lakes

Explosive -> Pyro/Hydro-clastic deposits

(clastic = fragmented)

• Magnitude

• Intensity

• Violence

• Dispersion

• Destructive potential

• pyroclasts: fragmented rocks originated by primary volcanic activity

• tephra: deposits of pyroclastic material

• vulkaniclastic: all clastic deposits with >25vol% vulkanic material

• hydroclastic: pyroclasts generated by magma-water interaction

• epiclastic: reworked deposits with volcanic matter <25vol%

• juvenile: derivates from magma -> quenched glass, crystals, mycrocrystalline rocks

• lithic: external rock fragments (Host rocks, older volcanic rocks)

• strombolian eruptions: episodic gas bursts

• foam collapse: degassing of low-viscosity magma

• phretomagmatic eruptions: hot magma meets cold water (e.g. submarine eruptions)

• plinian eruptions:

• Mass flux increase: widening of the vent -> ratio of rim to jet stream diameter decreases -> less air entrainment

• Gas content decrease: decreasing eruption velocity -> frictional and drag force at the rim of the gas thrust zone decrease -> less air entrainment

• all having the effect that admixing of air cannot sufficiently dilute erupting mixture -> eruption collapse -> pyroclastic flow

• Shield volcano

• Stratovolcano

• Caldera volcano

• Somma volcano

• Lava dome

• Scoria cone

• Tuff ring

• Maar

-> predominant eruption mechanism

-> predominant magma composition

-> long-term magma production rate

-> environmental conditions

-> geotctonic setting

Correlation between Tephras (rock that where erupted):

• petrographic features -> smear slides

• Bulkrock chemistry

• glass chemistry

• mineral chemistry (major element composition)

• relative stratigraphic order

• chemical fingerprinting can give information about the same volcano eruptiong at different times and on how to distinguish between volcanoes

• sedimentation rates and volumina

• Oak chronology: based on rings of oak trees -> patterns are used to determine the time when the tree died (12.483 yrs back in time without interuption)

• Wave chronology: layers of clay that emerged in a yearly rhythm (principle of pattern recognition)

• Snow accumulation/ice cores: gas concentration, layer thickness

• 14C is produces by 14N being hit by cosmic neutrons

• 14C is than incorporated into CO2 in the atmosphere

• biological uptake continuously -> stable 14C conc. in all living organisms

• decay starts by the time of death (half life = 5730)

• the ratio between 14C-activity and bulk carbon concentration is used to calculate the time since the organism died

• However there are 14C plateaus that decrease the accuracy

• 14C calibration by comparing to independant dating techniques

• K/Ar-method (based on K and Ar concentrations -> K decays to Ar -> ration shifts to Ar with time)

• Rb/Sr-method (based on Rb and Sr concentrations -> Rb decays to Sr)

• Oxygen Isotope Stratigraphy (18O is evaporates slower than 16O)

• Lithostratigraphy (deeper is older, finding correlations)

• Magnetosttratigraphy (earths magnetic orientation “frozen” in rock by cooling lava)

• 18O evaporated slower than 16O

• 18O is removed from the atmosphere quicker while moving polewards

• 18O enrichment of oceans and 16O enrichment of continental polar ice caps

• build up of continental ice shields lead to high 18O concentrations in the oceans and high 16O in the glacial atmosphere

• 16/18O composition in CaCO3 in froaminifera shells give information about temperature and glacial interglacial fluctuations

• Problem: absolute dating is missing

• Solution: Milankovitch climate theory -> orbital tuning -> radiation processes -> climatic processes -> delta18O

• Earths magnetic field

  • close to a dipole, centred at earths midpoint

  • magnetic poles close to geographic poles

  • produced in the earths interior (Fe-core) generated by turbulent convection of magma within the outer core

  • local disturbances in the convection can cause distortions nd even a change in polarity (reversal)

• magnetic minerals within rocks keep the magnetic information after crysatlization

• Photosynthesis: decreases DIC by CO2 uptake and slightly increases TA

• Respiration: reversed effects of photosynthesis

• CaCO3 dissolution: increases TA and DIC by CO3- input

• One CaCO3 during formation removes one part of DIC and two parts of TA as Ca2+ has a double positive charge

• anthropogenic C in the water column rises

• Omega-Calcite decreased by 0.2 units

• Omega-Aragoniite decreased by 0.15 units

TA, pH and DIC decrease in the Pacific from North to South

• two isotopes boric acid B(OH)3 and borate ion B(OH)4-

• boric acid conc. increases with lower pH

• both can be incorporated into biogneic CaCO3

• delta11Bsw changes with pH and can be found in calcifiers and then compared to bulk SW boron isotopic composition of today

• changing ocean circulation (circulation depth decrease in NADW and AAIW)

• changes in biological pump (iron fertilization lead to higher PP and thus higher C-uptake -> higher pH)

• backed up by evidence for CO2 leakage during last deglaciation (Pacific became a CO2 source)

• Due to increased circulation and and decreased iron fertilization the eastern equatorial pacific became a CO2 source

• lower atmospheric pCO2 during LGM

• 14C is only produced in the atmosphere and then secondaryly transported into the ocean

• reservoir effect

• deeper waters with low 14C conc. are isolated from overturning circulation

• radiocarbon is formed in the atmosphere by 14N being hit by a neutron, removing a proton from the core and turning 14N into 14C

• with time 14C turns back to 14N -> beta-decay

• A measured benthic marine 14C age will always be older than the corresponding planktic 14C age

• The difference tells us about deep ocean ventilation rates

• Water > ice > air > land

  60 : 5 : 2 : 1

• low latitude oceans are earths main storage for solar heat

• thermohaline circulation (THC) plays key role to supply heat to polar regions (regulating the amount of sea ice

• THC impacts earths radiation budget through the rate at which deep waters are exposed to the surface (release of CO2 to the atmosphere)

• Most heat transport in a thin layer of the upper ocean (75% below 4°C)

  -> permanent thermocline (100-1000m) seperates cold deep water from surface effects

• The Atlantic is chracterized by a northward heat transport (THC)

• N-Atlantic becomes warmer at the expense of the S-Atlantic

  -> heat piracy

Modell:

cooling of N-Atlantic based on NASA GISS temperature data

Hypothesis:

Weakening of Atlantic Meridionel Overturning Circulation (AMOC)

Trigger:

Ehanced meltwater discharge from Greenland ice sheet

Reliable ocean temperature estimates are crucial for the reconstruction and modelling of:

-> past oceanic salinity and density -> water column stratification -> thermohaline circulatioin

-> ice volume/ sea ice -> timing of ocean warming with respect to atmospheric change and continental ice sheet evolution

Proxies = measurable parameters, which reflect chemical/ physical/ biological conditions of past oceans

-> each proxy is constrained by distinct boundary conditions, therefore calibration of proxies is necessary

• cultivating experiments

• in-situ studies

• core-top studies in comparison to modern ocean parameters

Examples:

• Microfossil assemblage transfer functions

• Oxygen isotopes in planktonic foraminifers

• Strontium and d18O in corals

• Alkenones (biomarker)

• TEX 86 (biomarker)

• Mg/Ca in foraminifers

• Calcium isotopes in planktonic foraminifers

• The distribution of marine fauna/flora is dependant from environmental conditions (e.g. temp., salinity, nutrient)

• Specific species/species assemblages reflect very distinct marine environmental conditions. if these change, the faunal changes can be used to reconstruct past changes (e.g. productivity, changes in oceanic fronts)

• 18O evaporates later than 16O

  -> glacial: more 18O in the ocean

  -> interglacial: less 18O in the ocean

  -> ratio found in foraminifera shells tells about glaciation state

• Sr/Ca ratio changes 0.6-0.7% per °C

• Problems with this method:

  -> Low latitude glacial Sr-temp. from corals are too low (5-6°C cooler than modern)

  -> SW Sr/Ca change caused by release from weathering of fossil reefs during sealevel lowstands

  -> Unreliable glacial temp. reconstructions due to 1-3% change of oceanic Sr/Ca

  -> Coral Sr/Ca ratios are sensitive to calcite diagenesis

• temp. sensitive, long chain, di- and tri-unsaturated carbon bonds

  -> ratio of di- and tri- saturated C37 alkenones chnges as a function of temperature

  -> U^K’37 most likely refelcts annual SST from 10m water depth

• Crenarchaeota = microbes, single celled bacteria, plankton, highly concentrated

• composition of membrane lipids depend on growth temp.

• number of cyclopentane rings in sedimentary membrane lipids corelate to annual mean SST

• exeptional relationship between Mg/Ca and SST

• Mg/ca ratio gives information on calcification depth

• Small SST gradient between species = deep thermocline

• Large SST gradient = shallow thermocline

d44Ca can be used as a proxy for SST

Should have caused:

• Development of modern salinity contrast between Atlantic (Caribbean) and Pacific in surface waters -> started happening since 5.5 Ma and strengthened since 4.2 Ma

• Development of modern Caribbean warm pool -> started 4.4 Ma ago

• Intensification of Gulf Stream System

• Increase of heat, salt and moisture transfer into the N-Atlantic (heating of NW-Europe)

• Increased formation of N-Atlantic intermediate and deep sea water masses

What actually happened:

• Enhanced evaporation in N-Atlantic due to warming

• Freshening of Arctic Ocean facilitates sea ice fomation

• Sea ice raises albedo and reduces the heat exchange between ocean surface and atmosphere —> COOLING

• Fresher Arctic outflow slows down AMOC —> COOLING

After 4-5 Ma…

• Strengthening of the East Australian Current (EAC)

• Weakening of the Leeuwin Current (LC)

• Cooling of the Indian Ocean and warming of the W-Pacific

• Intensification of the E-W temperature gradient across the eq. Pacific

• El Nino >>> La Nina dominated climate state

• Onset of Pliocene Northern Hemisphere glaciation

Indian Ocean and E-Africa:

• Weakening, cooling, freshening of Australasian Mediterrane Water (AAMW) throughflow

• Intensification of E-W temperature gradient in the eq. Indian Ocean

• Shoaling of the thermocline

• Cooler surface ocean, less evaporatioon over Indian Ocean

• Less precipitation over E-Africa expected

-> Oscillates over geological timescales

Eccentricity: deviation of earths orbit around the sun from a perfect circle (400 ka and 100 ka)

Obliquity: angle between earths rotational axis and its orbital axis (41 ka)

Precission: change of orientation of earths rotational axis (23 ka)

-> have a strong effect on earths climate

-> warming events every 100 ka with cooling events in between

Glacials and inetrglacials are not consistant spread and retreat of ice sheets but a back and forth where single cooling and melting events (ice flow surges) are alternating -> (Heinrich event)

They follow an a priori subsurface water warming

• Warm Deep water passes the Shelf-slope front

• On the continental shelf that former deep water gets cold and saline

• Sinking due to gravity current plumes

• all ocean basins show signs of warming except the N-Atlantic which recorded cooling pre 2000 at shallow depth

• Most pronounced abyssal warming is seen in the southern ocean

• Antarctic bottom-water is warming, freshening and its volume is declining over the past decades

• sand/gravel -> transported from land sorting

• iron sands -> transported from land, physical enrichment

• diamonds -> transported from land, erosion on land

• phosphorites -> diagenetically formed in/on the sediment

• Cobalt-rich ferromanganese crusts

• Mn-nodules

• massive seafloor sulphides

UNCLOS -> United Nations Convention in the law of the sea

• 12M from shore: Territorial Sea

• 24M from shore: Contiguous Zone

• 200M from shore: Exclusive Economic Zione

• beyond: High Sea

Formula 1 (Distance formula): Line 60M seaward from foot of the slope

Formula 2 (Sediment thickness formula): Line where the thickness of sediment is at least 1% of distance to the foot of the slope

Constraint 1 (Distance constraint): 350M from the baseline (Coast)

Constraint 2 (Depth constraint): 100M from the 2.500m isobath

International Seabed Authority (30 employees)

-> regulates the extraction of mineral sources beyond the juristriction of national boundaries in the Area

• concentric growth around a nucleus (rock fragment, shark tooth, older nodules)

• single or aggregated nodules

• 1-20cm size

• density ~2.0g/cm3

• porosity 60%

• alternating, mm-wide fe- and Mn-rich layers

• aka ferro-manganese nodules

• Favorable conditions are in areas below the CCD, with low sedimentation rate, moderate sea surface productivity

• formed by precipitation from two sources

  1. hydrogenic:

     colloidal particles directly from cold ambient seawater and accretion around a nucleus on soft sediment forming hydrogenic nodules

  2. diagenetic:

     metal ions either within the soft sediment or at the sediment water interface from sub-oxic sediment pore waters where seawater is modified by chemical reactions within the sediment forming diagenetic nodules

hydrogenic: 1-10mm/Ma

diagenetic: 250mm/Ma

• Silicate weathering: Ca(Al2Si2)O8 + 2CO2 + 3H2O —> Al2Si2O5(OH)4 + 2HCO3- + Ca2+

• Carbonate precipitation and dissolution: Ca2+ + 2HCO3- <—> CaCO3 + CO2 + H2O

• surface sediments have porosities in the range of 0.4 (sand) to 0.9 (clay)

• porosity decreases with depth (in sediments) due to compaction

• Solutes can be transported within the pore space via molecular diffusion and pore water advection

• sediment pore water accounts for 6% of the global seawater volume

• sum, total of processes that bring out changes in a sediment or sedimentary rock

• EXCEPTIONS:

  changes after contact with atmosphere -> weathering

  chnages after exposure to elevated temperatures upon burial -> metamorphism

Molecular diffusion:

concentration gradients in stagnant solutions are leveled out in time by Brownian movement of molecules

Advection:

Transport of tthe aqueous medium itself

-> compaction of the sediment package can induce some upward directed advection of pore water (small compared to diffusion)

-> in particular tectonic settings lateral compression and mineral dehydration reactions can induce more intense pore water advection

BUT:

porosity and tortuosity need to be taken into account

a) Profile of non-reacting solute (e.g. Cl)

b) Substance that is depleted in the upper sediment layers (e.g. oxygen)

c) Profile of a solute that is consumed in a particular reactive layer (e.g. uranium)

d) Profile of a solute that is released in the upper sediment layers (e.g. silica)

e) Profile of a solute that is released in a particular reactive layer

f) Combination of release and consumption in reactive layers (e.g. manganese)

LOOK INTO THE STOICHIOMETRY FOR REDOX REACTIONS

• Organic matter degradation in marine sediments is mediated by microorganisms

• They catalyze redox reactions and conserve part of the liberated energy to maintain their metabolism

• Nature always tries to minimize internal energy (enthalpy, H in kJ/mol) and maximize entropy (S in J/mol/K, degree of disorder)

• reactions may proceed without external energy input if the process leads to an increase in entropy (e.g. molecular diffusion, evaporation) and/or a decrease in enthalpy

• Gibbs free energy (G in kJ/mol) is a measure of the overall energy and entropy of a chemical system

• Chemical systems tend to minimize their deltaG

• A reaction may proceed spontaneously or biologically catalyzed if the products have lower G values than the reactants

• In many cases the reaction can not proceed because intermediate products with high G values are formed

• An activation energy has to be overcome

• The rate of carbon oxidation depends on the rain rate of particulate organic carbon to the seafloor (POC RR)

• The POC RR is a function of primary and export production as well as carbon oxidation in the water column. These parameters decrease with increasing distance from shore

• hence, the relationship between oxidation rate and water depth

• Organic matter raining onto the seafloor at continental margins has experienced less water column remineralization and should thus have a higher content of labile organic material

• One could therefore expect a lower burial efficiency at continental margins

• This is nbot the case. A combination of the following factors can expalin this:

  1. Organic material consists of a range of constituents, with more labile components disappearing during the early stages of diagenesis

  2. Inorganic minerals, which are more abundant at continental margins, protect organic matter from oxidation

  3. Aerobic carbon degradation is more efficient than anaerobic degradation

The Gibb’s free energy which can be calculated from concentrations measured in the field. The available energy determines the vertical redox zonation observed in marine sedimentary environments (early diagenetic sequence).

• Rates of DOC degredation

• Thickness of the various biogeochemical zones

• Dissolved O2 is used up quickly due to high DOC RR

• Sulphate reduction starts at a depth of approximately 10cm after nitrate, manganese annd iron oxides are used up

• deep sea recieves very little DOC, thus oxygen is only consumed over a depth of several decimeters up to tens of meters

• Very little POC is left to drive sulphate reduction since most of the POC is already consumed by aerobic respiration

In the continental shelf sediments, aerobic remineralization of organic carbon predominates in deep-sea sediments

• largest pool in SW is N2 -> unavailable to mo0st marine organisms

• fixed by diazotrophs (N2 -> PON)

• Upon decay of biomass N is released in form of NH4+ and either assimilated by organiisms or converted to more oxidized compounds of fixed nitrogen

• In anoxic environments fixed N can be converted to N2 via reductive processes (e.g. denitrification)

  
  

• no internal source within the ocean

• mobilized through weathering of continental P-minerals (mainly apatite)

• due to anthropogenic activities, the phosphorus input to the ocean has approximately doubled -> main sources: fertilizer, deforestation, erosion sewage

• Fe in silicate minerals is referred to as non reactive since it is not bioavailable (e.g. to iron-reducing bacteria) and does not react with hydrogen sulphides

• Reactive Fe minerals are generated by silicate weathering

  FeMgSiO4 + 4CO2 + 4H2O —> Fe2+ + Mg2+ + H4SiO4 + 4HCO3

• Dissolved Fe2+ is oxidized to Fe3+ and mostly precipitated as ferrihydrite

  2Fe2+ + 1/2O2 + 5H2O —> 2Fe(OH)3 + 4H+

• Most of the Fe supplied to the oceans by rivers is in particulate form

• Most of the dissolved Fe is lost in the estuarine mixing zone

• Despite near complete removal of dissolved Fe in estuares there is a significant amount of dissolved Fe in costal waters

  -> much of Fe is supplied from continental margin sediments

  -> sediments represent a significant iron source to the ocean

• declining oxygen concentrations will increase benthic and pelagic denitrification, which will decrease the oceans fixed nitrogen inventory

  -> negative feedback for primary production and oxygen consumption

• Declining oxygen concentrations will increase sedimentary phosphorus and iron release, which will increase the oceans phosphorus and iron inventories

  -> positive feedback for primary production and oxygen consumption

• Benthic and pelagic denitrification

• The global magniitude of denitrification is a function of redox conditions, which implies that under more reducing conditions, the global inventory of fixed nitrogen decreases

• P is released into the pore water upon remineralization of organic material from iron oxides during iron reduction

• If the surface sediment is anoxic much of the P and Fe in the pore water can be recycled back into the watter column?

• Methanogenesis

• abiotically at high temperature

Most is oxidized to carbon dioxide by sulfate, a microbially mediated reaction called anaerobic oxidation of methane (AOM)

Thus, little of the Methane that is produced in the sediment actually reaches the water column or the atmosphere

CH4 + SO42- —> HCO3- + H2S + H2O

Manifestation of fluid flow characterized by:

• the occurence of methane derived authigenic carbonates (MDAC)

• methane bubble release

• chemoautotrophic fauna

• typical geochemical gradients

• biogeochemical processes such as AOM (anaerobic oxidation of methane)

• sometimes barite formation

• gas hydrates

• advecting pore fluids loaded with methane that can escape

• pore water overpressure

• methane and pathways

• Sediment compaction (found in places of sediment deposition -> continental margins)

• Stress/lateral & vertical pressure

• generation of water through reactions -> OM degradation/mineral conversion

• Stress and pressure exist at converging plates -> continental margins

  
  

• biogenic -> consumption of OM

• thermogenic -> cracking of OM

• both processes need organic matter -> abundant at continental margins

Continental margin of New Zealands North Island

-> Pacific plate piles up sediment -> folding -> cut by faults

• ice like substance that is stable at low temperatures and high pressures

• stability depends on the type of guest molecule within the different water cages

• because of this cage structure, gas hydrates belong to the clathrates

• 1m3 of hydrate produces 164m3 of gas at STP (standard temp. and pressure)

  

SBES (single beam echosounders)

• detect flares

• quantify flowrates

• evaluate the potential of marine CH4 on global CH4 budgets

MBES (multi beam echosounders)

• to detect bubbles in the water column and make spacially larger assessments of release locations and quantifications

• Methane dissolves into ocean water as it is under saturated with methane

• methane bubbles strp gases from the water column as they are undersaturated with regard to those gases (e.g. O2, N2)

• Bubbles change their composition within the water column

• Gas reaching the surface depends on

  • amount being released

  • initial bubble size

  • water depth

  • rising speed

• The solubility of gases in water decreases with

  • increasing temperature

  • increasing salinity

  • decreasing pressure

-> Gas hydrate formation around bubbles hinders gas exchange and thus slows down dissolution

• mainly through CO2 reduction within the sulphate free zone of the sediments (anoxic)

• also by fermentation

• C is strongly isotopically fractionated

• enables to distinguish the carbon source and the place of fluid origin

• CO2 + 4H2 —> CH4 + 2H2O

• When CO2 dissolves in water it exists in equilibrium with H2CO3

  CO2 + H2O <—> H2CO3

• H2CO3 dissociates into HCO3- and H+

  H2CO3 <—> HCO3- + H+

• The concnetration of the HCO3- will be more than 1% in solutions in the pH range ca. 4-8. n this pH range the HCO3- dissociates into CO32- and H+

  HCO3- <—> CO32- + H+

• when the CO2 concentration in the solution decreases (temp. increase, lower pressure, CO2 uptake by org)

• when the HCO3- and CO32- concentration increases through AOM/dissociation of OM

• influx of cold seawater (recharge)

• heating of seawater

• geochemical reactions along the path

• formation of hydrothermal precipitates due to mixing of hot fluid with cold seawater -> SMS

• T<100°C: in the water

  basalt is oxidized -> Fe-oxyhydroxide overgrowth

  basalt interacts with elements from seawater (K, Rb, Cs,B) -> creation of phylosilicates

• T>150°C: top part

  Mg is stripped from the water -> recristalzation of feldspar and creation of phylosilicates (smectite/chlorite)

  anhydrite formation (CaSO4, no water)

  gypsum formation (with water)

• T>200°C: deeper down

  reaction of the Va2+ of the basalt = albitisation of basalt (exchange of cations)

  Anhortite -> albite

• T>250°C:

  reduction of sulfate to H2S (coupled with iron oxidation) -> creation of free iron Fe2+

400°C

hot, acidic and reduced fluids are capable to leach Cu, Fe, Zn, Pb, Au, Ag, S ezc out of the rocks

At these temp. the metals are largely transported as chloride-complexes

The hot fluids ascend along. permeable zones because of their low density

At the contact with cold oxidized seawater all metals are precipitated as sulfides

Result: black smoker