1. Which is the preferred concentration scale used by marine chemists?
a. Molinity (mol/kg of SW)
à Why is the carbonate compensation depth in the pacific located at shallower water depth than in the Atlantic?
· Atlantic waters are younger and contain less CO2 than deep waters of the Pacific. Therefore, CaCO3 is better preserved in Atlantic sediments than in Pacific deposits.
· Increasing CO2 leads to shallower CCD (increasing solubility)
1. Explain the major advantage of pereferred concentration scale?
a. Conservative with changes of temperature and pressure
Molinity: mol/kg of SW
Which order of magnitude estimate is closest to the residence time of Cl- in the ocean?
1.2 x 10^8 years
1. How is the residence time for chemical constituents (element, molecule etc.) in the ocean defined?
a. T = R/F (t= residence time, F= influx, outflow , R= amount present in ocean, reservoir)
1. Explain which basic assumption has to be made in order to apply this residence time concept?
a. Steady State – the input equals the output, otherwise: accumulation not an equilibrium
equilibrium vs steady state
(equilibrium: concentrations are not changing, steady state: concentrations can change not dependent on all chemicals)
1. What has the longer residence time in the ocean: iron or phosphate? Explain why.
phosphate
a. PO43- has the longer residence time in the ocean. Phosphate, although being an essential component for building up biomass is almost never limiting. However, iron, as an important co-factor for many enzymatic processes is quickly taken up and stripped out of the seawater, once it is dissolved. Furthermore, iron is quickly precipitated under oxic conditions.
1. Which has the longer residence time in the ocean: the bromide ion (Br-) or the water itself?
a. Bromide = 100*106 yrs, super conservative; water 4*104 yrs
1. Mention and discuss three different processes that are affected by the total dissolved salt concentration (i.e. salinity) in the ocean.
a. Salinity decreases the freezing point of water, as it forms hydration sheets, which hinder the formation of hexagon clusters at low temperatures.
b. Salinity increases the density of seawater, as it acts as a “structure” breaker. It prevents the formation of hydrogen-bridge bonds between water molecules and thus also decreases the amounts of hexagon clusters, which can be formed. However, the volume decrease due to temperature is the stronger driver for this.
c. Salinity decreases the gas solubility of seawater. With higher salinity, less amount of a respective gas can be dissolved. However, temperature increase is the stronger driver for this.
1. What are the processes that alter seawater salinity at ocean boundaries?
a. Processes, that alter salinity are
evaporation,
precipitation (direct),
runoff (rivers),
groundwater flow,
ice formation,
brine-rejection during ice formation and
ice melting
1. Which of the three relationships between the concentration of chemical constituent and seawater salinity (figure below) indicates conservative behaviour?
a. conservative behaviour is shown in the righthand side graph, it shows a linear behaviour with salinity
b. non-conservative positive mixing (left)
c. non-conservative negative mixing (middle)
1. For any non-conservative cases in the figure below provide a possible cause of the non-conservative behaviour.
b. non-conservative positive mixing (left): high discharge, waste spills at river estuaries; or: redox-chemistry influenced reflux of nutrient
c. non-conservative negative mixing (middle): removal from solution, e.g. iron at river estuary
1. At which temperature does pure liquid water have its highest density? Explain the processes that determine the density of water.
- at T=4°C à lowest abundance of hexagons à highest density
- at T >or< 4°C à abundance of hexagons increases à density decreases
- at T<0°C à all H2O held in hexagons (ice-crystal-lattice structure) à all H2O molecules farthest apart à lowest possible density à ice is 8% lighter and floats
1. Explain the consequences of ocean circulation for the density characteristics of seawater?
a. Warm fresher water floats, cold high saline water sinks. Deep water formation happens in winter in high latitude waters as part of the meridional overturning circulation. (4)
b. Generally: warm and fresher water floats (lower density) and cold and saline water sinks (higher density). Deep water formation occurs at high latitudes e.g.: NADW/AAIW/AABW, when it cools down during its journey to colder polar waters. Additionally, the formation of ice, and the rejection of brine, might further increase the waters density, causing it to “drop” and form deep-waters. The thereby created “vacuum” is replenished with warmer and less saline surface waters, resulting in a global ocean circulation. The overall driver of this is the differing radiation budget on a global scale (e.g.: equator higher solar energy input, than in polar regions –> affects temperature).
1. Where does the inorganic carbon dissolved in river water originate from? Give two sources and explain the processes.
a. Atmosphere as CO2, remineralisation of plant material, weathering of Si rocks (Mg-Ca). (4)
weathering of rocks – dissolution of limestone and silicate-minerals (Albite); e.g.: CaCO3 + CO2 + H2O -> Ca2+ + 2HCO3-
atmospheric CO2 input – CO2 + H2O -> HCO3- + H+
remineralisation of plant material
1. Name 2 chemical species each that are found in rainwater and predominantly originate from (1) sea salt and (2) atmospheric gases.
a. 1. Na, K, Ca, Mg
b. 2. SO4 2-, NO3-, NH4+
1. Which type of rain is typically more acidic (i.e., lower in pH): continental or marine rain? Explain why.
a. Continental rain is usually more acidic,
b. influence of SO2 gases + NOx gases is higher in continental areas à acidic rain: formation of H2SO4 + H2SO3
1. Name 4 cations and 4 anions that belong to the major constituents of seawater?
a. Ca2+, Mg2+, Na+, K+ and Cl-, HCO3-, SO42-, Br-, F- (3)
1. Which ion has the longer residence time in the ocean: the potassium (K+) or calcium (Ca2+)? Explain why.
a. K+. Ca is involved in CaCO3 formation. (4)
b. Remember residence times: τ = mean conc. in ocean * (total ocean vol. / inflow per yr)
c. Although inflow per year of Ca2+ is higher (major cation of river discharge), mean concentration of Ca2+ in ocean is way lower (used in calcification à CaCO3) à K+ has the higher residence time, it is not subject to biological depletion, it behaves conservative.
1. Give two sources of acidity in rainfall. What is the approximate pH of rainfall over the open ocean, away from land
a. 1. CO2 natural, 2. SO2 and H2O2 polluted
b. 5.6 pH
1. Which pollution-related process can cause very low pH (even <3) in polluted air? Explain the process.
a. Introduction of fossil fuels into air (SO2)
b. SO2 + OH- -> H2SO4 (or SO2+H2O2)
1. Which processes determine the abundance of elements in riverwater. Discuss the processes.
a. Human impact: agriculture
b. biological processes in soils
c. weathering in rocks: dissolution of minerals
d. evaporation
e. (chemical nature of element/ion)
1. Provide two reasons why some chemical elements do not behave in a conservative manner in the ocean.
a. non-conservative: concentration of chemical species does not show linearity to change in salinity.
Possible processes that shift (positive or negative) the concentration of chemical species with respect of linearity to salinity: biological uptake, authigenic or biogenic precipitation, particle scavenging, additional supply/resuspension by sediments, aerosol-input, rivers.
1. What is the difference between molality and the molinity concentration scale (provide definitions)?
a. Mol/kg water and mol/kg seawater. (3)
b. Molality: moles per kg of pure water [mol/kg-water] ↔ Molinity: moles per kg of seawater [mol/kg-sw] Molinity incorporates the density differences occurring for seawater of different salinity.
1. For a seawater sample, what would you have to measure or know to convert concentrations from molarity to molinity
a. Molarity (mol per l) -> need to know weight of Seawater
b. 1l seawater = 1.025 kg (FW= 0.98 kg)
1. You have a seawater sample which has salinity of 35. Calculate very approximately, the molarity of dissolved salt in the sample
a. Molarity = mol/l Seawater= 35 g/kg
b. g/kg -> mol/l
c. teilen durch 1.025 -> 34.15 g/l
d. NaCl = 58.5 g/mol -> 34.15 teilen durch 58.5 = 580 mmol/l
1. Draw and label the axes for a temperature-salinity diagram. Plot the approximate locations of three lines of constant density (“isopycnals”) on this diagram.
1. In the open (deep) ocean, what percentage of the overlying biological productivity is buried as carbon in the sediments?
1 %
1. Which is the dominant cation and anion in (1) river water and (2) seawater?
a. 1. HCO3- (Anion), Ca+ (Cation)
b. 2. Cl- (Anion), Na+ (Cation)
1. Give three examples each for constituents of rain that originate (1) from sea salt particles, and (2) from atmospheric gases.
a. Na, K, Ca and SO4, NO3, CO2 (3)
b. From sea salt particles: Na, K, Ca and from atmospheric gases: SO4, NO3, CO2 (natural + pollution). There is a shift of Ion-ratios in rainfall from “marine” to “continental” rain.
1. What is the typical lifetime of sea-salt aerosol particles in air: hours – days – weeks – months?
up to 3 days à partially responsible for salt deposits on land.
can be transported considerable distances to land
1. Explain congruent and incongruent chemical weathering processes of minerals (no chemical equations required) and provide 1 example for each.
a. Congruent: simple dissolution -> all constituents end up in solution
olivine/pyroxenes/amphiboles/calcite/dolomite/gypsum/amberite/halite. Dissolution by acids.
b. Incongruent: dissolution and some pre-precipitation and/or oxidation forms secondary minerals
Plaglioklase, feldspar by acid. Biotite, K Feldspar, muscovite, volcanic glass
1. Explain the Stagnant Film Model for air-sea gas exchange and indicate the role of wind in this model. (5)
> turbulance on ocean surface layer depends on energy supplied by the wind
The stagnant film model describes the net gas flux between atmosphere and water as a function of differences in partial pressure and thus does not describe a system at equilibrium. As compared to other models, it takes the thickness z (in µm magnitude) of the boundary layer into account. The boundary layer is a laminar layer separating the turbulent bulk phases of water and atmosphere, thus is located directly at the phase boundary. We assume, that across this layer, gas exchange between atmosphere and liquid phase is only driven via molecular diffusion DG. Therefore, the previous deduction, that the gas exchange velocity Eg is determining the overall net flux of gas in or out of the liquid phase, can now be replaced with the term Eg = Dg/z. The thickness of the boundary layer is primarily wind driven and becomes smaller with higher windspeeds. Increasing winds, besides enhancing surface area, therefore increase the net flux of gases between atmosphere and water as the term Dg/z becomes bigger, as z becomes smaller.
F = (Dg/z) * (Gsw – Gsw-int)
a. Whereas G: concentration of gas in the seawater (sw) and directly at the seawater interface (sw-int.)
b. keep in mind: The differences in concentrations G are the main driver for gas exchange
-
Explain one of the approaches for the determination of the gas exchange coefficient
a. Gas exchange coefficients are usually determined by tracer experiments using e.g.: 226Ra -> 222Rn. The differences of the equilibrium observed in the mixed layer, as compared to waters below the mixed layer can be attributed to the degassing of Rn (previously Ra, not a gas). This can be extrapolated to other gases and conditions.
radon method (explained above)
global 14C inventories
dilibiral tracer experiment
direct flux measurements
1. Provide one example each for an element that is (1) added to the ocean and (2) removed from the ocean through the hydrothermal circulation, and discuss the addition and removal processes.
a. Hydrothermal fluid chemistry reflects the reaction of seawater with basalt. Therefore, at first:
b. (2) Mg + SO4 removal: Mg2+ + Basalt —> Mg-Basalt + Ca2+ + H+, removal of Magnesium associated with proton and Ca2+ release —> calcium is partially stripped out again due to precipitation with SO42- at high temperatures
c. (1) Input of sulphides due to reduction of seawater sulphate: SO42- —> H2S; also input of Mn, Fe, Cu, Zn, Si
1. Which of the following chemical constituents are typically found in high concentrations in high-temperature hydrothermal vent waters: (1) H2S, (2) Fe3+, (3) H4SiO4, (4) CH4, (5) Mg2+?
a. H2S, H4SiO4 and CH4 are typically found in hydrothermal vent fluids
1. Hot hydrothermal vent fluids have:
a. High pH, low [Mg2+]
b. Low pH, high [H4SiO4]
c. Low pH, high [Mg2+]
d. Low SO4 2-, high pH
a und d (mg is main removal)
1. How do (1) temperature and (2) pressure affect the solubility (Ksp) of calcite and aragonite in seawater? Explain the processes.
Ksp = apparent konstant (lab based, predicts chemical behaviour)
increases with decreasing temp
increases with increasing pressure
increases with increasing CO2 concentration
CaCO3 (s) -> Ca2+ (aq) + CO3 2- (aq)
1. Why does the Ca2+ concentration have rather little effect on the saturation level of seawater (Ω) for calcite and aragonite? Explain the relevant processes.
a. The concentration of CO32- is much more variable (esp. with depth) and in general lower, than the Ca2+ concentration. It is “limiting” and determines the saturation level of calcite and aragonite. Further only a very small fraction of Ca2+ does not behave conservatively (small conc. changes over depth)
b. general: saturation level: Ω = ([Ca2+] * [CO32-])/Ksp* à Ksp*: apparent, stochiometric solubility product
c. if Ω > 1 à supersaturation, precipitation is favored
d. if Ω < 1 à undersaturation, dissolution is favored
1. Where are nitrate concentrations higher: in the deep North Atlantic or the deep North Pacific? Explain why.
Nitrate concentrations are higher in the deep north pacific (remember: THC)
Conveyor belt is in depth in north pacific and in surface in north atlantic
new N supplied from 1. deep ocean and 2. atmosphere, meaning more addition of N in deeper waters in pacific than in atlantic (nitrification)
More nutrients in pacific bc: older, more time to accumulate nutrients and sink down
THC = termohaline circulation
1. Why would a primary producer prefer NH4+ over NO3- in the nitrogen assimilation process? Explain.
a. Requires less energy:
N-fixation requires a lot of energy,
some phytoplankton take up reduced nitrogen species (NH4+),
synthesis of NH3 without changes of oxidation number
1. Why does the presence of enhanced fixed nitrogen species (i.e., NO3-, NH4+) normally inhibit nitrogen fixation (diazotrophy)? Explain.
a. Diazotrophy (e.g.: the usage of the enzyme nitrogenase) is heavily energy dependent
b. N2 hat eine dreifachbindung und ist daher energetisch höher und braucht zu NH3 eine hohe energy
c. Fixed N-specie (No3-, NH4+) requires less energy to produce NH3
1. Why is the process of nitrification autotrophic (i.e., yields chemical energy)? Explain.
a. Nitrification: NH4/NH3+ zu NO3-
b. Yields energy: used to synthesize ATP: energy for biomass formation
c. NH3+O2 ->NO2- + 3H+ + 2e-
d. NO2- + H2O -> NO3- + 2H+ + 2e-
1. How many electrons are released per N atom when NH4+ is oxidized to NO3- by nitrifiers?
a. 8 e- are released: NH4+(-III) -> NO3- (+V)
1. Name four chemical constituents that we consider “fixed nitrogen”. Provide the oxidation number of N in each of these constituents.
NO3 (5+), NH4 (3-), NO2 (3+), DON (3-)
(Fixed Nitrogen: all species except N2)
1. What happens to
(1) NH3/NH4+ upon release in oxic, sun-lit surface waters,
(2) NH3/NH4+ upon release in oxic, dark sub-surface waters,
(3) NO2- in anoxic waters, and
(4) N2 in nitrate-depleted subtropical surface waters?
a. (1) Taken up by microorganisms as a readily available N source, or nitrified.
b. (2) Nitrified by bacteria
c. (3) Denitrification or anammox or ammonification to NH4 (DNRA)
d. (4) N2 fixation by diazotrophs (6)
Assimilation
a. Assimilation: preferentially taken up by phytoplankton/microorganisms as it is a readily available N source. NH3/NH4+ already has an oxidation number of -III (same as in PON) -> easy incorporation, easy transformation to glutamate (for further use)
Nitrification
a. Nitrification: microbially mediated slow oxidation to Nitrate, autotrophic, yields energy for ATP production (but only little)
NH3 -> Nitrosomonas -> NO2- -> Nitrobacter -> NO3-
Denitrification
a. Denitrification: dissimilatory nitrite reduction to N2, serves as an electron acceptor for heterotrophs; yet: more likely to happen to/ or in combination with NO3- it is a Nitrogen loss process
NO2- -> (N2O) -> N2
Anammox
a. Anammox: anaerobic ammonium oxidation to N2 in anoxic environments, synproportionation. It is a nitrogen loss process NH4+ + NO2- —> N2 + H2O
DNRA
a. DNRA: dissimilatory nitrate (nitrite) reduction to ammonium, anaerobic respiration process of heterotrophs using nitrate as an electron acceptor (NO3- ->) NO2- -> NH4+
N2 fixation
a. N2 fixation: diazotrophic bacteria fixate gaseous N2 to NH3/NH4+ with the enzyme nitrogenase heavily energy dependent and high Fe requirement N2 + 8H+ + E -> 2NH4+
1. How many electrons are needed to reduce nitrate to molecular nitrogen? Explain the process.
a. Nitrate: 2 NO3- (+V) à N2 (+-0)
b. 5 + 5 is 10. N2 fixation takes place by diazotrophs, which then have a readily available N source but still require Fe and P. (4)
1. Are humans capable of conducting nitrogen (N2) fixation through industrial processes? If yes, how do we do it?
a. Yes: Haber Bosch process -> high T and p + H2 and catalyzers
b. Haber-bosch = N2+3H2 -> 2NH3
c. balance through high pressure and temperature on right site
1. What is the thermodynamically stable form of N in most of the world ocean?
(a) NH4+
(b) N2
(c) NO3-
(d) DON
NO3-
because lowest energy state -> highest oxidation state
1. Discuss the main sources of silicon to the ocean?
a. Rivers >> aeolian (dust)> (basalt) weathering > hydrothermal and biSi when diatoms die
From land: weathering of quartz, Olivine, Kaoline (minerals combined with Fe, Mg, Ca)
In ocean: weathering of Quartz, feldspar, clay minerals
O2> Si> Al > Fe
mostly biSi and no pollutant
1. Discuss the major process driving the silicon cycle in the ocean?
Biological pump and recycling:
export of BiSi -> returning to surface by upwelling -> biological pump -> recycling
a. The largest part of dissolved Si stays in surface layer-remineralization loop or export-upwelling loop. The most of the terrigenous input accumulates in sediment, as it is not easily dissolved because lithogenic silica is in a mineral crystal lattice -> bad dissolution. Most biogenic silica stays in biological production loop because it is amorphous opal and easily diluted. Key players in the biogenic silica cycle are diatoms. The outcompete most other phytoplankton species, once c(Si) has reached a threshold of 2µmol/l. They play a major role in upwelling regions.
1. Where are the major regions with opal-rich sediments and what are the reasons for their occurrence?
a. Major regions for opal-rich sediments are dependent on the overlying productivity and silicic acid supply, the degree of preservation during sinking (type of opal → frustule thickness, also species differences, sinking speed, temperature, bacterial activity, distance of sinking, concentration in underlying waters), amount of non-silicious sedimentation → rate of dilution and burial. This usually aligns with upwelling areas → diatoms outcompete + strong CaCO3 dissolution due to OMZ beneath and in the Southern Ocean (High productivity, efficient sinking + very little dissolution (Tlow), high export flux + little non-silicious sedimentation) -> exceptionally large amount of Si-Sediments
1. The basic “building blocks” of clay minerals include:
(a) Silicate octahedra and Al tetrahedra
(b) Ionic crystals
(c) Silicate tetrahedra linked together in pairs
(d) Silicate tetrahedra linked together at their bases to form sheets
he two basic building blocks of all clay minerals are this silica tetrahedron and the aluminum octahedron. 1:1 or 2:1 clay refers to the ratio of these sheets:
1:1 clay has one of each sheet e.g. Kaolinite.
2:1 clays have two tetrahedral sheets either side of an aluminum octahedron sheet e.g. Montmorillonite
1. Write down the three dissociation products of phosphoric acid in order of decreasing tendency (i.e., high to low) to form ion pairs.
a. PO4 > HPO4 > H2PO4 (4)
b. Phosphate has the highest tendency to form ion pairs: PO43- > HPO42- > H2PO4- often bind to Mg or Ca
1. Name three biogenic substances which contain phosphorus.
a. ATP, DNA, phospholipids, phosphoesters, skeletal material, RNA
1. Identify 2 ocean regions where the observed nitrate concentration falls significantly below the expected values relative to phosphate (= 16 * phosphate). Why is that and what are the biogeochemical consequences?
a. Benguala, North Indian Ocean. Denitrification and anammox.
b. Generally, in low oxygen environments denitrification and anammox play an important role in organic matter recycling processes (see above). Both contribute to N2-loss and a shift from the Redfield-ratio of 16:1 to possibly significant lower relations. This is popular in the Benguela Upwelling System, North-West Indian Ocean upwelling system.
1. Phosphorus does not have a redox chemistry in seawater. What is the reason that we nevertheless speak about the indirect redox chemistry of phosphate in seawater?
a. Its redox chemistry is determined by the redox chemistry of Fe. Generally, PO43- shows strong adsorption to particles forming insoluble complexes. This happens especially with iron where soluble Fe(II) precipitates to non-soluble Fe(III)-PO4 species. Thus, it has an indirect redox chemistry with iron.
1. What is the average molar ratio between concentrations of dissolved nitrate and phosphate in the interior ocean?
a. Redfield ratio: 16:1 (P= 1 and N is 16)
b. Slope between 15 and 16
1. How does the process of denitrification affect this molar nitrate-to-phosphate ratio?
denitrifikation: NO3- to NO2- to N2
if nitrate depletes
-> resulting higher phosphate rate (bsp: 10:1)
1. The figure below shows a Bjerrum plot with six lines that represent different chemical species. Put the names of these six species next to the respective lines.
dotted line grey: H+
dotted line black: OH-
left to right:
H3PO4
H2PO4-
HPO4 2-
PO4 3-
1. Explain two oxygen measurement techniques.
a. In situ probes using an optical optode à oxygen is excited with a light impulse of specific wavelength à time and strength of the backscattering luminescence of oxygen is equivalent to its concentration
b. In situ amperometric oxygen probes à comprise a working electrode and a counter electrode. They are surrounded by an electrolytic liquid in a common chamber and a direct voltage is applied to both. Oxygen permeates from the water into the electrolyte through a membrane creating an electric current. The resulting current is proportional to the oxygen partial pressure in the medium.
c. Winkler Titration: Precipitation of oxygen as Mn(OH)3 and resuspension with Iodide, which forms I2. I2 can be titrated with Thiosulphate. The amount of formed I2 is ½ proportional to the oxygen within the sample
1. What’s AOU and advantages of using AOU.
a. The apparent oxygen utilization gives the difference between measured and theoretically possible oxygen concentration, if the respective water mass would be in equilibrium with the atmosphere and thus saturated to the degree salinity and temperature allows. Thus, it is only driven by primary production (during high photosynthetic activity AOU can be negative) or OM respiration.
b. AOU = c(O2)eq. – c(O2)measured
in surface waters can be negative bc pf supersaturation!!
1. Distribution of oxygen in the oceans?
a. Oxygen concentration in the ocean is probably still close to steady state, but generally oxygen concentrations are low at upwelling areas around the world.
b. The distribution of oxygen in depth profiles shows high concentrations of O2 in the surface mixed layer due to photosynthesis (e.g. 250µmol/L). In both e.g.: North Atlantic and North Pacific, concentrations drop, once the water masses are outside of the mixed layer, as an effect of OM respiration. This effect is larger and deeper (up to 1000m) in the pacific, than in the Atlantic (remember THC). Stretching below roughly 1000m, oxygen concentrations increase again, as most of the OM should be respired, and cold-water masses transported from elsewhere bring along oxygen. This leads to an increase in O2 concentration in the deep waters of the north Atlantic to almost the same as the surface layers (extremely cold and O2 rich deep waters).
1. Which of the following statement is “FALSE”
a. Conductivity-based measurement of salinity is superior to chemical titration because:
(a) It is more precise
(b) It can be automated
(c) It does not require a standard
(d) It is cheaper
(c) FALSE It does not require a standard
1. Draw vertical (depth) profiles of dissolved oxygen for waters off a) Bermuda in the North Atlantic Ocean; b) Hawaii in the North Pacific; c) the Greenland Sea.
bild einfügen
1. Explain how dissolved inorganic carbon concentrations in seawater determine the saturation levels (Ω) for calcite and aragonite?
- If CO2 concentration rises: more protons in water which can bind with CO3 2- and less Ca binds on CO3 2-
- pH is less (meaning more protons) -> less carbonate to calcify
- CO2 + H2O -> H2CO3 -> H+ + HCO3-
- HCO3- -> zu H+ + CO3 2-
1. Explain why is there such a clear relationship between the particulate organic carbon flux attenuation and the median temperature in the top 500 m?
a. The remineralization of organic material is largely temperature dependent (remember rate function: Q10 -> if temperature increases by 10°C -> 2-3x increase of “reaction”-rate (microbial processes)). Therefore, remineralization-rates and thus attenuation of particulate organic material in the upper 500m surface layer is largely temperature dependent. The warmer the surface ocean is, the less POC will be exported to deeper waters, due to enhanced microbial remineralization. However, once POC has been exported from surface layers of warmer oceans, the subsequent down transportation seems to be very effective, as the remaining POC might be more refractory and stable against remineralization.
1. How does the seawater pH affect the saturation level of seawater (Ω) for calcite and aragonite?
1. decrease with increasing CO2 concentration
2. high CO2 leads to lower pH resulting in decreased saturation
1. Name 3 biogenic minerals that are produced in the ocean. Also provide one marine producer for each mineral?
Calcite (coccolithophores, foraminifers),
aragonite (corals, pteropods),
biogenic opal (diatoms, sponges).
1. Give 3 reasons why the seawater changes from supersaturation for calcite in the surface ocean to undersaturation in the deep ocean. Explain the processes involved.
a. High P, lower T, higher CO2. (5)
a. K and Ω is shiftet which favours depletion in deep ocean (bc. CO3 2- is less abundant in higher depth)
b. The dissolution of Calcite and Aragonite is dependent on: Temperature (small effect): better dissolution with lower temperatures. Pressure (large effect): better dissolution with higher pressures. CO2-concentrations: CO32- + H2O + CO2 à 2 HCO3– (Bicarbonate Buffer System)
1. Where do we find more calcareous sediments: in the deep North Atlantic or the deep North Pacific? Explain why.
a. Deep North Atlantic -> thermohaline circulation: waters have lower CO2 concentrations (new water, less organic matter decay processes). CO2 is the main driver for CCD. If CO2 levels are higher, CCD is deeper
Which fraction of the organic matter produces in the surface layer typically reaches
the seafloor in the open ocean:
Name 3 biogenic minerals that are produced in the ocean. Also provide one marine
producer for each mineral?
Calcite (coccolithophores), aragonite (corals), opal (diatoms).
Give 3 reasons why the seawater changes from supersaturation for calcite in the
surface ocean to undersaturation in the deep ocean. Explain the processes involved.
High Pressure, lower Temperature, higher CO2.
New: How does the seawater pH affect the saturation level of seawater (Ω) for calcite and aragonite?
pH affects CO2 concentration
! decrease of co3 always leads to decrease of saturation levels
1. decrease pH with increasing CO2 concentration
2. high CO2 leads to lower pH resulting in decreased saturation of those compounds
more co2 -> less pH: decrease of carbonate (CO32-) -> decrease of saturation levels (increase of solubility)
2. Order the following three seawater constituents according to increasing non-ideal behaviour (i.e., decreasing activity coefficient): PO43- . F-, Ca2+)
Activity coefficient a(XYZ) a(PO43-) < a(Ca2+) < a(F-)
New: 1. Give 3 reasons why the seawater changes from supersaturation for calcite in the surface ocean to undersaturation in the deep ocean. Explain the processes involved.
High P
lower T
higher CO2 (=low pH).
b. K and Ω is shifted which favours depletion in deep ocean (bc. CO3 2- is less abundant in higher depth)
c. The dissolution of Calcite and Aragonite is dependent on: Temperature (small effect): better dissolution with lower temperatures. Pressure (large effect): better dissolution with higher pressures. CO2-concentrations: CO32- + H2O + CO2 à 2 HCO3– (Bicarbonate Buffer System)
new: Where do we find more calcareous sediments: in the deep North Atlantic or the deep North Pacific? Explain why
a. Deep North Atlantic à thermohaline circulation: waters have lower CO2 concentrations (new water, less organic matter decay processes). CO2 is the main driver for CCD. If CO2 levels are low, CCD is deeper.
b. Water in pacific is older: less o2 and more co2 -> pH decrease and solubility increase (saturation decreases) -> less calcareous in the pacific
pollution and sources of trace metals:
a. Natural: break down of rocks, hydrothermal vents, volcanic activity
b. Human -> POLLUTION: mining, smelting, burning of coal, waste water exposal
1. Similarities from trace metals to depth profile of macronutrients
a. macronutrients: si, C, N and P
b. trace metals: Cd (cadmium), Zn, Cu, Ni
b. Zinc resembles silicate (also replaces Cd in marine phytoplankton)
c. Cd resembles phosphate ->biological in marine diatoms
d. Ag resembles copper but better with si
1. Impact of fe, light and zooplankton grazers on diatoms and carbon export
Large diatoms: fe and light are limiting factors, are driving carbon export
fe: high impact, mostly fe limited (bc high requirement)
large diatoms are driving carbon export
light limitation leads to no growth
small diatoms: fe has low impact, almost no light limitation
never fe limited but grazing controlled
light: reduced growth
how does iron limits N2-fixation
a. Iron is a cofactor for nitrogen fixation
b. N2 fixation: diazotrophic bacteria fixate gaseous N2 to NH3/NH4+ with the enzyme nitrogenase heavily energy dependent and high Fe requirement N2 + 8H+ + E -> 2NH4+
anthropogenic impact on hydrothermal vents
resource exploitation (mining)
climate change
waste and litter dumping
Zuletzt geändertvor 2 Jahren
