Biogeochemistry

The solubility of CO2 in seawater (dependent on temperature and salinity)

When temperature/salinity go up K0 goes down -> solubility decreases

HCO3-: 88.6%

CO32-: 10.9%

CO2 (aq): 0.5%

Shows the concentration of the different carbon species in seawater relative to pH at equilibrium.

pK1*: [CO2*] = [HCO3-]

pK2*: [HCO3-] = [CO32-]

pKa = -log(Ka)

K = thermodynamic equilibrium constant = f (T,p) -> freshwater

K* = stoichiometric equilibrium constant = f (T, S, p) -> seawater

K* reflects non-ideal behavior of ions in seawater by making the activity constants yi part of the equilibrium constant

(activity) = y x [concentration]

A function of concentration (ci) and charge (zi) of all dissolved species

pCO2 = [CO2*]/K0 <-Henry’s Law (governs air-sea equilibrium and exchange

DIC = {CO2*] + [HCO3-] + [CO32-] (carbon book-keeping)

TA = [HCO3-] + [CO32-] + [B(OH)4-] -> acid binding capacity…let’s leave it at that for now

pH = -log(H+) (acidity of seawater)

• Dominated by carbonate alkalinity (=2205.2 µmol/kg) <- HCO3- and CO32-

• phosphate contributes to 100% to alaklinity and silicate to 5%

It is determined by alkalinity or rather the CO32- concentration as CO2 + CO32- + H2O —> 2HCO3-

• CO32- drives the buffer capacity

• for given pCO2 change in the atmosphere DIC change in tropical water is twice as high as in polar waters

• counterintuitive: solubility for CO2 increases with decreasing temperature

• explanation: [CO32-] is higher at high temperatures because of temp.-dependence of K2

• relates the fractional change in pCO2 to the fractional change of DIC (at constant TA)

• range is is about 8-15 for the modern surface ocean and inversely proportional to temperature

• for R = 10, at a 10% increase in pCO2 is associated to a 1% increase in DIC

• high R stands for a low CO2 buffering capacity

DIC and TA increase with depth. The physical and the biological and the carbonate counter pump transport DIC as well as TA to depth, pumping against the gradient.

-> light and nutrients

-> usually PP growth is max. where light and nutrient availability are balanced (co-limitation)

-> grazing by zooplankton

High surface temperature in tropics and subtropics -> strong thermocline -> low exchange with deep water -> low nutrient supply to surface layer

Pico: 0.2-2µm

Nano: 2-20µm

Micro: 20-200µm

Meso200µm-2cm

1. Pico-/nanophytoplankton -> grazing increases with primary production

1. Microphytoplankton -> grazing can’t keep up with primary production

1 is found in oligotrophic systems e.g. North Atlantic gyre whilst 2 is found in nutrient rich regions e.g. upwelling zones/temperate climates

10% -> 1t of phytoplankton results in 10g of biomass after 6 trophic levels

Size of the primary producers because of transfer efficiency

low nutrient supply -> pico-/nanophytoplankton -> unicellualar microzooplankton -> low export

high nutrient supply -> microphytoplankton -> large multicellular zooplankton -> efficient export

Tropics: reduced vertical mixing -> reduced nutrient supply -> reduced productivity

High latitides: reduced mixing depth -> increased light intensity -> higher productivity

Ocean warming:

-> higher metabolic rates

-> increased remineralization

->reduced export

New production: supported by external nutrient input; N in form of NO3

Regenerated production: recycling ofnutrients in the euphotic zone; N in the form of NH4

f-ratio = new production / total primary production

0 < f-ratio <1

oligotrophic areas = 0.01 - 0.3

eutrophic areas = 0.4 - 0.8

in a steady state ocean: new production = export production

depth where there is at least 1% of light (upper 30-120m)

shorter wavelengths penetrate deeper than longer wavelengths

1. purple

2. red

3. yellow

4. green

5. blue

80% is absorbed in the upper 10m

The ratio of C, N and P in phytoplankton tissue (typically C124N16P1)

• in the two major superfamilies of eukaryotic phytoplankton (red and green)

  • red: Dino, Prymn, Diatoms

  • green: Prasino, Chloro

• growth strategy (Bloomer/Survivalist)

  • Bloomer: growth machinery with low N:P ratio (<10), adapted for exponential growth, high proportion of growth machinery (nucleic acids: C10H12O7N4P)

  • Survivalist: Resource acquisition machinery with high N:P ratio (>30). Sustains growth under low nutrients. Lots of pigmentsand proteins (proteins: C4H6ON -> NO P)

Nope

• Denitrification (sink)

• Nitrogen fixation (source)

• PO4 (DIP) availability limits N2 fixation -> N cycle is controlled by P cycle

nitrate deficiency -> NO3 - 16PO4 + 2.9mmol/m3

phosphate deficiency -> 16PO4 - NO3

• The common ratio of N:P is 16:1 which also resembles the phytoplankton stoichiometry

• If the concentrations in a certain region differ from this ratio there is either a P or N deficit (P*/N*)

• depending on the different concentartions N* and P* can be calculated using the equation

• the 2.9mmol/m3 are the global offset that needs to be corrected in order to have a balanced equation

Oxygen Minimum Zones are regions in the oceans that are O2 deprived. This happens due to high productivity in the surface layer resulting in high export rates and subsequently in low oxygen concnetration due to take up by respiration

-> OMZs show an N deficit

-> denitrification and anammox result in N deficiency (used as oxidizers as O2 levels are low)

-> anoxic sediments release P and Fe

-> N loss and P release cause low N:P

-> yields negative N* values (N deficit)

-> High N-fixation rates by aolian Fe input e.g. dust from the Sahara

• N2 fixation biochemistry requires circa 10.100 times more Fe per cell than algae growing on NO3 or NH3

• high Fe supply from Sahara dustt input permitts high N2 fixtion by Trichodesmium

• this rapidly depletes the available supply of phosphate

-> leads to N:P anomaly in the Atlantic

• Metamorphism and volcanism release CO2

  CaCO3 +SiO2 -> CaSiO3 + CO2

• Weathering consumes CO2

  CaSiO3 + 2CO2 + H2O -> Ca2+ +2HCO3- + SiO2

—> Weathering feedback stabilizes atmospheric pCO2 at timescales of >1.000.000 years

• Calcification releases CO2

  Ca2+ + 2HCO3- -> CaCO3 + CO2 + H2O

• CaCO3 dissolution consumes CO2

  CaCO3 + CO2 + H2O -> Ca2+ + 2HCO3-

• Ratio of CaCO3 to organic carbon in the flux of particulate matter to depth

• Determines the biogenic CO2 sink/source term between ocean and atmosphere

Neritic environments:

• benthic production predominates

• mainly aragonite and high-magnesium calcite

• production rates 40-4000g/m2/yr

Oceanic environments

• pelagic production predominates

• mainly calcite

• production several orders of magnitude lower than neritic production (compensated by larger area)

• caclcifying phytoplankton

• evolved 225 M years ago

• about 250 extant species

• haplo-diplontic life cycle (diploid phase is the most common one, phases differ in tterms of their coccoliths)

10M years as 500m were deposited and then compacted to 100m of chalk (all coccos btw)

1. Contribute about half to total calcite in holocene sediments

2. Contribute to both organic carbon pump and carbonate counter pump

1. Accelerated photosyntthesis (CO2 transfer from Coccolith vesicle)

2. Photodamage protection (PAR and UV sunshade and energy dissipation)

3. Armor protection against infection, selective grazing and non selective grazing

1. Ca2+ + 2HCO3- -> CaCO3 + CO2 + H2O

2. CaCO3 + CO2 + H2O -> Ca2+ + 2HCO3-

Aragonite is aboutt 40% more soluble than calcite

Ω is the saturation state of CaCO3. When Ω > 1 CaCO3 is stable and when Ω is < 1 CaCO3 tends to dissolve.

-> Ω is mostly controlled by [CO32-]

• [CO32-] decreases with depth, therefore the solubility of calcite and aragonite increase witth depth

• The saturation horizon is the depth where Ω = 1

• the saturation horizon in the North Pacific is shallower than in the North Atlantic

depth below ehich sediments are carbonate free

Horizon seperatting well preserved from poorly preserved assemblages (is between saturation horizon and CCD)

More CO2 -> shallower satuarion depth

The older the deep water masses in the amoc the more CO2 due to respiration -> the shallower the saturation horizon

The different buffering capacities of seawater and freshwater lead to vastly different equilibration timescales:

freshwater: 1 month

seawater: 1 year

• 3000 Gt CO2 is the 2°C limit

• we already added ~ 2200 Gt CO2 ~ 75%

• 800 Gt CO2 are left

• We add 36 Gt CO2 every year

• Therfore we have another 20 years if we keep going like this

• Sunshades

• Stratospheric aerosols

• Increased cloud albedo

• Increased surface albedo

• Air capture

• (Afforestaion)/Reforestation

• Nutrient addition

• Enhanced Upwelling

• Enhanced Downwelling

• Carbonate addition

• OAE

• Fe-fertilization

• TErrestrial biomass dumping

• Marine biomass farming (Sargassum)

• Artificial Upwelling

• Biochar

• CO2 removal from SW using CCS

• Bioenergy with CCS

• Changes in community compositioin

• Possible shift in food web structure

• Risk of harmful algal blooms

• Enhances deep water acidification and deoxygenation

• Risk of higher production of climate relevant gases (e.g. N2O)

• Downstream effects on nutrient availability

  -> reduced nutrients in equatorial and upwelling areas

• fertilize algae (capture CO2)

• pump down CO2

• produce dimethyl sulphide, the precurser of nuclei that form sunlight reflecting clouds

OAE is in the ocean and EW is on land

Omega is well above one in the open surface ocean, thus CaCO3 wouldnt dissolve and just sink out

All dumping into the ocean is prohibited

• Keep warming below 2°C -> 1.5°C

• Rich countries must provide 100 billion dollars from 2020 as a floor

• Developed countries have to take the lead

• Aim for greehouse gases to peak as soon as possible

• Review of progress every four years

• N:P of 16:1 is an average over all phytoplankton taxa

• bacterial processes cause a continuous loss of N

• Diazotrophic cyanobacteria fill up the N deficit