System Earth 6b

Carbon cycle II

Misha Velthuis

m.velthuis@uva.nl

Tue 15 Oct 2024

Comments from last week

Questions from last week

Do we see less upwelling during El Niño years?

El Niño years

2002-2003
2004-2005
2006-2007
2009-2010
2014-2016 (strong one)
2018-2019
2023-2024

Note that primary production disappears at higher latitudes during the winter (no light).

In front of the coast of Ecuador more or less stable primary production.

"Coastal waters are more productive than the central ocean for two main reasons. First, runoff from land often contains a high abundance of nutrients which get deposited in coastal waters and stimulate production. Second, the shallower bottom along the continental shelf can trap nutrients and prevent them from sinking to greater depths. It is easier for these nutrients to be brought back to the surface when they remain trapped in the shallows."

From: Webb, P. (2021). Introduction to oceanography. Roger Williams University.

More biodiversity at higher latitudes?

Righetti, D., Vogt, M., Gruber, N., Psomas, A., & Zimmermann, N. E. (2019). Global pattern of phytoplankton diversity driven by temperature and environmental variability. Science advances, 5(5), eaau6253. link to report about article

Their study reveals that tropical waters hold the richest diversity of species at all times of the year. Phytoplankton diversity is particularly high in the seas of the Indonesian-Australian archipelago, in parts of the Indian Ocean and in the equatorial Pacific Ocean. In the subtropics, biodiversity drops off markedly beyond 30 degrees latitude North and South, reaching its lowest values around a latitude of 55 degrees. Diversity then picks up again slightly towards the poles.

Species diversity typically decreases continuously towards the poles, where it is normally at its lowest. Temperature could plausibly be the direct driver of this decline. According to metabolic theory, higher temperatures accelerate metabolism, mutations of genetic material and speciation. This explains why the tropics are richer in species than the mid-latitudes and the polar regions, as would be expected.

The study reveals that phytoplankton does not always behave in line with this theory. "Evidently, there are factors other than temperature affecting plankton diversity," Righetti says. Two of these might be the strong currents and turbulence, which are prevalent in the mid-latitudes, but less so in polar or tropical seas. "The seasonal fluctuations and ocean turbulence in these latitudes might suppress the development of biodiversity, even though the temperatures here are higher than in the polar oceans," the ecologist says.

From: Webb, P. (2021). Introduction to oceanography. Roger Williams University.

In temperate regions there is much more seasonal variation in the depth and intensity of the thermocline. The thermocline is shallower and stronger in the summer, and is deeper and weaker in the winter, so mixing of deep and surface water is more pronounced in the winter months. As with the poles, this winter mixing creates nutrient-rich water during the winter, but the lack of light limits winter productivity. When light levels increase in the spring, the combination of abundant light and nutrients creates a spring bloom of productivity. By late summer there is still plenty of light, but the nutrients have been depleted by the phytoplankton bloom, and the summer thermocline has prevented further mixing, so productivity declines. In the autumn, cooler temperatures weaken the thermocline, and increasing storms cause a deeper mixed layer to form, bringing nutrients back to the surface. At the same time, there is still sufficient light available that a smaller autumn bloom occurs. But this bloom is short-lived, as light declines throughout the autumn and into the winter. Again, there is little production during the winter due to light limitations, but the winter storms and deep thermocline recharge the water with nutrients for the next spring bloom.

Distribution biomass

Big flow small stock
small flow and big stock

Recap from last Friday

Carbon cycles

Organic

Inorganic

Multiple carbon cycles

Short-term
terrestrial
organic carbon cycle

Photosynthesis

CO₂ + H₂O → CH₂O + O₂

Respiration/ decomposition

CH₂O + O₂ → CO₂ + H₂O

Short-term organic carbon cycle

Although, spatial variation

Short-term
marine
organic carbon cycle

Multiple carbon cycles

Phytoplankton

Phytoplankton and zooplankton

Diatom (algae)

Cocolithophorid

Foraminifera (zooplankton)

Biological pump

biological pump.png

Input of organic material by phytoplankton (and then zooplankton).

Oxygen

Photic zone: high O₂ because diffusion with atmosphere + photosynthesis
Oxygen minimum zone: low O₂ because of decomposition/respiration + distance from atmosphere
Higher depths: high O₂ because bottom water was cold during subsidence, and solubility of gases increases as temperature of water decreases.
- BTW: solubility of gases in cold water is higher because of lower kinetic energy of gas molecules.

Nutrients

Like NO₃^- and PO₄^3-
Photic zone: primary production → nutrient depletion
Settling and decomposition of organic matter: high nutrient availability
(By the way: nutrients = "elements that are necessary for growth and exist at suboptimal concentrations". Water is e.g. generally not considered a nutrient in this context).

Carbon dioxide

Photic zone: photosynthesis → low CO₂
Higher depths, more CO₂ producing decomposition and respiration of settling organic matter + less "CO₂ consuming primary production" → increase of CO2
Bottom water = cold = high solubility for CO₂

Impact of aging bottom water

Nutrients increase

Oxygen decreases

But still: short-term organic carbon cycle

Long-term
organic
carbon cycle

Multiple carbon cycles

Long-term organic carbon cycle

Fossil carbon of terrestrial origin

Fossil carbon of marine origin

Even without humans, fossil carbon is oxidized

Today: inorganic carbon cycles

Short term sources and sinks of CO₂

CO2 in water

What happens when CO2 concentration in water increases?

Starting position: the three two-way reactions are in equilibrium. \[\frac{[HCO_3^{-}][H^{+}]}{[H_2CO_3]}, pK = 6\] \[\frac{[H^{+}][CO_3^{2-}]}{[HCO_3^{-}]}, pK = 9.19\]

When ([HCO₃^-]*[H⁺])/[H₂CO₃] is lower than 10^-6 the reaction will move to the right. When it is higher than 10^-6 it will move to the left.

Next: higher CO2 concentration in atmosphere causes more CO2 to diffuse and dissolve in the surface ocean. This will cause…

… reaction 1 to move to the right
… reaction 2 to move to the right
… reaction 3 to move to the left

Why does reaction 3 move to the left, when reaction 2 produces both bicarbonate ion (on the left side of reaction 3) and hydrogen ion (on the right side of reaction 3)?

Because the default concentration of hydrogen ion in the ocean is much lower than that of bicarbonate ion, and because reaction 2 creates both in equal amounts, the percentage-wise increase of hydrogen ion is higher than that of bicarbonate ion.

This means that the product of [H⁺] and the [CO₃^2-] (right side of reaction 3) will have increased more than [HCO₃^-] (left side of reaction 3).

So to ensure that ([H⁺]*[CO₃^2-])/[HCO₃^-] returns to 10^-9.19 (pK = 9.19), the reaction has to move to the left.

Some important results:

An increase of the CO₂ concentration in the atmosphere causes the ocean to acidify.
In the end, the increase of the [H⁺] concentration is smaller than it would have been without carbonate ion: the presence of carbonate ion slows down the acidification (buffer).
In the end, the concentration of all reactants and products will be higher, except carbonate ion.
- Buffer capacity is lost.
- Calcifiers (organisms that use CO₃^2- to build their shells) get in trouble.
As the concentration of dissolved CO₂ goes up, the rate at which the ocean takes up atmospheric CO₂ will go down.

Long term sources and sinks

Carbonate precipitation

Carbon cycles

Organic

Inorganic

Chemical weathering (CO2 in rain water)

CO2 dissolves into rain water:

One mole of CO2 produces one mole of carbonic acid.

Carbonate weathering:

Uses one mole of carbon from calcium carbonate, and one mole of carbon from carbonic acid (which exists in equilibrium with atmospheric CO2), and produces two moles of bicarbonate ion.

Silicate weathering:

Uses two moles of carbon from carbonic acid (which exists in equilibrium with atmospheric CO2), and produces two moles of bicarbonate ion.

Carbonate precipitation:

Uses two moles of bicarbonate ion, and produces one mole calcium carbonate and one mole carbonic acid (which exists in equilibrium with atmospheric CO2).

Carbonate weathering + carbonate precpitation:

Uses one mole of carbon from the atmospheric CO2 reservoir, and returns one mole of carbon to the atmospheric CO2 reservoir.

Carbonate weathering + carbonate precpitation:

Uses two moles of carbon from the atmospheric CO2 reservoir, and returns only one mole of carbon ato the atmospheric CO2 reservoir. The other is "locked away" in CaCO₃.

Carbonate+carbonate vs silicate+carbonate

Long-term sources and sinks

Visible in this graph:

Carbonate weathering takes as much carbon from the atmosphere as from the carbonate sedimentary rock (0.17 Gt(C)/yr).

Silicate weathering works on rocks that do not contain carbon: this proces only uses carbon from the atmosphere (0.03 Gt(C)/yr).

Of the 0.50 Gt(C)/yr that precipitates as marine carbonate sediment, 0.30 Gt(C)/yr returns as the result of sea-floor dissolution.

0.20 Gt(C)/yr gets stored as carbonate sedimentary rock.

0.17 Gt(C)/yr of the carbon that is stored in carbonate sedimentary rock is removed in carbonate weathering.

0.03 Gt(C)/yr of it, undergoes carbonate metamorphism, which ultimately leads to the CO2 that is released through volcanism.

Note that the carbon taken from the atmosphere also first turns to CO₂ (dissolved) and H₂CO₃, but this happens in rain water on the continent (rather than in the reservoir "oceanic CO₂ and H₂CO₃")).

Our near future together

End

my (none of your)
Business card

Personal projects

Mastodon account: https://social.edu.nl/deck/@MishaVelthuis

Blog: https://mishathings.org/

Music: https://mishathings.org/music_things/

Reading: https://bookrastinating.com/user/misha/books/read

OpenTech(AUC)

We are a group of students and staff members at Amsterdam University College. We care about Open Standards, Free Software, and Open Data.

We believe that people need to take back control over their digital lives, and we believe that we, at the university, have a big responsibility to help each other do so.

https://opentech-auc.org/

See for example: the internet is broken and this is what we can do about it.

Staff Students Platform

Staff Students Platform (SSP) is a bottom-up, grassroots collective of students and staff who are determined to work together to organize and facilitate the kind of events that we feel are necessary to (re)build understanding at AUC, in the face of the ongoing violence in Palestine and the protests addressing it.

https://staffstudentsplatform-auc.org/

System Earth 6b

Carbon cycle II

Misha Velthuis

m.velthuis@uva.nl

Tue 15 Oct 2024

Comments from last week

Questions from last week

Do we see less upwelling during El Niño years?

More biodiversity at higher latitudes?

Distribution biomass

Big flow small stock small flow and big stock

Recap from last Friday

Carbon cycles

Multiple carbon cycles

Short-term terrestrial organic carbon cycle

Short-term organic carbon cycle

Although, spatial variation

Short-term marine organic carbon cycle

Multiple carbon cycles

Phytoplankton

Phytoplankton and zooplankton

Biological pump

Impact of aging bottom water

But still: short-term organic carbon cycle

Long-term organic carbon cycle

Multiple carbon cycles

Long-term organic carbon cycle

Fossil carbon of terrestrial origin

Fossil carbon of marine origin

Even without humans, fossil carbon is oxidized

Today: inorganic carbon cycles

Short term sources and sinks of CO2

CO2 in water

Long term sources and sinks

Carbonate precipitation

Carbon cycles

Chemical weathering (CO2 in rain water)

Carbonate+carbonate vs silicate+carbonate

Long-term sources and sinks

Our near future together

End

my (none of your)Business card

Big flow small stock
small flow and big stock

Short-term
terrestrial
organic carbon cycle

Short-term
marine
organic carbon cycle

Long-term
organic
carbon cycle

Short term sources and sinks of CO₂

my (none of your)
Business card