Q5: How do variables such as the phytoplankton abundance and growth contribute
climate regulation? How can effects of the biosphere be quantified for radiation
budget calculations?
The activity of the biota, particularly marine organisms, can regulate climate by affecting
the composition of the atmosphere. For example, photosynthesis in the oceans is a major
sink of atmospheric CO2. The sinking of biogenic carbon to the deep sea removes (or
sequesters) carbon from atmospheric circulation for centuries. Phytoplankton are also a
source of sulfur compounds that are involved in cloud formation. Phytoplankton thus
help regulate climate, because cloud albedo and absorption of infrared radiation are
important in the Earth’s heat balance, as we have seen.
Biological Pump
The “biological pump” is the process by which phytoplankton production removes CO2
from atmospheric circulation. In the oceans, most of the phytoplankton production is
consumed in the upper ocean. However, some of the material such as dead organisms,
skeletal material and feces escapes consumption and sinks to the deep sea. In the deep
sea, this material is trapped in deep water currents or in sediments and is thus removed
from atmospheric circulation for long periods of time (centuries). The rate at which
carbon is removed by the biological pump varies over space and time. Biological factors
(production, predation, decomposition) and physical/chemical factors (density
stratification, acidity of the ocean, wind speed, etc.) affect the efficiency of the biological
pump.
Coccolithophore bloom off the Coast of Britanny
(http://visibleearth.nasa.gov/view_rec.php?id=705)
Coccolithophores under the Scanning Electron Microscope
www.msrc.sunysb.edu/octet/BP_Fig_1.gif
Phytoplankton, sulfur compounds, clouds and climate
Marine phytoplankton are a major source of volatile sulfur compounds, which control
cloud formation. Because clouds play a major role in regulating climate, the production
of DMSP by phytoplankton has been proposed as a possible mechanism by which the
activity of the biota can regulate climate
More specifically, marine algae produce dimethylsulfoniopropionate (DMSP), which is
converted to dimethylsufide (DMS) by phytoplankton and bacterial enzymes during the
decomposition of phytoplankton. DMS then enters the atmosphere where it is photooxidized to sulfate aerosols. DMS accounts for 95% of the natural marine input of sulfur
gases to the atmosphere. This is estimated to be about 50% of the total global biogenic
source of sulfur to the atmosphere. Sulfur compounds act as cloud condensation nuclei
(CNN) thus determining the amount of cloud cover. Cloud’s affect climate by reflecting
incoming solar radiation and also by absorbing infrared radiation from the Earth.
Algae → DMSP (+ phytoplankton) → DMS → sulfate aerosols → cloud seeds →
absorption and reflection of radiation from Earth and Sun
The function of DMS in phytoplankton is not well understood. There is evidence that it
serves as an osmolyte (to regulate osmotic pressure), cryoprotectant (to protect against
cold) and even as an antioxidant (to protect against decay).
Some challenges associated with understanding the regulation of climate by DMS
production are:
o DMS production is a result of DMSP production and its decomposition by
complex ecological interactions (e.g, grazing, viral lysis, bacterial
decomposition)
o DMS production varies with species and it not necessarily related to their
rate of biomass production.
Zooplankton = animals, phytoplankton = plants, plankton = drifters
Grazing: zooplankton graze on phytoplankton
Lysis: phytoplankton cells burst when they get grazed on or when infected by viruses;
when they burst, they release DMSP
Gerardo is interested in relationships between bacteria and phytoplankton