Biological pump

[5][6]: 526 [7] The biological pump can be divided into three distinct phases, the first of which is the production of fixed carbon by planktonic phototrophs in the euphotic (sunlit) surface region of the ocean.

[8] Once this carbon is fixed into soft or hard tissue, the organisms either stay in the euphotic zone to be recycled as part of the regenerative nutrient cycle or once they die, continue to the second phase of the biological pump and begin to sink to the ocean floor.

Inorganic nutrients and carbon dioxide are fixed during photosynthesis by phytoplankton, which both release dissolved organic matter (DOM) and are consumed by herbivorous zooplankton.

Trace metals such as magnesium, cadmium, iron, calcium, barium and copper are orders of magnitude less prevalent in phytoplankton organic material, but necessary for certain metabolic processes and therefore can be limiting nutrients in photosynthesis due to their lower abundance in the water column.

Calcium carbonate often forms remarkable deposits that can then be raised onto land through tectonic motion as in the case with the White Cliffs of Dover in Southern England.

One consequence of this is that when deep water upwells in warmer, equatorial latitudes, it strongly outgasses carbon dioxide to the atmosphere because of the reduced solubility of the gas.

These aggregates, known as marine snow, have sinking rates orders of magnitude greater than individual cells and complete their journey to the deep in a matter of days.

A portion of the POC is respired back to CO2 in the oceanic water column at depth, mostly by heterotrophic microbes and zooplankton, thus maintaining a vertical gradient in concentration of dissolved inorganic carbon (DIC).

[68] A large fraction of particulate organic matter occurs in the form of marine snow aggregates (>0.5 mm) composed of phytoplankton, detritus, inorganic mineral grains, and fecal pellets in the ocean.

The fraction of organic matter that leaves the upper mixed layer of the ocean is, among other factors, determined by the sinking velocity and microbial remineralisation rate of these aggregates.

[56] As illustrated by Turner in 2015, the vertical flux of sinking particles is mainly due to a combination of fecal pellets, marine snow and direct sedimentation of phytoplankton blooms, which are typically composed of diatoms, coccolithophorids, dinoflagellates and other plankton.

[56] Marine snow comprises macroscopic organic aggregates >500 μm in size and originates from clumps of aggregated phytoplankton (phytodetritus), discarded appendicularian houses, fecal matter and other miscellaneous detrital particles,[56] Appendicularians secrete mucous feeding structures or "houses" to collect food particles and discard and renew them up to 40 times a day .

[100] The main functional groups of marine phytoplankton that contribute to export production include nitrogen fixers (diazotrophic cyanobacteria), silicifiers (diatoms) and calcifiers (coccolithophores).

and prasinophytes (various genera of eukaryotes <2 μm)—are believed to contribute much less to carbon export from surface layers due to their small size, slow sinking velocities (<0.5 m/day) and rapid turnover in the microbial loop.

[105][106] In contrast, larger phytoplankton cells such as diatoms (2–500 μm in diameter) are very efficient in transporting carbon to depth by forming rapidly sinking aggregates.

[112] Absorption efficiency (AE) is the proportion of food absorbed by plankton that determines how available the consumed organic materials are in meeting the required physiological demands.

The term microbial loop was coined by Farooq Azam, Tom Fenchel et al.[118] in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.

In general, dissolved organic carbon is introduced into the ocean environment from bacterial lysis, the leakage or exudation of fixed carbon from phytoplankton (e.g., mucilaginous exopolymer from diatoms), sudden cell senescence, sloppy feeding by zooplankton, the excretion of waste products by aquatic animals, or the breakdown or dissolution of organic particles from terrestrial plants and soils.

[129] Whales and other marine mammals also enhance primary productivity in their feeding areas by concentrating nitrogen near the surface through the release of flocculent fecal plumes.

[132] The biological pump mediates the removal of carbon and nitrogen from the euphotic zone through the downward flux of aggregates, feces, and vertical migration of invertebrates and fish.

[134] Copepods and other zooplankton produce sinking fecal pellets and contribute to downward transport of dissolved and particulate organic matter by respiring and excreting at depth during migration cycles, thus playing an important role in the export of nutrients (N, P, and Fe) from surface waters.

On a global scale, they can influence climate, through fertilization events and the export of carbon from surface waters to the deep sea through sinking whale carcasses.

[137] In coastal areas, whales retain nutrients locally, increasing ecosystem productivity and perhaps raising the carrying capacity for other marine consumers, including commercial fish species.

With warming oceans and increasing melting of ice caps due to climate change, the organisms associated with the lipid pump may be affected, thus influencing the survival of many commercially important fish and endangered marine mammals.

[140][141][142] Luminous bacteria in light organ symbioses are successively acquired by host (squid, fish) from the seawater while they are juveniles, then regularly released into the ocean.

Diel (and seasonal) vertical migrators feeding on luminous food metabolize and release glowing fecal pellets from the surface to the mesopelagic zone (step 4).

Luminous bacteria attached to particles sink down to the seafloor, and sediment can be resuspended by oceanographic physical conditions (step 5) and consumed by epi-benthic organisms.

A common method is to estimate primary production fuelled by nitrate and ammonium as these nutrients have different sources that are related to the remineralisation of sinking material.

[161] They employed environmental data described in the IPCC Representative Concentration Pathways scenario 8.5, which predicts radiative forcing in the year 2100 relative to pre-industrial values.

They predicted changes in the range and distribution of these two phytoplankton species under these future ocean conditions, if realized, might result in reduced contribution to carbon sequestration via the biological pump.

The pelagic food web , showing the central involvement of marine microorganisms in how the ocean imports carbon and then exports it back to the atmosphere and ocean floor
Pump processes vary with depth
Photic zone: 0–100 m; Mesopelagic: 100–1000 m; Bathypelagic: 1000 to abyssal depths. Below 1000 m depth carbon is considered removed from the atmosphere for at least 100 years. Scavenging: DOC incorporation within sinking particles. [ 9 ]
Components of the biological pump
Size and classification of marine particles [ 11 ]
Adapted from Simon et al., 2002. [ 12 ]
DOM and POM
Connections between the different compartments of the living (bacteria/viruses and phyto−/zooplankton) and the nonliving (DOM/POM and inorganic matter) environment [ 15 ]
The fate of DOM in the ocean
Particulate inorganic carbon budget for Hudson Bay
Black arrows represent DIC produced by PIC dissolution. Grey lines represent terrestrial PIC. [ 17 ] Units are Tg C y −1
The White Cliffs of Dover are made almost entirely
of the plates of buried coccolithophores ( see below ↓ )
Oceanic Carbon Cycle — IPCC
Solubility pump: Air-sea exchange of CO 2
Processes in the biological pump [ 51 ]
Carbon fluxes in white boxes are in Gt C yr −1 and carbon masses in dark boxes are in Gt C
Marine snow, phytoplankton and the biological pump [ 61 ]
Budget calculations of the biological carbon pump are based on the ratio between sedimentation (carbon export) and remineralization (release to the atmosphere). [ 62 ]
The nitrogen fixing cyanobacteria Cyanothece sp. ATCC 51142
Morphology of zooplankton fecal pellets [ 112 ]
Collected from marine snow catchers (a–c) and sediment traps (d–f).
Morphological classes: (a, d) round, (b, e) cylindrical, and (c, f) ovoid.
Scale bar = 0.5 mm
The microbial loop is a marine trophic pathway which incorporates dissolved organic carbon (DOC) into the food chain
Gelatinous zooplankton biological pump
How jelly carbon fits in the biological pump. A schematic representation of the biological pump and the biogeochemical processes that remove elements from the surface ocean by sinking biogenic particles including jelly carbon. [ 126 ]
Jellyfish are easy to capture and digest and may be more important as carbon sinks than was previously thought. [ 131 ]
The whale pump is the role played by whales and other marine mammals recycling nutrients in the ocean
Bioluminescence shunt in the biological carbon pump in the ocean [ 146 ]
Diagram showing relative sizes (in gigatonnes) of the main storage pools of carbon on Earth. Cumulative changes (thru year 2014) from land use and emissions of fossil carbon are included for comparison. [ 147 ]
Effect of temperature on the biological pump
Effects of different water temperatures on organic carbon export and remineralization: more carbon is sequestered when temperature is colder compared to when is warmer. [ 9 ]
Arctic carbon fluxes influenced by sea ice decline
and permafrost thaw [ 154 ] [ 155 ]
Global estimate of the vertically integrated anthropogenic dissolved inorganic carbon (DIC) in the ocean in recent times (1990s)
Monitoring the ocean biological carbon pump [ 4 ] Pools, fluxes and processes that form the ocean biological carbon pump, and current methods used to monitor them. Bold black text and thick black arrows represent the key export pathways and interactions with other domains (land and atmosphere). Global stocks of the different carbon pools in the ocean are given in the box on the left; the four major kinds of pools – DIC , DOC , POC and PIC – are given in different colours.
This figure has been inspired by, and builds on, two earlier figures, one from the CEOS carbon from space report [ 163 ] and the other from the NASA EXPORTS plan. [ 164 ]
Multidisciplinary observations still needed in the deep water column
to properly understand the biological pump [ 165 ]
EOVs = Essential Ocean Variables