Calcareous nannofossils include the coccoliths and Calcareous nannofossils include the coccoliths and coccospheres of haptophyte algae and the associated nannoliths coccospheres of haptophyte algae and the associated nannoliths which are of unknown provenance.which are of unknown provenance. The organism which creates the coccosphere is called a The organism which creates the coccosphere is called a coccolithophore, they are phytoplankton (autotrophs that contain coccolithophore, they are phytoplankton (autotrophs that contain chloroplasts and photosynthesise).chloroplasts and photosynthesise). Their calcareous skeletons are found in marine deposits often Their calcareous skeletons are found in marine deposits often in vast numbers, sometimes making up the major component of a in vast numbers, sometimes making up the major component of a particular rock, such as the chalk of England. One freshwater particular rock, such as the chalk of England. One freshwater species has been reported.species has been reported. Formally coccolithophores are separated from other Formally coccolithophores are separated from other phytoplankton such as diatoms by the presence of a third flagella-phytoplankton such as diatoms by the presence of a third flagella-like appendage called a haptonema, although the flagella bearing like appendage called a haptonema, although the flagella bearing stage is often only one of a multi-stage life cycle.stage is often only one of a multi-stage life cycle.

A coccolith A coccolith is a single disc-like plate which is secreted by the is a single disc-like plate which is secreted by the algal organism and held in combination with several other, algal organism and held in combination with several other, sometimes varying shaped plates by an organic coating to form sometimes varying shaped plates by an organic coating to form the the coccospherecoccosphere.. On death the individual On death the individual coccolithscoccoliths invariably become separated invariably become separated and it is these that are most commonly preserved in the and it is these that are most commonly preserved in the sedimentary record.sedimentary record. Occasionally complete Occasionally complete coccospherescoccospheres are preserved and are preserved and provide valuable information, particularly regarding provide valuable information, particularly regarding coccospherescoccospheres which possess two or more morphologicaly different which possess two or more morphologicaly different coccolithscoccoliths.. There are two forms of There are two forms of coccolithscoccoliths, the , the holococcolithsholococcoliths which are which are formed from calcite crystals which are essentially identical in formed from calcite crystals which are essentially identical in shape and size and the shape and size and the heterococcolithsheterococcoliths which are formed from which are formed from larger calcite crystals which vary in size and shape. Most living larger calcite crystals which vary in size and shape. Most living forms are known to produce only forms are known to produce only heterococcolithsheterococcoliths and then only and then only during the non-motile stage of their life cycle.during the non-motile stage of their life cycle. Those that do produce Those that do produce holococcolithsholococcoliths do so only during their do so only during their motile stage.motile stage.

First recorded occurrences of calcareous First recorded occurrences of calcareous nannofossilsnannofossils ((nannolithsnannoliths) are from the late Triassic (Carnian).) are from the late Triassic (Carnian).

The locations from which the earliest The locations from which the earliest nannofossilsnannofossils are are found include; the Northern and Southern Calcareous Alps, found include; the Northern and Southern Calcareous Alps, Timor, North-West Australia and Queen Charlotte Islands Timor, North-West Australia and Queen Charlotte Islands (Canada), all low latitude sites at the time.(Canada), all low latitude sites at the time.

There are many claims for earlier occurrences but a lack of There are many claims for earlier occurrences but a lack of substantiated evidence means these must be excluded. One substantiated evidence means these must be excluded. One consequence of the first occurrence of calcareous consequence of the first occurrence of calcareous nannofossilsnannofossils in the late Triassic lies in the fact that this was in the late Triassic lies in the fact that this was the first time open ocean planktonic organisms utilised the first time open ocean planktonic organisms utilised calcareous skeletons and exported calcium carbonate into calcareous skeletons and exported calcium carbonate into the deep oceans. the deep oceans.

This has important repercussions in terms of This has important repercussions in terms of biogeochemical cycles.biogeochemical cycles.

Today Today coccolithophorescoccolithophores are one of the most important are one of the most important forms of phytoplankton found in the oceans, and may be forms of phytoplankton found in the oceans, and may be described as the grass of the sea.described as the grass of the sea.

Culture techniques have resulted in great advances in Culture techniques have resulted in great advances in the study of the study of coccolithophorecoccolithophore life cycles. life cycles.

The existence of a haploid and diploid phase has been The existence of a haploid and diploid phase has been proved by the extraction of DNA, with mitotic proved by the extraction of DNA, with mitotic reproduction occurring in both stages.reproduction occurring in both stages.

Syngamy (sexual reproduction) has not been Syngamy (sexual reproduction) has not been observed but is assumed to occur, the recent discovery observed but is assumed to occur, the recent discovery of combination of combination coccospherescoccospheres (where (where coccolithscoccoliths of two of two distinct forms occur on the same distinct forms occur on the same coccospherecoccosphere) has ) has meant the traditional classification will have to be meant the traditional classification will have to be radically revised and updated.radically revised and updated.

The defining feature of the haptophytes is the flagella-The defining feature of the haptophytes is the flagella-like haptonema which is generally coiled.like haptonema which is generally coiled.

It differs from the flagella proper in its internal It differs from the flagella proper in its internal structure and its basal attachment. During the non-structure and its basal attachment. During the non-motile phase the flagella disappear but the haptonema motile phase the flagella disappear but the haptonema often remains, the exact function of the haptonema is often remains, the exact function of the haptonema is not fully understood.not fully understood.

The algal cell contains a nucleus and two golden-The algal cell contains a nucleus and two golden-brown chloroplasts which may be moved around the cell brown chloroplasts which may be moved around the cell to optimise collection of available light.to optimise collection of available light.

The cell also contains mitochondria which contain The cell also contains mitochondria which contain enzymes which produce the energy for cell function, enzymes which produce the energy for cell function, vacuoles which deal with waste products and the Golgi vacuoles which deal with waste products and the Golgi body which is the site of body which is the site of coccolithcoccolith secretion in many secretion in many species. species.

In many species overlapping oval organic scales coat the In many species overlapping oval organic scales coat the outer cell membrane. These have concentric ridges on their outer cell membrane. These have concentric ridges on their distal faces and radiating ridges on their proximal faces. It distal faces and radiating ridges on their proximal faces. It seems the organic scales act as bases for the precipitation seems the organic scales act as bases for the precipitation of the calcite of the calcite coccolithscoccoliths..

A variety of A variety of coccolithcoccolith secretion strategies have been secretion strategies have been observed in different species, however it is probably true of observed in different species, however it is probably true of all all coccolithophorescoccolithophores that the production of that the production of coccolithscoccoliths is is controlled by light.controlled by light. Emiliania huxleyi Emiliania huxleyi has been observed to has been observed to start start coccolithcoccolith production within half an hour of being production within half an hour of being introduced to light, and produce an individual introduced to light, and produce an individual coccolithcoccolith in in one hour and a complete one hour and a complete coccospherecoccosphere in about thirty hours. in about thirty hours.

Plate (coccolith) consists of shields, plates, central area with or

without bars, spine, distal side (outward) and proximal side

Coccoliths morphology

Morphological components of coccoliths

The function of coccoliths is not known but may be one or more of four basic possibilities: •ProtectionProtection; from bacteria, physical damage, predators such as copepods or to form a chemical buffer zone.

•Flotation and buoyancyFlotation and buoyancy; aspherical forms may reduce sinking rates, the loss or addition of coccoliths may be a strategy employed to regulate position in the water column in order to optimise light or nutrient availability.

•Light regulationLight regulation; coccoliths may reflect sunlight protecting the cell from high light levels in the upper water column or refract sunlight into the cell allowing life in the lower photic zone. • BiochemistryBiochemistry; the cell may secrete calcite in order to expell a metabolic by-product enhancing the bichemical efficiency of the cell.

Kingdom: ProtistaKingdom: Protista

Division: ChrysophytaDivision: Chrysophyta

Class: CoccolithophyceaeClass: Coccolithophyceae

Classification is complicated by the fact that some Classification is complicated by the fact that some species are dimorphic, that is they possess more than species are dimorphic, that is they possess more than one one coccolithcoccolith on a single on a single coccospherecoccosphere.. This may lead to the belief that two species exist where This may lead to the belief that two species exist where in fact there is only one.in fact there is only one.

Also, pleomorphism (where a Also, pleomorphism (where a holococcolithholococcolith phase phase alternates with a alternates with a heterococcolithheterococcolith phase) may also result phase) may also result in in coccolithscoccoliths being placed in different species or even being placed in different species or even genera when in fact they are simply different stages in genera when in fact they are simply different stages in the life cycle of the same species.the life cycle of the same species.

CoccolithophoresCoccolithophores live in the photic zone (the surface waters, where live in the photic zone (the surface waters, where

sunlight reaches) and are photosynthesising (autotrophic); so are at the sunlight reaches) and are photosynthesising (autotrophic); so are at the

bottom of the marine food chain, excellentbottom of the marine food chain, excellent food for herbivorous food for herbivorous

bacteriabacteria..

Some have flagella (whip-like appendages) so unlike plants, are capable Some have flagella (whip-like appendages) so unlike plants, are capable

of movement; furthermore, they don't simply float around, but can of movement; furthermore, they don't simply float around, but can

swim.swim.

Although they are photosynthesising, some have been known to eat Although they are photosynthesising, some have been known to eat

bacteria.bacteria.

Reproduction is asexual-----simple division.Reproduction is asexual-----simple division.

Sensitive for temprature, more abundant at the tropics 100 000 cells/l.Sensitive for temprature, more abundant at the tropics 100 000 cells/l.

Coccolith Life-Style, Ecology and Reproduction

After death, they sink by rate of 15 cm/day.

Factors of dissolution

They form high proportion

of carbonate in the sediments

Recent 26%

Chalk (Cretaceous) 26%

Eocene 90%

They are largest producers of calcium carbonate on Earth today, and probably have been since the Late Jurassic. They dump about 1.5 million tons yearly of

limestone to the ocean floor.

Coccoliths and Sedimentation

Geologic history of coccoliths

Abundance of coccoliths in the stratigraphic column (Brasier, 1980).

As the groups name suggests calcareous As the groups name suggests calcareous nannofossilsnannofossils are small, are small, generally less than 30 microns across and usually between 5 and generally less than 30 microns across and usually between 5 and 10 microns (individual 10 microns (individual coccolithscoccoliths).). This has advantages and disadvantages. Advantages This has advantages and disadvantages. Advantages include:include:

•Good preservationGood preservation, their small size makes mechanical damage , their small size makes mechanical damage unlikely. unlikely.

•Widespread distributionWidespread distribution, as part of the phytoplankton , as part of the phytoplankton coccolithophorescoccolithophores are distributed throughout the photic zone are distributed throughout the photic zone (predominantly the upper 50m of the water column) across almost (predominantly the upper 50m of the water column) across almost all marine habitats. all marine habitats.

•A very large number of individual A very large number of individual coccolithscoccoliths may be may be preserved in a tiny amount of sediment hence only very preserved in a tiny amount of sediment hence only very small quantities of sample are needed to produce small quantities of sample are needed to produce statistically valid results. statistically valid results.

Disadvantages include:Disadvantages include:

•Because of dissolution of calcium carbonate at depth in sea Because of dissolution of calcium carbonate at depth in sea water (called the carbonate compensation depth (water (called the carbonate compensation depth (CCDCCD)), )), preservation is compromised in deep water sediments. preservation is compromised in deep water sediments. •Because of their small size and resistance to mechanical Because of their small size and resistance to mechanical breakdown breakdown nannofossilsnannofossils can be reworked, great care is therefore can be reworked, great care is therefore needed especially when utilising needed especially when utilising nannofossilsnannofossils for biostratigraphic for biostratigraphic studies. studies. •Again, because of the small size the opportunities for Again, because of the small size the opportunities for contamination are high, although careful and thorough preparation contamination are high, although careful and thorough preparation and collection techniques should significantly reduce this risk. and collection techniques should significantly reduce this risk.