Late Cretaceous and modern diatom ecology: implications for our changing oceans

Sin título

Photomicrographs of diatom resting spores. Scale bars =10 mm (From Davies and Kemp, 2016)

Diatoms are unicellular algae with golden-brown photosynthetic pigments with a fossil record that extends back to Early Jurassic. They live in aquatic environments, soils, ice, attached to trees or anywhere with humidity, and their remains accumulate forming diatomite, a type of soft sedimentary rock. The most distinctive feature of diatoms is their siliceous skeleton known as frustule that comprise two valves. The formation of this opaline frustule is linked  in modern oceans with the biogeochemical cycles of silicon and carbon.

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the Late Cretaceous the global climate change has been associated with episodes of outgassing from major volcanic events, orbital cyclicity and tectonism before ending with the cataclysm caused by a large bolide impact at Chicxulub, on the Yucatán Peninsula, Mexico. Following a major diatom radiation after the Cenomanian-Turonian anoxic event, the development of the first extensive diatomites provides the earliest widespread geological evidence for the rise to prominence of diatoms in ocean biogeochemistry. Studies of the greenhouse Cretaceous climates are especially topical since such warm, high CO2 periods of the past are often invoked as potential analogues for present warming trends (Davies and Kemp, 2016).

A. Chain of Stephanopyxis turri (From

A. Chain of Stephanopyxis turri (From Davies and Kemp, 2016)

Because their abundance and sensitivity to different parameters,  diatoms play a key role in Paleoceanography, particularly for evidence of climatic cooling and changing sedimentation rates in the Arctic and Antarctic oceans and to estimate sea surface temperature. Like Stephanopyxis, a common planktonic genus in the present oceans distinguished by its long stratigraphic range from the Albian to modern. Stephanopyxis can be found in tropical or warm water regions and evidence suggests a similar ecological adaptation during the Cretaceous. Meanwhile, resting spore development is generally associated with the onset of unfavourable environmental conditions and sporulation generally occurs in response to a sudden change in one or more environmental factors.

Since the start of the Industrial Revolution the anthropogenic release of CO2 into the Earth’s atmosphere has increased a 40%. In this context, warming of the present surface ocean is  leading to increased stratification in both hemispheres. Based on traditional views of diatom ecology, ocean stratification would  lead to decreased diatom production and a reduced effectiveness of the marine biological carbon pump. But recent ocean surveys, and records of the stratified seas of the Late Cretaceous, suggest that increased stratification may lead to increased rather than decreased diatom production and export. This would then result in a negative-rather than positive feedback to global warming (Davies and Kemp, 2016).

 

References:

A. Davies, A.E.S. Kemp, Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments, Cretaceous Research 65 (2016) 82-111

Martin, R. E. and Quigg, A. 2012 Evolving Phytoplankton Stoichiometry Fueled Diversification of the Marine Biosphere. Geosciences. Special Issue on Paleontology and Geo/Biological Evolution. 2:130-146.

Application of diatoms to tsunami studies.

Lisbon earthquake and tsunami in 1755 (From Wikipedia Commons)

Lisbon earthquake and tsunami in 1755 (From Wikipedia Commons)

Diatoms are unicellular algae with golden-brown photosynthetic pigments with a fossil record that extends back to Early Jurassic. The most distinctive feature of diatoms is their siliceous skeleton known as frustule that comprise two valves. They live in aquatic environments, soils, ice, attached to trees or anywhere with humidity and their remains accumulates forming diatomite, a type of soft sedimentary rock. Diatoms are the dominant marine primary producers in the oceans and play a key role in the carbon cycle and in the removal of biogenic silica from surface waters. But diatoms are also a valuable tool in reconstructing paleoenvironmental changes because of their sensitivity to environmental factors including salinity, tidal exposure, substrate, vegetation, pH, nutrient supply, and temperature found in specific coastal wetland environments. Through years, diatoms become part of the coastal sediments, resulting in buried assemblages that represent an environmental history that can span thousands of years. Diatoms alone cannot differentiate tsunami deposits from other kinds of coastal deposits, but they can provide valuable evidence for the validity of proposed tsunami deposits (Dura et al., 2015).

Electron microscope image of Diatoms from high altitude aquatic environments of Catamarca Province, Argentina (From Maidana and Seeligmann, 2006)

Electron microscope image of Diatoms from high altitude aquatic environments of Catamarca Province, Argentina (From Maidana and Seeligmann, 2006)

Tsunami deposits can be identify by finding anomalous sand deposits in low-energy environments such as coastal ponds, lakes, and marshes. Those anomalous deposits are diagnosed using several criteria such as floral (e.g. diatoms) and faunal fossils within the deposits. The delicate valves of numerous diatom species may be unusually well preserved when removed from surface deposits and rapidly buried by a tsunami.

Diatoms within the tsunami deposits are generally composed of mixed assemblages, because tsunamis inundated coastal and inland areas, eroding, transporting, and depositing brackish and freshwater taxa. Nonetheless, problems differentiating autochthonous (in situ) and allochthonous (transported) diatoms complicates reconstructions. In general, planktonic diatoms are considered allochthonous components in modern and fossil coastal wetland assemblages, while benthic taxa can be considered as autochthonous. Diatoms can also be used to estimate tsunami run-up  by mapping the landward limit of diatom taxa transported by the tsunami.

 

References:

Hemphill-Haley, E., 1996. Diatoms as an aid in identifying late Holocene tsunami deposits. The Holocene 6, 439–448.

Tina Dura, Eileen Hemphill-Haley, Yuki Sawai, Benjamin P. Horton, The application of diatoms to reconstruct the history of subduction zone earthquakes and tsunamis, Earth-Science Reviews 152 (2016) 181–197. DOI: 10.1016/j.earscirev.2015.11.017

Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford.

Barron, J.A. (2003). Appearance and extinction of planktonic diatoms during the past 18 m.y. in the Pacific and Southern oceans. “Diatom Research” 18, 203-224

Diatoms and Climate Change.

Diatoms living between crystals of annual sea ice in McMurdo Sound, Antarctica. From Wikimedia Commons.

Diatoms living between crystals of annual sea ice in McMurdo Sound, Antarctica. From Wikimedia Commons.

Diatoms are unicellular algae with golden-brown photosynthetic pigments with a fossil record that extends back to Early Jurassic. The most distinctive feature of diatoms is their siliceous skeleton known as frustule that comprise two valves. The formation of this opaline frustule is linked  in modern oceans with the biogeochemical cycles of silicon and carbon.

Because their abundance and sensitivity to different parameters,  diatoms play a key role in Paleoceanography , particularly for evidence of climatic cooling and changing sedimentation rates in the Arctic and Antarctic oceans and to estimate sea surface temperature. Also, diatom diversity can be used as a proxy for the influence of diatoms on marine export productivity and the carbon cycle.

Diatoms are thought to have diversified over the Cenozoic. Early Cenozoic oceans were relatively warm, but in the early to mid Eocene, ocean surface temperatures began to cool, and polar regions and tropical regions began to be more strongly differentiated. It was suggested that Late Eocene diatom proliferation likely occurred in response to subsidence of Southern Ocean land bridges and the concurrent development of circum-Antarctic upwelling.

Actinocyclus ingens Rattray and Thalassiosira convexa (SEM, Neogene diatoms from the Southern Ocean, ODP)

Actinocyclus ingens Rattray and Thalassiosira convexa (SEM, Neogene diatoms from the Southern Ocean, ODP)

Peak species diversity in marine planktonic diatoms occurred at the Eocene–Oligocene boundary followed by a pronounced decline, from which they have not recovered (Rabosky 2009).  During the early late Miocene, when temperatures and pCO2 were only moderately higher than today, diatoms lost about 20% of its diversity. Warmer oceans are linked with lower diatom diversity, suggesting that future warmer oceans due to anthropogenic warming may result in lower diatom diversity (Lazarus, 2014).

During the last 15 million years, diatom diversity is correlated with global carbon isotope record and with the past atmospheric pCO2, suggesting that diatoms have played a very important role in the evolution of mid-Miocene to Recent climate for their prominent role in the carbon pump.

References:

Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford.

Lazarus D, Barron J, Renaudie J, Diver P, Türke A (2014) Cenozoic Planktonic Marine Diatom Diversity and Correlation to Climate Change. PLoS ONE 9(1):e84857. doi:10.1371/journal.pone.0084857

Egan KE, Rickaby REM, Hendry KR, Halliday AN (2013) Opening the gateways for diatoms primes Earth for Antarctic glaciation. Earth and Planetary Science Letters 375: 34–43. doi: 10.1016/j.epsl.2013.04.030

The origin of modern phytoplankton.

plankton

A single valve of the diatom Thalassiosira pacifica, the coccolithophore Scyphospahaera apsteinii and a pair of phycomas of Pterosperma moebii. (From Falkowski 2004)

The term “phytoplankton” derives from Greek roots: φψτος (phytos) –related to plants – and πλαγκτον (plankton) meaning a “wanderer” or a “drifter”. It was coined by Christian Gottfried Ehrenberg in 1897 and describes a diverse, polyphyletic group of mostly single-celled photosynthetic organisms that drift with the currents in marine and fresh waters.

The evolutionary history of eukaryotic phytoplankton has been studied through morphological fossils and molecular biomarkers such as lipids or nucleic acids. Organic walled fossils  made by eukaryotic phytoplankton occur in rocks as old as 1.6 to 1.8 billion years, but their morphological diversity is low and their phylogenetic relationships obscure.

The acritarchs were dominant forms of eukaryotic phytoplankton during the NeoProterozoic and the Paleozoic. These forms diversified markedly, in parallel with the Cambrian and Ordovician radiations of marine invertebrates. The group began to decline in the Late Devonian. And of course, the End-Permian mass extinction marked a major transition in ocean ecosystem structure.

plankton

Geologic range and relative diversity of eukaryotic phytoplankton. From Martin 2012.

Diatoms, dinoflagellates and coccolithophores, appeared in the geologic record during the Mesozoic. The radiation of this modern eukaryotic phytoplankton is paralleled with a long-term increase in sea level with and expansion of flooded continental shelf area.

These taxa have been grouped under the informal heading of “red” algal lineages primarily on the basis of their chlorophyll-c plastids. The shift from green to red phytoplankton lineages may have actually begun during the late Paleozoic.

Trace elements were important in defining the evolutionary trajectory of these groups of phytoplankton. While green algae need higher concentrations of iron, zinc and copper, red forms need higher amounts of manganese, cobalt and cadmium. Geologic evidence indicates that oxygen levels in the Mesozoic were much higher and that helped the micronutrients used by the red phytoplankton to remain dissolved in the oceans and available for uptake.

Diatoms living between crystals of annual sea ice in McMurdo Sound, Antarctica. From Wikimedia Commons.

Diatoms living between crystals of annual sea ice in McMurdo Sound, Antarctica. From Wikimedia Commons.

But, changes in the availability of macronutrients, such as phosphorus, also contributed significantly to the success of these groups. The patterns of diversity in the fossil records of dinoflagellates and coccolithophorids are roughly concordant, but differs with that of diatoms. This reflect different ecological strategies. In contrast to dinoflagellates and coccolithophores, diatoms have evolved a nutrient storage vacuole that can retain sufficiently high concentrations of nitrate and phosphate such that a cell can undergo several divisions without the need for external macronutrients.

Human activities are altering ocean conditions at a speed unsurpassed in our Earth’s history. In modern oceans, the coccolithophores and other calcifying phytoplankton that live in surface waters may be devastated by the acidification, which reduces the availability of minerals needed to make and maintain their shells.
As the oceans warm, they may also become increasingly stratified, impeding upwelling and circulation. In such conditions, dinoflagellates could increase the frequency and surface area covered by toxic blooms in coastal habitats.

References:

Martin, R. E. and Quigg, A. 2012 Evolving Phytoplankton Stoichiometry Fueled Diversification of the Marine Biosphere. Geosciences. Special Issue on Paleontology and Geo/Biological Evolution. 2:130-146.

Falkowski PG, Katz ME, Knoll AH, Quigg A, Raven JA, Schofield O, Taylor FJ., The evolution of modern eukaryotic phytoplankton, Science. 2004 Jul 16; 305(5682):354-60