Tag: oceanography

Hadean Oceans

Oceans formed far more quickly than expected:

The Hadean eon, following the global-scale melting of the mantle, is expected to be a dynamic period, during which Earth experienced vastly different conditions. Geologic records, however, suggest that the surface environment of Earth was already similar to the present by the middle of the Hadean. Under what conditions a harsh surface environment could turn into a habitable one remains uncertain. Here we show that a hydrated mantle with small-scale chemical heterogeneity, created as a result of magma ocean solidification, is the key to ocean formation, the onset of plate tectonics and the rapid removal of greenhouse gases, which are all essential to create a habitable environment on terrestrial planets. When the mantle is wet and dominated by high-magnesium pyroxenites, the removal of carbon dioxide from the atmosphere is expected to be more than ten times faster than the case of a pyrolytic homogeneous mantle and could be completed within  160 ma. Such a chemically heterogeneous mantle would also produce oceanic crust rich in olivine, which is reactive with ocean water and promotes serpentinization. Therefore, conditions similar to the Lost City hydrothermal field may have existed globally in the Hadean seafloor.

Doggerland

500m wide, the beach is made of material dredged from the sea bottom 13 kilometers offshore and dumped on the existing beach. It’s an experimental coastal protection measure, its sands designed to spread over time to shield the Dutch coast from sea-level rise. The endeavor has made 21m cubic meters of Stone Age soil accessible to archaeologists. “The surprising thing is just how much DNA is still down there.”

2022-03-06: A map of Doggerland 11 ka BP:

Doggerland was, by any estimation, the most attractive landscape in northwestern Europe for Mesolithic hunter-gatherers and perhaps the continent’s most densely populated region at the time. Because of the seemingly inexhaustible resources present there, normally mobile Mesolithic societies may have been encouraged to create permanent or semipermanent settlements. While relatively few Mesolithic sites have been located on land, if Doggerland was indeed the heartland for these early Holocene communities, it stands to reason that many archaeological sites may lie beneath the North Sea. Seismic data has now given archaeologists a much better sense of Doggerland’s topography. They know where its rivers, lakes, and coastlines were located, and where its forests were found. They can use this information to speculate about where people may have lived.
This new type of research into Doggerland has the potential to once again dramatically alter the field of European prehistory. “We have a completely intact landscape with a state of preservation that we can often only dream of on land. I think we will have a lot of exciting discoveries to come. We are barely scratching the surface.”

Mesopelagic Fish

Mesopelagic fish that live 100-1000m below the surface constitute 95% of the world’s fish biomass, 10-30x more than previously thought. “This very large stock of fish that we have just discovered is untouched by fishers.”

2023-02-24: The seafloor is similarly underappreciated

The majority of the bottom of the ocean is covered in morbid ooze, 100m deep. This substance is made of the skeletons of an uncountable number of tiny creatures, raining down from above. The passage of material through this ooze is a substantial part of several biological, chemical, and geological cycles.

Ocean 20% mapped

Modern measurements of the depth and shape of the seabed now encompass 20.6% of the total area under water. When Seabed 2030 was launched in 2017, only 6% of the oceans had been mapped to modern standards. So, it is possible to make swift and meaningful gains. For example, a big jump in coverage would be achieved if all governments, companies, and research institutions released their embargoed data. Seabed 2030 is not seeking 5m resolution of the entire floor (close to something we already have of the Moon’s surface). 1 depth sounding in a 100m grid square down to 1500m will suffice; even less in much deeper waters.

Basketball-sized Cells

Possibly the largest Eukaryote cells:

These single-celled organisms, called xenophyophores, can grow as large as basketballs. Xenophyophores growing on the sediment can resemble carnations, roses, or lattices, and like corals in shallow water, their bodies create a unique habitat in the deep sea. Though surveys are difficult to conduct at the depths where they live and much of the abyssal plains have not been explored, we do know that xenophyophore meadows may cover large areas and that they inhabit the Atlantic and Pacific oceans. Xenophyophores “represent a little known element of marine biodiversity”. They are also, she added, “very fragile—so vulnerable to human disturbance.

2022-02-24: And the largest Prokaryote:

Thiomargarita magnifica, a bacterium living in Caribbean mangroves is visible to the naked eye, growing up to 2 centimeters—as long as a peanut—and 5000x bigger than many other microbes. What’s more, this giant has a huge genome that’s not free floating inside the cell as in other bacteria, but is instead encased in a membrane, an innovation characteristic of much more complex cells, like those in the human body. It implies the 2 branches of life are not as different as previously thought. The genome was huge, with 11m bases harboring 11k genes. Typically, bacterial genomes average 4m bases and 4k genes. The genome was so big because there are 500k copies of the same stretches of DNA.

Calcifying Plankton

Then the calcifying plankton took over. Nowadays, you’d be hard-pressed to find ocean waters less than 100 meters deep that don’t contain calcifying plankton. Despite their teeny size, they may account for 12% of the total biomass in the oceans. And they’ve completely altered the way carbon moves around the planet. 80% of the carbon-containing rocks on Earth are derived from the remains of these plankton and other marine calcifiers — even though by mass, these plankton may account for less than 0.2% of Earth’s carbon-containing life. Making the oceans more stable didn’t just benefit the calcifying critters. With so many species less likely to become extinct at the planet’s whim, all marine species were able to relax and take the time to evolve complex relationships with others. That’s why life became bigger, faster and more aggressive: What had been a struggle against the planet became a struggle between organisms.

Sargassum belt

Sargassum is a rust-colored seaweed that floats. In the Atlantic Ocean, the 2 dominant species have now expanded so much, likely due to agricultural runoff from the Amazon or Mississippi, that blooms practically stretch from the Gulf of Mexico to West Africa. The seaweed provides a habitat for 100s of species of fish and hatchling sea turtles, seahorses, crabs, shrimps, snails, and nudibranchs. But excessive amounts of it are washing ashore and blanketing beaches, with significant environmental and economic consequences.